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Journal ArticleDOI: 10.1080/09349847.2017.1361492

Frequency modulated thermal wave imaging for visualizing power density of electromagnetic waves on plane surfaces

01 Mar 2019-Research in Nondestructive Evaluation (The American Society for Nondestructive Testing)-Vol. 30, Iss: 2, pp 65-79
Abstract: In this article, Frequency Modulated Thermal Wave Imaging (FMTWI) [1–6] is introduced for the first time for determining power distribution of electromagnetic waves on plane surfaces. The advantage with this technique is that we can extract multiple amplitude and phase images from a single run of experiment. The applied excitation signal in this technique is a frequency modulated chirp signal instead of a single frequency signal used in conventional lock-in infrared (IR) thermography [7–11].The thermal images obtained using FMTWI can be used qualitatively, e.g., to detect field leakage near electromagnetic junctions and microstrip feed lines. As a practical demonstration of this technique, an example of 2 × 2 patch antenna array at 8 GHz is considered. First, amplitude images at various modulation frequencies are obtained. Next, signal to noise ratio (SNR) values at each frequency are calculated. It is seen that SNR is lower at higher frequencies. It is observed that at higher modulation frequenci...

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Topics: Wavelength (59%), Chirp (57%), Wave propagation (55%) ...read more
References
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Journal ArticleDOI: 10.1109/PROC.1984.12959
R. Bansal1Institutions (1)
01 Jul 1984-
Topics: Antenna measurement (70%), Omnidirectional antenna (67%), Microstrip antenna (67%) ...read more

4,282 Citations


Open accessBook
01 Jan 1966-
Abstract: Stationary Electric Fields. Stationary Magnetic Fields. Maxwell's Equations. The Electromagnetics of Circuits. Transmission Lines. Plane-Wave Propagation and Reflection. Two- and Three-Dimensional Boundary Value Problems. Waveguides with Cylindrical Conducting Boundaries. Special Waveguide Types. Resonant Cavities. Microwave Networks. Radiation. Electromagnetic Properties of Materials. Optics. Appendices. Index.

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Topics: Electromagnetics (59%), Waveguide (57%), Electromagnetic radiation (55%) ...read more

2,811 Citations


Journal ArticleDOI: 10.1063/1.2382738
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.

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Topics: Thermography (55%)

214 Citations


Open accessJournal ArticleDOI: 10.1016/J.NDTEINT.2011.06.008
Abstract: Pulsed, lock-in and frequency modulated thermography are three alternative nondestructive evaluation techniques. The defect imaging performance of these techniques are compared using: matched excitation energy; the same carbon fiber composite test piece and infrared camera system. The lock-in technique suffers from “blind frequencies” at which phase images for some defects disappear. It is shown that this problem can be overcome by using frequency modulated (chirp) excitation and an image fusion algorithm is presented that enhance phase imaging of defects. The signal-to-noise ratios (SNRs) of defect images obtained by the three techniques are presented. For the shallowest defects (depths 0.25 and 0.5 mm, 6 mm diameter), the pulsed technique exhibits the highest SNRs. For deeper defects the SNRs of the three techniques are similar in magnitude under matched excitation energy condition.

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  • Figure 4: Experimental setup
    Figure 4: Experimental setup
  • Table 3: Estimated amplitude of surface temperature oscillations for lock-in tests at various frequencies as imposed by the energy matching criterion
    Table 3: Estimated amplitude of surface temperature oscillations for lock-in tests at various frequencies as imposed by the energy matching criterion
  • Figure 2: Plot of logarithmic temperature rise (digital level) against logarithmic time over sound region in pulsed thermography experiment. The inset plot zooms around t = 1 second.
    Figure 2: Plot of logarithmic temperature rise (digital level) against logarithmic time over sound region in pulsed thermography experiment. The inset plot zooms around t = 1 second.
  • Figure 8: Experimental phase images at 16.7 mHz, 33.3 mHz, 50.0 mHz, 66.7 mHz and 83.3 mHz for lock-in thermography (8a-8e), and FMTWI (8f-8j), respectively.
    Figure 8: Experimental phase images at 16.7 mHz, 33.3 mHz, 50.0 mHz, 66.7 mHz and 83.3 mHz for lock-in thermography (8a-8e), and FMTWI (8f-8j), respectively.
  • Figure 10: Plot of maximum SNR as a function of defect depth, as in Table 6
    Figure 10: Plot of maximum SNR as a function of defect depth, as in Table 6
  • + 14

Topics: Thermography (53%), Nondestructive testing (51%), Chirp (51%)

123 Citations


Open accessJournal ArticleDOI: 10.1063/1.1556969
Abstract: With the use of a simple model, it is shown that a thin film of contaminant on a microwave window may absorb up to 50% of the incident power, even if the film thickness is only a small fraction of its resistive skin depth. This unexpectedly large amount of absorption is conjectured to have played a significant role in window failure. The temperature rise in a thin film is estimated.

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96 Citations