This invention relates to devices for detecting magnetic fields, and, more particularly, to a compact, highly sensitive magnetometer using high temperature superconductors.
A magnetometer, as the term is used herein, is a device for detecting changes in magnetic fields. The most sensitive magnetometers presently available for relatively low frequencies include a pickup coil which produces a change in an electrical signal responsive to a change in a magnetic field. The pickup coil is typically made from a material such as niobium that becomes superconducting below about 10 K. The electrical signal is detected by a Superconducting Quantum Interference Device (known by its acronym, SQUID), also typically made from niobium, that can detect the very small electrical signals produced by a small magnetic field change. Recently, SQUIDs made of high critical temperature (high-Tc) oxide ceramics have been fabricated, tested, and found operable.
Biomagnetometry, the measurement and study of magnetic fields produced by the human body, is one of the most demanding applications of magnetometers. The biomagnetometer uses magnetometers placed external to the body to measure extremely small magnetic fields produced by a source organ within the body, such as the brain or the heart. A typical biomagnetometer utilizes a sensitive superconducting magnetometer such as that described previously, placed within a dewar vessel to maintain the magnetometer below its superconducting critical temperature.
In a presently available commercial biomagnetometer, the dewar is cylindrical, about 4 feet long by 18 inches in diameter, and weighs about 80 pounds. The pickup coil is placed within a small appendage or "dewar tail" extending from the bottom of the main vessel, which contains the SQUID detector. The dewar is essentially a well-insulated vacuum bottle filled with liquid helium or, in some cases, cooled to liquid helium temperatures by a mechanical cooler. The presently available biomagnetometers require large gantry mechanisms to suspend them adjacent to the subject. Even then, the biomagnetometers are limited in their placement adjacent to the subject. The results attained with the currently available biomagnetometers could be improved if the pickup coil could be placed closer to the body of the subject, and if multiple pickup coils could be provided in configurable arrays.
There is a need for an improved magnetometer of very high sensitivity, operable for biomagnetometry and other applications, that is smaller and lighter than existing magnetometers. Such a magnetometer would desirably be more readily used in arrays and would be less costly to manufacture and operate. The present invention fulfills this need, and further provides related advantages.