JPH0527832B2 - - Google Patents

Description

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

[Prior art] In a conventional electron spin resonance apparatus, a cavity resonator is placed in a static magnetic field, and microwaves are absorbed by electron spin resonance of a sample housed in the cavity, and the balance of the cavity is adjusted. A detector detects the reflected microwaves generated by the collapse of the electron spin resonance signal, and obtains 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 an oscillator 1.
This is a microwave bridge for supplying microwaves from the cavity to the cavity 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 Rc in an equivalent circuit, and the impedance Zo of the cavity resonator when the sample is not undergoing electron spin resonance is expressed by the following formula.

Zo=Rc+j(ωL-1/ωC)...(1) On the other hand, when the sample undergoes electron spin resonance, L increases by the magnetic susceptibility χ of the sample and becomes L(1+χ), so
The impedance Zr of the cavity resonator at the time of resonance is a value expressed by the following formula.

Zr=Rc+j[ωL(1+χ)-1/ωC]...(2) If χ is expressed as a complex number as χ=χ'-jχ'', equation (2) is transformed into the following equation, Zr=(Rc+ωLχ'') +j[ωL(1+χ')-1/ωC] ...(3) In conventional electron spin resonance devices, the Q of the cavity resonator is based on the fact that the impedance changes from Zo to Zr as described above with resonance. The microwave intensity reflected externally due to the decrease in
As mentioned above, 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 equipment,
It was necessary to modulate the static magnetic field Ho at a frequency of about 100 KHz, for example, 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.

As a result, the configuration became complicated, and the circuit had to be designed with sufficient consideration for the signal-to-noise ratio.

The present invention has been made in view of this point,
The object of the present invention is to provide 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 signal-to-noise ratio.

[Means for solving the problem] In order to achieve this object, the electron spin resonance apparatus of the present invention includes means for generating a static magnetic field, means for sweeping the intensity of the static magnetic field, and a means for sweeping the intensity of the static magnetic field. a cavity resonator disposed, 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 for detecting microwaves; an automatic frequency control means for controlling an oscillation frequency of the microwave oscillator so as to reduce reflected microwaves based on an output signal of the detector; and an oscillation frequency of the microwave oscillator. The present invention is characterized by comprising a frequency detecting means for detecting a change in the frequency, and a means for recording the change in frequency detected by the frequency detecting means in relation to the sweeping of the static magnetic field.

[Effect] The resonant frequency o of the cavity resonator when the sample is not undergoing electron spin resonance is expressed by the following formula: o=1/2π√ ...(4) The resonant frequency r during resonance is expressed by the following formula: expressed.

r=1/2π√(1+')...(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 an automatic frequency control means to By keeping the body resonator always in a resonant state and recording changes in the oscillation frequency of the microwave oscillator in relation to the sweeping of the static magnetic field, the electron spin resonance signal is captured as a change in frequency.

By the way, the impedance of the cavity resonator changes from equation (1) to equation (3) due to electron spin resonance, and in the present invention, the resonance frequency of the cavity resonator accompanying such an impedance change is It has already been explained that the resonance signal is determined by focusing on the change from the value expressed by equation () to the value expressed by equation (5).
This is conventionally known as Q
This corresponds to understanding the resonance by focusing on the change in the imaginary term in equation (3), instead of the change in the imaginary term in equation (3). As in the present invention, even if the oscillation frequency of the microwave oscillator is changed in accordance with the change in the resonant frequency of the cavity resonator as it approaches the resonance point,
A change in Q occurs due to a change in the real term in equation (3), and resonance continues, so if the change in the resonant frequency of the cavity resonator is captured by the present invention, a resonance signal can be obtained.

[Example] Hereinafter, an example of the present invention will be described in detail using 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 magnetic field generated by a magnet 2. As shown in FIG. Microwaves from a microwave oscillator 3 having a variable oscillation frequency are supplied to the cavity resonator 1 via an attenuator 4 and a microwave bridge, such as a circulator 5. The microwave reflected by the cavity resonator 1 is sent to the microwave detector 6 via the circulator 5 and detected. Directional couplers 7 and 8 are provided on the microwave line between the oscillator 3 and the attenuator 4 and between the circulator 5 and the detector 6, and the reference microwave taken out from the directional coupler 7 is directionally coupled. It is added to the microwave sent from the circulator 5 to the detector 6 via the circulator 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 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, a signal is sent to the feedback circuit 10. The signal must have characteristics as shown in Figure 2 a or b with respect to frequency.

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°. By adjusting the phase shifter 9 to
The characteristics shown in Figures a and b are obtained.

Therefore, as the static magnetic field sweeps, the cavity resonator 1
When the sample inside undergoes electron spin resonance and the resonant frequency of the cavity resonator deviates from o, a detection signal Δ indicating the amount and direction of the deviation 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. is maintained. FIG. 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. This output signal corresponds to the resonance frequency r in equation (5), and an electron spin resonance signal with a dispersive waveform is 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 reference gate oscillator of the counter 11 is sufficiently increased, a sufficiently stable resonance signal can be obtained, and unlike conventional methods, it is possible to obtain a sufficiently stable resonance signal without considering the noise figure of the analog amplifier. There is no need for careful circuit design, and configurations such as a magnetic field modulation mechanism and 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 the two is 0° 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 another embodiment of the invention, in which the same components as in the embodiment of FIG. 1 are given the same numbers. In Figure 4, 15 is from several KHz to several
An oscillator that generates a modulation signal m of about 10KHz.
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 exhibits a frequency characteristic as shown in FIG. 5 a or b, rather than as shown in FIG. 2 a and b. At this time, since the microwave is modulated by the modulation signal m, that 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 differs depending on the shift to the lower side (see Figure 5a).
Therefore, if phase detection is performed based on the modulated signal m using the phase detector 16, a signal completely equivalent to Δ in the previous embodiment can be obtained at the output of the detector 16. Therefore, if this signal is fed back to the oscillator 3 via the feedback 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. , an electron spin resonance signal will be obtained.

[Effects of the Invention] As described in detail 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 signal-to-noise ratio is realized.

[Brief explanation of the drawing]

1 and 4 each show an embodiment of the present invention, FIGS. 2 and 5 show the characteristics of the signal obtained from the detector 6 with respect to frequency, and FIG. 3 shows the characteristics of the static magnetic field. FIG. 6 is a diagram showing the output signal of the counter 11 that monitors the change in the oscillation frequency of the oscillator 3 due to the sweep, and FIG. 6 is a diagram representing the configuration of a conventional electron spin resonance apparatus using an equivalent circuit. 1... Cavity resonator, 2... Magnet, 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 source.

Claims (1)

[Claims] 1. A means for generating a static magnetic field, a means for sweeping the intensity of the static magnetic field, a cavity resonator disposed within the static magnetic field, a microwave oscillator, and a microwave oscillator from the oscillator. a microwave bridge that supplies waves to the cavity resonator and extracts reflected microwaves from the cavity resonator; a microwave detector that detects the extracted microwaves; and a microwave detector that detects the extracted microwaves, based on the output signal of the detector. automatic frequency control means for controlling the oscillation frequency of the microwave oscillator so as to reduce reflected microwaves; a frequency detection means for detecting a change in the oscillation frequency of the microwave oscillator; an electron spin resonance apparatus, comprising: means for recording changes in frequency in relation to the sweeping of the static magnetic field. 2. The electron spin resonance apparatus according to claim 1, wherein the frequency detection means is a frequency counter.