Acoustic wave filters

Some of the present industrial uses of diamond coatings include cutting tools, optical windows, heat spreaders, acoustic wave filters, flat-panel displays, photomultiplier and microwave power tubes, night vision devices, and sensors. Because its thermal conductivity and electrical insulation qualities are high, diamond is used for heat sinks in x- ray windows, circuit packaging, and high-power electroific devices. Moreover, the high chemical stability and inertness of diamond make it ideal for use in corrosive environments and in prosthetic devices that require biocompatibility. 

Finger N., Kovacs G., Schoberl J., and Langer U., Accurate FEM/BEM-simulation of surface acoustic wave filters, presented at IEEE Ultrasonics, October 5-8, 2003, Honolulu, Hawaii. 

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). 

Lithium tantalate (LT) LiTaO, 1 1 Waveguide devices, optical modulators, surface acoustic wave filters, SHGs... 

Diamond has superior thermal conductivity, five times higher than that of pure copper at room temperature. Heat sinks are currently available on the market. The other products are infrared (IR) windows, cutting tools, and surface acoustic wave filters. 

Highly sensitive ultraviolet detector based on ZnO/UNbOj hybrid surface acoustic wave filter. Applied Physics Letters, 83,... 

Acousto-optic Filters. The newest type of spectrometer to become commercially available is the acousto-optic tunable filter (AOTF). An AOTF is a sohd-state, electronically tunable bandpass filter based on the diffraction of optical waves by acoustic waves in an optically anisotropic crystal. 

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 is increasing interest in the use of specific sensor or biosensor detection systems with the FIA technique (Galensa, 1998). Tsafack et al. (2000) described an electrochemiluminescence-based fibre optic biosensor for choline with flow-injection analysis and Su et al. (1998) reported a flow-injection determination of sulphite in wines and fruit juices using a bulk acoustic wave impedance sensor coupled to a membrane separation technique. Prodromidis et al. (1997) also coupled a biosensor with an FIA system for analysis of citric acid in juices, fruits and sports beverages and Okawa et al. (1998) reported a procedure for the simultaneous determination of ascorbic acid and glucose in soft drinks with an electrochemical filter/biosensor FIA system. 

Figure 10.14 Stroboscopic topograph of travelling surface acoustic waves in a LiNb03 IF filter...

Acoustic wave devices have been used, primarily as electronic bandpass filters, for more than 60 years, but the first reported use as a chemical sensor appeared in 1979 [16, p7],... 

In recent decades, PZ materials have been used at frontiers of scientific research and technology. Owing to their sensitivity, acoustic wave PZ devices have been widely used in electronics. These devices, such as wave or bandpass filters, have been... 

The materials listed in Table 5.1 are also not complete but the selection represents the most relevant composites which are of commercial interest. In addition to the performance issue, there is a strong tendency in research and development to reduce the costs. For that reason, a lot of research is devoted to the niobates as possible replacement for the tantalates, because niobium is cheaper than tantalum. In addition, compensated materials with very high values of the permittivity are currently under development. Recently, for the compound Ag(Nbi a Taa )03 with 0.35< x <0.65, er values of 450 were achieved for potential use as filters (to replace the surface-acoustic-wave devices) and planar antennas in mobile phones [19],... 

Ultrasonic separators, also known as acoustic cell filters, use a plane standing-wave to retain cells in a bioreactor. Kilburn et al. (1989) were the... 

Fig. 6.34 (a) Trapped-energy filter, (b) Surface acoustic wave (SAW) filter. 

Filters and delay lines of the form shown in Fig. 6.34(b) are made which exploit the surface acoustic wave (see Section 6.5.2 above). The SAW is propagated in the direction normal to the overlap of the interdigitated electrodes, the wavelength launched being related to the electrode spacing and width. For a combined space and half-width of 15 /nn (2sulfacc = 30 /nn) the structure will propagate a centre frequency of 100 MHz. That is it operates as a filter. 

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. 

AOTFs (101, 102) work on a different principal. This type of filter functions by the interaction of light with a traveling acoustic wave in an anisotropic medium. Both crystals and polymers have been used for the anisotropic medium. An acoustic transducer is bonded to one end of the material and an... 

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]. 

ZnO is a wide band gap semiconductor, which is used for various applications. Based on textured ZnO films one can build highly effective piezo field emitters. On the other hand ZnO is a very effective electron-excited phosphor. ZnO films easily withstand electron fluence more than 1 W/cm. ZnO films doped with Al, Ga, or In have a low resistivity of about 10 " Qcm and a high transparency of about 90%. This is sufficient for applications as a front contact in solar cells, liquid crystal displays etc. Dielectric ZnO films have a high electromechanical coupling factor that allow using ZnO in various surface acoustic wave (SAW) devices such as delay lines, delay-line filters, resonators, transducers and SAW convolvers. 

A modification of the Debye-Sears effect, i.e., the modulation of the refractive index by acoustical waves functioning as tunable grating, is now applied to fast scanning NIR spectroscopy The Acousto-Optic Tunable Filter (AOTF), (Harris and Wallace, 1969 Chang, 1981). In combination with array detectors, chemical imaging is possible (Treado et ah," 1992). 

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