This paper proposes a new method to measure the diameter of reinforcing bars (deformed bars), in reinforced concrete, using electromagnetic wave (radar). The method scans over the concrete surface, along the bar, and measures the average space of the ribs of the bar. The diameter of the bar is identified based on the relationship between the average space of the ribs and the diameter. Although the average space is measured by frequency analysis of the propagation time of the electromagnetic wave to and from the bar, this paper develops a more reliable method instead of the well-known FFT (Fast Fourier Transform) technique. That is, a method which applies a maximum likelihood method to the dynamic model of the sensor output (i.e., the propagation time). Lastly, the effectiveness of the method is demonstrated.

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