Design and construction of a low frequency wide band non-resonant transducer

Commercially available low frequency transducers often have a bandwidth of much less than 100%. This paper reviews the current technology for low frequency transducer construction and presents a non-resonant design giving an improved low frequency performance. Small, undamped piezo-electric cubic elements of 2 mm side length are used which operate below their first resonance frequency. In construction, the elements are air-backed and the front faces are bonded to a thin membrane across the end of an enclosure of 15 mm diameter. Using a low frequency excitation signal which has little energy at the first resonance frequency of the elements, an operating frequency range of 200-500 kHz can be achieved. A single element behaves virtually as a point source, but by arranging an array of elements over the membrane, a more collimated beam profile is obtained.