Air transducers in the 0.5-10-MHz frequency range are made with either one or two matching layers for broadband and efficient coupling of ultrasound into air. The authors present a design for the optimum value of the impedance of a second matching layer for maximum bandwidth and insertion loss. Theoretical designs predict a functional bandwidth of 30% and a two-way insertion loss of 35 dBs for a device operating at 1 MHz. Experimental results are in excellent agreement with theory. Silica aerogel samples are characterized, and designs that demonstrate their potential as matching layers for air transducer applications are shown. Also, results of transmission imaging through carbon-epoxy and Kevlar-epoxy samples are shown.
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