SU834627A1 - Magnetic field measuring device - Google Patents

Description

(54) DEVICE FOR MEASURING A MAGNETIC

FIELD

one

The invention relates to a measurement technique and can be used in cases where measurement or indication of extremely weak magnetic fields is required with a strength not exceeding E or measurement of small changes in large fields with the same accuracy.

Known magnetic field meters, based on the Josephson effect, with a sensitivity of about 10 O 1.

 This meter is not sensitive enough and rather cumbersome due to the use of superconductivity and the associated cryogenic technique.

Objective i of the invention is to increase the sensitivity and reduce the size of the device.

This goal is achieved by the fact that in a device containing a microwave generator, an amplifier with a magnetic probe in feedback and an output device, the magnetic probe is made in the form of a ferrite delay line.

In addition, the line-delay is made on a single-crystal rod of iron .ittrium garnet.

FIG. Figure 1 shows the sensitive element circuit of the proposed magnetic probe, which is directly placed in the measured magnetic field; in fig. 2 - dependence of the delay time of the magnetostatic wave on the magnetic field; in fig. 3 is a block diagram of the device; in fig. 4 - dependence of the system transmission coefficient on the magnetic field.

The magnetic probe (Fig. 1) contains an antenna 1, a single-crystal rod 2 made of yttrium iron garnet, a magnet 3, an antenna 4.

0 The device operates as follows. The ultra high frequency input signal is fed to a wire antenna 1 placed near the end of the rod 2 placed in a constant magnetizing field created by the magnet 3, the measured magnetic field also acts on the rod. Under such conditions, due to the heterogeneity of the internal magnetic field in the rod, a magnetostatic wave propagates inside the rod. At the other (output) rod end, this wave is converted into electromagnetic and is picked up by antenna 4. The velocity of the magnetostatic wave is several orders of magnitude (6-8) lower than the velocity of the electromagnetic wave, therefore the output signal is delayed relative to the input wave. The delay time is strongly dependent on the magnetic field H (Fig. 2), for example, when the magnetic field changes by 1E, the delay time changes by 10 MCS, and the -d value increases with increasing delay time, which is determined by the value of the field N. The sensitivity of the meter becomes maximum when the field corresponding to the maximum delay time. Having learned that due to the low speed of the magnetostatic wave on the rod 2 several millimeters in length hundreds of thousands of wavelengths are laid, it can be seen that to change the phase of the electromagnetic wave at the output relative to the phase of the input wave it is enough to change the magnetic field by no more than. The microwave signal from the microwave generator 5 (Fig. 3) is fed to the input of amplifier 6, the feedback circuit of which includes a magnetic probe 7. From the output of amplifier 6, the signal goes to output device 8 (receiver). Such a system (amplifier with a delay in the feedback circuit) has a comb-like view of the frequency dependence of the transmission coefficient K (Fig. 4). When the magnetic field changes, the comb shrinks or expands in frequency, and the position of the initial peak (at zero frequency) remains unchanged, and the larger the number of the peak, the less field is required to mix it by a distance equal to its width. required to offset the peak by its width is

to 1g

  2gHH7dri

 (

where K is the gain of the amplifier (taking into account the compensation for losses in the delay line);

() IgG10mks / e (Fig. 2).

Sxo

/

LL / 777/7 7,

Changing the floor causes a change in the amplitude of the signal at the receiver input.

A magnetic probe together with a magnet that generates a magnetizing field (200-400E) can be performed in a volume not exceeding 5-10 cm1. This volume does not exceed, and is often much smaller than, the known magnetic field meters (for example, quantum ones where cryogenic technology is required).

The use of a magnetic probe in the form of a ferrite delay line operating in the microwave range in the proposed meter, as well as the inclusion of its feedback loop on the amplifier of the microwave signal, makes it possible to measure magnetic fields with high accuracy.

Claims (2)

20 Formula of Invention I. A device for measuring a magnetic field containing a microwave generator, an amplifier with a magnetic probe in feedback, and an output device, characterized in that, in order to increase the sensitivity and reduce the size of the device, the magnetic probe is made in the form of a ferrite delay line. 2. A device according to claim 1, characterized in that the ferrite delay line is made on a single-crystal rod of an iron-yttrium garnet. Sources of information taken into account in the examination 1. "Analog-to-digital magnetometer with a superconducting sensor .-" Instruments of scientific research, 1967, No. 2. respiratory ifi / / W //// ig.1 ID T (and K sec) 270277Fig .g