SU1383179A1 - Electronic paramagnetic resonance radiospectrometer - Google Patents

Abstract

The invention relates to technical physics and can be used in the development of modulation-spectrometers and relaxometers of electron paramagnetic resonance and double electron-nuclear resonance. The aim of the invention is to increase the accuracy in measuring the relaxation parameters of paramagnetic substances by electron paramagnetic resonance (EPR). Relaxation parameters are determined by the location of extremes on the measured dependence of the amplitude of the 90% component of the EPR signal on the magnetic field modulation frequency. The type of measuring 1x relaxation parameters is determined according to the sign of the extremes of the measured amplitude dependence of 90%. EPR signal components of modulation frequency. The maxima of the y. Frequency dependence correspond to spin-lattice relaxation, and the minima to spin-spin relaxation. 2 Il. with (L

Description

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The invention relates to radio spectrum and can be used in the design of radio spectrometers for electron paramagnetic resonance (EPR, and, above all, for automated compact radio spectrometers, designed for express analysis of paramagnetic substances,

The purpose of the invention is to increase stability.

Figo presents a block diagram of the proposed EPR radio spectrometer; Fig. 2 shows the dependence of the output voltage and the synchronous detector on the mutual detuning of the frequencies of the microwave generator and measuring resonator (discriminating characteristic of the AFC channel) at two levels of frequency negotiation.

The radio spectrometer contains an electromagnet 1 with a control unit 2, a microwave generator 3, the output of which is connected through a circulator 4 to a microwave detector 5 and a measuring resonator 6, a recording unit 7, connected to the output of the microwave detector 5, an electron-mechanical frequency control channel, including an oscillator 8 modulation connected to the reference input of the synchronous detector 9, the signal input of which is connected to the output of the microwave detector 5, and the output to the control input of the microwave generator 3 and through a two-threshold circuit 10 An ionizer 6, an automatic modulation amplitude control channel, made in the form of a serially connected bandpass filter 12, an amplitude detector 13, an error amplifier 14, an attenuator 15, the bandpass filter 12 being connected to the output of the synchronous detector 9, and an attenuator 15 being connected between the generator output 8 of the modulation and the control input of the generator 3 microwave frequencies. The discriminatory characteristic of the electronic AFC at low levels of frequency mismatch is designated as curve 16 in FIG. 2, and at high levels it is equal to va 17 (for small frequency detuning frequency mismatch relates microwave generator 3 and resonator 6 is not prevsh1ayuschee retention zone electronic AFC).

The EPR radio spectrometer operates in the following manner

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The sample under study is placed in the measuring resonator 6, where it is influenced by the microwave power from the output of the microwave generator 3, the microwave power is supplied to the resonator 6 through the circulator 4, The measuring resonator 6 is placed in the interpolar gap of the electromagnet 1, When resonant conditions are met, the EPR signal is reflected from the resonator 6 of the electromagnetic wave is detailed by the microwave detector 5 and is recorded by the recording unit 7,

In an EPR radio spectrometer, the frequencies of the 3 microwave generator and measuring resonator 6 are automatically matched using the combined electronic mechanical AFC channel Dp of this output power of the 3 microwave frequency generator is frequency modulated by a signal from the output of the 8 modulation generator fed to the modulating input of the 3 microwave generator 3, Measuring the resonator 6 is in the channel of the AFC, the amplitude-frequency discriminator, at the output of which the frequency modulation of the microwave power is converted into amplitude modulation. The microwave power received from the resonator 6 is detected by the microwave detector 5 The detection signal of the AFC signal at the modulation frequency, the amplitude of which is proportional to the magnitude of the frequency difference of the resonator .6 and the microwave generator 3, arrives at the signal input detector 9, the reference input of which arrives the reference signal and the generator output 8 modulation. The output signal of the synchronous detector 9 is a control signal for auto-tuning the frequency of the microwave 3 generator over the frequency of the measuring resonator 6. The control signal is proportional to the degree of matching of the frequencies of the microwave generator 3 and the resonator 6, and the polarity carries information about the detuning sign.

This is the automatic tuning of the frequency of the microwave 3 generator to the frequency of the measuring resonator 6 at small detuning frequencies not exceeding the holding area of the electronic AFC,

With an increase in the mutual detuning of the frequencies of the 3 microwave generator and the resonator 6, the amplitude of the frequency modulation of the power automatically increases

The microwave at the output of the microwave generator 3, which is carried out using the channel of automatic control of the amplitude modulation, including a band-pass filter 12, an amplitude detector 13, an amplifier 14 errors and an attenuator 15,

The level of the frequency mismatch is controlled in the proposed device by the amplitude component of the AFC signal, having a frequency equal to twice the modulation frequency, and generated at the output of the synchronous detector 9 simultaneously with the main AFC signal (at the modulation frequency).

When the frequencies of the microwave generator 3 and the resonator 6 are exactly matched, the amplitude modulated signal reflected from the resonator 6 does not contain components at the modulation frequency (the level of the constant signal at the output of the synchronous detector 9 is zero), but contains the component at twice the modulation frequency whose amplitude at the matching point has the maximum value. When the frequency mismatch, the signal level at the double modulation frequency decreases by

The AFC signal at the doubled modulation frequency at the output of the microwave detector 5 is selected using a band-pass filter 12 tuned to twice the modulation frequency. The signal amplitude is measured by the amplitude detector 13 and fed to the input of the error amplifier 14, the second input of which receives the reference voltage U specifies the level at which the amplitude of the AFC signal is maintained at twice the modulation frequency. The amplifier 14 opshbki adjusts the amplitude of the modulation, using a modulation attenuator 15 connected between the output of the modulation generator 8 and the modulating input of the microwave generator 3. When . the mismatch between the frequencies of the microwave generator 3 and the resonator 6 increases the modulation amplitude and as a result of overmodulation — the expansion of the discriminatory characteristic of the electronic AFC (curve 17 on fGo2),. The retention zone of the electronic frequency control system also expands, the boundary values of which are determined by the voltage of the upper threshold U and the voltage of the lower threshold U two-threshold: circuit 10. Only for very large frequency detuning exceeding the zone

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holding the electronic AFC when the AFC signal exceeds one of the thresholds, a mechanical AFC is turned on, which mechanically adjusts the frequency of the measuring resonator 6 with the help of frequency tuning element 11. The threshold voltage, and, and is specified by a two-threshold circuit 10 (made, for example, on the basis of a B1-imdot trigger), which is also za-. remembers the sign of the pacci rotary and controls the drive of the frequency control element 1 of the resonator 6; the detuning sign is reflected on the polarity of the control signal of the two threshold cxeMbif input to the frequency control element 1 1.

Thus, at small detuning frequencies of the aeon of retention of the electric frequency control system, it is small (Fig. 2. I f), and at large detuning it increases (fig 2, uf) o

The proposed technical solution was used in the development of a serial version of an automated ZPR A3-4700 compact-size radio spectrometer. The K-54 klystron with a frequency of 9.4 GHz and a frequency tuning range of 50 MHz is used as a microwave generator. The date of the groove is mechanical frequency tuning - 80 MHz.

The proposed technical solution makes it possible to provide in the radio spectrometer an electronic tuning range of approximately 30–35 MHz, which is 3-4 times greater than the range achieved in the known device. In this case, a mechanical matching of the frequencies of the microwave generator and the resonator is ensured in the entire range of mechanical tuning of the resonator frequency. The relative frequency stability of the microwave generator in the entire range of changes in the frequency of the microwave generator is not less than 5-10.

Claims (1)

Claims of the invention Electron paramagnetic resonance spectrometer containing an electromagnet with a control unit; a microwave generator whose output is connected via a circulator With a microwave detector and a measuring resonator; a registration unit connected to the detector output 17