Frequency control in laser ultrasound with computer generated holography

Clark, Matt; Linnane, F.; Sharples, S. D.; Somekh, Michael Geoffrey

doi:10.1063/1.121235

Cited by 16 publications

(7 citation statements)

References 5 publications

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“…The spatial resolution of the optical and acoustic images can be defined using the detection beam size and generation patch size on the surface, respectively-providing a singular answer for the size and depths of subsurface defects becomes a challenge [35]. Lamb wave ultrasound inspection of single crystal materials has been investigated by the authors [36,37], with recent work published on imaging defects in carbon-fibre reinforced plastic materials [38]-for use in additive manufacturing, the anisotropy of the material will determine whether a subsurface pore can be distinguished. If a material is isotropic, detecting defects close to the surface (within 2λ g ) should be as resolvable as the material microstructure, with deeper defects having a lesser effect on the velocity measured.…”

Section: Discussionmentioning

confidence: 99%

Imaging Material Texture of As-Deposited Selective Laser Melted Parts Using Spatially Resolved Acoustic Spectroscopy

et al. 2018

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Additive manufacturing (AM) is a production technology where material is accumulated to create a structure, often through added shaped layers. The major advantage of additive manufacturing is in creating unique and complex parts for use in areas where conventional manufacturing reaches its limitations. However, the current class of AM systems produce parts that contain structural defects (e.g., cracks and pores) which is not compatible with certification in high value industries. The probable complexity of an AM design increases the difficulty of using many non-destructive evaluation (NDE) techniques to inspect AM parts—however, a unique opportunity exists to interrogate a part during production using a rapid surface based technique. Spatially resolved acoustic spectroscopy (SRAS) is a laser ultrasound inspection technique used to image material microstructure of metals and alloys. SRAS generates and detects `controlled’ surface acoustic waves (SAWs) using lasers, which makes it a non-contact and non-destructive technique. The technique is also sensitive to surface and subsurface voids. Work until now has been on imaging the texture information of selective laser melted (SLM) parts once prepared (i.e., polished with R a < 0 . 1 μ m)—the challenge for performing laser ultrasonics in-process is measuring waves on the rough surfaces present on as-deposited parts. This paper presents the results of a prototype SRAS system, developed using the rough surface ultrasound detector known as speckle knife edge detector (SKED)—texture images using this setup of an as-deposited Ti64 SLM sample, with a surface roughness of S a ≈ 6 μ m, were obtained.

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Section: Discussionmentioning

confidence: 99%

Imaging Material Texture of As-Deposited Selective Laser Melted Parts Using Spatially Resolved Acoustic Spectroscopy

et al. 2018

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“…Especially, the detection range is less than few meters, depending on the surface condition of the structure. Moreover, these devices can measure either out-of-plane or in-plane motion only [12].…”

Section: Concept Of Overall Systemmentioning

confidence: 99%

“…For guided wave generation, electromagnetic radiation from a laser is absorbed in the surface region of a structure, causing heating. The heated region undergoes thermal expansion, and non-contact guided waves are generated [12]. However, in the current laser excitation technique, it is difficult controlling the excitation source to generate desired arbitrary waveforms.…”

Section: Introductionmentioning

confidence: 99%

Development of a non-contact PZT excitation and sensing technology via laser

et al. 2011

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In recent years, guided wave based structural health monitoring (SHM) techniques have attracted much attention, because they are not only sensitive to small defects but also capable to cover a wide range in plate and pipe like structures. The guided waves in a structure can be generated and sensed by a variety of techniques. This study proposes a new wireless scheme for PZT excitation and sensing where power as well as data can be transmitted via laser. A generated waveform by modulation of a laser is wirelessly transmitted to a photodiode connected to a PZT on the structures. Then, the photodiode converts the light into an electrical signal and excite the PZT and the structure. Then, the reflected response signal received at the sensing PZT is re-converted into a laser, which is wirelessly transmitted back to another photodiode located in the data acquisition unit for damage diagnosis. The feasibility of the proposed power and data transmission scheme has been experimentally investigated in a laboratory setup. Using the proposed technology, a PZT transducer can be attached to a structure without complex electronic components and a power supply.

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“…Among the above usage the analysis of the frequency characteristics of LA is important [8,9], therefore experimental and theoretical method were used to get the LA S in water induced by TEA CO 2 LP in different situation and computing software was adopt to acquire the change law of the signal.…”

Section: Imentioning

confidence: 99%

Spectra of laser acoustic signals in water

Chen

Cheng

Zhu

2011

2011 International Conference on Electric Information and Control Engineering

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To get the spectra of laser acoustic signal(LAS) in water induced by CO2 laser pulse, and the relation to the parameters of laser pulse(LP). A peak-tail approximation of the actual CO2 LP is used to get the theoretical thermoelastic LAS, after FFT(Fast Fourier Transformation),the affection of the waveform parameters to the LAS spectra is given. And the higher frequency part is affected mainly by the peak while the lower frequency part is affected by the tail.Affection of attenuation to the spectra of LAS is researched and showed spectra at different distance to the source. Experimental research shows that: The spectra of LAS remain unchanged at the same experiment condition and by reducing gas pressure to 5kPa, LAS with peak frequency at 16kHz is obtained.

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Frequency control in laser ultrasound with computer generated holography

Cited by 16 publications

References 5 publications

Imaging Material Texture of As-Deposited Selective Laser Melted Parts Using Spatially Resolved Acoustic Spectroscopy

Imaging Material Texture of As-Deposited Selective Laser Melted Parts Using Spatially Resolved Acoustic Spectroscopy

Development of a non-contact PZT excitation and sensing technology via laser

Spectra of laser acoustic signals in water

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