Piezo-electric materials

The newest market for KYNAR resins is perhaps the most exciting and most challenging. This is the KYNAR Piezo Film. By definition, a piezo electric material is one that can change polarization in response to mechanical stress. The CH - CF repeat unit was found to exhibit the strongest piezo electric and pyro electric activity of all known polymers. This property was first reported in 1969 based on experiments using KYNAR PVDF. Since that time the piezo and pyro electric properties of PVDF have been the subject of many publications. 

V, is measured by striking one end of a bar of the material (by glueing a piezo-electric crystal there and applying a charge-difference to the crystal surfaces) and measuring the time sound takes to reach the other end (by attaching a second piezo-electric crystal there). Most moduli are measured by one of these last two methods. 

Among the various techniques of measurement one may be indicated as the most versatile the immersion technique (see Hartmann and Jarzynski, 1974 Hartmann, 1980). In this method acoustic waves are generated and received by two piezo-electric transducers, one acting as transmitter, the other as receiver the transducer material is... 

With the aid of a particular class of materials (thin-film piezoelectrics), incorporation of AW devices and conventional integrated circuit components on the same silicon substrate is in fact possible. Under the proper conditions, a number of piezoelectric materials can be deposited in thin-film form, typically by RF sputtering, and retain their piezoelectric nature. For this to occur, the crystallites that grow during deposition must be predominantly oriented in a single, piezo-electrically active crystallographic direction. Two such materials are 2 0 and AIN the former has been used as an overlayer on Si wafers to fabricate all of the FPW devices studied for sensor applications to date, and also for SAW resonators. Because extremely thin piezoelectric films are readily fabricated, both ZnO and AIN have been used to make bulk resonators that operate at much higher... 

Contrary to the (non-linear) converse piezo-electric effect v hen pressure is exerted upon a piezo material a voltage is generated - this is called the (linear) piezoelectric effect. 

Other miniaturised devices have used machined modules made of polymeric materials such as poly(methyl methacrylate) with diameters of 0.8 mm coupled with peristaltic or syringe pumps [106] or exploiting electrokinetic pumping [107], as well as silicon devices with piezo electric pumping [108]. 

Piezo-electric polymers are often materials like the p form of poly(vinylidene fluoride) in which the unit cell has a residual dipole moment. 

Chapter S.4 contains additional material on piezo-electricity. 

Uchino K (1997) Piezoelectric actuators and ultrasonic motors. Kluwer series in Electronic materials Science and technology, Norwell, MA Uchino K (2000) Eerroelectric devices. Marcel Dekker, New York, NY Valasek J (1921) Piezo-electric and allied phenomena in Rochelle Salt. Phys Rev 17 475 81 Waanders JW (1991) Piezoelectric ceramics, properties and applications. Philips Components, Academic, New York... 

Claeyssen, F. A new multi-mode piezo-electric motor. Proc. Int. Conf. on Intelligent Materials, ICIM96-ECSSM96, SPIE vol. 2779, Lyon, Prance (1996), pp. 634-637 also Proc. Actuator 96, Axon, Bremen, Germany (1996), pp. 152-155... 

Pyroelectricity. A sudden modification of the environmental temperature of the crystal (or ceramic) causes a modification in the length (thermal expansion) of the crystal axis whose direction matches with the polarization direction. Due to the piezo electric effect charging occurs. However, the permanent polarization changes with the temperature as the dipole moments in piezoelectric materials depends on the temperature. 

Due to the unidirectional chain orientation the material becomes piezo-electrically orthotropic, i.e. d i dz2- The draft direction is defined as the 1-direction. For very small strains, however, the material is widely isotropic. Due to its Youngs modulus which is essentially smaller compared to that of PZT, the influence of the stiffness of PVDF on the dynamics of the host structure in most cases is negligible. That is why PVDF films are especially appropriate for sensory applications. 

Motion is generated hy the piezo-electric effect in certain crystalline materials (for instance Quartz), ceramics such as PZT - Pb(ZrTi)03, and polymers (Polyvinyli-dene fluoride - PVDF). In addition, thin films with piezo-electric properties such as Aluminum Nitride (AIN)... 

The absorption of solid or liquid materials can also be measured using these techniques [9.86]. The laser illuminates the sample and the heat variations are coupled to a non-absorbing gas, which is in contact with the microphone. Piezo-electrical detection can also be used with solid or liquid samples. Elastic waves in the material are then detected. In Fig.9.13 an example of an acousto-optic spectrum of a powder is given. 

Ferroelectric liquid crystals are a novel state of matter, a very recent addition to the science of ferroelectrics which, in itself, is of relatively recent date. The phenomenon which was later called ferroelectricity was discovered in the solid state (on Rochelle salt) in 1920 by Joseph Valasek, then a PhD student at the University of Minnesota. His first paper on the subject [1] had the title Piezo-Electric and Allied Phenomena in Rochelle Salt. This was at the time when solid state physics was not a fashionable subject and it took several decades until the importance of the discovery was recognized. Valasek had then left the field. Later, however, the development of this branch of physics contributed considerably to our understanding of the electrical properties of matter, of polar materials in particular and of phase transitions and solid state physics in general. In fact, the science of ferroelectrics is today an intensely active field of research. Even though its technical and commercial importance is substantial, many breakthrough applications may still lie ahead of us. The relative importance of liquid crystals within this broader area is also constantly growing. This is illustrated in Fig. 1,... 

---