Piezoelectric detection

Based upon a piezoelectric 1-3-composite material, air-bome ultrasonic probes for frequencies up to 2 MHz were developped. These probes are characterized by a bandwidth larger than 50 % as well as a signal-to-noise ratio higher than 100 dB. Applications are the thickness measurement of thin powder layers, the inspection of sandwich structures, the detection of surface near cracks in metals or ceramics by generation/reception of Rayleigh waves and the inspection of plates by Lamb waves. 

Figure Bl.19.39. Schematic of the themiocoiiple probe in a scaiming themial profiler. The probe is supported on a piezoelectric element for modulation of tip-sample distance at frequency oi and to provide positioning. The AC thennal signal at oi is detected, rectified, and sent to the feedback loop, which supplies a voltage to the piezostack to maintain the average tip-sample spacing constant. (Taken from [209], figure 1.)...

To measure friction and shear response, one has to laterally drive one surface and simultaneously measure the response of a lateral spring mount. A variety of versions have been devised. Lateral drives are often based on piezoelectric or bimorph deflection [13, 71] or DC motor drives, whereas the response can be measured via strain gauges, bimorphs, capacitive or optical detection. 

A chemical microsensor can be defined as an extremely small device that detects components in gases or Hquids (52—55). Ideally, such a sensor generates a response which either varies with the nature or concentration of the material or is reversible for repeated cycles of exposure. Of the many types of microsensors that have been described (56), three are the most prominent the chemiresistor, the bulk-wave piezoelectric quartz crystal sensor, and the surface acoustic wave (saw) device (57). 

Sonic Methods A fixed-point level detector based on sonic-propagation characteristics is available for detection of a liquid-vapor interface. This device uses a piezoelectric transmitter and receiver, separated by a short gap. When the gap is filled with liquid, ultrasonic energy is transmitted across the gap, and the receiver actuates a relay. With a vapor filling the gap, the transmission of ultrasonic energy is insufficient to actuate the receiver. 

Titanium forms a series of oxoanions called titanates, which are prepared by heating Ti02 with a stoichiometric amount of the oxide or carbonate of a second metal. One of these compounds, barium titanate, BaTi03, is piezoelectric, which means that it becomes electrically charged when it is mechanically distorted. The ability to convert mechanical vibration into an electrical signal makes barium titanate useful for underwater sound detection. 

Figure 2 shows the brief principle of a laser-detected FFM. A sample is put on a piezoelectrical tube (PZT), which scans X, Y plane and controls the feedback of Z axis. The laser beam from a diode is focused on the mirror of the free end of a cantilever with lens, and the reflected beam falls on the center of a position-sensitive detector (PSD), a four-quadrant photodiode. When the sample contacts with the tip and relatively moves under the control of a computer, the reflected beam deflects and changes the position on the PSD due to the twist and deflection of the cantilever caused by the changes of surface roughness, friction force, and adhesive force between the sample and the tip. The extension and re-... 

Fig. 2—Brief principle of a laser-detected FFM. 1, laser beam 2, cantilever 3, tip 4, Sample 5, piezoelectrical tube 6, position-sensitive detector.

Nucleic acid hybridization can be detected by means of the piezoelectric QCM (= quartz crystal microbalance) (a) Y Okahata, Y Matsunobu, K Ijiro, M Mukae, A Murakami, K Makino. J. Am. Chem. Soc. 114 8299-8300, 1992 (b) S Yamaguchi, T Shimomura. Anal. Chem. 65 1925-1927,1993 (c) KIto, KHashimoto, Y Ishimori. Anal. Chim. Acta 327 29-35,1996 ... 

The initial stages of the STM experiment require the positioning of the tip in proximity of the surface such that a tunnelling current can be detected this often means moving the tip by several micrometres or even millimetres. The piezoelectric materials used for scanning are not suitable for this initial approach and most instruments therefore contain a second coarse positioning driver frequently this is also a piezoelectric material in a stick-slip kind of design.27... 

Methods exist for determining levels of diisopropyl methylphosphonate in air, soil, and water. These methods include separation by GC coupled with FID and flame photometric detection (FPD), determination by infrared and Raman spectroscopy, separation by ionization mass spectrometry, determination utilizing piezoelectric crystals, and determination by gas-sensitive microsensors. Table 6-2 summarizes the methods that have been used to analyze environmental samples for diisopropyl methylphosphonate. 

A number of studies (Kristoff and Guilbault 1983 Milanko et al. 1992) have investigated the use of coated and uncoated piezoelectric crystals in the detection and analysis of diisopropyl methylphosphonate in air samples. Piezoelectric crystals have a natural resonant frequency of oscillation that can be utilized to detect... 

Kristoff J, Guilbault GG. 1983. Application of uncoated piezoelectric crystals for the detection of an organic phosphonate. Anal Chim Acta 149 337-341. 

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