SU609378A1 - Quantum gradiometer - Google Patents

Abstract

An optically pumped QUANTUM GRADIENTOMETER containing two photoelectric sensors, one of which is self-generating and the other a resonant filter, each sensor consisting of a circular polarizer, an absorption cell, an RF coil, a photodetector and an amplifier, and a phase meter. A circuit with a recorder, the input of which is connected to the output of a sensor amplifier - a resonant filter, characterized in that, in order to improve noise immunity, a third sensor is inserted into it - a resonant filter, the amplifier output of which through the phase shifter is connected to the second input of the phase-measuring circuit, and the output of the self-generating sensor of the connections with the radio frequency coils of the other two sensors.i (Lo ^ o with ω ^ 00

Description

The proposed quantum gradiometer is designed to measure variations in the gradient of the magnetic field of the Earth, can be used to measure the magnetization of rocks, substances and living organisms, gradients of weak alternating magnetic fields arising in the process of cardiac activity of humans and large animals.

In known gradiometers, two optically pumped sensors are used, the difference frequency of which represents, in digital or analog form, the value of the gradient of the magnetic field strength between the points of location of the sensors Cl.

Also known is a quantum optically pumped gradiometer containing two. a sensor, one of which is self-generating and the other is a resonant filter, each sensor consists of a circular polarizer, an absorption cell, an radio frequency coil, a photodetector and an amplifier, and a phase-measuring circuit with a recorder, to the input of which the output of the amplifier of the resonant filter is connected, and the second The FAS input is connected to a Gz self-generating sensor amplifier.

Regarding the effect of external interference, the self-powered sensor is a broadband system, another sensor operating in a resonant filter mode has a substantially lower bandwidth. Thus, the measurement result of the phase difference of the signals will be affected by interference outside the sensor's passband — a resonant filter (multiplicative interference).

The purpose of the invention is to increase the noise stability of the gradiometer.

To do this, a third sensor is introduced into the quantum gradient meter - a resonant filter, the amplifier output of which is connected to the second input of the phase-matching circuit through the phase shifter, and the self-generated sensor is connected to the radio frequency coils of the other two sensors

The drawing shows a structural electrical circuit of a quantum gradiometer. Absorption cells 1-3 containing the working substance, e.g. cesium vapors, are subjected

optically pumped under the action of radiation from a spectral cetier lamp 4, excited by a high-frequency generator 5 passing through the light diodes 6, through lenses 7 and circular polarizers 8. The radiation transmitted through the absorption cells and lenses 9 is detected by photoreceivers 10-12. The signals from the photodetector outputs are amplified in blocks 13-15. The output of block 13 is connected to radio frequency coils 16. The outputs of blocks 14 and 15 are connected to the inputs of frequency multipliers (phase 17). The inputs and outputs of the blocks 17 are connected to the blocks 18 automatic stabilization of the phase. The output of one frequency multiplier (phase) 17 is connected to one of the inputs of the phase measuring circuit 19, the output of the other frequency multiplier (phase) 17 via the phase shifter 20 is connected to another input of the phase measuring circuit 19 connected to the input of the recorder 21. When the amplitude and phase balance in the ring of the feedback of the first sensor arises self-generation at the magnetic resonance frequency determined by the magnetic field strength. The generation signal simultaneously acts through the radio frequency coils 16 on the other two absorption cells 2 and 3, which act as resonant filters.

The information bandwidth of the D sensors operating in the resonant filter mode is determined by the linear part of the phase response characteristic of the magnetic resonance line. First approximation

one

Af

2Jr

2

where T2 is the transverse relaxation time of the absorption cell under the action of collision processes and pump light. For paraffin-coated cesium vapors, t is 4–7 MO, which corresponds to the M band of 25–40 Hz (7–10 nT). The slope of the phase-response characteristic of the resonant filter is 0.150, 25 nt / deg. Typical phase meters, for example, F2-13, have a resolution of the order of degrees, which corresponds to a resolution on the gradient of the magnetic field of 0.015-0.025 nt. A further increase in sensitivity is achieved; by connecting

to the outputs of the amplifying units 14 and 15 of the frequency (phase) multipliers 17, for example, based on a system of phase-locked loop (phase). To limit phase fluctuations in frequency (phase) multipliers arising under the influence of temperature, instability of power sources and other factors, signals from its inputs and outputs are connected to automatic phase stabilization circuits whose error signal from the outputs stabilizes the phase of output signals, phase shifter 20 to preset the phase of the signal from the absorption cell 3. Phase-measuring circuit 19 and the recorder 21 record the change in the magnetic field gradient between the absorption cells 2 and 3. Self-generating d Atchik in this device only

auxiliary role of magnetic resonance excitation in sensors of resonant filters. Therefore, the effect of multiplicative noise on a wide-band self-oscillating sensor is compensated in the phase-measuring circuit of sensor-resonant filters. The maximum gradient of the magnetic field measured by the device should not exceed the information bandwidth of the sensor and the sensor in order to avoid loss of sensitivity.

A quantum gradiometer layout, implemented in the above block diagram based on optically pumped absorption cells with cesium vapors, has a sensitivity of about 0.002 nt in a passband of about 25-30 Hz with a distance of 6 cm from each other.

Claims (1)

Optically pumped quantum quantum gradient meter containing two photoelectric sensors, one of which is self-generating and the other is a resonant filter, each of which consists of a circular polarizer, absorption cell, radio frequency coil, photodetector and amplifier, and a phase measuring circuit with a recorder, to the input . which is connected to the output of the sensor amplifier - a resonance filter, characterized in that, in order to increase noise immunity, a third sensor is introduced into it - a resonance filter, the amplifier output of which is connected through a phase shifter to the second input of the phase measuring circuit, and the output of the self-generating sensor is connected to the RF coils of the other two sensors. SU <„609378 1 609378 The proposed quantum gradiometer is designed to measure variations in the gradient of the Earth’s magnetic field, can be used to measure the magnetization of rocks, substances and living organisms, and gradients of weak alternating magnetic fields that occur during the cardiac activity of humans and large animals. Known gradiometers use two sensors with optical oscillation, the difference frequency of which is in digital or analog form the value of the gradient of the magnetic field between the locations of the sensors Cl j. Also known is a quantum gradient meter with optical pumping, which contains two sensors, one of which is self-generating and the other is a resonant filter, each of which consists of a circular polarizer, an absorption cell, an RF coil, a photo detector and an amplifier, and a phase measuring circuit with a recorder, to the input which the output of the amplifier of the sensor of the resonance filter is connected, and the second input of the phase-measuring circuit is connected to the amplifier of the self-generating sensor G2 ³ ].