JP2008180510A - Resonator and electron spin resonance spectrometer - Google Patents

Abstract

PROBLEM TO BE SOLVED: To improve detection sensitivity of an ESR spectroscopic device by making a microwave resonator used in the ESR spectroscopic device more efficient.
A parallel resonant circuit 1 including a coil L and a capacitor C ₁ is connected to one end of a balanced transmission line 4 via a resonant frequency adjusting circuit 2 including capacitors C ₂ and C ₃ connected in series to the balanced transmission line 4. Connected to. The other end of the balanced transmission line 4 is connected to a balanced / unbalanced converter (balun) 5 for driving the balanced transmission line 4. Impedance matching circuit 3 including a capacitor C _M is connected in parallel to the connecting portion of the balun 5. The high frequency line 6 is connected to one end of the impedance matching circuit 3.
[Selection] Figure 1

Description

  The present invention relates to a resonator and an electron spin resonance apparatus. In particular, in an electron spin resonance (ESR) spectrometer (ESR measurement apparatus), a sample is irradiated with microwaves, and a resonance absorption spectrum due to an ESR phenomenon is obtained. The present invention relates to a microwave resonator to be measured and an electron spin resonance spectrometer using the resonator.

In general, the ESR method is an effective measurement method that can directly detect atoms and molecules having unpaired electrons using the motion of magnetic moment of electrons. The ESR method mainly includes a pulse ESR method and a continuous wave ESR method (Continuous Wave-ESR method, CW-ESR method).
In an ESR spectrometer for measuring by the ESR method, a resonator is used to measure an ESR signal by arranging a sample to be measured inside or close to the sample.
As the surface coil resonator used in the ESR spectroscope for living bodies, for example, resonators described in Non-Patent Documents 1 and 2 below are known. Further, as described in Non-Patent Documents 3 and 4 and Patent Document 1, a surface coil type resonator using a surface coil and a balanced transmission line is used for ESR measurement. In either case, the microwave is applied to the sample by applying a coil of one or more turns to the sample surface.
Non-Patent Document 5 reports a resonator that measures the vicinity of the surface of the sample in the same manner as a surface coil by bringing the surface of the sample closer to one end of a cylindrical bridge, loop, and gap resonator. . Furthermore, Non-Patent Document 6 reports a resonator in which a pinhole is provided in a cavity resonator and leakage microwaves from the pinhole are applied to the sample surface. Non-Patent Document 7 reports a probe resonator for nuclear magnetic resonance (NMR). Further, Non-Patent Document 8 discloses automatic frequency control of an ESR spectrometer. Further, Patent Document 2 describes that it is effective to perform balance-unbalance conversion using a balun in order to drive the resonator.

Nishikawa, H .; Fujii, L .; J. et al. Berliner, Hellices and Surface Coils for Low-Field in Vivo ESR and EPR Imaging Applications, Journal of Magnetic Resonance, Vol. 62, pp. 79-86 (1985). M.M. Ono, K .; Ito, N.A. Kawamura, K .; C. Hsieh, H.M. Hirata, N.A. Tsuchihashi, and H.H. Kamada, A Surface-Coil-Type Resonator for Vivo ESR Measurements, Journal of Magnetic Resonance, Series B, Vol. 104, pp. 180-182 (1994). H. Hirata, H. et al. Iwai, and M.I. Ono, Analysis of a flexible surface-coil-type resonator for magnetic resonance measurement instruments, Review of Scientific Instruments, Vol. 66, no. 9, pp. 4529-4534 (1995). H. Hirata, T .; Walczak, and H.C. M.M. Swartz, Electronically Tunable Surface-Coil-Type Resonator for L-band EPR Spectroscopy, Journal of Magnetic Resonance, Vol. 142, no. 1, pp. 159-167 (2000). S. Petryakov, M.M. Chzhan, A.M. Samoulov, G.M. He, P.A. Kuppusamy, J. et al. L. Zweier, Journal of Magnetic Resonance, Vol. 151, pp. 124-128 (2001). Toshikatsu Miki, Motohiro Ikeya, “Scanning ESR Imaging”, Keiichi Ohno, “ESR Imaging” (IPC Co., Ltd., published on May 20, 1990), Chapter 9 J. et al. Murphy-Boesch, A.M. P. Koresky, Journal of Magnetic Resonance, Vol. 54, pp. 526-532 (1983). Hiroshi Hirata and Zhi-Wei Luo, Stability Analysis and Design of Automatic Frequency Control In Vivo EPR Spectroscopy. 46, pp. 1209-1215 (2001). Japanese Patent No. 3443010 “Resonator and Electron Spin Resonance Measuring Device” (registered on June 20, 2003) Japanese Utility Model Publication No. 60-149263 "Matching circuit of nuclear magnetic resonance apparatus"

In an ESR spectrometer, a sample is irradiated with microwaves, and a resonance absorption spectrum due to the ESR phenomenon of unpaired electrons existing in the sample is measured. In ESR spectroscopy for measuring a living body, a low magnetic field of about 8 mT to 45 mT is used. The frequency of the microwave in which the ESR phenomenon occurs in this magnetic field is, for example, about 250 MHz to 1200 MHz. The ESR spectrometer using a low magnetic field has a smaller energy gap for Zeeman splitting compared to the X-band ESR spectrometer (magnetic field 0.35T, microwave frequency of about 9.5 GHz) that is widely used for analytical chemistry. It is not easy to detect spelling with high sensitivity. Therefore, it is desired to develop a spectroscopic device that improves the detection sensitivity of the spectroscopic device and can detect even smaller signals. The main factors governing the detection sensitivity of the ESR spectrometer are the noise of the spectrometer, the microwave power, the high-frequency magnetic field generation efficiency of the microwave resonator, the number of unpaired electrons in the resonator, and the like.
In view of the above points, an object of the present invention is to improve the detection sensitivity of an ESR spectrometer by making the microwave resonator used in the ESR spectrometer more efficient.
In the past, a surface coil resonator for measuring the surface of a living body used in an ESR spectroscopic device has been configured by a combination of a surface coil, a transmission line, and a resonance circuit. Accordingly, high-frequency energy is also stored in portions other than the surface coil that contacts the sample.
Therefore, an object of the present invention is to improve the detection sensitivity of an ESR spectrometer by increasing the ratio of high-frequency energy stored in a surface coil.

According to the first solution of the present invention,
A parallel resonant circuit having one or a plurality of coils arranged close to or in contact with a measurement target, and a first capacitor connected in parallel with the coils;
A balanced transmission line having first and second ends and first and second other ends;
A first resonance frequency for adjusting a resonance frequency, including second and third capacitors that connect both ends of the parallel resonance circuit and the first end and the second end of the balanced transmission line in series, respectively. An adjustment circuit;
A balanced / unbalanced converter connected to the first and second other ends of the balanced transmission line;
A connecting portion between the balanced transmission line and the balanced / unbalanced converter; a fourth capacitor connected in parallel between the first other end and the second other end of the balanced transmission line; An impedance matching circuit for matching,
A measurement signal is input to the first or second other end of the balanced transmission line and supplied from the parallel resonance circuit to the measurement target, and energy absorption in the measurement target is detected by the parallel resonance circuit and the balanced transmission is performed. A resonator is provided for measuring the electron spin resonance signal by changing the input impedance of the first or second other end of the line.

According to the second solution of the present invention,
A resonator as described above;
A high-frequency line for inputting a measurement signal to the first or second other end of the balanced transmission line of the resonator and outputting an electron spin resonance signal;
A measurement signal input from the high-frequency line is supplied from the parallel resonance circuit of the resonator to a measurement object that is close to or in contact with the parallel resonance circuit, and energy absorption at the measurement object is detected by the parallel resonance circuit. An electron spin resonance spectrometer for measuring an electron spin resonance signal is provided by changing the input impedance of the high frequency line.

According to the present invention, the following specific effects can be obtained.
(1) It is possible to provide an ESR spectroscopic device provided with a resonator having a large proportion of high-frequency energy stored in the coil section.
(2) Since the capacitor for adjusting impedance matching is located away from the coil and away from the center of the magnet, it is easy to manually adjust the capacitance of the capacitor. In addition, since the position of the adjustment capacitor is far from the sample, the degree of exposure to the modulation magnetic field applied to the sample is low, and the reverse bias voltage applied to the variable capacitance diode is affected by the modulation magnetic field. Can be prevented.
(3) By providing the capacitor at a position away from the sample, the resonance frequency can be adjusted away from the sample in the same manner as the impedance matching adjustment described in (2) above. Furthermore, by using a variable capacitor, it is possible to provide a resonator that can adjust the resonance frequency with a voltage.
(4) When measuring measurement objects such as animals and living things, it is possible to compensate for changes in resonance frequency and impedance matching due to animal movement.

1. Resonator of First Embodiment FIG. 1 shows a configuration diagram of a first embodiment of a resonator.
The resonator includes a parallel resonant circuit 1, a resonant frequency adjusting circuit 2, an impedance matching circuit 3, a balanced transmission line 4, a balanced / unbalanced converter (balun) 5, and a high frequency line 6.
Resonator of the first embodiment includes a capacitor C ₁ connected in parallel with one or more coils L constituting the parallel resonance circuit. A parallel resonant circuit 1 including a coil L and a capacitor C ₁ is connected to one end of the balanced transmission line 4 via a resonant frequency adjusting circuit 2 including capacitors C ₂ and C ₃ connected in series to the balanced transmission line 4. . The other end of the balanced transmission line 4 is connected to a balanced / unbalanced converter (balun) 5 for driving the balanced transmission line 4. Impedance matching circuit including a capacitor C _M 3 is connected in parallel across the balun 5 (connection portion of the balun 5 and balanced transmission line 4). The high frequency line 6 is connected to one end of the impedance matching circuit 3.
Since the parallel resonant circuit 1 has high impedance at the time of resonance and it is difficult to match impedance with the balanced transmission line 4 as it is, capacitors C ₂ and C ₃ are connected in series between the parallel resonant circuit 1 and the balanced transmission line 4. Do some impedance matching. For example, a pair of coaxial cables arranged in parallel can be used as the balanced transmission line 4, and the impedance matching is adjusted by setting the length to a half wavelength, an integral multiple thereof, or an arbitrary length. the capacitor C _M can be kept away from the modulation magnetic field applied to the sample. Parallel resonant circuit 2 for a coil L and a capacitor C _1, because of the balance circuit, using a balun 5 to perform the balun to achieve a balance driving. For example, the balun 5 can be a half-wave balun using a coaxial line.
Since the balanced transmission line by only the capacitor C ₂ and C ₃ connected in series to 4 impedance matching or not is not sufficient and complete, the capacitor C _M which is connected to the balun 5 to the balanced transmission line 4, further microwave Impedance matching with the high-frequency line 6 (coaxial cable, waveguide, etc.) that supplies power is realized. Capacitor C _M, for example, by combining a capacitor and trimmer capacitor and a variable capacitance diode of a fixed predetermined capacity can be constructed. In the case of a fixed capacity, for example, the capacity can be set in advance to a desired value obtained in advance by actual measurement or simulation using a predetermined ESR device.
Further, the resonance frequency can be adjusted by adjusting the capacitances of the capacitors C ₁ , C ₂ , and C ₃ . At this time, for example, a variable capacitance diode is connected to or replaced with the capacitors C ₁ , C ₂ , and C ₃ , and a circuit that adjusts the voltage at both ends of each variable capacitance diode is provided, and applied to each variable capacitance diode from the circuit It is possible to adjust the resonance frequency by changing the voltage to be applied.

2. Resonator of Second Embodiment FIG. 2 shows a configuration diagram of a resonator according to a second embodiment.
This embodiment is a resonator capable of adjusting the resonance frequency and impedance matching. In this embodiment, a resonance frequency adjusting circuit 7 including capacitors C _T1 and C _T2 is connected in series between the balun 5 and the balanced transmission line 4 in the first embodiment. In this embodiment, the resonance frequency can also be adjusted by adjusting the capacitances of the capacitors C _T1 and C _T2 . In this case, the resonance frequency adjusting circuit 7 can adjust the range in which the resonance frequency is changed by using a variable capacitance diode or a combination of a trimmer capacitor and a fixed capacitance as the capacitors C _T1 and C _T2 .

3. Adjustment of Resonant Frequency and Impedance Matching FIG. 3 shows a configuration diagram of a resonant frequency tuning circuit including a variable capacitance diode and an impedance matching circuit.
This figure shows an example of a circuit in which variable capacitors including two fixed capacitors and a variable capacitor are used as the capacitors C _T1 and C _T2 as an example. The resonance frequency adjusting circuit (tuning circuit) 7 can adjust the resonance frequency by changing the voltage V1 for adjusting the resonance frequency. The impedance matching circuit (matching circuit) 3 can adjust the impedance matching by changing the voltage V2 for impedance matching. Incidentally, the impedance matching can be adjusted by the trimmer capacitor C _M. If the configuration as shown in the figure is used, the frequency and impedance matching can be adjusted by remote control because the voltage can be adjusted. In this case, by providing an automatic control circuit for executing the resonance frequency and matching control of the resonator, these can be automatically adjusted and controlled (details will be described later).
Note that the resonance frequency adjustment circuit 2 of FIG. 1 may also be adjusted by applying the variable capacitor as described above.

4). Electron Spin Resonance Spectrometer FIG. 4 shows a configuration diagram of an electron spin resonance (ESR) spectrometer.
This ESR measurement apparatus includes a microwave oscillator 101, a resonator 102, a bridge 103, a phase detector 105, a computer 107, a low frequency oscillator 109, an automatic frequency control circuit 110, an amplifier 111, a power supply 112, a magnet 116, and a modulation coil 117. Prepare.
In the ESR spectroscopic device, a carrier frequency (for example, continuous wave) is incident on the resonator 102 main body via a high-frequency line 6 (for example, a coaxial cable, a waveguide, or the like). The resonator 102 is adjusted so as to be matched when electron spin resonance does not occur. At this time, reflection does not occur if the resonator 102 is matched. On the other hand, when electron spin resonance occurs in the measurement target (sample) in contact with the surface coil L of the resonator 102, the input impedance of the resonator 102 changes. Then, matching is lost and a reflected wave from the resonator 102 is generated. The ESR signal is measured by receiving this reflected wave with the ESR spectroscope.

Details of the operation will be described below.
The resonator 102 corresponds to the resonator shown in the first and second embodiments. The microwave output from the microwave oscillator 101 is applied to the resonator 102 from the bridge 103 via the high-frequency line 6 shown in FIG. The impedance matching of the resonator 102 is adjusted, and the reflected microwave returns from the resonator 102 to the bridge 103 again, and is detected by the envelope line inside the bridge 103. The modulation signal output from the low frequency oscillator 109 is amplified by the amplifier 111 and applied to the modulation coil 117. When the electron spin resonance phenomenon occurs, the microwave reflected from the resonator 102 is amplitude-modulated by the perturbation of the modulation magnetic field generated by the modulation coil 117. By detecting the signal subjected to the envelope detection by the phase detector 105, the first derivative spectrum of the electron spin resonance absorption curve can be obtained. The computer 107 acquires the primary partial spectrum from the phase detector 105 and controls the power source 112 that controls the amplitude of the low frequency oscillator 109 and the current supplied to the magnet 116.
The sine wave signal of the oscillator inside the automatic frequency control circuit 110 is applied to the microwave oscillator 101, and the signal output from the microwave oscillator 101 is frequency-modulated. The microwave is also reflected by the resonator 102 by this frequency modulation. The signal detected inside the bridge 103 is sent to the automatic frequency control circuit 110 for phase detection. The output of the phase detection circuit in the automatic frequency control circuit 110 is superimposed on the modulation signal (sine wave) applied to the microwave oscillator 101. When the phase of the automatic frequency control circuit 110 is adjusted so that the difference between the microwave frequency (frequency of the microwave oscillator 101) and the resonance frequency of the resonator 102 becomes small, negative feedback control is realized, and the frequency of the microwave oscillator 101 is changed. The resonance frequency of the resonator 102 can be synchronized. The technique of automatic frequency control is a well-known technique and is described in Non-Patent Document 8, for example.

FIG. 5 shows a configuration diagram of an electron spin resonance (ESR) spectrometer including automatic tuning control (ATC) and automatic matching control (AMC).
This ESR spectroscopic apparatus is further provided with an automatic tuning control circuit 121 and an automatic matching control circuit 122 in addition to the ESR spectroscopic apparatus shown in FIG. The automatic tuning control circuit 121 outputs a frequency adjustment voltage V1, and the automatic matching control circuit 122 outputs a matching adjustment voltage V2. For example, the resonator 102 shown in FIG. 3 can be used.
In such an ESR spectrometer, the detection signal branched from the bridge 103 is input to the automatic tuning control circuit 121. The gain and phase characteristics of the automatic tuning control circuit 121 are adjusted so that the resonance frequency of the resonator 102 is synchronized with the frequency of the microwave transmitter 101, thereby realizing negative feedback control. Similarly, the detection signal branched from the bridge 103 is input to the automatic matching control circuit 122, and negative feedback control is performed so that the impedance of the resonator 102 matches the characteristic impedance of the transmission line. At this time, voltages output from the automatic tuning control circuit 121 and the automatic matching control circuit 122 are respectively applied to the variable capacitance diodes used as part of the tuning circuit 7 and the matching circuit 3 of the resonator 102 ( (Refer to FIG. 3 and the explanation thereof).

5. Advantages of the present invention / embodiment According to the present embodiment, the following remarkable effects can be obtained.
(1) It is possible to provide an ESR spectroscopic device provided with a resonator having a large proportion of high-frequency energy stored in the coil section. A resonator using a one-turn coil having a diameter of 10 mm (resonance frequency: 1180 MHz, no load Q 380) and a balanced transmission line having a half-wavelength was manufactured as a prototype with the configuration shown in FIG. When the generation efficiency of the high-frequency magnetic field was determined by a perturbation method using a metal sphere, the efficiency was 126 μT / W ^1/2 . Further, when the efficiency of the surface coil resonator described in Non-Patent Document 4 (resonance frequency 1130 MHz, no-load Q 262, single-turn coil diameter 10 mm) was measured, the generation efficiency of the high-frequency magnetic field was 44 μT / W ^1/2. Met. The generation efficiency of the high frequency magnetic field was improved by about 2.9 times. Since the signal strength of the ESR spectrum is proportional to the square of the generation efficiency of the high-frequency magnetic field, the signal strength of the spectrum is expected to increase by about 8 times. From this experimental result, it is shown that the detection sensitivity of the ESR spectroscopic device is improved about 8 times in the sample with a small loss by increasing the efficiency of the resonator.
(2) the capacitor C _M for adjusting the impedance matching is in a position away from the coil, because apart from the center of the magnet, it is easy to manually adjust the capacitance of the capacitor C _M. Capacitor C _M or, in the case of using a variable capacitor as part of the capacitor C _M, since the position of the capacitor C _M from the sample are separated, low degree of exposure to the modulation magnetic field applied to the sample, variable It is possible to prevent the reverse bias voltage applied to the capacitor diode from being influenced by the modulation magnetic field.
(3) By providing the capacitor at a position away from the sample, the resonance frequency can be adjusted at a position away from the sample as in the impedance matching adjustment described above. Furthermore, by using a variable capacitor, it is possible to provide a resonator that can adjust the resonance frequency with a voltage.
(4) When measuring an animal or the like, it is possible to provide an ESR spectrometer capable of compensating for changes in resonance frequency and impedance matching due to animal movement.

Next, an embodiment of the present invention will be compared with a probe resonator for nuclear magnetic resonance (NMR) described in Non-Patent Document 7. The probe resonator described in Non-Patent Document 7 has an embodiment shown in FIG. As an equivalent circuit, FIG. 3b and FIG. 3c is shown. A capacitor connected in series (C _{2 in the} non-patent document FIG. ₃ ) is used for adjusting impedance matching, and a capacitor C ₁ connected in parallel to the sample coil L is used for adjusting resonance frequency. . On the other hand, in this embodiment, when adjusting the impedance matching by using the capacitor C _M connected in parallel between the balanced transmission lines and the balun is a Non-Patent Document 7 different.
Also, the capacitors C _T1 and C _T2 shown in FIG. 2 of the present application are connected to the capacitors C ₂ and C ₃ via balanced transmission lines for the purpose of adjusting the resonance frequency. In the probe circuit described in Non-Patent Document 7, the resonance frequency is adjusted by adjusting a capacitor connected in parallel with the sample coil. In the electron spin resonance spectrometer, since the microwave frequency to be used is higher than that of NMR, if the adjustment work is performed near the coil, the resonance frequency and impedance matching are affected. Therefore, it is practically desirable that the resonance frequency and impedance matching can be adjusted at a location away from the coil. In particular, the configuration of the embodiment of the present invention shown in FIG. 2 can provide a resonator that can solve such a problem. In the configuration of the embodiment of the present invention shown in FIG. 1, impedance matching can be mainly adjusted at a location away from the coil.

The present invention can be appropriately applied to a microwave including VHF, UHF, SHF, and the like. In addition, when detecting a spin resonance signal, the present invention can be applied to the case where a magnetic field sweep or a frequency sweep is used.
Furthermore, the present invention can be applied to a wide range of ESR methods such as chemistry, physics, biology, and medicine. Moreover, it can utilize for various ESR methods, such as a pulse ESR method and a continuous wave ESR method.

The block diagram of 1st Embodiment of a resonator. The block diagram of 2nd Embodiment of a resonator. The block diagram of the resonant frequency tuning circuit and impedance matching circuit containing a variable capacity diode. The block diagram of an electron spin resonance (ESR) spectrometer. 1 is a configuration diagram of an electron spin resonance (ESR) spectrometer including automatic tuning control and automatic matching control.

Explanation of symbols

1 Parallel resonant circuit 2, 7 Resonance frequency adjustment circuit 3 Impedance matching circuit 4 Balanced transmission line 5 Balanced / unbalanced converter (balun)
6 High frequency lines

Claims (8)

A parallel resonant circuit having one or a plurality of coils arranged close to or in contact with a measurement target, and a first capacitor connected in parallel with the coils;
A balanced transmission line having first and second ends and first and second other ends;
A first resonance frequency for adjusting a resonance frequency, including second and third capacitors that connect both ends of the parallel resonance circuit and the first end and the second end of the balanced transmission line in series, respectively. An adjustment circuit;
A balanced / unbalanced converter connected to the first and second other ends of the balanced transmission line;
A connecting portion between the balanced transmission line and the balanced / unbalanced converter; a fourth capacitor connected in parallel between the first other end and the second other end of the balanced transmission line; An impedance matching circuit for matching,
A measurement signal is input to the first or second other end of the balanced transmission line and supplied from the parallel resonant circuit to the measurement target, and energy absorption in the measurement target is detected by the parallel resonant circuit and the balanced A resonator for measuring an electron spin resonance signal by changing the input impedance of the first or second other end of the transmission line.   2. The resonator according to claim 1, wherein the impedance matching circuit further includes a variable capacitance diode in parallel with the fourth capacitor, and adjusts an impedance by adjusting a voltage applied to the variable capacitance diode.   The resonator according to claim 1, wherein the resonance frequency is adjusted by adjusting capacitances of the second and third capacitors of the first resonance frequency adjustment circuit.   The resonator according to any one of claims 1 to 3, further comprising a second resonance frequency adjusting circuit for adjusting a resonance frequency in series between the other end of the balanced transmission line and the impedance matching circuit. .   The second resonance frequency adjustment circuit includes a variable capacitance capacitor including a variable capacitance diode and a capacitor, and adjusts a voltage applied to the variable capacitance diode to adjust a capacitance of the variable capacitance capacitor, thereby adjusting a resonance frequency. The resonator according to claim 4, wherein: A resonator according to any one of claims 1 to 5;
A high-frequency line for inputting a measurement signal to the first or second other end of the balanced transmission line of the resonator and outputting an electron spin resonance signal;
A measurement signal input from the high-frequency line is supplied from the parallel resonance circuit of the resonator to a measurement object that is close to or in contact with the parallel resonance circuit, and energy absorption at the measurement object is detected by the parallel resonance circuit. An electron spin resonance spectrometer for measuring an electron spin resonance signal by changing the input impedance of the high-frequency line.   An electron spin resonance spectrometer further comprising an automatic tuning control circuit that outputs a frequency adjustment voltage for adjusting the resonance frequency adjustment circuit of the resonator.   An electron spin resonance spectrometer further comprising an automatic matching control circuit that outputs a matching adjustment voltage for adjusting the impedance matching circuit of the resonator.

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