Piezoelectric vs Electrostatic
Ultrasonic transducers come in two basic types, piezoelectric and electrostatic. The main difference between the two is that piezoelectric transducers use a ceramic material whereas electrostatic transducers contain a thin metal membrane.
While their materials differ, they both rely on the piezoelectric effect in order to function. This effect has two parts to it. First, when an electrical current is applied to the material, the material changes shape which results in an ultrasonic sound wave. Second, when the returning echo hits the transducer, the material changes shape again generating an electrical current. This phenomenon makes distance measurement with ultrasonic sensors possible.
Piezoelectric transducers were the first to be used when in the 1950’s crystals derived from quartz were used as the transducer material. Within a few years ceramics were introduced and have been refined ever since.
Electrostatic transducers made their appearance when silicon micromachining processes made it possible to build devices that could work at ultrasonic frequencies. Instead of a ceramic material, a thin micro machined metal membrane is stretched over an electrode.
The main advantage of the electrostatic transducer is that it is more sensitive. Instead of dealing with a blanking distance of 12 – 18 inches, electrostatic transducers have a blanking distance of just 4 – 6 inches.
However, electrostatic transducers can’t be sealed in a housing making them vulnerable to the environment. Traditional ceramic transducers, on the other hand, can be sealed without any issue enabling them to be applied in rougher environments.