Piezoelectric pick

A standard probe (type MWB or SWB) is fixed to the probe holder and is mechanically connected to a further piezoelectric receiver. A noise generator, which is coupled to any point of the test object, provides a low frequency noise signal which is picked up by the piezoelectric receiver. The intensity of the signal allows the evaluation of the coupling quality. 

Fig. 7. Sketch of the apparatus for measuring inverse piezoelectric effect in polymer films. B vibrating cantilever beam, E electromagnetic exciter, P electromagnetic pick-up, S specimen film, M weight, C oscillator, Vt, V2 and V3 voltmeters, Sw switch, V d.c. bias source for measuring electrostriction effect. Drawn after Kawai (1) (1969) by permission of the Japan Society of Applied Physics...

Electrical output transducers exist in many forms and consist simply of elastic elements coupled with suitable displacement transducers such as capacitance, inductance and reluctance pick-ups, certain types of strain gauge, piezoelectric elements, potentiometers and eddy current probes. A selection of these is described in the following paragraphs. 

Piezoelectric detectors are one of the most promising solutions to this problem. They can be installed at various locations on the aircraft body where they can constantly monitor the integrity of the materials of which the body is made. If cracks begin to develop at any location on the body, they can be detected because they result in the formation of small-scale shock waves as air passes over the aircraft body. These shock waves cause minute distortions of the aircraft s surface. While these distortions are too small to he noticed by most ordinary procedures, they are large enough to create electrical signals in nearby piezoelectric devices that can he picked up and analyzed by processing units attached to them. 

By making the sensor element completely out of quartz, the tuning fork body itself is used both for the drive and for detection because of the piezoelectrical properties of the quartz material. Suitable electrode structures supply the drive voltages and pick up the acceleration voltages. 

Figure 2.36 shows a schematic of an experimental set-up proposed by Spinner and Teft (1961). The specimen is suspended from the driver and pick-up, both of which are usually piezoelectric transducers. The oscilloscope and voltmeter (or ammeter) are used to accurately determine the exact resonant frequency and its maximum amplitude (using Lissajous patterns, see Schreiber et al. (1973)). Alternatively, electronic audio equipment is now available to induce a wide range of vibration frequencies and the ensuing acoustic spectrum can be obtained by a Fourier transform. 

If a quartz plate is subjected to an alternating electric field, the reverse piezoelectric effect causes it to expand and contract at the field frequency. If this field frequency is made to coincide with the natural elastic frequency of the crystal, the plate resonates the direct piezoelectric effect then augments the applied electric field. This is the basis of the crystal oscillator and the quartz clock. See also CRYSTAL MICROPHONE CRYSTAL PICK-UP. 

The QCM method utilizes the piezoelectric property of quartz crystals to measure extremely low mass changes per unit area. When an alternating electric current is applied to the quartz crystal, the quartz crystal produces an acoustic oscillation. Such oscillation frequency is partially dependent on the thickness of the crystal. If biomolecules such as proteins adsorb on the aystal and thus increase the crystal thickness, the instrument will pick up the frequency change and the mass of adsorption can be calculated by Sauerbrey s equation (Eqn (2.5), where A/is frequency change /o, resonate frequency Am, mass change A, area between electrode p, density of quartz p, shear modulus of quartz). 

Using the designed PLLA fiber tweezers and catheter, we successfully picked up, held and extracted minute samples. On the basis of these experimental results, it appears that it is highly possible to realize various applications using the piezoelectricity of chiral polymers such as the PLLA fiber. 

Ultrasonic transducers for medical imaging utilize piezoelectric ceramics and composites to generate an ultrasonic beam that can penetrate soft tissue. The same transducer then picks up the reflections off internal structure, organs, fetus, etc. These transducers most often consist of square-cross-section piezoelectric rods in a polymer matrix. These are formed by a dice-and-fill process. Figure 3.47 shows various piezoelectric-polymer composites used to optimize the performance for various applications. The diced 1-3 composite is typically used in ultrasonic transducer applications. 

The system studied in this example is the 2-DOF pick-and-place mechanism mentioned earlier (Fig. la). The random vibration response is measured in the same direction as the excitation, using lightweight piezoelectric accelerometers. During a single experiment a single cycle is performed, in which the linear motors move from their rightmost to their leftmost position and back. The measured vibration response is conditioned and driven into a data acquisition... 

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