CN114487687B - Device and method for non-contact rapid measurement of penetration depth of metal plate - Google Patents
Device and method for non-contact rapid measurement of penetration depth of metal plate Download PDFInfo
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- 229910052751 metal Inorganic materials 0.000 title claims abstract description 142
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Abstract
The invention relates to a device and a method for rapidly measuring the skin depth of a metal plate in a non-contact way, belonging to the field of electromagnetic compatibility.
Description
Technical Field
The invention relates to the field of electromagnetic compatibility, in particular to a device and a method for quickly measuring the penetration depth of a metal plate in a non-contact manner.
Background
Both theoretically and practically speaking, the problem of electromagnetic field shielding is of great interest, and conductors generally act as good shields, the shielding of electromagnetic disturbances being in essence partly the skin effect caused by the interaction of electromagnetic waves and conductors. When an electromagnetic wave propagates in a conductor, its amplitude is attenuated continuously, and in order to measure the attenuation degree of the electromagnetic wave in a metal plate, the depth of field intensity amplitude attenuation to 1/e of amplitude at the surface is generally called a penetration depth d. The physical characteristic characterization quantity influencing the penetration depth of the electromagnetic waves comprises the following components: frequency (f), permeability (μ), conductivity (γ). I.e. different good conductors, different frequencies, and different skin depths.
The penetration depth is an important index parameter for analyzing the alternating current impedance, the current distribution and the electromagnetic shielding effectiveness of the conductor, and is closely and inseparably connected with the eddy current loss, so that the measurement of the penetration depth of the metal plate is necessary in actual life. From the knowledge of electromagnetism, it can be known that, simply applying the classical theoretical formula to calculate the skin depth usually requires the precondition of knowing the material properties, the power frequency, etc. However, nowadays, the physical properties of many new composite materials are difficult to be accurately confirmed in a short time, and the electromagnetic environment presents complex space-time characteristics. High-end customized intelligent instrument equipment meets the requirement of contact type measurement of the penetration depth, but a user needs to bear high research, development, operation and maintenance cost on one hand, and on the other hand, under the operating condition that the requirement on experimental operation is quite strict, a measurement system cannot be in direct contact with a test article, so that the currently popular technology is high in cost and difficulty when the penetration depth of a metal plate is obtained, and is severely limited in application range.
Disclosure of Invention
The invention aims to provide a device and a method for rapidly measuring the penetration depth of a metal plate in a non-contact way, so as to simply and rapidly measure the penetration depth of the metal plate.
In order to achieve the purpose, the invention provides the following scheme:
an apparatus for non-contact rapid measurement of skin depth of a metal sheet, said apparatus comprising: the device comprises a low-frequency signal generator, a transmitting ring, a receiving induction coil, a spectrum analyzer and a skin depth calculation module;
the transmitting ring and the receiving induction coil are respectively and oppositely arranged on two sides of the metal plate to be detected;
the low-frequency signal generator is connected with the transmitting ring, and the receiving induction coil is connected with the spectrum analyzer;
the low-frequency signal generator is used for generating a signal with a preset frequency and transmitting the signal with the preset frequency to the transmitting ring;
the transmitting ring is used for releasing electromagnetic pulses according to signals with preset frequency to form a magnetic field;
the receiving induction coil is used for generating an induced voltage in the magnetic field;
the spectrum analyzer is used for receiving the induced voltage and then displaying the waveform of the induced voltage;
and the skin depth calculation module is used for determining a skin depth curve of the metal plate to be detected according to the waveform of the induction voltage.
Optionally, the metal plate to be detected is a square metal plate;
the side length of the square metal plate is larger than 3 times of the diameter of the transmitting ring and larger than 3 times of the distance from the transmitting ring to the square metal plate.
Optionally, the axes of the transmitting ring and the receiving induction coil are overlapped, and the distance from the overlapped axis to the central axis of the metal plate to be measured is smaller than a distance threshold.
Optionally, the skin depth calculation module includes:
the induction voltage acquisition unit is used for acquiring the induction voltages of the metal plate to be detected under the same signal frequency when the thickness of the metal plate is different from that of the metal plate to be detected under the same signal frequency on the basis of keeping the output voltage of the low-frequency signal generator unchanged in the process that the low-frequency signal generator generates the signal with the same frequency;
the skin depth calculation unit is used for calculating a skin depth measurement value under the same signal frequency by using a skin depth calculation formula according to the induction voltages under the same signal frequency and at two different thicknesses; the skin depth calculation formula is determined by a quotient comparison method;
a cycle unit for changing the signal frequency and repeating the above steps to obtain a skin depth measurement at each signal frequency;
and the drawing unit is used for drawing a skin depth curve of the metal plate to be measured by taking the signal frequency as an abscissa and the skin depth measured value as an ordinate according to the skin depth measured values under various signal frequencies.
A method for non-contact rapid measurement of skin depth of a metal sheet using the apparatus described above, the method comprising:
keeping the output voltage of the low-frequency signal generator unchanged in the process that the low-frequency signal generator generates signals with the same frequency, and acquiring the induced voltages of the metal plate to be detected under the same signal frequency when the metal plate to be detected has two different thicknesses;
calculating a skin depth measurement value under the same signal frequency by using a skin depth calculation formula according to the induced voltages under the same signal frequency and at two different thicknesses; the skin depth calculation formula is determined by a quotient comparison method;
changing the signal frequency, repeating the above steps, and obtaining a skin depth measurement value at each signal frequency;
and drawing a skin depth curve of the metal plate to be measured by taking the signal frequency as an abscissa and the skin depth measured value as an ordinate according to the skin depth measured values under various signal frequencies.
Optionally, obtaining the induced voltage of the metal plate to be measured at two different thicknesses under the same signal frequency specifically includes:
acquiring the waveform peak values of the induced voltage of the metal plate to be detected under the same signal frequency when the metal plate to be detected has two different thicknesses; the unit of the waveform peak isdBmv；
Using formulas
The unit conversion is performed on the waveform peak of the induced voltage.
Optionally, the determination process of the skin depth calculation formula is as follows:
establishing the relation of the induced voltages of the metal plate to be measured under the same signal frequency in two different thicknesses respectively
And
(ii) a Wherein the content of the first and second substances,E 1is the thickness of the metal plate to be measuredd 1The induced voltage of the time-varying current,E 2is the thickness of the metal plate to be measuredd 2The induced voltage of the time-varying current,E 0is the output voltage of the low frequency signal generator,kis a coefficient of proportionality that is,dis a skin depth measurement;
by using a quotient comparison method, the ratio of the induced voltages of two different thicknesses under the same signal frequency is obtained
；
Determining the skin depth calculation formula under the same signal frequency according to the induced voltage ratio as
。
Optionally, the step of calculating the skin depth measurement value at the same signal frequency by using a skin depth calculation formula according to the induced voltages at two different thicknesses at the same signal frequency further includes:
keeping the output voltage of the low-frequency signal generator unchanged in the process that the low-frequency signal generator generates signals with the same frequency, and acquiring the thickness of the metal plate to be measured under the same signal frequencyd 3The induced voltage of time;
according to the thickness of the same signal frequencyd 2Induced voltage and thickness of timed 3The time induced voltage is calculated by using a skin depth calculation formula to calculate the thickness under the same signal frequencyd 2、d 3A corresponding skin depth measurement;
calculating the thickness of the same signal frequencyd 1、d 2Corresponding skin depth measurement and thicknessd 2、d 3The corresponding skin depth measurements are averaged and the average is taken as the skin depth measurement at the same signal frequency.
Optionally, the step of calculating the skin depth measurement value at the same signal frequency by using a skin depth calculation formula according to the induced voltages at two different thicknesses at the same signal frequency further includes:
using formulasd'= 
Calculating a theoretical value of the penetration depth under the same signal frequency; wherein the content of the first and second substances,d'for the theoretical value of the skin depth,ωin order to be the angular frequency of the frequency,ω=2πf，fin order to be the frequency of the signal,μthe magnetic conductivity of the metal plate to be measured is gamma, and the electric conductivity of the metal plate to be measured is gamma;
the relative error of the theoretical skin depth value at the same signal frequency and the measured skin depth value at the same signal frequency is calculated.
According to the specific embodiment provided by the invention, the invention discloses the following technical effects:
the invention discloses a device and a method for quickly measuring the skin depth of a metal plate in a non-contact way.
Drawings
In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings needed to be used in the embodiments will be briefly described below, and it is obvious that the drawings in the following description are only some embodiments of the present invention, and it is obvious for those skilled in the art to obtain other drawings without inventive exercise.
FIG. 1 is a schematic structural diagram of an apparatus for non-contact rapid measurement of skin depth of a metal plate according to the present invention;
FIG. 2 is a flow chart of a method for rapidly measuring the skin depth of a metal plate in a non-contact manner according to the present invention;
FIG. 3 is a skin depth comparison graph provided in example 1 of the present invention;
FIG. 4 is a skin depth contrast graph provided in example 2 of the present invention.
Detailed Description
The technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to the drawings in 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.
The invention aims to provide a device and a method for rapidly measuring the penetration depth of a metal plate in a non-contact way, so as to simply and rapidly measure the penetration depth of the metal plate.
In order to make the aforementioned objects, features and advantages of the present invention comprehensible, embodiments accompanied with figures are described in further detail below.
The present invention provides a device for non-contact rapid measurement of skin depth of a metal plate, as shown in fig. 1, the device comprises: the device comprises a low-frequency signal generator, a transmitting ring, a receiving induction coil, a spectrum analyzer and a skin depth calculating module.
The transmitting ring and the receiving induction coil are respectively and oppositely arranged on two sides of the metal plate to be detected. The low-frequency signal generator is connected with the transmitting ring, and the receiving induction coil is connected with the spectrum analyzer. The low-frequency signal generator is used for generating a signal with a preset frequency and transmitting the signal with the preset frequency to the transmitting ring. The transmitting ring is used for releasing electromagnetic pulses according to signals with preset frequency to form a magnetic field. The receiving induction coil is used for generating an induced voltage in a magnetic field. The spectrum analyzer displays the waveform of the induction voltage after receiving the induction voltage; and the skin depth calculation module determines a skin depth curve of the metal plate to be detected according to the waveform of the induction voltage.
The gathered signals are more beneficial to the whole measurement, and the method not only can enable the measurement to be more accurate, but also is beneficial to capturing weak signals. Therefore, in order to avoid the edge effect of the metal plate (especially in high frequency measurement), referring to fig. 1, the metal plate to be measured is a square metal plate, and the side length of the square metal plate is greater than 3 times of the diameter of the transmitting ring and greater than 3 times of the distance from the transmitting ring to the square metal plate. In FIG. 1, the diameter of the transmitting ring is 12cm, and the size of the metal plate is 1m × 1 m. The optimal placement of the transmitting ring should be as close as possible to the metal plate.
Illustratively, the axes of the transmitting ring and the receiving induction coil are overlapped, and the distance from the overlapped axis to the central axis of the metal plate to be measured is smaller than a distance threshold. Namely, the centers of the transmitting ring and the receiving induction coil are correspondingly placed near the central axis of the metal plate.
The preferable mode is as follows: the low frequency signal generator is of the type ZN 1042A. The type of the transmitting ring (transmitting coil) is ZN30303, and the transmitting frequency is 0.7kHz-1 MHz. The radius of the receiving induction coil is 2 cm. The metal plate to be measured is a solid metal plate.
Illustratively, the skin depth calculation module includes: the device comprises an induced voltage acquisition unit, a skin depth calculation unit, a circulation unit and a drawing unit.
The induced voltage acquisition unit is used for acquiring the induced voltage of the metal plate to be measured under the same signal frequency when the metal plate has two different thicknesses on the basis of keeping the output voltage of the low-frequency signal generator unchanged in the process of generating the signal with the same frequency by the low-frequency signal generator. The skin depth calculation unit is used for calculating a skin depth measurement value under the same signal frequency by utilizing a skin depth calculation formula according to induction voltages under the same signal frequency and at two different thicknesses; the skin depth calculation formula is determined by a quotient comparison method. The cyclic unit is used to vary the signal frequency and repeat the above steps to obtain a skin depth measurement at each signal frequency. The drawing unit is used for drawing a skin depth curve of the metal plate to be measured by taking the signal frequency as an abscissa and the skin depth measured value as an ordinate according to the skin depth measured value under various signal frequencies.
The measuring device does not need to be in direct contact with a test article, and the application range of the device is wider due to non-contact rapid measurement.
The invention provides a device for quickly measuring the skin depth of a metal plate in a non-contact manner based on the device for quickly measuring the skin depth of the metal plate in the non-contact manner, and also provides a method for quickly measuring the skin depth of the metal plate in the non-contact manner, wherein the method comprises the following steps as shown in figure 2:
and step S1, keeping the output voltage of the low-frequency signal generator unchanged in the process that the low-frequency signal generator generates signals with the same frequency, and acquiring the induced voltages of the metal plate to be measured with the same signal frequency in two different thicknesses.
Step S2, calculating the skin depth measurement value under the same signal frequency by using a skin depth calculation formula according to the induction voltages under the same signal frequency and the two different thicknesses; the skin depth calculation formula is determined by a quotient comparison method.
Step S3, changing the signal frequency, repeating the above steps, and obtaining a skin depth measurement at each signal frequency.
And step S4, drawing a skin depth curve of the metal plate to be measured by taking the signal frequency as an abscissa and the skin depth measured value as an ordinate according to the skin depth measured values under various signal frequencies.
For example, the step S1 of obtaining the induced voltages of the metal plate to be measured at two different thicknesses under the same signal frequency specifically includes: acquiring the waveform peak values of the induction voltage of a metal plate to be detected under the same signal frequency when the metal plate to be detected has two different thicknesses; the unit of the waveform peak isdBmv(ii) a Using formulas
The unit conversion is performed on the waveform peak of the induced voltage.
Illustratively, the determination process of the skin depth calculation formula in step S2 is:
s2-1, establishing the relation of the induced voltage of the metal plate to be measured under the same signal frequency when the metal plate has two different thicknesses
And
；
s2-2, obtaining the ratio of the induced voltages of two different thicknesses under the same signal frequency by using a quotient comparison method
；
S2-3, determining the skin depth calculation formula under the same signal frequency according to the ratio of the induced voltages as
。
Wherein the content of the first and second substances,E 1is the thickness of the metal plate to be measuredd 1The induced voltage of the time-varying current,E 2is the thickness of the metal plate to be measuredd 2The induced voltage of the time-varying current,E 0is the output voltage of the low frequency signal generator,kis a coefficient of proportionality that is,dis a skin depth measurement;
illustratively, step S2 is followed by:
generating the same kind of frequency in a low-frequency signal generatorKeeping the output voltage of the low-frequency signal generator unchanged in the signal process of the frequency, and acquiring the thickness of the metal plate to be measured under the same signal frequencyd 3The induced voltage of time;
according to the thickness of the same signal frequencyd 2Induced voltage and thickness of timed 3The time induced voltage is calculated by using a skin depth calculation formula to calculate the thickness under the same signal frequencyd 2、d 3A corresponding skin depth measurement;
calculating the thickness of the same signal frequencyd 1、d 2Corresponding skin depth measurement and thicknessd 2、d 3The corresponding skin depth measurements are averaged and the average is taken as the skin depth measurement at the same signal frequency.
Exemplarily, the step S2 further includes:
using formulasd'= 
Calculating a theoretical value of the penetration depth under the same signal frequency; wherein the content of the first and second substances,d'for the theoretical value of the skin depth,ωin order to be the angular frequency of the frequency,ω=2πf，fin order to be the frequency of the signal,μthe magnetic conductivity of the metal plate to be measured is gamma, and the electric conductivity of the metal plate to be measured is gamma;
the relative error of the theoretical skin depth value at the same signal frequency and the measured skin depth value at the same signal frequency is calculated.
The specific implementation of the measurement method of the present invention is described in detail below:
step 1: the instrument is placed according to figure 1, and the transmitting ring is positioned below the aluminum plate and corresponds to the center of the receiving coil. And connecting the transmitting loop with a low-frequency power signal generator, observing the spectrum analyzer, and reading the waveform peak value of the induced voltage. The reading value is in units of dBmv, which needs to be converted to volts V in step 2.
Step 2: using a formula
The induced voltage (i.e. spectrum analyzer display waveform peak value, unit: dBmv) received by receiving coil in experimental instrument is converted into voltage (V) unit, i.e. voltage (V) unit
And step 3: by varying the total thickness of the metal plate (d respectively1、d2) And reading the waveform peak of the spectrum analyzer. The received voltage (E) measured by placing two metal plates of different thickness at the same frequency while varying the thickness of the metal plates and ensuring that the current in the transmitting coil remains constant1、E2) Substitution formula
And calculating to obtain a group of measured skin depths d.
The invention is based on the correlation between the thickness and the penetration depth of the metal plate and the set transmitting voltage and receiving voltage during the test, if the transmitting voltage is E0The middle placing thickness is d1When the metal plate receives an induced voltage of E1The middle placing thickness is d2When the metal plate receives an induced voltage of E2. Then, the following relationship can be established:
wherein: the scale factor for measuring the influence of objective factors such as the radius of the transmitting ring and the receiving induction coil, the refraction and reflection of electromagnetic waves in free space, the distance from the transmitting ring to the metal plate, the distance from the metal plate to the receiving induction coil and the like on the skin depthkTo indicate.
d 1，d 2Is shown asThe same thickness of the metal plate.
It is important to note that in the experimental process, around the idea of controlling variables, we need to keep the radius of the transmitting ring and the receiving induction coil constant, keep the distance from the transmitting ring to the metal plate and the distance from the metal plate to the receiving induction coil constant, and only change the thickness of the metal plate, so as to ensure that E is equal to E1、E2Coefficient in equationkEqual, and not as a function of switching sheet metal thickness.
The method of the present invention is to change the thickness of the metal plate and ensure the emitting current to be unchanged, i.e. the emitted magnetic field to be unchanged, and is to better utilize two sets of data to eliminate and reduce the unknown quantity. The specific method comprises the following steps: when the same frequency point is measured, the output voltage of the low-frequency signal generator (the low-frequency signal generator is connected with the transmitting ring) is kept unchanged, so that E1、E2E in the formula0Are equal. For example, when the frequency of the signal is 50000Hz, the output voltage of the signal generator is kept at E even if the thickness of the metal plate is changed0=6.95V unchanged.
The invention skillfully places two metal plates with different thicknesses to obtain the induced voltage E of the receiving coil1、E2And if the quotient is removed, the following can be obtained:
the quotient division well eliminates almost the irrelevant error factors among the groups, and then the following results are obtained:
the skin depth d is thus obtained as:
step (ii) of4: using the classical formula of skin depthd'= 
And calculating to obtain a theoretical value of the penetration depth, and finally comparing and verifying with the measured value.
The classical theory of calculating skin depth is as follows:
from homogeneous wave equation:
and lossy media conditions:
because of the good conductor, the approximation condition can be substituted, i.e.:
the skin depth can be obtained:
wherein:
is the vector of the electric field and is,k e is the propagation coefficient (complex number) of the lossy medium,
to be the equivalent complex permittivity of the lossy medium,ω=2πfis the angular frequency of the wave to be transmitted,μis the magnetic permeability of the metal sheet,k' is a phase coefficient of the phase signal,k' is the attenuation coefficient of the lossy medium,jrepresenting the imaginary unit of the complex number, gamma is the conductivity of the metal plate.
By consulting the data, the conductivity of the solid metal aluminum plate is calculated to be gamma =3.774 × 107（S/m) Magnetic permeability ofμ=4π×10-7（H/m）。
And 5: and adjusting the low-frequency power signal generator to change the frequency of the signal sent by the low-frequency power signal generator, repeating the steps, measuring information under a plurality of frequency points, and finally drawing a penetration depth curve.
The invention provides a method for rapidly measuring the penetration depth of a metal plate in a non-contact manner by skillfully applying the definition of the penetration depth. Firstly, a magnetic field transmitting coil is arranged on one side of a metal plate, and a magnetic field receiving coil is arranged on the other side of the metal plate; then, metal plates of the same material and different thicknesses are switched and placed, and the penetration depth is calculated by comparing the induction voltage difference of the receiving coil; and finally, measuring information under a plurality of frequency points and drawing a penetration depth curve. The method is flexible and efficient, and by utilizing the principles of a quotient comparison method (the method can almost eliminate irrelevant error factors among groups) and electromagnetic induction, the penetration depth of the metal plate under different frequencies is quickly obtained by surrounding the idea of controlling variables, so that people can better master the penetrability of electromagnetic waves in the metal plate in the future and serve the detection and shielding fields.
Example 1
A magnetic field transmitting coil is placed on one side of the metal plate, and a magnetic field receiving coil is placed on the other side of the metal plate. By contrast, d is placed in the frequency band of 25kHz-50kHz1=0.5mm、d2The difference in induced voltage of the receiving coil when =1.5mm of two aluminum plates of different thickness was calculated by measuring the skin depth.
Step 1: the instrument is arranged according to the figure, and the transmitting ring is positioned below the aluminum plate and corresponds to the center of the receiving coil. And connecting the transmitting loop with a low-frequency power signal generator, observing the spectrum analyzer, and reading the waveform peak value of the induced voltage. As shown in the following table:
when a 0.5mm aluminum plate is placed in a frequency band of 125 kHz-50kHz, the induction voltage of the receiving coil is measured
The induction voltage of the receiving coil when a 1.5mm aluminum plate is placed in the frequency band of 225 kHz-50kHz is shown
Note: the emitted voltage in the table refers to the voltage emitted by the transmitting coil after the low-frequency signal generator is switched on.
Step 2: using equation 1dBmv =20log10(mv), i.e.
The induced voltage (in unit dBmv) received by the spectrometer in the experimental instrument is converted into voltage (V) unit. The results have been calculated for the rightmost column in tables 1 and 2 above.
And step 3: by varying the total thickness of the metal plate (d respectively1、d2) And reading the waveform peak of the spectrum analyzer. The received voltage (E) measured by placing two metal plates of different thickness at the same frequency while varying the thickness of the metal plates and ensuring that the current in the transmitting coil remains constant1、E2) Substitution formula
And calculating to obtain a group of measured skin depths d.
And 4, step 4: using formula of skin depthd'= 
And calculating to obtain a theoretical value of the penetration depth, and finally comparing with the measured value. As shown in the rightmost column of table 3.
The skin depth calculated by measurement in the frequency range of 325 kHz-50kHz is compared with the skin depth calculated by a theoretical formula
Note: the relative error calculation formula is:
and 5: and adjusting the low-frequency power signal generating source to change the frequency of the signal emitted by the low-frequency power signal generating source, repeating the steps, measuring information under a plurality of frequency points, and finally drawing a penetration depth curve. As shown in fig. 3.
As can be seen from the table, the skin depth as a whole, calculated by measurement, decreases with increasing frequency. It can be seen that this is consistent with the results of theoretical analysis. Moreover, the comparison shows that the skin depth obtained by the method provided by the invention is similar to the skin depth data calculated by a theoretical formula, thereby proving the feasibility of the method.
Example 2
A magnetic field transmitting coil is placed on one side of the metal plate, and a magnetic field receiving coil is placed on the other side of the metal plate. By contrast, d is placed in the frequency band of 40kHz-75kHz1=0.5mm、d2=1mm and d1=1mm、d2The difference of the induced voltage of the receiving coil when the two groups of aluminum plates with different thicknesses are 1.5mm is calculated, and the average penetration depth obtained by measurement is compared with a theoretical result.
The skin depth of the metal plate is reduced along with the increase of the frequency, the thickness (0.5 mm, 1mm and 1.5 mm) of the metal plate and the unit of the skin depth are in millimeter level, and the average skin depth obtained by measuring and calculating two groups of aluminum plates with different thicknesses is used for reducing random errors as much as possible, so that the measuring result is more accurate and reliable.
Step 1: the instrument is arranged according to the figure, and the transmitting ring is positioned below the aluminum plate and corresponds to the center of the receiving coil. And connecting the transmitting loop with the low-frequency power signal, observing the spectrum analyzer, and reading the waveform peak value of the induction voltage. As shown in the following table:
when a 0.5mm aluminum plate is placed in the frequency range of 440 kHz-50kHz, the induction voltage of the receiving coil is measured
When a 1mm aluminum plate is placed in the frequency range of 540 kHz-75kHz in the table, the induction voltage of the receiving coil is measured
When a 1.5mm aluminum plate is placed in the frequency band of 640 kHz-75kHz, the induction voltage of the receiving coil is measured
Note: the emitted voltage in the table refers to the voltage emitted by the transmitting coil after the low-frequency signal generator is switched on.
Step 2: using the equation 1dBmv =20log10(mv), i.e.
The induced voltage (in unit dBmv) received by the spectrometer in the experimental instrument is converted into voltage (V) unit. The results have been calculated for the rightmost column in tables 4, 5, and 6 above.
And step 3: by varying the total thickness of the metal plate (d respectively1、d2) And reading the waveform peak of the spectrum analyzer. The received voltage (E) measured by placing two metal plates of different thickness at the same frequency while varying the thickness of the metal plates and ensuring that the current in the transmitting coil remains constant1、E2) Substitution formula
And calculating to obtain a group of measured skin depths d. E1、E2
First group: the thickness (d) of two metal plates in the frequency range of 40kHz-75kHz1=0.5mm、d2=1 mm) to determine a set of skin depths d1。
Second group:the thickness (d) of two metal plates in the frequency range of 40kHz-75kHz1=1mm、d2=1.5 mm) is determined a set of penetration depths d2。
And calculating the skin depth d1、d2The average value of (d) is compared with the skin depth calculated by the theoretical formula, as shown in the following table:
the two groups of skin depths calculated by measurement in the frequency range of 740 kHz-75kHz and the average value thereof are compared with the skin depth calculated by a theoretical formula
Note: the relative error calculation formula is:
and 4, step 4: using formula of skin depthd'= 
And calculating to obtain a theoretical value of the penetration depth, and finally comparing with the measured value. As shown in the rightmost column of table 7 above.
And 5: and adjusting the low-frequency power signal generating source to change the frequency of the signal emitted by the low-frequency power signal generating source, repeating the steps, measuring information under a plurality of frequency points, and finally drawing a penetration depth curve. As shown in fig. 4.
It can be seen that, no matter the thickness of the metal plate and the power frequency are changed, or different emission voltages are set, the skin depth obtained by the skin depth measuring method and the skin depth calculated by the theoretical formula provided by the invention are well matched, and the result is in line with the expectation within the small error range acceptable by engineering. The method for rapidly measuring the penetration depth of the metal plate in a non-contact manner is simple and easy to implement, and can avoid factors which hinder the calculation of the penetration depth, such as unknown material characteristics, complex measurement and calculation, and the like.
The method disclosed by the invention is based on experimental measurement and quotient comparison calculation, combines the existing penetration depth calculation analytic expression, quickly obtains the penetration depth curve of the metal shielding plate, and can be widely applied to composite materials with complex attributes, electromagnetic shielding effectiveness analysis and reverse-thrust conductivity.
The embodiments in the present description are described in a progressive manner, each embodiment focuses on differences from other embodiments, and the same and similar parts among the embodiments are referred to each other.
The principles and embodiments of the present invention have been described herein using specific examples, which are provided only to help understand the method and the core concept of the present invention; meanwhile, for a person skilled in the art, according to the idea of the present invention, the specific embodiments and the application range may be changed. In view of the above, the present disclosure should not be construed as limiting the invention.
Claims (8)
1. An apparatus for non-contact rapid measurement of skin depth of a metal sheet, said apparatus comprising: the device comprises a low-frequency signal generator, a transmitting ring, a receiving induction coil, a spectrum analyzer and a skin depth calculation module;
the transmitting ring and the receiving induction coil are respectively and oppositely arranged on two sides of the metal plate to be detected;
the low-frequency signal generator is connected with the transmitting ring, and the receiving induction coil is connected with the spectrum analyzer;
the low-frequency signal generator is used for generating a signal with a preset frequency and transmitting the signal with the preset frequency to the transmitting ring;
the transmitting ring is used for releasing electromagnetic pulses according to signals with preset frequency to form a magnetic field;
the receiving induction coil is used for generating an induced voltage in the magnetic field;
the spectrum analyzer is used for receiving the induced voltage and then displaying the waveform of the induced voltage;
the skin depth calculation module is used for determining a skin depth curve of the metal plate to be detected according to the waveform of the induction voltage;
the skin depth calculation module includes: the device comprises an induced voltage acquisition unit, a skin depth calculation unit, a circulation unit and a drawing unit;
the induction voltage acquisition unit is used for acquiring the induction voltages of the metal plate to be detected under the same signal frequency when the thickness of the metal plate is different from that of the metal plate to be detected under the same signal frequency on the basis of keeping the output voltage of the low-frequency signal generator unchanged in the process that the low-frequency signal generator generates the signal with the same frequency; the skin depth calculation unit is used for calculating a skin depth measurement value under the same signal frequency by using a skin depth calculation formula according to the induction voltages under the same signal frequency and at two different thicknesses; the skin depth calculation formula is determined by a quotient comparison method; the penetration depth is calculated by the formula
Wherein, in the step (A),E 1is the thickness of the metal plate to be measuredd 1The induced voltage of the time-varying current,E 2is the thickness of the metal plate to be measuredd 2The induced voltage of the time-varying current,dis a skin depth measurement; the circulating unit is used for changing the signal frequency, and repeatedly calling the induction voltage acquisition unit and the penetration depth calculation unit to obtain a penetration depth measured value under each signal frequency; the drawing unit is used for drawing a skin depth curve of the metal plate to be measured by taking the signal frequency as an abscissa and the skin depth measured value as an ordinate according to the skin depth measured value under various signal frequencies.
2. The apparatus for non-contact rapid measurement of skin depth of metal plate according to claim 1, wherein said metal plate to be measured is a square metal plate;
the side length of the square metal plate is larger than 3 times of the diameter of the transmitting ring and larger than 3 times of the distance from the transmitting ring to the square metal plate.
3. The apparatus of claim 1, wherein the axes of said transmitting ring and said receiving coil are coincident, and the distance from the coincident axis to the central axis of the metal plate to be measured is less than a distance threshold.
4. A method for non-contact rapid measurement of skin depth of a metal sheet, wherein the method employs the apparatus of any one of claims 1-3, the method comprising:
keeping the output voltage of the low-frequency signal generator unchanged in the process that the low-frequency signal generator generates signals with the same frequency, and acquiring the induced voltages of the metal plate to be detected under the same signal frequency when the metal plate to be detected has two different thicknesses;
calculating a skin depth measurement value under the same signal frequency by using a skin depth calculation formula according to the induced voltages under the same signal frequency and at two different thicknesses; the skin depth calculation formula is determined by a quotient comparison method;
changing the signal frequency, repeating the above steps, and obtaining a skin depth measurement value at each signal frequency;
and drawing a skin depth curve of the metal plate to be measured by taking the signal frequency as an abscissa and the skin depth measured value as an ordinate according to the skin depth measured values under various signal frequencies.
5. The method as claimed in claim 4, wherein said obtaining the induced voltage of the metal plate to be measured at two different thicknesses at the same signal frequency comprises:
acquiring the waveform peak values of the induced voltage of the metal plate to be detected under the same signal frequency when the metal plate to be detected has two different thicknesses; the unit of the peak value of the waveform isdBmv；
Using formulas
The unit conversion is performed on the waveform peak of the induced voltage.
6. The method for non-contact rapid measurement of skin depth of metal plate according to claim 4, wherein said skin depth calculation formula is determined by:
establishing the relation of the induced voltages of the metal plate to be measured under the same signal frequency in two different thicknesses respectively
And
(ii) a Wherein the content of the first and second substances,E 1is the thickness of the metal plate to be measuredd 1The induced voltage of the time-varying magnetic field,E 2is the thickness of the metal plate to be measuredd 2The induced voltage of the time-varying current,E 0is the output voltage of the low frequency signal generator,kis a coefficient of proportionality that is,dis a skin depth measurement;
by using a quotient comparison method, the ratio of the induced voltages of two different thicknesses under the same signal frequency is obtained
；
Determining the skin depth calculation formula under the same signal frequency according to the induced voltage ratio as
。
7. The method of claim 6, wherein said step of calculating the skin depth measurement value at the same signal frequency according to the induced voltages at two different thicknesses at the same signal frequency by using the skin depth calculation formula further comprises the steps of:
keeping the output voltage of the low-frequency signal generator unchanged in the process that the low-frequency signal generator generates signals with the same frequency, and acquiring the thickness of the metal plate to be measured under the same signal frequencyd 3The induced voltage of time;
according to the thickness of the same signal frequencyd 2Induced voltage and thickness of timed 3The time induced voltage is calculated by using a skin depth calculation formula to calculate the thickness under the same signal frequencyd 2、d 3A corresponding skin depth measurement;
calculating the thickness of the same signal frequencyd 1、d 2Corresponding skin depth measurement and thicknessd 2、d 3The corresponding skin depth measurements are averaged and the average is taken as the skin depth measurement at the same signal frequency.
8. The method of claim 4, wherein said step of calculating the skin depth measurement value at the same signal frequency according to the induced voltages at two different thicknesses at the same signal frequency by using the skin depth calculation formula further comprises the steps of:
using formulasd'= 
Calculating a theoretical value of the penetration depth under the same signal frequency; wherein the content of the first and second substances,d'for the theoretical value of the skin depth,ωin order to be the angular frequency of the frequency,ω=2πf，fin order to be the frequency of the signal,μthe magnetic conductivity of the metal plate to be measured is gamma, and the electric conductivity of the metal plate to be measured is gamma;
the relative error of the theoretical skin depth value at the same signal frequency and the measured skin depth value at the same signal frequency is calculated.
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