| 摘要 |
<p>A magnetometer for detecting variations in a DC magnetic field. The magnetometer includes a magnetic field variation sensitive device that resonates at a characteristic resonant frequency by converting energy stored therein as a result of being excited by electromagnetic radiation at twice the resonant frequency when biased by a DC magnetic bias field within a predetermined field intensity range, in which the amplitude of the resonance varies with variations of the field intensity. The magnetometer further includes an excitation circuit (12, 14, R1, L1, C1) for exciting the device to resonate at the characteristic resonant frequency at an amplitude level that remains constant when the DC field intensity does not vary within the predetermined field intensity range; a DC voltage source (16) within the excitation circuit for biasing the device within the predetermined field intensity range; and a sensing instrument (18, 20) for sensing the amplitude of the resonance of the device at the characteristic resonant frequency. A variation in the amplitude of the resonance sensed by the sensing instrument indicates a variation in the intensity of the DC magnetic bias field. The magnetometer is utilized in a variety of different systems, including a system for actuating an output instrument, such as a traffic signal controller, in response to a predetermined threshold variation in a DC magnetic bias field, such as occurs when a motor vehicle moves into the vicinity of the magnetometer; a system for probing for materials whose presence affects the intensity of a DC magnetic bias field, such as buried pipes for ferromagnetic mineral deposits; a system for communicating in the low frequency range of the electromagnetic spectrum; and a system for guiding a probe with respect to the location of an object whose presence causes a variation in the intensity of a magnetic bias field.</p> |
