Piezo-electric crystals

V, is measured by striking one end of a bar of the material (by glueing a piezo-electric crystal there and applying a charge-difference to the crystal surfaces) and measuring the time sound takes to reach the other end (by attaching a second piezo-electric crystal there). Most moduli are measured by one of these last two methods. 

The tip is first brought near to the sample via a coarse Z positioner, such as a controlled approach piezo-electric motor. This provides a 10 A step size and so is capable of very precise and controlled movement. As soon as a tunnelling current is detected, the tip is stopped and the fine control system is operated. Thus the lip is mounted on the end of a hollow, cylindrical piezo crystal, a tube scanner (a piezo-electric crystal can be made to deform under the influence of a voltage applied across it). The tube scanner has four strip electrodes on the outside, providing movement in the x and y directions (lateral movement), and one electrode covering the whole of the inside. A... 

These nebulizers rely on a transducer made from a piezo-electric crystal which produces high frequency sound waves in the liquid in the nebulizing unit. The waves give rise to vertical capillaries of liquid ( fountains ) which, when the amplitude of the energy applied is sufficient, break up to provide an aerosol. 

Baker, P.G. Stimpson, P.G. Electronically controlled drug dehvery systems based on the piezo electric crystal. Respir. Drug Del. 1994, 4, 273-285. 

The components of a TS system are shown in Figure 11.39 (130). A resonance stethoscope is used to transmit crystalline vibrations in the sample to the audio frequency range where they are converted to electrical signals by use of a piezo-electric crystal. The stethoscope is constructed of quartz, which, because of its high Q value, operates mechanically both as a tuned pick-up sensor and as a self-exciting resonator. The unit incorporates a sample-holder head shaped as an acoustic transformer and fitted with a transmitter rod that mechanically matches the piezo-electric cell fixed on a heavy recoil... 

An apparatus similar to the one described by Lonvik (130) has been discussed by Clark (127). Improvements include a waveguide system that can be accurately and reproducibly positioned and the attachment of the piezo-electric crystal transducer. The system also includes a DTA sample holder for measurement of concurrent TS-DTA data. Furnace heating rates up to 100°C/min are required for some studies although the normal heating rate is 40°C/min. The maximum furnace temperature is 1000°C. 

A converter or transducer that contains piezo-electric crystals that change the incoming high-frequency electrical signal to mechanical vibration of the same frequency. 

Transducers contain a piezo-electric crystal that vibrates when an electric current is passed through it, producing an ultrasound beam which propagates through the soft tissues. Reflection or refraction of the ultrasound beam may occur when it reaches a soft tissue interface of different acoustic impedance. The reflected ultrasound beams then return to the transducer where they are converted to electrical currents and subsequently to form an image. When there is a large difference in impedance, for example at a hone-soft tissue interface, a bright echo is produced. 

George Newkome (Miami) demonstrated the commercial application of inclusion complexes in electronic sensors. The macrocyclic hexalactam (6), which can complex chloroform, was coated on to the surface of a piezo-electric crystal. Complexation of chloroform produced changes in ts vibration frequency with respect to a non-coated crystal, dependent upon the substrate concentration. Inexpensive devices ( 2) with sensitivities of parts per 10 5 have been developed. They are being used in the detection of trace amounts of chloroform as an environmental pollutant. 

Interactions between polyelectrolyte-coated surfaces in the absence and presence of SDS were examined using the interferometric surface force technique of either the Mark II type [12] or the Mark IV type [13]. Muscovite mica was obtained from Mica New York Corp. in New York (green mica) and from M. Watanabe Co. in Tokyo (ruby mica). It was cleaved to 1-3 m thin pieces and silvered on one side. The pieces were then glued (using Epon 1004 from Shell Chemicals) onto two half-cylindrical silica discs with the silvered side down. The surfaces were mounted in a crossed cylinder configuration inside the surface force apparatus with the upper surface connected to a piezoelectric tube and the lower one on a double cantilever spring. The distance between the surfaces in changed by means of motors or by means of the piezo-electric crystal. 

Ultrasound is a high frequency, mechanical vibration consisting of alternate waves of compression and rarefaction (Kremkau 1997 McDicken 1991). The waves are generated by piezo-electric crystals shaped into a transducer which focuses the ultrasound waves into a beam. Commonly used frequencies for the liver are 5.0 or 3.5 MHz corresponding to wavelengths in tissue of 0.3 and 0.5 mm respectively, and this is the theoretical best spatial resolution that can be achieved. 

Several Fabry-Perot interferometers can also be operated in series. Each etalon is adjusted by piezo electric crystals to peak at the same wavenumber but at different orders. Up to three Eabry-Perot interferometers have been scanned together (Hegyi etal., 1972 Kumcz etal., 1977). Several Fabry-Perot interferometers were flown in November 1995 as part of the Short- and Long-Wave Spectrometers on the Infrared Space Observatory (ISO). A more detailed description of these instmments is given at the end of the next section (5.7). 

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