Miniaturized capacitive transducer for detection of broadband ultrasonic displacement signals

Abstract

This article describes a miniaturized version of the capacitive transducer for the detection of broadband, ultrasonic displacement signals at the surface of a specimen. The overall size of the capacitive transducer is a cylinder of 11.11 mm in diameter and 22.86 mm in length, in which four different sizes of the sensing area of the capacitive electrode have been successfully tried, ranging from 1 to 5 mm in diameter. Examples of detected waveforms resulting from such excitations as a glass capillary fracture and the formation of cracks on the surface of a specimen are provided using the specimens of glass and epoxy plates, respectively. The amplitudes of the detected signals are shown to be proportional to the displacements normal to the surface of the specimen. These small transducers are especially well suited for measurements on a laboratory specimen which requires several of them to study an acoustic emission source, to characterize an elastic (or a viscoelastic) behavior of the material, or simply to study the wave propagation.