Wave filters, piezoelectric

Piezoelectric crystals, notably quartz, are used to control or limit the operating frequency of electrical circuits. A well-known example is their use in quartz clocks . The fact that a dielectric body vibrating at a resonant frequency can absorb considerably more energy than at other frequencies provides the basis for piezoelectric wave filters. The equivalent circuit for a piezoelectric body vibrating at frequencies close to a natural frequency is given in Fig. 6.3. At resonance the impedance due to L, and C falls to zero and, provided that Rx is small, the overall impedance is small. 

Use Electronic components piezoelectric control in filters, oscillators, frequency standards, wave filters, radio and TV components barrel-finishing abrasive. 

KNbOi (LB Number 1A-2). This crystal is ferroelectric below about 418 °C. Further phase transitions take place at about 225 °C and about — 10°C, retaining ferroelectric activity. The crystal has large electromechanical coupling constants and is useful in lead-free piezoelectric elements and SAW (surface acoustic wave) filters in communications technology (Fig. 4.5-13,4.5-14). 

The major piezoelectric applications are sensors (pickups, keyboards, microphones, etc.), electromechanical transducers (actuators, vibrators, etc ), signal devices, and surface acoustic wave devices (resonators, traps, filters, etc ). Typical materials are ZnO, AIN, PbTiOg, LiTaOg, and Pb(Zr.Ti)03 (PZT). 

There are several applications of ZnO that are due to its excellent piezoelectric properties [28,164]. Examples are surface-acoustic wave (SAW) devices and piezoelectric sensors [28,165-167]. Typically, SAW devices are used as band pass filters in the tele-communications industry, primarily in mobile phones and base stations. Emerging field for SAW devices are sensors in automotive applications (torque and pressure sensors), medical applications (chemical sensors), and other industrial applications (vapor, humidity, temperature, and mass sensors). Advantages of acoustic wave sensors are low costs, ruggedness, and a high sensitivity. Some sensors can even be interrogated wirelessly, i.e., such sensors do not require a power source. 

Piezoelectric filter A kind of electromechanical device in which electrical signals are converted to a mechanical wave by using a piezoelectric crystal. Thus, the former electric wave is delayed as it propagates across the crystal, and this delay is used to reinforce a desired frequency bandwidth with very high Q values. The quartz crystal is an example of the piezoelectric elements used for these filters [i],... 

The discovery by R. M. White of the University of California at Berkeley that surface acoustic waves could be excited and detected by lithographically patterned interdigital electrodes on the surface of piezoelectric crystals [42] has led to widespread use of SAW devices in a number of signal-processing applications. These include frequency filters, resonators, delay lines, convolvers, and correlators [43,44]. 

Surface acoustic wave (SAW) devices are widely used for frequency filtering in mobile communications [1]. Recently published works [2-10] have demonstrated the use of SAWs to manipulate liquid flow in microfluidic devices. A SAW is excited by the application of a radiofrequency (rf) signal to an interdigital transducer (IDT) on a piezoelectric substrate such as quartz or LiNbOs. The... 

As mentioned above, LC elastomers, especially LSCE with monodomain order, anisotropic LC networks, and gels, may be optimized to make a kind of smart material for molecular switching and piezoelectric or pyroelectric sensors, because of their sensitivity to environmental conditions (electric or stress fields, temperature, and radiation, etc.) and memory effect. Other applications include wave-guide, polarizers, optical filters, alignment, and compensation films for LCD displays. 

The brothers Jacques and Pierre Curie are credited with the discovery of piezoelectricity in a number of hemiedric crystals (Curie and Curie, 1880). Today, piezoelectrics are utiUzed in acousto-electronic devices and sensors based on bulk and surface acoustic waves, piezomechanical sensors to monitor pressure, power, and acceleration, as actuators for micropositioning devices, band pass filters with low insertion losses, as electro-optic devices for optical memories, displays for high-definition televisions, and possibly as transparent piezoelectric speaker membranes as well as miniaturized piezoelectric transformers and motors. As the classic piezoelectric material is a-quartz, the basic relationships are detailed below using it as a model structure. Further details on the piezoelectric properties of quartz, and of its history, discovery and utilization, are available elsewhere (Ballato, 2009). 

Oflier applications Other applications of thin films include pyroelectric detectors and surface acoustic wave (SAW) substrates. The latter devices consist of a piezoelectric substrate onto which interdigital electrodes are deposited, for example by screen printing. An elastic wave generated at the input interdigital transducer (IDT) travels along the surface and is detected by the output interdigital transducer (OIT). These devices are mainly used as delay lines and filters in microwave and television communications (see also Chilla et al., 2003). 

Surface acoustic wave (SAW) technology utilizes the production, control, transmission, and reception of acoustic waves formed on the surface of a piezoelectric substance. It has been used in telecommunications applications for over 50 years. SAW devices are used in mobile cellular phones and base stations as band-pass filters, and also serve as sensors for many other applications such as torque, pressure, temperature, humidity, and chemical sensors. 

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