Piezoceramic Ultrasonic Transducer with Frequency Controlled Radiation Pattern

A theoretical approach shows, that controllable aperture angles of the radiation pattern of an ultrasonic transducer can be realized by arranging interleaved piezoceramic hollow cylinders with different resonance frequencies to an annular array, where all array elements can be driven in parallel. With a controllable radiation pattern, measurements of position-angles of reflecting objects are possible. The requirements to realize such a transducer are that the piezoelectric material, the cylinders are made of, do have an appropriate high mechanical quality factor Q_m to get narrow resonance curves of the single cylinders and length dependent resonance frequencies of the cylinders (in the length extensional mode) that are different in such an extent, that allows a clearly separation of the single resonance curves. Our new method is presented by designing a cylindrical transducer consisting of four interleaved piezoceramic cylinders with resonance frequencies 55 kHz, 65 kHz, 75 kHz and 85 kHz. The reflected signals are detected by a receiver microphone installed in the center of the transducer. The transducer has an aperture angle of the radiated main lobe, that can be varied stepwise in the range of plusmn4deg to plusmn22deg by varying the driving frequency.