BIOMAGNETOMETERS FOR UNSHIELDED AND WELL SHIELDED ENVIRONMENTS

The paper describes magnetometers for operation in well shielded and u nshielded environments. For unshielded environments, the noise cancell ation is accomplished by spatial filtering using higher-order gradiome ters which are formed in software. The theory of the software formatio n of high-order gradiometers has been successfully tested experimental ly to the second-order gradient level, using a seven-channel prototype system. An unshielded, open environment system, designed to operate w ith third-order noise cancellation is presently under construction. It is a whole head system, consisting of a minimum of 64 sensing channel s, and is expected to be operational by late 1991. In the opposite ext reme, a magnetometer is being developed for operation in a well shield ed environment of a whole body superconducting shield. The high temper ature superconducting shield will operate in liquid nitrogen, while th e magnetometer detection system will operate in liquid helium. The hig h level of shielding will allow detection of biomagnetic signals using magnetometers. The whole body high temperature superconducting shield ed system is presently under development and a half scale working shie ld already exists. The complete whole body shielded system is expected to be operational in 1994/95.