An improved proton magnetometer for Earth's magnetic field observation
As a precision instrument to measure the earth magnetic field, proton magnetometer is widely used in different fields such as geological survey, buried objects detection and earth field variations. Due to poor signal to noise ratio (SNR) of the system, proton magnetometer suffers from low sensitivity which directly affects the performance. In order to increase the sensitivity, we present an improved proton magnetometer. First, the effect of matching resistance on Q value is discussed to enhance SNR, and high matching resistance has been chosen to improve the Q value of the resonant circuit. Second, noise induced by pre-amplifier is investigated in order to obtain low noise signal, and we adopt the JFET with noise figure less than 0.5dB as the pre-amplifier. Third, by using band-pass filter, low-noise output signal is obtained. Fourth, the method of period measurement based on CPLD is employed to measure frequency of the square wave shaped from the output sinusoidal signal. High precision temperature compensate crystal oscillator (TCXO) has been used to improve the frequency measurement accuracy. Last, experimental data is obtained through field measurements. By calculating the standard deviation, the sensitivity of the improved proton magnetometer is 0.15nT for Earth’s magnetic field observation. Experimental results show that the new magnetometer is sensitive to earth field measurement.
A Portable Differential Proton Magnetometer
Abstract The principle, construction, and operation of a portable proton magnetometer is described. The low cost of this instrument is within the means of the most modest archaeological budget. Its wide applicability to a variety of situations renders it a useful tool in many archaeological endeavors.
ROCKET-BORNE MAGNETOMETER
Abstract : A summation of the theory, design, and successful operation of two rocket-borne, wide-range rubidium-vapor magnetometers is presented. Each dual-gas-cell instrument will operate continuously in ambient magnetic fields ranging in intensity from less than 100 to more than 54,000 gammas. The constant-amplitude output signal varies in frequency directly with ambient field strength. Sensitivity is dependent upon the rubidium isotope employed. One magnetometer provides 6.99 cps/gamma, the other 4.67 cps/gamma. Self-oscillation has been achieved in fields greater than 1 oersted (100,000 gammas). Each instrument responds instantaneously (within limits of experimental error) to a step change in field intensity of several hundred gammas occurring in less than one microsecond. (Author)