Design of a High Efficiency Acoustic Phased Array Antenna for an Acoustic Wind Profiler

Summary

Improvements to the performance of acoustic wind profilers necessitate designing efficient acoustic antennas for the profilers, so that weak echoes can be received to enhance data availability.

An efficient acoustic antenna needs to optimize electrical to acoustic and acoustic to electrical conversion efficiency as measured at the antenna axis. It also needs to provide a good directional response, and be able to handle increased electrical power. Phased array antennas, designed using piezo-electric transducers, should provide better characteristics in this regard.

In the present study several different transducer elements were characterized with respect to their relative efficiencies. On the basis of this characterization, measurement of acoustic background noise at the expected site of antenna location and comparative study of atmospheric molecular absorption at the element peak efficiency frequencies, it is concluded that Motorola KSN 1025 A transducer is the best speaker element for the array antennas for profilers up to around 500 meters.

The present array antenna has been designed using 104 KSN 1025 A piezo-electric transducer elements. The corner elements were removed from a 16 × 8 element speaker matrix, yielding an irregular octagonal pattern. Before installing the elements in the array, each element was individually characterized for its transmit and receive conversion efficiency, and variations in the product of these efficiencies (conversion gain) amongst the different elements, has been usefully employed to taper the array gain from centre to periphery.

The antenna was systematically characterized, in an acoustic anechoic chamber, with respect to its axial transmit and receive conversion efficiencies and directional response.