Microwave control method and microwave controller for electron paramagnetic spectrometer

Abstract

The invention provides a microwave control method and a microwave controller for an electron paramagnetic spectrometer. The microwave control method for the electron paramagnetic spectrometer comprises the following steps: controlling a microwave source to generate a microwave signal for paramagnetic resonance detection; a first power division signal and a second power division signal are obtained through distribution; inputting the first power division signal into a resonant cavity, detecting a reflection signal of the resonant cavity after resonance absorption of the to-be-detected sample to obtain a first detection signal, and performing phase shift on the second power division signal to obtain an orthogonal local oscillation signal; performing frequency mixing on the first detection signal and the local oscillator signal to obtain an I down-conversion signal and a Q down-conversion signal; performing data processing to obtain detection result information; and error analysis is performed and the microwave source is corrected, so that the frequency of the output microwave signal is kept at the first working frequency. By establishing a feedback loop from output to microwave signal input of the microwave source, feedback control of microwave signals is realized, and high-precision microwave control in the electron paramagnetic spectrometer is further realized.

Description

Technical Field

[0001] This invention relates to the field of electron paramagnetic resonance technology, and more particularly to a microwave control method and microwave controller for an electron paramagnetic spectrometer. Background Technology

[0002] Electron paramagnetic resonance (EPR) is a spectroscopic technique used to study matter with unpaired electrons, and it is the only technique that can specifically identify the structure of free radicals. Based on EPR technology, electron paramagnetic spectrometers have been developed to study samples with paramagnetic moments, especially those with unpaired electrons.

[0003] To achieve accurate identification of free radicals, multiple high-precision systems need to work together. The microwave controller needs to generate high-precision, low-phase-noise radio frequency signals and acquire the obtained signals at high resolution. Currently proposed electron paramagnetic resonance (EPR) microwave control typically employs open-loop control. The frequency and power of its microwave source are easily affected by external interference, causing drift and affecting key parameters such as the resonant frequency and phase in the resonant cavity. Therefore, it cannot achieve high resolution and accuracy, and cannot meet the requirements for high-precision free radical detection.

[0004] Therefore, existing technologies still need to be improved and developed. Summary of the Invention

[0005] In view of the shortcomings of the prior art, the purpose of this invention is to provide a microwave control method and a microwave controller for an electron paramagnetic spectrometer, so as to solve the problem that the existing microwave control methods for electron paramagnetic spectrometers have low microwave output accuracy and low resolution, and cannot be used to achieve high-precision detection of free radicals.

[0006] The technical solution of the present invention is as follows: In a first aspect, the present invention provides a microwave control method for an electron paramagnetic spectrometer, comprising the following steps: A microwave source is controlled to generate a microwave signal for paramagnetic resonance detection, wherein the frequency of the microwave signal is a first operating frequency; The microwave signal is power-divided to obtain a first power-divided signal and a second power-divided signal; the first power-divided signal is input into the resonant cavity, and the microwave reflection signal after the sample under test undergoes resonant absorption in the resonant cavity is detected to obtain a first detection signal; the second power-divided signal is used for phase shifting to obtain a local oscillator signal orthogonal to the first power-divided signal; The first detection signal and the local oscillator signal are acquired, and the first detection signal and the local oscillator signal are mixed to obtain the I down-converted signal and the Q down-converted signal; The I down-conversion signal and Q down-conversion signal are sampled and processed to obtain the original baseband signal, and the detection result information is restored. Based on the original baseband signal, determine whether the frequency of the microwave signal has shifted, and correct the microwave source for the shift so that the frequency of the output microwave signal remains at the first operating frequency.

[0007] A further provision of the present invention includes the step of sampling and processing the I-down-converted signal and the Q-down-converted signal to obtain the original baseband signal, and then restoring the detection result information, comprising: The I down-converted signal and the Q down-converted signal are low-pass filtered to obtain the I signal baseband component and the Q signal baseband component. The I signal baseband component and the Q signal baseband component are sampled and processed to obtain the original baseband signal, which is used to reconstruct the detection result information.

[0008] A further provision of the present invention, after the step of controlling a microwave source to generate a microwave signal for paramagnetic resonance detection, wherein the microwave signal is a first operating frequency, further includes: The signal strength of the microwave signal is attenuated. The microwave signal after attenuation control is amplified with low noise. The signal power of the amplified microwave signal is located in the target signal power range, which is used to improve the signal-to-noise ratio.

[0009] A further provision of the present invention includes power distribution of the microwave signal to obtain a first power-divided signal and a second power-divided signal; the first power-divided signal is input into the resonant cavity, and the microwave reflection signal after the sample under test undergoes resonant absorption in the resonant cavity is detected to obtain a first detection signal; the second power-divided signal is used for phase shifting to obtain a local oscillator signal orthogonal to the first power-divided signal, comprising the following steps: The microwave signal is distributed into a first power-divided signal on a first power-divided path and a second power-divided signal on a second power-divided path by a power divider; In the first power divider, the sample to be tested is placed in the resonant cavity, and the sample to be tested is detected in conjunction with the first power divider signal; The first detection signal is obtained by detecting the reflected signal of the resonant cavity after the sample under test undergoes resonant absorption; On the second power divider, the second power divider signal is phase-shifted to obtain a local oscillator signal with a phase difference of 90 degrees from the first detection signal. The local oscillator signal is used to perform quadrature modulation on the first detection signal.

[0010] In a further embodiment of the present invention, the first operating frequency is an X-band frequency.

[0011] A further provision of the present invention includes the step of determining whether the frequency of the microwave signal has shifted based on the original baseband signal, and correcting the microwave source to maintain the frequency of the output microwave signal at the first operating frequency. Acquire the original baseband signal; Determine whether the frequency of the microwave signal is equal to the resonant frequency of the cavity based on the original baseband signal waveform; If the frequency of the microwave signal is not equal to the resonant frequency of the cavity, the microwave source control signal with the first working frequency is adjusted according to the error to correct the frequency of the output microwave signal.

[0012] A further provision of the present invention involves sampling and processing the I-signal baseband component and the Q-signal baseband component to obtain the original baseband signal. The step of using the original baseband signal to reconstruct the detection result information includes: The baseband components of the I signal and the baseband components of the Q signal are sampled by analog and digital methods to obtain the digital components of the I signal and the Q signal. The I signal digital component is used to represent the real part of the signal, and the Q signal digital component is used to represent the imaginary part of the signal. The amplitude and phase of the original baseband signal are obtained by reconstructing the real and imaginary parts of the signal. The original baseband signal is obtained based on the amplitude and phase of the original baseband signal.

[0013] Secondly, the present invention provides a microwave controller for implementing the microwave control method for an electron paramagnetic spectrometer described above; the microwave controller includes: a microwave source, a power divider, a phase shifter, a circulator, a resonant cavity, an I / Q mixer, and a measurement and control board; wherein... The output terminal of the microwave source is connected to the input terminal of the power divider, and is used to output a microwave signal with a frequency of the first operating frequency to the power divider. The first branch of the power divider is connected to the phase shifter, and the second branch of the power divider is connected to the input of the circulator. It is used to divide the microwave signal into a first power divided signal and a second power divided signal with the same power, and output the first power divided signal to the circulator and the second power divided signal to the phase shifter. The phase shifter is connected to the local oscillator signal terminal of the I / Q mixer and is used to phase shift the second power division signal to obtain a local oscillator signal orthogonal to the first power division signal, and output the local oscillator signal to the I / Q mixer. The circulator's sample detection terminal is connected to the resonant cavity, and the circulator's signal output terminal is connected to the radio frequency signal terminal of the I / Q mixer, for outputting the first power-divided signal to the resonant cavity; the resonant cavity is used to place the sample under test and to acquire and output the first detection signal to the circulator; the circulator outputs the first detection signal to the I / Q mixer; The baseband signal terminal of the I / Q mixer is connected to the signal acquisition terminal of the measurement and control board, and is used to mix the first detection signal and the local oscillator signal, and output the I down-converted signal and the Q down-converted signal to the measurement and control board. The signal output terminal of the measurement and control board is connected to the control terminal of the microwave source. It is used to process the I down-conversion signal and the Q down-conversion signal to obtain detection result information, and to determine whether the frequency of the microwave signal has shifted based on the original baseband signal, and to correct the microwave source for the shift.

[0014] A further embodiment of the present invention includes an attenuator and a low-noise amplifier; wherein the attenuator and the low-noise amplifier are located between the microwave source and the power divider; the input terminal of the attenuator is connected to the output terminal of the microwave source, and the output terminal of the attenuator is connected to the input terminal of the low-noise amplifier, for reducing the signal strength of the microwave signal; the output terminal of the low-noise amplifier is connected to the input terminal of the power divider, for amplifying the microwave signal and improving the signal-to-noise ratio of the microwave signal.

[0015] In a further embodiment of the present invention, the measurement and control board includes an FMC function daughter card, an FPGA daughter card, and a carrier board; wherein, The FMC function sub-card and the FPGA sub-card are respectively inserted on the carrier board. The FMC function sub-card is equipped with a signal acquisition module, an automatic frequency control module and a waveform generation module. The signal acquisition module is used to acquire the I down-converted signal and the Q down-converted signal in the I / Q mixer through the carrier board, perform analog-to-digital conversion and output the digital components of the I signal and the digital components of the Q signal to the FPGA sub-card. The input terminal of the automatic frequency control module is connected to the I / Q mixer, and the output terminal of the automatic frequency control module is connected to the waveform generation module. It is used to acquire the original baseband signal and determine whether the frequency of the microwave signal is equal to the resonant frequency of the cavity based on the waveform of the original baseband signal. If the frequency of the microwave signal is not equal to the resonant frequency of the cavity, an error signal is output to the waveform generation module based on the error. The waveform generation module is connected to the control terminal of the microwave source through the carrier board, and is used to output a microwave source control signal of the first operating frequency to the microwave source according to the error signal; The FPGA daughter card is equipped with a signal processing module, which is used to perform data processing and I / Q demodulation on the I down-conversion signal and the Q down-conversion signal to obtain detection result information; The carrier board is connected to the baseband signal terminal of the I / Q mixer, and is used to receive the I down-converted signal and the Q down-converted signal in the I / Q mixer and output the I down-converted signal and the Q down-converted signal to the FMC function sub-card 93, and is used to communicate with an external host computer in real time to transmit the detection result information.

[0016] This invention provides a microwave control method and a microwave controller for an electron paramagnetic spectrometer. The microwave control method for the electron paramagnetic spectrometer includes the following steps: controlling a microwave source to generate a microwave signal for paramagnetic resonance detection, wherein the frequency of the microwave signal is a first operating frequency; performing power distribution on the microwave signal to obtain a first power-divided signal and a second power-divided signal; inputting the first power-divided signal into a resonant cavity and detecting the microwave reflection signal after the sample under test undergoes resonant absorption in the resonant cavity to obtain a first detection signal; using the second power-divided signal for phase shifting to obtain a local oscillator signal orthogonal to the first power-divided signal; acquiring the first detection signal and the local oscillator signal, and mixing the first detection signal and the local oscillator signal to obtain an I-down-conversion signal and a Q-down-conversion signal; sampling and processing the I-down-conversion signal and the Q-down-conversion signal to obtain the original baseband signal, and restoring the detection result information; determining whether the frequency of the microwave signal has shifted based on the original baseband signal, and correcting the microwave source for the shift to maintain the frequency of the output microwave signal at the first operating frequency. In this invention, a feedback loop is established between the output and the microwave signal input from the microwave source to achieve feedback control of the microwave signal, thereby realizing high-precision and high-resolution control of the microwave in the electron paramagnetic spectrometer. Attached Figure Description

[0017] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on the structures shown in these drawings without creative effort.

[0018] Figure 1 This is a flowchart of the steps of the microwave control method for an electron paramagnetic spectrometer in this invention.

[0019] Figure 2 This is a schematic diagram of the connection relationship of the microwave controller in this invention.

[0020] Figure 3 This is a schematic diagram of the measurement and control board in this invention.

[0021] Figure 4 This is a schematic diagram of the internal modules of the FMC function sub-card in this invention.

[0022] The labels in the attached diagram are as follows: 1. Microwave source; 2. Attenuator; 3. Low-noise amplifier; 4. Power divider; 5. Circulator; 6. Resonant cavity; 7. Phase shifter; 8. I / Q mixer; 9. Measurement and control board; 91. Carrier board; 92. FPGA daughter card; 93. FMC function daughter card; 931. Signal acquisition module; 932. Waveform generation module; 933. Automatic frequency control module; 934. FMC interface; 94. External interface. Detailed Implementation

[0023] This invention provides a microwave control method and a microwave controller for an electron paramagnetic spectrometer. To make the objectives, technical solutions, and effects of this invention clearer and more explicit, the invention is further described in detail below with reference to the accompanying drawings and examples. It should be understood that the specific embodiments described herein are merely illustrative and not intended to limit the invention.

[0024] In the implementation methods and claims, unless otherwise specified in the text, the terms "a," "an," "the," and "the" may also include plural forms. If the embodiments of the present invention involve descriptions of "first," "second," etc., such descriptions are for descriptive purposes only and should not be construed as indicating or implying their relative importance or implicitly specifying the number of indicated technical features. Therefore, a feature defined with "first" or "second" may explicitly or implicitly include at least one of those features.

[0025] It should be further understood that the term "comprising" as used in this specification means the presence of the stated features, integers, steps, operations, elements, and / or components, but does not exclude the presence or addition of one or more other features, integers, steps, operations, elements, components, and / or groups thereof. It should be understood that when we say an element is "connected" or "coupled" to another element, it can be directly connected or coupled to the other element, or there may be intermediate elements. Furthermore, "connected" or "coupled" as used herein can include wireless connections or wireless coupling. The term "and / or" as used herein includes all or any unit and all combinations of one or more associated listed items.

[0026] It will be understood by those skilled in the art that, unless otherwise defined, all terms used herein (including technical and scientific terms) have the same meaning as commonly understood by one of ordinary skill in the art to which this invention pertains. It should also be understood that terms such as those defined in general dictionaries should be understood to have the same meaning as in the context of the prior art, and should not be interpreted in an idealized or overly formal sense unless specifically defined as herein.

[0027] Furthermore, the technical solutions of the various embodiments can be combined with each other, but only if they are feasible for those skilled in the art. If the combination of technical solutions is contradictory or cannot be implemented, it should be considered that such combination of technical solutions does not exist and is not within the scope of protection claimed by this invention.

[0028] Electron paramagnetic resonance (EPR) is a spectroscopic technique used to study substances with unpaired electrons, and it is the only technique capable of specifically identifying free radical structures. To achieve effective free radical identification, multiple high-precision systems need to work together. The inventors have found that existing EPR spectrometers mainly consist of a microwave detection and control system, a microwave and magnet system, a sample introduction and excitation system, and a control and data analysis system. The microwave detection and control system generates a high-precision radio frequency signal input to the magnet system, where a probe carrying a sample microwave resonator is exposed to the background magnetic field of the magnet system. Subsequently, the sample introduction and excitation system transports the sample and generates laser pulses. The resulting microwave signal is then detected and acquired by the microwave detection and control system, and finally transmitted to the control and data analysis system. Based on the microwave signal emitted by the sample, a microwave signal characterizing the sample's features can be obtained, particularly regarding its chemical state and molecular environment. Existing EPR microwave control typically employs open-loop control, making the microwave source's frequency and power susceptible to external interference, causing drift and affecting key parameters such as the resonant frequency and phase in the resonant cavity. In existing microwave control methods, phase-sensitive detection can achieve high sensitivity, but its time resolution is low. Direct detection methods, on the other hand, cannot completely separate 1 / f noise, and while they can achieve high time resolution, their sensitivity is extremely low. This makes it impossible to simultaneously achieve high-resolution and high-precision detection, thus failing to meet the requirements for high-precision free radical detection.

[0029] To solve the above-mentioned technical problems, the present invention provides a microwave control method for an electron paramagnetic spectrometer, comprising the following steps: S100. Control the microwave source to generate a microwave signal for paramagnetic resonance detection, wherein the frequency of the microwave signal is a first operating frequency.

[0030] The system controls a microwave source to generate a stable microwave signal for paramagnetic resonance (PMR) detection. Specifically, the microwave signal is selected at a first operating frequency, which can be an X-band frequency. For example, the microwave signal can be a signal with an X-band frequency. Specifically, a microwave band of 8-12 GHz can be selected. The frequency and amplitude of the microwave signal output by the microwave source change accordingly based on the frequency, amplitude, and phase of the input signal at the control terminal. Therefore, the microwave signal output by the microwave source can be indirectly controlled by controlling the input signal at the control terminal of the microwave source.

[0031] In another preferred embodiment of the present invention, after the step of controlling a microwave source to generate a microwave signal for paramagnetic resonance detection, wherein the microwave signal is a first operating frequency, the method further includes: M100, Attenuation control is applied to the signal strength of the microwave signal; M200 performs low-noise amplification on the microwave signal after attenuation control is completed. The signal power of the amplified microwave signal is located in the target signal power range, which is used to improve the signal-to-noise ratio.

[0032] To further improve the operational stability of the microwave signal and reduce noise introduction to enhance the signal-to-noise ratio (SNR), the microwave signal output from the microwave source undergoes further processing. First, the microwave signal is attenuated. Exemplarily, this can be achieved using any existing attenuator model. This attenuation adjusts the signal strength and power, preventing signal overload and protecting the equipment from damage, while simultaneously optimizing the microwave signal transmission in subsequent circuits and improving impedance matching. Preferably, the attenuation range is 0-40 dB. Further, the attenuated microwave signal undergoes low-noise amplification. This low-noise amplification enhances the weak microwave signal while reducing its own noise, thereby improving the system's SNR and overall performance. This low-noise amplification can be achieved using a low-noise amplifier (LNA) in the system. Since ordinary amplifiers increase signal noise, using a low-noise amplifier amplifies the signal while introducing as little noise as possible, achieving a noise figure of approximately 0.5 dB, thus improving the overall sensitivity of the paramagnetic resonance system. The target signal power range is preferably -70 dBm to -50 dBm, with a SNR better than 30 dB.

[0033] S200. The microwave signal is power-divided to obtain a first power-divided signal and a second power-divided signal; the first power-divided signal is input into the resonant cavity, and the microwave reflection signal after the sample under test undergoes resonant absorption in the resonant cavity is detected to obtain a first detection signal; the second power-divided signal is used for phase shifting to obtain a local oscillator signal orthogonal to the first power-divided signal.

[0034] Further, the microwave signal is power-divided to obtain a first power-divided signal and a second power-divided signal; the first power-divided signal is input into the resonant cavity, and the microwave reflection signal after the sample under test undergoes resonant absorption in the resonant cavity is detected to obtain a first detection signal; the second power-divided signal is used for phase shifting to obtain a local oscillator signal orthogonal to the first power-divided signal, including the following steps: S210. The microwave signal is distributed into a first power-divided signal on a first power-divided branch and a second power-divided signal on a second power-divided branch using a power divider. S220. On the first power divider circuit, the sample to be tested is placed in the resonant cavity, and the sample to be tested is detected in conjunction with the first power divider signal. S230. Detect the reflected signal of the resonant cavity after the sample under test undergoes resonant absorption to obtain the first detection signal; S240. On the second power divider branch, the second power divider signal is phase-shifted to obtain a local oscillator signal with a phase difference of 90 degrees from the first detection signal. The local oscillator signal is used to perform quadrature modulation on the first detection signal.

[0035] The microwave signal is split into two paths, a first power-divided signal and a second power-divided signal, through power distribution. The first and second power-divided signals are processed separately in each path. In some preferred embodiments, the signal power of the first and second power-divided signals is the same, and the phase, amplitude, and frequency of the first and second power-divided signals are also equal. The first power-divided signal is used for paramagnetic resonance detection, and the signal detection result fed back by the sample after paramagnetic resonance detection is used as the first detection signal. The first detection signal contains information such as the concentration of free radicals, which can be used to characterize the chemical structure of the sample. In the other branch, the second power-divided signal is phase-shifted, and the resulting local oscillator signal is orthogonal to the first power-divided signal.

[0036] S300: Acquire the first detection signal and the local oscillator signal, and mix the first detection signal and the local oscillator signal to obtain the I down-converted signal and the Q down-converted signal.

[0037] The first detection signal is a radio frequency signal. The first detection signal, which is orthogonal to each other, is mixed with the local oscillator signal to generate an I down-converted signal and a Q down-converted signal as output signals. The I down-converted signal and the Q down-converted signal have the same spectral structure as the first detection signal. Therefore, the I down-converted signal and the Q down-converted signal carry the detection information of the sample to be tested.

[0038] S400: Sample and process the I down-converted signal and Q down-converted signal to obtain the original baseband signal, and restore the detection result information.

[0039] The I-down-converted signal and Q-down-converted signal are sampled and processed. For example, the detection result information, which includes free radical structure information in the sample under test, is restored and extracted from the original baseband signal. For example, further I / Q demodulation of the I-down-converted signal and Q-down-converted signal may be performed to restore two orthogonal signals representing the real and imaginary parts of the signal, thereby restoring the detection result of the original baseband signal. In some cases, the EPR signal obtained from paramagnetic resonance is often weak and difficult to observe. Therefore, the signal can be amplified with low noise first, while minimizing its own introduced noise, thereby further improving the signal-to-noise ratio and system sensitivity. Specifically, the I-down-converted signal and Q-down-converted signal, or the processed original baseband signal, are amplified with low noise to achieve signal amplification and noise reduction for further signal processing.

[0040] In some preferred embodiments of the present invention, the step of sampling and processing the I down-converted signal and the Q down-converted signal to obtain the original baseband signal and then restoring the detection result information includes: S410. Perform low-pass filtering on the I down-converted signal and the Q down-converted signal to obtain the I signal baseband component and the Q signal baseband component. S420. The I signal baseband component and the Q signal baseband component are sampled and processed to obtain the original baseband signal, which is used to restore the detection result information.

[0041] Further, the steps of sampling and processing the I-signal baseband component and the Q-signal baseband component to obtain the original baseband signal, and using the original baseband signal to reconstruct the detection result information, include: S421. Perform analog-to-digital sampling on the I signal baseband component and the Q signal baseband component to obtain the I signal digital component and the Q signal digital component; S422, The digital component of the I signal is used to represent the real part of the signal, and the digital component of the Q signal is used to represent the imaginary part of the signal. The amplitude and phase of the original baseband signal are obtained by restoring the real part and the imaginary part of the signal. S423. Obtain the original baseband signal based on the amplitude and phase of the original baseband signal.

[0042] Specifically, the signal value s(t) of the original baseband signal at a certain moment can be expressed as:

[0043] Where A(t) is the amplitude of the original baseband signal as a function of time, φ(t) is the phase of the original baseband signal as a function of time, and f c If the carrier frequency is used, then the original baseband signal can be decomposed into two independent modulation signals that are orthogonal to each other:

[0044] Where I(t) is the I-signal baseband component of the instantaneous signal value of the original baseband signal, and Q(t) is the Q-signal baseband component. The I-signal baseband components and the Q-signal baseband components are orthogonal, therefore:

[0045]

[0046] Therefore, the original baseband signal can be indirectly obtained by acquiring the I-signal baseband components and Q-signal baseband components of the original baseband signal. During the I / Q demodulation of the first detection signal and the local oscillator signal, one I-signal baseband component and one Q-signal baseband component are obtained respectively. The I-signal baseband component and the Q-signal baseband component represent the real and imaginary parts of the original baseband signal, respectively. Therefore, the amplitude and phase of the original baseband signal, i.e., the first detection signal, can be deduced and reconstructed from the I-signal baseband components and the Q-signal baseband components. The amplitude of the original baseband signal is:

[0047] The phase of the original baseband signal is:

[0048] Since the amplitude and phase of the original baseband signal are determined by the modulation signal, i.e. the first detection signal, the original baseband signal can be derived by using the demodulated I signal baseband component and Q signal baseband component. The original baseband signal contains information about the first detection signal, which can then be used to obtain detection results with high time resolution and high sensitivity.

[0049] S500. Determine whether the frequency of the microwave signal has shifted based on the original baseband signal, and correct the microwave source for the shift so that the frequency of the output microwave signal remains at the first operating frequency.

[0050] Further, the step of determining whether the frequency of the microwave signal has shifted based on the original baseband signal, and correcting the microwave source to maintain the frequency of the output microwave signal at the first operating frequency, includes: S510. Acquire the original baseband signal; S520. Determine whether the frequency of the microwave signal is equal to the resonant frequency of the cavity based on the original baseband signal waveform. S530. If the frequency of the microwave signal is not equal to the resonant frequency of the cavity, adjust the microwave source control signal of the first working frequency according to the error to correct the frequency of the output microwave signal.

[0051] Specifically, the original baseband signal is obtained based on the baseband components of the I and Q signals. This original baseband signal includes the signal information acquired from the resonant cavity, as well as information such as waveform amplitude. Therefore, automatic frequency control can be performed on the original baseband signal.

[0052] For example, the automatic frequency control (AFC) module is used to automatically control the frequency of the microwave source based on the original baseband signal. It superimposes an 83.3 kHz square wave as a frequency modulation signal onto the original baseband signal frequency at the first operating frequency. The output signal frequency is then either v0 + 83.3 kHz or v0 - 83.3 kHz, where v0 is the cavity resonant frequency, which is selected from the first operating frequency, i.e., the X-band frequency. The actual microwave source output frequency fluctuates back and forth. Because this frequency fluctuates around the cavity resonant frequency, the amplitude of the final detected signal will also fluctuate. Since the frequency fluctuation is symmetrical about v0, the amplitude fluctuation is symmetrical. When the microwave frequency deviates from the cavity resonant frequency, the amplitude near the resonant frequency increases, while the amplitude far from the resonant frequency decreases, thus becoming asymmetrical. Using a pre-set frequency modulation signal as a reference signal, the output signal modulated by automatic frequency control is used as a detection signal. Multiplying and integrating the detection signal with the reference signal yields an error signal, which is proportional to the degree of frequency offset. The waveform generator adjusts the frequency of the output microwave source control signal based on the input value of the error signal, thereby achieving frequency feedback control.

[0053] Based on the same inventive concept, the present invention also provides a microwave controller for implementing the microwave control method for an electron paramagnetic spectrometer described above. The microwave controller includes: a microwave source 1, a power divider 4, a phase shifter 7, a circulator 5, a resonant cavity 6, an I / Q mixer 8, and a measurement and control board 9. The output terminal of the microwave source 1 is connected to the input terminal of the power divider 4, for outputting a microwave signal with a first operating frequency to the power divider 4. The first branch terminal of the power divider 4 is connected to the phase shifter 7, and the second branch terminal of the power divider 4 is connected to the input terminal of the circulator 5, for dividing the microwave signal into a first power-divided signal and a second power-divided signal with equal power, and outputting the first power-divided signal to the circulator 5 and the second power-divided signal to the phase shifter 7. The phase shifter 7 is connected to the local oscillator signal terminal of the I / Q mixer 8, for phase-shifting the second power-divided signal to obtain a local oscillator signal orthogonal to the first power-divided signal, and outputting... The local oscillator signal is sent to the I / Q mixer 8; the test sample detection terminal of the circulator 5 is connected to the resonant cavity 6, and the signal output terminal of the circulator 5 is connected to the radio frequency signal terminal of the I / Q mixer 8, for outputting the first power-divided signal to the resonant cavity 6; the resonant cavity 6 is used to set the test sample and to collect and output the first detection signal to the circulator; the circulator 5 outputs the first detection signal to the I / Q mixer 8; the baseband signal terminal of the I / Q mixer 8 is connected to the signal acquisition terminal of the measurement and control board 9, for mixing the first detection signal and the local oscillator signal, and outputting the I down-converted signal and the Q down-converted signal to the measurement and control board 9; the signal output terminal of the measurement and control board 9 is connected to the control terminal of the microwave source 1, for processing the I down-converted signal and the Q down-converted signal to obtain detection result information, and judging whether the frequency of the microwave signal has shifted according to the original baseband signal, and correcting the microwave source 1 for the shift.

[0054] The microwave source 1 is a high-purity microwave source, driven by a low-phase-noise radio frequency signal output from the measurement and control board 9, which generates the microwave signal. Specifically, the measurement and control board 9 outputs a high-purity, low-phase-noise control signal into the microwave source 1, thereby generating a stable microwave signal. The output microwave signal is split into two paths by the power divider 4. One path passes through the circulator 5 to the resonant cavity 6. After the sample under test is detected inside the cavity, the obtained microwave signal is then output by the circulator 5 to the I / Q mixer 8. The use of the circulator 5 ensures unidirectional signal transmission, avoids interference from reflected signals and other factors on the microwave field in the resonant cavity 6, and ensures the stability of the phase and amplitude of the microwave during operation. The other path of the power divider 4, after its phase is controlled by the phase shifter 7, is also output to the I / Q mixer 8, where it is mixed with the first detection signal obtained from the resonant cavity 6 as the local oscillator signal to obtain the corresponding I down-converted signal and Q down-converted signal. The signal is amplified by the low-noise amplifier 3 and then enters the detection module of the measurement and control board 9, where it undergoes data processing. The circulator 5 ensures that the microwave signal enters the resonant cavity 6 unidirectionally and guides the first detection signal generated by reflection into the detection end, protecting the microwave source 1 and stabilizing the cavity field. The phase shifter 7 and the power divider 4 are used to precisely control the phase of the local oscillator signal, which serves as a reference signal to provide a precise 90-degree phase difference reference for subsequent I / Q demodulation. The I / Q mixer 8 mixes the weak detection signal from the resonant cavity 6 with the phase-shifted local oscillator signal, and then demodulates it through the I / Q demodulator on the measurement and control board 9 to obtain two baseband signals: an in-phase (I) signal (i.e., the I signal baseband component) containing amplitude and phase information, and a quadrature (Q) signal (i.e., the Q signal baseband component). The original baseband signal is then calculated. Meanwhile, the automatic frequency control module 933 in the measurement and control board 9 detects the frequency error by comparing the received original baseband signal with the reference frequency. Based on the difference, it adjusts the control voltage input to the waveform generator. The waveform generator outputs the corrected X-band radio frequency signal as a control signal to the microwave source 1 to realize feedback control of the microwave signal frequency.

[0055] In some preferred embodiments, the microwave controller for the electron paramagnetic spectrometer further includes an attenuator 2 and a low-noise amplifier 3; wherein the attenuator 2 and the low-noise amplifier 3 are located between the microwave source 1 and the power divider 4; the input terminal of the attenuator 2 is connected to the output terminal of the microwave source 1, and the output terminal of the attenuator 2 is connected to the input terminal of the low-noise amplifier 3, for reducing the signal strength of the microwave signal; the output terminal of the low-noise amplifier 3 is connected to the input terminal of the power divider 4, for amplifying the microwave signal and improving the signal-to-noise ratio of the microwave signal.

[0056] In this invention, the signal strength is attenuated and controlled by attenuator 2, and then amplified with low noise by low-noise amplifier 3 to ensure that the power meets the requirements and to minimize noise as much as possible, thereby improving the recognizable sensitivity of subsequent paramagnetic resonance technology. The signal-to-noise ratio formula can be written as:

[0057] Where SNR is the signal-to-noise ratio, P s For signal power, P n This represents noise power.

[0058] The lower the noise power relative to the signal power, the higher the signal-to-noise ratio (SNR). Typically, a signal power of -70 dBm to -50 dBm and an SNR better than 30 dBm are required. Lower noise and a higher SNR result in higher subsequent recognition sensitivity.

[0059] In a preferred embodiment of the present invention, the measurement and control board 9 includes an FMC (FPGA Mezzanine Card) functional daughter card 93, an FPGA (Field-Programmable Gate Array) daughter card 92, and a carrier board 91. The FMC functional daughter card 93 and the FPGA daughter card 92 are respectively inserted onto the carrier board 91. The FMC functional daughter card 93 is equipped with a signal acquisition module 931, an automatic frequency control module 933, and a waveform generation module 932. The signal acquisition module 931 is used to acquire the I down-converted signal and Q down-converted signal from the I / Q mixer 8 through the carrier board 91, perform analog-to-digital conversion, and output the digital components of the I and Q signals to the FPGA daughter card 92. The input terminal of the automatic frequency control module 933 is connected to the I / Q mixer 8, and the output terminal of the automatic frequency control module 933 is connected to the waveform generation module 932. It is used to acquire the original baseband signal and determine whether the frequency of the microwave signal is equal to the resonance of the cavity based on the waveform of the original baseband signal. Frequency; if the frequency of the microwave signal is not equal to the resonant frequency of the cavity, an error signal is output to the waveform generation module 932 according to the error; the waveform generation module 932 is connected to the control terminal of the microwave source 1 through the carrier board 91, and is used to output a microwave source control signal of the first working frequency to the microwave source 1 according to the error signal to correct the frequency of the output microwave signal; the FPGA daughter card 92 is provided with a signal processing module, which is used to perform data processing and I / Q demodulation on the I down-conversion signal and Q down-conversion signal to obtain detection result information; the carrier board 91 is connected to the baseband signal terminal of the I / Q mixer 8, and is used to input the I down-conversion signal and Q down-conversion signal in the I / Q mixer 8 and output the I down-conversion signal and Q down-conversion signal to the FMC function daughter card 93, and is used to communicate with the external host computer in real time to transmit the detection result information.

[0060] The measurement and control board 9 includes a carrier board 91, an FPGA daughter card 92, and an FMC function daughter card 93. Both the FPGA daughter card 92 and the FMC function daughter card 93 are inserted into the carrier board 91. The carrier board 91 contains multiple external interfaces 94, responsible for signal transmission and other functions. The FPGA daughter card 92 mainly contains an FPGA chip and its auxiliary modules for rapid signal processing. Furthermore, the FMC function daughter card 93 can also be equipped with a low-pass filter. This low-pass filter is connected to the output of the I / Q mixer 8 and is used to perform low-pass filtering on the I-down-converted signal and the Q-down-converted signal to obtain the I-signal baseband component and the Q-signal baseband component. Simultaneously, exemplarily, the auxiliary modules can be selected from modules with other computing functions, such as high-speed serial transceivers, large-capacity memory, clock networks, etc., to assist in realizing various functions of the measurement and control board 9. The signal acquisition module 931 on the FMC function daughter card 93 can be an ADC (Analog-to-Digital Converter) module to acquire the I-signal baseband components and Q-signal baseband components and perform analog-to-digital conversion to obtain the I-signal digital components and Q-signal digital components. The waveform generation module 932 can be a waveform generator, and the automatic frequency control module 933 can be a four-channel pulse input / output module for signal acquisition and transmission. The four-channel pulse input / output module of the automatic frequency control module 933 acquires the signal frequency error information of the original baseband signal and outputs a corresponding error signal to the waveform generation module 932 according to the error magnitude. The waveform generation module 932 generates a precise frequency signal feedback based on the error and adjusts the parameters of the microwave source control signal. Simultaneously, the FMC function daughter card 93 described in this invention can be connected to external circuits and transmit data through various SMA connectors, and can be responsible for RF signal acquisition and output, etc., and can be directly connected to the FPGA daughter card 92 through the FMC interface 934. Preferably, the ADC module can be an AD9467 ADC module, and the waveform generator can be an AD9833 waveform generator. The FMC function daughter card 93 integrates key analog-to-digital / digital-to-analog converters, particularly a high-speed ADC for acquiring RF signals, and a waveform generator for generating initial stimuli. The FPGA daughter card 92 can be used to run customized digital signal processing algorithms, performing real-time noise reduction, accumulation, demodulation, and other operations on the data acquired by the ADC to quickly reconstruct a high signal-to-noise ratio signal. Simultaneously, the carrier board 91 provides system-level interfaces (such as SMA, power, and control buses) to enable collaboration between daughter cards and communication with the host computer. The automatic frequency control loop, located on the FMC function daughter card 93, is used to extract errors from the signal, generate a precise frequency signal, and feed it back to the microwave source 1, forming a fast frequency-locked loop to correct microwave frequency drift in real time.

[0061] This invention proposes a microwave control method and a microwave controller for an electron paramagnetic spectrometer. The microwave controller includes a microwave module and a measurement and control board. The microwave module includes a microwave source and a resonant cavity, ensuring high-precision control of the microwave signal. The measurement and control board is responsible for detecting and outputting corresponding radio frequency (RF) signals, realizing closed-loop microwave control. This controller, designed for the needs of electron paramagnetic spectrometers, achieves high-precision and stable RF signal output to ensure precise control of the frequency and phase of the electromagnetic field in the resonant cavity. Subsequently, it acquires the reflected signal after the sample undergoes resonant absorption in the resonant cavity, obtaining a high-precision, high-speed microwave signal. An FPGA performs rapid algorithmic processing on the signal to suppress noise and reconstruct a high-sensitivity signal, achieving a balance between high time resolution and high sensitivity. This microwave controller integrates RF signal acquisition, modulation, transmission, and reception, as well as high-speed signal reception and processing, providing a stable and efficient hardware foundation for electron paramagnetic spectrometer measurements.

[0062] This invention provides a microwave control method and a microwave controller for an electron paramagnetic spectrometer. The microwave control method for an electron paramagnetic spectrometer has the following advantages: By establishing a feedback loop between the output and the microwave source signal input, feedback control of the microwave signal is achieved, thereby realizing high-precision and high-resolution microwave control in the electron paramagnetic spectrometer.

[0063] Ultra-high precision microwave field control was achieved. Closed-loop control and circulator isolation ensured long-term stability of the microwave frequency and phase within the resonant cavity, a prerequisite for high-precision time-resolved and pulsed EPR experiments.

[0064] It provides a stable and reliable hardware foundation. The integrated design reduces external interference and connection losses, while the modular architecture improves system reliability and maintainability, providing a high-performance, standardized core controller for the EPR spectrometer.

[0065] This enhances the system's flexibility and scalability. The FMC-based design allows users to replace function daughter cards according to different experimental needs (such as different frequency bands or higher sampling rates) without redesigning the entire system.

[0066] It should be understood that the application of the present invention is not limited to the examples above. Those skilled in the art can make improvements or modifications based on the above description, and all such improvements and modifications should fall within the protection scope of the appended claims.

Claims

1. A microwave control method for an electron paramagnetic spectrometer, characterized in that the steps include... include: A microwave source is controlled to generate a microwave signal for paramagnetic resonance detection, wherein the frequency of the microwave signal is a first operating frequency; The microwave signal is power-divided to obtain a first power-divided signal and a second power-divided signal; the first power-divided signal is input into the resonant cavity, and the microwave reflection signal after the sample under test undergoes resonant absorption in the resonant cavity is detected to obtain a first detection signal; the second power-divided signal is used for phase shifting to obtain a local oscillator signal orthogonal to the first power-divided signal; The first detection signal and the local oscillator signal are acquired, and the first detection signal and the local oscillator signal are mixed to obtain the I down-converted signal and the Q down-converted signal; The I down-conversion signal and Q down-conversion signal are sampled and processed to obtain the original baseband signal, and the detection result information is restored. Based on the original baseband signal, determine whether the frequency of the microwave signal has shifted, and correct the microwave source for the shift so that the frequency of the output microwave signal remains at the first operating frequency.

2. The microwave control method for an electron paramagnetic spectrometer according to claim 1, characterized in that, The steps of sampling and processing the I-down-converted signal and Q-down-converted signal to obtain the original baseband signal and then restoring the detection result information include: The I down-converted signal and the Q down-converted signal are low-pass filtered to obtain the I signal baseband component and the Q signal baseband component. The I signal baseband component and the Q signal baseband component are sampled and processed to obtain the original baseband signal, which is used to reconstruct the detection result information.

3. The microwave control method for an electron paramagnetic spectrometer according to claim 1, characterized in that, After the step of controlling a microwave source to generate a microwave signal for paramagnetic resonance detection, wherein the microwave signal is a first operating frequency, the method further includes: The signal strength of the microwave signal is attenuated. The microwave signal after attenuation control is amplified with low noise. The signal power of the amplified microwave signal is located in the target signal power range, which is used to improve the signal-to-noise ratio.

4. The microwave control method for an electron paramagnetic spectrometer according to claim 1, characterized in that, The microwave signal is power-divided to obtain a first power-divided signal and a second power-divided signal; the first power-divided signal is input into the resonant cavity, and the microwave reflection signal after the sample under test undergoes resonant absorption in the resonant cavity is detected to obtain a first detection signal; The step of using the second power divider signal for phase shifting to obtain a local oscillator signal orthogonal to the first power divider signal includes: The microwave signal is distributed into a first power-divided signal on a first power-divided path and a second power-divided signal on a second power-divided path by a power divider; In the first power divider, the sample to be tested is placed in the resonant cavity, and the sample to be tested is detected in conjunction with the first power divider signal; The first detection signal is obtained by detecting the reflected signal of the resonant cavity after the sample under test undergoes resonant absorption; On the second power divider, the second power divider signal is phase-shifted to obtain a local oscillator signal with a phase difference of 90 degrees from the first detection signal. The local oscillator signal is used to perform quadrature modulation on the first detection signal.

5. The microwave control method for an electron paramagnetic spectrometer according to claim 1, characterized in that, The first operating frequency is the X-band frequency.

6. The microwave control method for an electron paramagnetic spectrometer according to claim 1, characterized in that, The steps of determining whether the frequency of the microwave signal has shifted based on the original baseband signal, and correcting the microwave source to maintain the frequency of the output microwave signal at the first operating frequency, include: Acquire the original baseband signal; Determine whether the frequency of the microwave signal is equal to the resonant frequency of the cavity based on the original baseband signal waveform; If the frequency of the microwave signal is not equal to the resonant frequency of the cavity, the microwave source control signal with the first working frequency is adjusted according to the error to correct the frequency of the output microwave signal.

7. The microwave control method for an electron paramagnetic spectrometer according to claim 2, characterized in that, The steps of sampling and processing the I-signal baseband component and the Q-signal baseband component to obtain the original baseband signal, and using the original baseband signal to reconstruct the detection result information, include: The baseband components of the I signal and the baseband components of the Q signal are sampled by analog and digital methods to obtain the digital components of the I signal and the Q signal. The I signal digital component is used to represent the real part of the signal, and the Q signal digital component is used to represent the imaginary part of the signal. The amplitude and phase of the original baseband signal are obtained by reconstructing the real and imaginary parts of the signal. The original baseband signal is obtained based on the amplitude and phase of the original baseband signal.

8. A microwave controller, characterized in that, The microwave controller is used to implement the microwave control method for an electron paramagnetic spectrometer as described in any one of claims 1-7; the microwave controller includes: a microwave source, a power divider, a phase shifter, a circulator, a resonant cavity, an I / Q mixer, and a measurement and control board; wherein, The output terminal of the microwave source is connected to the input terminal of the power divider, and is used to output a microwave signal with a frequency of the first operating frequency to the power divider. The first branch of the power divider is connected to the phase shifter, and the second branch of the power divider is connected to the input of the circulator. It is used to divide the microwave signal into a first power divided signal and a second power divided signal with the same power, and output the first power divided signal to the circulator and the second power divided signal to the phase shifter. The phase shifter is connected to the local oscillator signal terminal of the I / Q mixer and is used to phase shift the second power division signal to obtain a local oscillator signal orthogonal to the first power division signal, and output the local oscillator signal to the I / Q mixer. The circulator's sample detection terminal is connected to the resonant cavity, and the circulator's signal output terminal is connected to the radio frequency signal terminal of the I / Q mixer, for outputting the first power-divided signal to the resonant cavity; the resonant cavity is used to place the sample under test and to acquire and output the first detection signal to the circulator; the circulator outputs the first detection signal to the I / Q mixer; The baseband signal terminal of the I / Q mixer is connected to the signal acquisition terminal of the measurement and control board, and is used to mix the first detection signal and the local oscillator signal, and output the I down-converted signal and the Q down-converted signal to the measurement and control board. The signal output terminal of the measurement and control board is connected to the control terminal of the microwave source. It is used to process the I down-conversion signal and the Q down-conversion signal to obtain detection result information, and to determine whether the frequency of the microwave signal has shifted based on the original baseband signal, and to correct the microwave source for the shift.

9. The microwave controller according to claim 8, characterized in that, It also includes an attenuator and a low-noise amplifier; wherein the attenuator and the low-noise amplifier are located between the microwave source and the power divider; the input terminal of the attenuator is connected to the output terminal of the microwave source, and the output terminal of the attenuator is connected to the input terminal of the low-noise amplifier, for reducing the signal strength of the microwave signal; the output terminal of the low-noise amplifier is connected to the input terminal of the power divider, for amplifying the microwave signal and improving the signal-to-noise ratio of the microwave signal.

10. The microwave controller according to claim 8, characterized in that, The measurement and control board includes an FMC function daughter card, an FPGA daughter card, and a carrier board; wherein... The FMC function sub-card and the FPGA sub-card are respectively inserted on the carrier board. The FMC function sub-card is equipped with a signal acquisition module, an automatic frequency control module and a waveform generation module. The signal acquisition module is used to acquire the I down-converted signal and the Q down-converted signal in the I / Q mixer through the carrier board, perform analog-to-digital conversion and output the digital components of the I signal and the digital components of the Q signal to the FPGA sub-card. The input terminal of the automatic frequency control module is connected to the I / Q mixer, and the output terminal of the automatic frequency control module is connected to the waveform generation module. It is used to acquire the original baseband signal and determine whether the frequency of the microwave signal is equal to the resonant frequency of the cavity based on the waveform of the original baseband signal. If the frequency of the microwave signal is not equal to the resonant frequency of the cavity, an error signal is output to the waveform generation module based on the error. The waveform generation module is connected to the control terminal of the microwave source through the carrier board, and is used to output a microwave source control signal of the first operating frequency to the microwave source according to the error signal; The FPGA daughter card is equipped with a signal processing module, which is used to perform data processing and I / Q demodulation on the I down-conversion signal and the Q down-conversion signal to obtain detection result information; The carrier board is connected to the baseband signal terminal of the I / Q mixer, and is used to receive the I down-converted signal and the Q down-converted signal in the I / Q mixer and output the I down-converted signal and the Q down-converted signal to the FMC function sub-card 93, and is used to communicate with an external host computer in real time to transmit the detection result information.

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