A camera detection method and system based on electromagnetic signals

Abstract

This invention discloses a camera detection method and system based on electromagnetic radiation signals. The method includes the following steps: acquiring radio frequency signals from the environment and performing preprocessing and spectrum analysis; detecting and marking peak points in the spectrum; grouping the marked peak frequencies and calculating the basic interval frequency of each group; determining whether the basic interval frequency of each group matches the camera clock frequency range; if a match is found, retaining the corresponding peak frequency group; discarding or merging peak frequencies; and further determining whether horizontal synchronization signal component coupling occurs within each peak frequency of the retained peak frequency group; if such coupling occurs, a camera device is detected. This invention can utilize the specific signal spectrum generated by the coupling modulation of the data signal line and clock signal line on the CSI connection cable during camera operation to detect unknown, concealed cameras. It is suitable for private occasions such as confidential meetings and private conversations, with an effective distance of 20 centimeters.

Description

Technical Field

[0001] This invention belongs to the field of equipment testing, specifically relating to a camera testing method and system based on electromagnetic signals. Background Technology

[0002] Hidden cameras are increasingly becoming a serious threat to personal privacy in private settings. Cases of personal privacy or information being compromised by hidden cameras are also on the rise. In confidential meetings, hotel rooms, and other similar settings, it is necessary to ensure that participants are not carrying any filming equipment or that there are no filming devices in the environment. However, pinhole cameras are usually small and can be disguised as other objects, making them difficult for victims to detect with the naked eye.

[0003] Therefore, feasible and practical technical methods for detecting cameras are particularly important. Existing detection technologies, such as flow detectors, metal scanners, and thermal detectors, are not applicable to all camera devices: some cameras can save video locally and do not actively transmit video traffic to the outside world, so flow detectors are not suitable; metal scanners cannot distinguish between metal and different types of equipment, resulting in low detection efficiency and a high risk of false alarms; thermal detectors are easily interfered with by other electronic products in the environment and have limited detection scenarios.

[0004] In summary, there is currently no feasible detection technology for cameras. Summary of the Invention

[0005] The purpose of this invention is to address the shortcomings of existing technologies by providing a camera detection method based on electromagnetic radiation signals. This method utilizes a specific signal spectrum generated by the coupling modulation of the data signal line and clock signal line on the CSI connection line during normal operation of the camera to detect unknown, concealed cameras, with an effective detection distance of 20 centimeters.

[0006] The technical solution adopted in this invention is as follows:

[0007] A camera detection method based on electromagnetic radiation signals includes the following:

[0008] Acquire radio frequency signals in the environment:

[0009] The radio frequency signal is preprocessed and its spectrum is analyzed to detect and mark the peak points in the spectrum.

[0010] The marked peak frequencies are grouped and the basic interval frequency of each group is calculated. It is determined whether the basic interval frequency of each group matches the range of the camera clock frequency. If the match is successful, the corresponding peak frequency group is retained. After discarding or merging, it is further determined whether the horizontal synchronization signal component coupling phenomenon occurs in each peak frequency of the retained peak frequency group. If the phenomenon exists, the camera device is detected.

[0011] In the above technical solution, a radio frequency signal receiving device is used to collect radio frequency signals in the environment to be tested, and the operating frequency band of the device should cover 24-300 MHz.

[0012] Furthermore, the acquired radio frequency signals are processed as follows: first, a Fast Fourier Transform (FFT) is performed to generate the original spectrum, then a denoised spectrum is generated after smoothing, and peak points in the spectrum are selected and marked using a peak detection algorithm.

[0013] Furthermore, the processing of the acquired radio frequency signals can be implemented using Python.

[0014] Furthermore, the peak frequency grouping processing and matching judgment include the following:

[0015] Assume there are n peak frequencies, namely f1, f2, f3…f n ;

[0016] (1) Iterate through i from 1 to n and determine the frequency f. i ;j is iterated from i+1 to n to determine the frequency f. j Determine the fundamental interval frequency Δf between the two. ij =f j -f i If Δf ij If the following multiple relationship is satisfied, it indicates that the basic interval frequency matches the camera clock frequency, where f c Given a camera clock frequency, ranging from 20 to 24 MHz, if there is no match, continue iterating; if there is a match, set the rate f. i and f j Divide into one group, this group is G = (f i ,f j );

[0017] Δf ij =mf c m = 1, 2, 3...

[0018] (2) Traverse k from j+1 to n and calculate Δf ik =f k -f i If Δf ik With Δf ijIf the following multiple relationship exists, then the frequency f k Add to group G:

[0019] Δf ik =mΔf ij m = 1, 2, 3...

[0020] After traversal, multiple sets of peak frequencies will be obtained. If a set contains fewer than 3 peak frequencies, the set will be discarded. If the fundamental interval frequency Δf between set A and set B is greater than or equal to 3, the set will be discarded. A , Δf B If the following multiple relationship is met, or if the number of shared peak frequencies between the two groups exceeds four, then the two groups shall be merged:

[0021] Δf A =mΔf B m = 1, 2, 3...

[0022] Furthermore, there may be errors when comparing multiples between frequencies, with an allowable error of ±5%.

[0023] Furthermore, each peak frequency point within the retained peak frequency group is sequentially used as the center frequency for detection, and the sampling bandwidth is set to 2 MHz. If there is an intermodulation phenomenon between a certain frequency and the center frequency, and the frequency interval of the signal is within the range of 30 kHz to 100 kHz, it indicates that the frequency is the horizontal synchronization signal of the camera. The occurrence of horizontal synchronization signal coupling indicates that the camera has been successfully detected; otherwise, it indicates that there is no camera in the surrounding environment.

[0024] Furthermore, the present invention also provides a camera detection system based on electromagnetic radiation signals for implementing the above-mentioned method, comprising:

[0025] Signal receiving device, used to collect radio frequency signals in the environment, with an operating frequency band covering 24-300 MHz;

[0026] The signal analysis module is used to preprocess and perform spectrum analysis on the signals collected by the signal receiving device, detect and mark the peak points in the spectrum, group the marked peak frequencies and calculate the basic interval frequency of each group, determine whether the basic interval frequency of each group matches the camera clock frequency range, if the match is successful, retain the corresponding peak frequency group, discard or merge, and continue to determine whether there is a coupling phenomenon of the horizontal synchronization signal component in each peak frequency within the retained peak frequency group.

[0027] Beneficial effects: The signal collected by this invention is the electromagnetic signal generated on the CSI cable connecting the image sensor and the signal processor in the camera. Since the data line and clock line on the CSI cable are closely adjacent, the frequency of the data line transmitted on the data line will be coupled to the clock frequency and its harmonic frequencies and leak to the outside. This signal is the energy leaked by the camera itself when it is working normally. Therefore, it overcomes the condition that existing technologies such as traffic detectors require the device to actively transmit signals to the outside. It can not only detect network cameras that transmit video files in real time, but also detect cameras that shoot offline and save locally without actively emitting signals. Therefore, it is more suitable for detecting unknown and hidden cameras.

[0028] This invention matches the interval frequency calculated by signal processing with the camera clock signal frequency, and associates the camera's line transmission behavior with the signal spectrum performance. This allows for targeted determination of whether the signal is generated by the camera, thus overcoming the problem that existing technologies such as metal scanners cannot distinguish the type of electronic device detected, resulting in a lower false detection rate. Attached Figure Description

[0029] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other embodiments can be obtained from these drawings without creative effort.

[0030] Figure 1 This is a structural block diagram of the camera detection method based on electromagnetic radiation signals according to the present invention.

[0031] Figure 2 This is a schematic diagram of the connections between the various devices in the signal receiving and processing apparatus of the present invention, along with corresponding physical images.

[0032] Figure 3 This is a spectrum diagram of the processed electromagnetic radiation signal from the camera.

[0033] Figure 4 A schematic diagram of peak points marked by the peak detection algorithm.

[0034] Figure 5 This is a schematic diagram of a set of peak points selected from the data.

[0035] Figure 6 The observed coupling phenomenon of the line synchronization signal components. Detailed Implementation

[0036] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely illustrative and not intended to limit the invention.

[0037] This application will use terminology commonly employed by those skilled in the art to describe various aspects of the illustrative embodiments in order to convey the essence of their work to others skilled in the art. However, it will be apparent to those skilled in the art that alternative embodiments can be practiced using portions of the described aspects. For purposes of explanation, specific figures, materials, and configurations are set forth to provide a thorough understanding of the illustrative embodiments. However, it will be apparent to those skilled in the art that alternative embodiments can be implemented without specific details. In other instances, some well-known features have been omitted or simplified in order not to obscure the illustrative embodiments.

[0038] This invention provides a camera detection method based on electromagnetic radiation signals, comprising steps such as raw radio frequency signal acquisition, signal processing algorithm, peak interval calculation, peak frequency matching, and detection of horizontal synchronization signal coupling. The detection logic is as follows: Figure 1 As shown. Specifically, it may include the following:

[0039] Step 1: Use an RF signal receiving device to collect RF signals from the environment to be tested. The operating frequency band of the device must meet the frequency range of the main harmonics of the electromagnetic signal radiated by the basic clock when the camera is working normally, which is usually 24–300 MHz.

[0040] Step 2: Analyze the acquired broadband radio frequency signal using signal processing software. First, perform a Fast Fourier Transform (FFT) to generate the original spectrum. Then, use a peak detection algorithm to select the peak points in the spectrum.

[0041] Step 3: Use the peak frequency grouping algorithm to group the peak frequencies marked in Step 2 and calculate the basic interval frequency for each group. If the calculated basic interval frequency is within the given clock frequency range (20 MHz to 24 MHz) or is a multiple of the clock frequency, then retain the peak frequency group that meets the above conditions. Discard or merge the peak frequency groups that meet the conditions. If no peak frequency group exists, it proves that no camera was detected; if it exists, continue to Step 4.

[0042] Step 4: Sequentially set the center frequency of the RF receiver to the peak points of each group obtained in Step 3, and select a bandwidth of 2 MHz. Observe whether the frequency f of the horizontal synchronization signal appears in the frequency domain. 行This is a coupling phenomenon of line synchronization signal components at interval frequencies (30 kHz to 100 kHz). If this phenomenon is observed, it proves that the camera has been detected.

[0043] The present invention will be described in detail below through specific examples:

[0044] In this embodiment, the signal receiving device consists of a receiving antenna, a low-noise signal amplifier, and software radio. The signal receiving device is configured according to... Figure 2 The connection shown will collect radio frequency signals from the environment and transmit them to a host computer running signal analysis software. The selected equipment must cover the frequency range of electromagnetic radiation signals generated during the camera's CSI transmission, typically 24-300 MHz. In this example, the near-field probe operates in the 20-512 MHz band, the low-noise amplifier (LNA) in the 0.2-3000 MHz band, and the software-defined radio (USRP N210) in the 10-6000 MHz band, all meeting the above requirements. The computer used in this example is a Lenovo laptop, and Python is used to process the signals. It should be noted that the above hardware, equipment, and software are only one feasible embodiment and can be replaced with any other model of equipment that meets the frequency requirements.

[0045] In Python, the signal file is first subjected to a Fast Fourier Transform to obtain the original electromagnetic signal spectrum in the environment. Then, after multiple denoising and smoothing processes, the result is as follows: Figure 3 The waveform shown is illustrated. The average noise intensity acquired in this example has been shifted to 0 dB. Non-equally spaced peaks can be observed in the waveform. The Fast Fourier Transform (FFT) can be implemented using the `fft()` function from the NumPy library.

[0046] Next, each peak in the spectrum is labeled using a peak detection algorithm, such as... Figure 4 As shown in the figure, the red markers represent each detected peak. This peak detection algorithm can be implemented using the find_peaks() function in Python.

[0047] Considering interference from other signals in the environment, the frequency peaks in the spectrum may exhibit non-uniform spacing, necessitating grouping of the peak frequencies. The algorithm for peak frequency grouping is as follows:

[0048] Assume there are n peak frequencies, namely f1, f2, f3…f n .

[0049] (1) Iterate through i from 1 to n and determine the frequency f. i ;j is iterated from i+1 to n to determine the frequency f. j Determine the fundamental interval frequency Δf ij=f j -f i If Δf ij If the following multiple relationship is satisfied, it indicates that the basic interval frequency is matched, where f c Given the camera clock frequency, ranging from 20 to 24 MHz. If there is no match, continue iterating; if there is a match, set the rate f. i and f j Divide into one group, this group is G = (f i ,f j ).

[0050] Δf ij =mf c m = 1, 2, 3…

[0051] (2) Traverse k from j+1 to n and calculate Δf ik =f k -f i If Δf ik With Δf ij If the following multiple relationship exists, then the frequency f k Add it to group G.

[0052] Δf ik =mΔf ij m = 1, 2, 3…

[0053] After traversal, multiple peak frequency groups will be obtained. If the number of peak frequencies in a group is less than 3, the group will be discarded. If the basic interval frequencies of group A and group B satisfy the following multiple relationship, or the number of common peak frequencies of the two groups exceeds 4, the two groups will be merged.

[0054] Δf A =mΔf B m = 1, 2, 3…

[0055] Figure 5 After the above operations are completed, a set of peak frequency signals is obtained, with a frequency interval of approximately 48 MHz. If such a set of peak frequencies does not exist, it indicates that no camera has been detected. It should be noted that due to factors such as measurement errors in the receiving device and design errors in the camera chip, there may be errors when comparing the multiples between frequencies; the allowable error is within ±5%.

[0056] Each peak frequency point within the group is sequentially used as the center frequency for detection, and the sampling bandwidth is set to 2 MHz. For example... Figure 6As shown, if there is intermodulation between a certain frequency and the center frequency, and the frequency interval of this signal is within the range of 30 kHz to 100 kHz (the frequency interval in the figure is approximately 67 kHz), then this frequency indicates that it is the camera's horizontal sync signal, and the intermodulation is caused by signal coupling from the CSI cable. If such horizontal sync signal coupling is observed, it indicates that the camera has been successfully detected; otherwise, it indicates that there is no camera in the surrounding environment.

Claims

1. A camera detection method based on electromagnetic radiation signals, characterized in that, Including the following: Acquire radio frequency signals in the environment: The radio frequency signal is preprocessed and its spectrum is analyzed to detect and mark the peak points in the spectrum. The marked peak frequencies are grouped and the basic interval frequency of each group is calculated. It is determined whether the basic interval frequency of each group matches the range of the camera clock frequency. If the match is successful, the corresponding peak frequency group is retained. After discarding or merging, it is further determined whether the horizontal synchronization signal component coupling phenomenon occurs in each peak frequency of the retained peak frequency group. If the phenomenon exists, the camera device is detected. Peak frequency grouping and matching judgment include the following: Assuming coexistence The peak frequencies are respectively ; (1) Traverse i from 1 to n and determine the frequency. ;j is iterated from i+1 to n to determine the frequency. Determine the fundamental interval frequency between the two. ,like If the following multiple relationship is satisfied, it indicates that the basic interval frequency matches the camera clock frequency, where... Given a camera clock frequency, ranging from 20 to 24 MHz, if there is no match, continue iterating; if there is a match, the frequency will be... and Divided into one group, this group is ; ； (2) Traverse k from j+1 to n and calculate ,like and If the following multiple relationship exists, then the frequency will be... Join this group middle: ； After traversal, multiple peak frequency groups will be obtained. If a group contains fewer than 3 peak frequencies, the group will be discarded. If the fundamental interval frequency between group A and group B is... If the following multiple relationship is met, or if the number of shared peak frequencies between the two groups exceeds four, then the two groups shall be merged: ； Each peak frequency point in the retained peak frequency group is used as the center frequency for detection in sequence, and the sampling bandwidth is set to 2 MHz. If there is an intermodulation phenomenon between a certain frequency and the center frequency, and the frequency interval of the signal is in the range of 30 kHz to 100 kHz, it means that the frequency is the horizontal synchronization signal of the camera. The appearance of horizontal synchronization signal component coupling means that the camera has been successfully detected; otherwise, it means that there is no camera in the surrounding environment.

2. The camera detection method based on electromagnetic radiation signals according to claim 1, characterized in that, Radio frequency signals in the environment to be tested are collected using a radio frequency signal receiving device, and the operating frequency band of the device should cover 24-300 MHz.

3. The camera detection method based on electromagnetic radiation signals according to claim 1, characterized in that, The acquired radio frequency signals are processed as follows: first, a Fast Fourier Transform (FFT) is performed to generate the original spectrum, then a denoised spectrum is generated after smoothing, and peak points in the spectrum are selected and marked using a peak detection algorithm.

4. The camera detection method based on electromagnetic radiation signals according to claim 3, characterized in that, The processing of the acquired radio frequency signals is implemented using Python.

5. The camera detection method based on electromagnetic radiation signals according to claim 1, characterized in that, There may be errors when comparing multiples between frequencies; the permissible error is within ±5%.

6. A camera detection system based on electromagnetic radiation signals, characterized in that, The system is used to implement the method as described in any one of claims 1-5, comprising: A signal receiving device used to collect radio frequency signals in the environment, with an operating frequency band covering 24-300 MHz; The signal analysis module is used to preprocess and perform spectrum analysis on the signals collected by the signal receiving device, detect and mark the peak points in the spectrum, group the marked peak frequencies and calculate the basic interval frequency of each group, determine whether the basic interval frequency of each group matches the camera clock frequency range, if the match is successful, retain the corresponding peak frequency group, discard or merge, and continue to determine whether there is a coupling phenomenon of the horizontal synchronization signal component in each peak frequency within the retained peak frequency group.

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