A search and rescue positioning system and method based on near-field electromagnetic detection

Abstract

This invention discloses a search and rescue positioning system and method based on near-field electromagnetic detection, belonging to the field of search and rescue positioning. The system includes: receiving low-frequency magnetic induction signals emitted by a distress beacon worn by a trapped person, and obtaining a three-axis induced voltage signal; extracting the effective amplitude of the three axes based on the three-axis induced voltage signal, and obtaining the magnetic field amplitude and direction based on the effective amplitude; predicting the distance between the distress beacon and the receiver based on the magnetic field amplitude and a near-field magnetic field attenuation model; and determining the position coordinates of the distress beacon relative to the receiver based on the magnetic field direction and distance. This invention can solve the problems of weak penetration and low positioning accuracy of existing technologies in complex rubble environments, achieving rapid and accurate positioning of trapped persons.

Description

Technical Field

[0001] This invention belongs to the field of search and rescue positioning, and particularly relates to a search and rescue positioning system and method based on near-field electromagnetic detection. Background Technology

[0002] Currently, in disaster relief efforts such as earthquakes and mine accidents, the rapid location of trapped personnel is crucial to survival rates. Existing life detection technologies are mainly divided into two categories: passive and active. Passive technologies include video endoscopes, audio arrays, microwave radar, and infrared thermal imaging, which locate trapped individuals by capturing images, sounds, breathing, heartbeats, or body temperature—signs of life. These technologies are effective in open rubble or environments with thin barriers, but they generally suffer from limited penetration depth, susceptibility to environmental noise interference, bulky equipment, and complex operation. Active radio emergency distress devices, such as VHF radios or satellite locators, can achieve long-distance signal transmission in open areas. However, in enclosed spaces such as rubble and mines, high-frequency electromagnetic waves attenuate rapidly when encountering media such as concrete and rock, making it difficult to penetrate barriers several meters thick, thus hindering their effective application in actual rescue operations.

[0003] In summary, existing search and rescue positioning technologies suffer from the following main drawbacks: First, insufficient penetration capability; microwave and infrared signals attenuate drastically in reinforced concrete or metal environments, failing to cover thick obstacle scenarios. Second, poor environmental adaptability; background noise, multipath effects, and electromagnetic interference in rubble easily lead to missed or false alarms. Third, passive detection relies on signs of life in trapped individuals; if the trapped individual is unconscious or deeply buried, the success rate drops significantly. Fourth, equipment deployment is complex and inefficient, making it difficult to achieve large-scale rapid searches within the critical rescue time. Therefore, there is an urgent need for a search and rescue positioning solution that can actively penetrate obstacles, has strong anti-interference capabilities, and is easy to deploy. Summary of the Invention

[0004] To address the aforementioned technical problems, this invention provides a search and rescue positioning system and method based on near-field electromagnetic detection. Specifically, a search and rescue positioning system based on near-field electromagnetic detection includes: A distress beacon, placed at the end of the trapped person's device, is used to transmit low-frequency magnetic induction signals; The receiving and positioning device, installed at the rescue personnel's end, includes a signal receiving unit, a signal processing unit, and a positioning calculation unit; The signal receiving unit is used to receive the low-frequency magnetic induction signal and convert the low-frequency magnetic induction signal into an electrical signal; The signal processing unit is connected to the signal receiving unit and is used to extract magnetic field amplitude information and magnetic field direction information based on the electrical signal. The positioning calculation unit is connected to the signal processing unit and is used to obtain the position coordinates of the distress beacon based on the magnetic field amplitude information and magnetic field direction information.

[0005] Preferably, the distress beacon includes: A transmitting coil is used to generate the low-frequency magnetic induction signal; The control module, connected to the transmitting coil, is used to control the transmitting coil to periodically transmit a standardized distress signal sequence according to a preset format. A power module, connected to the control module and the transmitting coil, is used to provide electrical energy; The triggering module, connected to the control module, is used to generate an activation signal and send it to the control module when a preset triggering condition is detected, so that the distress beacon enters distress mode.

[0006] Preferably, the signal receiving unit includes a triaxial orthogonal coil array, which includes three mutually orthogonal coils for sensing magnetic field components in space and outputting triaxial induced voltage signals respectively.

[0007] Preferably, the signal processing unit includes: An amplitude extraction subunit, connected to the signal receiving unit, is used to filter and demodulate the triaxial induced voltage signal and extract the effective amplitude of the triaxial signal. The direction analysis subunit, connected to the amplitude extraction subunit, is used to normalize the effective amplitude of the three axes to obtain the direction cosine components of the magnetic field direction on each coordinate axis, and to analyze the azimuth and pitch angles of the magnetic field based on the direction cosine components. An amplitude synthesis subunit, connected to the amplitude extraction subunit, is used to calculate the synthesized magnetic field amplitude based on the triaxial effective amplitude using the Euclidean norm. The signal enhancement subunit, connected to the signal receiving unit, is used to perform coherent demodulation and coherent accumulation processing on the electrical signal.

[0008] Preferably, the positioning calculation unit includes: The distance estimation subunit, connected to the signal processing unit, is used to predict the distance between the distress beacon and the receiving and positioning device based on the synthetic magnetic field amplitude and a preset near-field magnetic field attenuation model. The coordinate calculation subunit, connected to the distance estimation subunit and the direction analysis subunit, is used to calculate the position coordinates of the distress beacon based on the distance, the direction cosine component, and the known position coordinates of the receiving and positioning device. The multi-point fusion subunit, connected to the coordinate calculation subunit, is used to obtain the preliminary position coordinates of the distress beacon calculated at multiple different measurement locations, and to perform fusion calculation on the preliminary position coordinates to output the optimized final position coordinates.

[0009] This invention also provides a search and rescue positioning method based on near-field electromagnetic detection, comprising: It receives low-frequency magnetic induction signals emitted by distress beacons worn by trapped personnel and obtains triaxial induced voltage signals; Based on the triaxial induced voltage signal, the effective amplitude of the three axes is extracted, and the magnetic field amplitude and magnetic field direction are obtained based on the effective amplitude of the three axes. Based on the magnetic field amplitude and the near-field magnetic field attenuation model, the distance between the distress beacon and the receiver is predicted. The position coordinates of the distress beacon relative to the receiving end are determined based on the direction of the magnetic field and the distance.

[0010] Preferably, the process of extracting the effective amplitude of the three axes includes: The triaxial induced voltage signal is pre-amplified and band-pass filtered to obtain the signal within the operating frequency band; The filtered signal is demodulated and its amplitude is extracted to obtain the effective amplitude of each axis.

[0011] Preferably, the process of obtaining the direction of the magnetic field includes: The effective amplitude of the three axes is normalized to obtain the direction cosine components of the magnetic field direction on each coordinate axis; The azimuth and elevation angles of the magnetic field are calculated based on the direction cosine components.

[0012] Preferably, the process of predicting the distance between the distress beacon and the receiver includes: The distance is calculated based on the inverse cubic relationship between the magnetic field amplitude and the distance, combined with the calibration coefficients obtained through calibration experiments.

[0013] Preferably, the process of determining the position coordinates of the distress beacon relative to the receiving end includes: The location coordinates of the distress beacon are calculated based on the known location coordinates of the receiver, the distance, and the direction cosine component of the magnetic field direction.

[0014] Compared with the prior art, the present invention has the following advantages and technical effects: This invention is based on near-field electromagnetic detection technology. By having the trapped person actively emit low-frequency magnetic induction signals, the penetration depth of the signal in complex media such as rock, soil, and concrete is significantly improved, enabling stable transmission even in environments with obstacles tens of meters thick. Simultaneously, the low-frequency magnetic field is less affected by environmental noise and multipath effects, exhibiting strong anti-interference capabilities and ensuring reliable positioning. Furthermore, the system employs an active beacon, allowing continuous distress signals even when the trapped person is unconscious, overcoming the limitations of passive detection. The receiving end uses a triaxial orthogonal coil and a multi-point fusion algorithm to quickly calculate the precise location. The device is lightweight and has low power consumption, making it easy for rescuers to carry and operate, thus effectively extending the golden rescue time and significantly improving search and rescue efficiency and success rate. Attached Figure Description

[0015] The accompanying drawings, which form part of this application, are used to provide a further understanding of this application. The illustrative embodiments and descriptions of this application are used to explain this application and do not constitute an undue limitation of this application. In the drawings: Figure 1 This is a schematic diagram of the system structure according to an embodiment of the present invention; Figure 2 This is a schematic diagram of the method flow according to an embodiment of the present invention; Figure 3 This is a schematic diagram of the structure of the low-power signal transmitter transmitting a low-frequency magnetic induction signal according to an embodiment of the present invention; Figure 4 This is a schematic diagram of a distance estimation subunit performing high-precision spatial positioning in a complex environment, according to an embodiment of the present invention. Figure 5 This is a schematic diagram illustrating the signal processing and positioning fusion process performed by the multi-point fusion subunit in an embodiment of the present invention. Figure 6 This is a comparison diagram of signal and noise in an embodiment of the present invention. Detailed Implementation

[0016] It should be noted that, unless otherwise specified, the embodiments and features described in this application can be combined with each other. This application will now be described in detail with reference to the accompanying drawings and embodiments.

[0017] It should be noted that the steps shown in the flowchart in the accompanying drawings can be executed in a computer system such as a set of computer-executable instructions, and although a logical order is shown in the flowchart, in some cases the steps shown or described may be executed in a different order than that shown here.

[0018] Example 1 like Figure 1 As shown, this embodiment provides a search and rescue positioning system based on near-field electromagnetic detection, including: A distress beacon, placed at the end of the trapped person's device, is used to transmit low-frequency magnetic induction signals; The receiving and positioning device, installed at the rescue personnel's end, includes a signal receiving unit, a signal processing unit, and a positioning calculation unit; The signal receiving unit is used to receive low-frequency magnetic induction signals and convert them into electrical signals. The signal processing unit, connected to the signal receiving unit, is used to extract magnetic field amplitude and magnetic field direction information based on the electrical signal. The positioning calculation unit, connected to the signal processing unit, is used to obtain the location coordinates of the distress beacon based on the magnetic field amplitude and direction information.

[0019] Furthermore, this embodiment, by setting up distress beacons and receiving and locating devices, and utilizing the cooperation of a signal receiving unit, a signal processing unit, and a positioning calculation unit, achieves the reception, processing, and positioning calculation of low-frequency magnetic induction signals emitted by trapped personnel. Its technical advantage lies in constructing a complete active search and rescue positioning system that overcomes the limitations of traditional passive detection methods in complex environments, enabling rapid discovery and location of trapped personnel and significantly improving rescue efficiency.

[0020] Furthermore, distress beacons include: The transmitting coil is used to generate low-frequency magnetic induction signals; The control module, connected to the transmitting coil, is used to control the transmitting coil to periodically transmit a standardized distress signal sequence according to a preset format. The power module, connected to the control module and the transmitting coil, is used to provide electrical energy; The trigger module, connected to the control module, is used to generate an activation signal and send it to the control module when a preset trigger condition is detected, so that the distress beacon enters distress mode.

[0021] Furthermore, this embodiment employs low-frequency magnetic induction, theoretically achieving a skin depth of 50–150m for media such as wet soil, concrete, and gravel at 3kHz, fully covering the 30m transmission requirement. By selecting a transmitting coil with a radius of 10–15cm and hundreds of turns, and matching it with a low-power drive circuit, 30m signal transmission can be achieved at milliwatt to watt-level power. On the other hand, the receiving end uses a triaxial orthogonal coil and a high-Q LC resonance, combined with coherent integration processing, which can effectively detect even microvolt-level input signals. The signal-to-noise comparison diagram is shown below. Figure 6 As shown.

[0022] Meanwhile, in complex disaster scenarios, multiple trapped individuals often transmit signals simultaneously, necessitating the receiver's ability to separate and precisely locate multiple targets. This embodiment employs a signal design combining frequency offset differentiation and timing coding, giving each beacon independent identification characteristics. At the receiver, a three-axis coil array, combined with narrowband filtering, can simultaneously extract at least three valid signals. Single-point ranging is susceptible to noise and attitude interference, but by deploying multiple receivers or performing mobile measurements at a single station, and utilizing methods such as weighted least squares, extended Kalman filtering, or particle filtering for data fusion, errors can be significantly reduced. Through meticulous design, it can simultaneously receive more than three rescue signals and achieve meter-level positioning.

[0023] The rescue window is typically defined as the "golden 72 hours" after a disaster, therefore the endurance of distress beacons is crucial. For example... Figure 3 As shown, this embodiment employs a low-power + intermittent transmission strategy: the beacon operates in a low duty cycle mode, significantly reducing average power consumption while ensuring signal periodicity and identifiability. For example, using a 3kHz carrier wave and transmitting a 100ms pulse within 1 second, the average power consumption can be reduced to less than 10% of the peak power consumption. In terms of power supply design, a high-energy-density lithium battery (e.g., 2000–5000mAh) is selected, coupled with power optimization circuitry, enabling continuous operation for over 72 hours. In low-temperature, humid, or shock environments, reliability can be further improved through dual-battery redundancy or energy harvesting auxiliary modules. Comprehensive analysis shows that ensuring continuous beacon transmission for over 72 hours is entirely feasible under existing power supply and low-power design capabilities.

[0024] This embodiment achieves low-power, long-endurance operation of the beacon by setting a transmitting coil, control module, and power module in the distress beacon and periodically transmitting a standardized distress sequence in a preset format, ensuring continuous transmission of identifiable signals within the critical 72-hour rescue period. At the same time, the standardized signal format facilitates the receiver's identification and differentiation of multiple targets, improving the system's practicality and reliability.

[0025] Furthermore, the signal receiving unit includes a triaxial orthogonal coil array, which comprises three mutually orthogonal coils used to sense magnetic field components in space and output triaxial induced voltage signals respectively. This embodiment, by employing a triaxial orthogonal coil array as the signal receiving unit, can sense magnetic field components in any direction in space, avoiding the signal blind zone problem caused by attitude changes in single-axis coils. This ensures reliable signal reception under any beacon attitude, providing a fundamental guarantee for subsequent direction calculation and positioning.

[0026] Furthermore, this embodiment establishes a right-handed coordinate system. - - The normals of the three-axis orthogonal coils coincide with the three axes respectively. The target signal operates in the low-frequency near field (e.g., 1–10kHz), satisfying the quasi-static approximation. After detecting abnormal triggering conditions (severe vibration, sudden pressure change, water ingress, etc.), the beacon automatically enters distress mode and periodically transmits "beacon heartbeat + SOS sequence + short device ID" in a uniform format. The operating frequency band is preferentially selected as 1–10kHz (which can be reduced to several hundred Hz for emergency mode if necessary). The transmitting coil is used in conjunction with LC resonance to enhance the magnetic field strength. A simple system of on-off keying (OOK) or narrowband BFSK is adopted to facilitate coherent accumulation detection under low signal-to-noise ratio conditions. The terminal uses an ultra-low power consumption design and a low duty cycle strategy to ensure continuous operation for ≥72 hours; the shell meets the requirements for shock resistance, waterproofing, dustproofing, and necessary explosion protection. The form can be customized according to the user as a hat brim / badge / wristband, etc., taking into account wearing comfort and coil size requirements. The transmitting coil can be modeled as a current loop, and the generated magnetic field strength approximately satisfies the Biot-Savart law: ; in, This represents the magnetic field at spatial location r. Represents the permeability of free space. Indicates the coil current. This represents the unit vector pointing from the current element to the field point. This indicates the distance from the receiving point to the center of the transmitting coil.

[0027] In the near-field region, which is much smaller than the wavelength, the magnetic field mainly exhibits a quasi-static field, and its amplitude decreases approximately inversely cubically with distance: ; in, This represents the magnetic field at spatial location r. The value represents the permeability of free space, and N represents the number of turns in the coil. Indicates the coil current. Indicates the coil radius. This indicates the distance from the receiving point to the center of the transmitting coil.

[0028] To enhance the emission magnetic moment, resonant excitation is employed: ; in, Indicates the transmission frequency. Indicates inductance. Indicates capacitance.

[0029] By selecting the right inductor With capacitor Make the transmission frequency It falls within the 1–10kHz range, achieving power concentration and efficiency improvement.

[0030] Furthermore, to facilitate weak signal detection, the transmitter in this embodiment employs a simple and robust modulation method, such as On-Off Keying (OOK) or Binary Frequency Shift Keying (BFSK). For example, in OOK mode, the transmitted signal is represented as: ; in, Indicates the combined amplitude of the three axes. Represents the permeability of free space. Represents a time variable. The baseband sequence consists of 0s and 1s and contains the SOS mode code.

[0031] Furthermore, the receiver incorporates a built-in triaxial orthogonal coil and a low-noise front-end, narrowband tuning to the operating frequency while suppressing power frequency and harmonic interference. The digital processing unit performs coherent demodulation and sliding correlation, matching with a preset SOS mode to achieve reliable detection of weak signals. After detection, the positioning process begins: the magnetic field direction (AoA) is calculated from the triaxial signal to obtain the azimuth indication; the distance level is given by combining the field strength-distance calibration relationship (near-field approximation |B|∝1 / r³). Multi-point observation (single-person movement or multiple people simultaneously direction finding) gradually converges to a 2-3m search circle through weighted least squares / extended Kalman / particle filter fusion. At close range, it can be linked with UWB, infrared, or microwave radar for sub-meter level precise positioning. In multi-target scenarios, the receiver separates multiple signal sources according to frequency offset and timing differences, and provides target marking and priority management.

[0032] The induced voltage measured by the triaxial orthogonal coil array at the receiving end is given by Faraday's law of electromagnetic induction: ; in, Indicates the induced voltage. Indicates the number of coil turns. This represents the magnetic flux passing through a single-turn coil. Represents a time variable. Indicates magnetic flux density. This indicates the area of ​​the receiving coil.

[0033] The output voltage is at its maximum when the receiver is aligned with the magnetic field direction. The triaxial structure ensures component output in any orientation.

[0034] By employing coherent demodulation and sliding correlation, the receiver can still detect known SOS mode sequences even in a strong noise background. Let the received signal be... , and template The relevant output is: ; when When aligning, Peaks are formed in the noise to confirm the existence of the signal.

[0035] in, R(τ) Represents the cross-correlation function value. r(t) This represents the actual measured signal at the receiving end. p Indicates the coordinates of the target beacon's location. Represents a time variable. Indicates the amount of time delay.

[0036] It is the induced voltage of a triaxial orthogonal coil. This is the effective amplitude across three axes, i.e., the amplitude after filtering / demodulation. The receiver is equipped with three sets of orthogonal coils, each operating along... , , Orientation arrangement. When the spatial magnetic field changes with time, the change in magnetic flux within the coil induces a voltage. The formula for the induced voltage of a triaxial coil is: ; ; ; in, This represents the induced voltage generated by the X-axis coil. This represents the induced voltage generated by the Y-axis coil. This represents the induced voltage generated by the Z-axis coil. Indicates the number of turns of the X-axis coil. Indicates the number of turns of the Y-axis coil. Indicates the number of turns of the Z-axis coil. These are the projections of the magnetic flux onto the effective area of ​​the triaxial coil.

[0037] The significance of the three-axis structure is that, regardless of how the beacon's attitude changes relative to the receiver, there is always at least one axis with a strong projection, and the combination of the three axes can recover spatial orientation information.

[0038] Furthermore, the signal processing unit includes: The amplitude extraction subunit is connected to the signal receiving unit and is used to filter and demodulate the triaxial induced voltage signal to extract the effective amplitude of the triaxial signal. The direction analysis subunit, connected to the amplitude extraction subunit, is used to normalize the effective amplitude of the three axes to obtain the direction cosine components of the magnetic field direction on each coordinate axis, and to analyze the azimuth and pitch angles of the magnetic field based on the direction cosine components. The amplitude synthesis subunit, connected to the amplitude extraction subunit, is used to calculate the synthesized magnetic field amplitude based on the triaxial effective amplitude using the Euclidean norm. The signal enhancement subunit, connected to the signal receiving unit, is used to perform coherent demodulation and coherent accumulation processing on the electrical signal.

[0039] Furthermore, this embodiment establishes an amplitude extraction subunit, a direction analysis subunit, a distance estimation subunit, and a coordinate calculation subunit, and establishes the connection relationships and data transmission paths between them. This realizes a complete signal processing chain from the original induced voltage to the final position coordinates. Through the step-by-step processing of amplitude extraction, direction analysis, distance estimation, and coordinate calculation, the three-dimensional spatial position of the distress beacon can be accurately calculated, providing accurate directional guidance for rescue personnel.

[0040] Furthermore, since the original triaxial voltages typically have small amplitudes and complex noise, they need to be converted into "comparable and fusionable" amplitude values, specifically including the following operations: Pre-amplifier low-noise amplifier: boosts weak induced voltage to the effective range of the ADC; Bandpass filtering: retains only the operating frequency band, suppressing power frequency and broadband noise; Synchronous sampling: Simultaneous sampling of all three axes avoids directional errors caused by asynchronous phase and amplitude. Demodulation / Amplitude Extraction: Converts a bandpass signal into a stable amplitude estimate. .

[0041] Furthermore, this embodiment induces voltage from a triaxial coil. A stable amplitude estimate is obtained With composite amplitude The steps include: Step 1: Determine the reference carrier frequency and bandwidth; Let the center frequency of the transmitting signal be... The center frequency of the receiver bandpass filter is aligned. ,bandwidth Select to cover Doppler / drift / device bias.

[0042] Step 2: Two equivalent implementations of amplitude extraction; Method A: Envelope detection (suitable for simple hardware and high real-time requirements); The envelope is obtained by full-wave rectification and low-pass filtering of the bandpass signal, and the mean / peak value of the envelope is used as the amplitude.

[0043] Method B: I / Q synchronous demodulation (suitable for weak signals and interference resistance); Generate a frequency reference and Multiplying the signal and applying a low-pass filter yields the in-phase component. Orthogonal components .

[0044] Amplitude value: The three axes can be executed separately.

[0045] For three axes, the amplitude is defined as: ; Note: Here This represents the "effective amplitude after filtering and demodulation," not the instantaneous absolute value of the original waveform. These represent the effective amplitudes of the induced voltages along the X, Y, and Z axes, respectively. This represents the induced voltage generated by the X-axis coil. This represents the induced voltage generated by the Y-axis coil, V. Z This represents the induced voltage generated by the Z-axis coil.

[0046] Step 3: Calibration and normalization of the three-axis amplitudes; Since triaxial coils may have differences in the number of turns, area, gain, and phase response, the gain of the triaxial channel should be calibrated to ensure that it has a consistent output for the same magnetic field strength.

[0047] Let the triaxial calibration coefficients be... Then the corrected amplitude is: ; Subsequent direction and distance calculations are used , These represent the effective amplitudes of the X, Y, and Z axis magnetic field signals after calibration and correction. This represents the calibration coefficient for the X-axis. This represents the calibration coefficient for the Y-axis. This represents the calibration coefficient for the Z-axis.

[0048] Step 4: Combine the three-axis amplitude for distance estimation and quality assessment; The composite amplitude is defined as the Euclidean norm of the three-axis amplitude: ; Project Explanation: The equivalent quantity corresponding to the amplitude of the spatial magnetic field can be used for distance estimation, signal existence determination, and dynamic weight allocation.

[0049] Step 5: Signal validity and quality threshold (enhancing robustness); To avoid "false directions" in pure noise, this embodiment sets thresholds and quality indicators: Amplitude threshold: Only then does the positioning calculation begin; Signal-to-noise ratio threshold: estimation Post-requirement ; Axial consistency: Avoid directional deviation caused by abnormal saturation or broken wires on a single axis.

[0050] Furthermore, this embodiment obtains the direction angle from the three-axis amplitude through direction analysis; including the following steps: Step 1: Direction cosine normalization; ; This result can be viewed as the direction cosine component (direction unit vector) of the magnetic field direction in three-dimensional coordinates.

[0051] in, Represents the direction cosine component on the X-axis. Represents the direction cosine component on the Y-axis. Represents the direction cosine component on the Z-axis. This represents the effective amplitude of the X-axis magnetic field signal after calibration and correction. This represents the effective amplitude of the Y-axis magnetic field signal after calibration and correction. This represents the effective amplitude of the Z-axis magnetic field signal after calibration and correction. This represents the combined total amplitude of the three-axis magnetic field amplitudes.

[0052] Step 2: Calculate the direction angle; ; ; in, The pitch angle, This is the azimuth angle. In engineering practice, it is recommended to use the arctangent function with quadrants to avoid... The problem of numerical values ​​close to 0.

[0053] Step 3: Sources and suppression of errors in direction resolution; Specifically, the main sources of error include: Inconsistent gain across three-axis channels (using calibration) solve); Local magnetic field distortion caused by multipath and metallic structures (solved by multi-point fusion and robust filtering); Low SNR causes amplitude estimation jitter (which is addressed using coherent accumulation and thresholding strategies).

[0054] In the positioning process, the core function of the triaxial coil is to simultaneously acquire magnetic field components in different directions. By normalizing the amplitude of the triaxial signals, the direction information of the magnetic field vector can be obtained, thereby calculating the approximate azimuth and elevation angles of the signal source. Compared with traditional single-axis direction finding, this method effectively avoids orientation deviations caused by attitude dependence, maintaining high orientation calculation accuracy even in complex environments. Regarding distance estimation, the near-field magnetic field strength and distance follow... The relative distance between the target and the receiver can be deduced by using the correlation between the received signal amplitude and the experimental calibration curve. However, single-point ranging is easily affected by coil attitude, local medium differences, and environmental noise, leading to large errors. Therefore, the actual system adopts a multi-point observation and data fusion strategy. By deploying multiple receiving devices, or collecting multiple observations during the movement of a single device, and then using algorithms such as weighted least squares, extended Kalman filtering, or particle filtering for fusion processing, random errors and systematic biases can be gradually eliminated, further converging towards the true location. Practice shows that, under reasonable geometric layout and signal-to-noise ratio conditions, this method can compress the original 10-meter uncertainty to the 1–2 meter range, meeting the positioning accuracy requirements for rubble search and rescue and complex underground environments.

[0055] Furthermore, this embodiment also includes data enhancement and signal enhancement; specifically, it includes the following steps: 1. Coherent demodulation and coherent accumulation (to improve SNR); Synchronous demodulation is performed for each sampling window, and continuous demodulation is performed for... Perform coherent accumulation in each window: ; in, This represents the signal result after coherent accumulation. This represents the received signal after synchronous demodulation in the i-th sampling window. This represents the reference signal template.

[0056] Coherent accumulation is equivalent to superimposing in-phase components, and theoretically, the effective signal can be calculated according to... Growth, while noise increases. This increases the equivalent signal-to-noise ratio.

[0057] 2. Multi-scale time window enhancement (balancing real-time performance and stability); Use both short and long windows: short windows are used for fast response (avoiding delay); long windows are used for stable estimation (suppressing jitter).

[0058] The final amplitude can be smoothed using weighted methods: ; in, This represents the final output amplitude after weighted smoothing. Represents the smoothing factor. . Indicates short-term amplitude. This indicates the amplitude over a long period of time.

[0059] 3. Data augmentation (augmentation strategies during algorithm training / calibration phases); If the system includes a learning-based classification / recognition module or needs to cover more scenarios, data augmentation should be performed during the calibration and training phases: Amplitude scaling: Simulates attenuation at different distances and media; Noise injection: superimposed power frequency interference, pulse interference, and broadband noise; Inter-axis inconsistency: analog channel gain drift and phase deviation; Attitude disturbance: Projection changes caused by the tilt of the analog coil.

[0060] These enhancements can be used to build more robust threshold, weight, and anomaly detection rules.

[0061] 4. Anomaly detection and fault tolerance (to avoid single-axis failure affecting positioning); The system in this embodiment also includes: Single-axis saturation / breakdown detection: When a certain axis is 0 for a long period of time or is saturated for a long period of time, the axis is marked as abnormal; Axis rejection and reconstruction: Abnormal axes can be temporarily rejected, and the direction can be estimated using the remaining two axes under constraints (accuracy decreases but does not interruption).

[0062] Furthermore, such as Figure 4 and Figure 5 As shown, the positioning solution unit includes: The distance estimation subunit, connected to the signal processing unit, is used to predict the distance between the distress beacon and the receiving and positioning device based on the synthetic magnetic field amplitude and a preset near-field magnetic field attenuation model. The coordinate calculation subunit, connected to the distance estimation subunit and the direction analysis subunit, is used to calculate the position coordinates of the distress beacon based on the distance, direction cosine components, and the known position coordinates of the receiving and positioning devices. The multi-point fusion subunit, connected to the coordinate solution subunit, is used to obtain the preliminary position coordinates of the distress beacon calculated at multiple different measurement locations, and to perform fusion calculations on the preliminary position coordinates to output the optimized final position coordinates.

[0063] Furthermore, the distance estimation involved in this embodiment includes the following process: 1. Near-field anticube relation: ; 2. Distance estimation by introducing calibration coefficients: ; in This can be obtained through calibration experiments: at a known distance Measurement of composite amplitude The inverse cubic model was fitted to obtain To adapt to different media conditions, a "Media / Scenario K-value Table" can be established, or a... Perform online adaptive correction.

[0064] Furthermore, this embodiment obtains coordinates from direction and distance through single-point three-dimensional coordinate inversion, including the following process: Let the coordinates of the receiver's position be... Then the beacon location for: ; This formula represents "from the receiving point along the direction..." walking distance "Obtain the target point". (When the receiver's position...) If the data has already been obtained from GNSS / distance measurement / surveying, it can be output directly. .

[0065] Furthermore, this embodiment improves accuracy and distortion resistance through multi-point fusion positioning. In environments such as ruins, tunnels, and underground, the local magnetic field may be distorted due to steel bars, metals, equipment currents, etc., making single-point inversion prone to errors. By repeatedly acquiring data at multiple measurement locations... and Local errors can be offset by statistical consistency.

[0066] Specifically, the least squares fusion objective function is expressed as follows: ; Weight design in fusion: assigning weights based on signal quality Higher quality observations have greater weight: For example, by or set up .

[0067] The weighted form is: ; in Desirable or The normalized form.

[0068] Furthermore, in this embodiment, the transmitting coil for the distress beacon to transmit low-frequency magnetic induction signals reuses the wireless charging coil inside a smartphone.

[0069] This embodiment proposes a highly integrated and portable approach to the transmitter structure: utilizing the existing wireless charging coil in a smartphone as the transmitting coil for low-frequency magnetic induction signals. The wireless charging system itself is based on the principle of near-field magnetic induction, and its coil size, number of turns, and driving circuit have been optimized for near-field magnetic field radiation, resulting in features such as small size, high efficiency, and ease of integration.

[0070] In practical implementation, without affecting the phone's original charging function, the wireless charging coil can generate a periodically changing magnetic field within a preset low-frequency range through software control or an additional drive module, serving as a transmitting beacon for the positioning system. This magnetic field forms a stable and predictable near-field distribution in space, which can be reliably sensed by an external triaxial receiving coil.

[0071] Compared to traditional magnetic induction positioning methods that require dedicated launching devices, it has the following technical advantages: 1) High integration: The transmitting coil directly reuses the existing hardware inside the mobile phone, without the need for additional volume and structural design; 2) Portability and ubiquity: As a personal device, mobile phones naturally have the advantage of being portable in scenarios such as rescue, emergency response, and personnel search; 3) Strong system consistency: The electromagnetic parameters of the wireless charging coil are stable and can be incorporated into the distance coefficient calculation process through unified calibration; 4) Easy system integration: Functions such as transmission control, signal modulation, and identity encoding can be implemented in conjunction with the mobile phone's computing and communication capabilities.

[0072] Therefore, using the wireless charging coil of a mobile phone as the transmitter of a low-frequency magnetic induction positioning system not only simplifies the system structure but also significantly improves the overall solution's deployability and engineering value in practical applications.

[0073] Example 2 like Figure 2 As shown, based on the same inventive concept, this embodiment also provides a search and rescue positioning method based on near-field electromagnetic detection, including: It receives low-frequency magnetic induction signals emitted by distress beacons worn by trapped personnel and obtains triaxial induced voltage signals; Based on the triaxial induced voltage signal, the effective amplitude of the three axes is extracted, and the magnetic field amplitude and direction are obtained based on the effective amplitude of the three axes. Based on the magnetic field amplitude and combined with the near-field magnetic field attenuation model, the distance between the distress beacon and the receiver is predicted. Determine the position coordinates of the distress beacon relative to the receiver based on the direction and distance of the magnetic field.

[0074] Furthermore, this embodiment provides a complete positioning process based on near-field electromagnetic detection by receiving low-frequency magnetic induction signals, extracting the effective amplitude of the three axes, synthesizing the magnetic field amplitude, analyzing the magnetic field direction, estimating the distance, and determining the position coordinates. It uses the magnetic field amplitude and direction information to calculate the beacon position, overcoming the shortcomings of traditional methods such as severe signal attenuation and positioning difficulties in complex environments.

[0075] Furthermore, in this embodiment, the low-frequency magnetic induction signal is a standardized distress sequence that is periodically transmitted according to a preset format; The default format includes beacon heartbeat signals, SOS sequences, and / or device identifiers.

[0076] Furthermore, the process of extracting the effective amplitude of the three axes includes: The triaxial induced voltage signal is pre-amplified and band-pass filtered to obtain the signal within the operating frequency band; The filtered signal is demodulated and its amplitude is extracted to obtain the effective amplitude of each axis.

[0077] Furthermore, this embodiment includes a signal enhancement step before extracting the effective triaxial amplitude: Coherent demodulation of the triaxial induced voltage signal and coherent accumulation of the demodulation results of multiple consecutive cycles are performed to improve the signal-to-noise ratio.

[0078] This embodiment effectively improves the detection capability of weak signals and suppresses environmental noise and interference by pre-amplifying, bandpass filtering, demodulating, and extracting amplitude from the triaxial induced voltage signal. It ensures that effective amplitude information can still be extracted stably even in a strong noise background, providing a high-quality data foundation for subsequent positioning calculations.

[0079] Furthermore, the process of obtaining the direction of the magnetic field includes: The effective amplitude of the three axes is normalized to obtain the direction cosine components of the magnetic field direction on each coordinate axis; The azimuth and elevation angles of the magnetic field are calculated based on the direction cosine components.

[0080] Furthermore, this embodiment normalizes the effective amplitude of the three axes to obtain the direction cosine component and calculate the azimuth and pitch angles, thereby achieving accurate analysis of the magnetic field direction. This avoids the attitude-dependent error caused by single-axis direction finding and can maintain high direction calculation accuracy in complex environments, providing rescue personnel with accurate target location.

[0081] Furthermore, the process of predicting the distance between the distress beacon and the receiver includes: The distance is calculated based on the inverse cubic relationship between magnetic field amplitude and distance, combined with the calibration coefficients obtained through calibration experiments.

[0082] Furthermore, this embodiment introduces a calibration coefficient K, which, based on the physical law of near-field magnetic field attenuation, enables quantitative estimation of beacon distance. The K value obtained through calibration experiments can adapt to different media and environmental conditions, improving the accuracy and adaptability of distance estimation.

[0083] Furthermore, the process of determining the position coordinates of the distress beacon relative to the receiving end includes: Calculate the location coordinates of the distress beacon based on the known location coordinates, distance, and direction cosine component of the magnetic field direction at the receiving end.

[0084] This embodiment organically combines direction and distance information to achieve three-dimensional coordinate inversion from the receiving point to the target point, which can intuitively output the location coordinates of the trapped person, making it convenient for rescuers to use directly.

[0085] Furthermore, in this embodiment, the transmitting coil for the distress beacon to transmit low-frequency magnetic induction signals reuses the wireless charging coil inside a smartphone.

[0086] Furthermore, the method in this embodiment also includes a multi-point fusion localization step: The steps of receiving, extracting, estimating, and determining are repeatedly performed at multiple different measurement locations to obtain the preliminary location coordinates of multiple distress beacons; the optimized final location coordinates are obtained by fusion calculation based on the multiple preliminary location coordinates.

[0087] Specifically, the fusion calculation uses the weighted least squares method, where the weight of each preliminary position coordinate is determined based on the signal quality of the corresponding measurement position.

[0088] This embodiment effectively overcomes the positioning errors caused by factors such as local magnetic field distortion and medium inhomogeneity in single-point measurement by repeatedly performing the positioning steps at multiple measurement locations and using multi-point fusion calculation. Through statistical fusion of multiple observations, the positioning accuracy and robustness are significantly improved, enabling meter-level or even sub-meter-level precise positioning in complex ruin environments.

[0089] The technical solution in this embodiment can significantly improve the efficiency and success rate of disaster relief, especially during the golden rescue time, enabling rapid location and rescue of trapped personnel and minimizing casualties.

[0090] The search and rescue positioning method based on near-field electromagnetic detection provided in this embodiment has all the advantages of the search and rescue positioning system based on near-field electromagnetic detection provided in Embodiment 1.

[0091] Example 3 This embodiment also discloses a computer device, including a memory, a processor, and a computer program stored in the memory, wherein the processor executes the computer program to implement the steps of the method described in Embodiment 1.

[0092] Example 4 This embodiment also discloses a computer-readable storage medium storing a computer program thereon, which, when executed by a processor, implements the steps of the method described in Embodiment 1.

[0093] Example 5 This embodiment also discloses a computer program product, including a computer program that, when executed by a processor, implements the steps of the method described in Embodiment 1.

[0094] The above are merely preferred embodiments of this application, but the scope of protection of this application is not limited thereto. Any variations or substitutions that can be easily conceived by those skilled in the art within the scope of the technology disclosed in this application should be included within the scope of protection of this application. Therefore, the scope of protection of this application should be determined by the scope of the claims.

Claims

1. A search and rescue positioning system based on near-field electromagnetic detection, characterized in that, include: A distress beacon, placed at the end of the trapped person's device, is used to transmit low-frequency magnetic induction signals; The receiving and positioning device, installed at the rescue personnel's end, includes a signal receiving unit, a signal processing unit, and a positioning calculation unit; The signal receiving unit is used to receive the low-frequency magnetic induction signal and convert the low-frequency magnetic induction signal into an electrical signal; The signal processing unit is connected to the signal receiving unit and is used to extract magnetic field amplitude information and magnetic field direction information based on the electrical signal. The positioning calculation unit is connected to the signal processing unit and is used to obtain the position coordinates of the distress beacon based on the magnetic field amplitude information and magnetic field direction information.

2. The system according to claim 1, characterized in that, The distress beacon includes: A transmitting coil is used to generate the low-frequency magnetic induction signal; The control module, connected to the transmitting coil, is used to control the transmitting coil to periodically transmit a standardized distress signal sequence according to a preset format. A power module, connected to the control module and the transmitting coil, is used to provide electrical energy; The triggering module, connected to the control module, is used to generate an activation signal and send it to the control module when a preset triggering condition is detected, so that the distress beacon enters distress mode.

3. The system according to claim 1, characterized in that, The signal receiving unit includes a triaxial orthogonal coil array, which comprises three mutually orthogonal coils used to sense magnetic field components in space and output triaxial induced voltage signals respectively.

4. The system according to claim 1, characterized in that, The signal processing unit includes: An amplitude extraction subunit, connected to the signal receiving unit, is used to filter and demodulate the triaxial induced voltage signal and extract the effective amplitude of the triaxial signal. The direction analysis subunit, connected to the amplitude extraction subunit, is used to normalize the effective amplitude of the three axes to obtain the direction cosine components of the magnetic field direction on each coordinate axis, and to analyze the azimuth and pitch angles of the magnetic field based on the direction cosine components. An amplitude synthesis subunit, connected to the amplitude extraction subunit, is used to calculate the synthesized magnetic field amplitude based on the triaxial effective amplitude using the Euclidean norm. The signal enhancement subunit, connected to the signal receiving unit, is used to perform coherent demodulation and coherent accumulation processing on the electrical signal.

5. The system according to claim 1, characterized in that, The positioning calculation unit includes: The distance estimation subunit, connected to the signal processing unit, is used to predict the distance between the distress beacon and the receiving and positioning device based on the synthetic magnetic field amplitude and a preset near-field magnetic field attenuation model. The coordinate calculation subunit, connected to the distance estimation subunit and the direction analysis subunit, is used to calculate the position coordinates of the distress beacon based on the distance, the direction cosine component, and the known position coordinates of the receiving and positioning device. The multi-point fusion subunit, connected to the coordinate calculation subunit, is used to obtain the preliminary position coordinates of the distress beacon calculated at multiple different measurement locations, and to perform fusion calculation on the preliminary position coordinates to output the optimized final position coordinates.

6. A search and rescue positioning method based on near-field electromagnetic detection, characterized in that, include: It receives low-frequency magnetic induction signals emitted by distress beacons worn by trapped personnel and obtains triaxial induced voltage signals; Based on the triaxial induced voltage signal, the effective amplitude of the three axes is extracted, and the magnetic field amplitude and magnetic field direction are obtained based on the effective amplitude of the three axes. Based on the magnetic field amplitude and the near-field magnetic field attenuation model, the distance between the distress beacon and the receiver is predicted. The position coordinates of the distress beacon relative to the receiving end are determined based on the direction of the magnetic field and the distance.

7. The method according to claim 6, characterized in that, The process of extracting the effective amplitude of the three axes includes: The triaxial induced voltage signal is pre-amplified and band-pass filtered to obtain the signal within the operating frequency band; The filtered signal is demodulated and its amplitude is extracted to obtain the effective amplitude of each axis.

8. The method according to claim 6, characterized in that, The process of obtaining the direction of the magnetic field includes: The effective amplitude of the three axes is normalized to obtain the direction cosine components of the magnetic field direction on each coordinate axis; The azimuth and elevation angles of the magnetic field are calculated based on the direction cosine components.

9. The method according to claim 6, characterized in that, The process of predicting the distance between the distress beacon and the receiver includes: The distance is calculated based on the inverse cubic relationship between the magnetic field amplitude and the distance, combined with the calibration coefficients obtained through calibration experiments.

10. The method according to claim 6, characterized in that, The process of determining the position coordinates of the distress beacon relative to the receiving end includes: The location coordinates of the distress beacon are calculated based on the known location coordinates of the receiver, the distance, and the direction cosine component of the magnetic field direction.

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