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Journal ArticleDOI

Applicability of LED-Based Excitation Source for Defect Depth Resolved Frequency Modulated Thermal Wave Imaging

TL;DR: A nonuniform frame capture technique to reduce the memory allocation space of the recorded video, based on varying the sampling rate with a change in instantaneous frequency and is specifically useful for frequency modulated excitation signal is proposed.
Abstract: This paper proposes an energy efficient instrumentation set-up for pulse-compression thermal-wave imaging with a low-power LED excitation source. The set-up consists of three different subsystems that are synchronised in time. The individual systems consist of a LED modulation circuitry, reference signal measurement circuitry, and an IR camera trigger signal generation circuitry for frame capture. A separate reference acquisition circuitry is useful in quantifying defect depth resolution. This paper also proposes a nonuniform frame capture technique to reduce the memory allocation space of the recorded video. The technique is based on varying the sampling rate with a change in instantaneous frequency and is specifically useful for frequency modulated excitation signal. The proposed technique is implemented on a carbon fiber reinforced polymer test-piece. The variation of pulse compression parameters with different defect dimension is studied, and the results are verified with an electro-thermal simulator. Further, an objective comparison of pulse compression experiment for different experiment duration is presented.
Citations
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Journal ArticleDOI
TL;DR: In this article, the step heating contribution is recorded separately by mean of an additional measurement, which can effectively enhance the defect information and improve the thermal contrast between defect and non-defect areas when halogen lamps are used in combination with pulse-compression in reflection mode.

30 citations

Journal ArticleDOI
TL;DR: This paper proposes an idea of employing sparse reconstruction-based technique for thermal imaging defect detection, and describes cross-validation method for optimization of a user parameter in sparse reconstruction method.
Abstract: This paper proposes an idea of employing sparse reconstruction-based technique for thermal imaging defect detection. The implementation of the reconstruction technique is tested on a carbon fiber reinforced polymer test piece with artificially drilled defects and the test results are compared with the established cross correlation method. The two processes are compared in terms of defect detectability, their SNR variation with defect depth and their computation complexity. When compared with cross correlation algorithm, the technique is expected to solve memory space problems by compressing all information from large cross-correlated pulse video into a single reconstructed image as an output. Furthermore, in existing cross correlation methods, the pulse peak time shifts with defect depth. Hence, defect quantification algorithms, such as SNR calculation, require multiple frame analysis. Such algorithms are comparatively simplified in sparse reconstruction technique. This paper explores sparse reconstruction algorithm for resolving close-spaced defects. This paper further describes cross-validation method for optimization of a user parameter in sparse reconstruction method.

12 citations


Cites background or methods from "Applicability of LED-Based Excitati..."

  • ...THE PARAMETER VALUES ([10]) USED ARE k|| = 4 W/m ◦C; ρ = 1600 kg/m3; AND c = 1200 J/kg ◦C...

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  • ...Furthermore, Roy and Tuli [10] show that a rise in time-bandwidth product does not improve the defect detection....

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  • ...A memory efficient nonuniform data acquisition method was suggested in [10]....

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Journal ArticleDOI
TL;DR: In this article , an orthogonal phase-coded linear frequency modulated (OPCLFM) excitation waveform was proposed to improve the SNR and depth resolvability of thermal wave radar (TWR) compared to the LFM waveform.
Abstract: Thermal wave radar (TWR) thermography is a high-efficient nondestructive testing technique to increase the signal-to-noise ratio (SNR) and to enhance target detection capability. However, the detection of subsurface defects, especially small-size defects, usually requires a distinctively high SNR and depth resolvability. This paper proposed an orthogonal phase-coded linear frequency modulated (OPCLFM) excitation waveform, which has significantly improved the SNR and depth resolvability of TWR compared to the LFM waveform. The pulse compression quality of the OPCLFM waveform was initially evaluated through a 1D thermal wave analytical model of carbon fiber reinforced polymer (CFRP) laminate. Results show that the OPCLFM waveform combined with the Kaiser window function compresses the largest sidelobe at least by 18.39 dB compared to the LFM waveform. Furthermore, the superior depth resolvability performance of the OPCLFM waveform was also validated by 3D finite element simulation. Finally, the effect of thermal conductivity on the depth resolvability performance of the OPCLFM waveform was evaluated quantitatively by a delaminated CFRP laminate.

4 citations

Journal ArticleDOI
TL;DR: The results and methods show applied use of this novel optical non-destructive testing technique for a variety of structures, especially for structures which operate in harsh environments.
Abstract: The adaptation of colloidal quantum dots loaded within a polymer for use in nondestructive testing can be used as an optical strain gauge due to the nanomaterial's strain sensing properties. In this paper, we utilized InP/ZnS colloidal quantum dots loaded within a polymer matrix applied onto the surface of a dog-bone foil precoated with an epoxy. By employing an empirical formula and a calibration factor, there is a propinquity between both the calculated optical strain and mechanical stress-strain reference data. Fluctuations are observed, which may be due to both additional strain responses not seen by the mechanical data and quantum dot blinking. These results and methods show the applied use of this novel optical nondestructive testing technique for a variety of structures, especially for structures that operate in harsh environments.

4 citations

Proceedings ArticleDOI
01 Sep 2018
TL;DR: In this article, a method for improving control of high-power optical and electrical types of excitation sources with possibility of voltage or current stabilization is proposed with the possibility of current stabilization.
Abstract: The aim of the paper is to study the possibilities for using one excitation source for transient as well as lock-in infrared thermography modes. Problems in controlling the high-power optical excitation sources in active thermography are analysed. Special attention is paid to high power LEDs as sources for thermal stimulation in thermography. A method for improving control of high-power optical and electrical types of excitation sources is proposed with possibility of voltage or current stabilization.

2 citations


Cites background from "Applicability of LED-Based Excitati..."

  • ...In recent year, there is a strong interest in using of LEDs as excitation sources in active thermography [2], [3]....

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References
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Journal ArticleDOI
TL;DR: This paper contains many of the important analytical methods required for the design of a Chirp radar system, and a method to reduce the time side lobes by weighting the pulse energy spectrum is explained in terms of paired echoes.
Abstract: A new radar technique has been developed that provides a solution for the conflicting requirements of simultaneous long-range and high-resolution performance in radar systems. This technique, called Chirp at Bell Telephone Laboratories, recognizes that resolution depends on the transmitted pulse bandwidth. A long high-duty-factor transmitted pulse, with suitable modulation (linear frequency modulation in the case of Chirp), which covers a frequency interval many times the inherent bandwidth of the envelope, is employed. The receiver is designed to make optimum use of the additional signal bandwidth. This paper contains many of the important analytical methods required for the design of a Chirp radar system. The details of two signal generation methods are considered and the resulting signal waveforms and power spectra are calculated. The required receiver characteristics are derived and the receiver output waveforms are presented. The time-bandwidth product is introduced and related to the effective increase in the performance of Chirp systems. The concept of a matched filler is presented and used as a reference standard in receiver design. The effect of amplitude and phase distortion is analyzed by the method of paired echoes. One consequence of the signal design is the presence of time side lobes on the receiver output pulse analogous to the spatial side lobes in antenna theory. A method to reduce the time side lobes by weighting the pulse energy spectrum is explained in terms of paired echoes. The weighting process is described, and calculated pulse envelopes, weighting network characteristics and dele-???

889 citations


"Applicability of LED-Based Excitati..." refers background in this paper

  • ...The SNR of the defect is known to increase from pulsed excitation by a factor of time-bandwidth product of the chirped excitation sequence [13]....

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Journal ArticleDOI
TL;DR: In this paper, the authors combined thermal wave and thermography to provide a short-time low-frequency phase angle image where non-thermal features can be suppressed using lock-in data analysis.
Abstract: Thermography and thermal wave techniques can be combined to provide in a short‐time low‐frequency phase angle images where nonthermal features can be suppressed. The principle is optical thermal wave generation simultaneously on the whole sample surface and sequential monitoring of all pixels using both thermographic techniques and lock‐in data analysis. Due to parallel stationary excitation one can use low modulation frequencies allowing for a depth range that is of relevance for applications.

638 citations


"Applicability of LED-Based Excitati..." refers methods in this paper

  • ...THERMAL imaging is a well-known nondestructive characterization technique [1]–[3], with lock-in thermography [4] and pulse thermography [5] been widely used....

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Journal ArticleDOI
TL;DR: In this article, it is shown that even with the low ambient temperatures experienced in Europe it is possible to use infrared thermography to identify correctly known areas of delamination in a concrete bridge structure and also to investigate the internal structure of a masonry bridge.
Abstract: Within recent years there has been an increase in the use of NDT methods to detect defects and anomalies in various civil engineering structures. Infrared thermography, which has been successfully used in the USA in civil engineering applications, is being increasingly applied in the UK as an NDT technique. For example, the technique is now included in the Building Regulations for the assessment of thermal insulation for all new non-domestic buildings from April 2002. One of the perceived limitations of infrared thermography is that in temperate climates it is too cold to use this technique since there is rarely the extreme solar exposure that has enabled the successful use of thermography to detect render debonding and concrete spalling utilising solar heating. However, with the advancements in modern technology it is now possible to detect smaller changes in temperature (down to 0.08 °C). This paper shows that even with the low ambient temperatures experienced in Europe it is possible to use infrared thermography to identify correctly known areas of delamination in a concrete bridge structure and also to investigate the internal structure of a masonry bridge.

359 citations


"Applicability of LED-Based Excitati..." refers methods in this paper

  • ...THERMAL imaging is a well-known nondestructive characterization technique [1]–[3], with lock-in thermography [4] and pulse thermography [5] been widely used....

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Journal ArticleDOI
TL;DR: In this paper, the authors provided the theory and mathematical analysis in support of a recently proposed frequency modulated thermal wave imaging for nondestructive subsurface defect detection in solids.
Abstract: This letter provides the theory and mathematical analysis in support of a recently proposed frequency modulated thermal wave imaging for nondestructive subsurface defect detection in solids. The authors illustrate how the technique simultaneously combines the advantages of both conventional pulse based thermography as well as modulated lock-in thermography. A specimen is heated for launching thermal waves into the sample, not at a single frequency (lock-in) or at all frequencies (pulse), but in a desired range of frequencies. While peak power requirement is reduced, phase images obtained retain known advantages. Experimental results from a carbon fiber reinforced plastic sample are presented in support.

250 citations


"Applicability of LED-Based Excitati..." refers methods in this paper

  • ...Frequency-modulated thermal-wave imaging is a relatively new thermal-wave imaging technique for defect detection [7]....

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Journal ArticleDOI
TL;DR: In this article, transient thermal non-destructive testing (NDT) is used for assessing aircraft composites, which can be used for both reducing manufacturing costs and out-ofservice time of aircraft due to maintenance.

182 citations


"Applicability of LED-Based Excitati..." refers methods in this paper

  • ...THERMAL imaging is a well-known nondestructive characterization technique [1]–[3], with lock-in thermography [4] and pulse thermography [5] been widely used....

    [...]