A synchronous magnetic field measuring device with same frequency resonance polarization

Abstract

The present invention discloses a synchronous magnetic field measuring device with same frequency resonance polarization, which comprises a probe, a polarization circuit, a high-precision frequency generating circuit, a high-resolution ADC acquisition circuit and an MCU processor; the probe comprises a polarization coil and a receiving coil, the polarization circuit uses a linear voltage regulator to drive a constant voltage, and generates a square wave signal of a certain polarization frequency by controlling a switch circuit to polarize the protons in the probe, the MCU processor sends the required frequency signal for polarizing the protons through the frequency generating circuit to drive the polarization circuit to send a square wave to the polarization coil in the probe, and performs ADC data acquisition and integral calculation while sending the frequency, so as to achieve synchronous full-cycle acquisition, calculate the effective amplitude, and finally determine the magnetic field frequency by the polarization frequency corresponding to the maximum amplitude. The measuring device has high precision, low hardware cost, small size, supports synchronous measurement, and has high measurement efficiency.

Description

Technical Field

[0001] The invention relates to the field of electromagnetic exploration equipment, and in particular to a same-frequency resonant polarization synchronous magnetic field measuring device. Background Art

[0002] The proton magnetometer uses a magnetic field measuring probe to polarize the internal protons with electric field. After the polarization stops, all protons perform Larmor precession in the direction of the electric field. The frequency of Larmor precession is proportional to the magnetic field. The relationship between the magnetic field and the frequency is B = 23.4874*f. The frequency signal amplitude generated by the magnetic field measuring probe is proportional to the number of proton precession, that is, the more protons precess, the greater the signal amplitude. As time goes by, all proton precession directions will eventually tend to equilibrium due to the same-sex repulsion. Finally, the output signal of the magnetic field measuring probe will be output in the form of exponential decay according to the frequency corresponding to the ambient magnetic field. Therefore, the proton magnetometer generally converts the measurement of the earth's magnetic field into the measurement frequency. The traditional proton magnetometer measurement method is to polarize the magnetic field measuring probe with a certain voltage, generate Larmor precession signal after polarization, and calculate the frequency through the resonance circuit, amplifier circuit, and frequency measurement circuit. The actual magnetic field value is calculated by the relationship between the magnetic field and the frequency.

[0003] However, since the earth's magnetic field signal is very weak, the signal generated by the magnetic field measurement probe is very small, generally in the range of a few uV. Therefore, the entire hardware circuit, especially the amplifier circuit, requires very low noise, otherwise the noise will mask the effective signal and make it impossible to measure. The amplifier circuit needs to be amplified by at least 100,000 times, and the self-noise of the entire system needs to be controlled at the 10nV level. Since the slight differences in the same components will make different instruments have large differences, this is very difficult in terms of hardware design. The general accuracy requirement of a proton magnetometer is 0.01nT, which is converted to a frequency with a minimum resolution of about 0.000426Hz, so the measurement frequency accuracy needs to reach 10 -4 To ensure the measurement accuracy, ultra-high precision frequency measurement is required, and the temperature stability and accuracy of the frequency measurement crystal must be guaranteed. Magnetic field measurement is to output a small analog signal. After amplification and shaping, its frequency will inevitably produce phase jitter and cause instability. For the subsequent measurement frequency, not only the high precision of the frequency must be guaranteed, but also the stability of the frequency must be guaranteed, which puts forward high requirements on hardware and software algorithms.

[0004] For example, the patent application "CN201010147845-An OVERHAUSER magnetometer" discloses a magnetometer, which uses radio frequency excitation signals to make the nitrogen oxide free radical solution produce electron and nuclear double resonance phenomenon (Overhauser effect), enhance the magnetization intensity of hydrogen protons along the direction of the geomagnetic field, solve the problem of too weak hydrogen proton precession signal in the proton magnetometer sensor, thereby improving the magnetic measurement accuracy of the sensor. However, its polarization object is electrons, and the oscillating high-frequency signal needs to be above MHZ frequency, and an additional Class C high-frequency power amplifier 8 needs to be installed to amplify it. In addition, when receiving the signal, it must be inside the amplifier. The receiving signal can only be amplified by installing a resonant amplifier circuit 12, and the probe structure is complex and precise, consisting of a high-frequency resonant cavity 9, a sealed glass bottle 10 containing a free radical solution, and a low-frequency receiving coil 11 wound around the outside of the glass bottle. In addition, a DC pulse generator 3 needs to be installed to generate a DC pulse for the probe, and the frequency measurement method of its frequency meter 5 is an intermittent measurement method (that is, the measurement frequency cannot be determined synchronously while the probe is polarized, and the two are performed separately). Therefore, in order to realize the Overhauser effect to complete the high-precision measurement of the magnetic field frequency, the magnetometer requires a relatively high hardware cost and a relatively complex measurement procedure, and the measurement efficiency is not high enough.

[0005] Therefore, there is an urgent need to design a magnetic field measurement device to accurately measure the frequency of the geological magnetic field, while reducing the development and production costs of the hardware, simplifying the measurement method, and improving the measurement efficiency. Summary of the invention

[0006] 1. Technical issues to be resolved

[0007] Based on this, in view of the shortcomings of the prior art, the present invention provides a synchronous magnetic field measurement device with same-frequency resonant polarization, which can not only realize high-precision measurement of magnetic field frequency, but also reduce hardware costs, simplify measurement procedures, and have a high degree of automation. At the same time, through the double coils in the probe, synchronous online measurement of magnetic field frequency during continuous polarization of protons is realized, thereby improving measurement speed and efficiency.

[0008] (II) Technical solution

[0009] In order to solve the above technical problems, the main technical solutions adopted by the present invention include:

[0010] A same-frequency resonant polarization synchronous magnetic field measuring device, the magnetic field measuring device comprises a probe, a polarization circuit, a high-precision frequency generating circuit, a high-resolution ADC acquisition circuit and an MCU processor;

[0011] The probe is a proton magnetic field measurement probe, which includes a polarization coil and a receiving coil. The polarization coil is connected to the polarization circuit, and the receiving coil is connected to the ADC acquisition circuit.

[0012] The polarization circuit uses a linear voltage regulator to drive the circuit at a constant voltage, and generates a square wave signal of a desired polarization frequency by controlling a switch circuit, so as to polarize the protons in the probe through a polarization coil;

[0013] The frequency generating circuit generates a signal with a frequency between 800 Hz and 4000 Hz;

[0014] The ADC acquisition circuit performs ADC data acquisition on the received signal of the receiving coil;

[0015] The MCU processor is connected to the frequency generating circuit and the ADC acquisition circuit respectively, and sends the required frequency signal for polarizing the protons through the frequency generating circuit to drive the polarization circuit to send a square wave to the polarization coil in the probe. While sending the frequency signal, ADC data acquisition and integral calculation are performed to achieve synchronous full-cycle acquisition, calculate the effective amplitude, and finally determine the magnetic field frequency through the polarization frequency corresponding to the maximum amplitude.

[0016] Furthermore, the receiving coil has the same parameters as the polarization coil and is reversely wound in an "8" shape. Preferably, the polarization coil has an internal resistance of 10Ω and an inductance of 30mH, and the polarization coil is polarized at a constant voltage with a current of about 1A.

[0017] Furthermore, the polarization coil and the receiving coil are sealed in the kerosene medium inside the probe.

[0018] Furthermore, a DDS generator or a CPLD is used as the frequency generating circuit in the frequency generating circuit, the MCU processor is a STM32F4 series single chip microcomputer, and the voltage of the linear voltage regulator is 12V.

[0019] Furthermore, the ADC acquisition circuit specifically uses ADS1271 to acquire signals.

[0020] Furthermore, the MCU processor integrates the whole cycle of the received signal, and each time the frequency scan is performed in steps of 20 Hz, 0.1 Hz, and 0.0001 Hz, each frequency has 5 cycles, and integrates and collects 5 whole cycles, and performs normalization processing.

[0021] Furthermore, no signal amplifier is provided between the receiving coil and the ADC acquisition circuit.

[0022] Furthermore, when measuring the polarization frequency, a binary fast scanning method is adopted, that is, the corresponding frequency is selected for polarization within the global magnetic field range, and the amplitude is recorded at the same time. A rough frequency scan is performed first, and then a fine frequency scan is performed within the rough frequency range determined in advance, so as to obtain the polarization frequency corresponding to the maximum amplitude.

[0023] Furthermore, the square wave signal of the polarization circuit is replaced by a sine wave signal.

[0024] (III) Beneficial effects

[0025] Compared with the prior art, the same-frequency resonant polarization synchronous magnetic field measurement device of the present invention has the following beneficial effects:

[0026] 1. The present invention uses a high-precision frequency generating circuit to generate a polarization frequency for protons, effectively improving the accuracy of magnetic field measurement. The polarization coil is square-wave polarized in the same voltage mode (of course, a more complex sine wave can also be controlled). The corresponding value of the external magnetic field frequency is determined by receiving the signal integration voltage generated by different frequencies. The coil is polarized at a certain frequency so that the current frequency resonates with the frequency generated by the external magnetic field, so that the protons in the probe output signals with the maximum amplitude. A high-resolution ADC is used to accurately collect the amplitude generated by the induction, so that effective accuracy can be guaranteed during subsequent integral operations. The induced signal generated by the polarization frequency is integrated and collected for a whole cycle, and the collected cycle time integral value is normalized to ensure that the difference in the amplitude generated by each frequency can be clearly distinguished. From the above, it can be seen that the present invention can make full use of the hardware advantages of each module to ensure the accuracy of magnetic field measurement.

[0027] 2. The magnetic field measuring device of the present invention does not require a tuning circuit for signal frequency selection and amplification, does not require a phase-locked amplifier circuit and a high-gain amplifier circuit to amplify a weak Larmor signal, and does not require a high-precision frequency measurement circuit to measure the frequency of the Larmor signal. Compared with patent application CN201010147845, the present application does not require a Class C power amplifier, a resonant amplifier circuit (because the present invention is based on the polarization resonance of protons, the oscillation high-frequency signal of the polarized protons only needs a frequency of a few KHZ, so there is no need to set a Class C power amplifier in the frequency generating circuit, and the signal receiving end of the probe also does not need to be provided with an amplifier circuit), a DC pulse generator, a frequency meter, etc., and the probe structure is simpler, which greatly reduces the hardware cost and has a small size and a simple measurement method.

[0028] 3. The measuring device of the present invention can receive the induced signal while polarizing the coil through the signal sending and signal receiving double-coil magnetic field measuring probe, thereby achieving a synchronous acquisition mode and reducing the cost and complexity of the probe, and realizing synchronous, fast and high-precision measurement of the magnetic field frequency (i.e., determining the frequency while polarizing); in addition, in terms of rapid determination of the magnetic field frequency, when determining the magnetic field frequency, multiple sweeping methods from coarse to fine can be used preferentially to further reduce the measurement time, quickly locate the measured magnetic field frequency, and further improve the measurement efficiency on the basis of synchronous online measurement of the magnetic field frequency. BRIEF DESCRIPTION OF THE DRAWINGS

[0029] The features and advantages of the present invention will be more clearly understood by referring to the accompanying drawings, which are schematic and should not be construed as limiting the present invention in any way. In the accompanying drawings:

[0030] Figure 1 This is a system structure block diagram of the same-frequency resonant polarization synchronous magnetic field measurement device in the present invention.

[0031] Figure 2 The figure is a winding diagram of the internal coil of the probe in the magnetic field measuring device of the present invention. DETAILED DESCRIPTION

[0032] The specific implementation of the present invention is further described in detail below in conjunction with the accompanying drawings and examples. The following examples are used to illustrate the present invention, but are not intended to limit the scope of the present invention.

[0033] In order to make the above-mentioned objects, features and advantages of the present invention more obvious and easy to understand, the specific embodiments of the present invention are described in detail below in conjunction with the accompanying drawings. In the following description, many specific details are set forth to facilitate a full understanding of the present invention. However, the present invention can be implemented in many other ways different from those described herein, and those skilled in the art can make similar improvements without violating the connotation of the present invention, so the present invention is not limited by the specific implementation disclosed below.

[0034] In the prior art, the protons in the magnetic field measuring probe undergo Larmor precession under the action of the magnetic field of the external environment, and their precession frequency is in a corresponding proportional relationship with the magnetic field. By polarizing the internal coil, a magnetic field is generated, which acts on the protons, causing a magnetic moment to be generated when the protons precess.

[0035] The traditional method is DC power polarization, while the measuring device of the present invention uses a square wave polarization of a certain frequency. The working principle of the measuring device is as follows: protons generate nuclear magnetic resonance under the action of an external magnetic field. Since it is frequency polarization, the probe will continue to polarize the protons, and it can be polarized again during the relaxation process. At the same time, frequency polarization can generate an alternating magnetic field in the coil, which has a strong electromotive force, and increases its signal amplitude in both aspects, reducing the difficulty of measuring small signals. And the inventors have experimentally verified that when the precession frequency generated by the external magnetic field on the protons is the same as the polarization frequency, the external magnetic field intensity resonates and superimposes with the internal polarized magnetic field, greatly improving the internal proton polarization ratio, so that the signal amplitude generated by the proton precession cutting coil is the largest, and the relaxation time is the longest. Based on this phenomenon, the corresponding polarization frequency can be extracted by identifying the signal amplitude, and finally the external magnetic field can be measured.

[0036] like Figure 1-2 As shown, the magnetic field measuring device of the present invention mainly includes a dual-coil magnetic field measuring probe, a polarization circuit, a high-precision frequency generating circuit, a high-resolution ADC acquisition circuit, an MCU processor and other parts. The working mode of each component is described as follows:

[0037] 1) Probe: The probe uses a special proton magnetic field measurement probe, which includes a polarization coil and a receiving coil. The polarization circuit is connected to the polarization coil, and the receiving coil is connected to the ADC acquisition circuit. The polarization coil parameter internal resistance is 10Ω, and the inductance is 30mH. The receiving coil for induction has the same parameters as the polarization coil. The polarization coil is polarized at a constant voltage with a current of about 1A, and the signal of the induced electromotive force generated by the receiving coil is collected at the same time.

[0038] like Figure 2 As shown, the polarization coil and the receiving coil in the double-coil magnetic field measurement probe are completely isolated, and the polarization coil and the receiving coil form a double coil sealed in kerosene, which can synchronously collect proton polarization and induced electromotive force signals, and there is no need to install additional Class C power amplifiers and resonant amplifier circuits at the input and output ends of the double-coil probe respectively.

[0039] 2) Polarization circuit: Use a 12V linear voltage regulator as a polarization circuit for constant voltage drive, generate the required frequency by controlling the switch circuit, and make the same voltage peak-to-peak value flow through the polarization coil during frequency polarization, and eliminate the difference caused by voltage instability to adapt to the measurement of magnetic field frequency. In addition, the polarization signal is preferably a square wave signal, thereby reducing the difficulty of signal control.

[0040] The polarization circuit provides driving capability for the probe polarization, and the coil generates different magnetic field strengths under different voltage polarization conditions, which causes differences in the subsequent received signal amplitude acquisition itself. Therefore, polarization needs to be driven by constant voltage, and the polarization coil supply voltage needs to be kept constant to eliminate the measurement error caused by the driving source.

[0041] 3) Frequency generation circuit: The high-precision frequency generation circuit provides a frequency source for the polarization circuit. Since the present invention polarizes protons, its signal generation frequency is between 800 Hz and 4000 Hz. The magnetic field resolution needs to reach 0.01 nT, and the corresponding frequency accuracy needs to reach 10 -4 Order of magnitude, in order to meet the frequency precision discrimination, DDS generator or CPLD can be used to generate high-precision frequency, CPLD is preferred as the frequency generation circuit, and a crystal oscillator with low temperature drift is required. CPLD frequency generation has high accuracy and strong real-time performance, and can accurately control the polarization frequency.

[0042] 4) ADC acquisition circuit: ADS1271 is used to collect the received signal. This ADC has a 24-bit resolution and a maximum sampling rate of 128ksps, which can collect the received signal with high precision. The high-resolution ADC acquisition circuit can use ADC to collect the signal after the probe receiving coil receives the resonance. Since the entire system is to judge the frequency of the integrated amplitude of the received signal, the ADC needs to have high resolution to effectively distinguish the slight difference in amplitude changes. It does not need to install a signal amplifier in the front.

[0043] Furthermore, in order to improve the measurement accuracy, the whole cycle of the received signal can be integrated, 5 cycles are sent for each frequency, and the 5 whole cycles are integrated and collected, and normalized, which can effectively improve the anti-interference ability, and at the same time, the size of the normalized value of each frequency can be clearly distinguished, and the maximum corresponding frequency value can be extracted. Each time the frequency scan frequency step is scanned in accordance with 20Hz, 0.1Hz, and 0.0001Hz, each frequency has 5 cycles, and each complete measurement time is about 1.85s, so that the magnetic field value can be quickly obtained.

[0044] 5) MCU processor: The MCU processor uses the STM32F4 series microcontroller to control all circuit parts, integrate and normalize the ADC collected data, and control the polarization frequency binary method to perform coarse and fine scanning step by step, so as to quickly and effectively extract the corresponding magnetic field frequency, and integrate and calculate the ADC conversion output signal to determine the actual magnetic field frequency.

[0045] In summary, the above embodiments have been tested and, under different magnetic field environments in different regions, through integral collection of different polarization frequencies, when the external magnetic field frequency is the same as the polarization frequency, the signal amplitude is maximum, and when the frequencies are different, the amplitude is significantly reduced. Therefore, the signal amplitude can be effectively and clearly distinguished, thereby obtaining the external environment magnetic field value, and achieving the purpose of quickly and accurately measuring the magnetic field.

[0046] To further illustrate the advantages of the magnetic field measuring device of the present invention, the main working process of the present invention is described in detail below: the MCU processor sends the required frequency signal for polarizing the protons through the frequency generating circuit, and this frequency drives the polarization circuit to send a square wave to the probe polarization coil, and performs ADC data acquisition while sending the frequency to achieve synchronous full-cycle acquisition. The MCU processor receives the ADC acquisition data for integration and calculates the final effective amplitude. In order to quickly locate the magnetic field frequency, it is necessary to adopt a frequency-by-frequency scanning method, that is, polarize the frequencies one by one within the global magnetic field range, record the amplitude at the same time, and first perform a rough frequency scan, and then a fine frequency scan. After high-resolution ADC acquisition, due to the full-cycle acquisition and different frequencies, the integrated value itself is differentiated. In order to eliminate this differentiation and improve accuracy, the signal integral value generated by each frequency needs to be time-normalized, that is, the integral value is averaged over the acquisition time, and then the normalized value is compared to finally determine the rough frequency interval.

[0047] When the MCU processor controls the polarization frequencies of the fine frequency and the rough frequency to be polarized one by one, the fine frequency scanning is the same as the rough frequency scanning measurement method, except that the scanning frequency is finely measured again in the determined rough frequency area (for example, the conventional dichotomy measurement method), and finally determines the final corresponding frequency value, which is the frequency value corresponding to the external environment magnetic field. Since the final frequency accuracy is relatively high, if the frequency is scanned one by one from small to large according to the minimum accuracy, it takes a lot of time to confirm the final frequency (but the sending period of each frequency should not be too large), so the present invention uses a hierarchical automatic frequency scanning method from coarse to fine in a synchronous online measurement method based on a double-coil probe to quickly and automatically determine the magnetic field frequency.

[0048] Figure 2 The figure shows the internal winding diagram of the probe coil. The medium inside the probe can be kerosene containing a large number of protons (or other conventional media containing a large number of protons). The polarization coil is exactly the same as the receiving coil, and preferably, each coil is reversely wound in an "8" shape. On the one hand, it can reduce the induced voltage generated by the polarization coil itself when it is polarized, and at the same time, it can superimpose the induced electromotive force generated by the receiving coil under the action of the magnetic field, thereby enhancing the receiving signal, thereby measuring the geological magnetic field frequency.

[0049] Through the synchronous magnetic field measurement device of the present invention, a measurement method of synchronous acquisition of same-frequency resonant polarization can be adopted for high-precision measurement. In terms of hardware, both high-precision frequency generation circuit and high-resolution ADC circuit are relatively easy to realize, and no capacitor resonance circuit is required, and there is no need to phase-lock the frequency drift in the traditional method. Since it is the acquisition of amplitude integral, only the integration time needs to be increased, and there is no need for a phase-locked amplifier circuit and a high-gain amplifier circuit to amplify the weak Larmor signal and a high-precision frequency measurement circuit to measure the Larmor signal frequency. Therefore, the complexity of hardware design can be effectively reduced, and the difference in measurement between instruments can be reduced; in data processing and frequency measurement, since it is an integral amplitude measurement, external interference can be effectively eliminated, the signal-to-noise ratio and dynamic range can be improved, and the measurement accuracy can be increased; therefore, the present invention uses a proton-based resonant frequency polarization method, which can effectively improve the recognition in the area with weak magnetic field, so that the changing magnetic field value can be accurately measured in the area with small magnetic field change, and the hardware cost is low, the volume is small, and the measurement efficiency is high.

[0050] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as those generally understood by those skilled in the art to which the present invention belongs. The terms used herein in the specification of the present invention are only for the purpose of describing specific embodiments and are not intended to limit the present invention. The various technical features of the above-described embodiments can be combined arbitrarily. In order to make the description concise, all possible combinations of the various technical features in the above-described embodiments are not described. However, as long as there is no contradiction in the combination of these technical features, they should be considered to be within the scope of this specification.

Claims

1. A synchronous magnetic field measuring device with same frequency resonance polarization, characterized in that: The magnetic field measuring device includes a probe, a polarization circuit, a high-precision frequency generating circuit, a high-resolution ADC acquisition circuit and an MCU processor; The probe is a proton magnetic field measurement probe, which includes a polarization coil and a receiving coil. The polarization coil is connected to the polarization circuit, and the receiving coil is connected to the ADC acquisition circuit. The polarization circuit uses a linear voltage regulator to drive the circuit at a constant voltage, and generates a square wave signal of a desired polarization frequency by controlling a switch circuit, so as to polarize the protons in the probe through a polarization coil; The frequency generating circuit generates a signal with a frequency between 800 Hz and 4000 Hz; The ADC acquisition circuit performs ADC data acquisition on the received signal of the receiving coil; The MCU processor is connected to the frequency generating circuit and the ADC acquisition circuit respectively, and sends the required frequency signal for polarizing the protons through the frequency generating circuit to drive the polarization circuit to send a square wave to the polarization coil in the probe. While sending the frequency signal, ADC data acquisition and integral calculation are performed to achieve synchronous full-cycle acquisition, calculate the effective amplitude, and finally determine the magnetic field frequency through the polarization frequency corresponding to the maximum amplitude.

2. The same frequency resonant polarization synchronous magnetic field measuring device according to claim 1 is characterized in that: The receiving coil has the same parameters as the polarization coil, and the coils are reversely wound in an "8" shape.

3. The same frequency resonant polarization synchronous magnetic field measuring device according to claim 2 is characterized in that: The polarization coil and the receiving coil are sealed in the kerosene medium inside the probe.

4. The same frequency resonant polarization synchronous magnetic field measuring device according to claim 1, characterized in that: The frequency generating circuit uses a DDS generator or a CPLD as the frequency generating circuit, the MCU processor is a STM32F4 series single chip microcomputer, and the constant voltage of the linear voltage regulator is 12V.

5. The same frequency resonant polarization synchronous magnetic field measuring device according to claim 1, characterized in that: The ADC acquisition circuit specifically uses ADS1271 to acquire signals.

6. The same frequency resonant polarization synchronous magnetic field measuring device according to claim 1, characterized in that: The MCU processor integrates the whole cycle of the received signal. When the frequency scanning step is scanned in accordance with 20Hz, 0.1Hz, and 0.0001Hz in sequence each time, each frequency has 5 cycles, and integrates and collects 5 whole cycles, and performs normalization processing.

7. The same frequency resonant polarization synchronous magnetic field measuring device according to claim 1, characterized in that: There is no need to arrange a tuning amplifier circuit between the receiving coil and the ADC acquisition circuit.

8. The same frequency resonant polarization synchronous magnetic field measuring device according to claim 1, characterized in that: When measuring the polarization frequency, a binary fast scanning method is adopted, that is, the corresponding frequency is selected for polarization within the global magnetic field range, and the amplitude is recorded at the same time. A rough frequency scan is performed first, and then a fine frequency scan is performed within the rough frequency range determined in advance to obtain the polarization frequency corresponding to the maximum amplitude.

9. The same frequency resonant polarization synchronous magnetic field measuring device according to claim 1, characterized in that: The square wave signal generated by the polarization circuit is replaced by a sine wave signal.

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