SU1553890A1 - Apparatus for recording epr signal - Google Patents

Abstract

The invention can be used in EPR radio spectrometers. The purpose of the invention is to increase the sensitivity by improving the output conditions of the EPR signal. To this end, the input and output waveguides of the resonator are installed coaxially and rotated relative to each other around their common axis at an angle of 90 °, and a receiving horn is installed outside the cavity cavity, which passes into the output waveguide. 2 Il.

Description

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The invention relates to the study of the magnetic properties of substances and can be used in EPR radio spectrometers.

The purpose of the invention is to increase sensitivity by improving the conditions for outputting an EPR signal from a resonator. .

Fig. 1 shows the proposed device-section, along its axis in the plane H of the intensity of the magnetic component of the microwave field in the resonator; 2 is the same, the cross section along its axis in the plane of the vector E of the intensity of the electric component of the microwave field in the resonator.

The device for recording the EPR signal consists of a spherical mirror 1 and a flat mirror made in the form of a diffraction grating 2, forming an open hemispherical

a resonator, a receiving horn 3, installed directly behind the diffraction grating 2 outside the cavity cavity and smoothly transferring into the output waveguide 4, the input connection slit 5 connecting the cavity cavity with the input waveguide 6 by means of a smooth transition 7 The sample 8 is attached directly to a diffraction grating 2 from the cavity cavity side and has the shape of a flat disk that fills the entire cross section of the resonator.

The diffraction grating 2 is made in the form of a flat disk from a one-dimensional metal grating with a period of 1 f b, where ft is the working wavelength. The diameter of the grille 2 is equal to the diameter of the inlet of the receiving horn 3, and they are installed so that the inlet apertures

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mko horn 3 is fully closed | lattice 2. The last requirement is made up of using an open resonator in the proposed device. The main power losses in open resonators are diffraction losses, i.e. power loss due to radiation from the cavity of the resonator to the surrounding space, and if this radiation is not blocked from receiving horn 3, the junction level of input 6 and output 4 waveguides will decrease, resulting in an increase in the power of radiation entering the microwave receiver in the absence of an EPR signal An increase in power trickling to the receiver in the absence of an EPR will cause a proportional increase in the noise power of the generator arriving at the receiver, which ultimately reduces the sensitivity of the radio spectrometer. The shielding of the inlet of the horn 3 by the diffraction grating 2 increases the separation between the input waveguide 6 and the output waveguide 4, which increases the sensitivity of the radio spectrometer.

Input b and output 4 waveguides are installed coaxially to the resonator. The output waveguide 4 is oriented so that its wide wall is parallel to the slots of the lattice 2, the input waveguide 6 is rotated relative to the output waveguide 4 around their common axis at an angle of 90. The transition 7 connecting the input waveguide 6 to the connection slot 5 has the shape of a rectangular waveguide constant width with a gradually decreasing (from the input waveguide 6 to the slit 5 of the input coupling) height. The polarizing magnetic field is directed along the cavity axis.

The device that implements the proposed method works as follows

A resonator with a paramagnetic sample 8 is placed in a source of a magnetic field, such as a superconducting solenoid. A microwave radiation generator is turned on, the signal from which is fed through the input waveguide 6 and the transition 7 is fed to the communication slot 5.

By changing the distance between the spherical mirror 1 and the diffraction grating 2, the resonant frequency of the resonator is tuned to the frequency of the supplied microwave radiation, in

as a result of which microwave oscillations are excited in the resonator, the polarization of these oscillations is such that

the electric vector is parallel to the slots in the diffraction grating 2. Rotating as a whole the diffraction grating 2, the receiving horn 3 and the output waveguide 4 around the longitudinal axis of the resonator, achieve the minimum value of microwave radiation at the output of the waveguide 4 in the absence of an EPR signal. Then, at the occurrence of a resonant4 paramagnetic

5, the rotation of the polarization plane records the EPR signal by changing the intensity of the microwave radiation at the output of the waveguide 4.

In the device for operation in the two-millimeter range, the diameter of the spherical mirror 1 and the diffraction grating 2 is 12 mm. The radius of curvature of the spherical mirror 1 is equal to 13 mm. The width of the slits of the diffraction grating

5 2-60 µm, the period of the following slits in the diffraction grating 2 is 120 µm. Such a design of the diffraction grating 2 in the two-millimeter wavelength range of the microwave radiation provides almost complete transparency for radiation with an electric vector, orthogonally polarized with respect to the slit, and specularity (reflectivity) for radiation that is parallel to the slits The device also contains rectangular input b and output 4 waveguides (type of wave H10) with a cross section of 0 8 8x1.6 mm suspended in coaxially and mutually orthogonal along polarisations waves located in them (wide wall of the waveguide 6 is orthogonal to the wide wall of the waveguide 4). In the center of the spherical 5 mirror I (along the longitudinal axis of the resonator) a communication hole (slot) 5 is made connecting the resonator with the input waveguide 6 by means of a smooth transition 7, Hole 5 connection is made in the form of a rectangular gap 0.08x1.6 mmg. Transition 7 has the shape of a waveguide of constant width (1.6 mm) with a smoothly varying height from 0.08 to 0.8 mm and a length of 20 mm, which corresponds to approximately ten wavelengths. The coupling parameter of the resonator with sample 8 and the input waveguide 6 is approximately equal to one. The output of the communication element is formed by a diffraction

a grating 2 and a receiving horn 3 installed directly behind it. The receiving horn 3 has a cone shape with an aperture angle of approximately 10 The diameter of the inlet of the horn 3 is equal to the diameter of the diffraction grating 2, i.e. 12 mm. The lattice slits 2 are parallel to the wide wall of the output WAVEGUIDE 4.

 The horn 3 and the diffraction grating 2 are installed so that the diffraction grating 2 completely covers the inlet of the horn 3. This protects the input of the horn 3 from the penetration of microwave radiation scattered by the open resonator into the surrounding space due to diffraction energy loss, and thereby increase the level of isolation between the input 6 and output 4 waveguides, which contributes to an increase in the sensitivity of the radio spectrometers by reducing the contribution of generator noise to the total noise of the radio spectrometer.

The EPR signal is recorded as follows.

The paramagnetic sample under study is fixed on a diffraction grating mounted on a receiving horn connected to the output waveguide, after which the whole structure is placed in the hole of the superconducting solenoid so that the sample is at the center of the magnetic field of the solenoid. A spherical mirror with an input waveguide is preliminarily fastened in the opening of the solenoid. This part of the design of the resonator is not dismantled during the sample replacement process. The output waveguide is then connected to the microwave receiver and a microwave generator is switched on. Further, by changing the distance between the diffraction grating and the spherical mirror, the resonator is tuned to the frequency of the microwave generator, equal to about 150 GHz, which corresponds to

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wavelength ft 2 mm. The criterion for the coincidence of the frequencies of the generator and the resonator is the minimum of microwave radiation reflected from the resonator. Then, rotating the output waveguide around its axis, achieve a minimum of power at the microwave receiver, which corresponds to the maximum isolation between the generator and the receiver.

Claims (1)

After tuning the resonator, a solenoid power source that generates a polarizing magnetic field is set, the resonance value of the magnetic field is set to be equal to a paramagnetic sample with a g-factor of a free electron of about 55 kOe, and the EPR signal is recorded from the change in the microwave radiation level in the output waveguide. Invention Formula A device for recording an EPR signal containing a hemispherical resonator, one of the walls of which is a flat mirror made in the form of a one-dimensional diffraction grating with a period of 1 "A, where ft is the working wavelength, and a communication element made in the form of an opening in the other a wall which is a spherical mirror, characterized in that, in order to increase the sensitivity by improving the conditions for outputting the EPR signal from the resonator, the input and output rectangular waveguides are mounted coaxially and rotated relative to each other around their common axis ka 90 ° angle, outside the cavity of the resonator a receiving horn is installed with an opening angle of Yu °, which passes into the output rectangular waveguide, and the horn is mounted so that its inlet is completely closed by a diffraction grating whose diameter is equal to the diameter the mouth of the horn, and the wide wall of the output waveguide is parallel to the slits of the diffraction grating. / 7 /1.5 UHH / HUUUHU / U,, fH  ///// S / s