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.
Comparison of a Designed Scalar Proton Precession Magnetometer with a Scalar Calibrated 3-Axis Fluxgate Magnetometer
This paper proposes the basic theory of the Larmor precession effect and A low noise earth field proton precession Magnetometer (PPM) design is implemented and a scalar calibrated 3-axis Fluxgate magnetometer is introduced. In the end, a Scalar earth magnetic field measurement Comparison between Our designed PPM and Our calibrated 3-axis Fluxgate Magnetometer (Using 3 single-axis FLC100 Magnetometer manufactured by Stefan Mayor Company) is done. Our proposed 3-axis Fluxgate Magnetometer consists of 3 single-axis FLC100 which are exactly perpendicular to each other with many mechanical efforts and is well-calibrated with 3-axis Helmholtz Coil and Scalar algorithm. Our calibrated 3-axis Fluxgate and Our designed PPM is calibrated based on magnetic earth measurement around 50000nT.
Comparing Cesium and Potassium magnetometers
Geometrics staff of engineers and physicists have reviewed the article Development of a high 
sensitivity potassium magnetometer for near surface geophysical mapping published in the May issue of First Break. We have found the article contains inaccuracies and some theoretical misstatements that we feel should be addressed. To that end we offer the following comments: 
1. Equation (4) (on page 83) is incorrect in that the author has ignored the effect of bandwidth on system performance. It is not the total noise that is of concern but the noise density (typically in nanovolts per root Hz) that is at issue. Components in the noise that are 
far from the Larmor frequency are easily filtered out in the electronics. However, there is no way to effectively remove noise that is very near the Larmor frequency. This is why, in spite of its much narrower line width, the performance of the Potassium is not better than that of a Cesium magnetometer. We can verify this through direct comparison of published specifi- 
cations. 
2. The Cesium magnetometer is capable of 0.0004nT/√Hz- RMS. It should be noted that there are several Cesium magnetometer array installations using high performance counting 
systems wherein low noise data is being collected at 100Hz or 120Hz on up to 7 or 8 sensors simultaneously (Naval Research Labs and Oakridge National Labs MTADS systems). All statements referring to a maximum of 10Hz sample rate and low sensitivity specifications (0.05nT) are in error.