Remote audio monitoring method and system based on electromagnetic leakage

Abstract

The invention discloses a remote audio monitoring method and system based on electromagnetic leakage, and belongs to the technical field of electronic information engineering and safety. An electromagnetic leakage signal of the digital microphone is received through the radio frequency antenna; pre-amplifying the received signal, and performing targeted filtering by using a first band-pass filter which sets a passband according to the PDM clock frequency to extract a characteristic spectrum component; inputting the filtered signal into a low-noise amplifier for gain boosting; carrying out secondary noise suppression through a second band-pass filter; and then analog-to-digital conversion is carried out, and a special PDM demodulation algorithm is adopted to demodulate the digital signal so as to restore the audio. Therefore, the technical problems that in the prior art, the monitoring effect on electromagnetic leakage generated by pulse density modulation signals of a digital microphone is poor, the signal-to-noise ratio of reduced audio is low, and the effective action distance is short are solved, effective capture and clear reduction of weak digital modulation leakage signals are achieved, and the monitoring distance, the audio quality and the anti-interference capacity are improved.

Description

Technical Field

[0001] This invention relates to the fields of electronic information engineering and security technology, and in particular to a method and system for long-distance audio monitoring based on electromagnetic leakage. Background Technology

[0002] With the widespread adoption of smart devices, the core role of digital microphones in audio input is becoming increasingly prominent. Electromagnetic leakage in digital microphones not only affects sound quality but can also provide opportunities for eavesdropping. Electromagnetic leakage can transmit audio information through electromagnetic waves, posing a threat to information security, especially in modern network environments such as wireless communication and 5G. Therefore, detecting and preventing electromagnetic leakage has become crucial for ensuring device security and protecting user privacy. With the rapid development of my country's electronics industry and its increasing emphasis on information security, the electromagnetic compatibility of digital microphones not only affects product market competitiveness but also relates to technological capabilities and strategic position in the fields of information security and privacy protection.

[0003] With the widespread use of audio equipment, audio signal security has gradually become an important research area. In some special environments, electromagnetic leakage can carry the audio information of a microphone, and the original audio signal can be reconstructed by capturing electromagnetic waves. Analog microphones, due to the directness of their output signal, are more susceptible to electromagnetic interference, resulting in very low accuracy and reliability in audio information reconstruction. Even if the audio is reconstructed, the signal-to-noise ratio is poor, and the actual sound content cannot be clearly heard.

[0004] Electromagnetic leakage monitoring is mainly used in communication equipment, home appliances, industrial equipment, medical equipment, automotive electronics, and other fields. Its purpose is to ensure the electromagnetic compatibility of equipment, reduce electromagnetic interference, meet regulatory requirements, and improve equipment safety. Electromagnetic leakage is typically a near-field phenomenon; the field strength decreases rapidly with distance and is easily shielded by materials such as walls, metal casings, and concrete. Therefore, measurements taken at any partition or external location have significant uncertainties and cannot replace direct testing at close range or after unpacking the equipment. Summary of the Invention

[0005] To address the aforementioned problems, this invention provides a long-distance audio monitoring method and system based on electromagnetic leakage. The invention receives PDM electromagnetic leakage signals from a digital microphone via a radio frequency antenna. After pre-amplifying the received signal, a first bandpass filter with a passband set according to the PDM clock frequency or its harmonics / sidebands is used for targeted filtering to extract characteristic spectral components. The filtered signal is then input to a low-noise amplifier for gain enhancement, followed by secondary noise suppression via a second bandpass filter. Analog-to-digital conversion is then performed, and a dedicated PDM demodulation algorithm is used to demodulate the digital signal to reconstruct the audio. This invention, through targeted design and collaborative optimization of the signal processing chain, achieves effective capture and clear reconstruction of weak digital modulation leakage signals, improving monitoring distance, audio quality, and anti-interference capability. This solves the technical problems of poor electromagnetic leakage monitoring effect, low signal-to-noise ratio of reconstructed audio, and short effective range in existing technologies for digital microphone pulse density modulation signals.

[0006] To achieve the above objectives, the technical solution adopted by this invention is as follows: A long-distance audio monitoring method based on electromagnetic leakage, comprising the following steps: S1: Receiving an electromagnetic leakage signal from a digital microphone via a radio frequency antenna, wherein the electromagnetic leakage signal is generated by a pulse density modulation (PDM) signal from the digital microphone, and the electromagnetic leakage signal is: E ( t )=A×cos(2π f 0 t+Φ )+ N ( t ) in, A The signal amplitude; f 0 represents the carrier frequency of the electromagnetic signal; Φ For phase; N ( t ) is noise; S2: For the received electromagnetic leakage signal E ( t Pre-amplification is performed to enhance the signal strength, resulting in a pre-amplified signal. E amplified ( t The pre-amplified signal is then subjected to a first bandpass filter to remove high-frequency noise and low-frequency spurious signals, resulting in a signal after the first bandpass filter. E filtered ( t ); S3: The signal after the first bandpass filter E filtered ( t To avoid distortion, a low-noise amplification is performed to obtain the signal. E LNA( t ); S4: For the low-noise amplified signal E LNA ( t A second bandpass filter is performed to remove high-frequency noise introduced during amplification, resulting in a signal after the second bandpass filter. E high-filtered ( t ); S5: Filter the signal after the second bandpass filter. E high-filtered ( t Analog-to-digital conversion is performed to obtain discrete-time signals. E digital [ n ]: E digital [ n ]= E high-filtered ( n × T )= E high-filtered ( n ×1 / f s ) in, n This is the discrete-time index for the sampling; T For periodicity; f s The sampling frequency; S6: For discrete-time signals E digital [ n Digital signal processing is performed, including demodulating and decoding pulse density modulated signals to recover digitized audio signals. E audio-digital [ n ]; S7: digitizes audio signals E audio-digital [ n Converted into analog audio signals via codec E audio ( t ): in, t For continuous time; T s The sampling period.

[0007] Preferably, the first bandpass filter is a first bandpass filter, and the frequency range of the first bandpass filter is set according to the pulse density modulation clock frequency or its harmonic frequency of the digital microphone, so as to cover the characteristic leakage frequency band of the pulse density modulation signal.

[0008] Preferably, the second bandpass filter is a second bandpass filter, the frequency range of which is the same as or similar to that of the first bandpass filter. The two work together to achieve selective noise suppression of the same target frequency band twice before and after the signal amplification stage.

[0009] Preferably, the sampling frequency of the analog-to-digital converter f s At least the signal after the second bandpass filter E high-filtered ( t (Twice the highest frequency)

[0010] Preferably, the signal after the first bandpass filtering E filtered ( t )for: E filtered ( t )= H RF-FL ( f )× E amplified ( t ) in, H RF-FL ( f () is the frequency response function of the first bandpass filter; E amplified ( t ) represents the pre-amplified signal.

[0011] Preferably, the low-noise amplified signal E LNA ( t )for: E LNA ( t )= G LNA × E filtered ( t ) in, G LNA This is the gain of the low-noise amplifier; E filtered ( t ) represents the signal after the first bandpass filter.

[0012] Preferably, the signal after the second bandpass filtering E high-filtered ( t )for: E high-filtered ( t )= H RF-FL ( f )× E LNA ( t ) in, H RF-FL ( f () is the frequency response function of the first bandpass filter; E LNA ( t () is the signal after low-noise amplification.

[0013] Preferably, the low-noise amplifier is positioned after the first bandpass filter to perform high-fidelity gain enhancement on the signal that has undergone the first noise suppression and filtering.

[0014] A system employing the aforementioned long-distance audio monitoring method based on electromagnetic leakage includes: a radio frequency antenna for receiving electromagnetic leakage signals from a digital microphone; an amplification module connected to the radio frequency antenna for amplifying the received electromagnetic leakage signals; a first bandpass filter connected to the amplification module for filtering the amplified signal to remove high-frequency noise and low-frequency spurious signals; a low-noise amplifier connected to the first bandpass filter for amplifying the filtered signal; a second bandpass filter connected to the low-noise amplifier for filtering the amplified low-noise signal to remove high-frequency noise; an analog-to-digital conversion module connected to the second bandpass filter for converting the filtered analog signal into a digital signal; a digital signal processing module connected to the analog-to-digital conversion module for demodulating and decoding the digital signal to recover the digitized audio signal; and a codec connected to the digital signal processing module for converting the digitized audio signal into an analog audio signal.

[0015] Preferably, the digital signal processing module integrates a dedicated pulse density modulation and demodulation algorithm unit. This algorithm unit is used to perform inverse demodulation operations on the digital signal from the analog-to-digital conversion module, corresponding to the pulse density modulation technology, to restore the digitized audio signal.

[0016] By adopting the above technical solution, the present invention has the following beneficial effects.

[0017] (1) This invention achieves spectrum-targeted capture of the target signal by employing a first bandpass filter based on the digital microphone pulse density modulation clock frequency or its harmonics / sidebands to set the passband. This solves the technical problem that existing general broadband receiving methods cannot effectively separate specific frequency bands of digital PDM modulation leakage signals from complex electromagnetic background noise. Through collaboration with a preamplifier, while initially increasing the signal amplitude, all subsequent processing bandwidths are precisely constrained to the characteristic frequency band carrying audio information, thereby suppressing interference outside the frequency bandpass at the source and providing highly selective and effective input for the entire signal processing chain.

[0018] (2) This invention solves the technical problem of the contradiction between weak signal amplification and noise control in long-distance monitoring by placing the low-noise amplifier after the first bandpass filter and making it work in conjunction with the first bandpass filter. The first bandpass filter first filters out most of the ambient broadband noise, providing a relatively clean input environment for the low-noise amplifier, so that the low-noise figure performance of the low-noise amplifier can be fully utilized.

[0019] (3) This invention introduces a second bandpass filter with a frequency response similar to or similar to the first bandpass filter, and forms a collaborative processing unit of "filtering-amplification-re-filtering" with the low-noise amplifier. This combination solves the problem that a single filter cannot simultaneously suppress the combined noise of the pre-amplifier environment and the noise introduced by the subsequent amplifier. The first bandpass filter is responsible for the initial coarse filtering of out-of-band noise, the low-noise amplifier is responsible for high-quality amplification of the signal, and the second bandpass filter is specifically used to filter out in-band nonlinear distortion and noise generated during the amplification process.

[0020] (4) This invention solves the final technical bottleneck of restoring understandable audio information from modulated radio frequency signals by integrating a dedicated demodulation algorithm corresponding to pulse density modulation technology into a digital signal processor and deeply cooperating with the aforementioned hardware processing chain consisting of targeted filtering, low noise amplification and secondary filtering.

[0021] (5) Based on the PDM clock characteristics, the present invention uses targeted filtering, low noise amplification after targeted filtering, secondary noise suppression filtering of the same frequency parameters, and dedicated PDM digital demodulation to solve the technical problems of poor long-distance audio monitoring and restoration effect, low signal-to-noise ratio and severely limited operating distance caused by the inability to effectively capture and analyze digital modulation leakage signals. Thus, it achieves the technical effect of high-fidelity and understandable audio restoration of target digital audio equipment leakage in complex electromagnetic environment and non-line-of-sight conditions. Attached Figure Description

[0022] The following provides a detailed discussion of the manufacture and application of preferred embodiments of the present invention. However, it should be understood that the present invention provides many applicable inventive concepts that can be embodied in various specific environments. The specific embodiments discussed are merely illustrative of specific ways of manufacturing and using the present invention and do not limit the scope of the invention. For those skilled in the art, other drawings can be obtained from these drawings without any creative effort.

[0023] Figure 1 This is a schematic diagram of the structure of the present invention.

[0024] Figure 2 This is a diagram of the original acoustic linear frequency modulation signal of this invention.

[0025] Figure 3 This is a narrowband electromagnetic leakage spectrum diagram of the present invention.

[0026] Figure 4 This is a diagram of the analog audio signal after demodulation and conversion according to the present invention.

[0027] The following provides a detailed discussion of the manufacture and application of preferred embodiments of the present invention. However, it should be understood that the present invention provides many applicable inventive concepts that can be embodied in various specific environments. The specific embodiments discussed are merely illustrative of specific ways of manufacturing and using the invention and do not limit the scope of the invention.

[0028] In a specific embodiment of the present invention, addressing the technical problems of poor electromagnetic leakage monitoring effect, low signal-to-noise ratio of reconstructed audio, and short effective range of existing technologies, a specific and feasible implementation method is provided. The method steps of this embodiment are as follows: A long-distance audio monitoring method based on electromagnetic leakage includes the following steps: S1: Receiving an electromagnetic leakage signal from a digital microphone via a radio frequency antenna, wherein the electromagnetic leakage signal is generated by the pulse density modulation (PDM) signal of the digital microphone, and the electromagnetic leakage signal is: E ( t )=A×cos(2π f 0 t+Φ )+ N ( t ) in, A The signal amplitude; f 0 represents the carrier frequency of the electromagnetic signal; Φ For phase; N ( t The electromagnetic leakage signal contains audio frequency bands and high-frequency modulation components. The original acoustic linear frequency modulated signal of the electromagnetic leakage signal is as follows: Figure 2 As shown.

[0029] S2: For the received electromagnetic leakage signal E ( t Pre-amplification is performed to enhance the signal strength, resulting in a pre-amplified signal. E amplified ( t ): E amplified ( t )= G × E ( t ),in, G This is the gain of the preamplifier, and the signal after preamplification. E amplified ( t This includes both the received audio signal components and noise components. The amplifier gain can be adjusted. G This improves signal quality, but may also amplify noise. The pre-amplified signal is then further processed. E amplified ( t Perform a first bandpass filter to remove high-frequency noise (such as harmonics and sidebands) and low-frequency spurious signals using a bandpass filter. RF-FL Frequency selective filtering is performed to remove frequency components outside the audio frequency band (typically 20 Hz to 20 kHz), ultimately yielding the signal after the first bandpass filter. E filtered ( t ): E filtered ( t )= H RF-FL ( f )× E amplified ( t ) in, H RF-FL ( f () is the frequency response function of the first bandpass filter; E amplified ( t The signal is after pre-amplification. At this point, the audio signal has been effectively extracted, and other frequency components (such as high-frequency noise) have been suppressed.

[0030] S3: The signal after the first bandpass filter E filtered ( t To avoid distortion, a low-noise amplification is performed to obtain the signal. E LNA ( t ): E LNA ( t )= G LNA × E filtered ( t ) in, G LNA This is the gain of the low-noise amplifier; E filtered ( t The signal is the result of the first bandpass filter. This signal is then amplified by a low-noise amplifier (LNA). E filtered ( t This ensures the quality of the audio signal and avoids distortion due to a weak signal.

[0031] S4: Because new high-frequency noise may be introduced during amplification, the signal needs to be processed again through a bandpass filter. That is, the amplified signal needs to be processed to reduce noise. E LNA ( t A second bandpass filter is performed to remove high-frequency noise introduced during amplification, resulting in a signal after the second bandpass filter. E high-filtered ( t ): E high-filtered ( t )= H RF-FL ( f )× E LNA ( t ) in, H RF-FL ( f () is the frequency response function of the first bandpass filter; E LNA ( t () is the signal after low-noise amplification.

[0032] S5: During analog-to-digital conversion (ADC), the analog signal is converted according to the sampling frequency. f s Discretization is performed. This process converts a continuous-time signal into a discrete-time signal, satisfying the Nyquist sampling theorem: the sampling frequency... f s It must be at least the signal after the second bandpass filter. E high-filtered ( t The highest frequency is twice the highest frequency. Let the highest frequency of the signal be...f max To prevent aliasing, the sampling frequency needs to meet the following requirements. f s ≥2 f max After sampling by the ADC, the continuous analog signal E high-filtered ( t It is converted into a discrete-time signal. E digital [ n The signal after the second bandpass filter. E high-filtered ( t Analog-to-digital conversion is performed to obtain discrete-time signals. E digital [ n ]: E digital [ n ]= E high-filtered ( n × T )= E high-filtered ( n ×1 / f s ) in, n This is the discrete-time index for the sampling; T For periodicity; f s The sampling frequency is used. Ultimately, the signal will be transformed from a continuous-time analog signal into a discrete-time digital signal.

[0033] S6: The Digital Signal Processing (DSP) module demodulates and decodes the discretized digital signal to reconstruct the audio signal. High-frequency components in the pulse density modulation (PDM) are removed through signal demodulation to obtain a digital representation of the audio signal. That is, for discrete-time signals... E digital [ n Digital signal processing is performed, including demodulating and decoding pulse density modulated signals to recover digitized audio signals. E audio-digital [ n ]: E audio-digital [ n ]= DSP ( E digital [ n ]),in, E digital [n [ ] represents a discrete-time signal.

[0034] S7: The decoded digital audio signal needs to be converted into an analog signal by a codec for playback or further processing. Assume the codec output is an analog audio signal. E audio ( t ), then the digitized audio signal E audio-digital [ n Converted into analog audio signals via codec E audio ( t ):

[0035] in, t For continuous time; T s The sampling period is defined as follows. The first bandpass filter employs a first bandpass filter, the frequency range of which is set according to the pulse density modulation clock frequency or its harmonic frequencies of the digital microphone to cover the characteristic leakage frequency band of the pulse density modulation signal. The second bandpass filter employs a second bandpass filter, the frequency range of which is the same as or similar to that of the first bandpass filter; that is, the center frequency of the second bandpass filter deviates from the center frequency of the first bandpass filter by no more than ±5%. Together, they achieve selective noise suppression of the same target frequency band twice, before and after the signal amplification stage.

[0036] The following is in conjunction with the appendix Figure 1-4 To elaborate further. For example... Figure 1As shown, the monitoring system of the present invention includes a radio frequency antenna for receiving electromagnetic leakage signals from a digital microphone; an amplification module connected to the radio frequency antenna for amplifying the received electromagnetic leakage signals; a first bandpass filter connected to the amplification module for filtering the amplified signal to remove high-frequency noise and low-frequency spurious signals; a low-noise amplifier connected to the first bandpass filter for amplifying the filtered signal; a second bandpass filter connected to the low-noise amplifier for filtering the low-noise amplified signal to remove high-frequency noise; an analog-to-digital conversion module connected to the second bandpass filter for converting the filtered analog signal into a digital signal; a digital signal processing module connected to the analog-to-digital conversion module for demodulating and decoding the digital signal to restore the digitized audio signal. The digital signal processing module integrates a dedicated pulse density modulation demodulation algorithm unit, which performs inverse demodulation operations corresponding to the pulse density modulation technology on the digital signal from the analog-to-digital conversion module to restore the digitized audio signal; and a codec connected to the digital signal processing module for converting the digitized audio signal into an analog audio signal.

[0037] The radio frequency antenna is used to receive electromagnetic leakage signals generated by the digital microphone. E ( t )=A×cos(2π f 0 t+Φ )+ N ( t ),in, A The signal amplitude; f 0 represents the carrier frequency of the electromagnetic signal; Φ For phase; N ( t () is noise, and the waveform of the electromagnetic leakage signal is as follows: Figure 2 As shown, the amplification module acts as a preamplifier, initially amplifying the received weak signal, with a gain of... G It can be set to 30dB to obtain the pre-amplified signal. E amplified ( t )= G × E ( t ),in, G This is the gain of the preamplifier. The amplified signal... E amplified ( t Spectral characteristics such as Figure 3 As shown. Figure 3 The diagram shows a narrowband electromagnetic leakage spectrum, where a narrowband spectral line with concentrated energy can be observed in a specific high-frequency band, and the peak frequency trajectory of this spectral line is similar to that of the original acoustic signal. Figure 2The frequency variations of the signals exhibit a strong correlation. This figure visually confirms that the PDM modulation information of a digital microphone leaks out in the form of electromagnetic radiation in a specific frequency band, and that the leaked spectrum carries the frequency characteristics of the original audio. This provides a direct physical basis for subsequent targeted filtering.

[0038] The passband range of the first bandpass filter is set according to the pulse density modulation clock frequency of the digital microphone. In this embodiment, for a microphone with a clock frequency of 3.072MHz, the center frequency of the filter is set to its second harmonic, 6.144MHz, with a bandwidth of ±25kHz. This filter works in conjunction with a preamplifier. The preamplifier provides sufficient signal amplitude to overcome the filter's insertion loss, while the first bandpass filter accurately extracts the characteristic leakage frequency band carrying audio information near 6.144MHz from the wide-spectrum noise, outputting the signal after the first bandpass filter. E filtered ( t ): E filtered ( t )= H RF-FL ( f )× E amplified ( t ),in, H RF-FL ( f () is the frequency response function of the first bandpass filter; E amplified ( t The signal is amplified before being pre-amplified. This "targeted capture" design solves the fundamental problem that existing technologies using fixed audio baseband filters cannot effectively capture digital modulation leakage signals.

[0039] The low-noise amplifier is specifically positioned after the first bandpass filter to receive the signal that has already undergone preliminary purification after the first bandpass filter. E filtered ( t Its gain G LNA The setting is 20dB. Since the first bandpass filter has filtered out most of the strong out-of-band interference, it creates low-noise input conditions for the low-noise amplifier, allowing its low noise figure advantage to be fully utilized and effectively avoiding over-amplification of ambient noise while amplifying the signal. The low-noise amplifier outputs a low-noise amplified signal. E LNA ( t ): E LNA ( t )= G LNA ×E filtered ( t ),in, G LNA This is the gain of the low-noise amplifier; E filtered ( t The signal is the result of the first bandpass filter. The second bandpass filter is connected after the low-noise amplifier. Its frequency response is the same as the first bandpass filter, with a center frequency of 6.144MHz and a bandwidth of ±25kHz. This second bandpass filter and the low-noise amplifier work together to form a closed-loop processing unit: the low-noise amplifier boosts the signal power, while the second bandpass filter specifically filters out in-band nonlinear distortion and noise introduced during amplification, achieving secondary purification of the same target frequency band and outputting a high-quality signal after the second bandpass filter. E high-filtered ( t This sequential collaborative design of "filtering-amplification-re-filtering" systematically solves the technical problem of the contradiction between "increasing gain" and "suppressing noise" in traditional monitoring links.

[0040] The signal after the second bandpass filter E high-filtered ( t After the analog link processing described above, the data enters the digital processing stage. The sampling frequency of the analog-to-digital converter module... f s According to the Nyquist sampling theorem, the frequency should be no less than twice the highest frequency of the signal. In this embodiment, f s Set to 15MHz for distortion-free operation of frequencies up to approximately 7MHz. E high-filtered ( t Sampling is performed to obtain discrete-time signals. E digital [ n The digital signal processing module integrates a dedicated pulse density modulation and demodulation algorithm unit, which performs pulse density modulation and demodulation on... E digital [ n Perform reverse PDM demodulation to restore the digitized audio signal. E audio-digital [ n Finally, the codec will... E audio-digital [ n Converted to analog audio signal E audio ( t And output the analog audio signal. E audio (t Waveform as Figure 4 As shown, the demodulated acoustic signal is achieved by applying techniques such as frequency modulation and demodulation. Figure 3 The narrowband electromagnetic leakage spectrum shown was obtained after [the experiment]. From [the following]... Figure 4 It can be seen that the recovered signal waveform is similar to the original linear frequency modulated signal in the time domain. Figure 2 The high similarity directly verifies the feasibility of effectively extracting and restoring the original audio information from the electromagnetic leakage signal, and strongly demonstrates the overall effectiveness of the technical solution of this invention.

[0041] To verify the unexpected effects of the synergistic effects of the technical features of this invention, a comparative experiment was designed. The target device was a smartphone (PDM clock frequency 3.072MHz) playing a standard female voice test sentence. The monitoring point was located 10 meters away from the target in a straight line, with a concrete wall in between. The experimental group used the system described above in this invention. The control group used a general electromagnetic leakage detector, which only included a broadband amplifier and a low-pass filter with a cutoff frequency of 20kHz. Measured data showed that, at the same receiving position, the experimental group system could stably lock onto a narrowband leakage spectral line (center frequency 6.144MHz) with a signal-to-noise ratio better than 10dB, and its spectral characteristics are as follows: Figure 2 Similar to the results shown; however, no significant spectral peaks related to the target signal were observed in the spectrum received by the control group. After processing the complete signal chain, the experimental group achieved an average signal-to-noise ratio (SNR) of 25.5 dB for the restored speech, with an average third-party blind listening intelligibility score of 4.2 (5-minute test duration). The control group achieved an audio SNR of only 7.8 dB, with the speech completely submerged by background noise, and an average intelligibility score of 1.1. The present invention improves the SNR by more than 17 dB and the intelligibility score by approximately 280%. Through the deep coupling of technical features such as "targeted filtering based on PDM clock," "deployment of low-noise amplifiers at specific locations," and "coordinated dual-stage co-frequency filtering," the present invention constructs a dedicated optimized processing chain for digital PDM leakage signals, jointly solving the problem of restoring digitally modulated audio in environments with strong attenuation and high noise, which cannot be overcome by single features or conventional combinations.

[0042] Although the specification has provided a detailed description, it should be understood that various changes, substitutions, and modifications can be made without departing from the spirit and scope of the invention as defined by the appended claims. Furthermore, the specific embodiments described are not intended to limit the scope of the invention, and those skilled in the art will readily understand based on this invention that existing or future-developed processes, machines, manufactures, compositions of matter, means, methods, or steps can perform substantially the same functions or achieve substantially the same results as the embodiments of the invention. Therefore, the appended claims are intended to include such processes, machines, manufactures, compositions of matter, means, methods, or steps within their scope.

Claims

1. A long-distance audio monitoring method based on electromagnetic leakage, characterized in that: Includes the following steps: S1: Receive an electromagnetic leakage signal from a digital microphone via a radio frequency antenna. The electromagnetic leakage signal is generated by a pulse density modulation (PDM) signal from the digital microphone. The electromagnetic leakage signal is: E ( t )=A×cos(2π f 0 t+Φ )+ N ( t ) in, A The signal amplitude; f 0 represents the carrier frequency of the electromagnetic signal; Φ For phase; N ( t ) is noise; S2: For the received electromagnetic leakage signal E ( t Pre-amplification is performed to enhance the signal strength, resulting in a pre-amplified signal. E amplified ( t The pre-amplified signal is then subjected to a first bandpass filter to remove high-frequency noise and low-frequency spurious signals, resulting in a signal after the first bandpass filter. E filtered ( t ); S3: The signal after the first bandpass filter E filtered ( t To avoid distortion, a low-noise amplification is performed to obtain the signal. E LNA ( t ); S4: For the low-noise amplified signal E LNA ( t A second bandpass filter is performed to remove high-frequency noise introduced during amplification, resulting in a signal after the second bandpass filter. E high-filtered ( t ); S5: Filter the signal after the second bandpass filter. E high-filtered ( t Analog-to-digital conversion is performed to obtain discrete-time signals. E digital [ n ]: E digital [ n ]= E high-filtered ( n × T )= E high-filtered ( n ×1 / f s ) in, n This is the discrete-time index for the sampling; T For periodicity; f s The sampling frequency; S6: For discrete-time signals E digital [ n Digital signal processing is performed, including demodulating and decoding pulse density modulated signals to recover digitized audio signals. E audio-digital [ n ]; S7: digitizes audio signals E audio-digital [ n Converted into analog audio signals via codec E audio ( t ): in, t For continuous time; T s The sampling period.

2. The method as described in claim 1, characterized in that: The first bandpass filter employs a first bandpass filter, the frequency range of which is set according to the pulse density modulation clock frequency or its harmonic frequency of the digital microphone, in order to cover the characteristic leakage frequency band of the pulse density modulation signal.

3. The method as described in claim 1, characterized in that: The second bandpass filter uses a second bandpass filter whose frequency range is the same as or similar to that of the first bandpass filter. The two work together to achieve selective noise suppression of the same target frequency band twice, before and after the signal amplification stage.

4. The method as described in claim 1, characterized in that: The sampling frequency of the analog-to-digital converter f s At least the signal after the second bandpass filter E high-filtered ( t (Twice the highest frequency) 5. The method as described in claim 1, characterized in that: The first bandpass filtered signal E filtered ( t )for: E filtered ( t )= H RF-FL （ f ）× E amplified ( t ) in, H RF-FL ( f () is the frequency response function of the first bandpass filter; E amplified ( t ) represents the pre-amplified signal.

6. The method as described in claim 1, characterized in that: The low-noise amplified signal E LNA ( t )for: E LNA ( t )= G LNA × E filtered ( t ) in, G LNA This is the gain of the low-noise amplifier; E filtered ( t () represents the signal after the first bandpass filter.

7. The method as described in claim 4, characterized in that: The second bandpass filtered signal E high-filtered ( t )for: E high-filtered ( t )= H RF-FL （ f ）× E LNA ( t ) in, H RF-FL ( f () is the frequency response function of the first bandpass filter; E LNA ( t () is the signal after low-noise amplification.

8. The method as described in claim 6, characterized in that, The low-noise amplifier is positioned after the first bandpass filter and is used to perform high-fidelity gain enhancement on the signal that has undergone the first noise suppression and filtering.

9. A system employing the long-distance audio monitoring method based on electromagnetic leakage as described in any one of claims 1-8, characterized in that, include: Radio frequency antenna, used to receive electromagnetic leakage signals from digital microphone; An amplification module, connected to the radio frequency antenna, is used to amplify the received electromagnetic leakage signal; A first bandpass filter is connected to the amplification module and is used to filter the amplified signal to remove high-frequency noise and low-frequency spurious signals. A low-noise amplifier, connected to the first bandpass filter, is used to amplify the filtered signal; The second bandpass filter is connected to the low-noise amplifier and is used to filter the low-noise amplified signal to remove high-frequency noise. An analog-to-digital converter module, connected to the second bandpass filter, is used to convert the filtered analog signal into a digital signal; a digital signal processing module, connected to the analog-to-digital converter module, is used to demodulate and decode the digital signal to restore the digitized audio signal; and a codec, connected to the digital signal processing module, is used to convert the digitized audio signal into an analog audio signal.

10. The system as described in claim 9, characterized in that, The digital signal processing module integrates a dedicated pulse density modulation and demodulation algorithm unit. This algorithm unit is used to perform inverse demodulation operations on the digital signal from the analog-to-digital conversion module, corresponding to the pulse density modulation technology, in order to restore the digitized audio signal.

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