Comparison of Absolute Sensitivity Limits of Various Ultrasonic and Vibration Transducers

Fortunko, C. M.; Boltz, E. S.

doi:10.4028/www.scientific.net/msf.210-213.471

Cited by 4 publications

(5 citation statements)

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“…Since the sensitivity of the beam deflection technique is proportional to the square root of the laser power, it can be enhanced by employing laser sources with larger output power. However, the unprecedented sensitivity of the PZ transducers cannot be reached by optical techniques based on photodiode detection [30]. We anticipate that further quantitative analysis of the shape of the detected signals could open an interesting new way to probe the evolution of the contact mirror deformation which would in turn reveal the detailed dynamics of the contact area, including the propagation of elastic waves under the mechanical touch.…”

Section: Discussionmentioning

confidence: 99%

“…Detection of elastic waves may be carried out using surface-deployed sensors that operate through transduction mechanisms based on piezoelectric, electrostatic, electromagnetic or optical (mainly light interferometric) principles [29]. Of these, PZ sensors are the most sensitive [30], making them particularly useful to detect low momentum-transfer impacts. Ball-rod [18], [27] and ball-plate [7], [8], [9], [10], [19], [31], [32], [33] experiments involving the detection of ballimpact-induced elastic waves were realized.…”

Section: Contact Time Measuring Techniquesmentioning

confidence: 99%

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Optical Detection of Impact Contact Times with a Beam Deflection Probe

2017

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We present an optical detection technique, called the beam deflection probe, to accurately measure contact times of normal-incidence impacts of steel and sapphire spheres with a transparent glass block. It exploits the deformation of the area that is in a mechanical touch during the rebound. The deformation of the surface acts as a dynamic contact mirror. When illuminated by a laser beam, total internal reflection takes place at the contact mirror, the beam is deflected from it, and its angular deflection history is monitored by a quadrant photodiode. A simple threshold-level data processing of the photodiode signals is used to determine the impact duration. It is shown that the shape of the signal is highly dependent on the location of the impact relative to the center of the laser-beam illuminated area while the determination of the contact time does not depend on the impact position. Using an automated ball release mechanism, the contact time of low-velocity impacts was measured for various ball diameters and approach velocities conforming to the Hertz contact theory. The proposed optical detection of contact times supplements the existing measurement techniques and represents the only alternative to the piezoelectric detection when contact times are to be measured on the microsecond scale.

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Section: Discussionmentioning

confidence: 99%

Section: Contact Time Measuring Techniquesmentioning

confidence: 99%

Optical Detection of Impact Contact Times with a Beam Deflection Probe

2017

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“…After compensation for absorption, the cross-correlation between the detected signals is compared with another waveform, that which is detected at y after an impulsive excitation at x. Imperfect compensation for the non-flat spectrum produced by the source at s leads to an imperfect correspondence between these two waveforms. tudes of $3 Â 10 À12 , and rms displacement amplitudes of $10 À15 m. Nevertheless, as Fortunko established [11], modern piezoelectrics can be very sensitive and the best devices have noise floors close to the thermal limit.…”

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confidence: 99%

On the emergence of the Green’s function in the correlations of a diffuse field

Lobkis

Weaver²

2001

The Journal of the Acoustical Society of America

936

597

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It is shown that a diffuse field is not devoid of phase information, but has a correlation function equal to the Green's function. More specifically, the cross-correlation between diffuse signals in two transducers is very nearly equal to the direct response of one transducer to an impulse applied to the other. This is true whether the diffuse field is one that was created by a distant source, or (if the detectors are sufficiently sensitive) created by thermal fluctuations in the specimen. Here we outline and review proofs, and laboratory demonstrations, from three recent archival publications.

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“…The minimal detectable displacement of any displacement-measuring sensor, defined as the value corresponding to a signal-to-noise ratio of unity, is set by the fundamental limit called the thermal rattle or phonon shot noise [32]. However, all optical detection techniques, regardless of whether they are interferometric or non-interferometric, have a much larger minimum detectable displacement, which is given by the photon shot noise [23].…”

Section: Methodsmentioning

confidence: 99%

“…However, all optical detection techniques, regardless of whether they are interferometric or non-interferometric, have a much larger minimum detectable displacement, which is given by the photon shot noise [23]. The amplitude of this noise is about two orders of magnitude larger than the phonon noise [32]. The limiting resolution of the detected displacement due to the quantum laser amplitude noise (the photon shot noise) is independent of the frequency; it dominates the detector noise if the interferometric laser output power P L is around 1 mW, and has a value of:

4.5 \times 10^{- 17} \sqrt{\frac{Δ f}{P_{normalL}}} m \sqrt{normalJ}

where Δ f is the measuring frequency bandwidth of the optical sensor.…”

Section: Methodsmentioning

confidence: 99%

A Homodyne Quadrature Laser Interferometer for Micro-Asperity Deformation Analysis

Pogačnik

Požar

Kalin

et al. 2013

Sensors

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We report on the successful realization of a contactless, non-perturbing, displacement-measuring system for characterizing the surface roughness of polymer materials used in tribological applications. A single, time-dependent, scalar value, dubbed the collective micro-asperity deformation, is extracted from the normal-displacement measurements of normally loaded polymer samples. The displacement measurements with a sub-nanometer resolution are obtained with a homodyne quadrature laser interferometer. The measured collective micro-asperity deformation is critical for a determination of the real contact area and thus for the realistic contact conditions in tribological applications. The designed measuring system senses both the bulk creep as well as the micro-asperity creep occurring at the roughness peaks. The final results of our experimental measurements are three time-dependent values of the collective micro-asperity deformation for the three selected surface roughnesses. These values can be directly compared to theoretical deformation curves, which can be derived using existing real-contact-area models.

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Comparison of Absolute Sensitivity Limits of Various Ultrasonic and Vibration Transducers

Cited by 4 publications

References 0 publications

Optical Detection of Impact Contact Times with a Beam Deflection Probe

Optical Detection of Impact Contact Times with a Beam Deflection Probe

On the emergence of the Green’s function in the correlations of a diffuse field

A Homodyne Quadrature Laser Interferometer for Micro-Asperity Deformation Analysis

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