CHARACTERIZATION OF AIR-COUPLED TRANSDUCERS

This paper describes a theoretical and experimental study for determin ation of the through-air system impulse response and insertion loss wi th different air-coupled ultrasonic transducers. Wide-band piezopolyme r transducers (PVDF) are employed in both transmission and reception m odes and their behavior assessed by means of mathematical modeling and experiment. Specifically, a linear systems approach, modified to incl ude the influence of attenuation in the propagation medium, was used t o design suitable PVDF transducers for wide-band operation in air. Sui table devices were then manufactured for determination of the transmis sion and reception response characteristics of piezocomposite and elec trostatic transducers when operating in the air environment. A range o f transducers was evaluated, including 1-3 connectivity composites of different ceramic volume fraction and mechanical matching conditions, in addition to electrostatic devices of varying design. To complement the investigation, relative performances for narrow-band operation are also presented under transmission and transmit-receive conditions. De spite the obvious measurement difficulties, good agreement between the ory and experiment was observed and the methodology is shown to provid e a convenient and robust procedure for comparison of through-air tran sducers operating in the frequency range 50 KHz to 2 MHz. Although hig hly resonant, the most effective composite transducers under considera tion demonstrate an improvement in two-way insertion loss of 22.4 dB a nd 11.5 dB over a corresponding electrostatic pair, under narrow-band and wide-band operation, respectively.