Piezoelectric sandwich transducer

The general representation of the most common type of power transducer of the piezoelectric "sandwich-type" is given in Fig. 3. The transducer itself forms part of a whole assembly which together constitutes the source of power ultrasound for sonochemical applications. 

Since the unloaded QCM is an electromechanical transducer, it can be described by the Butterworth-Van Dyke (BVD) equivalent electrical circuit represented in Fig. 12.3 (box) which is formed by a series RLC circuit in parallel with a static capacitance C0. The electrical equivalence to the mechanical model (mass, elastic response and friction losses of the quartz crystal) are represented by the inductance L, the capacitance C and the resistance, R connected in series. The static capacitance in parallel with the series motional RLC arm represents the electrical capacitance of the parallel plate capacitor formed by both metal electrodes that sandwich the thin quartz crystal plus the stray capacitance due to the connectors. However, it is not related with the piezoelectric effect but it influences the QCM resonant frequency. 

Figure 3.48 Exploded schematic view of a flow-cell FPW liquid sensor. The silicon chip containing die thin silicon-nitride membrane, piezoelectric film and transducers is sandwiched between two etched silicon chips. The upper chip is a cap with fluid inlet and outlet fittings, b also provides vias for contact to a temperature-sensing polysilicon resistor deposited on the FPW chip below it. The lower chip introduces transducer contact leads and protects the underside of the membrane fitm contact with the fluid. (Hgwc courtesy of Beo Costello, Bokeley Microliulratitents, Inc.)...

Electret materials are meanwhile used in a large number of modern high-tech applications including microphones, acoustic sensors, transducers, radiation and pollution dosimeters, power generators, filters, and many more. Additionally, electret technology is of great interest in the field of biomaterials, for instance in callus formation and wound healing [10, 11], When used in cellular or in multilayer sandwich structures, polymer electrets can exhibit piezoelectricity. Such materials are ferroelectrets, as they show typical features of ferroelectric materials such as piezo-and pyroelectricity [12-17],... 

The highly elastic material region of the displacement amplifier in Fig. 6.19a is locally concentrated, while the designs in Fig. 6.19b and c make use of the global elastic behaviour of metallic materials. The so-called moonie transducer in Fig. 6.19b consists of a piezoelectric disk sandwiched between two metal end caps. The ceramic is poled in the thickness direction and uses the dai mode. In this way the small radial displacement of the disk is transformed into a much longer axial displacement normal to the surface of the... 

Optic to mechanical transducer using photocooductor piezoelectric polymer sandwich. Research Disclosure, p. 117 (March 1980). 

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