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Optical calibration for both out-of-plane and in-plane displacement sensitivity of acoustic emission sensors.

Theobald, P D (2009) Optical calibration for both out-of-plane and in-plane displacement sensitivity of acoustic emission sensors. Ultrasonics, 49 (8). pp. 623-627.

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Abstract

The use of piezoelectric sensors for acoustic emission (AE) monitoring provides an extremely sensitive 25 detection method of AE events. The sensors are used to detect the stress waves, resulting from an AE 26 event, which arrive at the surface of a structure. The sensors provide high sensitivity, and are generally 27 based on a high-Q design where the sensor is used to detect AE events around its resonance. Sensitivity 28 calibration of these sensors is essential for accurate assessment of the AE measurement and particularly 29 important for sensors mounted on safety critical structures. This paper proposes an optical method which 30 enables both the out-of-plane and in-plane displacement sensitivity of an AE sensor to be established 31 independently from each other. In the method, a laser homodyne interferometer is used to measure 32 the out-of-plane and in-plane displacement of the surface of a large test block excited by a repeatable 33 source transducer. The out-of-plane displacement is measured by aligning the laser beam perpendicular 34 to the surface with time gating of the receive waveform used to isolate only the direct arrival of the lon- 35 gitudinal wave produced by the piston source transducer. For the in-plane displacement measurement, 36 the laser beam is aligned parallel to the surface to intersect a small optically reflective step with the time 37 waveform being gated to measure only the direct shear arrival produced using a normal incidence shear 38 wave source transducer. In each case, the interferometer measurement is followed by coupling the sensor 39 under test to the measurement surface, which is then exposed to the same acoustic field and the sensor 40 output signal measured. This substitution method allows the sensor sensitivity to be obtained in terms of 41 volts per unit displacement for both the out-of-plane and the in-plane surface displacement. The method 42 provides a comprehensive description of an AE sensor response to different planes of displacement and 43 offers the potential for a traceable sensor calibration to units of length.

Item Type: Article
Subjects: Acoustics
Acoustics > Ultrasound
Last Modified: 02 Feb 2018 13:15
URI: http://eprintspublications.npl.co.uk/id/eprint/4524

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