Characterizing ultrasonic transducers using radiation efficiency and reception noise figure

Abstract

Transducer performance is considered separately for transmission and reception operations. The transmission operation is traditionally characterized by its traditional transfer function. Using a Thevenin source, the transfer function may be scaled to become the absolute radiation efficiency. Transmission lines are accurately modeled, and a matched impedance design is recommended. The reception operation also is characterized by its traditional transfer function. However, reception sensitivity is defined as the signal-to-noise ratio achieved by the combined transducer, transmission line, and preamplifier. The thermal noise arises from the media and other noise sources contributed by the transducer, transmission line, and preamplifier. An absolute sensitivity measure is defined as the acoustic noise figure, which is the sum of individual transducer and preamplifier noise figures. The transducer noise figure is independent of the receiver load impedance and depends critically on dissipative loss. Preamplifier noise figure performance requires noise matching to the transducer. High performance design methods are presented that incorporate transmission lines, which include loss. Modeled examples are used to demonstrate performance.