A novel transducer for active or passive sensing has been developed and tested experimentally. It features a steel wire
acting as a wave guide between a piezoceramic element and the structure under test. Some advantages of the wire-guided
transducer include its applicability to structures operating at high temperature, which otherwise preclude the
surface mounting of piezoceramics, its small contact area to the structure, which enables several such transducers to be
deployed in an arc around a known crack location as an acoustic emission sensor array, and its low cost and ease of
installation. Another potential advantage is simplified signal processing for source localization, which is developed in
this paper and evaluated experimentally.
The various steel wires used in our experiments to date are less than 1 mm in diameter and between 10 cm and 100 cm in
length. The wire guides have been studied with active excitation under a pulse excitation as used in ultrasonic testing, at
a relatively high frequency such as 1 MHz, and in the frequency range of 100 kHz to 500 kHz which is often of interest
for Lamb wave generation in thin plates or for acoustic emission sensing. Our tests confirm that the wire acts as a
cylindrical rod in which the fastest wave is the lowest longitudinal mode, displaying a sharp arrival, and in which the
lowest flexural mode and lowest torsional mode are also excited; we report excellent agreement between measured and
predicted wave speeds, as expected.
We show experimental results in which a group of wire-guided transducers permit the localization of an impact on a thin
plate and discuss the automation of this task for use in the field. We also show the ability of the wire-guided transducer
to detect acoustic emission events simulated physically by pencil lead breaks.