1. PIEZO ELECTRIC TRANSDUCER

2. WORKING PRINCIPLE If the dimensions of the piezoelectric crystals are changed by the application of a mechanical force, an electric potential appears across certain surfaces of a crystal due to displacement of charges and vice-versa. This principle is known as piezoelectric effect.

3. PIEZO ELECTRIC MATERIALS • Ammonium dihydrogen phosphate • Rochelle salt • Lithium sulphate • Dipotassium tartrate • Potassium dihydrogen phosphate • Quartz • Ceramics

4. WORKING • Metal electrodes are attached to the selected faces of piezoelectric crystal to detect electric charge developed. • As mechanical force is applied on crystal, scattered charge inside crystal is going to be arranged at specific faces that is responsible for electricity production. • Q α F so Q = K.F (K – Charge Sensitivity)

5. ADVANTAGES • High frequency response • High output • Rugged construction • Small size

6. DISADVANTAGES • Output is affected by change in temperature. • Poor steady state response • Charge decreases over a time period due to dissipation by crystal itself. • Can not measure static conditions.

7. APPLICATIONS • Accelerometers • Pressure cells • Force cells • Piezoelectric microphone • Guitar pick-up • Hearing aid • Home security alarms

8. MATHEMATICAL EXPRESSION V0 = gtP where • g – crystal voltage sensitivity (Vm/N) • P - applied pressure (N/m2) • t – crystal thickness

9. NUMERICAL PROBLEM A force of 8 N is impressed upon a Piezo-electric crystal having dimensions of 6mm x 6mm x 1.5 mm thick. For the crystal materials- • Charge sensitivity = 140 x 10^(-12) C/N • Permittivity = 12 x 10^(-9) N/m and • Modulus of elasticity = 11.5 x 10^6 N/m2 Make the calculations for the voltage generated, capacitance, and the strain introduced in the crystal