Near-field scanning system and rapid scanning method for electromagnetic radiation measurement

Abstract

The invention relates to the technical field of electromagnetic radiation measurement, and discloses a near-field scanning system and a rapid scanning method for electromagnetic radiation measurement. The near-field scanning system comprises a data acquisition unit, a probe control moving unit and a control unit; the data acquisition unit comprises a vector network analyzer and a spectrum analyzer which are used for frequency domain measurement, an oscilloscope and a radio frequency signal source which are used for time domain measurement, and a near-field electromagnetic probe; the probe control moving unit is used for controlling the near-field electromagnetic probe to move along a set route in the X direction, the Y direction and the Z direction; the control unit is used for synchronously controlling the data acquisition unit and the probe control moving unit; according to the rapid scanning method, by judging the gradient amplitude and the local self-adaptive threshold value of each scanning point, the scanning points are encrypted at the place where the electromagnetic field changes rapidly, rough scanning is carried out at the place where the electromagnetic field changes slowly, and compared with equal-interval uniform sampling, the number of the scanning points can be reduced, and the efficiency of a near-field scanning system can be improved.

Description

Technical Field

[0001] The present invention relates to the technical field of electromagnetic radiation measurement, in particular to a near-field scanning system and a fast scanning method for electromagnetic radiation measurement. Background Art

[0002] With the rapid development of high-speed and high-frequency circuits, the continuous increase in circuit complexity and clock frequency, the electromagnetic compatibility problem in electronic equipment has become increasingly serious. Especially in high-frequency circuits, the size of the traces or electronic components on the circuit board can reach 1 / 4 wavelength, which essentially produces an antenna effect and becomes a source of interference. If the radiation of related electronic equipment is not restricted and protected, its electromagnetic radiation will interfere with the normal operation of the equipment itself and even the entire electronic system, and then affect its external electromagnetic environment. The resulting electromagnetic interference problem has become one of the important issues that need to be paid attention to for the further development of current electronic technology.

[0003] In the process of studying electromagnetic problems, although the use of full-wave simulation analysis software has brought great convenience, allowing researchers to conduct detailed analysis of the electromagnetic radiation characteristics of the equipment after modeling, many electronic devices cannot be equivalently modeled. Near-field scanning technology uses electric / magnetic field probes to flexibly and conveniently obtain electromagnetic field distribution information around the device, allowing engineers or researchers to use this information to accurately locate the interference source in the device and rectify the electromagnetic interference of the device. Near-field scanning technology has become a new hot spot in the field of electromagnetic compatibility research, and has also become a new way to accurately locate electromagnetic radiation interference sources, analyze electromagnetic radiation characteristics, and thus solve electromagnetic compatibility problems.

[0004] For traditional near-field scanning systems, some important technical problems have not yet been solved. First, analyzing electromagnetic interference problems in the frequency domain can no longer meet the analysis needs of researchers. Many electromagnetic compatibility problems can be better quantified in the time domain, while existing near-field scanning systems can only measure electromagnetic signals in the frequency domain, but not in the time domain. For example, a 210mm×150mm×25mm planar near-field EMC scanner proposed by Hangzhou Dianzi University only realizes data collection in the frequency domain using a spectrum analyzer.

[0005] Secondly, the existing commercial near-field scanning systems are expensive and the scanning space they achieve is small. Therefore, it is necessary to design a near-field scanning system that can provide a large scanning space, and its structure should be relatively simple and cheap. For example, the ICSCANNER series near-field scanning system of the German LANGER EMV-Technik company is a representative commercial near-field scanning system, and its working space can reach 400mm×600mm×120mm, but its disadvantage is that it is expensive.

[0006] Due to the high density of electronic components in high-performance integrated circuits, there may be multiple radiation sources on the circuit board during operation. In order to capture the near-field changes of electromagnetic radiation sources, in addition to high spatial resolution probes, high-density sampling is usually required. Currently, traditional near-field scanning technology mostly uses an equally spaced point-by-point sampling method, which often requires a large number of scanning points and consumes huge sampling time costs. Summary of the invention

[0007] In view of the above problems, the purpose of the present invention is to provide a near-field scanning system and a fast scanning method for electromagnetic radiation measurement, which can measure the near-field scanning system in the time domain and the frequency domain, and can realize dense sampling in areas where the magnetic field changes rapidly and rough sampling in areas where the magnetic field changes slowly, thereby reducing the number of scanning points and improving the scanning efficiency. The technical solution is as follows:

[0008] A near-field scanning system for electromagnetic radiation measurement comprises a data acquisition unit, a probe control moving unit and a control unit;

[0009] The data acquisition unit includes a vector network analyzer and a spectrum analyzer for frequency domain measurement, an oscilloscope and a radio frequency signal source for time domain measurement, and a near-field electric / magnetic probe; when measuring the electromagnetic field of a passive device under test, port 1 of the vector network analyzer is connected to the device under test, and port 2 is connected to the near-field electric / magnetic probe; port 1 of the oscilloscope is connected to the near-field electric / magnetic probe, and the output signal of the radio frequency signal source is divided into two signals through a two-way power divider, one of which is connected to the passive device under test, and the other is connected to port 2 of the oscilloscope as a reference signal; when measuring the electromagnetic field of an active device under test, one port of the spectrum analyzer is connected to the near-field electric / magnetic probe;

[0010] The probe control moving unit is used to control the near-field electric / magnetic probe to move along a set route in three directions of X, Y, and Z, and to stay at each set scanning point for a specific time to collect data;

[0011] The control unit is used to synchronously control the data acquisition unit and the probe control moving unit, complete the data acquisition and transmit it back to the computer through the network cable for processing.

[0012] Furthermore, the probe control moving unit adopts a three-axis screw slide scanning frame, including screw slides in three directions of XYZ and an L-shaped bracket, there are two X-direction screw slides; the two ends of the Y-direction screw slide are respectively driven by stepper motors arranged on the two X-direction screw slides, so that it moves along the X-axis direction; the Z-direction screw slide is driven by a stepper motor arranged on the Y-direction screw slide, so that it moves along the Y-axis direction; the L-shaped bracket is driven by a stepper motor arranged on the Z-direction screw slide, so that it moves along the Z-axis direction; the L-shaped bracket is provided with a pipe fitting for fixing the near-field electric / magnetic probe.

[0013] A rapid scanning method for electromagnetic radiation measurement comprises the following steps:

[0014] Step 1: Perform an initial rough scan of the device under test at a set sampling interval to obtain a source data image of the field strength; the source data image includes the position coordinates of the scanning point and the field strength amplitude corresponding to the scanning point;

[0015] Step 2: Use the source data obtained by scanning to calculate the gradient amplitude of the field strength at each scanning point, and use the local adaptive threshold method to determine the scanning point where the field strength gradient change is greater than the set threshold, and take it as a high gradient point;

[0016] Step 3: Around the high gradient point, add an appropriate number of additional scanning points and perform scanning;

[0017] Step 4: Extract electromagnetic field two-dimensional image data together with the additional scan data and source data.

[0018] Furthermore, the gradient amplitude of the field intensity data at the scanning point calculated in step 2 is specifically:

[0019] For scan points inside the source data image, the central difference method is used to approximate the derivative:

[0020] gradX(x,y)=(Z(x,y+1)-Z(x,y-1)) / h

[0021] gradY(x,y)=(Z(x+1,y)-Z(x-1,y)) / h

[0022] Among them, gradX(x,y) and gradY(x,y) represent the derivatives of the scanning point with coordinates (x,y) in the image in the X direction and Y direction respectively; in the two-dimensional function Z(x,y), x and y are spatial coordinates, and Z is the field intensity amplitude at the corresponding coordinate scanning point; h represents the step size, which is a small positive number;

[0023] For the scan points at the edge of the source data image, the forward difference method is used to approximate the derivative:

[0024] gradX(x,1)=(Z(x,2)-Z(x,1))

[0025] gradX(x,n)=(Z(x,n)-Z(x,n-1))

[0026] gradY(1,y)=(Z(2,y)-Z(1,y))

[0027] gradY(m,y)=(Z(m,y)-Z(m-1,y))

[0028] Wherein, m and n represent the number of rows and columns of the source data image respectively;

[0029] Compute the gradient magnitude:

[0030]

[0031] Furthermore, the local adaptive threshold method in step 2 is specifically:

[0032] Step a: Define a local neighborhood: For each point in the source data image, define a rectangular or circular area as the local neighborhood;

[0033] Step b: Calculate the local average value: Calculate the average value of the field strength amplitude obtained by all scans in the local neighborhood, denoted as μ;

[0034] Step c: Calculate the threshold: Calculate the mean threshold T based on the local average:

[0035] T=μ+k*σ

[0036] Where σ is the standard deviation of the field strength amplitude in the local neighborhood, and k is a constant;

[0037] Step d: Judgment: Compare the threshold T obtained at each scanning point with the gradient amplitude |gradZ|. If the gradient amplitude of a scanning point is greater than T, then the point is a high gradient point, and additional scanning points are added around the high gradient point.

[0038] The beneficial effects of the present invention are:

[0039] 1) The near-field scanning system proposed in the present invention can realize a variety of electromagnetic field radiation measurement methods in the time domain and frequency domain, and provides a convenient near-field radiation emission test platform for various electromagnetic radiation devices such as integrated circuits and antennas.

[0040] 2) The three-dimensional scanning support composed of a stepping motor and a lead screw can save costs and has a larger scanning space.

[0041] 3) The present invention can realize automatic scanning of the system and also integrates functions such as time-frequency domain data acquisition, data processing, and data plotting.

[0042] 4) The fast scanning method universal for time domain and frequency domain proposed in the present invention can encrypt the scanning points in places where the electromagnetic field changes quickly and perform rough scanning in places where the electromagnetic field changes slowly by judging the gradient amplitude of the scanning point and the size of the local adaptive threshold. Compared with uniform scanning at equal intervals, it can reduce the number of scanning points and improve the efficiency of the near-field scanning system. BRIEF DESCRIPTION OF THE DRAWINGS

[0043] Figure 1The figure is a structural block diagram of the near-field scanning system for electromagnetic radiation measurement of the present invention.

[0044] Figure 2 This is a scanning flow chart of the near-field scanning system for electromagnetic radiation measurement of the present invention.

[0045] Figure 3 This is a schematic diagram of the “S” type scanning path.

[0046] Figure 4 This is a schematic diagram of the structure of a three-axis lead screw slide scanning frame.

[0047] Figure 5 The figure is a flow chart of the scanning method.

[0048] Figure 6 This is the block diagram of the first measurement method.

[0049] FIG7( a ) is a time domain magnetic field distribution measurement result 1 measured by an oscilloscope.

[0050] FIG7( b ) is a time domain magnetic field distribution measurement result 2 measured by an oscilloscope.

[0051] Figure 8 The second measurement method block diagram

[0052] FIG9( a ) is a frequency domain magnetic field distribution measurement result 1 measured by a spectrum analyzer.

[0053] FIG9( b ) is the frequency domain magnetic field distribution measurement result 2 measured by a spectrum analyzer.

[0054] Fig.10 This is the third measurement method.

[0055] FIG11( a ) is a frequency domain magnetic field distribution measurement result 1 measured by a vector network analyzer.

[0056] FIG11( b ) is the frequency domain magnetic field distribution measurement result 2 measured by a vector network analyzer.

[0057] FIG12( a ) is a frequency domain uniform measurement result at f=500 MHz.

[0058] FIG12( b ) is the measurement result of the frequency domain fast scanning method at f=500 MHz.

[0059] Figure 13(a) shows the frequency domain uniform measurement scanning point distribution (4916 scanning points).

[0060] Figure 13(b) shows the scanning point distribution of the frequency domain fast scanning method (2883 scanning points).

[0061] FIG14( a ) is a time domain uniform measurement result at t=5 ns.

[0062] FIG14( b ) is the measurement result of the time domain fast scanning method at t=5 ns.

[0063] Figure 15(a) shows the uniform measurement scan point distribution in the time domain (2050 scan points).

[0064] Figure 15(b) shows the scanning point distribution of the time domain fast scanning method (1055 scanning points).

[0065] In the figure: 1-X-axis stepper motor and lead screw guide rail; 2-Y-axis stepper motor and lead screw guide rail; 3-Z-axis stepper motor and lead screw guide rail; 4-pipe fitting; 5-L-type bracket. DETAILED DESCRIPTION

[0066] The entire near-field scanning system of the present invention can be divided into a data acquisition part, a probe movement control part, and a system software control part.

[0067] 1. Data collection part:

[0068] The structural block diagram of the near-field scanning system for electromagnetic radiation measurement of the present invention is as follows: Figure 1 As shown, the data acquisition part consists of a vector network analyzer, a spectrum analyzer, an oscilloscope, an RF signal source, and a near-field electric / magnetic probe. The electric / magnetic probe is connected to the instrument via a coaxial cable. Among them, the instruments used for frequency domain measurement are a vector network analyzer and a spectrum analyzer. The vector network analyzer is used for electromagnetic field measurement of passive devices under test. At this time, port 1 of the vector network analyzer needs to be connected to the device under test, and port 2 of the vector network analyzer needs to be connected to the electric / magnetic probe. The spectrum analyzer is used for measurement of active devices under test. At this time, only one port of the spectrum analyzer needs to be connected to the electric / magnetic probe. The instruments used for time domain measurement are an oscilloscope and an RF signal source. Port 1 of the oscilloscope is connected to the electric / magnetic probe. The output of the RF signal source is divided into two signals through a two-way power divider. One signal is connected to the passive device under test, and the other signal is connected to port 2 of the oscilloscope as a reference signal. The two instruments can be used together to measure the time domain electromagnetic field of the passive device under test. Different measuring instruments are connected to a network switch and then to a computer. The computer has self-developed control software that controls the IP address of each instrument to perform instrument initialization, parameter setting, data acquisition and other functions.

[0069] 2. Control the moving part of the electric / magnetic probe

[0070] It is realized by using the structure of a 3D scanning bracket. There is control software written in the computer, which is connected to the 3D scanning bracket through the serial port. The motion control of the XYZ axis of the 3D scanning bracket is realized by the control software. For a detailed introduction of the 3D scanning bracket, see Figure 4, which consists of a three-axis lead screw slide rail scanning frame. The slide table is driven by the rotation of the stepper motor and controlled by the computer through the serial port. The electric / magnetic probe is fixed on the Z axis of the three-dimensional scanning bracket. The movement of the electric / magnetic probe is achieved by controlling the movement of the three axes. For the flow chart, see Figure 2 The near-field scanning system implemented by the present invention is a point-by-point near-field scanning system. Figure 3 As shown in the figure, the point-by-point near-field scanning system will stay at each point for a period of time to collect data, and then move to the next point to scan, and then return to the origin after traversing all the points repeatedly. Figure 3 The "S"-shaped scanning path shown passes through each point only once during scanning, and there is no need to return to the initial scanning point of each row. This moving path is the shortest, which can save scanning time and improve scanning efficiency.

[0071] This embodiment uses a three-axis screw slide rail scanning frame as a scanning motion platform. Figure 4 The effective travel of the screw rails of the three axes is 600mm×600mm×300mm, and the positioning accuracy of the repeated motion is 0.05mm. A stepper motor is fixed at one end of each rail, and the rotation of the stepper motor drives the slide to move.

[0072] The third comprises screw guide rails in three directions, XYZ, wherein there are two stepper motors in the X direction, and one each in the Y and Z directions. The two ends of the Y-direction screw guide rail are driven by stepper motors arranged on the X-direction screw guide rail to move along the X-axis direction; the Z-direction screw guide rail is driven by stepper motors arranged on the Y-direction screw guide rail to move along the Y-axis direction; the slide is driven by stepper motors arranged on the Z-direction screw guide rail to move along the Z-axis direction; a pipe 4 for fixing the near-field electric / magnetic probe is arranged on the slide.

[0073] The movable stroke of the screw rods in the X and Y directions is 600mm, the movable stroke of the screw rod in the Z direction is 300mm, and the repeatable positioning accuracy of the screw rods in the three directions is 0.05mm; the pipe fitting 4 is a cylindrical acrylic tube with a length of 500mm and a diameter of 30mm, which is used to fix the near-field electric / magnetic probe, and can easily replace different types of electric / magnetic probes and adjust the direction of the electric / magnetic probe. During actual measurement, the electric / magnetic probe is fixed to the lower part of the acrylic tube, and the connected coaxial cable passes through the entire acrylic tube from the tail end of the electric / magnetic probe and then connects to the measuring instrument; the L-shaped bracket 5 is an L-shaped acrylic fixing bracket, which is used to fix the acrylic tube on the Z-direction screw rod slide rail.

[0074] 3. System software control part

[0075] The software is designed with LabVIEW, which can synchronously control the data acquisition part and the probe control movement part, collect data and transmit it back to the computer through the network cable for processing, and finally draw an electromagnetic field distribution map. The software interface can be divided into 5 parts:

[0076] The automated scanning part of the system: The scanning method used is Figure 3 The point-by-point scanning method can set the scanning XYZ range and scanning accuracy.

[0077] The system's instrument setting interface: communicates with instruments through different IP addresses, and can perform initialization settings, parameter control, data acquisition and transmission, etc. for vector network analyzers, oscilloscopes, and spectrum analyzers.

[0078] The data processing part of the system: processes the collected time domain and frequency domain data.

[0079] The image display part of the system: displays the processed electromagnetic data and the waveform data of each point in the acquisition process of different instruments.

[0080] Manual control part of the system: controls the forward and backward distance and speed of the three axes XYZ.

[0081] 4. Quick scanning method

[0082] The present invention also proposes a fast scanning method, which can perform dense scanning in areas where the electromagnetic field changes quickly and rough scanning in areas where the electromagnetic field changes slowly, by calculating the gradient amplitude of the collected data and calculating the local adaptive threshold of the image as the basis for judging high gradient points. The flowchart of the proposed scanning method is shown in FIG. Figure 5 As shown, it includes the following four steps:

[0083] First, an initial rough scan with a large sampling interval (an "S"-shaped scanning path may be used) is performed to obtain a source data image, which includes the scanned position coordinates and the field intensity amplitude of the corresponding points.

[0084] Secondly, the source data obtained by scanning is used to calculate the gradient amplitude of the field intensity at each scanning point, and the scanning points with fast field intensity gradient changes are determined by using the local adaptive threshold.

[0085] Again, add an appropriate number of additional scan points around this scan point.

[0086] Finally, the additional scanned samples are used together with the source data to extract accurate 2D image data of the electromagnetic field.

[0087] Compared with the traditional uniform scanning method with equal intervals, this method reduces the number of scanning points under the condition of the same accuracy and can improve the scanning efficiency of the near-field scanning system.

[0088] The gradient is the derivative of a multivariable function at a certain point along the directions of the coordinate axes. In image processing, we usually deal with a two-dimensional function Z(x,y), where x and y are spatial coordinates, i.e., the position coordinates in the source data, and Z is the magnitude of the field at the corresponding coordinate point. The gradient vector consists of two components: gradX and gradY, which represent the derivatives of the image in the x and y directions, respectively.

[0089] For points inside the image (i.e. points not on the edge), the central difference method is used to approximate the derivative. The formula for the central difference method is:

[0090] gradX(x,y)=(Z(x,y+1)-Z(x,y-1)) / h

[0091] gradY(x,y)=(Z(x+1,y)-Z(x-1,y)) / h

[0092] This method approximates the derivative of a point by calculating the difference between the function values ​​of the points on either side of the point (x, y) and then dividing it by h (h is a small positive number representing the step size). This method is commonly used in numerical differentiation because it has high accuracy.

[0093] For the points at the edge of the image, since there are not enough points to apply the central difference method, we use the forward difference method to approximate the derivative. The formula for the forward difference method is:

[0094] gradX(x,1)=(Z(x,2)-Z(x,1))

[0095] gradX(x,n)=(Z(x,n)-Z(x,n-1))

[0096] gradY(1,y)=(Z(2,y)-Z(1,y))

[0097] gradY(m,y)=(Z(m,y)-Z(m-1,y))

[0098] m and n represent the number of rows and columns of the image respectively. This method approximates the derivative of a point by calculating the difference between the function value of the point and its previous point.

[0099] The gradient magnitude is the modulus of the gradient vector, which indicates the length of the gradient vector. The calculation formula for the gradient magnitude is:

[0100]

[0101] This formula calculates the square root of the sum of the squares of gradX and gradY to get the gradient magnitude. The larger the gradient magnitude, the faster the image value changes at that point. The gradient of the scan point is approximated by the central difference method and the forward difference method, and then the gradient magnitude is calculated.

[0102] The threshold determination will be carried out below. By comparing the obtained gradient amplitude with a threshold value T, it is determined which scanning point has a large gradient change, and then additional scanning points are added around this scanning point. The local adaptive threshold method is an image binarization technology that calculates the threshold based on the local neighborhood information of each pixel in the image. Unlike the global threshold method, the local adaptive threshold method can handle the situation where the brightness changes greatly in the image and obtain a better binarization effect. The places where the brightness changes greatly in the image are the areas with high field strength amplitude. These areas usually require extra attention in electromagnetic compatibility testing.

[0103] The basic principle of the local adaptive threshold method is as follows:

[0104] 1) Define a local neighborhood: For each point in the image, define a local neighborhood, usually a rectangular or circular area, which can be 3x3, 5x5 or other sizes.

[0105] 2) Calculate the local average value: Calculate the average value of the field strength amplitude obtained from all scans in the local neighborhood, denoted as μ.

[0106] 3) Calculate the threshold: Calculate the mean threshold T based on the local average value:

[0107] T=μ+k*σ

[0108] where σ is the standard deviation of the field amplitude in the local neighborhood, and k is a constant, usually 0.5 or 1.

[0109] 4) Judgment: Compare the threshold T obtained at each scanning point with the gradient amplitude |gradZ|. If the gradient amplitude of a scanning point is greater than T, the point is a high gradient point, and an appropriate number of additional scanning points are added around the high gradient point.

[0110] 5. Multiple measurement methods

[0111] The network port is used to control and communicate with the instrument in real time. Different IP addresses are assigned to different instruments through the network switch, so that all instruments can be controlled simultaneously. Only one measurement method can be implemented at the same time. The following will describe the three measurement methods and the experimental layout diagram of the measurement.

[0112] The present invention can realize three measurement methods in total. The first method is to use an oscilloscope plus a radio frequency signal source to realize the time domain electromagnetic radiation measurement of passive devices. The second method is to use a spectrum analyzer to measure the electromagnetic radiation of active devices. The third method is to use a vector network analyzer to measure the electromagnetic radiation of passive devices.

[0113] The first measurement method implemented in the present invention is: Figure 6 As shown in the figure, the 2 channels of the oscilloscope are connected to the electric / magnetic probe, and the output of the RF signal source is divided into two signals through a two-way power divider, one of which is connected to the passive device under test, and the other is connected to the 1 port of the oscilloscope as a reference signal, so that the phase information of the measured signal can be obtained. The computer remotely controls the oscilloscope through the network cable to collect data, and then transmits the collected data back to the computer through the network cable for analysis and processing. The magnetic field distribution measurement results in the time domain shown in Figures 7 (a) and (b) are obtained.

[0114] The second measurement method implemented in the present invention is as follows: Figure 8 As shown, first, the electric / magnetic probe is fixed to the bottom of the three-dimensional scanning bracket 4, and then connected to the spectrum analyzer through a coaxial cable through a low-noise amplifier. The purpose of the low-noise amplifier is to allow the electric / magnetic probe to measure a smaller frequency domain signal, which is conducive to the collection of weak signals. The computer remotely controls the spectrum analyzer through the network cable to perform initialization settings and data collection, and then transmits the data of the spectrum analyzer back to the computer through the network cable for analysis and processing. The magnetic field distribution measurement results in the time domain shown in Figures 9 (a) and (b) are obtained.

[0115] The third measurement method implemented in the present invention is: Fig.10 As shown, first, the electric / magnetic probe is fixed to the bottom of the three-dimensional scanning bracket 4, and then connected to the 2-port of the vector network analyzer through a coaxial cable, and the 1-port of the vector network analyzer is connected to the passive device under test. The computer remotely controls the vector network analyzer through the network cable to set parameters and collect data, and then transmits the collected data back to the computer through the network cable for analysis and processing. The magnetic field measurement distribution results in the time domain shown in Figures 11 (a) and (b) are obtained.

[0116] Figures 12(a) and (b) are comparisons of the frequency domain uniform measurement results of f=500MHz and the results of the fast scanning method. Figures 13(a) and (b) are the position distribution of the scanning points using uniform and equal-interval scanning and the position distribution of the scanning points using the fast scanning method of the present invention. It can be seen that under the same scanning accuracy, the magnetic field measurement data obtained by the two methods are basically consistent. In addition, the number of scanning points of the fast scanning method of the present invention is 2883 scanning points, while the number of scanning points of the uniform and equal-interval scanning is 4941 scanning points, which significantly saves the time of near-field scanning and improves the measurement efficiency.

[0117] Figures 14(a) and (b) are comparisons of the time domain uniform measurement results and the fast scanning method results at t = 5ns, and Figures 15(a) and (b) are the position distribution of the scanning points using uniform and equal-interval scanning and the position distribution of the scanning points using the fast scanning method of the present invention. It can be seen that under the same scanning accuracy, the magnetic field measurement data obtained by the two methods are basically consistent. In addition, the number of scanning points of the fast scanning method of the present invention is 1055 scanning points, while the number of scanning points of the uniform and equal-interval scanning is 2046 scanning points, which significantly saves the time of near-field scanning and improves the measurement efficiency.

Claims

1. A near-field scanning system for electromagnetic radiation measurement, characterized in that: It includes a data acquisition unit, a probe control moving unit and a control unit; The data acquisition unit includes a vector network analyzer and a spectrum analyzer for frequency domain measurement, an oscilloscope and a radio frequency signal source for time domain measurement, and a near-field electric / magnetic probe; When measuring the electromagnetic field of a passive device under test, port 1 of the vector network analyzer is connected to the device under test, and port 2 is connected to a near-field electric / magnetic probe; port 1 of the oscilloscope is connected to a near-field electric / magnetic probe, and the output signal of the radio frequency signal source is divided into two signals by a two-way power divider, one of which is connected to the passive device under test, and the other is connected to port 2 of the oscilloscope as a reference signal; When measuring the electromagnetic field of an active device under test, one port of the spectrum analyzer is connected to a near-field electric / magnetic probe; The probe control moving unit is used to control the near-field electric / magnetic probe to move along a set route in three directions of X, Y, and Z, and to stay at each set scanning point for a specific time to collect data; The control unit is used to synchronously control the data acquisition unit and the probe control moving unit, complete the data acquisition and transmit it back to the computer through the network cable for processing.

2. The near-field scanning system for electromagnetic radiation measurement according to claim 1, characterized in that: The probe control moving unit adopts a three-axis screw slide scanning frame, including screw slides in three directions of XYZ and an L-shaped bracket, wherein there are two screw slides in the X direction; the two ends of the Y direction screw slide are respectively driven by stepper motors arranged on the two X direction screw slides to move along the X axis; the Z direction screw slide is driven by a stepper motor arranged on the Y direction screw slide to move along the Y axis; the L-shaped bracket is driven by a stepper motor arranged on the Z direction screw slide to move along the Z axis; and a pipe fitting for fixing a near-field electric / magnetic probe is provided on the L-shaped bracket.

3. A rapid scanning method for electromagnetic radiation measurement, characterized in that: The following steps are involved: Step 1: Perform an initial rough scan of the device under test at a set sampling interval to obtain a source data image of the field strength; the source data image includes the position coordinates of the scanning point and the field strength amplitude corresponding to the scanning point; Step 2: Use the sampled source data to calculate the gradient amplitude of the field strength at each scanning point, and use the local adaptive threshold method to determine the scanning point where the field strength gradient change is greater than the set threshold, and take it as a high gradient point; Step 3: Add additional scanning points around the high gradient point and perform scanning; Step 4: Extract electromagnetic field two-dimensional image data together with the additional scan data and source data.

4. The rapid scanning method for electromagnetic radiation measurement according to claim 3, characterized in that: In step 2, the gradient amplitude between the field intensity data at the scanning points is calculated as follows: For scan points inside the source data image, the central difference method is used to approximate the derivative: gradX(x,y)=(Z(x,y+1)-Z(x,y-1)) / h gradY(x,y)=(Z(x+1,y)-Z(x-1,y)) / h Among them, gradX(x,y) and gradY(x,y) represent the derivatives of the scanning point with coordinates (x,y) in the image in the X direction and Y direction respectively; in the two-dimensional function Z(x,y), x and y are spatial coordinates, that is, the position coordinates in the source data, and Z is the field intensity amplitude at the corresponding coordinate scanning point; h represents the step size, which is a small positive number; For the scan points at the edge of the source data image, the forward difference method is used to approximate the derivative: gradX(x,1)=(Z(x,2)-Z(x,1)); gradX(x,n)=(Z(x,n)-Z(x,n-1)); gradY(1,y)=(Z(2,y)-Z(1,y)); gradY(m,y)=(Z(m,y)-Z(m-1,y)); Wherein, m and n represent the number of rows and columns of the source data image respectively; Compute the gradient magnitude:

5. The rapid scanning method for electromagnetic radiation measurement according to claim 3, characterized in that: In step 2, the local adaptive threshold method is specifically: Step a: Define a local neighborhood: For each point in the source data image, define a rectangular or circular area as the local neighborhood; Step b: Calculate the local average value: Calculate the average value of the field strength amplitude obtained by all scans in the local neighborhood, denoted as μ; Step c: Calculate the threshold: Calculate the mean threshold T based on the local average: T=μ+k*σ Where σ is the standard deviation of the field strength amplitude in the local neighborhood, and k is a constant; Step d: Judgment: Compare the threshold T obtained at each scanning point with the gradient amplitude |gradZ|. If the gradient amplitude of a scanning point is greater than T, then the point is a high gradient point, and additional scanning points are added around the high gradient point.

Images