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Presents a concept in the design of an impedance matching structure for air coupled ultrasonic transducers. Function of air-coupled ultrasonic transducers; Principle of impedance matching layer using high impedance material and propagation space; Mechanical impedance of transducer structure.

Proposes a matching layer design concept for narrowband continuous wave devices. Mechanical impedance of transducers; Principle of high efficiency matching layer; Discussion of practical design process.

This paper presents a novel design principle for designing multilayer polymer-metal structures which are well suited for front surface impedance conversion (matching) and for back surface acoustic absorption. It is shown that a polymer layer with an outer metal layer, when loaded by a low impedance propagation medium, acts as an efficient impedance converter. The resulting impedance seen at the inner polymer surface is increased and the structure provides the same performance as a traditional quarter-wavelength matching layer. Experimental evidence is also shown for a double-matching scheme for a lead zirconate titanate (PZT) transducer using an inner polymer-metal multilayer and an outer polymer quarterwavelength layer, resulting in a 55% bandwidth at 2.6 MHz with air backing. Also, it is theoretically shown that multiple layers of a lossy polymer adhesive-metal structure produce low propagation velocity and high absorption. Experimental proof of this ultrasonic multilayer backing absorber is provided. Design theories based on both a simplified mass and spring model and a rigorous one-dimensional wave model have been developed and show fair agreement. [ABSTRACT FROM AUTHOR]