Piezoelectric energy applications

Another important concern for piezoelectric resonator applications is the amount of energy lost due to internal damping forces. A system capable of resonant oscillations will have, associated with it, a figure of merit called the material quality factor Q. The quality factor relates the energy stored to the energy dissipated per cycle. Mechanical losses can arise from intrinsic mechanisms such as thermal phonons (lattice vibrations) or defects in crystals. As the temperature increases, the thermal phonon population increases and the intrinsic phonon loss will also increase. The presence of this loss causes the stress and strain to differ in phase angle. A measure of this deviation is the relationship... 

The basis for the present-day generation of ultrasound was established as far back as 1880 with the discovery of the piezoelectric effect by the Curies [1-3]. Most modern ultrasonic devices rely on transducers (energy converters) which are composed of piezoelectric material. Such materials respond to the application of an electrical potential across opposite faces with a small change in dimension. This is the inverse of the piezoelectric effect and will be dealt with in detail later (Chapter 7). If the potential is alternated at high frequencies the crystal converts the electrical energy to mechanical... 

A number of works are devoted to the electrochemical preparation of ZnO, which may have application in photocatalysis, ceramics, piezoelectric transducers, chemical sensors, photovoltaics, and others. ZnO has the same band-gap energy as Ti02, and the oxygenation capacities for both compounds should be similar. Ya-maguchi et al. [155] prepared photoactive zinc oxide films by anodizing a zinc plate. Such films could decompose gaseous acetaldehyde with the aid of black lights. 

PIEZOELECTRICITY. Electric energy created by application of pressure to ceramics of plastics. Devices utilizing this phenomenon are gas flame igniters, ultrasonic welding tools, and sonar navigation aids. 

The practical application of ultrasonics requires effective transducers to change electrical energy into mechanical vibrations and vice versa. Transducers are usually piezoelectric, ferroelectric, or magnetostrictive. The application of a voltage across a piezoelectric crystal causes it to deform with an amplitude of deformation proportional to the voltage. Reversal of the voltage causes reversal of the mechanical strain. Quartz and synthetic ceramic materials are used. 

The compression of a powder is a complex process that is usually affected by different kinds of problems. These problems have been widely investigated and mainly concern the volume reduction and the development of a strength between the particles of the powder sufficient to ensure tablet integrity [82], The application of ultrasonic energy shows a great ability to reduce and even avoid these problems [83], Ultrasound refers to mechanical waves with a frequency above 18 kHz (the approximate limit of the human ear). In an ultrasound compression machine, this vibration is obtained by means of a piezoelectric material (typically ceramics) that acts as a transducer of alternate electric energy of different frequencies in mechanical energy. An acoustic coupler, or booster, in contact with the transducer increases the amplitude of the vibration before it is transmitted (usually in combination with mechanical pressure) to the material to be compressed. 

Devices based on piezoelectric crystals, which allow transduction between electrical and acoustic energies, have been constructed in a number of conrigurations for sensor applications and materials characterization. This cluqtter examines those devices most commonly utilized for sensing a( licatithickness-shear mode (TSM) resonator, the surface acoustic wave (SAW) device, the acoustic plate mode (APM) device, and the flexural plate wave (FPW) device. Each of these devices, shown schematically in Figure 3.1, uses a unique acoustic mode. 

Cady in World War II realized that such a mechanical resonance of a vibrating crystal could be used in frequency control. This discovery had an important influence on radio communications.Alternating electric fields, such as those generated by the radio tubes of the time, were applied to plates of piezoelectric crystals and the expansions and contractions of the plates were caused to react on electrical circuits. If the natural frequency of the mechanical vibration of the quartz plate coincided with the frequency of oscillation of the electric circuit, resonance between the two took place and energy was acquired by the mechanical oscillators. Later. Rochelle salt and barium titanate, which are each both ferroelectric and piezoelectric, were used. ° In ferroelectric crystals, the polarization or dipole moment is reversed or reoriented upon application of an electric field. Ferroelasticity is another property displayed by some crystals in which stress can cause the interconversion between two stable orientational states. These physical properties of crystals are of great use in modern technology. 

Selected classes of asymmetric crystal structures exhibit the property of piezoelectricity. With the application of a mechanical strain, piezoelectric materials develop an electrical potential difference across them conversely, when a potential difference is applied to these materials, a displacement occurs. The efficiency of the conversion between mechanical energy and electrical energy is described by the electromechanical coupling constant, which practically ranges to values as high as 0.7 a value of 1 would imply complete conversion between mechanical and electrical energy. 

Pseudohalide crystals like the fulminates with asymmetric ions can be piezoelectric, while crystals which are sensitive to electric fields probably have ferroelectric phases. Electric fields generated on the application of thermal shock and pressure on piezoelectric crystals can cause electrical breakdown which readily leads to the formation of localized hot spots and the initiation of an explosive process. These ideas would need detailed study and can provide insights into the behaviour of energy rich crystals. 

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