Steel reinforcing bar detection using electromagnetic method

An electromagnetic method is developed to locate the position of the steel rebar. An AC current of 4.2 KHz is applied to a circular coil with diameter of about 10 cm to produce the excitation magnetic field. Another coil wrapped around a 1 cm ferrite core is used to detect the induced magnetic field by steel rebar. From the signal amplitude after demodulation, the depth information of the steel rebar can be obtained. For signal amplitude detection, lock-in amplifier or diode demodulation method is normally used. For lock-in amplifier, the hardwire is somewhat complex; and for diode demodulation, the linearity is not good and the signal amplitude must be over the turn-on voltage of the diode. We develop a very simple software demodulation method, which can be easily realized by labview. This simple method needs no hardwire and will have advantage for our future multi-channel system. The noise level of this method is also low, which is comparable with lock-in amplifier method.