CN111983330B - Dielectric Constant Measurement System and Method Based on Van Atta Array - Google Patents

Abstract

The present application relates to a Van Atta array-based dielectric constant measurement system and method. The system includes a measurement antenna array, a Van Atta array, and a permittivity calculation device. The measurement antenna array is set in the far-field area of the Van Atta array, and is used to transmit the measurement signal and receive the reflected signal after the measurement signal is acted on by the object to be measured and reflected by the Van Atta array. The Van Atta array is set opposite the measurement antenna array, and the aperture is larger than the diameter of the object to be measured. The operating frequency and polarization mode are set according to the measurement signal, and the retrospective pattern covers the measurement antenna array. The dielectric constant calculating device calculates the dielectric constant of the object to be tested according to the received reflected signal. The above system uses the electromagnetic wave backtracking function of the Van Atta array to automatically reflect the measurement signal that has been affected by the object to be measured back to the measurement antenna array, which can ensure the energy and signal-to-noise ratio of the reflected signal received at the measurement antenna array, and improve the measurement accuracy and its performance. stability.

Description

Dielectric Constant Measurement System and Method Based on Van Atta Array

technical field

The present application relates to the technical field of dielectric constant measurement, and in particular, to a dielectric constant measurement system and method based on a Van Atta array.

Background technique

The complex permittivity is an important electromagnetic parameter of material, which reflects the ability of material to store and consume electromagnetic energy, and is one of the inherent characteristics of material. Different substances, different states of matter, or different material compositions are reflected in the complex permittivity. In scientific research and engineering applications, the complex permittivity is usually measured to obtain the relevant information of the material, including shape, internal structure, composition Changes in composition and properties, etc.

Generally speaking, when measuring the complex permittivity of the object to be tested, the structure of the object to be tested cannot be destroyed, so the antenna array is usually used to measure the object to be tested. Specifically, as shown in Figure 1, the measurement signal is transmitted through the transmitting antenna (array), and the measurement signal after the object to be measured is received by the receiving antenna (array), and the algorithm is passed according to the signal received by the receiving antenna (array). Solve for the complex permittivity of the test object. Due to the difference in the material and structure of the object to be tested, its effect on the measurement signal is different. When using the inverse scattering problem to solve the dielectric constant of the object to be tested, the signal energy and signal-to-noise ratio directly affect the calculation accuracy. Therefore, how to choose the best setting mode of the receiving antenna (array) for different objects to be tested to improve the signal energy and signal-to-noise ratio, thereby improving the accuracy of the dielectric constant measurement results is an important problem faced by the current dielectric constant measurement system.

SUMMARY OF THE INVENTION

Based on this, it is necessary to provide a dielectric constant measurement system and method based on a Van Atta array, which can improve and stabilize the dielectric constant measurement results in view of the above technical problems.

A dielectric constant measurement system based on a Van Atta array includes a measuring antenna array, a Van Atta array and a dielectric constant calculation device.

The measurement antenna array is set in the far-field area of the VanAtta array, which is used to transmit the measurement signal using the preset frequency and polarization, and to receive the reflection signal after the measurement signal is acted on by the object to be measured and reflected by the VanAtta array, and sends the reflection signal. to permittivity calculation equipment.

The VanAtta array is set opposite the measurement antenna array. The diameter of the VanAtta array is larger than the diameter of the object to be measured. The operating frequency and polarization mode of the VanAtta array are set according to the measurement signal. The retrospective pattern of the VanAtta array covers the measurement antenna array.

The dielectric constant calculating device is connected with the measuring antenna array, receives the reflected signal of the measuring signal sent by the measuring antenna array, and calculates the dielectric constant of the object to be measured according to the reflected signal.

One of the embodiments further includes a measurement antenna array switch array for controlling the time when the antennas in the measurement antenna array transmit the measurement signal.

In one embodiment, the dielectric constant calculation device includes a vector network analyzer and a dielectric constant calculation unit, the dielectric constant calculation unit is pre-installed with dielectric constant calculation software based on an inverse scattering algorithm, and the dielectric constant calculation software is based on the vector network The output of the analyzer calculates the dielectric constant of the analyte.

In one embodiment, the elements of the VanAtta array adopt a low-profile structure.

In one embodiment, the measurement antenna array includes a probe for receiving the reflected signal.

A dielectric constant measurement method based on a VanAtta array, using the system described in any one of the above embodiments to measure the dielectric constant of a test object placed in the far-field region of the VanAtta array, the method comprising:

The measurement signal is transmitted with a preset frequency, polarization and duration using the measurement antenna array.

The dielectric constant calculation device is used to receive the reflection signal of the measurement signal sent by the measurement antenna array, and calculate the dielectric constant of the object to be measured according to the reflection signal.

In one embodiment, before the step of using the measurement antenna array to transmit a measurement signal with a preset frequency, polarization and duration, the method further includes:

Use the standard calibrator to calibrate the system, and obtain the calibration coefficient value of the transceiver antenna pair of the measurement antenna array.

A dielectric constant measurement device based on a Van Atta array, using the system described in any one of the above embodiments to measure the dielectric constant of a test object placed in the far-field region of the Van Atta array, the device includes:

The measurement signal transmitting module is used for transmitting the measurement signal with the preset frequency, polarization mode and duration by using the measurement antenna array.

The dielectric constant calculation module is used to receive the reflected signal of the measurement signal sent by the measurement antenna array by using the dielectric constant calculation device, and calculate the dielectric constant of the object to be measured according to the reflected signal.

A computer device, comprising a memory and a processor, the memory stores a computer program, when using the system described in any one of the above embodiments to measure the dielectric constant of a test object placed in the far-field region of the VanAtta array, The processor implements the following steps when executing the computer program:

The measurement signal is transmitted with a preset frequency, polarization and duration using the measurement antenna array.

The dielectric constant calculation device is used to receive the reflection signal of the measurement signal sent by the measurement antenna array, and calculate the dielectric constant of the object to be measured according to the reflection signal.

A computer-readable storage medium on which a computer program is stored, when the system described in any one of the above embodiments is used to measure the dielectric constant of a test object placed in the far-field region of the VanAtta array, the computer program The following steps are implemented when executed by the processor:

The measurement signal is transmitted with a preset frequency, polarization and duration using the measurement antenna array.

The dielectric constant calculation device is used to receive the reflection signal of the measurement signal sent by the measurement antenna array, and calculate the dielectric constant of the object to be measured according to the reflection signal.

The above-mentioned dielectric constant measurement system, method, device, computer equipment and storage medium based on the Van Atta array, the parameters of the Van Atta array are set according to the size of the object to be measured and the parameters of the measured antenna array, and the object to be measured is placed far away from the Van Atta array. The field area is located between the oppositely set measurement antenna array and the Van Atta array. The Van Atta array’s retrospective function of electromagnetic waves is used to automatically reflect the measurement signal affected by the object to be measured back to the position of the measurement antenna array. Different structures and materials of the test object can ensure the energy and signal-to-noise ratio of the reflected signal received at the antenna array, which makes the measurement accuracy of the system higher and more stable.

Description of drawings

Fig. 1 is a kind of dielectric constant measuring method in the prior art;

2 is a schematic diagram of the composition of a dielectric constant measurement system based on a Van Atta array in one embodiment;

Fig. 3 is the array element arrangement schematic diagram of Van Atta array in one embodiment;

4 is a schematic flowchart of a method for measuring dielectric constant based on a Van Atta array in another embodiment;

FIG. 5 is a diagram of the internal structure of a computer device in one embodiment.

Detailed ways

In order to make the purpose, technical solutions and advantages of the present application more clearly understood, the present application will be described in further detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are only used to explain the present application, but not to limit the present application.

In one embodiment, as shown in FIG. 2 , a Van Atta array-based dielectric constant measurement system is provided, including a measuring antenna array, a VanAtta array, and a dielectric constant calculation device.

The measurement antenna array is set in the far-field area of the VanAtta array, which is used to transmit the measurement signal using the preset frequency and polarization, and to receive the reflection signal after the measurement signal is acted on by the object to be measured and reflected by the VanAtta array, and sends the reflection signal. to permittivity calculation equipment.

The VanAtta array is set opposite the measurement antenna array. The diameter of the VanAtta array is larger than the diameter of the object to be measured. The operating frequency and polarization mode of the VanAtta array are set according to the measurement signal. The retrospective pattern of the VanAtta array covers the measurement antenna array.

The dielectric constant calculating device is connected with the measuring antenna array, receives the reflected signal of the measuring signal sent by the measuring antenna array, and calculates the dielectric constant of the object to be measured according to the reflected signal.

Specifically, the measurement antenna array in the system includes a transmitting antenna and a receiving antenna. The transmitting antenna is used to transmit the measurement signal, and the receiving antenna is used to receive the reflected signal after the action of the object to be measured and the reflection of the VanAtta array. The frequency of the measurement signal can be preset according to the test requirements, and can theoretically be any electromagnetic frequency band.

，其中R为Van Atta阵与待测物的距离。Van Atta阵回溯方向图的宽度根据测量天线阵列确定，即需要覆盖测量天线阵列的天线测量范围，可以通过调整阵元的波束宽度、设定恰当的阵元间距，调整Van Atta阵的回溯方向图的宽度。The indicators of the Van Atta array are set according to the frequency, polarization mode and measurement range of the measurement antenna array, as well as the size of the object to be measured. According to the working principle of the Van Atta array, it can be regarded as a transmitting antenna array. The operating frequency λ and polarization mode of the array element are determined according to the frequency and polarization mode of the measurement signal emitted by the measurement antenna array. The size of the array element is generally It can be equivalent to the half wavelength of the operating frequency λ; the aperture D of the entire Van Atta array is generally larger than the diameter of the object to be tested, and the object to be tested can be placed in the far-field region (Fronhofer region) of the Van Atta array, that is, the Van Atta array. The caliber D of the Atta array needs to meet the

, where R is the distance between the Van Atta array and the object to be tested. The width of the retrospective pattern of the Van Atta array is determined according to the measurement antenna array, that is, it needs to cover the antenna measurement range of the measuring antenna array. The retrospective pattern of the Van Atta array can be adjusted by adjusting the beam width of the array element and setting the appropriate array element spacing. width.

In use, the Van Atta array-based permittivity measurement system is typically placed in a microwave anechoic chamber. Since the actual test system is different from the numerical model, the system needs to be calibrated with a standard calibrator before the test, and the calibration coefficient c is obtained:

是根据计算模型计算所得的场值，

是指一对发射/接收天线之间的s参数。标准定标物是指准确知道介电常数的物体，因此其测量数据可以作为系统校准的根据。in,

is the field value calculated according to the computational model,

Refers to the s-parameter between a pair of transmit/receive antennas. The standard calibrator refers to an object whose dielectric constant is accurately known, so its measurement data can be used as the basis for system calibration.

可以根据实测电场数据

和校准系数c求得：Calibrated electric field data

According to the measured electric field data

And the calibration coefficient c is obtained:

For each pair of transmit/receive antennas, due to the differences in their production and installation, the corresponding calibration coefficients need to be calculated, and then a calibration coefficient matrix is formed:

和

分别是第

个天线作为发射天线，第

个天线作为接收天线时根据计算模型计算所得的场值和

参数。且根据校准场的种类，可以把校准分为两类：入射场校准和散射场校准，分别针对于入射场和散射场进行校准。in,

and

respectively

antenna as the transmitting antenna, the first

When two antennas are used as receiving antennas, the field values calculated according to the calculation model and

parameter. And according to the type of calibration field, calibration can be divided into two categories: incident field calibration and scattered field calibration, which are calibrated for incident field and scattered field respectively.

When making measurements, place the object to be measured in the far-field area of the VanAtta array, and use the measurement antenna array to transmit measurement signals with a preset frequency, polarization, and duration. The measuring antenna array receives the reflected signal after the action of the object to be measured and reflected by the VanAtta array, and calculates the dielectric constant of the object to be measured according to the reflected signal. Specifically, a calibration matrix is used to convert the measured S-parameters into field values. The transmission method of the measurement signal during measurement can be divided into two categories according to the realization form of the measurement antenna array: one is to use a single antenna to transmit the measurement signal in turn through multiple antenna arrays, and the reflected signal received by all antennas is used for testing; A single antenna receives the reflected signal at different positions multiple times to form a virtual equivalent antenna receiving array. When the measuring antenna array receives the reflected signal, it should be located in the far-field region of the scattered field of the VanAtta array.

The dielectric constant calculation device uses the inverse scattering algorithm to calculate the dielectric constant of the object to be tested. The inverse scattering algorithm can be the BORN algorithm, the filter back propagation method, the Born iteration method, the contrast source method, etc. In the calculation process, the Van Atta array can be regarded as a boundary condition with backtracking and phase delay functions.

The above-mentioned dielectric constant measurement system based on the Van Atta array sets the parameters of the Van Atta array according to the size of the object to be measured and the measurement antenna array parameters, places the object to be measured in the far-field area of the Van Atta array, and makes it located in a relatively set Between the measurement antenna array and the Van Atta array, the retrospective function of the Van Atta array to electromagnetic waves is used to automatically reflect the measurement signal that has been affected by the object to be measured back to the position of the measurement antenna array. It can ensure the energy and signal-to-noise ratio of the reflected signal received at the measurement antenna array, so that the measurement accuracy of the system is higher and more stable.

Preferably, the array elements of the Van Atta array are arranged as shown in FIG. 3 , a plurality of array elements 302 are evenly arranged on the printed circuit board 303 in a center-symmetric manner, and radio frequency cables are used on the back of the printed circuit board 303 to connect the center-symmetrical array elements 302 are connected in pairs through feeding points 301.

One of the embodiments further includes a measurement antenna array switch array for controlling the time when the antennas in the measurement antenna array transmit the measurement signal. Specifically, according to the system measurement requirements, the antennas in the measurement antenna array can be independently controlled individually or in groups through the measurement antenna array switch array, so as to control the switch state of each (group) antenna, adjust the transmission duration of the test signal, and adapt to different test requirements.

In one embodiment, the dielectric constant calculation device includes a vector network analyzer and a dielectric constant calculation unit, the dielectric constant calculation unit is pre-installed with dielectric constant calculation software based on an inverse scattering algorithm, and the dielectric constant calculation software is based on the vector network The output of the analyzer calculates the dielectric constant of the analyte. Commercial instruments such as impedance analyzers or self-developed electromagnetic transceiver systems can also be used to replace vector network analyzers.

In one embodiment, the antenna type of the measurement antenna array may be a horn antenna, a patch antenna, a slot antenna, a helical antenna, a Yagi-Uda antenna and other common antennas and their arrays; Broadband and frequency-invariant antennas and arrays thereof such as cone, cone, disc cone and bowtie antennas. The measurement antenna array also includes probes for receiving reflected signals, including coaxial probes with terminal openings, non-uniform coaxial probes, and anisotropic probes, etc., to measure smaller and thinner objects to be measured.

In one embodiment, the array element in the Van Atta array is a low-profile structure or a three-dimensional structure, such as a helical antenna and other broadband antenna forms, so as to realize retroreflection in a wider frequency band. Among them, the Van Atta array used for probe measurement generally uses a low-profile form to match the characteristics of the probe's small radiation field range.

A method for measuring the permittivity of a Van Atta array, using the system described in any one of the above embodiments to measure the permittivity of a test object placed in the far-field region of the Van Atta array, comprising the following steps:

Step 402, using the measurement antenna array to transmit the measurement signal with a preset frequency, polarization mode and duration.

Step 404 , use a dielectric constant calculating device to receive the reflected signal of the measurement signal sent by the measuring antenna array, and calculate the dielectric constant of the object to be measured according to the reflected signal.

In one embodiment, before the step of using the measurement antenna array to transmit the measurement signal with a preset frequency, polarization mode and duration, the method further includes:

Use the standard calibrator to calibrate the system, and obtain the calibration coefficient value of the transceiver antenna pair of the measurement antenna array.

It should be understood that although the various steps in the flowchart of FIG. 4 are sequentially displayed according to the arrows, these steps are not necessarily executed in the order indicated by the arrows. Unless explicitly stated herein, the execution of these steps is not strictly limited to the order, and these steps may be performed in other orders. Moreover, at least a part of the steps in FIG. 4 may include multiple sub-steps or multiple stages. These sub-steps or stages are not necessarily executed and completed at the same time, but may be executed at different times. The execution of these sub-steps or stages The sequence is also not necessarily sequential, but may be performed alternately or alternately with other steps or sub-steps of other steps or at least a portion of a phase.

A dielectric constant measurement device based on a Van Atta array, using the system described in any one of the above embodiments to measure the dielectric constant of a test object placed in the far-field region of the Van Atta array, the device includes:

The measurement signal transmitting module is used for transmitting the measurement signal with the preset frequency, polarization mode and duration by using the measurement antenna array.

The dielectric constant calculation module is used to receive the reflected signal of the measurement signal sent by the measurement antenna array by using the dielectric constant calculation device, and calculate the dielectric constant of the object to be measured according to the reflected signal.

In one of the embodiments, a system calibration module is further included, which is used for calibrating the system by using a standard calibrator to obtain the calibration coefficient value of the pair of transmitting and receiving antennas of the measurement antenna array.

For specific limitations on a method and device for measuring dielectric constant based on a Van Atta array, reference may be made to the above definition of a dielectric constant measuring system based on a Van Atta array, which will not be repeated here. Each module in the above-mentioned VanAtta array-based dielectric constant measurement device can be implemented in whole or in part by software, hardware, and combinations thereof. The above modules can be embedded in or independent of the processor in the computer device in the form of hardware, or stored in the memory in the computer device in the form of software, so that the processor can call and execute the operations corresponding to the above modules.

In one embodiment, a computer device is provided, and the computer device may be a terminal, and its internal structure diagram may be as shown in FIG. 5 . The computer equipment includes a processor, memory, a network interface, a display screen, and an input device connected by a system bus. Among them, the processor of the computer device is used to provide computing and control capabilities. The memory of the computer device includes a non-volatile storage medium, an internal memory. The nonvolatile storage medium stores an operating system and a computer program. The internal memory provides an environment for the execution of the operating system and computer programs in the non-volatile storage medium. The network interface of the computer device is used to communicate with an external terminal through a network connection. The computer program, when executed by the processor, implements a Van Atta array-based permittivity measurement method. The display screen of the computer equipment may be a liquid crystal display screen or an electronic ink display screen, and the input device of the computer equipment may be a touch layer covered on the display screen, or a button, a trackball or a touchpad set on the shell of the computer equipment , or an external keyboard, trackpad, or mouse.

Those skilled in the art can understand that the structure shown in FIG. 5 is only a block diagram of a part of the structure related to the solution of the present application, and does not constitute a limitation on the computer equipment to which the solution of the present application is applied. Include more or fewer components than shown in the figures, or combine certain components, or have a different arrangement of components.

A computer device, comprising a memory and a processor, the memory stores a computer program, when using the system described in any one of the above embodiments to measure the dielectric constant of a test object placed in the far-field region of the VanAtta array, The processor implements the following steps when executing the computer program:

The measurement signal is transmitted with a preset frequency, polarization and duration using the measurement antenna array.

The dielectric constant calculation device is used to receive the reflection signal of the measurement signal sent by the measurement antenna array, and calculate the dielectric constant of the object to be measured according to the reflection signal.

In one embodiment, when the processor executes the computer program, the processor further implements the following steps: calibrating the system by using a standard calibrator, and obtaining a calibration coefficient value of the pair of transmitting and receiving antennas of the measurement antenna array.

A computer-readable storage medium on which a computer program is stored, when the system described in any one of the above embodiments is used to measure the dielectric constant of a test object placed in the far-field region of the VanAtta array, the computer program The following steps are implemented when executed by the processor:

The measurement signal is transmitted with a preset frequency, polarization and duration using the measurement antenna array.

The dielectric constant calculation device is used to receive the reflection signal of the measurement signal sent by the measurement antenna array, and calculate the dielectric constant of the object to be measured according to the reflection signal.

In one embodiment, when the computer program is executed by the processor, the following steps are further implemented: calibrating the system by using a standard calibrator, and obtaining calibration coefficient values of the pair of transmitting and receiving antennas of the measurement antenna array.

Those of ordinary skill in the art can understand that all or part of the processes in the methods of the above embodiments can be implemented by instructing relevant hardware through a computer program, and the computer program can be stored in a non-volatile computer-readable storage In the medium, when the computer program is executed, it may include the processes of the above-mentioned method embodiments. Wherein, any reference to memory, storage, database or other medium used in the various embodiments provided in this application may include non-volatile and/or volatile memory. Nonvolatile memory may include read only memory (ROM), programmable ROM (PROM), electrically programmable ROM (EPROM), electrically erasable programmable ROM (EEPROM), or flash memory. Volatile memory may include random access memory (RAM) or external cache memory. By way of illustration and not limitation, RAM is available in various forms such as static RAM (SRAM), dynamic RAM (DRAM), synchronous DRAM (SDRAM), double data rate SDRAM (DDRSDRAM), enhanced SDRAM (ESDRAM), synchronous chain Road (Synchlink) DRAM (SLDRAM), memory bus (Rambus) direct RAM (RDRAM), direct memory bus dynamic RAM (DRDRAM), and memory bus dynamic RAM (RDRAM) and so on.

The technical features of the above embodiments can be combined arbitrarily. In order to make the description simple, all possible combinations of the technical features in the above embodiments are not described. However, as long as there is no contradiction in the combination of these technical features It is considered to be the range described in this specification.

The above-mentioned embodiments only represent several embodiments of the present application, and the descriptions thereof are specific and detailed, but should not be construed as a limitation on the scope of the invention patent. It should be pointed out that for those skilled in the art, without departing from the concept of the present application, several modifications and improvements can be made, which all belong to the protection scope of the present application. Therefore, the scope of protection of the patent of the present application shall be subject to the appended claims.

Claims (10)

1. a dielectric constant measurement system based on Van Atta array, is characterized in that, described system comprises measuring antenna array, VanAtta array and dielectric constant computing equipment, The measurement antenna array is arranged in the far-field area of the VanAtta array, and is used to transmit measurement signals using a preset frequency and polarization, and to receive the measurement signals after the action of the object to be measured and the reflection of the VanAtta array. reflect the signal, and send the reflected signal to the dielectric constant calculation device; Described VanAtta array and described measurement antenna array are arranged opposite, the aperture of described VanAtta array is larger than the diameter of described object to be measured, the operating frequency and polarization mode of described VanAtta array are set according to described measurement signal, described VanAtta array The backtracking pattern of the array covers the measurement antenna array; The dielectric constant calculation device is connected to the measurement antenna array, receives the reflected signal of the measurement signal sent by the measurement antenna array, and calculates the dielectric constant of the object to be measured according to the reflected signal. 2 . The system according to claim 1 , further comprising a measurement antenna array switch array for controlling the time when the antennas in the measurement antenna array transmit the measurement signal. 3 . 3. The system according to claim 1, wherein the dielectric constant calculation device comprises a vector network analyzer and a dielectric constant calculation unit, and the dielectric constant calculation unit is pre-installed with a dielectric constant based on an inverse scattering algorithm. A dielectric constant calculation software, the dielectric constant calculation software calculates the dielectric constant of the object to be tested according to the output of the vector network analyzer. 4. The system according to any one of claims 1 to 3, wherein the array elements of the Van Atta array adopt a low-profile structure. 5. The system according to any one of claims 1 to 3, wherein the measurement antenna array comprises a probe for receiving the reflected signal. 6. a kind of dielectric constant measurement method based on VanAtta array is characterized in that, use the system as described in any one of claim 1 to 5 to measure the test object that is placed in the far-field area of described VanAtta array. dielectric constant, the method includes: using the measurement antenna array to transmit measurement signals with a preset frequency, polarization and duration; The dielectric constant calculation device is used to receive the reflection signal of the measurement signal sent by the measurement antenna array, and calculate the dielectric constant of the object to be measured according to the reflection signal. 7. The method according to claim 6, wherein before the step of using the measurement antenna array to transmit measurement signals with a preset frequency, polarization and duration, the method further comprises: The system is calibrated using a standard calibrator, and the calibration coefficient value of the pair of transmit and receive antennas of the measurement antenna array is obtained. 8. A dielectric constant measuring device based on Van Atta array, characterized in that, using the system as described in any one of claims 1 to 5 to measure the test object placed in the far-field area of the Van Atta array. dielectric constant, the device includes: a measurement signal transmitting module, configured to transmit a measurement signal with a preset frequency, polarization mode and duration by using the measurement antenna array; The permittivity calculation module is configured to use the permittivity calculation device to receive the reflection signal of the measurement signal sent by the measurement antenna array, and calculate the permittivity of the object to be measured according to the reflection signal. 9. A computer device comprising a memory and a processor, wherein the memory stores a computer program, wherein the processor implements the steps of the method in claim 6 or 7 when the processor executes the computer program. 10. A computer-readable storage medium on which a computer program is stored, characterized in that, when the computer program is executed by a processor, the steps of the method of claim 6 or 7 are implemented.

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