Micro-fluxgate Magnetic Sensing Elements Using Closely-coupled Excitation And Pickup Coils

This paper describes micro-fluxgate magnetic sensing elements using magnetic thin films and closely-coupled excitation and pickup coils based on a solenoid-shape coil structure. The basic structure is presented at Transducers '93 conference. In order to improve the sensitivity of the sensing element, coupling structure between excitation and pickup coils, and the formation method of permalloy magnetic films are investigated. The closely-coupled coil structure allows to excite the magnetic core in a optimal condition with reduced excitation current. The addition of Indium in the plating bath of permalloy greatly reduce the degradation of magnetic core due to the thermal treatment process. The sensitivity of the improved sensing element is 2700VK at the excitation frequency of 3MHz. The resolution is measured to be 4xlO-ST.