Directionally attached piezoelectric

Barrett, R. Intelligent rotor blade structures development using directionally attached piezoelectric crystals. MSc-thesis, Univ. of Maryland, College Park, MD (1990)... 

FIGURE 9.4 The direct force measurement apparatus shown here ean measure the forees between two eurved molecularly smooth surfaces in liquids. Mica surfaces, either raw or eoated, are the primary surfaees used in this apparatus. The separation between the surfaces is measured by optieal teehniques to better than 10 nm. The distance between the two surfaces is controlled by a three-stage meehanism that ineludes a voltage-driven piezoelectric crystal tube supporting the upper mica surface this crystal tube can be displaced less than 10 nm in a controlled fashion. A force-measuring spring is attached to the lower mica surface and its stiffness can be varied by a factor of 1,000 by shifting the position of a movable clamp. Reprinted with permission from Proc. Natl. Acad Sci. USA, 84, July 1987, 4722. 

This paper described a number of the means for measuring the piezoelectric coefficients of bulk materials and thin films. In bulk materials, excellent references are available. Numerous means have been used over the years to measure the piezoelectric coefficients, which can be loosely grouped as charge-based and displacement-based. Accurate data can be obtained by many of the techniques, and agreement between measurement types is usually reasonable, provided that comparable excitation levels are utilized. In contrast, for thin films attached to substrates, the mechanical boundary conditions differ in charge and displacement based techniques. As a result, the direct and converse coefficients are not identical. In addition, perhaps because of the relative immaturity of the field, the numerous possible artifacts are not always accounted for, which can lead to erroneous results in thin film measurements. 

Not only PAHs, pesticides and PCBs, but also other pollutants have been isolated with excellent results by USAL. One case in point is the leaching of total organic pollutants from particulate samples [145] by using a direct ultrasonic leacher, where the transducer was bonded directly to the bottom of the sample vessel (see Fig. 2.6A). The ultrasonic piezoelectric transducer was used at two different power settings (25 and 50 W). The transducer was tightly attached to the glass sample vessel and a condenser... 

Litzkow et al. (1990) also used a piezoelectric sensor to detect S. oryzae, R. dominica, and S. cerealella in cereal commodities including corn, wheat, and rice stored in containers such as trucks, ships, railroad cars, and storage bins. The piezoelectric sensor was placed in the container or attached to a probe for generating electricity in response to vibrations at frequencies above 500 Hz. Hickling et al. (1997a) considered that placing the hard, plane piezoelectric surface in direct contact with the commodity does not... 

As shown in Figure 4.10, the tip is attached to a piezoelectric ceramic, a material that will expand in one direction and contract in another when a current is passed. By changing the current flowing through the ceram-... 

The school of Bowen [36] used the AFM technique for direct measurement of the adhesion force between a colloidal probe and membrane surfaces. Colloidal probes were prepared by attaching an 11 pm polystyrene sphere with epoxy resin to a V-shaped AFM tipless cantilever (Fig. 7.2). The AFM allowed the measurement of the force between the colloidal probe and a membrane sample as a function of the displacement of the sample, where a piezoelectric crystal varied the sample displacement. A laser beam reflected from the back of the cantilever fell on a split photodiode that detected small changes in the deflection of the cantilever. To convert the deflection to a force, it was necessary to know the spring constant of the cantilever and to define the zero of the force. The spring constant specified by the manufacturer was 0.4 N m The zero of the force was chosen where the deflection was independent of the piezo position (where the coUoidal probe and the membrane surface were far apart.)... 

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