**4. Pressure Sensitive Paints (PSP) and Pressure Sensitive Molecular Film (PSMF)**

There have been no appropriate techniques for the measurement of gas pressure on a solid surface inside micro‐systems. To measure pressure distributions in a low density gas‐flows with high Knudsen number, a pressure sensitive paint (PSP) technique [10, 11] have been adopted.

The pressure measurement technique using PSP is based on the oxygen quenching of lumi‐ nescent molecules. PSP is composed of luminescent molecules and a binder material to fix the luminescent molecules to a solid surface. Figure 11 depicts the schematic energy level diagram for PSP and oxygen molecules. When PSP layer applied to the surface is illuminated by UV light, the luminescent molecules are excited by absorption of photon energy, and then the molecules emit luminescence. On the other hand, oxygen molecule with triplet ground state acts as a quencher of the luminescence. As a result, the phosphorescence intensity decreases as an increase in partial pressure of oxygen. Pressure on the solid surface can be deduced from the relationship between pressure and the luminescence intensity (Stern‐Volmer plot [11]).

$$\frac{I\_{\text{ref}}}{I} = \sum\_{n=1}^{N} A\_n \left(\frac{P}{P\_{\text{ref}}}\right)^n \tag{3}$$

ThePSMF sample was appliedto a glass slide, andthe sample was setinside a vacuum chamber evacuated by vacuum pumps to examine the pressure sensitivity. Pure oxygen gas was supplied into the chamber, and the pressure in the chamber was monitored by a capacitance manometer. The temperature of the sample was controlled by a Peltier element. A xenon‐arc lamp with a band‐pass filter (400 ± 20 nm) was used as an excitation light source illuminating the sample via an optical fiber. The luminescence was filtered by a long‐pass filter (600 nm) to eliminate the light from the xenon‐arc lamp, and was detected by an image intensified CCD

High Knudsen Number Flow — Optical Diagnostic Techniques 43

The PSMF based on Pd(II) Mesoporphyrin IX (PdMP), which is used as luminescent molecules, has been fabricated and it is clarified that the pressure sensitivity of PSMF of PdMP is suffi‐ ciently high [14]. However, the PSMF composed of PdMP cannot be applicable to the pressure range higher than 130 Pa due to saturation of oxygen quenching of PdMP; this is caused by the long life time of PdMP, which is so long (1.0 msec [15]) that most of luminescent molecules are quenched. It is desired for PSMF to work around an atmospheric pressure, because the most micro‐devices are used in an atmospheric pressure. In order to fabricate a useful PSMF for an atmospheric pressure range, four samples of PSMFs are prepared, composed of Pt(II) Mesoporphyrin IX (PtMP), Pt(II) Mesoporphyrin IX dimethylester (PtMPDME), Pt(II) Proto‐ porphyrin IX (PtPP) and Cu(II) Mesoporphyrin IX dimethylester (CuMPDME). Those lumi‐ nescent molecules have shorter life time compared with PdMP (e.g. the life time of PtMPDME and CuMPDME are 0.14 msec and 0.1 msec, respectively [15]). Figure 12 shows the pressure sensitivities offour PSMFs below 21 kPa (equalto the partial pressure of oxygen in atmospheric pressure) [16]. The horizontal axis of the Stern‐Volmer plot is the normalized pressure *P*/*P*ref and the vertical axis is the inverse luminescent intensity ratio *I*ref/*I*, where *I*ref is the reference luminescent intensity at the reference pressure *P*ref = 1.0 × 10‐<sup>2</sup> Pa. It is clarified that the pressure sensitivity of PtMP is highest among the four tested PSMFs and is comparable to that of conventional PSPs. The temperature dependency of PSMF also has to be studied, because that of PSP is the main factor of the measurement error. PSMF was applied to the measurement of

camera (512 × 512 pixels, 14 bit).

micro gas‐flows [17].

**Figure 12.** Stern-Volmer plots of PSMFs [16]

where *I* is the luminescence intensity and *P* is the oxygen pressure. *I*ref is the luminescence intensity at a known reference pressure *P*ref. The coefficients *An* are the constants called as the Stern‐Volmer coefficients determined by calibration tests. The luminescence intensity *I* of the ideal PSP (*N* = 1) depends inversely on *P* following to Eq. 3, but actual PSPs have nonlinear dependence of *I* ‐<sup>1</sup> on *P*. In practice, a second‐order polynomial (*N* = 2) is commonly used.

Because PSP works as a so‐called ʺmolecular sensorʹʹ, it seems also suitable for analyses of high Knudsen number flows, which require diagnostic tools in the molecular level. However, an application of PSP to micro‐devices is very difficult, because conventional PSPs are very thick compared to the dimension of micro‐devices owing to the use of polymer binders. Moreover, they do not have sufficient spatialresolution forthe pressure measurement of micro‐flows due to the aggregation of luminescent molecules in polymer binders [12].

Pressure‐sensitive molecular films (PSMFs) have been developed by using the Langmuir‐ Blodgett (LB) technique [13] to fabricate thin films, and tested to confirm the feasibility of the pressure measurement around micro‐devices [14]. PSMF with nanometer order thickness and high spatial resolution is suitable for analyses of micro‐flows.

LB films are fabricated according to the following procedure. First, a drop of a dilute solution of amphiphilic molecules in a volatile solvent is spread on the interface between air and sub‐ phase. After the solvent is evaporated, a monolayer of the molecules remains on the interface. The monolayer is transferred to a substrate with compressing the monolayer so as to control the order of the molecules.

In some cases, arachidic acid (AA) has been adopted as a spacer molecule to control the intermolecular spacing of luminescent molecules, and to form a stable LB film with highly ordered structure. However, it is desirable for high pressure sensitivity to adjust the molar ratio of luminophore and AA [14].

**Figure 11.** Schematic energy level diagram. S: Singlet state, T: Triplet state.

ThePSMF sample was appliedto a glass slide, andthe sample was setinside a vacuum chamber evacuated by vacuum pumps to examine the pressure sensitivity. Pure oxygen gas was supplied into the chamber, and the pressure in the chamber was monitored by a capacitance manometer. The temperature of the sample was controlled by a Peltier element. A xenon‐arc lamp with a band‐pass filter (400 ± 20 nm) was used as an excitation light source illuminating the sample via an optical fiber. The luminescence was filtered by a long‐pass filter (600 nm) to eliminate the light from the xenon‐arc lamp, and was detected by an image intensified CCD camera (512 × 512 pixels, 14 bit).

The PSMF based on Pd(II) Mesoporphyrin IX (PdMP), which is used as luminescent molecules, has been fabricated and it is clarified that the pressure sensitivity of PSMF of PdMP is suffi‐ ciently high [14]. However, the PSMF composed of PdMP cannot be applicable to the pressure range higher than 130 Pa due to saturation of oxygen quenching of PdMP; this is caused by the long life time of PdMP, which is so long (1.0 msec [15]) that most of luminescent molecules are quenched. It is desired for PSMF to work around an atmospheric pressure, because the most micro‐devices are used in an atmospheric pressure. In order to fabricate a useful PSMF for an atmospheric pressure range, four samples of PSMFs are prepared, composed of Pt(II) Mesoporphyrin IX (PtMP), Pt(II) Mesoporphyrin IX dimethylester (PtMPDME), Pt(II) Proto‐ porphyrin IX (PtPP) and Cu(II) Mesoporphyrin IX dimethylester (CuMPDME). Those lumi‐ nescent molecules have shorter life time compared with PdMP (e.g. the life time of PtMPDME and CuMPDME are 0.14 msec and 0.1 msec, respectively [15]). Figure 12 shows the pressure sensitivities offour PSMFs below 21 kPa (equalto the partial pressure of oxygen in atmospheric pressure) [16]. The horizontal axis of the Stern‐Volmer plot is the normalized pressure *P*/*P*ref and the vertical axis is the inverse luminescent intensity ratio *I*ref/*I*, where *I*ref is the reference luminescent intensity at the reference pressure *P*ref = 1.0 × 10‐<sup>2</sup> Pa. It is clarified that the pressure sensitivity of PtMP is highest among the four tested PSMFs and is comparable to that of conventional PSPs. The temperature dependency of PSMF also has to be studied, because that of PSP is the main factor of the measurement error. PSMF was applied to the measurement of micro gas‐flows [17].

**Figure 12.** Stern-Volmer plots of PSMFs [16]

*I*ref *<sup>I</sup>* = ∑ *n*=1 *N An*( *<sup>P</sup> P*ref

to the aggregation of luminescent molecules in polymer binders [12].

high spatial resolution is suitable for analyses of micro‐flows.

**Figure 11.** Schematic energy level diagram. S: Singlet state, T: Triplet state.

dependence of *I*

Biomedical Engineering

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the order of the molecules.

ratio of luminophore and AA [14].

where *I* is the luminescence intensity and *P* is the oxygen pressure. *I*ref is the luminescence intensity at a known reference pressure *P*ref. The coefficients *An* are the constants called as the Stern‐Volmer coefficients determined by calibration tests. The luminescence intensity *I* of the ideal PSP (*N* = 1) depends inversely on *P* following to Eq. 3, but actual PSPs have nonlinear

Micro-Nano Mechatronics — New Trends in Material, Measurement, Control, Manufacturing and Their Applications in

Because PSP works as a so‐called ʺmolecular sensorʹʹ, it seems also suitable for analyses of high Knudsen number flows, which require diagnostic tools in the molecular level. However, an application of PSP to micro‐devices is very difficult, because conventional PSPs are very thick compared to the dimension of micro‐devices owing to the use of polymer binders. Moreover, they do not have sufficient spatialresolution forthe pressure measurement of micro‐flows due

Pressure‐sensitive molecular films (PSMFs) have been developed by using the Langmuir‐ Blodgett (LB) technique [13] to fabricate thin films, and tested to confirm the feasibility of the pressure measurement around micro‐devices [14]. PSMF with nanometer order thickness and

LB films are fabricated according to the following procedure. First, a drop of a dilute solution of amphiphilic molecules in a volatile solvent is spread on the interface between air and sub‐ phase. After the solvent is evaporated, a monolayer of the molecules remains on the interface. The monolayer is transferred to a substrate with compressing the monolayer so as to control

In some cases, arachidic acid (AA) has been adopted as a spacer molecule to control the intermolecular spacing of luminescent molecules, and to form a stable LB film with highly ordered structure. However, it is desirable for high pressure sensitivity to adjust the molar

‐<sup>1</sup> on *P*. In practice, a second‐order polynomial (*N* = 2) is commonly used.

)*<sup>n</sup>* (3)

The flow in a converging‐diverging nozzle was examined for the demonstration, because the pressure considerably changes in a nozzle and it was easy to compare the result with a numerical one.

Figure 13 shows the geometry of a converging‐diverging micro‐nozzle, which was two dimensional geometry, and the thickness of the micronozzles was 1.0 mm, and the width of the throat was 103 μm, the diverging length was 492 μm and the diverging angle was 23.5 degrees. The micro‐nozzle was put on a holder with an inlet and outlet port, and then it was covered with the PSMF deposited glass (see Figure 13b). Air was supplied from the inlet port, and the outlet port was evacuated by a scroll pump. PtMP was employed as a luminophore of PSMF. Luminescent intensity of PSMF was detected through a fluorescent microscope. The images were taken with the exposure time of 8.0 s, and 32 pictures were averaged to reduce the noise.

The micro‐nozzle flow was analyzed by the direct simulation Monte Carlo (DSMC) method [18], which is a popular method for high Knudsen number flow analysis. The numerical

High Knudsen Number Flow — Optical Diagnostic Techniques 45

Figure 14 shows the pressure distribution of the micro‐nozzle with the inlet pressure *Pin* = 10.0 kPa and the outlet pressure *Pout* = 1.0 kPa, where the wind‐off images were taken at *Pin* = *Pout* = 1.0 kPa. The numerical result by DSMC is also shown in the lower side of Figure 14. Moreover, the pressure profiles along the centerline are shown in Figure 14b. Though the pressure profile contains some noise as shown in Figure 14b, it is clearly observed that the pressure distribution obtained by PSMF is quantitatively in good agreement with that by DSMC. Especially, the sharp pressure drop near the throat was captured by PSMF, and this result indicates that the spatial resolution of PSMF is high enough for micro‐scale measurement. The pressure value at ‐300 μm from the throat is about 8 kPa as shown in Figure 14b and is smaller than P*in* = 10.0 kPa, which was measured at ‐10 mm. This pressure drop may be caused by wall friction and

Department of Micro‐Nano Systems Engineering, Nagoya University, Nagoya, Japan

Gas Dynamics 1988, Space‐Related Studies, AIAA; 391‐406.

JSME International Journal Series B 1996;39(1) 95‐100.

molecules. Molecular Physics 1976;31(4) 1199‐1211.

Gas Dynamics 1991: 1482‐1489.

[1] Fujimoto T, Niimi T. Three Dimensional Structures of Interacting Freejets. Rarefied

[2] Niimi T, Fujimoto T, Taoi N. Flow Fields of Interacting Parallel Supersonic Free Jets.

[3] Mori H, Taniguchi M, Nishihira R, Niimi T. Experimental Analyses of Linear‐Type

[4] Niimi T, Fujimoto T, Shimizu N. Planar Measurement of Temperature in Rarefied Gas Flow by LIF Images. Proceedings of 17th International Symposium on Rarefied

[5] Bray R. G, Hochstrasser R. M. (1976). Two‐photon absroption by rotating diatomic

Aerospike Nozzles with and without Sidewalls. AIAA paper 2005; 1350.

conditions were adjusted to the PSMF experimental conditions.

the acceleration at the converging area of the nozzle.

**Author details**

Tomohide Niimi

**References**

**Figure 13.** Micro-nozzle.

**Figure 14.** Pressure distribution inside the micro-nozzle [17].

The micro‐nozzle flow was analyzed by the direct simulation Monte Carlo (DSMC) method [18], which is a popular method for high Knudsen number flow analysis. The numerical conditions were adjusted to the PSMF experimental conditions.

Figure 14 shows the pressure distribution of the micro‐nozzle with the inlet pressure *Pin* = 10.0 kPa and the outlet pressure *Pout* = 1.0 kPa, where the wind‐off images were taken at *Pin* = *Pout* = 1.0 kPa. The numerical result by DSMC is also shown in the lower side of Figure 14. Moreover, the pressure profiles along the centerline are shown in Figure 14b. Though the pressure profile contains some noise as shown in Figure 14b, it is clearly observed that the pressure distribution obtained by PSMF is quantitatively in good agreement with that by DSMC. Especially, the sharp pressure drop near the throat was captured by PSMF, and this result indicates that the spatial resolution of PSMF is high enough for micro‐scale measurement. The pressure value at ‐300 μm from the throat is about 8 kPa as shown in Figure 14b and is smaller than P*in* = 10.0 kPa, which was measured at ‐10 mm. This pressure drop may be caused by wall friction and the acceleration at the converging area of the nozzle.

## **Author details**

The flow in a converging‐diverging nozzle was examined for the demonstration, because the pressure considerably changes in a nozzle and it was easy to compare the result with a

Micro-Nano Mechatronics — New Trends in Material, Measurement, Control, Manufacturing and Their Applications in

Figure 13 shows the geometry of a converging‐diverging micro‐nozzle, which was two dimensional geometry, and the thickness of the micronozzles was 1.0 mm, and the width of the throat was 103 μm, the diverging length was 492 μm and the diverging angle was 23.5 degrees. The micro‐nozzle was put on a holder with an inlet and outlet port, and then it was covered with the PSMF deposited glass (see Figure 13b). Air was supplied from the inlet port, and the outlet port was evacuated by a scroll pump. PtMP was employed as a luminophore of PSMF. Luminescent intensity of PSMF was detected through a fluorescent microscope. The images were taken with the exposure time of 8.0 s, and 32 pictures were averaged to reduce

numerical one.

Biomedical Engineering

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the noise.

**Figure 13.** Micro-nozzle.

**Figure 14.** Pressure distribution inside the micro-nozzle [17].

#### Tomohide Niimi

Department of Micro‐Nano Systems Engineering, Nagoya University, Nagoya, Japan

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**Chapter 4**

**Precision Micro Machining Methods and**

**1. Ultra‐precision/micro machining of die steel by elliptical vibration**

A novel method to attain ultra‐precision sculpturing in micro/nano scale for difficult‐to‐cut materials is introduced. Elliptical vibration cutting technology is well‐known for its excellent performance in achieving ultra‐precision machining of steel materials with single crystal diamond tools. Elliptical vibration locus is generally controlled and held to a constant in practice. On the contrary, the proposed method utilizes the variations of the elliptical vibration locus in a positive manner. Depth of cut can be actively controlled in elliptical vibration cutting by controlling vibration amplitude in the thrust direction. By utilizing this as a fast tool servo function in elliptical vibration cutting, high performance micro/nano sculpturing can be attained without using conventional fast tool servo technology. Following sections describe the development of the high performance micro/nano sculpturing system and ultra‐precision/

The authors have developed "elliptical vibration cutting" technology [2], and have demon‐ strated that ultra‐precision machining of difficult‐to‐cut materials, such as hardened steel and hard/brittle materials, can be attained practically by applying ultrasonic elliptical vibration to single crystal diamond tools [3]. Several ultrasonic elliptical vibration tools and their control systems were also developed in the past studies [4]. Since variation of vibration amplitudes causes deterioration of machining accuracy and surface quality, most research efforts were dedicated to keeping the elliptical vibration locus ultra‐precisely constant. Otherwise, ultra‐

> © 2013 Shamoto et al.; licensee InTech. This is an open access article 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.

© 2013 Shamoto et al.; licensee InTech. This is a paper 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.

Eiji Shamoto, Norikazu Suzuki, Takashi Kato and

**Mechanical Devices**

Burak Sencer

**cutting [1]**

micro machining applications.

precision cutting cannot be achieved in practice.

**1.1. Introduction**
