Activation of a timing fork sensor In Figures 1013 and 1014

Activation of a timing fork sensor. In Figures 10.13 and 10.14, piezoelectric plates are used to drive the tines of a tuning fork into resonance. This is done by applying voltage pulses to the piezoelectric plate, which in turn expands and contracts rapidly, applying a pulse of force to the tines, driving them into oscillations. Consider one of these plates, 100 mu m times 100 mu m in area and 8 mu m thick, made of SiO_2 with the following properties: piezoelectric coefficient 2.31 C/N, relative permittivity 4.63 (see Figure 10.49). and coefficient of elasticity 110 MPa. To apply the voltage the piezoelectric plate is plated on both sides by deposition of aluminum. A voltage pulse of 12 V is applied to the piezoelectric plate: Calculate the maximum displacement the piezoelectric plate can provide. Calculate the maximum force it can apply. Discuss the force and displacement and their adequacy for the actuation of the tines.

Solution

Sound waves are produced by vibrating objects. Whether it be the sound of a person\'s voice, the sound of a piano, the sound of a trombone or the sound of a physics book slamming to the floor, the source of the sound is always a vibrating object.

A tuning fork serves as a useful illustration of how a vibrating object can produce sound. The fork consists of a handle and two tines. When the tuning fork is hit with a rubber hammer, the tines begin to vibrate. The back and forth vibration of the tines produce disturbances of surrounding air molecules. As a tine stretches outward from its usual position, it compresses surrounding air molecules into a small region of space; this creates a high pressure region next to the tine. As the tine then moves inward from its usual position, air surrounding the tine expands; this produces a low pressure region next to the tine. The high pressure regions are known as compressions and the low pressure regions are known as rarefactions. As the tines continue to vibrate, an alternating pattern of high and low pressure regions are created. These regions are transported through the surrounding air, carrying the sound signal from one location to another.