Bimorphs

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. 

The IR filter is realized by a PS layer with a modulation of porosity, which constitutes an interference filter as described in detail in the next section. The 30 pm thick porous layer is then released from the substrate by electropolishing, which is easily done in situ by increasing the etching current density above JPS. This process is commonly applied to form free-standing PS membranes and PS tubes [Tj 1], The internal strain between the Si3N4 layer used for masking and the porous layer lifts the filter up to its rest position, as shown in Fig. 10.10. The filter is suspended at two microactuator arms, which work as thermal bimorph actua-... 

Lu, L., et al., Highly stable air working bimorph actuator based on a graphene nanosheet/carbon nanotube hybrid electrode. Advanced Materials, 2012. 24(31) p. 4317-4321. 

In Part II, we discuss the essential elements of STM instrumentation. Except for a few cross-references, all the chapters can be read independently. The chapter on piezodrives starts with an introduction to piezoelectricity and piezoelectric ceramics at the general physics level. Three major types of piezodrives, the tripod, the bimorph, and the tube, are analyzed in detail. The chapter on vibration isolation starts with general concepts and vibration meas-... 

If larger displacements are required, an arrangement as shown in Fig. 9.7, the bimorph, can be applied. The principle is similar to the bimetal thermometer. Two thin plates of piezoelectric material are glued together. By applying a voltage, one plate expands and the other one contracts. The composite flexes. 

A common arrangement of a PZT bimorph is to pole both plates in the same direction (normal to the plane). When it is used, both outer electrodes are grounded. The driving voltage is applied to the center electrode. Such an arrangement reduces the stray field of the applied voltage to a minimum, and simplifies mounting. 

The following is the treatment of bimorphs presented by Curie (1889a). As shown in Fig. 9.8, immediately after the application of a voltage V, a strain d-nV 2lh) is generated. It in turn generates a stress cti in the x direction ... 

Fig. 9.7. Bimorph. Although the word bimorph is a trade name of Vernitron, Inc., it was described and analyzed by Curie (1889a). The most common mode of connection is to ground the two outer electrodes and to apply a voltage to the center electrode. The operation is similar to the bimetal thermometer. (By courtesy of Morgan Matroc, Inc., Vernitron Division, Bedford, Ohio.)...

Another application of elementary geometry gives the deflection Az at the end of the bimorph. 

Fig. 9.8. Deflection of a bimorph. Two long, thin plates of piezoelectric material are glued together, with a metal film sandwiched in between. Two more metal films cover the outer surfaces. Both piezoelectric plates are poled along the same direction, perpendicular to the large surface, labeled z. (A) By applying a voltage, stress of opposite sign is developed in both plates, which generates a torque. (B) The bimorph flexes to generate a stress to compensate the torque. The neutral plane, where the stress is zero, lies at hi i from the central plane.

As an example, a bimorph with the same material and dimensions as used in the last section, PZT-4D, 20 mm long and 2 mm thick, has a sensitivity of 2.74 A/V. This is substantially higher than the stretching mode, 17 A/V. 

However, it is very difficult to construct a three-dimensional scanner based on bimorphs. An example of such a design is reported by Muralt et al. (1986). It is much more complicated than the tripod scanner. 

In this section, we describe the tube scanner, which has high piezo constants as well as high resonance frequencies. Moreover, it is much simpler than both the tripod scanners and bimorph-based scanners. The tube scanner soon became the predominant STM scanner after its invention by Binnig and Smith (1986). 

Muralt, P., Pohl, D. W., and Denk, W. (1986). Wide-range, low-operating-voltage, bimorph STM Application as potentiometer. IBM J. Res. Develop. 30, 443-450. 

Fig. 4. (a) Anticlastic deformation of a bimorph in a magnetic field (saddle form), (b) Fixation of a bimorph on its sample holder and measurement principle of the deformation of any magnetostrictive bimorph using the... 

Aside from the A effect which is an interesting feature for designing resonant mechanical devices, MSMM show a GMR (AR) effect (Quandt and Ludwig 1999,2000). Thus, as already introduced in section 3.3, the bending of a magnetostrictive bimorph... 

Various types of the so-called magnetostrictive inchworm type of motor have been proposed and built. A two-leg travelling machine using a magnetostrictive bimorph actuator with 7.5 /zm-thick polyimtde is shown in fig. 86b (Honda et al. 1994 Arai and Honda 1996). In an alternating magnetic field, it can travel in one direction. The maximum speed of approximately 5 mm/s was obtained around the mechanical resonant frequency... 

Optical microactuators like a micromirror for scanning applications have been proposed by Orsier et al. (1996). A two-dimensional bimorph (Si 4- magnetostrictive film) is driven remotely by two differently oriented magnetic fields working at different frequencies in order to obtain the bending and torsional vibrations due to the magnetostrictive strain. 

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

Cantilever bimorphs (see Section 6.5.2 below) with small masses attached to their free end can be used as accelerometers provided that the frequency of the vibrations to be detected is well below the resonance frequency of the transducer. 

Fig. 6.27 Cantilever bimorphs showing (a) series connection and (b) parallel connection of beams.

The total charge density u(l) appearing on each surface of the bimorph half is... 

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