Piezoelectric forks

For speakers or buzzers, audible by humans, devices with a rather low resonance frequency are used (kilohertz range). Examples are a bimorph consisting of two piezoceramic plates bonded together, and a piezoelectric fork consisting of a piezodevice and a metal fork. A piezoelectric buzzer is shown in Figure 4.1.12, which has merits such as high electric power efficiency, compact size and long life. 

Damped oscillations no yes liquids and some dry products. Employs oscillating dement which is normally a vibrating fork or paddle driven mechanically (Fig. 6.33a) or by a piezoelectric crystal vibrating at its resonant frequency. When immersed in the material there is a frequency or amplitude shift due to viscous damping which is sensed usually by a reluctive transducer (Section 6.3.3). 

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. 

Fig. 7.2.6 Functional principle of a silicon micromachined tuning fork, the tines are excited by piezoelectric actuators, the Coriolis forces bend the suspensions and are detected by piezoresistive resistors in the suspension bars. Source Conti Temic, Produktlinie Sensorsysteme...

In the shear force mode, a microelectrode is horizontally vibrated at its resonance frequency using a piezoelectric positioner (Fig. 11a) [31, 32]. The detection and monitoring of the amplimde of the oscillation can be carried out via optical, piezo, or tuning fork methods (Fig. 1 Ib-d). 

An alternative crystal geometry is the quartz piezoelectric tuning fork of Mason, whose wide, thin arms oscillate in their own planes and set up primarily plane shear waves in the liquid surrounding them. The components 31m and %m are again obtained from measurements of the change in resonant frequency and electrical resistance produced by the presence of the liquid. The frequency range is from 0.5 to 10 kHz. Pulsed waves in a metal plate immersed in the liquid can be followed to determine viscoelastic properties in the range from 1 to 7 MHz. ... 

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