High-resolution photothermal pulse compression thermal imaging detection method based on nonlinear frequency modulation
A non-linear frequency modulation and pulse compression technology, applied in the direction of material defect testing, etc., can solve the problems of limited detection depth range and unfavorable high-resolution pulse compression thermal imaging, and achieve high signal-to-noise ratio, easy to implement, and simple method Effect
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Embodiment 1
[0048] Step 1) Use the nonlinear frequency modulation signal whose instantaneous frequency curve shown in formula (1) is a concave quadratic function as the excitation signal, and transmit the excitation signal to heat the sample to be tested, wherein the initial frequency f of the excitation signal is 1 =0.1×(1-0.6)Hz,, stop frequency f 2 =0.1×(1+0.6)Hz, excitation duration T c =130s; the waveform of the excitation signal is as figure 2 (a) as shown by the solid line;
[0049] Step 2) Use the infrared thermal imager to obtain the thermal wave echo signal on the surface of the sample to be tested. The waveform of the thermal wave echo signal is as follows: figure 2 (a) as shown by the dotted line;
[0050] Step 3) Use formula (3) to process the excitation signal and the thermal wave echo signal through matched filtering to obtain the output signal of the matched filtering, as shown in figure 2 (b) shown.
Embodiment 2
[0052] Step 1) Use the nonlinear frequency modulation signal whose instantaneous frequency curve shown in formula (1) is a concave quadratic function as the excitation signal, and transmit the excitation signal to heat the sample to be tested, wherein the initial frequency f of the excitation signal is 1 =0.1×(1-0.6)Hz,, stop frequency f 2 =0.1×(1+0.6)Hz, excitation duration T c =130s; the waveform of the excitation signal is as image 3 (a) as shown by the solid line;
[0053] Step 2) Use the infrared thermal imager to obtain the thermal wave echo signal on the surface of the sample to be tested. The waveform of the thermal wave echo signal is as follows: image 3 (a) as shown by the dotted line;
[0054] Step 3) Using formula (3) to perform matching filter processing on the excitation signal and the thermal wave echo signal to obtain a matched filter output signal;
[0055] Step 4) Process the output signal of the matched filter plus a Gaussian window function to obtain ...
Embodiment 3
[0057] Step 1) Use the nonlinear frequency modulation signal whose instantaneous frequency curve shown in formula (1) is a concave quadratic function as the excitation signal, and transmit the excitation signal to heat the sample to be tested, wherein the initial frequency f of the excitation signal is 1 =0.1×(1-0.6)Hz, stop frequency f 2 =0.1×(1+0.6)Hz, excitation duration T c =130s; the waveform of the excitation signal is as Figure 4 (a) as shown by the solid line;
[0058] Step 2) Use the infrared thermal imager to obtain the thermal wave echo signal on the surface of the sample to be tested. The waveform of the thermal wave echo signal is as follows: Figure 4 (a) as shown by the dotted line;
[0059] Step 3) Using formula (3) to perform matching filter processing on the excitation signal and the thermal wave echo signal to obtain a matched filter output signal;
[0060] Step 4) Process the matched filter output signal with a Kaiser window function to obtain the phot...
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