Ultrasonic signals are like audible sound waves, except the frequencies are much higher.

Ultrasonic transducers have piezoelectric crystals which resonate to a desired frequency and convert electric energy into acoustic energy and vice versa.

Diagram A shows how sound waves transmitted in the shape of a cone are reflected back to the transducer. At this stage, an output signal is produced to perform some kind of indicating or control function.

A minimum distance from the sensor is required to provide a time delay so that the “echoes” can be interpreted. Variables which can affect the operation of an ultra- sonic sensor include: target surface angle, reflective surface roughness, change in temperature or humidity. The targets can have any kind of reflective form and even round objects are an acceptable target.