SU1626228A1 - Device for measuring quasi-stationary magnetic - Google Patents

Abstract

This invention relates to a measurement technique and is intended to measure low quasistatic magnetic fields. The purpose of the invention is to improve the accuracy and sensitivity of measurements - is achieved by the fact that the core of the solenoid 5 is made in the form of a rod with a mirror end, and the compensator is made in the form of a mirror galvanometer with a photodetector. The device contains a laser 1, a beam splitter 2, mirrors 3, a magnetic rod 4, an oscillator 6, a mirror 7 galvanomatoa, a beam splitter 8. raster diaphragm 9. lenses 10, 11, a mirror galvanometer 13, raster diaphragm 14 , photodetector 17. resonant amplifier 18, source 19 of constant voltage. 2 Il.

Description

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FIG L

This invention relates to a measurement technique and is intended to measure low quasistatic magnetic fields.

The purpose of the invention is to improve the accuracy and sensitivity of measurements.

Fig. 1 shows a block diagram of a device for measuring infra-low magnetic fields; figure 2 - the dependence of the deformation X of the magnetostriction rod from the applied magnetic field.

The device (Fig. 1) contains a laser 1, optically coupled to a Michelson interferometer containing a beam splitter 2, mirrors 3, and the mirror of the interferometer signal arm is the mirror end of a magnetostrictive rod 4 placed in a solenoid coil 5 connected to a bias oscillator 6, galvanometer mirror 7, located at the output of the interferometer, optically coupled to a beam splitter 8, in the transmitted beam of which there is a first raster diaphragm 9 located between the first and second objectives and 10 and 11, and the photodetector 12, which is in the focus of the lens 11 and connected to the amplifier of the mirror galvanometer 13, and in the reflected beam of the splitter 8 - the second raster diaphragm 14, located between the third and fourth lenses 15 and 16, the photodetector 17, which is In the focus of the lens 16, connected to the resonant amplifier 18, the output of which is connected to the output of the device, a constant voltage source 19 is also connected to the solenoid 5.

The device works as follows.

The interference pattern formed at the output of the interferometer is oriented relative to the raster diaphragm 9 so that the bright bands are completely blocked by it. Thus, the position of the operating point for the photodetector 12 corresponds to the minimum of the interference pattern. The raster diaphragm 14 is set so that the operating point of the photodetector 17 corresponds to the section of the maximum steepness of the interference pattern. The stable position of the operating point of both photodetectors is provided by a feedback circuit with the amplifier of the mirror galvanometer 13 as a control unit. The shift of the bands due to destabilizing factors (temperature, pressure, vibrations) causes an error signal at the output of the photodetector 12, which is

The coupling acts on the galvanometer mirror 7, which causes the latter to rotate by an angle that compensates for the shift of interference fringes on raster diaphragms 9 and 14. Compensation of the displacement of the interference pattern relative to the rasters of the diaphragms 9 and 14 is produced in a frequency band much smaller than the resonant frequency of the magnetostriction rod 4,

which is a sensitive element of the device. The resonant frequency of the longitudinal oscillations of the rod 4 is:

15

Fp (0.4-0.8) C / 2L.

where C is the speed of sound; L is the length of the rod. The rod is placed in a test alternating magnetic field of the solenoid 5 of the frequency FI, equal to the natural resonant frequency of the rod Fp, which is provided by the solenoid 5 and the oscillator 6 of the magnetization. To set the operating point to zero

the dependences X (H) (Fig. 2) a constant voltage source 19 is additionally connected to the winding of the solenoid.

In the absence of a measurable magnetic field, the operating point is at zero dependence of the deformation on the magnetic field, while in the spectrum of frequencies of oscillations of the length of the rod, and hence of the oscillations of the interference pattern, there are only even harmonics 2Fi, 4Fi, ..., etc.

When an external measured quasistatic magnetic field is applied, the operating point on the characteristic (Fig. 2) is shifted, and in the spectrum of oscillations of the rod, and consequently, of the oscillations of the interference

The patterns appear odd harmonics Fi, 3Fi, ... etc.

The oscillations of the rod at the frequency FI are resonantly amplified by Q times (Q is the Q of the rod at the resonant frequency Fi).

Photodetector 17c resonant amplifier 18 measures the amplitude of the first harmonic of the interference signal, the magnitude of which determines the magnetic field. In the experiment with sensitivity

an interferometer of 10 μm / Hz, a rod length of 1 m with a mechanical Q, a minimum measurable magnetic field of 10 A / m is obtained, which is two orders of magnitude lower than in the known device.

Claims (1)

Invention Formula A device for measuring quasis-tic magnetic fields containing a laser optically connected to a Michelson interferometer, in the signal arm of which a solenoid is placed with a core of magnetostrictive material connected to a bias generator and a constant voltage source, a photodetector connected to an interferometer output through an optical input , and for electrical output - with a compensator amplifier, characterized in that, in order to increase the accuracy and sensitivity of the measurements, the solenoid core Execute a rod with a mirrored end, the compensator is configured in the form of a mirror galvanometer fotopriemniFig .2 com, optically connected to the interferometer output through the galvanometer mirrors located successively ps the beam, the beam splitter, the first lens, the first raster diaphragm and the second lens in which the photodetector is in focus, the third lens, the second raster diaphragm, and the fourth lens The focus of which is the second photodetector, the electrical output of which is connected to the input of a resonant amplifier, the output of which is connected to the output of the device va.