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Using a high-temperature superconductor radio frequency superconducting quantum interference device planar gradiometer as the sensor, we developed a saw-tooth wave excitation eddy-current nondestructive evaluation device. By analyzing the amplitudes of harmonics in the response signal of the sample, we successfully detected artificial defects in an aluminum plate and estimated the defect depth. We also demonstrated the possibility of constructing three-dimensional profiles of a defect. In our program for data processing, we employed a multiplying method to calculate the amplitudes of the harmonics, which was much faster than that using fast Fourier transforms. During the experiment, the x-y stage movement, data acquisition and data processing could be performed simultaneously.