Piezoelectric ringing

A compact ultrasonic rotory motor, as tiny as 3 mm in diameter, has been developed at the Pennsylvania State University. As shown in Figure 4.1.37, the stator consists of a piezoelectric ring and two concave/convex metal endcaps with windmill shaped slots bonded together, so as to generate a coupling of the up-down and torsional vibrations [60]. Since the number of components is reduced and the fabrication process is much simplified, the fabrication price is decreased remarkably, and a disposable design becomes feasible. When driven at 160 kHz, a maximum revolution of 600 rpm and a maximum torque of 1 mN m were obtained for a 11 mm diameter motor. 

Fig. 4.1. As shown on the left, the configuration of conducting plates on the flat faces of piezoelectric disks produces one-dimensional strain and electric field conditions with a guard-ring arrangement. On the right, the typical electrostatic conditions are shown. The axis through the thickness of the disk is chosen as the x axis.

The zincblende (ZB), or sphalerite, structure is named after the mineral (Zn,Fe) S, and is related to the diamond structure in consisting entirely of tetrahedrally-bonded atoms. The sole difference is that, unlike diamond, the atoms each bond to four unlike atoms, with the result that the structure lacks an inversion center. This lack of an inversion center, also characteristic of the wurtzite structure (see below), means that the material may be piezoelectric, which can lead to spurious ringing in the free-induction decay (FID) when the electric fields from the rf coil excite mechanical resonances in the sample. (Such false signals can be identified by their strong temperature dependence due to thermal expansion effects, and by their lack of dependence on magnetic field strength). 

Acoustic ringing of the probe assembly after an RF pulse is a pesky problem which often limits the measurements of nuclides with low gyromag-netic ratios (it can also strongly interfere with measurements of samples containing piezoelectric components). The disturbance is often misinterpreted as a particularly long dead-time disturbance, until one notices that, unlike normal dead-time components, it disappears when B is set to zero. It is difficult to remove because it follows the phase of the RF pulse and thus cannot be eliminated by any simple RF phase-cycling. 

Fig. 12.2. The pocket-size STM. Vibration isolation and damping are achieved by a stack of stainless-steel plates separated by viton O rings (not shown) in between. On the top metal plate are the louse and the piezoelectric tripod. 1, A metal plate with the sample holder, with only one of the three screws tightened. 2, Piezoelectric plate. 3, Annodized aluminum feet. 4, Tip holder. 5, The current lead. Viton pieces on the edges of the metal plates are used for isolating the vibration transmitted through the wires. (After Gerber et al., 1986.)...

Piezoelectric Disk a) Piezoelectric Bimorph (Disk Type) (a) Ring Mesa (Bulk Si 8nl/min (100V,lHz) l.OmHjO... 

Moisture analyzers include a large variety of designs listed here. The list includes their inaccuracies (1) electrolytic hygrometer (2-5% FS), (2) capacitance (3% FS), (3) impedance (3% FS), (4) piezoelectric (10% AR or 2 ppm by volume), (5) heat of adsorption, (6) infrared (0.5-1% FS), (7) microwave (for a 1-15% moisture range, error is within 0.5%, less if corrected for density), (8) Karl Fischer titrator (0.5-1% FS), (9) drying oven (0.5-1% FS), (10) dipole, (11) cavity ring down, (12) fast neutron (0.2% in solid s density corrected), and (13) radio-frequency absorption (5 ppm). 

Like NQR signals, piezoelectric and magnetoacoustic ringing signals are linearly polarized. Unlike NQR, there are rarely more than one or a few crystals or domains contributing to the ringing signal therefore, under circularly polarized excitation, one... 

Cyclosilicates are those compounds with three or more tetrahedra linked in closed, ring-like structures. The ratio between Si and O is 1 3. This group includes the important gem species beryl and the tourmaline group. The 11 members of the tourmaline group display an unusual property known as piezoelectricity. When pressure is applied to a crystal, an electrical charge builds up at either end of it. This makes these minerals useful in pressure gauges and other electrical equipment. Quartz and a few other, less common minerals, also display this property. 

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