Piezo-electric technolog

The piezo-electric effect of deformations of quartz under alternating current (at a frequency in the order of 10 MHz) is used by coating the crystal with a selectively binding substance, e. g. an antibody. When exposed to the antigen, an antibody-antigen complex will be formed on the surface and shift the resonance frequency of the crystal proportionally to the mass increment which is, in turn, proportional to the antigen concentration. A similar approach is used with surface acoustic wave detectors [142] or with the surface plasmon resonance technology (BIAcore, Pharmacia). 

A variant, with reminiscences to sec. 1.5, is based upon the capillary instability of jets, a topic that has drawn recent interest because of the increasing application of ink jet printers. Such printers are based on the deflection of a liquid jet in an electric field. The idea goes back to Sweet ), and has given rise to much printing technology. For the present purpose, oscillations in the jet are not produced by an elliptic orifice, but applied externally, say piezo-electrically. Dynamic surface or interfacial tensions can be obtained from, for Instance, the (quadrupole) oscillations of drops that have just broken away from the jet, or from the oscillations in the jet just before breaking. Measurements can be carried out down to lO" s" l... 

Another engineering challenge was to dispense volumes in the 20 nL-ljaL volume range. At the top end of this scale, a variety of tip-based syringe-driven devices are available, e.g., Matrix Platemate (Matrix Technologies Corp., Lowell, MA). To achieve nanoliter dispensing, two platforms are available the piezo-electric inkjet dispenser and the solenoid inkjet dispenser (90-92). 

Uchino K (1997) Piezoelectric actuators and ultrasonic motors. Kluwer series in Electronic materials Science and technology, Norwell, MA Uchino K (2000) Eerroelectric devices. Marcel Dekker, New York, NY Valasek J (1921) Piezo-electric and allied phenomena in Rochelle Salt. Phys Rev 17 475 81 Waanders JW (1991) Piezoelectric ceramics, properties and applications. Philips Components, Academic, New York... 

Piezo. This is the same basic print head technology as in continuous inkjet. The ink jet droplets are forced out through the nozzle after an electrical signal to the piezoelectric crystal causes a pressure wave to be set up in the ink (Figure 2.35b). The wave can be produced in the bend mode, as in Figure 2.35b or in a push or shear mode. An important variation on piezo technology is the Xaar... 

Piezoelectric inkjet is currently the technology of choice for most emerging industrial applications. In this technology, a piezo crystal (commonly lead zirconium titanate) undergoes distortion when an electric field is applied, and this distortion is used to mechanically create a pressure pulse that causes a drop to be ejected from the nozzle (Fig. 3). There are many variations of piezo inkjet architectures including tube, edge, face, moving wall, and piston. 

During later operation it suffices to measure the electrical quantities in order to compute the mechanical actuator quantities on the basis of the model, thereby compensating the hysteresis and creep of the piezo actuator. Since the computing process is quite complex and has to be executed in realtime, this control method is presently only implemented for low-frequency operations. However, the applicable frequency range of this inverse control method will grow in conjunction with the technological progress in the field of microelectronics [364]. 

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