CN114039189B - Low-frequency magnetic antenna with compensation function and self-adaptive compensation method - Google Patents
Low-frequency magnetic antenna with compensation function and self-adaptive compensation method Download PDFInfo
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- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
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- H—ELECTRICITY
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Abstract
The invention discloses a low-frequency magnetic antenna with a compensation function and a self-adaptive compensation method, wherein the low-frequency magnetic antenna comprises a magnetic antenna, an amplifying circuit and a resolver, and the magnetic antenna consists of a magnetic core and a coil; the three-axis measurement values of the angular rate sensor and the magnetic field sensor equivalently represent vibration angular rate components and magnetic field components corresponding to the magnetic antenna; the amplifying circuit comprises a low-noise amplifying circuit and is used for amplifying the space induction signal output by the magnetic antenna and outputting the amplified space induction signal to the resolver; the resolver is used for solving a noise value according to the variable quantity output by the angular rate sensor and the magnetic field sensor and subtracting the noise value from the space induction signal output by the magnetic antenna. The invention detects the vibration mode of the antenna in real time, determines the induced electromotive force generated in the antenna coil based on the vibration mode, and corrects the output value of the antenna in real time, thereby inhibiting the interference generated by the vibration of platforms such as aircrafts and the like, and improving the sensitivity and the signal-to-noise ratio of the magnetic antenna.
Description
Technical Field
The invention belongs to the technical field of low-frequency communication, and relates to a low-frequency magnetic antenna with a compensation function and a self-adaptive compensation method.
Background
In the communication field, the path attenuation of low-frequency electromagnetic waves is low, and high-loss media can be spanned, so these frequency bands (hundreds of Hz to hundreds of kHz) are often used as main frequency bands for cross-media communication, and are applied to cross-media environments such as underwater, underground, caves, and the like. Since the low-frequency wavelength is as high as several hundred meters to several hundred kilometers, the magnetic antenna is almost the only antenna technology capable of realizing miniaturized reception in low-frequency communication.
Magnetic antennas consist of a magnetic core and a coil, as is common in medium-wave radios, for example. However, most of known magnetic antenna design methods are based on static conditions, such as the prior document 1 (liukai ka et al. Design and manufacture of underwater magnetic receiving antenna [ J ]. Ship electronic engineering.2016.10) and the prior document 2 (liu er et al. Design and application of lightning monitoring circuit based on low-frequency magnetic antenna [ J ]. Electromagnetic arrester.2019.06).
Most antennas are designed to be used in a static environment, and the influence of vibration is not considered. Some scholars have recently paid attention to: when the antenna has some specific vibration, its sensitivity is reduced, resulting in the reduction or even interruption of communication quality, see prior document 3 (korean super et al. Research on the influence mechanism of antenna vibration on digital communication system [ J ]. Proceedings of radio wave science. 2021.1 (36)).
In low frequency communications, the effect of vibration on the magnetic antenna is particularly severe. Because the induced voltage generated by cutting the magnetic lines of force of the earth when the metal conductors such as coils, cables and the like mechanically vibrate is directly superposed on the output signal, the phenomenon is called the geomagnetic vibration pickup effect. Most of the magnetic induction signals are very weak, induction voltage generated by the geomagnetic vibration pickup effect is enough to submerge real signals, most of the natural characteristic frequency (a few Hz to dozens of kHz) of mechanical vibration interference or mechanical movement is overlapped with the frequency band of low-frequency communication, and the natural characteristic frequency cannot be directly filtered by a conventional filter circuit, digital signal processing and other methods, so that the noise floor is raised, and the sensitivity of the antenna is reduced. See the literature (gming et al, ultralow frequency towed antenna motion induced noise analysis, computer and teaching engineering, 2016.44 (12)).
In a vibration environment, the following two methods are adopted for improving the antenna sensitivity: one is to adopt methods such as mechanical damping to reduce the local vibration intensity of the antenna, namely to add a vibration damper to the antenna; another is to mount the antenna by a cable to an area remote from the vibration source, such as a trailing antenna, which is more common in a submarine antenna.
However, the mechanical vibration damper has a limited vibration damping effect, and rather, the mechanical vibration damper has enhanced resonance at certain natural characteristic frequencies, so that the noise reduction effect is poor. Although the towed antenna can keep the antenna away from a vibration source, the antenna still can avoid generating new vibration interference due to turbulent fluid and cutting of earth magnetic lines by a cable in the towing process.
Disclosure of Invention
In order to solve the above problems, the present invention provides a low frequency magnetic antenna with a compensation function, which detects a vibration mode of the antenna in real time, determines an induced electromotive force generated in an antenna coil based on the vibration mode, and corrects an output value of the antenna in real time, thereby suppressing interference generated by vibration of platforms such as an aircraft, and improving sensitivity and a signal-to-noise ratio of the magnetic antenna.
Another object of the present invention is to provide an adaptive compensation method for a low frequency magnetic antenna with compensation function.
The invention adopts the technical scheme that a low-frequency magnetic antenna with a compensation function comprises
The magnetic antenna consists of a magnetic core and a coil and is used for outputting a space induction signal;
the device comprises an angular rate sensor and a magnetic field sensor which are both arranged on a magnetic core, wherein three-axis measurement values of the angular rate sensor and the magnetic field sensor equivalently represent vibration angular rate components and magnetic field components corresponding to a magnetic antenna;
the amplifying circuit comprises a low-noise amplifying circuit and is used for amplifying the space induction signal output by the magnetic antenna and outputting the amplified signal to the resolver;
and the resolver is used for simultaneously acquiring output signals of the angular rate sensor and the magnetic field sensor and space induction signals output by the magnetic antenna, solving a noise value according to the variable quantities output by the angular rate sensor and the magnetic field sensor, and subtracting the noise value from the space induction signals output by the magnetic antenna to realize noise suppression.
Further, the angular rate sensor can measure the angular rate change of three axes X ', Y' and Z ', and the magnetic field sensor can measure the static magnetic field parameters of three axes X', Y ', and Z'; the X, Y and Z coordinates of the magnetic core are in parallel relation with the X ', Y' and Z 'coordinates of the angular rate sensor and the X', Y 'and Z' coordinates of the magnetic field sensor.
Furthermore, the magnetic core is arranged on the system equipment through a vibration reduction bracket, and a shielding box is arranged outside the coil and used for shielding the interference of a space radiation electric field and allowing a low-frequency magnetic field to penetrate into the magnetic core.
Further, the square root spectral density of the thermal noise and 1/f noise generated by the low noise amplifying circuit itself is
And (4) stages.
Furthermore, the coil is wound by adopting a differential structure, and the port of the coil is connected with a low-noise amplifying circuit.
Further, the magnetic core is of a roll structure or a slotted structure.
Further, the resolver comprises a microprocessor, and the microprocessor comprises an adaptive noise cancellation algorithm module for operating an adaptive noise cancellation algorithm;
the adaptive noise cancellation algorithm module comprises
The coupling algorithm module is used for calculating an induction signal x (k) generated by the magnetic antenna due to low-frequency mechanical vibration according to output values of the angular rate sensor and the magnetic field sensor; and
the adaptive algorithm module is used for dynamically adjusting parameters of the digital filter according to the induction signal x (k), enabling the output value of the digital filter to approach an interference electromotive force n (k) actually generated by the magnetic antenna due to low-frequency mechanical vibration through an LMS algorithm, namely a noise value, and finally subtracting the approach value of n (k) from the space induction signal y (k) output by the magnetic antenna through a canceller so as to extract the approach value of an expected signal s (k), namely the approach value of the expected signal s (k)
Further, the coupling algorithm module calculates an induction signal x (k) generated by the magnetic antenna due to the low-frequency mechanical vibration according to formula (5):
wherein E represents the induced electromotive force of the magnetic antenna due to vibration, N represents the number of turns of the coil, and the vector (B) x ,B y ,B z ) The magnetic field intensity of the space where the magnetic antenna is located in the three-axis direction is calculated and obtained through magnetic flux phi measured by the magnetic field sensor; (omega) X ,ω Y ,ω Z ) The angular rate of the magnetic antenna in the three-axis direction is measured by an angular rate sensor; (S) X ,S Y ,S Z ) Representing the equivalent area of the coil in the three axial directions;
and performing modulo calculation on the vector E to obtain an induction signal x (k) generated by the magnetic antenna due to low-frequency mechanical vibration.
A self-adaptive compensation method of a low-frequency magnetic antenna with a compensation function specifically comprises the following steps:
the coupling algorithm module collects output values of the angular rate sensor and the magnetic field sensor and calculates an induction signal x (k) generated by the magnetic antenna due to low-frequency mechanical vibration; the low-frequency mechanical vibration original signals acquired by the angular rate sensor and the magnetic field sensor have no coupling effect with the induction signals of the magnetic antenna, namely x (k) is not related to the expected signals s (k) output by the magnetic antenna, the interference electromotive force n (k) and s (k) actually generated by the magnetic antenna due to low-frequency mechanical vibration are also not related to each other, and only n (k) is related to z (k); therefore, by the LMS algorithm, when the condition of formula (6) is satisfied, z (k) is made to trend toward n (k);
min ε(k)＝E[(n(k)-z(k)) 2 ] (6)
wherein epsilon (k) represents an error between z (k) and disturbed electromotive force n (k), z (k) represents an output value corresponding to a time when an induction signal x (k) generated when the magnetic antenna vibrates is taken as input by the digital filter, and k represents a time;
the coefficient K of each tap in the digital filter (10) is corrected in real time by looking up a data table, and the data table is obtained by experimental measurement;
the approximate value of n (k) is subtracted from the space induction signal y (k) output by the magnetic antenna through the canceller, so as to extract the approximate value of the expected signal s (k), namely
Further, the weight coefficient w of the digital filter is reduced by gradient decreasing method in the process of making z (k) trend to n (k) 0 ，w 1 ，w 2 ……w m-1 The method for solving specifically comprises the following steps:
repeating the steps 2 to 4 at the moment of 5, k +1, continuing the iteration until the algorithm is converged, and finally obtaining the weight coefficient w of the digital filter according to the weight coefficient matrix of the filter 0 ，w 1 ，w 2 ……w m-1 The value of (c).
The invention has the beneficial effects that:
the invention adopts the sensor to obtain the vibration state of the antenna, and improves the signal-to-noise ratio and the sensitivity of the magnetic antenna through a self-adaptive noise cancellation algorithm; the concrete characteristics are as follows:
(1) Compared with the traditional antenna (only a magnetic core and a coil), the antenna disclosed by the invention consists of an antenna, a low-noise amplification circuit and a self-adaptive noise cancellation algorithm module. The antenna adopts a feedback loop to be capable of adaptively measuring and inhibiting the interference generated by different vibration frequencies, particularly the vibration interference of a few Hz level which cannot be inhibited by the traditional antenna.
(2) The antenna is integrated with a sensor for measuring vibration and space magnetic field intensity, and the data of the sensor is collected by a resolver, and then induced electromotive force x (k) generated by the transformation of the projection area of the antenna coil in the direction of the earth magnetic field is calculated by a coupling algorithm. And finally, the signal s (k) received by the antenna can be extracted quickly and accurately through an adaptive algorithm.
(3) The null offset of the antenna output signal s (k) is mainly related to the vibration sensor and the magnetic field sensor, and the sensors with different precisions and bandwidths influence the precision of the antenna output value. The inputs to the calculation process are related to the sensor acquisition data, which is equivalent to coupling the antenna vibration data into the adaptive algorithm. And calculating the coefficient of the correlation coefficient of the vibration noise at the input end of the digital filter.
(4) The invention utilizes the vibration pickup effect to calculate the interference generated by vibration by acquiring the vibration data which is not related to the system. The method is mainly used for solving the influence of Hz-level low-frequency interference on the antenna and improving the signal-to-noise ratio of signal acquisition. The interference of Hz level can not be inhibited by means of traditional filter circuit or digital filter, etc., and the inhibition of the interference is the main advantage of the invention.
Drawings
In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings used in the description of the embodiments or the prior art will be briefly described below, it is obvious that the drawings in the following description are only some embodiments of the present invention, and for those skilled in the art, other drawings can be obtained according to the drawings without creative efforts.
FIG. 1 is a block diagram of an embodiment of the present invention.
Fig. 2 is a magnetic antenna coordinate system in an embodiment of the present invention.
Fig. 3 is a schematic block diagram of an adaptive antenna design in an embodiment of the present invention.
Fig. 4 is a schematic block diagram of an adaptive noise cancellation algorithm according to an embodiment of the present invention.
Fig. 5 is a schematic block diagram of a low frequency magnetic antenna in an embodiment of the present invention.
Fig. 6 is a structure diagram of a magnetic core in the embodiment of the present invention.
Fig. 7 is a diagram of a coil structure in the embodiment of the present invention.
Fig. 8 is another structural view of the magnetic core in the embodiment of the present invention.
Fig. 9 is a flowchart of an adaptive compensation method for a low-frequency magnetic antenna with compensation function according to an embodiment of the present invention.
The magnetic field sensor comprises a coil 1, a shielding box 2, an angular rate sensor 3, a magnetic core 4, a vibration reduction support 5, a magnetic field sensor 6, a low-noise amplification circuit 7, a microprocessor 8, an adaptive noise cancellation algorithm module 9, a coupling algorithm module 9-1, an adaptive algorithm module 9-2, a digital filter 10 and a canceller 11.
Detailed Description
The technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to the embodiments of the present invention, and it is obvious that the described embodiments are only a part of the embodiments of the present invention, and not all of the embodiments. All other embodiments, which can be derived by a person skilled in the art from the embodiments given herein without making any creative effort, shall fall within the protection scope of the present invention.
In the case of the example 1, the following examples are given,
a low-frequency magnetic antenna with a compensation function is shown in figure 1 and comprises a magnetic antenna, an amplifying circuit and a resolver.
The magnetic antenna consists of a magnetic core 4 and a coil 1 and is used for outputting a space induction signal; the shielding box 2 is arranged outside the coil 1, and the space induction signal output by the magnetic antenna is amplified by the low-noise amplifying circuit 7 and then output to the resolver.
And the resolver is used for simultaneously acquiring the sensor signal and the antenna output signal and calculating an antenna output value after noise cancellation through an internal adaptive noise cancellation algorithm module 9.
An angular rate sensor 3 and a magnetic field sensor 6 are arranged in the middle of the magnetic antenna, the angular rate sensor 3 can measure the angular rate variation of the three axes X ', Y' and Z ', and the magnetic field sensor 6 can measure the static magnetic field parameters of the three axes X', Y ', and Z'. The angular rate sensor 3 and the magnetic field sensor 6 are both arranged on the magnetic core 4 in a strapdown mode, namely X, Y and Z coordinates of the magnetic core 4 are in parallel relation with X ', Y' and Z 'coordinates of the angular rate sensor 3 and X', Y ', Z' coordinates of the magnetic field sensor 6; therefore, the measured values of the angular rate sensor 3 and the magnetic field sensor 6 are equivalent to the vibration angular rate components and the magnetic field components of the three axes X, Y and Z of the magnetic antenna.
The angular rate sensor 3 is used for measuring the vibration vector of the magnetic antenna, and the magnetic field sensor 6 is used for measuring the magnetic field intensity of the magnetic antenna and the static magnetic field of the earth.
The vibration reduction bracket 5 plays a role in fixing the magnetic core 4 and further reducing vibration; the shielding box 2 can shield the interference of space radiation electric field and can allow the penetration of low-frequency magnetic field. The magnetic antenna is arranged on system equipment through a damping support 5, and the system equipment is an antenna receiving system of a fixed base or a movable platform, such as a vehicle, an underwater vehicle and the like; the damping mount 5 has insulating properties.
The principle of the magnetic antenna for acquiring signals is that a magnetic field with space change is captured through a magnetic core 4, induced voltage (Faraday's law of electromagnetic induction) is generated through a coil 1, the coil 1 is wound by adopting a differential structure (see a schematic diagram in figure 7), and a port (a leaked conducting wire) of the coil 1 is connected with a low-noise amplifying circuit 7.
The low-noise amplifying circuit 7 is used for amplifying the induction signal in the space where the magnetic antenna is located; since the power density of the thermal noise and 1/f noise generated by the low-noise amplification circuit 7 itself is low, the circuit has a high signal-to-noise ratio. "1/f noise" is low frequency noise known in the art, with the noise power density being highest at a few Hz. The noise of Hz level is difficult to process by electronic means such as a filter; according to the embodiment of the invention, vibration is measured through the sensor in a vibration pickup mode, magnetic field change is calculated through the vibration, finally, a noise value is obtained according to the change amount, and the noise value is subtracted through the measured value, so that effective noise suppression is realized.
As shown in fig. 3, the signal y (k) output by the low-noise amplifying circuit 7 (i.e. the space induction signal output by the magnetic antenna) is the voltage output sensed by the coil 1, and includes a desired signal s (k) to be measured and an interference electromotive force n (k) actually generated by the magnetic antenna causing the coil 1 to cut the magnetic lines of space due to low-frequency mechanical vibration.
The resolver comprises a microprocessor 8, wherein the microprocessor 8 comprises an adaptive noise cancellation algorithm module 9 used for running an adaptive noise cancellation algorithm, and the adaptive noise cancellation algorithm module 9 comprises a coupling algorithm module 9-1 and an adaptive algorithm module 9-2.
And the coupling algorithm module 9-1 is used for calculating an induction signal x (k) generated when the magnetic antenna vibrates according to the acquired values of the angular rate sensor 3 and the magnetic field sensor 6.
As shown in fig. 2, when the magnetic antenna vibrates, the magnetic antenna will generate angular displacement in the three axes X, Y and Z, causing the equivalent area S of the coil 1 to change in the three axes. When the equivalent area S is changed, the coil 1 of the magnetic antenna can generate induced electromotive force, so that a space induction signal y (k) output by the magnetic antenna is interfered; the induced electromotive force is calculated according to formula (1):
wherein E represents an induced electromotive force, ε, generated by vibration of the magnetic antenna X 、ε Y 、ε Z Respectively representing the components of the induced electromotive force E in the three axial directions of X, Y, and Z.
ΔΦ X ，ΔΦ Y ，ΔΦ Z The variation of the magnetic flux in the three-axis directions of X, Y and Z, N represents the number of turns of the coil 1, and in the magnetic field, the variation of the magnetic flux is as follows:
ΔΦ＝B×ΔS (2)
where Δ S represents an equivalent area change amount of the coil 1 passing through the magnetic antenna, and B represents a geomagnetic offset amount.
Further, an induced electromotive force E of the magnetic antenna due to the vibration is represented as:
wherein
Hadamard product of a representation vector, (B) X ,B Y ,B Z ) Represents the component of the geomagnetic deviation B in the three-axis direction, (Delta S) X ,ΔS Y ,ΔS Z ) Representing the component of the equivalent area variation in the three-axis direction; since the change of the geomagnetic offset B requires a very long movement distance, even if the magnetic antenna is in a moving platform of an aircraft or a ship, the change of the geomagnetic offset B at the current moment is negligible, and the change of the induced electromotive force E is only related to the equivalent area change Δ S, as shown in formula (4):
in the formula (omega) X ,ω Y ,ω Z ) Angular velocity of the magnetic antenna in three axial directions, (S) X ,S Y ,S Z ) The equivalent area of the coil 1 in the three axial directions is shown; the induced electromotive force E of the magnetic antenna due to the vibration is obtained by substituting the formula (4) into the formula (3), see formula (5):
in the formula, vector (B) X ,B Y ,B Z ) The magnetic field strength in the three-axis direction of the space in which the magnetic antenna is located is calculated from the magnetic flux Φ measured by the magnetic field sensor 6, see equation (2). And performing modulo calculation on the vector E to obtain an induction signal x (k) generated by the system due to interference (low-frequency mechanical vibration).
An adaptive algorithm module 9-2 for calculatingThe induction signal x (k) dynamically adjusts the parameters of the digital filter 10, the output value of the digital filter 10 is made to approach the interference electromotive force n (k) actually generated by the magnetic antenna due to low-frequency mechanical vibration through the LMS algorithm, namely the noise value, and finally the approach value of n (k) is subtracted from the space induction signal y (k) output by the magnetic antenna through the canceller 11, thereby extracting the approach value of the expected signal s (k), namely the expected signal s (k)
The angular rate sensor 3 collects the three-axis angular acceleration W = [ omega ] of the magnetic antenna (after vibration reduction processing) under the antenna body coordinate system x ,ω y ,ω z ] T The area of the magnetic core 4 and the area of the coil 1 of the magnetic antenna are known, so that the change of the cross section area of the coil 1 in the three-axis direction at the speed can be calculated by the microprocessor 8; wherein W = [ omega ] x ,ω y ,ω z ] T And (omega) X ,ω Y ,ω Z ) Are substantially the same.
The magnetic field sensor 6 is used for acquiring the magnetic field intensity B = [ B ] of the space where the magnetic antenna is located x ,B y ,B z ] T Wherein B = [ B ] X ,b Y ,b Z T ]And vector (B) X ,B Y ,B Z ) Are substantially the same.
In the case of the example 2, the following examples are given,
the main frame is LMS (Least Mean Square) algorithm, and the algorithm is composed of an adaptive algorithm module and an FIR (Finite Impulse Response) digital filter. The adaptive algorithm satisfies the minimum MSE criterion, i.e. the error function is obtained
The minimum value is reached, and the minimum value,
indicating whether the desired signal calculated by the adaptive algorithm is generally in error with the ideal desired signal, which is the final output value of the present invention, isClosest to the ideal measurement, s (k) denotes the ideal measurement. In reality, any instrument cannot obtain an ideal value, a measured value has certain error, if x (k) is directly counteracted with an induction signal, the convergence direction of the mean square error of the obtained value and the ideal value cannot be controlled, and the measurement error is increased depending on the drift condition of an x (k) sensor.
As shown in fig. 9, the coupling algorithm module 9-1 collects the output values of the angular rate sensor 3 and the magnetic field sensor 6, and calculates an induced signal x (k) generated by the magnetic antenna due to low-frequency mechanical vibration; because the low-frequency mechanical vibration original signals collected by the angular rate sensor 3 and the magnetic field sensor 6 have no coupling effect with the magnetic antenna induction signals, namely x (k) and s (k) are not related to each other, n (k) and s (k) are also not related to each other, and only n (k) and z (k) are related to each other; n (k) in the embodiment of the invention is obtained by calculating the original data x (k), namely, a measuring means irrelevant to the magnetic signal is used, the filter coefficient with larger relevance is estimated, and the reliability is higher. When the condition of equation (6) is satisfied, z (k) is made to trend toward n (k), and the desired signal s (k) is extracted from the induction signal of the coil 1 by the canceller.
min ε(k)＝E[(n(k)-z(k)) 2 ] (6)
Where ∈ (k) represents an error between z (k) and the disturbed electromotive force n (k), z (k) represents an output value corresponding to a time when the digital filter 10 receives the induced signal x (k) generated when the magnetic antenna vibrates as an input, k represents a time, and z (k) is a k-th element value in the buffer in the program.
Therefore, ε (k) calculated according to equation (6) may be used as an input parameter to the magnetic antenna filtering algorithm to participate in the iterative operation. The digital filter 10 may be implemented as a conventional FIR filter; different from the known LMS algorithm, the embodiment of the invention is improved on the basis of the LMS algorithm, a coefficient K is added at the input end of the algorithm, the conventional filtering algorithm is equivalent to K =1, and the time period of the iterative algorithm is longer. The coefficient K of each tap in the FIR filter is adaptively modified in this embodiment. The basis for the correction is determined by epsilon (k) by looking up a data table, by which the input value x (k) is corrected in real time in the solver program, see fig. 3-4, and the addition of compensation allows for a rapid correction of the measurement error. For example, when the measurement in the present period finds that epsilon (k) falls in a certain region of the data table, each tap coefficient in the region is selected for calculation, and the data table is obtained through experimental measurement.
The approximate value of n (k) is subtracted from the space induction signal y (k) output from the magnetic antenna by the canceller 11, thereby extracting the approximate value of the desired signal s (k), i.e., the approximate value of n (k) is extracted
The data table measurement principle is to build an experimental environment with known magnetic field excitation in a laboratory, and the environment can simulate noise interference generated by the low-frequency vibration condition of an antenna by applying the known low-frequency excitation to the magnetic antenna. And testing the LMS algorithm by using the known excitation, and modifying and recording the coefficient K value according to the iteration period and the error of the LMS algorithm. And finally, obtaining a coefficient K value data table with the least iteration times and the lowest error of the LMS algorithm used by the antenna to be tested according to the recorded values.
Wherein, virtual environment is built to available finite element software of experimental environment, for example Maxwell, also can be used to magnetic shield case Helmholtz coil and build true experimental environment. The former is inefficient, but the accuracy depends on the accuracy of the antenna model parameters. The latter has the disadvantages of complex construction environment, high cost and long test period, but has high accuracy because a real antenna is used as a measured object. The former can be used to determine the range of excitation setting required by the test, and the latter can be used to verify the real measured object.
In the process of making z (k) trend to n (k), the weight coefficient w of the digital filter is reduced by gradient 0 ，w 1 ，w 2 ……w m-1 The solution is performed as follows:
at the moment of 5, k +1, repeating the steps 2 to 4, continuing the iteration until the algorithm is converged, and finally obtaining the weight coefficient w of the digital filter 10 according to the weight coefficient matrix of the filter 0 ，w 1 ，w 2 ……w m-1 The value of (c).
In fig. 4, the step length u is generally a fixed value, and can be determined according to requirements such as early-stage tests and calculation periods in different projects, the larger u is, the shorter u is, but the larger u is, and the smaller u is, the longer u is, and the smaller u is, the longer u is, and the error is.
The frame of the adaptive noise cancellation algorithm of the embodiment of the invention adopts third-party measurement data (data measured by two sensors) to calculate the change of the coefficient in the filtering algorithm, thereby effectively solving the interference of vibration of several Hz levels and greatly improving the sensitivity of the antenna used in a mobile platform.
In the case of the example 3, the following examples are given,
an application of a 60Hz low frequency receiving antenna, as shown in fig. 5; the magnetic core 4 of the magnetic antenna is a silicon steel material having high permeability characteristics. In order to suppress the influence of the eddy current generated by the alternating magnetic field on the induced voltage, the magnetic core 4 is in a coil structure to cut off the eddy current loop, and an insulating layer is arranged between layers of the silicon steel coil, as shown in fig. 6. The insulating layer can be made of high-resistance materials such as insulating rubber, insulating paint and the like. When the magnetic core 4 is a solid core, when the received magnetic field alternates, eddy current is generated in the cross section of the magnetic core 4, and the eddy current forms an alternating magnetic field, which finally affects the electromotive force (i.e. the measured value) output by the induction coil. It is therefore necessary to break the eddy currents so that they do not form a closed loop. The magnetic core 4 can be realized by slotting in the cross section besides the roll structure, as shown in fig. 8; however, the slotting easily affects the magnetic volume of the magnetic core, the processing difficulty is high, and the strength of the magnetic core 4 can be affected to a certain extent.
The traditional coil is wound by adopting a single-end electrified solenoid mode, but the induced electromotive force is easily interfered. As shown in fig. 7, the coil 1 of the magnetic antenna in the embodiment of the present invention adopts a double-wire winding manner, the winding directions of the two coils 1 are the same, the number of turns of the two coils 1 is the same, the output voltage of the coil 1 is a differential signal, and the interference electromotive forces with the same magnitude and opposite polarities are generated on the two single-ended energized coils due to the interference, so that the output ends can be automatically cancelled, the influence of the interference on the measurement accuracy is reduced, and the anti-interference capability of the output signal is improved.
The damping mount 5 serves to damp mechanical vibrations of the magnetic antenna. When the magnetic antenna vibrates, the projected area of the coil 1 in the current magnetic field vector direction changes, and a matching induced electromotive force with the vibration frequency is generated, so that the normal output signal of the magnetic antenna is interfered. In the present embodiment, the magnetic antenna has a receiving frequency of 60HZ, and therefore the vibration damping mount 5 is mainly used to suppress mechanical vibration of about 60 HZ.
The low-noise amplification circuit 7 is mainly composed of a low-noise differential operational amplifier (OPA 2189), an isolation amplifier (ISO 224), and a compensation amplifier (INA 849). The front end of the low-noise amplifying circuit 7 filters high-frequency interference caused by space radiation through a capacitor, and reduces the input impedance of the circuit at high frequency, wherein the capacitance values are respectively C1=2.2 μ F, C2=1 μ F and C3=1 μ F. The OPA2189 can amplify and output the differential signal output by the magnetic antenna, and the power density of the thermal noise generated by the circuit is very low
And the output is a differential signal. The first amplifier INA849 (specifically, the low noise amplifier in fig. 5) is used to convert the differential signal into a single-ended signal. ISO224 is used for isolating the amplifying circuit from the rear-end acquisition circuit and reducingThe back-end circuit interferes the acquisition circuit in a coupling mode, but an ISO224 chip generates 3dB attenuation on an input signal, so that the gain of the second INA849 amplification circuit (compensation amplifier) is designed to be 3dB for compensating the attenuation of the circuit.
The resolver is a microprocessor circuit with a DSP chip (model TMS 28335) as a core, and comprises a processor module, an AD acquisition interface, a serial port communication interface and the like. The resolver is used for collecting sensor data and signals of the low-noise amplifying circuit 7, calculating interference electromotive force generated by vibration of the magnetic antenna at the current moment through a coupling algorithm, and calculating expected signals through the digital filter 10
Is substantially the same as s (k) at the far right side in fig. 3.
The coupling algorithm in the resolver is used to calculate the coupling data of the disturbing electromotive force generated by the vibration of the coil 1. The principle is that the variation of the induction area of the coil 1 is calculated by collecting the current vibration frequency of the magnetic antenna, and then the current corresponding induced electromotive force is calculated according to the collected value of the magnetic field sensor 6, which is shown in formula (7):
where ∈ denotes an induced electromotive force, Φ denotes a magnetic flux passing through the coil 1, B denotes a magnetic field strength passing through the coil 1, S denotes a projected area of the coil 1 in the magnetic field, and N denotes the number of turns of the coil 1.
According to the formula (1), the electromotive force vector E = (epsilon) generated by vibration in the triaxial direction under the current state can be calculated x ,ε y ,ε z ). Then | E | is the disturbing electromotive force x (k) generated by the vibration in fig. 3.
The digital filter 10 module of this embodiment takes the induced signal x (k) generated by the magnetic antenna due to the low-frequency mechanical vibration and the space induced signal y (k) output by the magnetic antenna as input, and iteratively calculates the approximation value of the interference electromotive force n (k) generated due to the vibration. Finally, the approximate value of y (k) and n (k) is subtracted by a canceller to obtain s (k). The interference of the magnetic antenna caused by vibration is effectively reduced through a multi-iteration algorithm, empirical data do not need to be prepared in advance, the output precision or sensitivity of equipment depends on the precision and response bandwidth of the sensor, and the receiving sensitivity of the magnetic antenna is greatly improved.
The above description is only for the preferred embodiment of the present invention, and is not intended to limit the scope of the present invention. Any modification, equivalent replacement, or improvement made within the spirit and principle of the present invention shall fall within the protection scope of the present invention.
Claims (9)
1. A low-frequency magnetic antenna with compensation function is characterized by comprising
The magnetic antenna consists of a magnetic core (4) and a coil (1) and is used for outputting a space induction signal;
the angular rate sensor (3) and the magnetic field sensor (6) are both arranged on the magnetic core (4), and three-axis measurement values of the angular rate sensor (3) and the magnetic field sensor (6) equivalently represent vibration angular rate components and magnetic field components corresponding to the magnetic antenna;
the amplifying circuit comprises a low-noise amplifying circuit (7) which is used for amplifying the space induction signal output by the magnetic antenna and outputting the amplified space induction signal to the resolver;
the resolver is used for simultaneously collecting output signals of the angular rate sensor (3) and the magnetic field sensor (6) and space induction signals output by the magnetic antenna, solving a noise value according to variation output by the angular rate sensor (3) and the magnetic field sensor (6), and subtracting the noise value from the space induction signals output by the magnetic antenna to realize noise suppression;
the resolver comprises a microprocessor (8), the microprocessor (8) comprising an adaptive noise cancellation algorithm module (9) for running an adaptive noise cancellation algorithm;
the adaptive noise cancellation algorithm module (9) comprises
The coupling algorithm module (9-1) is used for calculating an induction signal x (k) generated by the magnetic antenna due to low-frequency mechanical vibration according to output values of the angular rate sensor (3) and the magnetic field sensor (6); and
the adaptive algorithm module (9-2) is used for dynamically adjusting parameters of the digital filter (10) according to the induction signal x (k), enabling the output value of the digital filter (10) to approach an interference electromotive force n (k) actually generated by the magnetic antenna due to low-frequency mechanical vibration through an LMS algorithm, namely a noise value, and finally subtracting the approach value of the n (k) from the space induction signal y (k) output by the magnetic antenna through a canceller (11), so that the approach value of the expected signal s (k), namely the approach value of the expected signal s (k) is extracted
2. A low-frequency magnetic antenna with compensation function according to claim 1, characterized in that said angular rate sensor (3) is able to measure the variation of angular rate in three axes X3, Y ', Z', and the magnetic field sensor (6) is able to measure the static magnetic field parameters in three axes X ", Y", Z "; the X, Y and Z coordinates of the magnetic core (4) are in parallel relation with the X ', Y' and Z 'coordinates of the angular rate sensor (3) and the X', Y ', and Z' coordinates of the magnetic field sensor (6).
3. A low-frequency magnetic antenna with compensation function according to claim 1, characterized in that the magnetic core (4) is mounted to the system equipment through a vibration damping bracket (5), and a shielding box (2) is mounted outside the coil (1) for shielding the interference of the space radiation electric field and allowing the penetration of the low-frequency magnetic field.
4. Low-frequency magnetic antenna with compensation function according to claim 1, characterized in that the square-root spectral density of the thermal noise and 1/f noise generated by the low-noise amplification circuit (7) itself is as follows
And (4) stages.
5. A low-frequency magnetic antenna with compensation function according to claim 1, characterized in that the coil (1) is wound in a differential structure, and the port of the coil (1) is connected with the low-noise amplification circuit (7).
6. A low frequency magnetic antenna with compensation according to claim 1, characterized in that the magnetic core (4) is of a roll or slot configuration.
7. The low-frequency magnetic antenna with compensation function according to claim 1, wherein the coupling algorithm module (9-1) calculates the induced signal x (k) of the magnetic antenna due to the low-frequency mechanical vibration by using the formula (5):
wherein E represents an induced electromotive force generated by vibration of the magnetic antenna, N represents the number of turns of the coil (1), and the vector (B) x ,B y ,B z ) The magnetic field intensity of the space where the magnetic antenna is located in the three-axis direction is calculated by magnetic flux phi measured by the magnetic field sensor (6); (omega) X ,ω Y ,ω Z ) The angular rate of the magnetic antenna in the three-axis direction is represented and measured by an angular rate sensor (3); (S) X ,S Y ,S Z ) The equivalent area of the coil (1) in the three axial directions is shown;
and performing modulo calculation on the vector E to obtain an induction signal x (k) generated by the magnetic antenna due to low-frequency mechanical vibration.
8. The adaptive compensation method for a low-frequency magnetic antenna with compensation function according to claim 1, is characterized by comprising the following steps:
a coupling algorithm module (9-1) collects output values of the angular rate sensor (3) and the magnetic field sensor (6) and calculates an induction signal x (k) generated by the magnetic antenna due to low-frequency mechanical vibration; the low-frequency mechanical vibration original signals collected by the angular rate sensor (3) and the magnetic field sensor (6) have no coupling effect with the induction signals of the magnetic antenna, namely x (k) is not related to the expected signals s (k) output by the magnetic antenna, the interference electromotive force n (k) and s (k) actually generated by the magnetic antenna due to low-frequency mechanical vibration are also not related to each other, and only n (k) is related to z (k); therefore, by the LMS algorithm, when the condition of formula (6) is satisfied, z (k) is made to tend to n (k);
min ε(k)＝E[(n(k)-z(k)) 2 ] (6)
wherein epsilon (k) represents an error between z (k) and n (k), z (k) represents an output value corresponding to a time when the digital filter (10) receives an induction signal x (k) generated when the magnetic antenna vibrates as an input, and k represents a time;
the coefficient K of each tap in the digital filter (10) is corrected in real time by looking up a data table, and the data table is obtained by experimental measurement;
an approximate value of n (k) is subtracted from a space induction signal y (k) output by a magnetic antenna through a canceller (11), so that an approximate value of a desired signal s (k), namely the approximate value of the desired signal s (k) is extracted
9. Method for the adaptive compensation of a low-frequency magnetic antenna with compensation function according to claim 8, characterized in that the weighting coefficient w of the digital filter (10) is reduced by gradient in the process of making z (k) trend towards n (k) 0 ，w 1 ，w 2 ……w m-1 The method for solving specifically comprises the following steps:
step 1, selecting weight coefficients, and enabling an initial coefficient matrix w (k) =0, k =0;
step 2, calculating the output n (k) = X of the digital filter (10) at the current time k T (k) w (k), wherein X (k) = [ X (k), X (k-1),. X (k-m + 1) ]] T I.e. the output value of the coupling algorithm in the continuous acquisition time;
step 3, calculating error signal
Step 4, calculating the weight coefficient matrix of the digital filter (10) of the next period
μ is an adaptive convergence coefficient, which is fullFoot
Wherein λ max Is an X (k) autocorrelation matrix R x The maximum eigenvalue of (d);
at the moment of 5, k +1, repeating the steps 2 to 4, continuing the iteration until the algorithm is converged, and finally obtaining the weight coefficient w of the digital filter (10) according to the filter weight coefficient matrix 0 ，w 1 ，w 2 ……w m-1 The value of (c).
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