Self-aligning capacitive transducer for the detection of broadband ultrasonic displacement signals

This paper describes a self-aligning capacitive transducer for detecting broadband ultrasonic signals in structural components. The fixed electrode is the specimen surface while the adjustable electrode is pivoted on a ball mount so designed that the electrode aligns itself parallel to the specimen surface when pressed against it. The working gap between the adjustable electrode and the specimen surface is set by a mechanically driven differential micrometer. The design of the transducer permits minimization of the electrode gap to maximize the sensitivity of the transducer to small amplitude, surface displacement signals. It is demonstrated that such a capacitive transducer is well suited to obtaining a high-fidelity response to transient surface displacement signals which are of broad bandwidth and low amplitude.