**3. Sensor based on millimeter band resonant gallery modes**

In order to define an innovative temperature sensor with high RF performance, we will take advantage of the dielectric properties of the sensitive material, the machining of coplanar membrane lines, and the characteristics of gallery modes. This new detection device is based on the modification of the resonance frequency of the dielectric resonator at the presence of a temperature variation. This is done by means of a perovskite material deposited above this resonator whose dielectric constant varies with a change in temperature.

The general concept chosen is to modify the electromagnetic coupling that exists in the device by temperature (see **Figure 2**). This concept allows for a very high sensitivity. Indeed, variable coupling can be achieved by modifying (globally or locally) the environment around the electromagnetic field lines by directly modifying the electromagnetic properties of the sensitive material.

In other words, a change in temperature leads to a change in the permittivity of the sensitive material and therefore a change in the electromagnetic field. This change affects the electrical parameters of the resonator, namely, the resonance frequency and the quality factor. Thus, a resonator designed to operate at a center frequency f0 for a particular gallery mode sees this shift as a function of the variation in the dielectric constant of the sensitive material. The electromagnetic field is therefore used to measure the temperature variation. The detection principle is then based on the shift in the resonance frequency of the gallery modes in the dielectric resonator. The latter and the sensitive material are used here to measure the influence of the permittivity of this material and to deduce the temperature variation.

In addition, this type of detection technique based on electromagnetic transduction has shown interesting results for the realization of an oscillator in the first place and subsequently for specific gas and pressure detection applications. These passive microwave sensors have been designed using the relaxation phenomenon present in sensitive materials. In particular, the installation of a functional TiO2-based

**161**

**Figure 3.**

*Optimal Temperature Sensor Based on a Sensitive Material*

**4. Study of the geometric parameters of the sensor**

(see **Figure 3**) [8, 9], we have several samples taken in his laboratory.

with RSupport = 0.8 mm radius and HSupport = 230 μm height.

microwave sensor in the Ka-band has been proposed for gas concentration detection. This detector is based on the direct variation of the dielectric properties of the

There are parameters that can modify the dielectric characteristics of a material such as temperature, for example. In our case, the aim is for this modification to generate a frequency variation in the microwave domain. The basic element is the sensing material whose dielectric constant varies with temperature. The choice of the sensitive material is not obvious because of the requirements imposed, which complicate the integration of dielectric materials into microelectronic circuits or their use in the manufacture of the sensor. To achieve this, we have carried out an in-depth bibliographical study in order to find the appropriate material that meets our specifications. Among the materials proposed in the literature, we chose lead-lanthanum-zirconatetitanate (Abbreviated in PLZT). As a result, and as part of our collaboration with the Faculty of Computer Science and Materials Sciences, Silesian University of Poland

Also referred to as lanthanum-doped lead zirconate titanate, this material meets our needs in terms of temperature range and operating frequency. In particular, it has a dielectric property that depends on the change in temperature (see **Figure 4**) [10, 11]. Indeed, the variation in temperature has an impact on the properties of this material since it causes a relatively large change in its dielectric permittivity [12]. This PLZT will then detect the temperature change through its integration into the microwave circuit described in **Figure 1**, with a radius of RPLZT = 3.25 mm and a

The system is based relatively on the use of a dielectric resonator and two coplanar membrane lines. These lines serve as an excitation support for the RD gallery modes. The study of the mechanism of operation of these two components was widely discussed in the literature [13–15]. Thus, the RD has a radius of RRD = 3.25 mm, a thickness of HRD 360 μm, and a relative dielectric permittivity of 80. This dielectric resonator is held on the line plane by an Alumina (Al2O3) wedge

The RD's gallery mode excitation mechanism and sensitive material were selected,

and a radar interrogation was carried out to transmit temperature information.

*Samples of PLZT material taken by Wawrzała and Korzekwa at the Silesian University of Poland.*

*DOI: http://dx.doi.org/10.5772/intechopen.90733*

resonator at the presence of a gas.

thickness of HPLZT = 10 μm.

**Figure 2.** *Principle of electromagnetic transduction.*

*Perovskite and Piezoelectric Materials*

In addition, it is important to note that the gallery modes have the particularity of not having any energy at the center of the resonator. As mentioned earlier, the larger the azimuth number, the larger the area. The central part can therefore be used to fix the resonator; we can add a shim to the circuit in order to maintain it or adjust its position in relation to the coupling circuit (lines) without disturbing its operation. Finally, these modes are no longer stationary but progressive when the resonator is excited by a progressive wave source, whose propagation constant is close to that of the gallery mode. The mode then propagates in the azimuthal direction. This type of excitation for gallery modes results in a directional coupling with the line. Therefore, this coupling will make it possible to consider the design of a directional filter with a narrow bandwidth, which in turn will allow temperature

In order to define an innovative temperature sensor with high RF performance, we will take advantage of the dielectric properties of the sensitive material, the machining of coplanar membrane lines, and the characteristics of gallery modes. This new detection device is based on the modification of the resonance frequency of the dielectric resonator at the presence of a temperature variation. This is done by means of a perovskite material deposited above this resonator whose dielectric

The general concept chosen is to modify the electromagnetic coupling that exists

In other words, a change in temperature leads to a change in the permittivity of the sensitive material and therefore a change in the electromagnetic field. This change affects the electrical parameters of the resonator, namely, the resonance frequency and the quality factor. Thus, a resonator designed to operate at a center frequency f0 for a particular gallery mode sees this shift as a function of the variation in the dielectric constant of the sensitive material. The electromagnetic field is therefore used to measure the temperature variation. The detection principle is then based on the shift in the resonance frequency of the gallery modes in the dielectric resonator. The latter and the sensitive material are used here to measure the influence of the permittivity of this material and to deduce

In addition, this type of detection technique based on electromagnetic transduction has shown interesting results for the realization of an oscillator in the first place and subsequently for specific gas and pressure detection applications. These passive microwave sensors have been designed using the relaxation phenomenon present in sensitive materials. In particular, the installation of a functional TiO2-based

in the device by temperature (see **Figure 2**). This concept allows for a very high sensitivity. Indeed, variable coupling can be achieved by modifying (globally or locally) the environment around the electromagnetic field lines by directly modify-

measurement thanks to the shift in its resonance frequency.

ing the electromagnetic properties of the sensitive material.

constant varies with a change in temperature.

the temperature variation.

*Principle of electromagnetic transduction.*

**3. Sensor based on millimeter band resonant gallery modes**

**160**

**Figure 2.**

microwave sensor in the Ka-band has been proposed for gas concentration detection. This detector is based on the direct variation of the dielectric properties of the resonator at the presence of a gas.
