JPH0531418B

PURPOSE:To reduce the influence of an external noise by providing a hollow pipe and a plate for electromagnetic shielding, and arranging plural high-frequency components of a high-frequency magnetic field detection in the hollow part at both sides of the plate. CONSTITUTION:The magnetic field 5 consists of the metallic cylindrical hollow pipe 5A and the metallic disk 5B inscribed in the hollow pipe 5A and they are connected electrically on the periphery; and a balanced load 7 consists of a balanced high-frequency coil 1 and a balanced impedance matching circuit 6 connected to the coil 1. Further, the load 7 is connected to one terminal of the disk 5B and a transmission line 8 connected to an unbalanced high-frequency transmitter receiver and the load 7 and a balanced/unbalanced converter 9 which performs the balanced/unbalanced conversion of the transmitter and receiver and connected to the other side of the disk 5B. Then, a shield lid 12 is holed and the capacitor of the matching circuit 6 is rotated to make a matching adjustment of impedance.