SU328789A1 - - Google Patents

Description

This invention relates to electronic devices that use quantum resonance effects and, in particular, the phenomena of magnetic resonance and free nuclear precession.

In the well-known Fini magnetometer, containing a sample coil, a switching device, a time relay, a video pulse generator, an amplifier, a precision reference generator, a key and an indicator necessary for measuring, a 90-degree phase shift between the precession signal and the reference signal is manually performed , which significantly increases the measurement time and complicates the measurement process.

The proposed nuclear magnetometer is characterized in that it contains a generator of a turning radio pulse, one input of which is connected to a video pulse generator, the second input is connected to a precision ION reference generator, and the output is connected to a switching device. All this will allow a 90-degree phase shift of the precession signal relative to the frequency of the reference oscillator automatically. This will significantly shorten the measurement time and simplify the measurement process.

The drawing shows the scheme of the proposed highly sensitive nuclear magnetometer. The preparation of the sample for precession excitation, consisting of its magnetization and rotation of the magnetization along the measured magnetic field HQ, is performed in the same way as in the well-known Fini magnetometer. Sample I is magnetized by a strong polarizing magnetic field 2 (H,.; By passing a direct current into the coil 3 surrounding the sample.

The axis of the coil is oriented perpendicular to the measured field (iUlo)

The switching on and off of the polarizing field is carried out by means of a switching device 5 controlled by time relay 6. The polarization current is taken from the battery 7. The polarizing field is turned off with a long time constant, so that the nuclear magnetization vector remains all the time oriented along the resulting field Hp-Hb and at the end of the switching off process is directed along the measured field Ho. To excite the precession of the magnetization after the termination of the shutdown process at the time specified by the time relay 6, an RF pulse with a filling frequency equal to the precession frequency and the duration determined by the video pulse generator 9 is applied to the coil 3 from the generator B of the turning radio pulse. During the period of this pulse, the vector of nuclear sample magnetization makes forced precession, lagging behind the radio frequency magnetic field created by this pulse 90 ° in phase and deviating simultaneously from the field direction HO (perfect mutation). The nutation rate is determined by the amplitude of the radio frequency field. The duration and amplitude of the RF pulse are chosen so that by the end of this pulse the magnetization vector lies in a plane perpendicular to the HQ field. After the end of the RF pulse, the nuclear magnetization vector precesses freely around the field HO, inducing coil 3 with an electromotive force with a precession frequency. This signal is amplified by the amplifier U and fed to the input of the synchronous detector I, to the second input of the synchronous detector receives the frequency of the precision reference oscillator 12 through the switch 18, which determines the signal comparison time and controlled relay 6. The integrated difference signal of the synchronous detector is monitored by the indicator 14. Integration time determined by the highest signal-to-noise ratio. When the frequency of the reference signal is equal to the precession frequency, and the phase difference between the signals 90, indicator 14 will give a zero reading. When precession is excited by an rf pulse in this magnetometer circuit, a 90-degree phase shift is provided automatically when the frequencies of these signals coincide. The rotating pulse generated by the generator 8 is filled with oscillations of the reference generator, the alternating current generated in this coil 3 by this voltage, and hence the RF field, will be shifted in phase by 90 relative to the reference voltage. In turn, the magnetization vector during the period of the radio frequency pulse, having accomplished the forced precession, will lag by 900 relative to the radio frequency field if the frequency of the reference generator coincides with the precession frequency. Finally, the emf induced by the precessing magnetization in coil 3 will be shifted in phase by 900 relative to the precessing magnetization. The sum of the three phase shifts of 90 each gives the resulting phase shift of 90 ° between the reference voltage and the precession signal. Thus, to obtain a zero reading of the indicator 14, only the frequency of the reference voltage needs to be adjusted. When the indicator reads zero, the frequency of the reference voltage coincides with the precession frequency, and to measure an external magnetic field, it is sufficient to measure this frequency with a frequency meter i5, SUMMARY OF THE INVENTION Reference oscillator, key, indicator and frequency meter, characterized in that, in order to reduce the measurement time, it contains a turning radio pulse generator, one input D of which is connected to a video pulse generator, the second input is connected to a power reference generator, and the output is connected to a switching device.

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