Fundamental studies for determining covering thickness and diameter of reinforcing bars by means of electromagnetic test (1st report - study on basic characteristics of test coil )

摘要

Electromagnetic test has been established for the nondestructive test of metal materials and components, while, in recent years, it was also applied to the determination of size, cover and location of reinforcing bars in concrete. Design of a test coil for electromagnetic test is very important, because shape, size and structure of test coil dominate a measurable range of cover. In this studies, some mutual induction coils and self induction coils were analyzed by numerical computation such as calculation for Viot-Savart's law and axisymmetric three dimensional Finite Element Method. And after the numerical analysis, actual coils that were manufactured along the results of numerical analysis were tested by experiments. The results show that the mutual induction type test coil having larger excitation coil and smaller pickup coil is suitable for determination of size, cover and location of reinforcing bars. And, it is also known from our studies that higher test frequency should be selected for better signal phase separation for determination of reinforcing bar diameter.