Subsurface flaw detection in metals by photoacoustic microscopya

Thomas, R. L.; Pouch, John J.; Wong, Y. H.; Favro, L. D.; Kuo, P. K.; Rosencwaig, Allan

doi:10.1063/1.327726

Cited by 203 publications

(56 citation statements)

References 4 publications

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“…The above described procedure for quantitative analysis requires the determination of the blind frequency and of the correlation coefficient C, when the material's thermal properties are known. Conventional experimental C values when using the phase in lock-in experiments range from 1.5 to 2 [37] with a value of C = 1.82 typically adapted in experimental studies [38,39]. PPT results agree with this value range either for homogeneous or composite materials [35,36].…”

Section: Quantitative Depth Estimation In the Frequency Domainsupporting

confidence: 72%

Depth Retrieval Procedures in Pulsed Thermography: Remarks in Time and Frequency Domain Analyses

Theodorakeas

Koui

2018

Applied Sciences

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Featured Application: The present study intends to show the potentiality of pulsed thermographic imaging to quantitatively characterise hidden defects in Carbon Fibre Reinforced Polymers. By comparing the performance of different depth retrieval procedures, it was possible to evaluate the produced depth estimation accuracy and to define the impact of different experimental and analysis parameters in quantitative analysis. Abstract:In the present study, a Carbon Fibre Reinforced Polymer (CFRP) sample of trapezoid shape, consisting of internal artificial delaminations of various sizes and depth locations, is investigated by means of optical pulsed thermography for the retrieval of quantitative depth information. The main objectives of this work are to evaluate the produced depth estimation accuracy from two contrast-based depth inversion procedures as well as to correlate the acquired results with characteristics such as the location and size of the detected features and with analysis parameters such as the selection of the sound area. Quantitative analysis is performed in both the temporal and frequency domains, utilising, respectively, the informative parameters of thermal contrast peak slope time and blind frequency. The two depth retrieval procedures are applied for the depth estimation of features ranging in size from 3 mm to 15 mm and in depth from 0.2 mm to 1 mm. The results of the present study showed that the two different analyses provided efficient depth estimations, with frequency domain analysis presenting a greater accuracy. Nevertheless, predicting errors were observed in both cases and the factors responsible for these errors are defined and discussed.

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Section: Quantitative Depth Estimation In the Frequency Domainsupporting

confidence: 72%

Depth Retrieval Procedures in Pulsed Thermography: Remarks in Time and Frequency Domain Analyses

Theodorakeas

Koui

2018

Applied Sciences

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“…The depth profiling of the sample is possible by varying the chopping frequency. [39][40][41] Thomas et al 42 detected subsurface flaws in aluminum in the PA magnitude to a depth of approximately one diffusion length (∼180 to 800 μm) over a wide range of chopping frequencies. Other than spectral measurements, the PA technique can also be used in several other applications such as the measurement of thermal diffusivity, 43 detection of phase transitions, 44 and luminescence quantum efficiency.…”

Section: Introductionmentioning

confidence: 99%

Low-power noncontact photoacoustic microscope for bioimaging applications

2017

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Abstract. An inexpensive noncontact photoacoustic (PA) imaging system using a low-power continuous wave laser and a kilohertz-range microphone has been developed. The system operates in both optical and PA imaging modes and is designed to be compatible with conventional optical microscopes. Aqueous coupling fluids are not required for the detection of the PA signals; air is used as the coupling medium. The main component of the PA system is a custom designed PA imaging sensor that consists of an air-filled sample chamber and a resonator chamber that isolates a standard kilohertz frequency microphone from the input laser. A sample to be examined is placed on the glass substrate inside the chamber. A laser focused to a small spot by a 40× objective onto the substrate enables generation of PA signals from the sample. Raster scanning the laser over the sample with micrometer-sized steps enables high-resolution PA images to be generated. A lateral resolution of 1.37 μm was achieved in this proof of concept study, which can be further improved using a higher numerical aperture objective. The application of the system was investigated on a red blood cell, with a noiseequivalent detection sensitivity of 43,887 hemoglobin molecules (72.88 × 10 −21 mol or 72.88 zeptomol). The minimum pressure detectable limit of the system was 19.1 μPa. This inexpensive, compact noncontact PA sensor is easily integrated with existing commercial optical microscopes, enabling optical and PA imaging of the same sample. Applications include forensic measurements, blood coagulation tests, and monitoring the penetration of drugs into human membrane.

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“…Photothermal detection [5] removed this problem, however, it became clear that the depth range needed for many applications required such low modulation frequencies that it took a long time to generate an image. To give an example, to look 0.1 mm deep into polymers one needs about 1 Hz [6] even with signal phase [7][8][9]. This may be acceptable for a point measurement, but not for one pixel of an image.…”

Section: Introductionmentioning

confidence: 99%