SU661324A1 - Electron paramagnetic resonance radiospectrometer - Google Patents

Description

The invention relates to instruments and means for observing, recording, and determining parameters of electron paramagnetic resonance (EPR) spectra. Commercially available commercially available radio spectrometers, Rubin 1 and RE1306 2, are designed to monitor and record the EPR spectra. The output signal of these radio spectra, which is a function of the magnetic susceptibility of the sample under study, will also vary from the power of the microwave generator, the modulation amplitude of the polarizing magnetic field, the gain of the amplifier and other devices included in the radio spectrometers. Such radio spectrometers, being essentially indicators, and not measuring instruments, do not allow the possibility of accurately recording the spectra and determining their parameters. These deficiencies are eliminated in the device for determining the concentration of paramagnetic particles. - electron paramagnetic resonance radiospectrometer 3. It contains a microwave path with (L modulator, amplification and amplification of the RF device with a synchronous RF detector, connected to the output of the microwave path, RF modulator polarizing magnetic field RF device adjustable transmission coefficient, whose input is connected to the high-frequency modulator of the magnetic field, and the output to the modulation output of the microwave modulator The microwave path consists of a generator, a circulator, a working resonator, a modulator and a detector. in n A polarized magnet, a measured sample is placed.The microwave modulator serves to create a compensation signal.The RF amplifier device consists of a signal amplifier at the modulation frequency of a polarizing field, a synchronous RF detector, and an integrated amplifier signal. to the output of the microwave path and controls the RF device with an adjustable transmission coefficient, the input of which is connected to the output of the RF modulator of the polarizing field, and the output to the modulation input of the microwave modulator.

Such a paramagnetic particle concentration meter uses the zero compensation method of measurement, and the signal from the microwave path output, which is the difference between the EPR signal from the sample being measured and the compensation signal, is fed to the input of the negative feedback circuit: amplifying 7 Converting RF device, RF device with adjustable transmission coefficient, microwave modulator. This automatic control system continuously maintains the equality of the signal from the sample and the compensation signal. In this case, the magnitude of the modulating signal arriving at the microwave modulator varies in accordance with the change in the EPR signal from the sample being measured. Thus, the signal at the output of the RF amplifier device corresponds to the first derivative of the EPR spectrum from the sample being measured.

Some of the EPR spectrum information is extracted from the second derivative of the spectrum. The known device allows only the first derivative to be recorded.

Moreover, in a number of cases, simultaneous recording of both the first and second derivatives of the EPR spectrum is required. This is especially necessary, for example, in the study of the kinetics of chemical processes, rapid reactions, short-lived radicals and in other similar cases.

The purpose of the present invention is to extend the functionality of a radio spectrometer by synchronously recording the first and second derivatives of the EPR spectrum.

For this purpose, a low-frequency modulator of a polarizing magnetic field, an amplifier-converter low-frequency device, a low-frequency device with an adjustable transmission coefficient, and a summing device are introduced into the radio spectrometer. The input of the amplifier-converting woofer device is connected to the output of the synchronous high-frequency detector. The input of the low-frequency device with adjustable transmission coefficient is connected to the low-frequency modulator of the magnetic field, and the control circuit is connected to the output of the amplifier-low-frequency converter device. One input of the summing device is connected to the output of the amplifier-RF device, the other input is connected to the output of the low-frequency device with an adjustable transmission coefficient, and the output is connected to the control circuit of the RF device with an adjustable transmission coefficient.

The drawing shows the block diagram of the proposed RA;, EPR spectrometer.

The radio spectrometer contains a polarizing magnet 1, a microwave path 2, an amplifying converter RF device 3, a high frequency module 4 polarizing a magnetic field, a high frequency device 5 with an adjustable transmission coefficient, a high frequency converting low frequency device 6, a low frequency modulator 7 polarizing magnetic field, low-frequency device 8, with adjustable transmission coefficient and summing device 9.

The microwave path 2 is made using a direct amplification radio-spectrometer reflector circuit and includes a generator 10, a circulator 11, a detector 12 and a working resonator 13 in which the sample 14 is placed. To create a compensation signal, the microwave signal 2 is equipped with a reflective microwave modulator 15 connected with the working resonator 13.

The RF amplifier 3 includes a selective RF amplifier 16 tuned to the frequency of the RF modulation of the magnetic field, a synchronous RF detector 17, and an integrated error signal amplifier 18. The output of the integrated amplifier 18 is connected to one of the inputs of the summing device 9.

Amplifier low-frequency device 6 contains a selective low-frequency amplifier 19 tuned to the frequency of the low-frequency modulation of the magnetic field, a synchronous low-frequency detector 20 and an integrated signal amplifier 21 signal fault. The output of the amplifier-converting low-frequency device 6 is connected to the output of the synchronous high-frequency detector 17, and the output is connected to the control circuit of the low-frequency device 8 with adjustable transmission coefficient.

The input of the low-frequency device 8 with adjustable m. The transmission coefficient is connected to the low-frequency modulator 7 of the magnetic field, and the output is connected to the second input of the summing device 9. The input of the high-frequency device 5 with an adjustable transmission coefficient is connected to the output of the summing device 9, and the output - to the input of the microwave modulator 15.

The proposed radio spectrometer works as follows.

The generator 10, through the circulator 11, excites in the resonator 13 an electromagnetic microwave field, at the antinodes of the magnetic component of which the sample under study is 14. At a polarizing field of magnet 1 corresponding to the lines of the EPR spectrum, a microwave ESR occurs in sample 14 energy. This leads to a decrease in the quality factor of the resonator 13 and a change in the power supplied through the circulator 11 to the detector 12.

The intensity of the polarizing field in the volume of sample 14 is modulated with the help of an RF modulator of 4 using a sinusoidal law with an amplitude much smaller than the width of the EPR spectrum lines. At the same time, the polarizing polarity is modulated by the low-frequency modulator 7. This modulation is also carried out according to a sinusoidal law with an amplitude much smaller than the width of the spectrum line. The frequency of the second modulation is significantly lower than the frequency of the first modulation. As a result, the output of the detector 12 is separated by a signal, depending on

magnetic susceptibility of the sample 14. The component of this signal, having the frequency of the first modulation (HF modulation), has the form of amplitude-modulated oscillations. The amplitude of the carrier oscillation is proportional to the first derivative of the line of the EPR spectrum of sample 14. The frequency of the envelope is equal to the frequency of the second modulation (LF modulation), and the amplitude is proportional to the second derivative of the line of the spectrum.

Part of the microwave energy from the resonator 13 enters the reflective microwave modulator Ttor 15. The electromagnetic wave reflected from the modulator 15 is modulated by the amplitude of the signal coming from the output of the RF device 5.

The output signal of the RF device 5 is generated using the signal of the RF modulator 4, fed to the input of the RF device 5 and the signal of the low frequency modulator 7, fed through the low frequency device 8 with an adjustable gain and summation device 9 to the control circuit (second input) RF device 5. This output modulating signal also has the form of amplitude-modulated oscillations.

The reflected modulated electromagnetic wave through the resonator 13 and the circulator 11 enters the detector 12. As a result, at the output of the detector 12, a compensation signal is selected, having the form of amplitude-modulated oscillations. The carrier frequency of this signal is equal to the frequency of the HF modulation, and the frequency of the envelope is LF modulation.

Thus, the frequencies of the carriers and the envelopes of both signals allocated at the output of the detector. 12 are respectively equal. The carrier and envelope phases of the compensation signal differ, respectively, from the carrier and envelope phases of the EPR signal by 180 °. As a result, the amplitude of the carrier of the resulting signal allocated at the output of the detector 12 is equal to the difference of the amplitude of the carrier EPR signal from sample 14 and the amplitude of the carrier of the compensation signal, and the amplitude of the envelope of the resulting signal is equal to the difference of the amplitudes of the envelopes of these signals.

The resulting signal is fed to an amplifier-converter RF device 3, where it is amplified by a selective RF amplifier 16 and detected by a synchronous RF detector 17. The signal component of the output signal of the synchronous RF detector 17 (an error signal) is fed to an integrating amplifier 18 signal error.

The amplified and integrated error signal from the output of the amplifier-converter RF device 3 is fed to one of the inputs of the summing device 9. The signal from the low-frequency modulator 7 magnetic field is fed to the other input of the summing device 9 through the low-frequency device 8 with an adjustable transmission ratio. The sum signal from the output of the device 9 is fed to the control circuit of the RF device 5 with an adjustable transmission coefficient. Changes in this signal cause changes in the transmission coefficient of the RF device 5, and, consequently, the magnitude of the signal fed to the microwave modulator 15 from the RF modulator 4 of the magnetic field.

At the same time, the output envelope of the resulting signal is extracted at the output of the synchronous high-frequency detector 17. This envelope from the output of the synchronous high-frequency detector 17 is fed to an amplifier-converting low-frequency device 6, where it is amplified by the low-frequency amplifier 19 and detected by a synchronous low-frequency detector 20. The error signal from the output of the synchronous low-frequency detector 20 is fed to the integrating error 21 amplifier . The amplified and integrated signal of the error is fed to the control circuit of the low-frequency device 8 with an adjustable gain. Changes in this signal cause changes in the transmission coefficient of the device 8, and, consequently, of the signal input to the summing device 9 from the low-frequency modulator 7 of the magnetic field.

The component of the sum signal in the control circuit of the RF device 5, which is proportional to the error signal at the output of the integrating amplifier 18, changes the gain of the RF device 5 so that the amplitude of the compensation signal carrier

at the output of detector 12, it becomes equal to the amplitude of the carrier of the EPR signal from sample 14 and the amplitude of the carrier of the resultant signal decreases to zero. Since this is amplitude equality

constantly maintained, the signal at the output of the integrating amplifier 18 is always proportional to the magnitude of the first derivative of the line of the EPR spectrum from sample 14.

At the same time, the error signal from the output of the amplifier-low-frequency amplifier 6 to the control circuit of the low-frequency device 8 changes the component of the sum signal proportional to the low-frequency modulator signal 7. This change is made so that the amplitude of the output envelope of the compensation signal detector 12 becomes equal to the amplitude of the envelope of the EPR signal from sample 14 and the amplitude of the resultant envelope decreases to zero.

This equality of amplitudes is also constantly maintained. Therefore, the signal at the output of the amplifier-converting woofer device 6 is always proportional to the magnitude of the second derivative of the line of the EPR spectrum from sample 14.

Since to create a compensation signal in the microwave modulator 15, a part of the microwave energy entering the resonator 13 is used, the instability of the microwave generator 10

will not affect the stability of the output signals of the radio spectrometer. For the same reason, the output signals will not depend on changes in the Q-factor of the resonator 13, for example, when the dielectric loss of the sample changes, or when changing, the samples.

The instability of the transmission coefficient of the circuits common to the EPR signal and the compensation signal (microwave detector 12 - amplifying RF device 3 and synchronous high-frequency detector 17 - amplifying low frequency device 6 also does not affect the output signals of the radio spectrometer.) .

The amplitudes of the first and second derivatives of the EPR signal are linearly dependent on the amplitudes of the corresponding modulations of the magnetic field. Therefore, the instability of the output signals of modulators 4 and 7 have the same effect on both the EPR signal and the compensation signal.

Consequently, the instability of the high frequency modulator 4 and the low frequency modulator 7 of the polarizing magnetic field will not affect the output signals of the radio spectrometer.

Thus, the proposed radio spectrometer allows precision and simultaneously register the first and second derivatives of the EPR spectrum from the sample under study.

Claims (3)

1. Radiospectrometer “Rubin. THEN and operating instructions, 5B1, 550.198. THAT 1972. 2. Radio spectrometer RE1306. MOT and operating instructions. L., 1974. 3. Author's certificate of the USSR 528493, cl. G 01 N 27/78, 1976.