JPS61140847A - Electron spin resonance device - Google Patents

Abstract

PURPOSE:To obtain an electron spin resonance signal as digital information by controlling a microwave oscillator and placing a cavity resonator invariably in a resonance state, and recording variation in oscillation frequency accompanying a magnetic field sweep. CONSTITUTION:The sample in the cavity resonator 1 makes electron spin resonance as a magnetostatic field is swept and when the resonance frequency of the cavity resonator shifts from f0, a detection signal DELTAf indicating the extent and direction of the shift is obtained from a detector 6. A feedback circuit 10 amplifies the signal property and feeds it back to the oscillator 3, so the oscillation frequency of the oscillator 3 varies following up the shift in the resonance frequency due to the resonance and the cavity resonator 1 is held invariably in the resonance state. A figure shows the output signal of a counter 11 which monitors variation in the oscillation frequency of the oscillator 3 accompanying the sweep of the magnetostatic field. An electron spin resonance signal with a dispersed waveform is obtained from the output signal.

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Field of Application 1] The present invention relates to an electronic spin resonance device, and more particularly to an electron spin resonance device that can extract a resonance signal not as an analog signal but as a digital signal.

[Prior art 1] In a conventional electron spin resonance apparatus, a cavity resonator is placed in a static magnetic field, and microwaves are absorbed by the electron spin resonance of a sample housed in the cavity resonator, and the balance of the cavity is adjusted. A detector detects the reflected microwaves generated by the collapse of the beam, and generates an electron spin resonance signal.

When such a configuration is expressed as an equivalent circuit, it becomes as shown in FIG. In Fig. 6, 1 is a microwave oscillator, 2 is a cavity resonator, 3 is a sample housed in the cavity resonator 2, 4 is a microwave detector, and 5 is a cavity that receives the microwave from the oscillator 1. This is a microwave bridge for supplying microwaves to the resonator 2 and for transmitting reflected microwaves from the cavity resonator 2 to the detector 4.

The cavity resonator is expressed as a series circuit of l, C, and Re in an equivalent circuit, and the impedance ZO of the cavity when sample r1 is not undergoing electron spin resonance is expressed by the following formula.

70=RC+,j(ωL-1/θ)C)...(1
) On the other hand, when sample r1 undergoes electron spin resonance, L increases by the magnetic susceptibility χ of the sample and becomes L(1+χ), so the impedance 7r of the cavity resonator at the time of resonance becomes a value expressed by the following formula. .

7r = Rc -1-j [θ>l (1+χ)-1
/ωC]...(2) Expressing χ as a complex number as χ=χ'-jχ'', equation (2) is transformed into the following equation, 7r = (RC+ω1-χ'')+j[ω1-(1+χ ')-110>C]...(3) In the conventional electron spin resonance device, the Q of the cavity resonator decreases due to the impedance changing from 70 to 7' as described above with resonance. The microwave intensity reflected to the outside is detected, and as mentioned earlier, the obtained resonance signal is essentially an analog signal.

[Problems to be Solved by the Invention] In this way, when the output signal is an analog signal, stability of the output is required when no resonance signal is output (that is, when electron spin resonance is not occurring).

Therefore, in conventional electron spin resonance imaging, the static magnetic field HO
It was necessary to modulate the signal at a frequency of, for example, 100K H1, and extract the resonance signal using a lock-in amplifier, taking advantage of the fact that a modulation component appears on the output side only when resonance occurs.

Therefore, the configuration becomes complicated, and the circuit must be designed with sufficient consideration given to the SN ratio.

The present invention has been made in view of this point, and an object of the present invention is to provide an electron spin resonance device that can obtain an electron spin resonance signal as digital information, has an accurate configuration, and can obtain a high signal-to-noise ratio. There is.

Means for Solving Problem F] To achieve this object, the electron spin resonance apparatus according to the present invention includes a means for generating a static magnetic field, a means for sweeping the -3=static field, and a means for sweeping the static magnetic field. a cavity resonator disposed in a magnetic field, a microwave oscillator, a microwave bridge that supplies microwaves from the oscillator to the cavity resonator and extracts reflected microwaves from the cavity resonator;
a microwave detector that detects the extracted microwave;
automatic frequency control means for controlling the oscillation frequency of the microwave oscillator based on the output signal of the detector to prevent reflected microwaves from being generated from the cavity resonator; It is characterized in that the change in is recorded in relation to the sweep of the static magnetic field.

[Effect 1 The resonant frequency fo of the cavity resonator when sample F1 is not undergoing electron spin resonance is expressed by the following formula, fo = 1/2πF
...(4) The resonance frequency fr at the time of resonance is expressed by the following formula.

fr=1/2 π, 11-Z')
=・ (5) In the present invention, we focus on the change in the resonant frequency of the cavity resonator accompanying this resonance, and control the microwave oscillator using the automatic frequency controller -4= stage to ensure that the cavity resonator always resonates. By recording the change in the oscillation frequency of the microwave oscillator in conjunction with the sweeping of the static magnetic field, the electron spin resonance signal is captured as a change in frequency.

[Example] Hereinafter, one embodiment of the present invention will be explained with reference to the drawings.

FIG. 1 shows the configuration of an embodiment of the present invention, in which reference numeral 1 denotes a cavity resonator placed within a static field generated by a magnet 2. In FIG. Microwaves from a microwave oscillator 3 with a variable oscillation frequency are transmitted to the cavity resonator 1 through an attenuator 4. It is supplied via a microwave bridge, for example a circulator 5. The microwave reflected by the cavity resonator 1 is sent to a microwave detector 6 via a circuit 5 and detected.

A directional coupler 7 is provided on the microwave line between the oscillator 3 and the attenuator 40 and between the circulator 5 and the detector 6.
．． 8 is provided, and the reference microwave taken out from the directional coupler 7 is added to the microwave sent from the circulator 5 to the detector 6 via the directional coupler 8. 9
is a phase shifter inserted into the reference microwave line.

A detection signal obtained from the detector 6 is sent to the oscillator 3 via a frequency control feedback circuit 10, thereby controlling the oscillation frequency of the oscillator 3. 11 is a microwave frequency counter for counting the oscillation frequency, and the count output is recorded in the recording device 12. 13
14 is a directional coupler for extracting the microwave from the oscillator 3 and sending it to the counter, and 14 is a power source for sweeping the static magnetic field.

In the configuration as described above, when the resonant frequency of the resonator 1 changes due to electron spin resonance, in order to detect it and automatically control the oscillation frequency of the oscillator 3 to follow it, the feedback circuit 10 is The signal to be sent must have characteristics as shown in FIG. 2(a) or (1)) with respect to frequency f.

The reference microwave line is provided for this purpose, and when adding the reference microwave to the microwave sent from the circulator 5 to the detector 6 in the directional coupler 8, it is set so that the phase difference between the two becomes 90 degrees. By adjusting the phase shifter 9, the characteristics shown in FIG. 2(a) or (b) can be obtained.

Therefore, when the sample in the cavity resonator 1 undergoes electron spin resonance as the static magnetic field sweeps, and the resonant frequency of the cavity resonator deviates from fo, the detection signal indicating the period and direction of the deviation changes to f.
is obtained from the detector 6.

Since the feedback circuit 10 appropriately amplifies this detection signal and feeds it back to the oscillator 3, the oscillation frequency of the oscillator 3 changes to follow the shift in the resonance frequency due to resonance, and the cavity resonator 1 is always in a resonant state. Retained. Figure 3 shows the output signal of the counter 11 that monitors the change in the oscillation frequency of the oscillator 3 as the static magnetic field is swept. electron spin resonance signals are obtained.

This resonance signal is obtained as digital information as an output signal of the counter 11. Therefore, if the stability of the oscillation frequencies of the microwave oscillator 3 and the M quasi-gate oscillator of the counter 11 is sufficiently increased, a sufficiently stable resonance signal can be obtained, and the noise figure of the analog amplifier, etc., can be taken into account as in the conventional method. There is no need to perform careful circuit design, and configurations such as a magnetic field modulation mechanism and a lock-in amplifier are also unnecessary.

Note that there are also conventional devices that are provided with a reference microwave line. However, the purpose of this is to keep the operating level of the detector constant regardless of the magnitude of the microwave power supplied from the oscillator to the cavity resonator, so the reference microwave is When adding the microwaves sent from the circulator to the detector, the phase shifter is adjusted so that the phase difference between them becomes Oo or 180°. Therefore, when using such a conventional device, it is necessary to readjust the phase shifter so that the phase difference becomes 90'.

FIG. 4 shows the structure of a third embodiment of the invention, in which the same components as in the embodiment of FIG. 1 are given the same numbers. In Fig. 4, 15 is an oscillator that generates a modulation signal fm of about 10 KHz,
The microwave oscillator 3 generates microwaves modulated by this modulation signal. 16 is a phase detector for detecting the phase of the detection signal obtained from the detector 6 based on the modulation signal.

In this embodiment, the phase shifter 9 is set so that the phase difference is 0° or 180°, as in the conventional example described above. Therefore, the signal obtained from the detector 6 does not have the characteristics as shown in FIGS. 2(a) and 2(b) with respect to the frequency f, but
It exhibits characteristics as shown in figure (a) or (b). At this time, since the microwave is modulated by the modulation signal fm, the modulation signal also appears in the output signal, but the phase of the signal shifts to the side where the resonant frequency of resonator 1 becomes higher. The phase is different depending on the case where it is shifted to the lower side (the fifth
(See figure (a)). Therefore, if the phase detector 16 is used to perform phase detection based on the modulated signal fm, the output of the detector 16 will contain a signal completely equivalent to Δf that is applied to I in the previous embodiment.
You can get rid of it. Therefore, return this signal)! By feeding back to the oscillator 3 via the circuit 10, the oscillation frequency of the oscillator 3 is controlled so that the cavity resonator 1 is always in a resonant state, just as in the embodiment shown in FIG.
It will be +7.

[Effects of the Invention] ■As detailed above, according to the present invention, an electron spin resonance apparatus that can obtain an electron spin resonance signal as digital information, has a simple configuration, and can obtain a high S/N ratio is realized. Ru.

[Brief explanation of the drawing]

1 and 4 are diagrams each showing an embodiment of the present invention, FIGS. 2 and 5 are diagrams each showing the characteristics of the signal obtained from the detector 6 with respect to frequency, and FIG. A counter 11 monitors changes in the oscillation frequency of the oscillator 3 as the oscillator 3 sweeps.
FIG. 6 is a diagram showing the configuration of a conventional electron spin resonance apparatus using an equivalent circuit. 1: Cavity resonator 2: VA stone 3: Microwave oscillator 5: Circulator 6: Microwave detector 7.8, 13: Directional coupler 9: Phase shifter 10: Frequency control feedback circuit 11: Microwave Frequency counter 12: Recording device 14: Power supply

Claims (2)

[Claims] (1) A means for generating a static magnetic field, a cavity resonator disposed within the static magnetic field, a microwave oscillator, supplying microwaves from the oscillator to the cavity resonator, and causing the cavity resonance. a microwave bridge that extracts reflected microwaves from the microwave, a microwave detector that detects the extracted microwaves, and a cavity resonator that controls the oscillation frequency of the microwave oscillator based on the output signal of the detector. automatic frequency control means for preventing reflected microwaves from being generated from the microwave oscillator, and recording changes in the oscillation frequency of the microwave oscillator in relation to the sweeping of the static magnetic field. Spin resonator. (2) The electron spin resonance apparatus according to claim 1, wherein the oscillation frequency of the microwave oscillator is measured by a frequency counter.