CN112432588B - Method for measuring thickness of wave-absorbing coating through magnetic saturation characteristic - Google Patents
Method for measuring thickness of wave-absorbing coating through magnetic saturation characteristic Download PDFInfo
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- CN112432588B CN112432588B CN202011422827.3A CN202011422827A CN112432588B CN 112432588 B CN112432588 B CN 112432588B CN 202011422827 A CN202011422827 A CN 202011422827A CN 112432588 B CN112432588 B CN 112432588B
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- G01—MEASURING; TESTING
- G01B—MEASURING LENGTH, THICKNESS OR SIMILAR LINEAR DIMENSIONS; MEASURING ANGLES; MEASURING AREAS; MEASURING IRREGULARITIES OF SURFACES OR CONTOURS
- G01B7/00—Measuring arrangements characterised by the use of electric or magnetic techniques
- G01B7/02—Measuring arrangements characterised by the use of electric or magnetic techniques for measuring length, width or thickness
- G01B7/06—Measuring arrangements characterised by the use of electric or magnetic techniques for measuring length, width or thickness for measuring thickness
- G01B7/10—Measuring arrangements characterised by the use of electric or magnetic techniques for measuring length, width or thickness for measuring thickness using magnetic means, e.g. by measuring change of reluctance
- G01B7/105—Measuring arrangements characterised by the use of electric or magnetic techniques for measuring length, width or thickness for measuring thickness using magnetic means, e.g. by measuring change of reluctance for measuring thickness of coating
Abstract
The invention discloses a method for measuring the thickness of a wave-absorbing coating through magnetic saturation characteristics, which comprises the steps of firstly building a wave-absorbing coating thickness measuring model according to an excitation coil, an iron core, a magnetic sensor, a tested piece and the like, sequentially increasing current in the excitation coil after the building of the measuring model is completed, measuring the magnetic induction intensity at a set point through the magnetic sensor when a measured magnetic layer reaches a magnetic saturation state, recording the current at the time, removing the magnetic induction intensity of the set point after the tested piece is removed, then building a magnetic induction intensity mathematical model at the set point according to the measuring model, and finally reversely solving the magnetic induction intensity mathematical model to obtain the thickness of the coating.
Description
Technical Field
The invention belongs to the technical field of wave-absorbing coating thickness measurement, and particularly relates to a method for measuring the wave-absorbing coating thickness through magnetic saturation characteristics.
Background
All major military strong countries in the world continuously develop new technologies aiming at stealth and anti-stealth technologies, and try to get a first chance in the competition of national defense and security. In the stealth technology, the key to mastering the advanced wave-absorbing material coating technology is to master the stealth technology. The wave-absorbing material is a material capable of absorbing or greatly reducing the electromagnetic wave energy projected on the surface of the wave-absorbing material so as to reduce the electromagnetic wave interference. According to the difference of wave-absorbing mechanism, it can be divided into electric loss type and magnetic loss type. The former mostly uses conductive carbon black or graphite, and the latter usually uses a mixture of iron, etc., such as ferrite and carbonyl iron. The thickness measuring object aimed at by the invention is a magnetic loss type material, and the material has certain ferromagnetism and the characteristic of magnetic saturation.
According to the wave absorbing mechanism of the magnetic loss type wave absorbing coating, the electromagnetic parameters of the coating material, the composition structure of the coating, the thickness of the coating and the like determine the wave absorbing performance of the coating. The electromagnetic parameter (epsilon) of the wave-absorbing coating with uniform single-layer structurer,μr) Is fixed toThe parameter that determines the absorption properties is the coating thickness. It is important that the single-layer coating achieves the requirements of thinness (thickness), lightness (weight), width (frequency band), strong absorption and the like. When the thickness of the wave-absorbing coating is too thin, the wave-absorbing and stealth effects are very limited, and when the thickness is too thick, the whole weight of the stealth fighter is increased, and the maneuvering performance and the fuel consumption of the stealth fighter are greatly increased. In conclusion, the thickness of the invisible warplane wave-absorbing coating is an important design and detection index in the construction and quality evaluation of the invisible warplane wave-absorbing coating.
The coating layer having a uniform single-layer structure can be classified into a magnetic matrix and a non-magnetic matrix according to the difference in the matrix material. The thickness measuring object aimed by the patent is a non-magnetic matrix magnetic coating material. As the thickness measurement by the destructive method can cause irreversible damage to the surface of a fighter plane, the nondestructive method, namely nondestructive testing, is adopted in the actual thickness measurement occasion. Common nondestructive testing methods include magnetic methods, eddy current methods, double beam microscopy, and the like. The magnetic method is characterized in that the magnetism of the wave-absorbing coating material and a permanent magnet in the probe mutually attract to pull a cantilever beam in the probe to deform, and a piezoelectric strain gauge on the cantilever beam generates corresponding deformation to output a voltage related to the magnetic force, so that the thickness information of the coating is obtained. Because the cantilever beam self receives the influence of gravity, during the thickness measurement, the locating position of probe can produce great influence to the cantilever beam deformation to cause great influence to the thickness measurement accuracy. The eddy current method can only be used under the condition that the electric conductivity of the substrate is far larger than that of the coating, and when the difference between the electric conductivities of the substrate and the coating is not large, the eddy current method has great influence on the thickness measurement accuracy.
With the discovery of physical phenomena such as various tunneling magneto-resistance (TMR) effects, hall effects, etc., various magnetic sensors are being used more and more. In the field of nondestructive testing, more and more instruments for sensing various physical parameters by using magnetic sensors appear. The researched magnetic loss type wave-absorbing material has high saturation magnetization and conductivity, and has larger magnetic loss and dielectric loss when being used as the wave-absorbing material, so that the wave-absorbing material has strong absorption capacity to electromagnetic waves.
Because the magnetic wave-absorbing coating has unique electromagnetic characteristics, the change of the spatial electromagnetic characteristics caused by the thickness change can be sensed by using a magnetic sensor, so that the thickness of the magnetic wave-absorbing coating can be subjected to nondestructive detection.
Disclosure of Invention
The invention aims to overcome the defects of the prior art and provides a method for measuring the thickness of a wave-absorbing coating through magnetic saturation characteristics, which measures the thickness of a tested piece in real time by using a secondary field after the magnetization of a magnetic coating and a magnetic saturation effect.
In order to achieve the aim, the invention provides a method for measuring the thickness of a wave-absorbing coating through magnetic saturation characteristics, which is characterized by comprising the following steps of:
(1) establishing a thickness measuring model
(1.1) inserting an iron core into the excitation coil, and arranging a point a at a position which is far away from a probe l at the lower end of the iron core in the direction of a perpendicular line of the iron core and is used for placing a magnetic sensor; after the exciting coil is electrified, the magnetic induction intensity at the point a is measured by the magnetic sensor and is marked as B1；
(1.2) placing an excitation coil inserted into an iron core at the midpoint of a tested piece, wherein the distance from a probe at the lower end of the iron core to the surface of the tested piece is D, after the excitation coil is electrified, magnetizing a coating of the tested piece by a magnetic field excited by the excitation coil, at the moment, generating a magnetic field by the magnetic coating, superposing the magnetic field with the magnetic field excited by the excitation coil at a point a, and measuring the magnetic induction intensity at the point a through a magnetic sensor;
(1.3) sequentially increasing the current in the exciting coil, repeating the operations in the steps (1.1) and (1.2), when the magnetic layer reaches a magnetic saturation state, the magnetic field generated by the magnetic coating layer is not increased any more, and recording the current I at the moment1And magnetic induction B at point a3；
(2) According to the thickness measurement model, a magnetic induction intensity mathematical model at the point a is constructed
(2.1) obtaining the magnetic field intensity M in the coating through polynomial fitting according to the magnetization curve of the coating per se2；
Wherein, wjExpressing polynomial fitting parameters, j is 0,1,2, …, N denotes fitting order; h represents the external magnetic field intensity;
(2.2) calculating the magnetic field intensity M of the magnetic field excited by the exciting coil on the axis of the lower end face of the iron core1；
Wherein μ represents the permeability of the iron core, μ0Denotes the permeability of air, n denotes the number of turns of the exciting coil, rpDenotes the radius of the core, phi denotes the diameter of the exciting coil;
(2.3) equating the magnetic coating after magnetization saturation to be a radius r, a height h and a magnetic field intensity
Uniformly magnetized cylindrical permanent magnet of, then according to M1And M2Calculating the magnetization of equivalent cylindrical permanent magnet
D is the distance between a probe at the lower end of the iron core and the surface of the tested piece, and h is the thickness of the coating;
(2.4) constructing a magnetic induction intensity mathematical model at the point a;
(3) calculating the thickness h of the coating;
order to
Order to
Solving h in the formula (4) to obtain the thickness h of the coating;
the invention aims to realize the following steps:
the invention relates to a method for measuring the thickness of a wave-absorbing coating through magnetic saturation characteristics, which comprises the steps of firstly building a wave-absorbing coating thickness measuring model according to an excitation coil, an iron core, a magnetic sensor, a tested piece and the like, sequentially increasing current in the excitation coil after the building of the measuring model is completed, measuring the magnetic induction intensity at a set point through the magnetic sensor when a measured magnetic layer reaches a magnetic saturation state, recording the current at the time, removing the magnetic induction intensity of the set point after the tested piece is removed, then building a magnetic induction intensity mathematical model at the set point according to the measuring model, and finally reversely solving the magnetic induction intensity mathematical model to obtain the coating thickness.
Meanwhile, the method for measuring the thickness of the wave-absorbing coating through the magnetic saturation characteristic also has the following beneficial effects:
(1) according to the invention, the relation between the magnetic field strength of the corresponding probe and the thickness of the tested piece is deduced by establishing the relation between the magnetic field excited by the coating in the magnetic saturation state and the thickness of the tested piece.
(2) The invention utilizes the magnetic saturation characteristic of the magnetic material to be measured, can greatly improve the accuracy and precision of thickness measurement, and can be used for the thickness measurement of all magnetic coatings with the magnetic saturation characteristic.
(3) Compared with other magnetic coating thickness measuring methods, the thickness measuring method provided by the invention is simpler to operate, more convenient to use and higher in measuring result accuracy.
(4) The probe has a simpler structure, and the subsequent design and manufacture of the probe simplify larger workload.
Drawings
FIG. 1 is a flow chart of a method for measuring the thickness of a wave-absorbing coating through magnetic saturation characteristics according to the invention;
FIG. 2 is a model diagram of the thickness of a wave-absorbing coating measured by magnetic saturation characteristics according to the present invention;
FIG. 3 is a simulated comparison curve of coating thickness.
Detailed Description
The following description of the embodiments of the present invention is provided in order to better understand the present invention for those skilled in the art with reference to the accompanying drawings. It is to be expressly noted that in the following description, a detailed description of known functions and designs will be omitted when it may obscure the subject matter of the present invention.
Examples
FIG. 1 is a flow chart of a method for measuring the thickness of a wave-absorbing coating through magnetic saturation characteristics.
In this embodiment, as shown in fig. 1, the method for measuring the thickness of a wave-absorbing coating by using magnetic saturation characteristics according to the present invention includes the following steps:
s1, as shown in figure 2, establishing a thickness measuring model
S1.1, inserting an iron core into an excitation coil, and arranging a point a at a position, which is far away from a probe l at the lower end of the iron core, in the direction of a perpendicular line of the iron core, wherein the point a is used for placing a magnetic sensor; after the exciting coil is electrified, the magnetic induction intensity at the point a is measured by the magnetic sensor and is marked as B1；
S1.2, placing an excitation coil inserted into an iron core at the midpoint of a tested piece, wherein the distance from a probe at the lower end of the iron core to the surface of the tested piece is D, magnetizing a coating of the tested piece by a magnetic field excited by the excitation coil after the excitation coil is electrified, at the moment, generating a magnetic field by the magnetic coating, superposing the magnetic field with the magnetic field excited by the excitation coil at a point a, and measuring the magnetic induction intensity at the point a through a magnetic sensor; in the embodiment, since the effect of the secondary field after the coating is magnetized by itself is very small compared with the external field excited by the coil, only the magnetization effect of the external magnetic field excited by the coil on the coating is considered here;
s1.3, sequentially increasing the current in the exciting coil, repeating the operations of the steps S1.1 and S1.2, and when the magnetic layer reaches a magnetic saturation state, the magnetic field generated by the magnetic coating does not increase, namely B3-B1If the value of (D) is kept constant, the current I at that time is recorded1And magnetic induction B at point a3；
S2, constructing a magnetic induction intensity mathematical model at the point a according to the thickness measurement model
S2.1, obtaining the magnetic field intensity M in the coating through polynomial fitting according to the magnetization curve of the coating per se2；
Wherein, wjExpressing polynomial fitting parameters, j is 0,1,2, …, N denotes fitting order; h represents an external magnetic field excited by the coil;
s2.2, calculating the magnetic field intensity M of the magnetic field excited by the exciting coil at the position of the probe on the axis of the lower end face of the iron core1；
Wherein μ represents the permeability of the iron core, μ0Denotes the permeability of air, n denotes the number of turns of the exciting coil, rpDenotes the radius of the core, phi denotes the diameter of the exciting coil;
s2.3, the magnetic coating space magnetic field after magnetization is very complicated, the thickness of the magnetic coating to be measured is in the um level, the thickness is very thin, and only the magnetic field distribution on the axis is discussed, so that the magnetic coating after magnetization saturation can be equivalent to a magnetic coating with a radius ofr, height h, magnetic field strength of
Of a uniformly magnetized equivalent cylindrical permanent magnet, the axis of which coincides with the axis of the cylindrical core, as shown in fig. 2, then according to M1And M2Calculating the magnetization of equivalent cylindrical permanent magnet
D is the distance between a probe at the lower end of the iron core and the surface of the tested piece, and h is the thickness of the coating;
s2.4, constructing a magnetic induction intensity mathematical model at the point a;
s3, calculating the thickness h of the coating;
in this embodiment, for B3Equation (c) except for the thickness value h and the equivalent cylindrical permanent magnet magnetization
And an equivalent cylindrical permanent magnet radius r, all of which may be measured or known constant. But equivalent cylindrical permanent magnet magnetization
And the radius r of the equivalent cylindrical permanent magnet depends only on the thickness value h under the condition that the applied magnetic field is not changed. Therefore, the thickness and the magnetic induction B at the probe3There is a one-to-one correspondence.
For simple calculation, the formula (4) is first simplified as follows:
order to
Order to
Solving h in the formula (4) to obtain the thickness h of the coating;
in this example, the theoretical value was calculated by the above method in the range of the coating thickness of 0 to 1000 um. And in finite element software, a corresponding thickness measurement model is set up for simulation to obtain a simulation value, and then the relative error is calculated, as shown in table 1.
TABLE 1
The curves of the theoretical calculation value and the simulated value are shown in fig. 3, and it can be seen from fig. 3 that the curves of the theoretical value and the simulated value almost have the same trend, and the two curves almost coincide. And the two curves are smooth and have good linear relation. As can be seen from Table one, the error between the theoretical value and the simulated value is small and within the acceptable range. Therefore, the invention can be applied to the actual coating thickness measurement, and has higher accuracy and more convenient operation.
Although illustrative embodiments of the present invention have been described above to facilitate the understanding of the present invention by those skilled in the art, it should be understood that the present invention is not limited to the scope of the embodiments, and various changes may be made apparent to those skilled in the art as long as they are within the spirit and scope of the present invention as defined and defined by the appended claims, and all matters of the invention which utilize the inventive concepts are protected.
Claims (2)
1. A method for measuring the thickness of a wave-absorbing coating through magnetic saturation characteristics is characterized by comprising the following steps:
(1) establishing a thickness measuring model
(1.1) inserting an iron core into the excitation coil, and arranging a point a at a position which is far away from a probe l at the lower end of the iron core in the direction of a perpendicular line of the iron core and is used for placing a magnetic sensor; after the exciting coil is electrified, the magnetic induction intensity at the point a is measured by the magnetic sensor and is marked as B1；
(1.2) placing an excitation coil inserted into an iron core at the midpoint of a tested piece, wherein the distance from a probe at the lower end of the iron core to the surface of the tested piece is D, after the excitation coil is electrified, magnetizing a coating of the tested piece by a magnetic field excited by the excitation coil, at the moment, generating a magnetic field by the magnetic coating, superposing the magnetic field with the magnetic field excited by the excitation coil at a point a, and measuring the magnetic induction intensity at the point a through a magnetic sensor;
(1.3) sequentially increasing the current in the exciting coil, repeating the operations in the steps (1.1) and (1.2), when the magnetic coating reaches a magnetic saturation state, the magnetic field generated by the magnetic coating does not increase any more, and recording the current I at the moment1And magnetic induction B at point a3；
(2) According to the thickness measurement model, a magnetic induction intensity mathematical model at the point a is constructed
(2.1) obtaining the magnetic field intensity M in the coating through polynomial fitting according to the magnetization curve of the coating per se2；
Wherein, wjExpressing polynomial fitting parameters, j is 0,1,2, …, N denotes fitting order; h represents the external magnetic field intensity;
(2.2) calculating the magnetic field intensity M of the magnetic field excited by the exciting coil on the axis of the lower end face of the iron core1；
Wherein μ represents the permeability of the iron core, μ0Denotes the permeability of air, n denotes the number of turns of the exciting coil, rpDenotes the radius of the core, phi denotes the diameter of the exciting coil;
(2.3) equating the magnetic coating after magnetization saturation to be a radius r, a height h and a magnetic field intensity
Uniformly magnetized cylindrical permanent magnet of, then according to M1And M2Calculating the magnetization of equivalent cylindrical permanent magnet
D is the distance between a probe at the lower end of the iron core and the surface of the tested piece, and h is the thickness of the coating;
(2.4) constructing a magnetic induction intensity mathematical model at the point a;
(3) calculating the thickness h of the coating;
order to
Order to
Solving h in the formula (4) to obtain the thickness h of the coating;
2. the method for measuring the thickness of the wave-absorbing coating according to claim 1, wherein the axis of the equivalent cylindrical permanent magnet is coincident with the axis of the inserted iron core.
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| FR2105435A5 (en) * | 1970-09-07 | 1972-04-28 | Commissariat Energie Atomique | Induction detector for thin film thickness monitoring - esp for monitoring liquid sodium in nuclear installations |
| JPS5952425A (en) * | 1982-09-17 | 1984-03-27 | Hitachi Ltd | Magneto-resistance effect type head |
| US7036739B1 (en) * | 1999-10-23 | 2006-05-02 | Ultracard, Inc. | Data storage device apparatus and method for using same |
| WO2002088627A1 (en) * | 2001-05-01 | 2002-11-07 | Em-Tech Llc | Measurements of coating on metal |
| JP4451111B2 (en) * | 2003-10-20 | 2010-04-14 | 株式会社荏原製作所 | Eddy current sensor |
| UA11668U (en) * | 2005-04-20 | 2006-01-16 | Serhii Ivanovych Lytvyn | Device for measuring thickness of coating |
| ITMI20071167A1 (en) * | 2007-06-08 | 2008-12-09 | Danieli Off Mecc | METHOD AND DEVICE FOR THE CONTROL OF THE COATING THICKNESS OF A METAL METAL PRODUCT |
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| US20100171493A1 (en) * | 2009-01-07 | 2010-07-08 | Robert Standen | Method and device for measuring thickness of a substrate |
| CN102235851A (en) * | 2010-04-22 | 2011-11-09 | 李长青 | Coating thickness measuring probe |
| CN102735152B (en) * | 2012-06-06 | 2014-08-27 | 电子科技大学 | Calibrating and measuring method of microwave absorbing coating thickness measuring instrument |
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| CN103852000B (en) * | 2014-03-24 | 2016-05-25 | 电子科技大学 | The eddy current detection method of multilayer conductive coating layer thickness and device |
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