Photoelectric sensor system conversion efficiency calibration system and method based on reverberation chamber

Abstract

The invention discloses a photoelectric sensor system conversion efficiency calibration system and method based on a reverberation chamber, and belongs to the technical field of photoelectric sensor conversion efficiency calibration, the system comprises an electric wave reverberation chamber, a transmitting antenna, a reference antenna and a photoelectric field sensor system; the photoelectric field sensor system is composed of a photoelectric sensor, a laser source, a photoelectric detector, a polarization maintaining optical fiber and a single-mode optical fiber. In the calibration process, the reference antenna and the photoelectric sensor system are used as receiving ends respectively, receiving power at different stirring positions in the reverberation chamber is sampled to obtain two groups of transfer functions, and the total efficiency of the photoelectric sensor system is determined by comparing the two groups of transfer functions under the condition that the radiation efficiency of the reference antenna is known. The conversion efficiency of the photoelectric sensor system is obtained by combining the relation among the power, the field intensity and the total efficiency in the free space; and the effective averaging of the incident direction and the polarization state is realized by using the uniform and isotropic electromagnetic field characteristics of the reverberation chamber.

Description

A conversion efficiency calibration system and method for photoelectric sensor systems based on a reverberation chamber Technical Field

[0001] This invention belongs to the field of conversion efficiency calibration technology for photoelectric sensors, and particularly relates to a conversion efficiency calibration system and method for photoelectric sensor systems based on a reverberation chamber. Background Technology

[0002] For the ultra-wideband characteristics of photoelectric field sensors, traditional standard field calibration methods (TEM cell, GTEM cell, microwave anechoic chamber, etc.) suffer from time-consuming point-by-point testing. Although the standard field method provides a well-defined uniform field region for calibration, the size of the required uniform region, absorber performance, and reference antenna performance vary greatly with frequency, making it difficult to perform full-band measurements of ultra-wideband photoelectric field sensors in the same facility. Furthermore, the wide frequency response of photoelectric field sensors also complicates the entire calibration process. Therefore, researchers primarily conduct tests at a specific frequency point or within a specific frequency range. In addition, calibration based on the standard field method is highly sensitive to the sensor's orientation because these sensors use anisotropic crystals (lithium niobate, LiNbO3), which typically can only measure a single component of the electric field.

[0003] Reverberation chambers possess a high quality factor, enabling them to generate relatively large field strengths with relatively small input power, producing controllable transient fields with wide bandwidth, high power, and large dynamic range. Within an RC chamber, the electromagnetic field is statistically homogeneous and isotropic due to the rotation of a mechanical stirrer. Therefore, the overall probe response, averaged under different incident angles and polarization states, can be measured, making the measurement results insensitive to specific probe pointing and alignment errors. Furthermore, the wide usable frequency range of RC chambers (typically 200 MHz – 18 GHz) allows for repeatable measurements in a single test environment, simplifying the testing scenario. Therefore, a mature reverberation chamber calibration and testing system can be established based on the reverberation chamber, forming a standardized calibration method for photoelectric field sensors. Summary of the Invention

[0004] This invention provides a reverberation chamber-based photoelectric sensor system conversion efficiency calibration system and method. It introduces statistical radio theory into the analysis of photoelectric field sensor conversion efficiency performance, and analyzes and verifies the accuracy of photoelectric field sensor efficiency by comprehensively statistical analysis and test results. It establishes a mature reverberation chamber calibration and testing system and forms a standardized calibration method for photoelectric field sensors.

[0005] To achieve the above objectives, the present invention adopts the following technical solution:

[0006] A photoelectric sensor system conversion efficiency calibration system based on a reverberation chamber includes a radio reverberation chamber, a transmitting antenna, a reference antenna, a control terminal, an electrical signal extraction unit, a power amplifier, and a photoelectric sensor system. The control terminal is used to set the test process and test parameters, and to record and process the acquired data. The output terminal of the power amplifier is connected to the feed terminal of the transmitting antenna to inject electromagnetic energy into the radio reverberation chamber. The reference antenna and the photoelectric sensor are set in the test area of ​​the radio reverberation chamber to synchronously acquire and receive samples at multiple stirring positions. The output signal of the reference antenna and the output signal of the photoelectric sensor system are respectively input to the electrical signal extraction unit. The electrical signal extraction unit includes a spectrum analyzer or a vector network analyzer to perform power measurement or data sampling on the two signals and convert the obtained measurement data into data that can be processed by the control terminal.

[0007] The photoelectric sensor system consists of a photoelectric sensor, a laser source, a photodetector, a polarization-maintaining fiber, and a single-mode fiber. The photoelectric sensor is connected to the external laser source and photodetector via the polarization-maintaining fiber and the single-mode fiber, respectively. The optical output end of the laser source is connected to the optical input end of the photoelectric sensor via the polarization-maintaining fiber to provide incident light to the photoelectric sensor and maintain the stability of the incident light polarization state. The photoelectric sensor modulates the incident light under the action of the electromagnetic field in the reverberation chamber. The modulated optical signal is transmitted to the optical input end of the photodetector via the single-mode fiber. The photodetector converts the received modulated optical signal into an electrical signal and outputs the electrical signal to the electrical signal extraction unit for measurement and data acquisition processing.

[0008] A method for calibrating the conversion efficiency of a photoelectric sensor system based on a reverberation chamber includes the following steps:

[0009] Using the reference antenna and photoelectric sensor system as receivers, the received power at different stirring positions in the reverberation chamber is sampled. Under the premise of obtaining a sufficient number of independent samples and ensuring that the reverberation chamber is fully stirred, two sets of transfer functions are obtained.

[0010] Given the radiation efficiency of the reference antenna, the overall efficiency of the photoelectric sensor system is determined by comparing two sets of transfer functions.

[0011] By combining the relationship between power, field strength and total efficiency in free space, the conversion efficiency of the photoelectric sensor system can be obtained.

[0012] Beneficial effects: This invention provides a photoelectric sensor system conversion efficiency calibration system and method based on a reverberation chamber, which has the following advantages compared with the prior art:

[0013] 1. Significantly reduced calibration uncertainty and improved result consistency and comparability: By utilizing the statistically uniform and isotropic electromagnetic field distribution characteristics of the reverberation chamber, the response under different incident angles and polarization states is statistically averaged, reducing the sensitivity to sensor polarization characteristics and placement position, effectively weakening the systematic deviation caused by probe pointing, alignment errors and crystal anisotropy, thereby improving the repeatability and stability of conversion efficiency calibration results.

[0014] 2. Reduced dependence on field source and environmental conditions, and improved engineering applicability: Compared with standard field facilities such as TEM cells and microwave anechoic chambers, which are highly dependent on the size of the uniform region, the performance of the absorbing material, and the broadband consistency of the reference antenna with frequency, the method of this invention can cover a wide range of available frequencies and carry out repeatable measurements in a single reverberation chamber environment, reducing dependence on switching between multiple facilities and complex site conditions, and making it easier to promote and apply in laboratories and engineering sites.

[0015] 3. It achieves high field strength and wide dynamic range calibration under low input power, improving efficiency and safety: The high quality factor of the reverberation chamber enables the generation of high field strength with relatively low input power, and can form a wide-bandwidth, controllable transient / steady-state electromagnetic environment, meeting the wide frequency response and wide dynamic range testing requirements of photoelectric field sensors; at the same time, it reduces high-power external field radiation and safety risks, and facilitates the realization of automated, batch and standardized rapid calibration processes.

[0016] 4. Compared with the traditional standard field point-by-point calibration method, the present invention simplifies the test process and shortens the calibration time while still obtaining accurate and repeatable calibration results, making it suitable for efficient calibration of broadband photoelectric field sensor systems. Attached Figure Description

[0017] Figure 1 is a schematic diagram of the conversion efficiency calibration system of the photoelectric sensor system based on the reverberation chamber in an embodiment of the present invention;

[0018] Figure 2 is a schematic diagram of the photoelectric sensor system in an embodiment of the present invention;

[0019] Figure 3 is a schematic diagram of the frequency response curve obtained by testing the photoelectric sensor system using the standard field method in an embodiment of the present invention;

[0020] Figure 4 is the average transfer function curve of the cavity obtained by the reverberation chamber calibration method in an embodiment of the present invention.

[0021] Figure 5 shows the overall efficiency of the photoelectric sensor system obtained by the reverberation chamber calibration method in an embodiment of the present invention.

[0022] Figure 6 shows the conversion efficiency results of the photoelectric sensor system obtained by the reverberation chamber calibration method in an embodiment of the present invention.

[0023] Figure 7 is a schematic diagram comparing the frequency response curves of the photoelectric sensor system in the embodiment of the present invention, including the frequency response curves obtained by the standard field method and the reverberation chamber method. Detailed Implementation

[0024] The present invention will now be described in detail with reference to the accompanying drawings and specific embodiments:

[0025] As shown in Figure 1, the photoelectric sensor system conversion efficiency calibration system based on a reverberation chamber includes the following components: a control terminal, a photoelectric sensor system, a reverberation chamber, a vector network analyzer (VNA), a power amplifier, an attenuator, a transmitting antenna, and a reference antenna.

[0026] The control terminal described in this solution is a PC, server, etc. It is used to set the test frequency and sample quantity, and also controls the testing instrument (VNA) via SCPI command programs to achieve data transmission and reading for post-processing.

[0027] As shown in Figure 2, the photoelectric field sensor system mainly includes a laser source, an optical electric field sensor, a photodetector, an electrical signal extraction unit such as a vector network analyzer or spectrum analyzer, polarization-maintaining fiber, single-mode fiber, and radio frequency cable. The laser source outputs an optical power of 5 dBm and operates at a wavelength of 1550 nm; the photodetector operates at a wavelength of 1100-1700 nm with a modulation bandwidth up to 18 GHz; the integrated optical electric field sensor is made of lithium niobate crystal (LiNbO3) and has a size of [missing information]. (Including packaging). It has advantages such as broadband response, high dynamic range, and small size, and has minimal impact on the surrounding field distribution. When the linearly polarized laser output from the laser enters the integrated optical electric field sensor through the polarization-maintaining fiber, the spatial electric field signal is modulated onto the light wave due to the electro-optic effect of the lithium niobate crystal. Finally, the optical signal is input into the photodetector through a single-mode fiber, and the spatial electric field information, such as intensity, frequency, and phase information, is obtained by the electrical signal extraction unit.

[0028] The reverberation chamber comprises a main chamber body and test components housed within it: a stirrer (vertical and horizontal), a transmitting antenna, a reference antenna, and an integrated optical electric field sensor. The sensor is connected to an external laser source and a photodetector via polarization-maintaining fiber and single-mode fiber, respectively. The dimensions of the reverberation chamber are... The minimum usable frequency is 200 MHz, and the inner wall surface of the cavity body is a smooth metal conductor.

[0029] A conversion efficiency calibration method for photoelectric sensor systems based on a reverberation chamber, wherein the conversion efficiency coefficient is used to quantify the relationship between received power (voltage) and ambient field strength, and is defined as: ;

[0030] By measuring the overall efficiency of the photoelectric sensor system in a reverberation chamber and combining this with the relationship between power, field strength, and overall efficiency in free space, the conversion efficiency of the photoelectric sensor system can be further derived. The testing principle and process are as follows:

[0031] First, the photoelectric field sensor is placed within the test area of ​​the reverberation chamber as the receiving end. A stirrer is set to rotate at predetermined step angles to achieve thorough mixing. Under thorough mixing conditions, the S-parameters at each mixing position are collected and statistically averaged. The chamber transfer function between the transmitting antenna (Tx antenna) and the photoelectric field sensor system can then be constructed from the S-parameters. : ;in, , and These are the S-parameters measured by VNA. The radiation efficiency of the transmitting antenna. The radiation efficiency of the photoelectric sensor system;

[0032] Next, the reference antenna is selected as the receiver; similarly, the transfer function in this scenario... Defined as: ,

[0033] Provided a sufficient number of independent samples are obtained and the reverberation chamber is adequately stirred, the cavity transfer functions measured under the two receiving conditions show good consistency, namely: ,

[0034] At this point, the radiation efficiency of the photoelectric field sensor system It can be represented as: ,in, , , , These are the S-parameters measured by VNA. Given the known radiation efficiency of the reference antenna. The value represents the average value at different stirring positions. In this experiment, the stirrer used a 2° step and a total of 180 test samples were collected.

[0035] If impedance matching at the receiver is considered, the overall efficiency of the photoelectric field sensor system is... It can be represented as: ,

[0036] Free space received power With the electric field intensity of the incident wave The relationship between them can be determined by the effective area of ​​the antenna. To describe, for a plane wave, its power density is: The effective area of ​​the antenna Represented as: ,

[0037] Therefore, the received power is: ,in, , which is the characteristic impedance of free space. It's the wavelength. The directivity coefficient of the antenna is given by equation (8). Substituting equation (8) into equation (1), the conversion efficiency coefficient can be expressed as: .

[0038] Although the directivity of the photoelectric field sensor is unknown and difficult to measure, its design consists of a dipole with two electrodes. Considering that the dipole etched in the photoelectric sensor is very small, its directivity coefficient can be approximated as the infinitesimal directivity coefficient of a dipole antenna, i.e., 1.5. Therefore, the conversion efficiency coefficient can be evaluated simply by measuring its overall efficiency using a reverberation chamber. .

[0039] To verify the effectiveness of the proposed method and the accuracy of the test results, the test results of the reverberation chamber method and the standard-field method were compared. For the reverberation chamber (RC method), the photoelectric sensor system was tested in the frequency range of 200 MHz - 3.5 GHz; for the standard-field method (SF method), the test was conducted in a TEM cell in the low-frequency range (200 MHz – 1 GHz) and in a microwave anechoic chamber in the high-frequency range (1 GHz – 3.5 GHz).

[0040] The application effects of this invention will be described in detail below based on the actual test results.

[0041] Based on the standard field method, a uniform field strength of 50V / m was ensured in the TEM cell and microwave anechoic chamber. The corresponding received power of the system was recorded, and its frequency response curve from 200 MHz to 3.5 GHz was obtained, as shown in Figure 3. This curve was used to compare the test results with the reverberation chamber calibration method proposed in this invention. In the figure, the error bar represents the expanded uncertainty of the standard field method at a 95% confidence level. .

[0042] Figure 4 shows the cavity average transfer function results obtained by the reverberation chamber calibration method proposed in this invention, with the cavity average transfer function as the reference antenna (solid line) and the photoelectric field sensor (dotted line) as the receiving end, respectively. and Meanwhile, the system's noise floor (dotted line) is also shown in the figure to ensure a sufficiently high signal-to-noise ratio.

[0043] Figure 5 shows the measured results of the overall efficiency of the photoelectric sensor in the reverberation chamber calibration method proposed in this invention. As can be seen from the figure, the efficiency of the photoelectric field sensor is low, with the overall efficiency remaining at -123 to -98 dB within the test frequency range.

[0044] Figure 6 shows the measured results of the photoelectric sensor conversion efficiency evaluated by the reverberation chamber calibration method proposed in this invention. To verify the repeatability and measurement consistency of the method, the figure shows four independent test curves. It can be seen that the test results highly overlap across the entire frequency band, exhibiting only slight fluctuations, indicating that the method has good repeatability and stability.

[0045] Based on formula (6), with the conversion efficiency coefficient known... Then, by setting the incident electric field amplitude to 50 V / m, the corresponding sensor output power can be calculated. This yields the frequency response under a field strength of 50 V / m. The result is compared with the frequency response measured by the standard field method, as shown in Figure 7. The two methods generally agree well across the entire test frequency band: the continuous frequency response curve obtained by the RC method falls entirely within the uncertainty range of the standard field method, and both exhibit consistent trends with frequency variation. This indicates that the proposed reverberation chamber calibration method is comparable to the standard field method in terms of accuracy, while also possessing better broadband continuous characterization capabilities.

[0046] In summary, the reverberation chamber-based photoelectric sensor system conversion efficiency calibration method proposed in this invention utilizes the statistically uniform and isotropic electromagnetic field environment of the reverberation chamber to treat the photoelectric sensor system as a whole and combine it with the reference antenna method to achieve rapid calibration of conversion efficiency. This method effectively reduces the sensitivity to probe pointing and alignment, reduces the time cost of frequency-by-frequency standard field calibration, and can achieve wide-band, repeatable calibration testing in a single test environment, making it suitable for engineering applications.

[0047] The above description is only a preferred embodiment of the present invention. It should be noted that for those skilled in the art, several improvements and modifications can be made without departing from the principle of the present invention, and these improvements and modifications should also be considered within the scope of protection of the present invention.

Claims

1. A photoelectric sensor system conversion efficiency calibration system based on a reverberation chamber, characterized in that, The system includes a reverberation chamber, a transmitting antenna, a reference antenna, a control terminal, an electrical signal extraction unit, a power amplifier, an attenuator, and a photoelectric sensor system. The control terminal is used to set the test process and test parameters, and to record and process the acquired data. The output of the power amplifier is connected to the feed terminal of the transmitting antenna to inject electromagnetic energy into the reverberation chamber. The reference antenna and the photoelectric sensor are located within the test area of ​​the reverberation chamber and are used to simultaneously acquire and receive samples at multiple stirring positions. The output signals of the reference antenna and the photoelectric sensor system are respectively input to the electrical signal extraction unit. The electrical signal extraction unit includes a spectrum analyzer or a vector network analyzer, used to perform power measurement or data sampling on the two signals, and convert the obtained measurement data into data that can be processed by the control terminal.

2. The photoelectric sensor system conversion efficiency calibration system based on a reverberation chamber according to claim 1, characterized in that, The photoelectric sensor system consists of a photoelectric sensor, a laser source, a photodetector, a polarization-maintaining fiber, and a single-mode fiber. The photoelectric sensor is connected to the external laser source and photodetector via the polarization-maintaining fiber and the single-mode fiber, respectively. The optical output end of the laser source is connected to the optical input end of the photoelectric sensor via the polarization-maintaining fiber to provide incident light to the photoelectric sensor and maintain the stability of the incident light polarization state. The photoelectric sensor modulates the incident light under the action of the electromagnetic field in the reverberation chamber. The modulated optical signal is transmitted to the optical input end of the photodetector via the single-mode fiber. The photodetector converts the received modulated optical signal into an electrical signal and outputs the electrical signal to the electrical signal extraction unit for measurement and data acquisition processing.

3. The photoelectric sensor system conversion efficiency calibration system based on a reverberation chamber according to claim 1, characterized in that, The lowest usable frequency of the reverberation chamber is 200 MHz, and the inner wall surface of the chamber body is a smooth metal conductor.

4. A method for calibrating the conversion efficiency of a photoelectric sensor system based on a reverberation chamber, characterized in that, Includes the following steps: Using the reference antenna and the photoelectric sensor system as receivers, the received power at different stirring positions in the reverberation chamber was sampled to obtain two sets of transfer functions. Given the radiation efficiency of the reference antenna, the overall efficiency of the photoelectric sensor system was determined by comparing the two sets of transfer functions. The conversion efficiency of the photoelectric sensor system was then derived by combining the relationship between the received power in free space, the electric field strength of the incident wave, and the overall efficiency of the photoelectric sensor system.

5. The method for calibrating the conversion efficiency of a photoelectric sensor system based on a reverberation chamber according to claim 4, characterized in that, The two sets of transfer functions are: the cavity transfer function between the transmitting antenna and the photoelectric field sensor system. The transfer function between the reference antenna and the reference antenna ， ， ,in, 、 and These are the S-parameters measured by VNA. The radiation efficiency of the transmitting antenna. The radiation efficiency of the photoelectric sensor system.

6. The method for calibrating the conversion efficiency of a photoelectric sensor system based on a reverberation chamber according to claim 5, characterized in that, The radiation efficiency of the photoelectric field sensor for: ,in, 、 、 、 These are the S-parameters measured by VNA. Given the known radiation efficiency of the reference antenna. This represents the average value at different stirring positions.

7. The method for calibrating the conversion efficiency of a photoelectric sensor system based on a reverberation chamber according to claim 6, characterized in that, The overall efficiency of the photoelectric sensor system is: ,in, These are the S-parameters measured by VNA. The radiation efficiency of the photoelectric field sensor. This represents the average value at different stirring positions.

8. The method for calibrating the conversion efficiency of a photoelectric sensor system based on a reverberation chamber according to claim 4 or 7, characterized in that, The relationship between free-space received power, incident wave electric field intensity, and the overall efficiency of the photoelectric sensor system is as follows: ,in, For free space receiving power, The electric field intensity of the incident wave, The overall efficiency of the photoelectric sensor system. The characteristic impedance of free space, It's the wavelength. It is the directivity coefficient of the antenna.

9. The method for calibrating the conversion efficiency of a photoelectric sensor system based on a reverberation chamber according to claim 8, characterized in that, The conversion efficiency of the photoelectric sensor system is: 。

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