Broadband Calibration of Acoustic Emission and Ultrasonic Sensors from Generalized Ray Theory and Finite Element Models

Wu, Bill S.; McLaskey, Gregory C.

doi:10.1007/s10921-018-0462-8

Cited by 21 publications

(30 citation statements)

References 20 publications

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“…The detector is a piezoelectric sensor with a sufficiently flat and wide frequency response to resolve normal surface displacement waveforms with amplitudes in the 1-pm range and propagating at acoustic velocities. Sensor calibration 34 , 35 reveals a reasonably flat frequency response between 10 kHz and 5 MHz. The circular contact tip of the conically shaped lead zirconate titanate (PZT) crystal has a 1-mm diameter and is covered by a protective nickel foil.…”

Section: Resultsmentioning

confidence: 94%

Isolated detection of elastic waves driven by the momentum of light

et al. 2018

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Electromagnetic momentum carried by light is observable through the mechanical effects radiation pressure exerts on illuminated objects. Momentum conversion from electromagnetic fields to elastic waves within a solid object proceeds through a string of electrodynamic and elastodynamic phenomena, collectively bound by momentum and energy continuity. The details of this conversion predicted by theory have yet to be validated by experiments, as it is difficult to distinguish displacements driven by momentum from those driven by heating due to light absorption. Here, we have measured temporal variations of the surface displacements induced by laser pulses reflected from a solid dielectric mirror. Ab initio modelling of momentum flow describes the transfer of momentum from the electromagnetic field to the dielectric mirror, with subsequent creation/propagation of multicomponent elastic waves. Complete consistency between predictions and absolute measurements of surface displacements offers compelling evidence of elastic transients driven predominantly by the momentum of light.

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Section: Resultsmentioning

confidence: 94%

Isolated detection of elastic waves driven by the momentum of light

et al. 2018

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“…This same trend also appears below 100 Hz for the blue Rx curve and for the purple Rx curve below 5 kHz. This apparent linear behavior is sometimes attributed to intrinsic sensor characteristics [ 23 ]. However, its dependence on Z in values found here indicates that a different origin produces this observation.…”

Section: Resultsmentioning

confidence: 99%

“…The sensitivity level for SE1000HI is comparable to that of a recent small aperture sensor (KRN Services, BB-PCP) at higher frequencies, as reported in [ 3 ]. Recent works [ 22 , 23 ] have also extended the calibration frequency down to 1 kHz for several UT and AE sensors. This method is based on a ball drop and finite element displacement calculation.…”

Section: Introductionmentioning

confidence: 99%

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

Ono

2018

Sensors

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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.

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“…An array of 16 Panametrics V103 ultrasonic piezoelectric sensors, sampled at 1 MHz, were coupled to the granite blocks using superglue on both the top (PZ1–PZ8) and bottom surfaces (PZ9–PZ16) to measure ground motion in the z direction. Output from these sensors is approximately proportional to vertical ground displacement in the 60‐ to 700‐kHz band and acceleration in the 1‐ to 10‐kHz band (Wu & McLaskey, ).…”

Section: Mechanics Of the Experimentsmentioning

confidence: 99%

Contained Laboratory Earthquakes Ranging From Slow to Fast

McLaskey

2019

JGR Solid Earth

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Loading a 3-m granite slab containing a saw-cut simulated fault, we generated slip events that spontaneously nucleate, propagate, and arrest before reaching the ends of the sample. This work shows that slow (0.07 mm/s slip speeds) and fast (100 mm/s) contained slip events can occur on the same fault patch. We also present the systematic changes in radiated seismic waves both in time and frequency domain. The slow earthquakes are 100 ms in duration and radiate tremor-like signals superposed onto a low-frequency component of their ground motion. They are often preceded by slow slip (creep) and their seismic radiation has an ω −1 spectral shape, similar to slow earthquakes observed in nature. The fastest events have slip velocity, stress drop, and apparent stress (0.2 m/s, 0.4 MPa, and 1.2 kPa, respectively) similar to those of typical M −2.5 earthquakes, with a single distinct corner frequency and ω −2 spectral falloff at high frequencies, well fit by the Brune earthquake source model. The gap between slow and fast is filled with intermediate events with source spectra depleted near the corner frequency. This work shows that a fault patch of length p with conditions favorable to rupture can radiate in vastly different ways, based on small changes in p h * ; where h * is a critical nucleation length scale. Such a mechanism can help explain atypical scaling observed for low-frequency earthquakes that compose tectonic tremor.Plain Language Summary Some faults slip slowly and silently, while others are locked and then slip spontaneously in an abrupt fashion. There is debate on whether slow and fast slip are distinct processes or lie on a continuum of fault slip modes in nature. Recent laboratory observations show that a single fault can slip in both modes and at some intermediate velocities, creating a spectrum of slow to fast earthquakes. We have conducted laboratory earthquake experiments where we force a fault cut in a 3-m-long granite rock to slip under pressure. The experiments show that by giving a rupture more distance to accelerate before it runs in to unfavorable fault conditions and dies, it can emit high-frequency energy more efficiently and exhibit resemblance to natural regular earthquakes. On the other hand, if a rupture barely accelerates before stopping, it will emit weak tremors. This proposed mechanism and the seismic consequences highlighted in this study may explain the puzzling behavior of deep tectonic tremor sometimes radiated from slow earthquakes.A family of slow earthquakes have been observed in the past 20 years with the deployment of continuous GPS recording systems and high-sensitivity borehole seismometers and strain meters. Independent Key Points:• We generate contained earthquake-like slip events on a 3 m dry, homogeneous granite fault that do not rupture through the sample ends • We create a spectrum of slow to fast events, ranging from M −3.2 events with 50 kPa stress drop to M −2.5 quakes with 0.4 MPa stress drop • Slow events produce tremor-like seismic radiation and have an ω −1 spe...

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Broadband Calibration of Acoustic Emission and Ultrasonic Sensors from Generalized Ray Theory and Finite Element Models

Cited by 21 publications

References 20 publications

Isolated detection of elastic waves driven by the momentum of light

Isolated detection of elastic waves driven by the momentum of light

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

Contained Laboratory Earthquakes Ranging From Slow to Fast

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