**Dipping Deposition Study of Anodized-Aluminum Pressure-Sensitive Paint for Unsteady Aerodynamic Applications**

Hirotaka Sakaue

[50] T. Schimert, C. Hanson, J. Brady, et. al. " Advanced in small-pixel, large-format al‐ pha-silicon bolometer arrays", Proceedings of SPIE, Volume 7298, 72980T (2009) [51] C. Trouilleau, B. Fieque, S. Noblet, F. Giner et.al. "High Performance uncooled-amor‐ phous silicon TEC less XGA IRFPA with 17 micron pixel pitch" Proceedings of SPIE

[52] E. Pop, D. Mann, Q. Wang, K. Goodson, H. Dai, Thermal Conductance of an Individ‐ ual Single-Wall Carbon Nanotube above Room Temperature Nano Letters 6, 96

[53] A. Akturk, N. Goldsman, G. Metze, "Self-consistent modeling of heating and MOS‐ FET performance in 3-D integrated circuits," IEEE Trans. on Elect. Dev. 52 (11):

[54] Ashok K. Sood, E. James Egerton, Yash R. Puri, Gustavo Fernandes, Jimmy Xu, Akin Akturk, Neil Goldsman, Nibir K. Dhar, Madan Dubey, Priyalal S. Wijewarnasuriya and Bobby I Lineberry, " Design and Development of CNY based Micro-bolometer for IR Imaging Applications" Proceedings of SPIE, Volume 8353, 83533A, May 2012

[55] Gustavo Fernandes, Jin Ho Kim, Jimmy Xu, Ashok K. Sood, Nibir K. Dhar and Ma‐ dan Dubey, " Unleashing Giant TCR from Phase –Changes in Carbon Nanotube

[56] Rongtao Lu, Jack J. Shi, F. Javier Baca and Judy Z. Wu, " High Performance Multi‐ wall Carbon Nanotube Bolometer" Journal of Applied Physics, 108, 084305 ( 2010).

[57] Rongtao Lu, Rayyan Kamal and Judy Z. Wu, " A comparative study of 1/f noise and temperature coefficient of resistance in multiwall and single-wall carbon nanotube

Composites" Proceedings of SPIE Volume 8868, 88680S, September 2013

bolometers" nanotechnology, Volume 22, 265503 (2011).

Volume 7298, 72980Q, (2009).

208 Optical Sensors - New Developments and Practical Applications

(2006)

2395-2403 (2005).

Additional information is available at the end of the chapter

http://dx.doi.org/10.5772/57416

#### **1. Introduction**

In aerospace engineering, anodized-aluminum pressure-sensitive paint (AA-PSP) has been used in short duration time tests [1 - 12], unsteady flow visualizations, and unsteady pressure measurements [13 – 25]. Because of its nano-open structure (Figure 1), AA-PSP yields high mass diffusion that results in a pressure response time on the order of ten microseconds [26]. This structure enables oxygen gas to interact directly with luminophores on the pore surface, which provides fast response to pressures. By applying an AA-PSP, we can obtain global surface pressure information instead of pointwise information that may result in wide applications in pressure detection fields. AA-PSP is an optical sensor that consists of a molecular pressure probe (luminophore) and an anodized aluminum as a supporting matrix. As schematically shown in Figure 2, the luminophore on the anodized-aluminum surface is excited by an illumination source and gives off luminescence. This luminescence is related to gaseous oxygen in a test gas, a process called oxygen quenching. Because the gaseous oxygen can be described as a partial pressure of oxygen as well as a static pressure, the luminescence from an AA-PSP can be described as a static pressure. See Section 3.2 for a detailed description.

The luminophore is directly related to important parameters of AA-PSPs, such as the lumi‐ nescent signal level, pressure sensitivity, temperature dependency, and response time. Mainly three types of luminophores are commonly used for PSP in general, such as ruthenium complex, porphyrin, and pyrene. Each luminophore has an optimum excitation wavelength, and its peak wavelength of luminescence varies by the luminophore as well. For AA-PSP, the luminophore is applied on the anodized-aluminum surface by the dipping deposition method [27]. This method requires a luminophore, a solvent, and an anodized-aluminum coating. The

© 2014 The Author(s). Licensee InTech. This chapter is distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/3.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

anodized-aluminum

in unsteady measurement applications.

process.

**Figure 3.** Schematic description of dipping deposition method.

**2. Materials and luminophore application**

coated model AA-PSP model

luminophore solution

In this chapter, the luminophore application method of dipping deposition is studied. This includes steady- and unsteady-state characterizations of AA-PSP, such as the signal level, pressure sensitivity, temperature dependency, and response time. The study of this method will expand our selection of luminophores onto an anodized aluminum, which will be beneficial for fabricating AA-PSP for various aerodynamic-measurement purposes especially

Anodized-aluminum coated samples were prepared from a sheet of pure aluminum, anodi‐ zation process, and cut in pieces (10 mm × 10 mm). The anodization process and the lumino‐ phore-application process were as follows. The anodization process gives an anodized aluminum of 20 nm pore size with the thickness of 10 ± 1 µm. The thickness was measured by an eddy current apparatus (Kett, LZ-330). Bathophen ruthenium (RuDPP) from GFS Chemicals

**• Step1 Pretreatment.** An aluminum sheet was dipped in a 2% sodium hydroxide solution for 2 min to remove an excess oxidized layer. The surface was rinsed by water after this

**• Step3 Anodized layer modification.** The anodized sheet was dipped in a 5 % phosphoric

**• Step4 Luminophore application (dipping deposition).** For a given luminophore (RuDPP), the solvent polarity, luminophore concentration, and dipping duration were varied to study

) was applied to the aluminum

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211

was used as a luminophore. It is a conventional luminophore for AA-PSP.

**• Step2 Anodization.** A constant current density (10 mA/cm2

sheet, which was connected to anode in 1 M sulfuric acid at 0 °C.

acid for 20 min at 30 °C. After this process, the sheet was rinsed by water.

dipping deposition

Dipping Deposition Study of Anodized-Aluminum Pressure-Sensitive Paint for Unsteady Aerodynamic Applications

**Figure 2.** Schematic description of anodized-aluminum pressure-sensitive paint (AA-PSP).

application procedure is schematically shown in Figure 3. This method first dissolves the luminophore in solvent, and anodized-aluminum coating is dipped in the solution to apply the luminophore on the anodized-aluminum surface. However, this method was not quite understood, so that other luminophores were not successfully applied on an anodizedaluminum surface. For a given luminophore, a selection of solvent may influence to the AA-PSP characterizations: the signal level, pressure sensitivity, temperature dependency, and response time. The luminophore concentration may influence to the AA-PSP characterizations, because the amount of luminophore on an anodized-aluminum surface may change with the concentration used in the dipping deposition. The dipping duration can be another important parameter that influences the AA-PSP characterizations, because it would influence the amount of luminophore applied on the anodized-aluminum surface. The effects on the dipping duration as well as the above mentioned dipping parameters would give us fundamental knowledge to apply various luminophores on the anodized-aluminum coating. However, the effects of these parameters on AA-PSP have not been studied.

**Figure 3.** Schematic description of dipping deposition method.

In this chapter, the luminophore application method of dipping deposition is studied. This includes steady- and unsteady-state characterizations of AA-PSP, such as the signal level, pressure sensitivity, temperature dependency, and response time. The study of this method will expand our selection of luminophores onto an anodized aluminum, which will be beneficial for fabricating AA-PSP for various aerodynamic-measurement purposes especially in unsteady measurement applications.

## **2. Materials and luminophore application**

application procedure is schematically shown in Figure 3. This method first dissolves the luminophore in solvent, and anodized-aluminum coating is dipped in the solution to apply the luminophore on the anodized-aluminum surface. However, this method was not quite understood, so that other luminophores were not successfully applied on an anodizedaluminum surface. For a given luminophore, a selection of solvent may influence to the AA-PSP characterizations: the signal level, pressure sensitivity, temperature dependency, and response time. The luminophore concentration may influence to the AA-PSP characterizations, because the amount of luminophore on an anodized-aluminum surface may change with the concentration used in the dipping deposition. The dipping duration can be another important parameter that influences the AA-PSP characterizations, because it would influence the amount of luminophore applied on the anodized-aluminum surface. The effects on the dipping duration as well as the above mentioned dipping parameters would give us fundamental knowledge to apply various luminophores on the anodized-aluminum coating. However, the

Oxygen Quenching Luminophore

Model Surface

**Figure 2.** Schematic description of anodized-aluminum pressure-sensitive paint (AA-PSP).

100nm

Porous Coating

**Figure 1.** Nano-open structure of anodized-aluminum surface. Surface image was taken using a scanning electron mi‐

Excitation Luminescence

Gaseous Oxygen

croscope.

210 Optical Sensors - New Developments and Practical Applications

effects of these parameters on AA-PSP have not been studied.

Anodized-aluminum coated samples were prepared from a sheet of pure aluminum, anodi‐ zation process, and cut in pieces (10 mm × 10 mm). The anodization process and the lumino‐ phore-application process were as follows. The anodization process gives an anodized aluminum of 20 nm pore size with the thickness of 10 ± 1 µm. The thickness was measured by an eddy current apparatus (Kett, LZ-330). Bathophen ruthenium (RuDPP) from GFS Chemicals was used as a luminophore. It is a conventional luminophore for AA-PSP.


the luminophore application process. After the dipping, AA-PSP was rinsed with the same solvent used. Then, remained solvents on AA-PSP samples were evaporated in a vacuum chamber at 50 °C for about 3 hours.

In total eight solvents (hexane, toluene, dichloromethane, chloroform, acetone, *N*,*N*-dimethyl formamide, dimethyl sulfoxide, and water) were selected for the solvent-polarity study in order from non-polar to the highest polarity index. The luminophore concentration was selected from a very dilute case of 0.001 mM to 10 mM, where the luminophore reached to its saturation. The dipping duration was varied from a very short dipping of 1 s to a very long dipping of 100,000 s (over 1 day). Even though the upper limit of the dipping duration would be infinity, the author assumed that over 1 day of dipping duration would be enough to understand the change in the AA-PSP characterizations. The reference AA-PSP, which was labeled as AAPSPref, was created by dichloromethane as a solvent, the concentration of 0.1 mM, and the dipping duration of one hour.

To study the effect on the solvent polarity, 11.7 mg of RuDPP was dissolved in 100 ml of eight different solvents based on the polarity index (Table 1 (a)). If RuDPP is dissolved completely, the concentration was 0.1 mM. If not dissolved, the solution was saturated with excess RuDPP remained. Anodized-aluminum samples were dipped in RuDPP solutions. The dipping time was one hour at room conditions. Eight different AA-PSP samples were labeled based on their polarity index of solvents (Table 1 (a)).

To study the effect on the luminophore concentration, dichloromethane was chosen as a solvent. The concentration had the range of the fifth order of magnitude; it was varied from 0.001 mM to 10 mM. The dipping duration was one hour at room conditions. Table 1 (b) lists the luminophore application conditions related to the concentration. Prepared AA-PSPs were labeled (also listed in Table 1 (b) as Sample ID).

To study the effect on the dipping duration, dichloromethane was chosen as a solvent, and the concentration of the luminophore solution was fixed at 0.1 mM. The duration was varied from 1 s to 100,000 s. Table 1 (c) lists the conditions related to the dipping duration. Prepared AA-PSPs are labeled based on their dipping conditions, which are also listed in Table 1 (c) as Sample ID.

#### **3. Steady-state characterization**

Figure 4 schematically describes the calibration system, which consists of a spectrometer (Hitachi High Technologies, F-7000) and a pressure- and temperature-controlled chamber. This system characterizes the luminescent spectrum of an AA-PSP sample with varying pressures and temperatures. For characterization, an AA-PSP sample was placed in the test chamber. The excitation wavelength was set at 460 nm by a monochromator via a xenon lamp illumination in the spectrometer unit. The chamber has optical windows that passed the excitation from the illumination unit and the luminescence from the sample. The luminescence from AA-PSP samples was measured from 570 to 800 nm for a given pressure and a given

temperature. The luminescent signal of an AA-PSP was then determined by integrating the spectrum from 600 to 700 nm. For pressure calibration, the chamber was connected to a pressure controlling unit (Druck DPI515), with settings from 5 to 120 kPa at a constant temperature at 25 °C. For temperature calibration, a sample heater/cooler was controlled to vary the temperature from 10 to 50 °C with a constant pressure at 100 kPa. The test gas was

**(c)**

**Table 1.** (a). Luminophore application conditions: solvent polarity. Dipping solvent was selected based on the polarity index. RuDPP concentration was fixed at 0.1 mM, and anodized-aluminum coatings were dipped at room temperature for one hour. (b). Luminophore application conditions: luminophore concentration. RuDPP concentration was varied from 0.001 mM to 10 mM. Dipping solvent was dichloromethane, and anodized-aluminum coatings were dipped at room temperature for one hour.(c). Luminophore application conditions: dipping duration. Dipping duration was varied from 1 to 100,000 s. Dichloromethane was chosen as a solvent, and RuDPP concentration was fixed at 0.1 mM.

**Sample ID Polarity Index Solvent** AAPSPind00 0.1 Hexane AAPSPind02 2.4 Toluene AAPSPref 3.1 Dichloromethane AAPSPind04 4.1 Chloroform AAPSPind05 5.1 Acetone

Dipping Deposition Study of Anodized-Aluminum Pressure-Sensitive Paint for Unsteady Aerodynamic Applications

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213

AAPSPind06 6.4 *N*,*N*-dimethylformamide AAPSPind07 7.2 Dimethylsulfoxide AAPSPind10 10.2 Water

**(a)**

**(b)**

**Sample ID Luminophore Concentration (mM)**

AAPSP00.001 0.001 AAPSP00.010 0.01 AAPSPref 0.1 AAPSP01.000 1 AAPSP10.000 10

**Sample ID Dipping Duration (s)**

AAPSP1 1 AAPSP10 10 AAPSP100 100 AAPSP1000 1,000 AAPSPref 3,600 AAPSP100000 100,000 Dipping Deposition Study of Anodized-Aluminum Pressure-Sensitive Paint for Unsteady Aerodynamic Applications http://dx.doi.org/10.5772/57416 213

the luminophore application process. After the dipping, AA-PSP was rinsed with the same solvent used. Then, remained solvents on AA-PSP samples were evaporated in a vacuum

In total eight solvents (hexane, toluene, dichloromethane, chloroform, acetone, *N*,*N*-dimethyl formamide, dimethyl sulfoxide, and water) were selected for the solvent-polarity study in order from non-polar to the highest polarity index. The luminophore concentration was selected from a very dilute case of 0.001 mM to 10 mM, where the luminophore reached to its saturation. The dipping duration was varied from a very short dipping of 1 s to a very long dipping of 100,000 s (over 1 day). Even though the upper limit of the dipping duration would be infinity, the author assumed that over 1 day of dipping duration would be enough to understand the change in the AA-PSP characterizations. The reference AA-PSP, which was labeled as AAPSPref, was created by dichloromethane as a solvent, the concentration of 0.1 mM,

To study the effect on the solvent polarity, 11.7 mg of RuDPP was dissolved in 100 ml of eight different solvents based on the polarity index (Table 1 (a)). If RuDPP is dissolved completely, the concentration was 0.1 mM. If not dissolved, the solution was saturated with excess RuDPP remained. Anodized-aluminum samples were dipped in RuDPP solutions. The dipping time was one hour at room conditions. Eight different AA-PSP samples were labeled based on their

To study the effect on the luminophore concentration, dichloromethane was chosen as a solvent. The concentration had the range of the fifth order of magnitude; it was varied from 0.001 mM to 10 mM. The dipping duration was one hour at room conditions. Table 1 (b) lists the luminophore application conditions related to the concentration. Prepared AA-PSPs were

To study the effect on the dipping duration, dichloromethane was chosen as a solvent, and the concentration of the luminophore solution was fixed at 0.1 mM. The duration was varied from 1 s to 100,000 s. Table 1 (c) lists the conditions related to the dipping duration. Prepared AA-PSPs are labeled based on their dipping conditions, which are also listed in Table 1 (c)

Figure 4 schematically describes the calibration system, which consists of a spectrometer (Hitachi High Technologies, F-7000) and a pressure- and temperature-controlled chamber. This system characterizes the luminescent spectrum of an AA-PSP sample with varying pressures and temperatures. For characterization, an AA-PSP sample was placed in the test chamber. The excitation wavelength was set at 460 nm by a monochromator via a xenon lamp illumination in the spectrometer unit. The chamber has optical windows that passed the excitation from the illumination unit and the luminescence from the sample. The luminescence from AA-PSP samples was measured from 570 to 800 nm for a given pressure and a given

chamber at 50 °C for about 3 hours.

212 Optical Sensors - New Developments and Practical Applications

and the dipping duration of one hour.

polarity index of solvents (Table 1 (a)).

**3. Steady-state characterization**

as Sample ID.

labeled (also listed in Table 1 (b) as Sample ID).


**Table 1.** (a). Luminophore application conditions: solvent polarity. Dipping solvent was selected based on the polarity index. RuDPP concentration was fixed at 0.1 mM, and anodized-aluminum coatings were dipped at room temperature for one hour. (b). Luminophore application conditions: luminophore concentration. RuDPP concentration was varied from 0.001 mM to 10 mM. Dipping solvent was dichloromethane, and anodized-aluminum coatings were dipped at room temperature for one hour.(c). Luminophore application conditions: dipping duration. Dipping duration was varied from 1 to 100,000 s. Dichloromethane was chosen as a solvent, and RuDPP concentration was fixed at 0.1 mM.

temperature. The luminescent signal of an AA-PSP was then determined by integrating the spectrum from 600 to 700 nm. For pressure calibration, the chamber was connected to a pressure controlling unit (Druck DPI515), with settings from 5 to 120 kPa at a constant temperature at 25 °C. For temperature calibration, a sample heater/cooler was controlled to vary the temperature from 10 to 50 °C with a constant pressure at 100 kPa. The test gas was dry air. For the signal level characterization, all the AA-PSP samples were measured with the same optical setup in the spectrometer but replacing samples in the chamber at constant pressure and temperature of 100 kPa and 25 °C, respectively. Throughout our characteriza‐ tions, reference conditions were 100 kPa and 25 °C. The signal level, *η*, pressure sensitivity, *σ*, and temperature dependency, *δ*, were characterized from the luminescent signals of AA-PSPs. Definitions and procedures to derive these characterizations are described in Sections 3.1, 3.2, and 3.3.

**3.2. Pressure sensitivity**

controlled model [27]:

**3.3. Temperature dependency**

*δ* =

*d*(*I* / *Iref* ) *dT* <sup>|</sup>

*T* =*Tref*

conditions.

[29]:

Based on the Stern-Volmer relationship, the luminescent intensity, *I*, is related to a quencher

Dipping Deposition Study of Anodized-Aluminum Pressure-Sensitive Paint for Unsteady Aerodynamic Applications

Where *I0* is the luminescent intensity without quencher and *Kq* is the Stern-Volmer quenching constant. The quencher is oxygen, which is described by the oxygen concentration, [*O2*]. For AA-PSP, [*O2*] can be described by the adsorption and surface diffusion of the adsorbed oxygen on an anodized-aluminum surface. We can describe [*O2*] by the partial pressures of oxygen as well as the static pressures. These are combined with Equation (3) to give the adsorption-

*<sup>I</sup>* =1 <sup>+</sup> *Kq <sup>O</sup>*<sup>2</sup> (3)

http://dx.doi.org/10.5772/57416

= *B* ⋅*γ* (*%*) (5)

<sup>2</sup> (*%* / °*C*) (7)

<sup>=</sup>*cT* <sup>0</sup> <sup>+</sup> *cT* <sup>1</sup>*<sup>T</sup>* <sup>+</sup> *cT* <sup>2</sup>*<sup>T</sup>* <sup>2</sup> <sup>+</sup> *cT* <sup>3</sup>*<sup>T</sup>* <sup>3</sup> (6)

(4)

215

*I*0

*Iref*

*<sup>σ</sup>* <sup>=</sup> *<sup>d</sup>*(*Iref* / *<sup>I</sup>*) *<sup>d</sup>*(*<sup>p</sup>* / *pref* ) <sup>|</sup>

*I Iref* *<sup>I</sup>* <sup>=</sup> *<sup>A</sup>* <sup>+</sup> *<sup>B</sup>*( *<sup>p</sup>*

change. This corresponds to a slope of the Equation (4) at the reference conditions:

*p*= *pref*

AA-PSP, like PSP in general, has a temperature dependency [30]. This influences the lumi‐

Where cT0, cT1, cT2, and cT3 are calibration constants, respectively. We defined the temperature dependency, *δ*, which is a slope of the temperature calibration at the reference conditions (Equation (7)). If the absolute value of *δ* is large, it tells us that the change in luminescent signal over a given temperature change is also large. This is unfavorable condition as a pressure

=*cT* <sup>1</sup> + 2*cT* <sup>2</sup>*Tref* + 3*cT* <sup>3</sup>*Tref*

nescent signal, which can be described as the third order polynomial in Equation (6):

sensor. On the contrary, zero *δ* means that AA-PSP is not temperature dependent:

*pref* ) *γ*

Where *A*, *B*, and *γ* are calibration constants, respectively. Here, *ref* denotes our reference

Pressure sensitivity, *σ* (%), describes the change in the luminescent signal over a given pressure

**Figure 4.** Schematic of AA-PSP calibration setup.

#### **3.1. Signal Level**

The luminescent signal, *I*, was determined by the integration of AA-PSP spectrum from 600 to 700 nm. Based on Liu *et al*., this can be described by the gain of the photo-detector in our spectrometer, *G*, the emission from AA-PSP, *IAAPSP*, the excitation in the spectrometer, *Iex*, and the measurement setup component, *fset* [28]:

$$I = G I\_{AAPSP} I\_{ex} f\_{set} \tag{1}$$

In our calibration setup, *G*, *Iex*, and *fset* were the same for all AA-PSP samples. We nondimensionalized the luminescent signal by that of AAPSPref, *IAAPSPref*. All luminescent signals were determined at the reference conditions. We call this value as the signal level, *η*, shown in Equation (2):

$$\eta = \frac{I}{I\_{AAPS\,\text{Pref}}} \begin{ (\%)} & & & \\ & & & \end{ (2)}$$

Dipping Deposition Study of Anodized-Aluminum Pressure-Sensitive Paint for Unsteady Aerodynamic Applications http://dx.doi.org/10.5772/57416 215

#### **3.2. Pressure sensitivity**

dry air. For the signal level characterization, all the AA-PSP samples were measured with the same optical setup in the spectrometer but replacing samples in the chamber at constant pressure and temperature of 100 kPa and 25 °C, respectively. Throughout our characteriza‐ tions, reference conditions were 100 kPa and 25 °C. The signal level, *η*, pressure sensitivity, *σ*, and temperature dependency, *δ*, were characterized from the luminescent signals of AA-PSPs. Definitions and procedures to derive these characterizations are described in Sections 3.1, 3.2,

grating

Hitachi High Tech F-7000

monochromater

*I* =*GI AAPSP Iex f set* (1)

(*%*) (2)

test chamber

temperature controller

AA-PSP

spectrum

excitation

The luminescent signal, *I*, was determined by the integration of AA-PSP spectrum from 600 to 700 nm. Based on Liu *et al*., this can be described by the gain of the photo-detector in our spectrometer, *G*, the emission from AA-PSP, *IAAPSP*, the excitation in the spectrometer, *Iex*, and

In our calibration setup, *G*, *Iex*, and *fset* were the same for all AA-PSP samples. We nondimensionalized the luminescent signal by that of AAPSPref, *IAAPSPref*. All luminescent signals were determined at the reference conditions. We call this value as the signal level, *η*, shown in

> *<sup>η</sup>* <sup>=</sup> *<sup>I</sup> I AAPS*Pr*ef*

luminescence

photo-detector

xenon lamp

mirror

and 3.3.

gas supply

pressure controller

**3.1. Signal Level**

Equation (2):

**Figure 4.** Schematic of AA-PSP calibration setup.

the measurement setup component, *fset* [28]:

vacuum pump

214 Optical Sensors - New Developments and Practical Applications

Based on the Stern-Volmer relationship, the luminescent intensity, *I*, is related to a quencher [29]:

$$\frac{I\_0}{I} = 1 + Kq[O2] \tag{3}$$

Where *I0* is the luminescent intensity without quencher and *Kq* is the Stern-Volmer quenching constant. The quencher is oxygen, which is described by the oxygen concentration, [*O2*]. For AA-PSP, [*O2*] can be described by the adsorption and surface diffusion of the adsorbed oxygen on an anodized-aluminum surface. We can describe [*O2*] by the partial pressures of oxygen as well as the static pressures. These are combined with Equation (3) to give the adsorptioncontrolled model [27]:

$$\frac{Iref}{I} = A + B \left(\frac{p}{p\_{ref}}\right)^{\gamma} \tag{4}$$

Where *A*, *B*, and *γ* are calibration constants, respectively. Here, *ref* denotes our reference conditions.

Pressure sensitivity, *σ* (%), describes the change in the luminescent signal over a given pressure change. This corresponds to a slope of the Equation (4) at the reference conditions:

$$\sigma = \frac{d\left(I\_{ref} / I\right)}{d\left(p \mid p\_{ref}\right)}\Big|\_{p=p\_{ref}} = B \cdot \gamma \quad \text{(\%\prime)}\tag{5}$$

#### **3.3. Temperature dependency**

AA-PSP, like PSP in general, has a temperature dependency [30]. This influences the lumi‐ nescent signal, which can be described as the third order polynomial in Equation (6):

$$\frac{I}{I\_{ref}} = c\_{T0} + c\_{T1}T + c\_{T2}T^2 + c\_{T3}T^3 \tag{6}$$

Where cT0, cT1, cT2, and cT3 are calibration constants, respectively. We defined the temperature dependency, *δ*, which is a slope of the temperature calibration at the reference conditions (Equation (7)). If the absolute value of *δ* is large, it tells us that the change in luminescent signal over a given temperature change is also large. This is unfavorable condition as a pressure sensor. On the contrary, zero *δ* means that AA-PSP is not temperature dependent:

$$\delta = \frac{d\left(I \mid I\_{ref}\right)}{dT}\Big|\_{T=T\_{ref}} = c\_{T1} + 2c\_{T2}T\_{ref} + 3c\_{T3}T\_{ref} \,^2 \, \text{(\%)} \, ^\circ \text{C} \tag{7}$$

Overall, our *δs* showed negative (see Section 5.3). This means that *δ*min is the most temperature dependent and *δ*max the least temperature dependent.

**4.1. Response time**

response time, derived from Equation (8).

**5. Characterization results**

*pnorm* <sup>=</sup> *<sup>p</sup>* <sup>−</sup> *<sup>p</sup>*min *p*max − *p*min

RuDPP particles were dropped to the solvents.

**Figure 6.** RuDPP dissolved in solvents with range of polarity index.

We used the 90 % rise of *pnorm* to determine the response time.

The luminescent signal was converted to a normalized pressure, *pnorm* to characterize the

Dipping Deposition Study of Anodized-Aluminum Pressure-Sensitive Paint for Unsteady Aerodynamic Applications

Where *min* and *max* denote the minimum and maximum values of a step change, respectively.

Photographs of RuDPP solution were taken to qualitatively verify the solubility of RuDPP (Figure 6). All solvents dissolved RuDPP except for the solvent with lowest polarity index (hexane). Toluene, which was the second lowest solvent in our test, partially dissolved RuDPP. Water, which gave the highest polarity index in our test, partially dissolved RuDPP, but it dissolved RuDPP completely after about one day. Other solvents dissolved RuDPP as soon as

Figure 7 (a) and (b) show luminescent spectra of AAPSPref with varying pressures and temperatures, respectively. Spectra were normalized by the luminescent peak at the reference

<sup>=</sup> (*Iref* / *<sup>I</sup>* <sup>−</sup> *<sup>A</sup>*)1/*<sup>γ</sup>* <sup>−</sup>(*Iref* / *<sup>I</sup>*min <sup>−</sup> *<sup>A</sup>*)1/*<sup>γ</sup>*

(*Iref* / *<sup>I</sup>*max <sup>−</sup> *<sup>A</sup>*)1/*<sup>γ</sup>* <sup>−</sup>(*Iref* / *<sup>I</sup>*min <sup>−</sup> *<sup>A</sup>*)1/*<sup>γ</sup>* (8)

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217

#### **4. Unsteady-state characterization**

MHz [31].

**4.1. Response time** 

*p p p p*

to determine the response time.

max min min

**5. Characterization results** 

Equation (8).

*p*

A vertical shock tube for characterizing the response time is schematically shown in Figure. 5 (a). The length of the driver and driven sections are 1420 mm and 5530 mm, respectively. The driven section has a square cross section of 100 mm × 100 mm, and a test section is installed at the end of the driven section. The test gas was dry air and initially set at room conditions. When the diaphragm between the driver and the driven sections is ruptured, a planar shock wave propagates into the driven section. We set the driver pressure as 400 kPa that created a planar shock wave with the Mach number of 1.30. A vertical shock tube for characterizing the response time is schematically shown in Figure. 5 (a). The length of the driver

The schematic description of the test section is shown in Figure. 5 (b). An AA-PSP sample was fixed on a flat plate placed on the bottom wall of the shock tube. The samples were illuminated by a continuous 400 nm laser. A planar shock wave and its normal reflection created a step change of pressure. A photomultiplier tube (PMT, Hamamatsu R7236) was used to detect the intensity change of luminescence from the AA-PSP sample through a 605 ± 40 nm band-pass filter. The output signal from the PMT was amplified by Hamamatsu C1053-03 through an analog low-pass filter with a cutoff frequency of 1 MHz. The filtered signal was then digitized to 12 bits and sampled on an A/D converter (Yokogawa, DL1540C) at a rate of 200 MHz [31]. and driven sections are 1420 mm and 5530 mm, respectively. The driven section has a square cross section of 100 mm × 100 mm, and a test section is installed at the end of the driven section. The test gas was dry air and initially set at room conditions. When the diaphragm between the driver and the driven sections is ruptured, a planar shock wave propagates into the driven section. We set the driver pressure as 400 kPa that created a planar shock wave with the Mach number of 1.30. The schematic description of the test section is shown in Figure. 5 (b). An AA-PSP sample was fixed on a flat plate placed on the bottom wall of the shock tube. The samples were illuminated by a continuous 400 nm laser. A planar shock wave and its normal reflection created a step change of pressure. A photomultiplier tube (PMT, Hamamatsu R7236) was used to detect the intensity change of luminescence from the AA-PSP sample through a 605 ± 40 nm band-pass filter. The output signal from the PMT was amplified by Hamamatsu C1053-03 through an analog low-pass filter with a cutoff frequency of 1 MHz. The filtered signal was then digitized to 12 bits and sampled on an A/D converter (Yokogawa, DL1540C) at a rate of 200

The luminescent signal was converted to a normalized pressure, *pnorm* to characterize the response time, derived from

1

(8)

min

Where *min* and *max* denote the minimum and maximum values of a step change, respectively. We used the 90 % rise of *pnorm*

Photographs of RuDPP solution were taken to qualitatively verify the solubility of RuDPP (Figure 6). All solvents dissolved RuDPP except for the solvent with lowest polarity index (hexane). Toluene, which was the second lowest solvent in our test,

min 1 1

**Figure 5.** (a). Schematic description of shock tube. (b). Test section and optical setup of the shock tube.

Figure 5. **(a).** Schematic description of shock tube. **(b).** Test section and optical setup of the shock tube.

 *I I A I I A I I A I I A*

*ref ref ref ref*

1

max

*norm* 

#### **4.1. Response time**

Overall, our *δs* showed negative (see Section 5.3). This means that *δ*min is the most temperature

A vertical shock tube for characterizing the response time is schematically shown in Figure. 5 (a). The length of the driver and driven sections are 1420 mm and 5530 mm, respectively. The driven section has a square cross section of 100 mm × 100 mm, and a test section is installed at the end of the driven section. The test gas was dry air and initially set at room conditions. When the diaphragm between the driver and the driven sections is ruptured, a planar shock wave propagates into the driven section. We set the driver pressure as 400 kPa that created a planar

The schematic description of the test section is shown in Figure. 5 (b). An AA-PSP sample was fixed on a flat plate placed on the bottom wall of the shock tube. The samples were illuminated by a continuous 400 nm laser. A planar shock wave and its normal reflection created a step change of pressure. A photomultiplier tube (PMT, Hamamatsu R7236) was used to detect the intensity change of luminescence from the AA-PSP sample through a 605 ± 40 nm band-pass filter. The output signal from the PMT was amplified by Hamamatsu C1053-03 through an analog low-pass filter with a cutoff frequency of 1 MHz. The filtered signal was then digitized to 12 bits and sampled on an A/D converter (Yokogawa, DL1540C) at a rate of 200 MHz [31].

A vertical shock tube for characterizing the response time is schematically shown in Figure. 5 (a). The length of the driver and driven sections are 1420 mm and 5530 mm, respectively. The driven section has a square cross section of 100 mm × 100 mm, and a test section is installed at the end of the driven section. The test gas was dry air and initially set at room conditions. When the diaphragm between the driver and the driven sections is ruptured, a planar shock wave propagates into the driven section. We set the driver pressure as 400 kPa that created a planar shock wave with the Mach number of

The schematic description of the test section is shown in Figure. 5 (b). An AA-PSP sample was fixed on a flat plate placed on the bottom wall of the shock tube. The samples were illuminated by a continuous 400 nm laser. A planar shock wave and its normal reflection created a step change of pressure. A photomultiplier tube (PMT, Hamamatsu R7236) was used to detect the intensity change of luminescence from the AA-PSP sample through a 605 ± 40 nm band-pass filter. The output signal from the PMT was amplified by Hamamatsu C1053-03 through an analog low-pass filter with a cutoff frequency of 1 MHz. The filtered signal was then digitized to 12 bits and sampled on an A/D converter (Yokogawa, DL1540C) at a rate of 200

dependent and *δ*max the least temperature dependent.

**4. Unsteady-state characterization**

216 Optical Sensors - New Developments and Practical Applications

shock wave with the Mach number of 1.30.

(a) (b)

**4.1. Response time** 

*p p p p*

to determine the response time.

max min min

**5. Characterization results** 

Equation (8).

*p*

Figure 5. **(a).** Schematic description of shock tube. **(b).** Test section and optical setup of the shock tube.

**Figure 5.** (a). Schematic description of shock tube. (b). Test section and optical setup of the shock tube.

 *I I A I I A I I A I I A*

*ref ref ref ref*

1

max

optical window

vent

air supply

diaphragm

*norm* 

The luminescent signal was converted to a normalized pressure, *pnorm* to characterize the response time, derived from

band-pass filter

1

(8)

luminescence

optical window

PMT laser

excitation

AA-PSP sample

min

Where *min* and *max* denote the minimum and maximum values of a step change, respectively. We used the 90 % rise of *pnorm*

Photographs of RuDPP solution were taken to qualitatively verify the solubility of RuDPP (Figure 6). All solvents dissolved RuDPP except for the solvent with lowest polarity index (hexane). Toluene, which was the second lowest solvent in our test,

min 1 1

1.30.

MHz [31].

driver section 1420mm

driven section 5530mm

The luminescent signal was converted to a normalized pressure, *pnorm* to characterize the response time, derived from Equation (8).

$$p\_{\text{norm}} = \frac{p - p\_{\text{min}}}{p\_{\text{max}} - p\_{\text{min}}} = \frac{\{\mathbf{I}\_{\text{ref}} \mid \mathbf{I} - \mathbf{A} \}^{1/\gamma} - \{\mathbf{I}\_{\text{ref}} \mid \mathbf{I}\_{\text{min}} - \mathbf{A} \}^{1/\gamma}}{\{\mathbf{I}\_{\text{ref}} \mid \mathbf{I}\_{\text{max}} - \mathbf{A} \}^{1/\gamma} - \{\mathbf{I}\_{\text{ref}} \mid \mathbf{I}\_{\text{min}} - \mathbf{A} \}^{1/\gamma}} \tag{8}$$

Where *min* and *max* denote the minimum and maximum values of a step change, respectively. We used the 90 % rise of *pnorm* to determine the response time.

## **5. Characterization results**

Photographs of RuDPP solution were taken to qualitatively verify the solubility of RuDPP (Figure 6). All solvents dissolved RuDPP except for the solvent with lowest polarity index (hexane). Toluene, which was the second lowest solvent in our test, partially dissolved RuDPP. Water, which gave the highest polarity index in our test, partially dissolved RuDPP, but it dissolved RuDPP completely after about one day. Other solvents dissolved RuDPP as soon as RuDPP particles were dropped to the solvents.

**Figure 6.** RuDPP dissolved in solvents with range of polarity index.

Figure 7 (a) and (b) show luminescent spectra of AAPSPref with varying pressures and temperatures, respectively. Spectra were normalized by the luminescent peak at the reference conditions. We can see that, as increasing the pressure, the luminescent spectrum decreased due to oxygen quenching [29]. As the temperature increases, we can see the spectrum de‐ creased due to the thermal quenching [29]. It was noticed that the luminescent peak was shifted

spectra of AAPSPref. Thick line shows the spectrum at reference conditions of 100 kPa and 25 C. **Figure 7.** (a). Pressure spectra of AAPSPref. Thick line shows the spectrum at reference conditions of 100 kPa and 25 °C. (b). temperature spectra of AAPSPref. Thick line shows the spectrum at reference conditions of 100 kPa and 25 °C.

, was determined from Equation (2). Figure 8 (a) shows the signal level,

**5.1. Luminescent signal** 

normalized by the signal of AAPSPref at 100 kPa. The

The signal level,

Figure 7. **(a).** Pressure spectra of AAPSPref. Thick line shows the spectrum at reference conditions of 100 kPa and 25 C. **(b).** temperature

luminophore application method of dipping deposition greatly influenced the signal level. AAPSPind00 from the polarity index of 0.1 (hexane) showed very low RuDPP application on anodized aluminum, indicated by the signal level. Note that hexane did not dissolve RuDPP (Figure 6). AAPSPind02 from the polarity index of 2.4 (toluene) applied RuDPP well on anodized aluminum, which can be seen from the signal level. Here, toluene partially dissolved RuDPP. As increasing

was shown as a bar with the determined value. It is obvious that the

, related to the polarity index,

from 650 to 635 nm by increasing the pressure from 5 to 120 kPa. For temperature spectra, the peak was shifted from 640 to 645 nm by increasing the temperature from 10 to 50 °C. As described in Section 3, we integrated an obtained spectrum from 600 to 700 nm to determine

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219

The signal level, *η*, was determined from Equation (2). Figure 8 (a) shows the signal level, *η*, related to the polarity index, normalized by the signal of AAPSPref at 100 kPa. The *η* was shown as a bar with the determined value. It is obvious that the luminophore application method of dipping deposition greatly influenced the signal level. AAPSPind00 from the polarity index of 0.1 (hexane) showed very low RuDPP application on anodized aluminum, indicated by the signal level. Note that hexane did not dissolve RuDPP (Figure 6). AAPSPind02 from the polarity index of 2.4 (toluene) applied RuDPP well on anodized aluminum, which can be seen from the signal level. Here, toluene partially dissolved RuDPP. As increasing polarity index, RuDPP applied on anodized aluminum. However, the application suddenly dropped between polarity index at 6.4 of *N*, *N*-dimethyl amide and at 7.2 of dimethyl sulfoxide. The application brought back at the highest polarity index of 10.2 (water). The highest signal level of 1.89 was obtained from AA-PSPind05. It can be said that a range of polarity index of solvent exists that applies RuDPP. However, this range does not correspond to the range of dissolving RuDPP.

It is assumed that RuDPP remains as solution if it is dissolved well in a solvent. This assumption can be supported that *N*, *N*-dimethyl amide and dimethyl sulfoxide did not apply RuDPP well onto anodized aluminum. On the other hand, RuDPP applies onto anodized aluminum if it is partially dissolved in a solvent. This can be supported that toluene and water applied RuDPP onto anodized aluminum, even though these dissolved RuDPP partially. If a solvent did not dissolve RuDPP, it would not be applied onto anodized aluminum. This can be seen from the

As we increased the luminophore concentration from 0.001 mM to 0.1 mM, *η* increased (Figure 8 (b)). Note that the vertical axis in Figure 8 (b) was shown as log scale. The *η* was shown as a bar with the determined value. Even though we increased the concentration more than 0.1 mM, *η* decreased roughly by a half. This may be due to the concentration quenching [29]. There was an optimum concentration to maximize *η*. The maximum *η* was obtained from

There was a peak dipping duration to maximize *η* (Figure 8 (c)). Note that the vertical axis in Figure 8 (c) was shown as log scale. The *η* was shown as a bar with the determined value. The maximum *η* was obtained from AAPSP1000, whose dipping duration was 1,000 s. For a short dipping duration, the luminophore would remain in the luminophore solution instead of applying onto the anodized surface. Roughly, the difference of *η* was a factor of 8.5 by varying the dipping duration. Even though we increased the dipping duration over 1,000 s, *η* de‐ creased. This may be due to the concentration quenching, influencing to the luminophore

AAPSP00.100, whose luminophore concentration was 0.1 mM.

as the luminescent intensity, *I*, for a given pressure and a temperature.

**5.1. Luminescent signal**

result of hexane.

application [29].

from 650 to 635 nm by increasing the pressure from 5 to 120 kPa. For temperature spectra, the peak was shifted from 640 to 645 nm by increasing the temperature from 10 to 50 °C. As described in Section 3, we integrated an obtained spectrum from 600 to 700 nm to determine as the luminescent intensity, *I*, for a given pressure and a temperature.

#### **5.1. Luminescent signal**

conditions. We can see that, as increasing the pressure, the luminescent spectrum decreased due to oxygen quenching [29]. As the temperature increases, we can see the spectrum de‐ creased due to the thermal quenching [29]. It was noticed that the luminescent peak was shifted

5 kPa

(a)

wavelength (nm)

120 kPa

10 C

integrated range

50 C

integrated range

600 650 700 750 800

(b) Figure 7. **(a).** Pressure spectra of AAPSPref. Thick line shows the spectrum at reference conditions of 100 kPa and 25 C. **(b).** temperature

**Figure 7.** (a). Pressure spectra of AAPSPref. Thick line shows the spectrum at reference conditions of 100 kPa and 25 °C. (b). temperature spectra of AAPSPref. Thick line shows the spectrum at reference conditions of 100 kPa and 25 °C.

wavelength (nm)

600 650 700 750 800

luminophore application method of dipping deposition greatly influenced the signal level. AAPSPind00 from the polarity index of 0.1 (hexane) showed very low RuDPP application on anodized aluminum, indicated by the signal level. Note that hexane did not dissolve RuDPP (Figure 6). AAPSPind02 from the polarity index of 2.4 (toluene) applied RuDPP well on anodized aluminum, which can be seen from the signal level. Here, toluene partially dissolved RuDPP. As increasing

was shown as a bar with the determined value. It is obvious that the

, related to the polarity index,

, was determined from Equation (2). Figure 8 (a) shows the signal level,

spectra of AAPSPref. Thick line shows the spectrum at reference conditions of 100 kPa and 25 C.

**5.1. Luminescent signal** 

normalized spectrum

0

1

2

3

4

normalized spectrum

0

1

2

3

4

218 Optical Sensors - New Developments and Practical Applications

normalized by the signal of AAPSPref at 100 kPa. The

The signal level,

The signal level, *η*, was determined from Equation (2). Figure 8 (a) shows the signal level, *η*, related to the polarity index, normalized by the signal of AAPSPref at 100 kPa. The *η* was shown as a bar with the determined value. It is obvious that the luminophore application method of dipping deposition greatly influenced the signal level. AAPSPind00 from the polarity index of 0.1 (hexane) showed very low RuDPP application on anodized aluminum, indicated by the signal level. Note that hexane did not dissolve RuDPP (Figure 6). AAPSPind02 from the polarity index of 2.4 (toluene) applied RuDPP well on anodized aluminum, which can be seen from the signal level. Here, toluene partially dissolved RuDPP. As increasing polarity index, RuDPP applied on anodized aluminum. However, the application suddenly dropped between polarity index at 6.4 of *N*, *N*-dimethyl amide and at 7.2 of dimethyl sulfoxide. The application brought back at the highest polarity index of 10.2 (water). The highest signal level of 1.89 was obtained from AA-PSPind05. It can be said that a range of polarity index of solvent exists that applies RuDPP. However, this range does not correspond to the range of dissolving RuDPP.

It is assumed that RuDPP remains as solution if it is dissolved well in a solvent. This assumption can be supported that *N*, *N*-dimethyl amide and dimethyl sulfoxide did not apply RuDPP well onto anodized aluminum. On the other hand, RuDPP applies onto anodized aluminum if it is partially dissolved in a solvent. This can be supported that toluene and water applied RuDPP onto anodized aluminum, even though these dissolved RuDPP partially. If a solvent did not dissolve RuDPP, it would not be applied onto anodized aluminum. This can be seen from the result of hexane.

As we increased the luminophore concentration from 0.001 mM to 0.1 mM, *η* increased (Figure 8 (b)). Note that the vertical axis in Figure 8 (b) was shown as log scale. The *η* was shown as a bar with the determined value. Even though we increased the concentration more than 0.1 mM, *η* decreased roughly by a half. This may be due to the concentration quenching [29]. There was an optimum concentration to maximize *η*. The maximum *η* was obtained from AAPSP00.100, whose luminophore concentration was 0.1 mM.

There was a peak dipping duration to maximize *η* (Figure 8 (c)). Note that the vertical axis in Figure 8 (c) was shown as log scale. The *η* was shown as a bar with the determined value. The maximum *η* was obtained from AAPSP1000, whose dipping duration was 1,000 s. For a short dipping duration, the luminophore would remain in the luminophore solution instead of applying onto the anodized surface. Roughly, the difference of *η* was a factor of 8.5 by varying the dipping duration. Even though we increased the dipping duration over 1,000 s, *η* de‐ creased. This may be due to the concentration quenching, influencing to the luminophore application [29].

**5.2. Pressure calibration**

polarity index of 10.2 (water).

Figure 9 shows pressure calibrations related to the polarity index, fitted with the adsorption controlled model in Equation (4). The reference was set at atmospheric conditions. The relationship between the luminescent ratio, *Iref/I*, and the pressure ratio, *p/pref*, was non-linear at low pressure region. We can see that the calibration was influenced by the solvent polarity.

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221

The pressure sensitivity, *σ*, was shown as a bar with the determined value from Equation (5) (Figure 9). The solvent polarity greatly influenced *σ*, even though the same luminophore was applied onto the same anodized aluminum. The highest *σ* of 0.62 was obtained from AAPSPref. This showed the peak sensitivity as varying the solvent polarity. Another peak was seen at the

**Figure 9.** Pressure calibration and pressure sensitivity, σ, related to the polarity of solvent.

Figure 8. **(a).** Signal level, , related to the polarity index. **(b).** Signal level, , related to the luminophore concentration. **(c).** Signal level, , related to the dipping duration **Figure 8.** (a). Signal level, η, related to the polarity index. (b). Signal level, η, related to the luminophore concentration. (c). Signal level, η, related to the dipping duration

#### **5.2. Pressure calibration**

polarity index

concentration (mM)

dipping duration (s)

100

101

102

103

104

105

0.001

0.01

0.1

1

10

0

16

26

25

2

4

6

13 14

8

10

220 Optical Sensors - New Developments and Practical Applications

AAPSPind10

AAPSPind04

AAPSPind07

AAPSPind06

AAPSPind00

49

43

(c). Signal level, η, related to the dipping duration

Figure 8. **(a).** Signal level,

related to the dipping duration

(a)

AAPSP10.000

AAPSP01.000

signal level,

84 100

signal level, h (%) 0 50 100 150 200

(%)

AAPSPind02

AAPSPref

AAPSPind05

189

(b)

signal level,

AAPSP00.001

67

69

28

signal level, h (%) 0 50 100 150 200

AAPSP100000

100

AAPSP00.010

100

(%)

AAPSPref

139

AAPSP100

167

AAPSP1000

AAPSPref

(c)

signal level,

AAPSP10

signal level, h (%) 0 50 100 150 200

(%)

**Figure 8.** (a). Signal level, η, related to the polarity index. (b). Signal level, η, related to the luminophore concentration.

, related to the luminophore concentration. **(c).** Signal level,

,

, related to the polarity index. **(b).** Signal level,

AAPSP1

20

45

Figure 9 shows pressure calibrations related to the polarity index, fitted with the adsorption controlled model in Equation (4). The reference was set at atmospheric conditions. The relationship between the luminescent ratio, *Iref/I*, and the pressure ratio, *p/pref*, was non-linear at low pressure region. We can see that the calibration was influenced by the solvent polarity.

The pressure sensitivity, *σ*, was shown as a bar with the determined value from Equation (5) (Figure 9). The solvent polarity greatly influenced *σ*, even though the same luminophore was applied onto the same anodized aluminum. The highest *σ* of 0.62 was obtained from AAPSPref. This showed the peak sensitivity as varying the solvent polarity. Another peak was seen at the polarity index of 10.2 (water).

**Figure 9.** Pressure calibration and pressure sensitivity, σ, related to the polarity of solvent.

Figure 10 shows pressure calibrations related to the luminophore concentration, fitted with the adsorption controlled model in Equation (4). We can see two groups in calibrations: the luminophore concentration up to 0.1 mM and the concentration higher than 0.1 mM. The former showed steeper calibrations than the latter. This tells us that the former group was more pressure sensitive than the latter.

The pressure sensitivity, *σ*, was determined by using Equation (5). This value was listed in the bar scale (Figure 10). AA-PSP with the luminophore concentration up to 0.1 mM showed *σ* around 60%, while AA-PSP with higher concentration than 0.1 mM showed *σ* around 30%. This tells us that even though the amount of luminophore over 0.1 mM was dissolved in the dipping solution, *σ* did not increase. The decrease in *σ* may be due to the concentration quenching [29].

Figure 10.Pressure calibration and pressure sensitivity, , related to the he luminophore concentration. **Figure 10.** Pressure calibration and pressure sensitivity, σ, related to the he luminophore concentration.

AAPSP100 and AAPSP1, respectively. Even though the fifth order difference in the dipping duration was provided, a minimal

of 65% and the minimum

was determined from Equation (5).

of 52% were obtained from

Figure 11 shows the pressure calibrations related to the dipping duration. The value of *σ* was determined from Equation (5). This value was shown as a bar scale in Figure 11. The maximum *σ* of 65% and the minimum *σ* of 52% were obtained from AAPSP100 and AAPSP1, respectively. Even though the fifth order difference in the dipping duration was provided, a minimal effect

Dipping Deposition Study of Anodized-Aluminum Pressure-Sensitive Paint for Unsteady Aerodynamic Applications

was seen on the pressure sensitivity.

Iref/I

0.0

0.2

0.4

0.6

0.8

1.0

1.2

Figure 11.Pressure calibration and pressure sensitivity,

100

101

102

103

104

105

**5.3. Temperature calibration** 

**5.3. Temperature calibration**

dipping duration (s)

12. The 

temperature. The temperature dependency,

dependent if it is more pressure sensitive.

showed a similar tendency to

pressure sensitivity, s (%)

Figure 12 shows temperature calibrations related to the polarity index. Calibration plots were fitted with the third order polynomial described in Equation (6). We can see a monotonic decrease of the luminescent signal with increase of the temperature. The temperature depend‐

0 20 40 60

pressure sensitivity,

**Figure 11.** Pressure calibration and pressure sensitivity, σ, related to the dipping duration.

, related to the dipping duration.

(%)

52

pressure (kPa) 0.0 0.2 0.4 0.6 0.8 1.0 1.2

AAPSP1 AAPSP10 AAPSP100 AAPSP1000 AAPSPref AAPSP100000

Figure 12 shows temperature calibrations related to the polarity index. Calibration plots were fitted with the third order polynomial described in Equation (6). We can see a monotonic decrease of the luminescent signal with increase of the

, was determined from Equation (7), which was listed as a bar scale in Figure

by varying the solvent polarity. This tells us that AA-PSP is more temperature

AAPSP10

65

63 62

59

AAPSP100

AAPSPref AAPSP1000

AAPSP100000

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223

AAPSP1

56

Figure 11 shows the pressure calibrations related to the dipping duration. The value of

This value was shown as a bar scale in Figure 11. The maximum

effect was seen on the pressure sensitivity.

Figure 11 shows the pressure calibrations related to the dipping duration. The value of *σ* was determined from Equation (5). This value was shown as a bar scale in Figure 11. The maximum *σ* of 65% and the minimum *σ* of 52% were obtained from AAPSP100 and AAPSP1, respectively. Even though the fifth order difference in the dipping duration was provided, a minimal effect was seen on the pressure sensitivity.

Figure 11.Pressure calibration and pressure sensitivity, , related to the dipping duration. **Figure 11.** Pressure calibration and pressure sensitivity, σ, related to the dipping duration.

#### **5.3. Temperature calibration 5.3. Temperature calibration**

Figure 10 shows pressure calibrations related to the luminophore concentration, fitted with the adsorption controlled model in Equation (4). We can see two groups in calibrations: the luminophore concentration up to 0.1 mM and the concentration higher than 0.1 mM. The former showed steeper calibrations than the latter. This tells us that the former group was more

The pressure sensitivity, *σ*, was determined by using Equation (5). This value was listed in the bar scale (Figure 10). AA-PSP with the luminophore concentration up to 0.1 mM showed *σ* around 60%, while AA-PSP with higher concentration than 0.1 mM showed *σ* around 30%. This tells us that even though the amount of luminophore over 0.1 mM was dissolved in the dipping solution, *σ* did not increase. The decrease in *σ* may be due to the concentration

pressure sensitive than the latter.

222 Optical Sensors - New Developments and Practical Applications

Iref/I

0.0

0.2

0.4

0.6

0.8

1.0

1.2

Figure 10.Pressure calibration and pressure sensitivity,

0.001

0.01

0.1

1

10

effect was seen on the pressure sensitivity.

concentration (mM)

This value was shown as a bar scale in Figure 11. The maximum

**Figure 10.** Pressure calibration and pressure sensitivity, σ, related to the he luminophore concentration.

Figure 11 shows the pressure calibrations related to the dipping duration. The value of

, related to the he luminophore concentration.

(%)

pressure (kPa) 0.0 0.2 0.4 0.6 0.8 1.0 1.2

33

31

AAPSP10.000

AAPSP01.000

AAPSP00.001 AAPSP00.010 AAPSPref AAPSP01.000 AAPSP10.000

AAPSP100 and AAPSP1, respectively. Even though the fifth order difference in the dipping duration was provided, a minimal

pressure sensitivity, s (%) 0 10 20 30 40 50 60 70

pressure sensitivity,

AAPSP00.010

AAPSP00.001 <sup>57</sup>

AAPSPref

of 65% and the minimum

58

62

was determined from Equation (5).

of 52% were obtained from

quenching [29].

Figure 12 shows temperature calibrations related to the polarity index. Calibration plots were fitted with the third order polynomial described in Equation (6). We can see a monotonic decrease of the luminescent signal with increase of the temperature. The temperature dependency, , was determined from Equation (7), which was listed as a bar scale in Figure 12. The showed a similar tendency to by varying the solvent polarity. This tells us that AA-PSP is more temperature dependent if it is more pressure sensitive. Figure 12 shows temperature calibrations related to the polarity index. Calibration plots were fitted with the third order polynomial described in Equation (6). We can see a monotonic decrease of the luminescent signal with increase of the temperature. The temperature depend‐

ency, *δ*, was determined from Equation (7), which was listed as a bar scale in Figure 12. The *δ* showed a similar tendency to *σ* by varying the solvent polarity. This tells us that AA-PSP is more temperature dependent if it is more pressure sensitive.

The temperature dependency, *δ*, was determined from Equation (7), which was listed as a bar scale in Figure 13. As we increased the luminophore concentration, *δ* decreased. Roughly, *δ* became more than a half by setting the luminophore concentration from 0.001 to 10 mM.

Dipping Deposition Study of Anodized-Aluminum Pressure-Sensitive Paint for Unsteady Aerodynamic Applications

Figure 13.Temperature calibration and temperature dependency related to the luminophore concentration.

The temperature calibrations showed the decrease in *I* with increase of the temperature.

The value of

increase of the temperature.

concentration (mM)

0.001

0.01

0.1

1

10

I/Iref

0.6

0.8

1.0

1.2

1.4

1.6

duration, we can see that

temperature dependency.

Figure 14 shows the temperature calibrations related to the dipping duration. The calibrations were fitted with Equation (6).

Figure 14 shows the temperature calibrations related to the dipping duration. The calibrations were fitted with Equation (6). The temperature calibrations showed the decrease in *I* with

temperature dependency,

**Figure 13.** Temperature calibration and temperature dependency related to the luminophore concentration.

factor of 2. Compared to the effect on the pressure sensitivity, the dipping duration showed a greater effect on the

The value of *δ* was determined from Equation (7), which was listed as a bar scale in Figure 14. With increase the dipping duration, we can see that *δ* decreased until 100 s and increased over this dipping duration. The difference of *δ* was roughly a factor of 2. Compared to the

was determined from Equation (7), which was listed as a bar scale in Figure 14. With increase the dipping

was roughly a

decreased until 100 s and increased over this dipping duration. The difference of

temperature dependency, h (%/C) 0.0 -0.5 -1.0 -1.5 -2.0 -2.5




temperature (<sup>o</sup>

AAPSP10.000



AAPSP01.000

10 20 30 40 50

C)

(%/ºC)

AAPSP00.010

AAPSPref

AAPSP00.001

AAPSP00.001 AAPSP00.010 AAPSPref AAPSP01.000 AAPSP10.000

http://dx.doi.org/10.5772/57416

225

Figure 12.Temperature calibration and temperature dependency related to the polarity index. **Figure 12.** Temperature calibration and temperature dependency related to the polarity index.

concentration decreases, the calibrations became steep. This tells us that the temperature dependency tends to increase as the luminophore concentration decreases. The temperature dependency, , was determined from Equation (7), which was listed as a bar scale in Figure 13. As we increased the luminophore concentration, decreased. Roughly, became more than a half by setting the luminophore concentration from 0.001 to 10 mM. Figure 13 shows temperature calibrations related to the luminophore concentration. Calibra‐ tion plots were fitted with Equation (6). The calibrations show a monotonic decrease in luminescent signal as the temperature increased. As the concentration decreases, the calibra‐ tions became steep. This tells us that the temperature dependency tends to increase as the luminophore concentration decreases.

Figure 13 shows temperature calibrations related to the luminophore concentration. Calibration plots were fitted with Equation (6). The calibrations show a monotonic decrease in luminescent signal as the temperature increased. As the The temperature dependency, *δ*, was determined from Equation (7), which was listed as a bar scale in Figure 13. As we increased the luminophore concentration, *δ* decreased. Roughly, *δ* became more than a half by setting the luminophore concentration from 0.001 to 10 mM.

ency, *δ*, was determined from Equation (7), which was listed as a bar scale in Figure 12. The *δ* showed a similar tendency to *σ* by varying the solvent polarity. This tells us that AA-PSP is

more temperature dependent if it is more pressure sensitive.

I/Iref

0.6

polarity index

0.8

1.0

1.2

1.4

1.6

224 Optical Sensors - New Developments and Practical Applications

Figure 12.Temperature calibration and temperature dependency related to the polarity index.

**Figure 12.** Temperature calibration and temperature dependency related to the polarity index.

AAPSPind07

AAPSPind06


the luminophore concentration decreases.

increased the luminophore concentration,

luminophore concentration decreases.

0

2

4

6


8

10

The temperature dependency,

concentration from 0.001 to 10 mM.

Figure 13 shows temperature calibrations related to the luminophore concentration. Calibration plots were fitted with Equation (6). The calibrations show a monotonic decrease in luminescent signal as the temperature increased. As the concentration decreases, the calibrations became steep. This tells us that the temperature dependency tends to increase as

Figure 13 shows temperature calibrations related to the luminophore concentration. Calibra‐ tion plots were fitted with Equation (6). The calibrations show a monotonic decrease in luminescent signal as the temperature increased. As the concentration decreases, the calibra‐ tions became steep. This tells us that the temperature dependency tends to increase as the

temperature dependency, h (%/C) 0.0 -0.5 -1.0 -1.5 -2.0 -2.5

AAPSPind05


temperature dependency,



temperature (C) 10 20 30 40 50

AAPSPind10

AAPSPind02


decreased. Roughly,

, was determined from Equation (7), which was listed as a bar scale in Figure 13. As we

(%/ºC)

AAPSPind00

AAPSPref


AAPSPind04

became more than a half by setting the luminophore

AAPSPind00 AAPSPind02 AAPSPref AAPSPind04 AAPSPind05 AAPSPind06 AAPSPind07 AAPSPind10

Figure 13.Temperature calibration and temperature dependency related to the luminophore concentration. **Figure 13.** Temperature calibration and temperature dependency related to the luminophore concentration.

Figure 14 shows the temperature calibrations related to the dipping duration. The calibrations were fitted with Equation (6). The temperature calibrations showed the decrease in *I* with increase of the temperature. The value of was determined from Equation (7), which was listed as a bar scale in Figure 14. With increase the dipping duration, we can see that decreased until 100 s and increased over this dipping duration. The difference of was roughly a Figure 14 shows the temperature calibrations related to the dipping duration. The calibrations were fitted with Equation (6). The temperature calibrations showed the decrease in *I* with increase of the temperature.

temperature dependency. The value of *δ* was determined from Equation (7), which was listed as a bar scale in Figure 14. With increase the dipping duration, we can see that *δ* decreased until 100 s and increased over this dipping duration. The difference of *δ* was roughly a factor of 2. Compared to the

factor of 2. Compared to the effect on the pressure sensitivity, the dipping duration showed a greater effect on the

effect on the pressure sensitivity, the dipping duration showed a greater effect on the temper‐ ature dependency.

changes from the electrical noise. Response times of AA-PSP were determined at the 90 % rise of *pnorm* (Section 4.1). The results ranged from 30 to 40 µs. In our setup, the thickness of anodized aluminum was 10 µm. This had ±10 % uncertainty from our instrument (Kett LZ-330). Kameda *et al*. reported that response time of AA-PSP is proportional to the squared value of its thickness, which corresponds to about ±20 % uncertainty in our measurement results [26]. Response time results were within this uncertainty, even though there were variations in step response of AA-PSPs. Considering the thickness uncertainty, response times of AA-PSPs can be said on the order of ten microseconds with the anodized-aluminum thickness of 10 µm. Sakaue *et al*. reported that the response time of AA-PSP showed a minimal effect by the luminophore selected [31]. This indicates that the response time of AA-PSP has smaller effect

Dipping Deposition Study of Anodized-Aluminum Pressure-Sensitive Paint for Unsteady Aerodynamic Applications

on the luminophore application parameters than the effect on AA-PSP thickness.

running time (ms) -0.02 0.00 0.02 0.04 0.06 0.08 0.10

**Figure 15.** Response time results related to the solvent polarity.

influenced by the luminophore-application parameters.

time (s)

0 20 40 60 80 100

**6. Discussion: AA-PSP characterizations related to Luminophore**

p

norm

0.0

0

**Application Parameters**

0.2

0.4

pnorm

0.6

0.8

1.0

1

90% rise

FIG. 12. Hirotaka Sakaue

Table 2 lists the maximum and minimum values of AA-PSP characterizations: signal level, pressure sensitivity, and temperature dependency. The signal level was greatly influenced by varying the solvent polarity. The difference was a factor of 14.5. The second largest effect was the dipping duration. The difference in the signal level was a factor of 8.4. The luminophore concentration influenced the signal level for a factor of 3.6. Overall, the signal level was most

The pressure sensitivity was greatly influenced by the solvent polarity. The difference in the sensitivity was a factor of 10.3. By varying the luminophore concentration, the difference was

AA-PSPind02 AA-PSPind03 AA-PSPind04 AA-PSPind05 response time (s) 30 30 40 30

including thickness uncertainty (s) 25 to 37 25 to 37 33 to 49 25 to 37

http://dx.doi.org/10.5772/57416

227

Figure 14.Temperature calibration and temperature dependency related to the dipping duration. **Figure 14.** Temperature calibration and temperature dependency related to the dipping duration.

smaller effect on the luminophore application parameters than the effect on AA-PSP thickness.

#### **5.4. Response time 5.4. Response time**

shows response time results of AA-PSPs. Because each shock tube measurement was done by a single measurement, electrical noise with high frequency content still existed. This limited the response time characterization. The limited results were shown from the solvent polarity: AAPSPind02, AAPSPind03, AAPSPind04, and AAPSPind05. These had relatively high signal levels and pressure sensitivities to separate their luminescent signal changes from the electrical noise. Response times of AA-PSP were determined at the 90 % rise of *pnorm* (Section 4.1). The results ranged from 30 to 40 s. In our setup, the thickness of anodized aluminum was 10 m. This had ±10 % uncertainty from our instrument (Kett LZ-330). Kameda *et al*. reported that response time of AA-PSP is proportional to the squared value of its thickness, which corresponds to about ±20 % uncertainty in our measurement results [26]. Response time results were within this uncertainty, even though there were A normalized step change of pressure, *pnorm*, was converted from luminescent signals through the Equation (8). Figure 15 shows response time results of AA-PSPs. Because each shock tube measurement was done by a single measurement, electrical noise with high frequency content still existed. This limited the response time characterization. The limited results were shown from the solvent polarity: AAPSPind02, AAPSPind03, AAPSPind04, and AAPSPind05. These had relatively high signal levels and pressure sensitivities to separate their luminescent signal

variations in step response of AA-PSPs. Considering the thickness uncertainty, response times of AA-PSPs can be said on the order of ten microseconds with the anodized-aluminum thickness of 10 m. Sakaue *et al*. reported that the response time of AA-PSP showed a minimal effect by the luminophore selected [31]. This indicates that the response time of AA-PSP has

A normalized step change of pressure, *pnorm*, was converted from luminescent signals through the Equation (8). Figure 15

changes from the electrical noise. Response times of AA-PSP were determined at the 90 % rise of *pnorm* (Section 4.1). The results ranged from 30 to 40 µs. In our setup, the thickness of anodized aluminum was 10 µm. This had ±10 % uncertainty from our instrument (Kett LZ-330). Kameda *et al*. reported that response time of AA-PSP is proportional to the squared value of its thickness, which corresponds to about ±20 % uncertainty in our measurement results [26]. Response time results were within this uncertainty, even though there were variations in step response of AA-PSPs. Considering the thickness uncertainty, response times of AA-PSPs can be said on the order of ten microseconds with the anodized-aluminum thickness of 10 µm. Sakaue *et al*. reported that the response time of AA-PSP showed a minimal effect by the luminophore selected [31]. This indicates that the response time of AA-PSP has smaller effect on the luminophore application parameters than the effect on AA-PSP thickness.

**Figure 15.** Response time results related to the solvent polarity.

p

norm

effect on the pressure sensitivity, the dipping duration showed a greater effect on the temper‐

temperature (<sup>o</sup>


10 20 30 40 50


C)

AAPSP100000

AAPSPref

(%/ºC)

AAPSP10


AAPSP1000


AAPSP100

AAPSP1 AAPSP10 AAPSP100 AAPSP1000 AAPSPref AAPSP100000

Figure 14.Temperature calibration and temperature dependency related to the dipping duration.

smaller effect on the luminophore application parameters than the effect on AA-PSP thickness.

A normalized step change of pressure, *pnorm*, was converted from luminescent signals through the Equation (8). Figure 15 shows response time results of AA-PSPs. Because each shock tube measurement was done by a single measurement, electrical noise with high frequency content still existed. This limited the response time characterization. The limited results were shown from the solvent polarity: AAPSPind02, AAPSPind03, AAPSPind04, and AAPSPind05. These had relatively high signal levels and pressure sensitivities to separate their luminescent signal changes from the electrical noise. Response times of AA-PSP were determined at the 90 % rise of *pnorm* (Section 4.1). The results ranged from 30 to 40 s. In our setup, the thickness of anodized aluminum was 10 m. This had ±10 % uncertainty from our instrument (Kett LZ-330). Kameda *et al*. reported that response time of AA-PSP is proportional to the squared value of its thickness, which corresponds to about ±20 % uncertainty in our measurement results [26]. Response time results were within this uncertainty, even though there were variations in step response of AA-PSPs. Considering the thickness uncertainty, response times of AA-PSPs can be said on the order of ten microseconds with the anodized-aluminum thickness of 10 m. Sakaue *et al*. reported that the response time of AA-PSP showed a minimal effect by the luminophore selected [31]. This indicates that the response time of AA-PSP has

A normalized step change of pressure, *pnorm*, was converted from luminescent signals through the Equation (8). Figure 15 shows response time results of AA-PSPs. Because each shock tube measurement was done by a single measurement, electrical noise with high frequency content still existed. This limited the response time characterization. The limited results were shown from the solvent polarity: AAPSPind02, AAPSPind03, AAPSPind04, and AAPSPind05. These had relatively high signal levels and pressure sensitivities to separate their luminescent signal

temperature dependency, h (%/C) 0.0 -0.5 -1.0 -1.5 -2.0 -2.5

AAPSP1


temperature dependency,

**Figure 14.** Temperature calibration and temperature dependency related to the dipping duration.


ature dependency.

I/Iref

0.6

dipping duration (s)

100

101

102

103

104

105

0.8

1.0

1.2

1.4

1.6

226 Optical Sensors - New Developments and Practical Applications

**5.4. Response time** 

**5.4. Response time**

#### FIG. 12. Hirotaka Sakaue **6. Discussion: AA-PSP characterizations related to Luminophore Application Parameters**

running time (ms)

Table 2 lists the maximum and minimum values of AA-PSP characterizations: signal level, pressure sensitivity, and temperature dependency. The signal level was greatly influenced by varying the solvent polarity. The difference was a factor of 14.5. The second largest effect was the dipping duration. The difference in the signal level was a factor of 8.4. The luminophore concentration influenced the signal level for a factor of 3.6. Overall, the signal level was most influenced by the luminophore-application parameters.

The pressure sensitivity was greatly influenced by the solvent polarity. The difference in the sensitivity was a factor of 10.3. By varying the luminophore concentration, the difference was a factor of 2. The difference was a factor of 1.2 by varying the dipping duration. Among the dipping parameters, the pressure sensitivity was most influenced by the solvent polarity.

The effect of AA-PSP response time due to the dipping deposition method was smaller than the effect by the thickness uncertainty of AA-PSP. With the anodized-aluminum thickness of 10 µm, the response time characterization was within the thickness uncertainty. The response

Dipping Deposition Study of Anodized-Aluminum Pressure-Sensitive Paint for Unsteady Aerodynamic Applications

http://dx.doi.org/10.5772/57416

229

The author would like to thank his colleagues for technical supports: Dr. K. Morita (JAXA), Mr. Y. Iijima (JAXA), Ms. K. Ishii (The University of Tokyo), Mr. Y. Yamada (The University of Electro-Communications), and Prof. Y. Sakamura (Toyama Prefectural University).

Institute of Aeronautical Technology, Japan Aerospace Exploration Agency / Chofu, Tokyo,

[11] Hayashi T, *et al*. 2012. 28th International Symposium on Shock Waves, Vol. 1, ISBN

time was on the order of ten microseconds.

Address all correspondence to: sakaue@chofu.jaxa.jp

[1] Nakakita K, *et al*. 2000. AIAA2000-2523.

[3] Ishiguro Y, *et al.* 2007. AIAA2007-01187.

[4] Miyamoto K, *et al*. 2010. AIAA2010-4798.

[6] Disotell KJ, Gregory JW. 2011. Rev. Sci. Instrum. 82:075112.

[8] Yang L, *et al*. 2012. Int. J. Heat Fluid Flow 37: 9 – 21.

[9] Yang L, *et al*. 2012. Sens. Actuators B 161:100 – 7.

[10] Yang L, *et al*. 2012. Exp. Therm. Fluid Sci. 40:50 –56.

[5] Morita K, *et al*. 2011. AIAA2011-3724.

[7] Disotell KJ, *et al*. 2012. AIAA2012-2757.

978-3-642-25687-5, pp. 607 – 613.

[2] Nakakita K, Asai K. 2002. AIAA2002-2911.

**Acknowledgements**

**Author details**

Hirotaka Sakaue\*

Japan

**References**

The temperature dependency was greatly influenced by the solvent polarity. The difference was a factor of 8. The differences by the luminophore concentration and the dipping duration were on the same order, which was a factor of 2. The temperature dependency was influenced by the dipping parameters, but the change was not as large as that of the pressure sensitivity. Overall, the solvent polarity influenced the most of the AA-PSP characterizations.


**Table 2.** The maximum and minimum AA-PSP characterizations.

#### **7. Conclusions**

The luminophore application method of dipping deposition was studied to provide the relationship between this method and AA-PSP characterizations for fabricating an optimized optical pressure sensor for unsteady aerodynamic applications. The characterizations were the signal level, pressure sensitivity, temperature dependency, and response time. Three impor‐ tant parameters in the luminophore application method were studied: solvent polarity, luminophore concentration, and dipping duration. It was found that the AA-PSP characteri‐ zations were related to one another. Therefore, an absolute optimization of the luminophore application method was not obtained. However, the relationship among these characteriza‐ tions and the luminophore-application parameters were revealed, which were concluded as follows.

The solvent polarity was the most influencing parameter. The signal level showed the widest range from 13% to 189% compared to the signal level of the reference AA-PSP (100%). The pressure sensitivity ranged from 6 to 62 %, and the temperature dependency from -0.2 to -1.6 %/°C. It was seen that the pressure-sensitive AA-PSP was also temperature sensitive. It was shown qualitatively by photograph that the solubility was related to the solvent polarity. Well luminophore-dissolved solvents did not show higher AA-PSP outputs. This may be that the luminophore remained in the solvent and was not applied onto the anodized-aluminum surface well.

The luminophore concentration and dipping duration greatly influenced to the signal level. However, the influence to the pressure sensitivity and the temperature dependency was relatively small. The difference was less than or equal to a factor of 2.

The effect of AA-PSP response time due to the dipping deposition method was smaller than the effect by the thickness uncertainty of AA-PSP. With the anodized-aluminum thickness of 10 µm, the response time characterization was within the thickness uncertainty. The response time was on the order of ten microseconds.

#### **Acknowledgements**

a factor of 2. The difference was a factor of 1.2 by varying the dipping duration. Among the dipping parameters, the pressure sensitivity was most influenced by the solvent polarity.

The temperature dependency was greatly influenced by the solvent polarity. The difference was a factor of 8. The differences by the luminophore concentration and the dipping duration were on the same order, which was a factor of 2. The temperature dependency was influenced by the dipping parameters, but the change was not as large as that of the pressure sensitivity.

η (%) 189 13 100 27.5 167.1 20.1 σ (%) 62 6 62 31 65 52 δ (%/ºC) -0.2 -1.6 −0.6 −1.4 −1.1 −2.4

The luminophore application method of dipping deposition was studied to provide the relationship between this method and AA-PSP characterizations for fabricating an optimized optical pressure sensor for unsteady aerodynamic applications. The characterizations were the signal level, pressure sensitivity, temperature dependency, and response time. Three impor‐ tant parameters in the luminophore application method were studied: solvent polarity, luminophore concentration, and dipping duration. It was found that the AA-PSP characteri‐ zations were related to one another. Therefore, an absolute optimization of the luminophore application method was not obtained. However, the relationship among these characteriza‐ tions and the luminophore-application parameters were revealed, which were concluded as

The solvent polarity was the most influencing parameter. The signal level showed the widest range from 13% to 189% compared to the signal level of the reference AA-PSP (100%). The pressure sensitivity ranged from 6 to 62 %, and the temperature dependency from -0.2 to -1.6 %/°C. It was seen that the pressure-sensitive AA-PSP was also temperature sensitive. It was shown qualitatively by photograph that the solubility was related to the solvent polarity. Well luminophore-dissolved solvents did not show higher AA-PSP outputs. This may be that the luminophore remained in the solvent and was not applied onto the anodized-aluminum

The luminophore concentration and dipping duration greatly influenced to the signal level. However, the influence to the pressure sensitivity and the temperature dependency was

relatively small. The difference was less than or equal to a factor of 2.

**Solvent Polarity Luminophore Concentration Dipping Duration max. min. max. min. max. min.**

Overall, the solvent polarity influenced the most of the AA-PSP characterizations.

**Table 2.** The maximum and minimum AA-PSP characterizations.

228 Optical Sensors - New Developments and Practical Applications

**7. Conclusions**

follows.

surface well.

The author would like to thank his colleagues for technical supports: Dr. K. Morita (JAXA), Mr. Y. Iijima (JAXA), Ms. K. Ishii (The University of Tokyo), Mr. Y. Yamada (The University of Electro-Communications), and Prof. Y. Sakamura (Toyama Prefectural University).

## **Author details**

Hirotaka Sakaue\*

Address all correspondence to: sakaue@chofu.jaxa.jp

Institute of Aeronautical Technology, Japan Aerospace Exploration Agency / Chofu, Tokyo, Japan

#### **References**


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230 Optical Sensors - New Developments and Practical Applications

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*Edited by Mohamad Yasin, Sulaiman Wadi Harun and Hamzah Arof*

This book is a compilation of works presenting recent developments and practical applications in optical sensor technology. It contains 10 chapters that encompass contributions from various individuals and research groups working in the area of optical sensing. It provides the reader with a broad overview and sampling of the innovative research on optical sensors in the world.

Optical Sensors - New Developments and Practical Applications

Optical Sensors

New Developments and Practical Applications

*Edited by Mohamad Yasin,* 

*Sulaiman Wadi Harun and Hamzah Arof*

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