On the Piezoelectric Detection of Guided Ultrasonic Waves.

Kanji Ono

doi:10.3390/ma10111325

Abstract

In order to quantify the wave motion of guided ultrasonic waves, the characteristics of piezoelectric detectors, or ultrasonic transducers and acoustic emission sensors, have been evaluated systematically. Such guided waves are widely used in structural health monitoring and nondestructive evaluation, but methods of calibrating piezoelectric detectors have been inadequate. This study relied on laser interferometry for the base displacement measurement of bar waves, from which eight different guided wave test set-ups are developed with known wave motion using piezoelectric transmitters. Both plates and bars of 12.7 and 6.4 mm thickness were used as wave propagation media. The upper frequency limit was 2 MHz. Output of guided wave detectors were obtained on the test set-ups and their receiving sensitivities were characterized and averaged. While each sensitivity spectrum was noisy for a detector, the averaged spectrum showed a good convergence to a unique receiving sensitivity. Twelve detectors were evaluated and their sensitivity spectra determined in absolute units. Generally, these showed rapidly dropping sensitivity with increasing frequency due to waveform cancellation on their sensing areas. This effect contributed to vastly different sensitivities to guided wave and to normally incident wave for each one of the 12 detectors tested. Various other effects are discussed and recommendations on methods of implementing the approach developed are provided.

Highlights

In structural health monitoring (SHM) and nondestructive evaluation (NDE) fields, guided ultrasonic waves are widely utilized [1,2]
While the surface displacement of such waves can be characterized without contact using laser instruments in well-equipped laboratories, practical detection methods ordinarily use piezoelectric detectors, especially for low pm-level signals
Most manufacturers have supplied industrial ultrasonic transducers and acoustic emission (AE) sensors with a certificate with a pulse-echo response or with a relative performance chart to a reference standard. These are for normally incident waves (NIW) of longitudinal mode

Summary

Introduction

In structural health monitoring (SHM) and nondestructive evaluation (NDE) fields, guided ultrasonic waves are widely utilized [1,2]. Most manufacturers have supplied industrial ultrasonic transducers and AE sensors with a certificate with a pulse-echo response or with a relative performance chart to a reference standard. These are for normally incident waves (NIW) of longitudinal mode. For this type of waves, conventional face-to-face calibration methods have recently been demonstrated to provide receiving sensitivity in absolute scale. This new approach utilized a laser interferometer as the basis of displacement calibration [9]. Pulse-excited transmitters were characterized for their displacement outputs, which were used to drive receiving sensors

Methods

Results

Discussion

Conclusion