JP2008180569A - Esr device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an ESR device capable of preventing position deviation of an ESR spectrum to a set magnetic field originated in a drift of a resonance frequency, when measuring ESR. <P>SOLUTION: In this ESR device, a sample is installed in a high frequency resonator placed in a static magnetic field, and the ESR spectrum is measured by sweeping and controlling static magnetic field intensity. The ESR device includes an AFC circuit for feeding back a frequency fluctuation portion caused by the drift of the resonance frequency of the high frequency resonator to the high frequency oscillator, and correcting automatically an oscillation frequency on the high frequency oscillator side in accordance with the resonance frequency of the high frequency resonator, and part of output from the AFC circuit is fed back also to a magnetic field control circuit for controlling the static magnetic field, and deviation of a resonance magnetic field of the ESR spectrum caused by the drift of the resonance frequency of the high frequency resonator is corrected. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to an improvement of a magnetic field control method in an ESR apparatus.

  An ESR apparatus is a type of magnetic resonance apparatus that irradiates a sample to be measured placed in a static magnetic field with microwaves and records as a spectrum how the irradiated microwaves are absorbed by the sample to be measured. . When free radicals exist in the sample to be measured, microwave absorption occurs as the static magnetic field is swept, and an absorption spectrum reflecting the free radical molecular structure is recorded on the recorder. By analyzing this absorption spectrum, information on the molecular structure of the free radical can be obtained.

  FIG. 1 is a configuration diagram of a conventional reflective ESR apparatus. The microwave oscillated from the microwave oscillator 1 is branched into an appropriate power by the directional coupler 2, and then sent to the cavity resonator 5 installed in the gap between the magnetic poles 4 of the electromagnet through the circulator 3. . A coupling degree adjusting mechanism (not shown) is provided between the cavity resonator 5 and the microwave line. By matching between the cavity resonator 5 and the microwave line, the cavity resonator 5 It is adjusted so that there is no reflected wave.

  A measurement sample 6 is set inside the cavity resonator 5. When the static magnetic field is swept by the opposing magnetic poles 4 and the ESR phenomenon occurs, the microwave is absorbed and the Q value of the cavity resonator is changed, the balance of matching is lost, and the reflection from the cavity resonator 5 is reflected. Produce waves. This reflected wave is sent to the microwave detector 7 via the circulator 3 and the phase is detected. For the purpose of performing this phase detection, a part of the microwave power of the microwave oscillator 1 branched by the directional coupler 2 is adjusted in phase by the phase shifter 8 provided in the bypass line, and then the microwave. Input to the detector 7.

  This bypass line is provided for the purpose of keeping the operating level of the microwave detector 7 constant regardless of the magnitude of the microwave power reflected from the cavity resonator 5. This corresponds to the bias power.

  The microwave absorption signal from the sample 6 is phase-detected and then recorded on a recorder (not shown) through the preamplifier 9, the bandpass filter 10, and the amplifier 11.

  In such measurement, the frequency of the microwave supplied to the cavity resonator 5 always matches the resonance frequency of the cavity resonator 5 and is constantly controlled so that no extra reflected wave is generated. Need to be. For this reason, in a normal reflection type ESR device, even if the resonance frequency of the cavity resonator 5 drifts due to an environmental change such as a temperature change, the microwave frequency automatically changes accordingly. The function to go is given. This is called AFC (automatic frequency control).

  The AFC will be described with reference to FIG. First, a modulation component is supplied from the 70 kHz modulation oscillator 12 to the microwave oscillator 1 via the amplifier 13. Based on this, frequency modulation (FM) of 70 kHz is applied to the microwave itself, and the modulated microwave is supplied to the cavity resonator 5.

  As a result, as shown in FIG. 2, when the microwave frequency matches the resonance frequency of the cavity 5 (state C), a 70 kHz component having a very small amplitude is superimposed on the reflected wave of the microwave. Only. However, when the microwave frequency is slightly shifted from the resonance frequency of the cavity resonator 5 (states B and D), a 70 kHz component having a very large amplitude is superimposed on the reflected wave of the microwave. It can be determined from the phase of the 70 kHz component whether the microwave frequency is shifted higher or lower than the resonant frequency of the cavity resonator 5.

  The reflected microwave including the 70 kHz component is detected by the microwave detector 7, amplified by the preamplifier 9, and then subjected to the phase detection of the 70 kHz component by the phase detector 16 via the bandpass filter 14 and the amplifier 15 for 70 kHz. Do.

  In this way, the phase detection and DC conversion of the 70 kHz component is fed back to the microwave oscillator 1 via the low-pass filter 17 and the adder 18 so as to be close to zero. A varactor diode (voltage variable capacitance element) is installed in the cavity of the microwave oscillator 1, and a microwave frequency change corresponding to the magnitude of the fed back DC voltage can be caused. Thus, even if the microwave frequency deviates from the resonance frequency of the cavity resonator 5 due to drift of the cavity resonator 5 or the like, the microwave frequency can be automatically controlled following the deviation. .

Hiroaki Ohya, Atsushi Yamauchi, “Electron Spin Resonance-Microcharacterization of Materials”, Kodansha Scientific, published on September 20, 1989, p.33.

  By the way, in ESR measurement, a quartz double tube may be used to insulate between the resonator and the sample to vary the temperature of the sample. However, it is difficult to completely eliminate the influence of the temperature control of the sample on the resonator temperature. If the temperature of the resonator changes, the resonator volume changes due to thermal expansion / contraction of the resonator wall, and the resonance frequency of the resonator drifts.

  In addition, the resonant frequency of the resonator may change due to changes in the properties of the sample due to temperature or changes in other environmental factors.

  The AFC detects the resonance frequency drift and stabilizes the oscillation frequency of the microwave oscillator by following the resonance frequency drift of the resonator.

  However, the fact that the resonance frequency drifts means that the resonance magnetic field also drifts from the principle of magnetic resonance. That is, the position shift of the ESR spectrum with respect to the set magnetic field occurs.

  In the case of a sample with a narrow line width of the ESR resonance absorption line or when only a change with time in signal intensity is observed by fixed point observation, the positional deviation of the ESR spectrum has a significant adverse effect on the measurement.

  In view of the above points, an object of the present invention is to provide an ESR device capable of preventing a position shift of an ESR spectrum with respect to a set magnetic field derived from a resonance frequency drift during ESR measurement.

In order to achieve this object, an ESR device according to the present invention includes:
In an ESR apparatus in which a sample is placed in a high-frequency resonator placed in a static magnetic field, and the ESR spectrum is measured by sweeping and controlling the static magnetic field strength.
The ESR device includes an AFC circuit that feeds back a frequency fluctuation caused by a drift in the resonance frequency of the high-frequency resonator to the high-frequency oscillator and automatically corrects the oscillation frequency on the high-frequency oscillator side according to the resonance frequency of the high-frequency resonator. As well as
A part of the output of the AFC circuit is also fed back to the magnetic field control circuit that controls the static magnetic field, thereby correcting the deviation of the resonant magnetic field of the ESR spectrum accompanying the drift of the resonant frequency of the high frequency resonator. It is characterized by that.

Further, in an ESR apparatus for measuring an ESR spectrum by installing a sample in a high-frequency resonator placed in a static magnetic field, and sweeping and controlling the static magnetic field strength,
The ESR device includes an AFC circuit that feeds back a frequency fluctuation caused by a drift in the resonance frequency of the high-frequency resonator to the high-frequency oscillator and automatically corrects the oscillation frequency on the high-frequency oscillator side according to the resonance frequency of the high-frequency resonator. As well as
A magnetic field control circuit that reads the oscillation frequency of the high-frequency oscillator automatically corrected by the AFC circuit, calculates the deviation of the resonant magnetic field of the ESR spectrum from the frequency fluctuation, and controls the static magnetic field based on the calculation result Control is performed to correct a shift in the resonant magnetic field of the ESR spectrum accompanying the drift of the resonant frequency of the high-frequency resonator.

Further, the calculation is performed using the following ESR resonance conditional expression:
ΔH = (h · Δν) / (gβ)
It is characterized by being performed based on. Where ΔH is the resonance magnetic field deviation, h is the Planck constant, Δν is the resonance frequency variation, g is the g value of the ESR spectrum, and β is the Bohr magneton.

According to the ESR device of the present invention,
In an ESR apparatus in which a sample is placed in a high-frequency resonator placed in a static magnetic field, and the ESR spectrum is measured by sweeping and controlling the static magnetic field strength.
The ESR device includes an AFC circuit that feeds back a frequency fluctuation caused by a drift in the resonance frequency of the high-frequency resonator to the high-frequency oscillator and automatically corrects the oscillation frequency on the high-frequency oscillator side according to the resonance frequency of the high-frequency resonator. As well as
A part of the output of the AFC circuit is also fed back to the magnetic field control circuit that controls the static magnetic field, thereby correcting the deviation of the resonant magnetic field of the ESR spectrum accompanying the drift of the resonant frequency of the high frequency resonator. So
At the time of ESR measurement, it is possible to provide an ESR device capable of preventing the positional deviation of the ESR spectrum with respect to the set magnetic field derived from the resonance frequency drift.

Further, in an ESR apparatus for measuring an ESR spectrum by installing a sample in a high-frequency resonator placed in a static magnetic field, and sweeping and controlling the static magnetic field strength,
The ESR device includes an AFC circuit that feeds back a frequency fluctuation caused by a drift in the resonance frequency of the high-frequency resonator to the high-frequency oscillator and automatically corrects the oscillation frequency on the high-frequency oscillator side according to the resonance frequency of the high-frequency resonator. As well as
A magnetic field control circuit that reads the oscillation frequency of the high-frequency oscillator automatically corrected by the AFC circuit, calculates the deviation of the resonant magnetic field of the ESR spectrum from the frequency fluctuation, and controls the static magnetic field based on the calculation result Since the control is performed to correct the deviation of the resonance magnetic field of the ESR spectrum accompanying the drift of the resonance frequency of the high-frequency resonator,
At the time of ESR measurement, it is possible to provide an ESR device capable of preventing the positional deviation of the ESR spectrum with respect to the set magnetic field derived from the resonance frequency drift.

  Embodiments of the present invention will be described below with reference to the drawings.

  FIG. 3 shows an embodiment of a reflection type ESR apparatus according to the present invention. The same components as those in FIG. 1 will be described with the same numbers.

  The microwave oscillated from the microwave oscillator 1 is branched into an appropriate power by the directional coupler 2, and then sent to the cavity resonator 5 installed in the gap between the magnetic poles 4 of the electromagnet through the circulator 3. . A coupling degree adjusting mechanism (not shown) is provided between the cavity resonator 5 and the microwave line. By matching between the cavity resonator 5 and the microwave line, the cavity resonator 5 It is adjusted so that there is no reflected wave.

  A measurement sample 6 is set inside the cavity resonator 5. When the static magnetic field is swept by the opposing magnetic poles 4 and the ESR phenomenon occurs, the microwave is absorbed and the Q value of the cavity resonator is changed, the balance of matching is lost, and the reflection from the cavity resonator 5 is reflected. Produce waves. This reflected wave is sent to the microwave detector 7 via the circulator 3 and the phase is detected. For the purpose of performing this phase detection, a part of the microwave power of the microwave oscillator 1 branched by the directional coupler 2 is adjusted in phase by the phase shifter 8 provided in the bypass line, and then the microwave. Input to the detector 7.

  This bypass line is provided for the purpose of keeping the operating level of the microwave detector 7 constant regardless of the magnitude of the microwave power reflected from the cavity resonator 5. This corresponds to the bias power.

  The microwave absorption signal from the sample 6 is phase-detected and then recorded on a recorder (not shown) through the preamplifier 9, the bandpass filter 10, and the amplifier 11.

  In such measurement, the frequency of the microwave supplied to the cavity resonator 5 always matches the resonance frequency of the cavity resonator 5 and is constantly controlled so that no extra reflected wave is generated. Need to be. For this reason, in a normal reflection type ESR device, even if the resonance frequency of the cavity resonator 5 drifts due to an environmental change such as a temperature change, the microwave frequency automatically changes accordingly. The function to go is given. This is called AFC (automatic frequency control).

  The AFC will be described with reference to FIG. First, a modulation component is supplied from the 70 kHz modulation oscillator 12 to the microwave oscillator 1 via the amplifier 13. Based on this, frequency modulation (FM) of 70 kHz is applied to the microwave itself, and the modulated microwave is supplied to the cavity resonator 5.

  As a result, as shown in FIG. 2, when the microwave frequency matches the resonance frequency of the cavity 5 (state C), a 70 kHz component having a very small amplitude is superimposed on the reflected wave of the microwave. Only. However, when the microwave frequency is slightly shifted from the resonance frequency of the cavity resonator 5 (states B and D), a 70 kHz component having a very large amplitude is superimposed on the reflected wave of the microwave. It can be determined from the phase of the 70 kHz component whether the microwave frequency is shifted higher or lower than the resonant frequency of the cavity resonator 5.

  The reflected microwave including the 70 kHz component is detected by the microwave detector 7, amplified by the preamplifier 9, and then subjected to the phase detection of the 70 kHz component by the phase detector 16 via the bandpass filter 14 and the amplifier 15 for 70 kHz. Do.

  In this way, the phase detection and DC conversion of the 70 kHz component is fed back to the microwave oscillator 1 via the low-pass filter 17 and the adder 18 so as to be close to zero. A varactor diode (voltage variable capacitance element) is installed in the cavity of the microwave oscillator 1, and a microwave frequency change corresponding to the magnitude of the fed back DC voltage can be caused. Thus, even if the microwave frequency deviates from the resonance frequency of the cavity resonator 5 due to drift of the cavity resonator 5 or the like, the microwave frequency can be automatically controlled following the deviation. .

  The output of the adder 18 is also fed back to the electromagnet generating a static magnetic field applied to the sample 6. That is, a current corresponding to the deviation of the resonance magnetic field of the ESR spectrum that varies depending on the variation of the resonance frequency is added by the current control circuit 19 and supplied to the electromagnet. Thereby, the deviation of the resonance magnetic field of the ESR spectrum is superimposed on the static magnetic field and applied to the sample, and the apparent resonance position of the ESR spectrum does not cause a deviation.

  FIG. 4 shows another embodiment of the reflective ESR apparatus according to the present invention. The same components as those in FIG. 3 will be described with the same numbers.

  The microwave oscillated from the microwave oscillator 1 is branched into an appropriate power by the directional coupler 2, and then sent to the cavity resonator 5 installed in the gap between the magnetic poles 4 of the electromagnet through the circulator 3. . A coupling degree adjusting mechanism (not shown) is provided between the cavity resonator 5 and the microwave line. By matching between the cavity resonator 5 and the microwave line, the cavity resonator 5 It is adjusted so that there is no reflected wave.

  A measurement sample 6 is set inside the cavity resonator 5. When the static magnetic field is swept by the opposing magnetic poles 4 and the ESR phenomenon occurs, the microwave is absorbed and the Q value of the cavity resonator is changed, the balance of matching is lost, and the reflection from the cavity resonator 5 is reflected. Produce waves. This reflected wave is sent to the microwave detector 7 via the circulator 3 and the phase is detected. For the purpose of performing this phase detection, a part of the microwave power of the microwave oscillator 1 branched by the directional coupler 2 is adjusted in phase by the phase shifter 8 provided in the bypass line, and then the microwave. Input to the detector 7.

  This bypass line is provided for the purpose of keeping the operating level of the microwave detector 7 constant regardless of the magnitude of the microwave power reflected from the cavity resonator 5. This corresponds to the bias power.

  The microwave absorption signal from the sample 6 is phase-detected, and then recorded on a recorder (not shown) through the preamplifier 9, the pan-pass filter 10, and the amplifier 11.

  In such measurement, the frequency of the microwave supplied to the cavity resonator 5 always matches the resonance frequency of the cavity resonator 5 and is constantly controlled so that no extra reflected wave is generated. Need to be. For this reason, in a normal reflection type ESR device, even if the resonance frequency of the cavity resonator 5 drifts due to an environmental change such as a temperature change, the microwave frequency automatically changes accordingly. The function to go is given. This is called AFC (automatic frequency control).

  The AFC will be described with reference to FIG. First, a modulation component is supplied from the 70 kHz modulation oscillator 12 to the microwave oscillator 1 via the amplifier 13. Based on this, frequency modulation (FM) of 70 kHz is applied to the microwave itself, and the modulated microwave is supplied to the cavity resonator 5.

  As a result, as shown in FIG. 2, when the microwave frequency matches the resonance frequency of the cavity 5 (state C), a 70 kHz component having a very small amplitude is superimposed on the reflected wave of the microwave. Only. However, when the microwave frequency is slightly shifted from the resonance frequency of the cavity resonator 5 (states B and D), a 70 kHz component having a very large amplitude is superimposed on the reflected wave of the microwave. It can be determined from the phase of the 70 kHz component whether the microwave frequency is shifted higher or lower than the resonant frequency of the cavity resonator 5.

  The reflected microwave including the 70 kHz component is detected by the microwave detector 7, amplified by the preamplifier 9, and then subjected to the phase detection of the 70 kHz component by the phase detector 16 via the bandpass filter 14 and the amplifier 15 for 70 kHz. Do.

  The phase is detected in this way, and the 70 kHz component obtained as a direct current component is fed back to the microwave oscillator 1 via the low-pass filter 17 and the adder 18 so that it becomes close to zero. A varactor diode (voltage variable capacitance element) is installed in the cavity of the microwave oscillator 1, and a microwave frequency change corresponding to the magnitude of the fed back DC voltage can be caused. Thus, even if the microwave frequency deviates from the resonance frequency of the cavity resonator 5 due to drift of the cavity resonator 5 or the like, the microwave frequency can be automatically controlled following the deviation. .

  The variation Δν of the resonance frequency of the microwave oscillator 1 is measured by the frequency counter 20. This measurement result is converted by the controller 21 into a resonance magnetic field deviation ΔH of the ESR spectrum based on the following resonance condition (1).

ΔH = (h · Δν) / (gβ) (1)
Where ΔH is the resonance magnetic field deviation, h is the Planck constant, Δν is the resonance frequency fluctuation, g is the g value of the ESR spectrum, and β is the Bohr magneton. Then, a current corresponding to the deviation of the resonance magnetic field in the ESR spectrum is added by the current control circuit 19 and supplied to the electromagnet. Thereby, the deviation of the resonance magnetic field of the ESR spectrum is superimposed on the static magnetic field and applied to the sample, and the apparent resonance position of the ESR spectrum does not cause a deviation.

  In the above embodiment, a cavity resonator is used, but a loop gap resonator or a dielectric resonator may be used instead of the cavity resonator. Further, instead of the microwave, a radio wave such as UHF, a millimeter wave such as a V band, a submillimeter wave of 300 GHz or more, or the like may be used. However, when using millimeter waves such as V-band, sub-millimeter waves of 300 GHz or more, etc., a superconducting magnet is used as a static magnetic field generation source. Must be installed in the bore of the magnet.

  Widely applicable to ESR devices.

It is a figure which shows an example of the conventional ESR apparatus. It is a figure which shows the principle of AFC. It is a figure which shows one Example of the ESR apparatus concerning this invention. It is a figure which shows another Example of the ESR apparatus concerning this invention.

Explanation of symbols

1: microwave oscillator, 2: directional coupler, 3: circulator, 4: magnetic pole, 5: cavity resonator, 6: sample, 7: microwave detector, 8: phase shifter, 9: preamplifier 10: band pass filter, 11: amplifier, 12: modulation oscillator, 13: amplifier, 14: band pass filter, 15: amplifier, 16: phase detector, 17: low pass filter, 18: adder, 19: current Control circuit, 20: frequency counter, 21 controller

Claims (3)

In an ESR apparatus in which a sample is placed in a high-frequency resonator placed in a static magnetic field, and the ESR spectrum is measured by sweeping and controlling the static magnetic field strength.
The ESR device includes an AFC circuit that feeds back a frequency fluctuation caused by a drift in the resonance frequency of the high-frequency resonator to the high-frequency oscillator and automatically corrects the oscillation frequency on the high-frequency oscillator side according to the resonance frequency of the high-frequency resonator. As well as
A part of the output of the AFC circuit is also fed back to the magnetic field control circuit that controls the static magnetic field, thereby correcting the deviation of the resonant magnetic field of the ESR spectrum accompanying the drift of the resonant frequency of the high frequency resonator. An ESR device characterized by that. In an ESR apparatus in which a sample is placed in a high-frequency resonator placed in a static magnetic field, and the ESR spectrum is measured by sweeping and controlling the static magnetic field strength.
The ESR device includes an AFC circuit that feeds back a frequency fluctuation caused by a drift in the resonance frequency of the high-frequency resonator to the high-frequency oscillator and automatically corrects the oscillation frequency on the high-frequency oscillator side according to the resonance frequency of the high-frequency resonator. As well as
A magnetic field control circuit that reads the oscillation frequency of the high-frequency oscillator automatically corrected by the AFC circuit, calculates the deviation of the resonant magnetic field of the ESR spectrum from the frequency fluctuation, and controls the static magnetic field based on the calculation result An ESR apparatus characterized by being controlled to correct a shift of a resonance magnetic field of an ESR spectrum accompanying a drift of a resonance frequency of the high-frequency resonator. The calculation is performed using the following ESR resonance conditional expression:
ΔH = (h · Δν) / (gβ)
The ESR apparatus according to claim 2, wherein the ESR apparatus is performed based on: Where ΔH is the resonance magnetic field deviation, h is the Planck constant, Δν is the resonance frequency variation, g is the g value of the ESR spectrum, and β is the Bohr magneton.

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