Next Article in Journal
BLocate: A Building Identification Scheme in GPS Denied Environments Using Smartphone Sensors
Next Article in Special Issue
Photoacoustic Energy Sensor for Nanosecond Optical Pulse Measurement
Previous Article in Journal
DTM-Aided Adaptive EPF Navigation Application in Railways
Previous Article in Special Issue
Generation and Analysis of Ultrasound Images Using Plane Wave and Sparse Arrays Techniques
Open AccessFeature PaperArticle

Frequency Dependence of Receiving Sensitivity of Ultrasonic Transducers and Acoustic Emission Sensors

Department of Materials Science and Engineering, University of California, Los Angeles (UCLA), Los Angeles, CA 90095, USA
Sensors 2018, 18(11), 3861; https://doi.org/10.3390/s18113861
Received: 13 October 2018 / Revised: 5 November 2018 / Accepted: 7 November 2018 / Published: 9 November 2018
(This article belongs to the Special Issue Ultrasonic Sensors 2018)
Receiving displacement sensitivities (Rx) of ultrasonic transducers and acoustic emission (AE) sensors are evaluated using sinewave packet excitation method and compared to the corresponding data from pulse excitation method with a particular emphasis on low frequency behavior below 20 kHz, down to 10 Hz. Both methods rely on the determination of transmitter displacement characteristics using a laser interferometric method. Results obtained by two calibration methods are in good agreement, with average spectral differences below 1 dB, indicating that the two calibration methods yield identical receiving sensitivities. At low test frequencies, effects of attenuation increase substantially due to increasing sensor impedance and Rx requires correction in order to evaluate the inherent sensitivity of a sensor, or open-circuit sensitivity. This can differ by more than 20 dB from results that used common preamplifiers with ~10 kΩ input impedance, leading to apparent velocity response below 100 kHz for typical AE sensors. Damped broadband sensors and ultrasonic transducers exhibit inherent velocity response (Type 1) below their main resonance frequency. In sensors with under-damped resonance, a steep sensitivity decrease occurs showing frequency dependence of f2~f5 (Type 2), while mass-loaded sensors exhibit flat displacement response (Type 0). Such behaviors originate from sensor characteristics that can best be described by the damped harmonic oscillator model. This model accounts for the three typical behaviors. At low frequencies, typically below 1 kHz, receiving sensitivity exhibits another Type 0 behavior of frequency independent Rx. Seven of 12 sensors showed this flat region, while three more appear to approach the Type 0 region. This appears to originate from the quasi-static piezoelectric response of a sensing element. In using impulse method, a minimum pulse duration is necessary to obtain spectral fidelity at low frequencies and an approximate rule is given. Various factors for sensitivity improvement are also discussed. View Full-Text
Keywords: ultrasonic transducers; acoustic emission sensors; receiving sensitivity; low frequency characteristics; sinewave excitation; impulse method; open-circuit sensitivity; input impedance; frequency independent sensitivity; damped harmonic oscillator; minimum pulse duration ultrasonic transducers; acoustic emission sensors; receiving sensitivity; low frequency characteristics; sinewave excitation; impulse method; open-circuit sensitivity; input impedance; frequency independent sensitivity; damped harmonic oscillator; minimum pulse duration
Show Figures

Figure 1

MDPI and ACS Style

Ono, K. Frequency Dependence of Receiving Sensitivity of Ultrasonic Transducers and Acoustic Emission Sensors. Sensors 2018, 18, 3861.

Show more citation formats Show less citations formats
Note that from the first issue of 2016, MDPI journals use article numbers instead of page numbers. See further details here.

Article Access Map by Country/Region

1
Back to TopTop