Piezoelectric Systems

If the acceleration is variable, as in sinusoidal movement, piezoelectric systems are ideal. In case of a constant acceleration, and hence a force that is also constant, strain gages may be employed. For petroleum applications in boreholes, however, it is better to use servo-controlled accelerometers. Reverse pendular accelerometers and single-axis accelerometers are available. 

The on-line piezoelectric system of Fig. 7.18C was used for the quantitative gravimetric determination of total fat in foods. The extract obtained by rinsing the cryogenic trap with -hexane was aspirated to the low-pressure injection valve of the FI system, which injected the extract into an n-hexane carrier that drove the injected plug to the flow-cell for monitoring with the aid of an At-Cut 10 MHz piezoelectric quartz crystal coated with gold plated electrodes. The throughput and relative standard deviation thus achieved were 6 samples/h and 2.3%, respectively [120]. 

The introduction of ferroelectric nanoparticles in polymeric matrices seems attractive for improving the dielectric permittivity of polymeric-based materials. New pyro-and piezoelectric systems have been proposed, and better efficiency has been obtained by using ferroelectric particles with d 700 nm. However, the understanding of correlations between structure and macroscopic properties needs to be improved. Nevertheless, it is interesting to note that smart hybrid materials have been prepared by combining organic and inorganic phases, which illustrates the versatility of such nanocomposites. 

It is obvious that materials with mechanical stress—electricity interactions are technologically very interesting sensors can be made that catch mechanical vibrations and transform those to an electrical signal, mechanical tensions can be measured electronically, and so on. Piezoelectric systems are not the only mechanism for mechanical sensorics (see Table 28.1) but are certainly abundant and sometime very practical to work with. Also, within the textile community there is increasing interest in piezoelectricity. 

Becker, J. and Luber, L. Comparison of Piezoelectric Systems and Aerodynamic Systems for Aircraft Vibration Alleviation. 5th Annual Int. Symp. on Smart Struct. Mat., San Diego/CA (1998)... 

PVDF was discovered by Dr. Heiji Kawai in 1969 [32]. Although PVDF is a piezoelectric system, it is a ferroelectric cum piezoelectric material as explained earlier, with a Curie point of 103 °C. PVDF possesses various phases such as a, p, y, and 5, among which p-phase has the most responsive piezoelectric properties. Compared with all ferroelectric polymers, PVDF has a dielectric constant with a reasonable chemical and mechanical durability [4,32]. In general, the physical properties of PVDF make it the most valuable material for application in sensors. 

The analysis presented above was made by Hilezer and Mailecki [4,119], and it h dear from this that single-phase piezoelectric systems, both ceramics and piezopolyinets. do not fulfill all the requirements to be applied in hydrophones and ultrasonic transducers for medical diagnosis. They can be fulfilled by multiphase system composite materials consisting of piezoelectric ceramics and a polymer. Properties of the composites depend on the properties of particular phases, the volume fractim of the phases, and the means of their connectivity. 

A major advance in force measurement was the development by Tabor, Win-terton and Israelachvili of a surface force apparatus (SFA) involving crossed cylinders coated with molecularly smooth cleaved mica sheets [11, 28]. A current version of an apparatus is shown in Fig. VI-4 from Ref. 29. The separation between surfaces is measured interferometrically to a precision of 0.1 nm the surfaces are driven together with piezoelectric transducers. The combination of a stiff double-cantilever spring with one of a number of measuring leaf springs provides force resolution down to 10 dyn (10 N). Since its development, several groups have used the SFA to measure the retarded and unretarded dispersion forces, electrostatic repulsions in a variety of electrolytes, structural and solvation forces (see below), and numerous studies of polymeric and biological systems. 

The apparatus consists of a tip-position controller, an electrochemical cell with tip, substrate, counter and reference electrodes, a bipotentiostat and a data-acquisition system. The microelectrode tip is held on a piezoelectric pusher, which is mounted on an inchwomi-translator-driven x-y-z tliree-axis stage. This assembly enables the positioning of the tip electrode above the substrate by movement of the inchwomi translator or by application of a high voltage to the pusher via an amplifier. The substrate is attached to the bottom of the electrochemical cell, which is mounted on a vibration-free table [, and ]. A number... 

Potassium Phosphates. The K2O—P20 —H2O system parallels the sodium system in many respects. In addition to the three simple phosphate salts obtained by successive replacement of the protons of phosphoric acid by potassium ions, the system contains a number of crystalline hydrates and double salts (Table 7). Monopotassium phosphate (MKP), known only as the anhydrous salt, is the least soluble of the potassium orthophosphates. Monopotassium phosphate has been studied extensively owing to its piezoelectric and ferroelectric properties (see Ferroelectrics). At ordinary temperatures, KH2PO4 is so far above its Curie point as to give piezoelectric effects in which the emf is proportional to the distorting force. There is virtually no hysteresis. 

Fig. 19. Ink-jet system (a) piezoelectric ink-jet firing chamber and (b) bubble formation ia thermal ink-jet technology.

In the ceramics field many of the new advanced ceramic oxides have a specially prepared mixture of cations which determines the crystal structure, through the relative sizes of the cations and oxygen ions, and the physical properties through the choice of cations and tlreh oxidation states. These include, for example, solid electrolytes and electrodes for sensors and fuel cells, fenites and garnets for magnetic systems, zirconates and titanates for piezoelectric materials, as well as ceramic superconductors and a number of other substances... 

Another important hut little-known piezoelectric effect is found in some electronic systems. Speaking produces pressure variations that propagate through the air. Forces are produced on anything in contact with this vibrating air so that when contact is with a piezoelectric crystal, tiny voltage variations are produced. A ci ystal microphone is designed to make use of this piezoelectric effect. 

The compounds K5Nb3OFi8 and Rb5Nb3OFi8 display promising properties for their application in electronics and optics. The compounds can be used as piezoelectric and pyroelectric elements due to sufficient piezo- and pyroelectric coefficients coupled with very low dielectric permittivity. In addition, the materials can successfully be applied in optic and optoelectronic systems due to their wide transparency range. High transparency in the ultraviolet region enables use of the materials as multipliers of laser radiation frequencies up to the second, and even fourth optical harmonic generation. 

Phase transition irreversible, 225 order - disorder, 224-228 reversible, 225, 229, Physicochemical properties of ammonium hydrofluoride, 39 deviations from ideal, 149 ideal system, 148 NbF5 and TaFs, 25 niobium containing melts, 150 tantalum containing melts, 151 M5Nb3OFlg, 234-235 Piezoelectric properties, 245-247 Plasma chemical decomposition equipment, 311... 

---