Abstract
A unique embeddable high-fidelity transducer is introduced here, presenting design parameters and National Institute of Standards and Technology (NIST) calibration. Traditionally, acoustic emission studies are conducted by placing an array of sensors on the surface of the specimen being tested, but the physical constraints of many practical testing geometries preclude surface placement of sensors. Advantages of embedded sensors include the following: (a) mode conversion is avoided so the measured waveforms are simpler and easier to interpret; (b) the sensor(s) can be located close to the area of crack growth; (c) a greater length of signal can be recorded before being contaminated by surface reflections/mode conversions; (d) embedded sensors may be less susceptible to accidental movement or damage; and (e) embedded sensors can be used when free surfaces are not accessible. To date no such transducers have been available. As a surface sensor, the device is sensitive to partial displacement; as an embedded sensor, the device is sensitive to particle velocity. The presented design yields sensitivity equal to commercial resonant devices (2.34-V output per mm per s embedded; 2.8 V/nm surface) while maintaining the high-fidelity of the NIST displacement sensors (±2.5 dB from 10 KHz to 1 MHz). The embedded response is calibrated with the theoretical solution for Lamb’s problems.
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