I. Introduction
Recently magnetocardiography (MCG) has drawn the attention of many researchers around the world due to its diagnostic capabilities over electrocardiography and its improved functions [1]–[3]. MCG utilizes a highly sensitive magnetic sensor (such as SQUID) placed in a relatively strong magnetic shield. The latter is one of the reasons why the MCG failed to take the leading position due to its heavy weight and high cost of the shielding room. The ultimate goal of such systems is to utilize a highly sensitive sensor in an unshielded environment. However, this goal is very difficult to achieve and requires very complicated techniques for noise reduction and gradiometers [4]. Hence, we proposed a new open type, light weighted, and low cost shielding system. The performance of the system was deeply investigated in [5]–[7]. As described in [6], along the -axis [see Fig. 1(a)] without active shielding the shielding factor (SF) was as low as 20 with the use of passive shield only. Hence, the active shielding for such an open type system is indispensible. The experimental results seen in [6], show the efficiency of the active shielding; however, the attained noise levels were not enough for MCG measurement.
Structure of the system. (a) Symbolic construction of the system showing the position of the compensation coils. (b) Schematic diagram showing all components of the active compensation and testing equipments.