The high-frequency response of these transducers makes a good choice for various applications.they don’t require external power for working and are therefore self-generating. The advantages and limitations of piezoelectric transducers include the following. These are used in ultrasonic imaging in medical applications.Īdvantages and Limitations of Piezoelectric Transducers.Used by automotive industries to measure detonations in engines.In strain gauges to measure force, stress, vibrations etc….They are used in seismographs to measure vibrations in rockets.As piezoelectric materials cannot measure static values these are primarily used for measuring surface roughness, in accelerometers and as a vibration pickup.At this point, quartz produces longitudinal ultrasonic waves of large amplitude. Resonance takes place when the frequency of the electronic oscillatoris equal to the natural frequency of the quartz. Due to converse piezoelectric effect the crystal starts contracting and expanding alternatively thus creating mechanical vibrations. Due to this, an e.m.f is induced in 元 which is transferred to the quartz crystal through plates A and B. When the battery is turned ON the oscillator produces high-frequency alternating voltage pulses with a frequency f=1÷(2π√L1C1). The coils L1 and L2, which forms secondary of the transformer, are connected to the electronic oscillator. The primary of the transformer is inductively coupled to the electronic oscillator. Here, the quartz crystal is placed between two metal plates A and B which are connected to the primary 元 of the transformer. The circuit of the ultrasonic transduceris given below. In this effect when electricity is applied to a piezoelectric material, it undergoes physical deformations proportional to applied charge. The ultrasonic piezoelectric transducer works on the principle of the converse piezoelectric effect. So in a piezoelectric transducer when mechanical stress is applied a proportional electric voltage is generated which is amplified using charge amplifier and used for calibration of applied stress. So the charge amplifier is usually placed very near to the sensor. The capacitance of the lead wire that connects the transducer and piezoelectric sensor also affects the calibration. To draw very low current the resistance R1 is very high. A charge amplifier is used to measure the produced charge without dissipation. Here quartz crystal coated with silver is used as a sensor to generate a voltage when stress is applied on it. The working of a basic piezoelectric transducer can be explained by the below figure. When the ratio b/a is greater than 1 the charge produced by transverse arrangement will be greater than the amount generated by longitudinal arrangement. In the transverse effect, the charge generated is given by Piezoelectric coefficient d of quartz crystal is around 2.3 * 10 -12 C/N. Where F is the applied force,d is the piezoelectric coefficient of the crystal. In the longitudinal effect, the charge generated is given by Rochelle salt gives the highest output values but it is sensitive to environmental conditions and cannot be operated above 1150F. Slowly varying parameters can be measured with quartz. Quartz is a highly stable crystal which is naturally available but it has small output levels. Unfortunately, there is no piezoelectric material which has all these properties. The materials used for measurement purpose should have frequency stability, high output values, insensitive to the extreme temperature and humidity conditions and which can be available in various shapes or should be flexible to be manufactured into various shapes without disturbing their properties. There are certain requirements to be met by the piezoelectric materials to be used as transducers. Not all piezoelectric materials can be used in piezoelectric transducers. Artificially manufactures piezoelectric materials are Polyvinylidene difluoride, PVDF or PVF2, Barium titanate, Lead titanate, Lead zirconate titanate (PZT), Potassium niobate, Lithium niobate, Lithium tantalate, and other lead-free piezoelectric ceramics. Naturally Available Ones: Quartz, Rochelle salt, Topaz, Tourmaline-group minerals, and some organic substances as silk, wood, enamel, bone, hair, rubber, dentin.