Successive approximation method for the measurement of thickness using pulsed eddy current

In pulsed eddy-current testing (PECT), material thickness and defect depth are indicated by features such as time to peak and peak value. Before testing, the relationship between thickness/depth and features must be established in advance. This requires multiple reference samples with known thickness/depth. On the other hand, the parameters of each material, such as electrical conductivity and magnetic permeability should be known in advance when calculating by computer. It is time consuming and expensive. In this paper, a new processing scheme is proposed to separate the geometric and conductivity parameters. The thickness/depth of the specimen is quantified into a series of formal unit thickness. There is an excitation frequency which corresponds to every unit thickness level. Using the rich frequency components of the pulsed eddy current response signal, they can be used to scan the thickness of the specimen step by step. When the scanned thickness is close to the thickness, the current frequency is very different with the reference frequency. So this frequency is used to calculate the thickness. In this method, the initial values of the thickness and frequency are detected first to calculate the thickness. It is help to separate the geometric and conductivity parameters. Thus this scheme only requires one reference sample and one known thickness/depth specimen for each material, which significantly reduces the cost of testing.