A mobile terminal non-inductive theft prevention method and device based on low-frequency magnetic field frequency domain characteristics

Abstract

This invention discloses a mobile terminal-based contactless anti-theft method and device based on the frequency domain characteristics of low-frequency magnetic fields. The method involves activating a magnetic field transmitting module to emit a set low-frequency magnetic field. Based on this magnetic field, a dual-mode sensing receiver collects raw three-axis magnetic field data. After high-pass filtering to remove the DC component of the Earth's magnetic field, three-dimensional AC magnetic field data is obtained. The Euclidean norm of the three-dimensional AC magnetic field data is calculated, converting it into a one-dimensional scalar signal. Based on this one-dimensional scalar signal, the Gosser algorithm is used to extract the magnetic field energy value corresponding to the target frequency in the magnetic field. The data is then demodulated and the area identification code is verified to obtain the verification result. Combining the magnetic field energy value and the verification result, a hysteresis comparison and multi-level decision logic are used to determine the security status of the protected object. When the alarm triggering conditions are met, the corresponding alarm operation is executed. This invention solves the problems of poor physical connection experience, susceptibility to false alarms due to wireless radio frequency obstruction, and high hardware tag costs in existing technologies.

Description

Technical Field

[0001] This invention relates to the field of short-range area monitoring and security management technology, specifically to a mobile terminal contactless anti-theft method and device based on the frequency domain characteristics of low-frequency magnetic fields. Background Technology

[0002] Driven by the widespread adoption of electronic information and IoT technologies, the display and experience scenarios for mobile terminals and various high-value items are increasing, leading to a continuous rise in the demand for security control within short-distance areas. Currently, anti-theft technologies on the market are mainly divided into four categories: First, mechanical anti-theft solutions based on physical connections, which use physical cables such as retractable ropes and anti-theft buckles to bind the protected object to the display stand, relying on contact switches to detect abnormal disconnection; second, electronic fence technology based on wireless radio frequency signal strength, which uses the signal attenuation characteristics of devices such as Bluetooth and Wi-Fi to estimate distance and construct a virtual protective boundary; third, identification technology based on additional hardware tags, which uses RFID or UWB electronic tags in conjunction with base stations to achieve location-based anti-theft; and fourth, behavior analysis technology based on a single inertial sensor, which relies on accelerometers and gyroscopes to detect the movement state of the protected object to determine whether theft has occurred. These technologies are widely used in scenarios such as shopping mall displays, store experiences, and exhibition displays, meeting basic anti-theft needs to a certain extent.

[0003] However, existing technologies face numerous insurmountable problems in practical applications: mechanical anti-theft solutions, constrained by physical cables, severely impact user grip and freedom of movement; mechanical structures are prone to wear and tear, leading to high false alarm rates; and messy cables detract from aesthetically pleasing displays. Wireless radio frequency signals are easily absorbed by human tissue, are greatly affected by obstruction and multipath effects, exhibiting drastic signal fluctuations; and attenuation gradients are gradual at close range, failing to establish clear protection boundaries, resulting in significant false alarms and missed alarms. Hardware tagging solutions suffer from resource redundancy and intrusion; the inherent sensing and computing capabilities of smart terminals are not utilized; forced tagging damages product appearance; and UWB is expensive while RFID is susceptible to metal interference, hindering widespread adoption across all product categories. Single inertial sensor solutions cannot distinguish between normal user experience and theft, lack absolute position constraints, suffer from cumulative drift, and struggle to balance sensitivity and false alarm rates. These issues make it difficult for existing technologies to balance user experience, deployment costs, and protection accuracy, failing to meet the demands for high-precision, seamless security control.

[0004] Therefore, there is an urgent need for a mobile terminal-based contactless anti-theft method based on the frequency domain characteristics of low-frequency magnetic fields to solve the problems of poor physical connection experience, false alarms due to wireless radio frequency obstruction, and high cost of hardware tags in existing technologies. Summary of the Invention

[0005] To address this, the present invention provides a mobile terminal contactless anti-theft method and device based on the frequency domain characteristics of low-frequency magnetic fields, which solves the problems of poor physical connection experience, wireless radio frequency being easily blocked and false alarms, high cost of hardware tags, and insufficient accuracy of inertial sensing in existing anti-theft technologies, and achieves contactless, low-cost, and high-precision security management of mobile terminals and items.

[0006] To achieve the above objectives, the present invention provides the following technical solution: a mobile terminal contactless anti-theft method based on low-frequency magnetic field frequency domain characteristics, characterized in that it includes:

[0007] By activating the magnetic field transmission module, a set low-frequency magnetic field is emitted; the set low-frequency magnetic field is a low-frequency signal that is not an integer multiple of the power frequency and is superimposed with a unique regional identity code.

[0008] Based on the aforementioned low-frequency magnetic field, raw triaxial magnetic field data is acquired through a dual-mode sensing receiver; the raw triaxial magnetic field data is then subjected to high-pass filtering to remove the DC component of the Earth's magnetic field, thereby obtaining three-dimensional AC magnetic field data.

[0009] Based on the three-dimensional AC magnetic field data, the Euclidean norm is calculated; based on the Euclidean norm, the three-dimensional AC magnetic field data is converted into a one-dimensional scalar signal.

[0010] Based on the one-dimensional scalar signal, the magnetic field energy value corresponding to the target frequency in the set low-frequency magnetic field is extracted by the Gosser algorithm; the area identity code in the set low-frequency magnetic field is demodulated and the area identity code is verified to obtain the verification result.

[0011] Based on the magnetic field energy value and the verification result, the safety status of the protected object is determined by setting hysteresis comparison and multi-level decision logic, and the corresponding alarm operation is executed when the alarm triggering condition is met.

[0012] As a preferred embodiment of a mobile terminal contactless anti-theft method based on the frequency domain characteristics of low-frequency magnetic fields, the carrier frequency of the set low-frequency magnetic field is 15Hz to 30Hz; the set low-frequency magnetic field drives an H-bridge circuit through bipolar pulse width modulation, and in conjunction with an LC series resonant circuit, shapes the driving signal into a quasi-sine wave; and regional identity codes are superimposed through frequency shift keying or amplitude shift keying.

[0013] As a preferred embodiment of a mobile terminal-based contactless anti-theft method based on the frequency domain characteristics of low-frequency magnetic fields, the calculation formula for the three-dimensional AC magnetic field data is as follows:

[0014]

[0015] In the formula, This represents the three-dimensional alternating magnetic field data at time n. This represents the three-dimensional alternating magnetic field data at time n-1; This represents the original three-dimensional magnetic field data at time n; This represents the original three-dimensional magnetic field data at time n-1; These are the filter coefficients.

[0016] As a preferred embodiment of a mobile terminal-based contactless anti-theft method based on the frequency domain characteristics of low-frequency magnetic fields, the Euclidean norm is calculated using the following formula:

[0017]

[0018] In the formula, The signal is a one-dimensional scalar signal at time n. , , These represent the components of the three-dimensional AC magnetic field data at time n in the x-axis, y-axis, and z-axis directions, respectively.

[0019] As a preferred embodiment of a mobile terminal-based contactless anti-theft method based on the frequency domain characteristics of low-frequency magnetic fields, in the process of extracting the magnetic field energy value corresponding to the target frequency in the set low-frequency magnetic field using the Gossel algorithm, the formula for calculating the magnetic field energy value is as follows:

[0020]

[0021]

[0022]

[0023]

[0024] In the formula, The angular frequency corresponding to the target frequency; To set the carrier frequency for the low-frequency magnetic field; This represents the sampling rate of the original triaxial magnetic field data; These are the iteration coefficients; This is the result of the iterative calculation at time n. N represents the total number of sampling points in a single energy extraction. This represents the magnetic field energy value corresponding to the target frequency.

[0025] As a preferred solution for a mobile terminal-based contactless anti-theft method based on the frequency domain characteristics of low-frequency magnetic fields, a high threshold is preset during the process of determining the security status of the protected object by setting hysteresis comparison and multi-level decision logic. and low threshold ,and > ;when When, the protected object is determined to be in a safe state; when And the duration exceeds the detection time. When this condition is met, it is determined to be an alarm trigger condition.

[0026] This invention also provides a mobile terminal contactless anti-theft system based on low-frequency magnetic field frequency domain characteristics, employing the above-mentioned mobile terminal contactless anti-theft method based on low-frequency magnetic field frequency domain characteristics, comprising:

[0027] The low-frequency magnetic field transmitting unit is used to transmit a set low-frequency magnetic field by activating the magnetic field transmitting module; the set low-frequency magnetic field is a low-frequency signal that is not an integer multiple of the power frequency and is superimposed with a unique regional identification code.

[0028] The three-dimensional AC magnetic field data acquisition unit is used to acquire raw three-axis magnetic field data through a dual-mode sensing receiver based on the set low-frequency magnetic field; and to perform high-pass filtering on the raw three-axis magnetic field data to remove the DC component of the geomagnetic field and obtain three-dimensional AC magnetic field data.

[0029] A three-dimensional AC magnetic field data conversion unit is used to calculate the Euclidean norm based on the three-dimensional AC magnetic field data; and to convert the three-dimensional AC magnetic field data into a one-dimensional scalar signal based on the Euclidean norm.

[0030] The magnetic field energy value acquisition and regional identity code verification unit is used to extract the magnetic field energy value corresponding to the target frequency in the set low-frequency magnetic field based on the one-dimensional scalar signal using the Gosser algorithm; demodulate the regional identity code in the set low-frequency magnetic field and complete the regional identity code verification to obtain the verification result.

[0031] The safety status determination and processing unit is used to determine the safety status of the protected object based on the magnetic field energy value and the verification result by setting hysteresis comparison and multi-level decision logic, and to execute the corresponding alarm operation when the alarm triggering condition is met.

[0032] As a preferred embodiment of a mobile terminal contactless anti-theft system based on the frequency domain characteristics of low-frequency magnetic fields, in the low-frequency magnetic field transmitting unit, the carrier frequency of the set low-frequency magnetic field is 15Hz to 30Hz; the set low-frequency magnetic field drives an H-bridge circuit through bipolar pulse width modulation, and in conjunction with an LC series resonant circuit, shapes the driving signal into a quasi-sine wave; and superimposes the regional identity code through frequency shift keying or amplitude shift keying.

[0033] As a preferred solution for a mobile terminal-based contactless anti-theft system based on low-frequency magnetic field frequency domain characteristics, the calculation formula for the three-dimensional AC magnetic field data in the three-dimensional AC magnetic field data acquisition unit is as follows:

[0034]

[0035] In the formula, This represents the three-dimensional alternating magnetic field data at time n. This represents the three-dimensional alternating magnetic field data at time n-1; This represents the original three-dimensional magnetic field data at time n; This represents the original three-dimensional magnetic field data at time n-1; These are the filter coefficients.

[0036] As a preferred solution for a mobile terminal-based contactless anti-theft system based on the frequency domain characteristics of low-frequency magnetic fields, the Euclidean norm in the three-dimensional AC magnetic field data conversion unit is calculated as follows:

[0037]

[0038] In the formula, The signal is a one-dimensional scalar signal at time n. , , These represent the components of the three-dimensional AC magnetic field data at time n in the x-axis, y-axis, and z-axis directions, respectively.

[0039] As a preferred solution for a mobile terminal contactless anti-theft system based on the frequency domain characteristics of low-frequency magnetic fields, in the magnetic field energy value acquisition and area identity coding verification unit, during the process of extracting the magnetic field energy value corresponding to the target frequency in the set low-frequency magnetic field using the Gossel algorithm, the calculation formula for the magnetic field energy value is as follows:

[0040]

[0041]

[0042]

[0043]

[0044] In the formula, The angular frequency corresponding to the target frequency; To set the carrier frequency for the low-frequency magnetic field; This represents the sampling rate of the original triaxial magnetic field data; These are the iteration coefficients; This is the result of the iterative calculation at time n. N represents the total number of sampling points in a single energy extraction. This represents the magnetic field energy value corresponding to the target frequency.

[0045] As a preferred solution for a mobile terminal-based contactless anti-theft system based on low-frequency magnetic field frequency domain characteristics, the security status determination and processing unit, in the process of determining the security status of the protected object through hysteresis comparison and multi-level decision logic, presets a high threshold. and low threshold ,and > ;when When, the protected object is determined to be in a safe state; when And the duration exceeds the detection time. When this condition is met, it is determined to be an alarm trigger condition.

[0046] The present invention has the following advantages:

[0047] First, accurate boundary control: relying on the cubic inverse attenuation characteristics of low-frequency magnetic fields, an "electronic cliff" is constructed to achieve centimeter-level steep boundary determination, solving the problem of ambiguous boundaries in traditional radio frequency technology.

[0048] Second, it has strong anti-interference capabilities: low-frequency magnetic fields can penetrate non-magnetic media, and combined with vector synthesis and frequency domain filtering, it can completely avoid human body obstruction, posture rotation and power grid interference.

[0049] Third, it is suitable for a wide range of scenarios: the dual-form transmitter and dual-mode receiver cover scenarios such as independent islands and long display tables, and are compatible with the protection of both smart and non-smart items.

[0050] Fourth, seamless and low-cost deployment: Reuse the built-in sensors of smart terminals, eliminating the need for mandatory labeling or expensive base stations, and eliminating mechanical wear, thus reducing hardware and maintenance costs.

[0051] Fifth, high security and robustness: It has regional identity code verification and magnetic saturation attack defense, and the delayed decision logic avoids false alarms due to critical jitter, making it suitable for complex business environments. Attached Figure Description

[0052] To more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings in the following description are merely exemplary, and those skilled in the art can derive other embodiments based on the provided drawings without creative effort.

[0053] The structures, proportions, sizes, etc. illustrated in this specification are only for the purpose of assisting those skilled in the art in understanding and reading the content disclosed herein, and are not intended to limit the conditions under which the present invention can be implemented. Therefore, they have no substantial technical significance. Any modifications to the structure, changes in the proportions, or adjustments to the size, without affecting the effects and objectives that the present invention can produce, should still fall within the scope of the technical content disclosed in the present invention.

[0054] Figure 1This is a flowchart illustrating a mobile terminal contactless anti-theft method based on low-frequency magnetic field frequency domain characteristics provided in Embodiment 1 of the present invention.

[0055] Figure 2 This is a schematic diagram of the specific implementation process of a mobile terminal contactless anti-theft method based on low-frequency magnetic field frequency domain characteristics provided in Embodiment 1 of the present invention;

[0056] Figure 3 This is a schematic diagram of the deployment of a centralized hollow coil structure in a mobile terminal contactless anti-theft method based on low-frequency magnetic field frequency domain characteristics provided in Embodiment 1 of the present invention;

[0057] Figure 4 This is a schematic diagram of the edge-surrounding large coil deployment in a mobile terminal contactless anti-theft method based on low-frequency magnetic field frequency domain characteristics provided in Embodiment 1 of the present invention;

[0058] Figure 5 This is a schematic diagram of the independent hardware tag hardware architecture in a mobile terminal contactless anti-theft method based on low-frequency magnetic field frequency domain characteristics provided in Embodiment 1 of the present invention;

[0059] Figure 6 This is a schematic diagram of the architecture of a mobile terminal contactless anti-theft system based on the frequency domain characteristics of a low-frequency magnetic field, provided in Embodiment 2 of the present invention.

[0060] Figure 7 This is a schematic diagram of the specific device architecture of a mobile terminal contactless anti-theft system based on the frequency domain characteristics of a low-frequency magnetic field, as provided in Embodiment 2 of the present invention. Detailed Implementation

[0061] The following specific embodiments illustrate the implementation of the present invention. Those skilled in the art can easily understand other advantages and effects of the present invention from the content disclosed in this specification. Obviously, the described embodiments are only some, not all, of the embodiments of the present invention. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0062] Example 1

[0063] See Figure 1 and Figure 2 Embodiment 1 of the present invention provides a mobile terminal contactless anti-theft method based on the frequency domain characteristics of low-frequency magnetic fields, comprising the following steps:

[0064] S1. By activating the magnetic field transmission module, a set low-frequency magnetic field is transmitted; the set low-frequency magnetic field is a low-frequency signal that is not an integer multiple of the power frequency and is superimposed with a unique regional identity code.

[0065] S2. Based on the set low-frequency magnetic field, the original triaxial magnetic field data is acquired by a dual-mode sensing receiver; the original triaxial magnetic field data is subjected to high-pass filtering to remove the DC component of the geomagnetic field and obtain three-dimensional AC magnetic field data.

[0066] S3. Based on the three-dimensional AC magnetic field data, the Euclidean norm is calculated; based on the Euclidean norm, the three-dimensional AC magnetic field data is converted into a one-dimensional scalar signal.

[0067] S4. Based on the one-dimensional scalar signal, extract the magnetic field energy value corresponding to the target frequency in the set low-frequency magnetic field using the Gosser algorithm; demodulate the area identity code in the set low-frequency magnetic field and complete the area identity code verification to obtain the verification result.

[0068] S5. Based on the magnetic field energy value and the verification result, the safety status of the protected object is determined by setting hysteresis comparison and multi-level decision logic, and the corresponding alarm operation is executed when the alarm triggering condition is met.

[0069] In this embodiment, in step S1, a set low-frequency magnetic field is emitted by activating the magnetic field emission module; the set low-frequency magnetic field is a low-frequency signal that is not an integer multiple of the power frequency and is superimposed with a unique regional identity code.

[0070] Specifically, after the magnetic field transmitting module is activated, the internal MCU main control unit generates a specific control signal to drive the H-bridge power drive stage circuit. This, in conjunction with the LC resonant circuit, completes signal shaping and amplification, ultimately transmitting a set low-frequency magnetic field. The carrier frequency of this low-frequency magnetic field is set to 15Hz–30Hz. Choosing a frequency that is not an integer multiple of the power frequency is to physically avoid interference from the global power grid's power frequency and its harmonics, ensuring the stability of the magnetic field signal. The superimposed unique regional identification code is achieved through amplitude shift keying (OOK) or frequency shift keying (FSK) modulation, giving each protected region's magnetic field signal a unique identification characteristic. This provides a basis for the subsequent receiver to distinguish its own signal from interference signals from neighboring regions, laying the foundation for anti-crosstalk.

[0071] In this embodiment, the magnetic field transmitting module, serving as the core base station of the system, is deployed in the controlled area, such as a display table. Its function is not to transmit data, but rather to construct a scalar field with specific spatial gradient characteristics. This magnetic field is physically confined to the near-field region (…). ), utilizing the fact that the magnetic dipole field strength decreases with the cube of the distance ( The characteristics of ) form a "electronic fence" with clear physical boundaries.

[0072] After the magnetic field emission module is started, the MCU main control unit does not directly output a square wave, but instead generates a specific frequency through a timer. The signal is a sinusoidal pulse width modulation (SPWM) signal. This signal drives a full-bridge inverter circuit consisting of four MOSFETs. Compared to a simple square wave drive, SPWM can significantly reduce the high-order harmonic components in the drive current, reducing electromagnetic interference to surrounding electronic equipment.

[0073] The LC resonant circuit consists of a transmitting coil. Matching capacitor It is configured in series. The specific parameter configuration of the LC resonant circuit is as follows:

[0074] Assume coil inductance Target frequency Then the matching capacitor Selected as:

[0075]

[0076] In the resonant state, the LC resonant circuit exhibits purely resistive behavior, even when the supply voltage is low (e.g., The coil can also generate a resonant high voltage several times that of the power supply voltage, thus producing an ampere-level excitation current in the coil with relatively low power consumption, ensuring that the magnetic field coverage radius reaches [a certain value]. above.

[0077] In this embodiment, the field topology design of the magnetic field emission module includes a central radiation type and an edge fence type;

[0078] Central radial type, such as Figure 3 As shown, a hollow coil with a diameter of 15cm and 200 turns is used. The coil's interior is a non-magnetic support frame or air medium, without a ferromagnetic core, and relies entirely on current excitation. The magnetic field it generates follows the magnetic dipole model, with the strongest component in the Z-axis direction perpendicular to the table. The magnetic field strength decreases with distance in an inverse cubic ratio (1 / r³). At 0.5m, the magnetic field strength is the baseline value B, at 1.0m it decreases to B / 8, at 2.0m it decreases to B / 64, and the signal is weak at 3.0m. It is suitable for small, independent display scenarios such as independent islands and single mobile phone booths, and can form a hemispherical protective magnetic field centered on the coil.

[0079] Edge fence type Figure 4 As shown, the coil is laid along the edge of the long display table (under the tabletop or on the side), with a width of 0.8m and a length of 2.0m, forming a large-size rectangular closed conductor loop. Based on the integral superposition effect of the Biot-Savart law, the coil generates a cylindrical wave magnetic field, forming a uniform and flat area with magnetic flux fluctuation of less than 3dB inside the tabletop, ensuring signal stability when the user moves the protected object within the tabletop; when the protected object crosses 10cm beyond the edge of the table, the magnetic field exhibits a steep drop with a downward slope exceeding 12dB / oct, which can quickly identify boundary crossing behavior and is suitable for scenarios such as rectangular experience tables and multi-person shared long tables.

[0080] In this embodiment, in step S2, based on the set low-frequency magnetic field, the original triaxial magnetic field data is acquired by a dual-mode sensing receiver; the original triaxial magnetic field data is subjected to high-pass filtering to remove the DC component of the geomagnetic field and obtain three-dimensional AC magnetic field data.

[0081] Specifically, the dual-mode sensing receiver is a software-multiplexed terminal or a stand-alone hardware tag. It has a built-in magnetic sensor that captures a set low-frequency magnetic field signal from the surrounding environment in real time, simultaneously acquiring raw magnetic field data along the x, y, and z axes. Since the raw three-axis magnetic field data contains a DC component from the Earth's magnetic field, which interferes with the extraction of the target magnetic field signal, a first-order IIR high-pass filtering algorithm is used to process the raw data. Through filtering circuitry or algorithm calculations, the time-invariant DC component of the Earth's magnetic field is completely removed, ultimately yielding three-dimensional AC magnetic field data containing only the set low-frequency alternating magnetic field characteristics, providing a clean data source for subsequent signal analysis.

[0082] Software-defined tags (Soft-Tags) are designed for smart devices such as smartphones and tablets that integrate triaxial Hall sensors or magnetoresistive sensors. By embedding monitoring services into the hardware abstraction layer or application framework layer of the operating system (Android / iOS / HarmonyOS), existing sensor data can be directly reused.

[0083] The independent hardware tag (Hard-Tag) is for non-smart items (such as styluses, earphones, and watches). It adopts a low-power microcontroller and discrete magnetic sensor architecture, and has independent power management and audible and visual alarm circuits.

[0084] In this embodiment, the sampling rate is used as the basis for the calculation. Acquire raw magnetic field data .

[0085] The Earth's magnetic field is removed using a first-order IIR high-pass filter to obtain three-dimensional AC magnetic field data. The calculation formula is as follows:

[0086]

[0087] In the formula, This represents the three-dimensional alternating magnetic field data at time n. This represents the three-dimensional alternating magnetic field data at time n-1; This represents the original three-dimensional magnetic field data at time n; This represents the original three-dimensional magnetic field data at time n-1; The filter coefficients are set to a cutoff frequency of 1. .

[0088] In this embodiment, in step S3, the Euclidean norm is calculated based on the three-dimensional AC magnetic field data; and the three-dimensional AC magnetic field data is converted into a one-dimensional scalar signal based on the Euclidean norm.

[0089] Specifically, regarding the three-dimensional AC magnetic field data obtained in step S2, considering that the protected object (such as a mobile phone or tablet) will rotate during user experience, causing irregular fluctuations in the magnetic field components along the x, y, and z axes, but the total magnetic field energy remains constant. Since the Euclidean norm can accurately characterize the total energy of a three-dimensional vector, the Euclidean norm is obtained by calculating the squares and square roots of the x, y, and z axis components of the three-dimensional AC magnetic field data. Based on this norm, the three-dimensional vector signal, which is originally susceptible to attitude influence, is transformed into a one-dimensional scalar signal that is only related to the magnetic field strength and independent of attitude, completely eliminating the interference of attitude rotation on signal detection.

[0090] The formula for calculating the Euclidean norm is as follows:

[0091]

[0092] In the formula, The signal is a one-dimensional scalar signal at time n. , , These represent the components of the three-dimensional AC magnetic field data at time n in the x-axis, y-axis, and z-axis directions, respectively.

[0093] In this embodiment, in step S4, based on the one-dimensional scalar signal, the magnetic field energy value corresponding to the target frequency in the set low-frequency magnetic field is extracted by the Gosser algorithm; the area identity code in the set low-frequency magnetic field is demodulated and the area identity code is verified to obtain the verification result.

[0094] Specifically, the one-dimensional scalar signal obtained in step S3 contains the core features of the set low-frequency magnetic field. The Gosser algorithm is used to perform frequency domain analysis on this signal. This algorithm pre-calculates the angular frequency and iteration coefficients corresponding to the target frequency, and after multiple rounds of iterative calculations, it calculates the magnetic field energy value corresponding to the target frequency. Compared with the traditional FFT algorithm, it has less computational load and is more targeted, accurately extracting effective signal energy in complex noisy environments. Simultaneously, for the area identification code superimposed in the set low-frequency magnetic field, the corresponding encoding information is obtained by detecting changes in the strength or frequency shift of the signal envelope. This information is then compared with the whitelist encoding preset at the receiving end to complete the area identification code verification. If the encoding matches, it is determined to be a valid signal; if it does not match, it is considered neighboring cell interference or malicious magnetic interference, thus obtaining an accurate verification result.

[0095] The formula for calculating the magnetic field energy value is as follows:

[0096]

[0097]

[0098]

[0099]

[0100] In the formula, The angular frequency corresponding to the target frequency; To set the carrier frequency for the low-frequency magnetic field; This represents the sampling rate of the original triaxial magnetic field data; These are the iteration coefficients; This is the result of the iterative calculation at time n. N represents the total number of sampling points in a single energy extraction. This represents the magnetic field energy value corresponding to the target frequency.

[0101] This algorithm is equivalent to an extremely high A bandpass filter with a value. Even if The signal is submerged in large-amplitude random motion noise, as long as the integration window... Large enough (e.g.) ), It can still accurately reflect the target signal strength.

[0102] In this embodiment, in step S5, based on the magnetic field energy value and the verification result, the safety status of the protected object is determined by setting hysteresis comparison and multi-level decision logic, and the corresponding alarm operation is executed when the alarm triggering condition is met.

[0103] Specifically, combining the magnetic field energy value obtained in step S4 with the area identity code verification result, a preset hysteresis comparison and multi-level decision logic is initiated. First, it determines whether the verification result is a valid signal; if it is an invalid signal, it is directly determined to be in a safe state; if it is a valid signal, the magnetic field energy value is compared with a preset high threshold. and low threshold A comparison is performed. When the magnetic field energy value is greater than the high threshold, the protected object is determined to be in a safe area and remains silent; when the magnetic field energy value is less than the low threshold and the duration exceeds the set detection time, the alarm trigger condition is met. Additionally, optional verification can be performed using Bluetooth signal strength indication; only when… The final lock alarm is only triggered when the device is lost and the Bluetooth RSSI is below a preset value (e.g., -85dBm), further eliminating interference factors such as momentary metal obstruction. Once the alarm conditions are confirmed, the software-multiplexed terminal uses its own speaker, flashlight, and wireless network module to emit alarm signals, while the independent hardware tag activates its piezoelectric buzzer and high-brightness LED to perform an audible and visual alarm.

[0104] Among them, the architecture of the independent hardware tag is as follows: Figure 5 As shown, all functional modules are integrated within the tag's housing, with the core being the microcontroller unit (MCU). This MCU serves as the central processing unit for the entire tag, coordinating the orderly operation of each module, running simplified frequency domain signal processing algorithms, and executing alarm logic decisions. A magnetic field sensor chip, working in conjunction with the MCU, collects triaxial magnetic field strength data from the environment in real time, converting the analog signal into a digital signal and transmitting it to the MCU to provide data support for subsequent analysis. The tag's built-in tamper-evident contacts / switches are crucial physical security detection mechanisms. Once the tag is forcibly removed from the surface of the protected item, its state changes, immediately sending a trigger signal to the MCU. The power supply unit consists of a button cell battery or a small lithium battery paired with a power management unit (PMU). This provides a stable operating voltage for all components, including the MCU, sensors, and alarms, while also effectively managing low-power sleep modes to ensure long-term tag operation. The alarm execution components include a piezoelectric buzzer and a high-brightness LED indicator. When the MCU determines that there is an abnormal situation such as displacement or removal, it will drive the piezoelectric buzzer to emit a high-decibel audio alarm and control the high-brightness LED indicator to flash, so as to achieve a clear local warning through a combination of visual and auditory means.

[0105] The working principle of stand-alone hardware tags is as follows:

[0106] The magnetic field sensor continuously monitors magnetic field signals at a specific frequency. The MCU receives and analyzes this data. If it determines that the tag has left the safe area covered by the magnetic field, or receives a removal signal triggered by the tamper switch, it will immediately activate the alarm execution component.

[0107] To achieve the goal of more than 2 years of battery life from a single CR2450 battery, the tag also features a three-level sleep mechanism: Level 0 is deep sleep, triggered when an object remains still for more than 1 minute. At this time, the MCU shuts down, the magnetic sensor is powered off, and only the MEMS accelerometer runs at a frequency of 1Hz to detect "motion interruption," with power consumption below 2μA; Level 1 is motion monitoring, triggered when the accelerometer detects a vibration ΔG>0.1g. The MCU is woken up and the magnetic sensor is turned on, collecting Z-axis data at a low sampling rate of 10Hz for simple amplitude threshold judgment, with power consumption of approximately 50μA; Level 2 is precise locking, triggered by a suspected magnetic field signal detected in Level 1. At this time, the system runs at full speed, enabling 100Hz sampling on all three axes and Gosser floating-point operations for precise distance calculation and ID verification, with power consumption of approximately 2mA and lasting only for milliseconds, minimizing energy consumption.

[0108] In this embodiment, a defense mechanism against malicious interference from magnets is also designed:

[0109] When the receiver detects that the value of any axis in the raw data of the triaxial magnetic sensor reaches the sensor's upper limit and remains so for a set time, the algorithm determines it as a "magnetic saturation attack," meaning someone is attempting to saturate and disable the sensor using a strong magnet. At this point, regardless of whether a target frequency signal is detected, the system will forcibly trigger the highest priority audible and visual alarm.

[0110] The application scenarios of this invention are as follows:

[0111] In smart terminal display scenarios such as mobile phones in shopping malls, this invention eliminates the need for physical cables, does not damage the product's appearance, and allows users to freely experience the product while achieving safety control.

[0112] In high-value electronic device display scenarios at exhibitions, this invention adapts to different booth layouts through a dual-form transmitter, is compatible with the protection of both smart and non-smart devices, and reduces deployment costs.

[0113] In the context of digital product experience in stores, this invention can avoid interference caused by human body obstruction and posture rotation, stably monitor the product's on-site status, and reduce false alarms and missed alarms.

[0114] In the display scenarios of bags and accessories in luxury stores, this invention achieves seamless protection through independent hardware tags, without affecting the aesthetics of product display, while ensuring the safety of items.

[0115] In the management of critical electronic equipment in office areas, this invention relies on the penetrating characteristics of low-frequency magnetic fields to operate stably in complex environments, enabling boundary control and in-situ detection of the equipment.

[0116] It should be noted that the method of this disclosure embodiment can be executed by a single device, such as a computer or server. The method of this embodiment can also be applied to a distributed scenario, where multiple devices cooperate to complete the task. In such a distributed scenario, one of these devices may execute only one or more steps of the method of this disclosure embodiment, and the multiple devices will interact with each other to complete the method described.

[0117] It should be noted that the above description describes some embodiments of this disclosure. Other embodiments are within the scope of the appended claims. In some cases, the actions or steps recorded in the claims can be performed in a different order than that shown in the above embodiments and still achieve the desired result. Furthermore, the processes depicted in the drawings do not necessarily require a specific or sequential order to achieve the desired result. In some embodiments, multitasking and parallel processing are also possible or may be advantageous.

[0118] Example 2

[0119] See Figure 6 Embodiment 2 of the present invention also provides a mobile terminal contactless anti-theft system based on the frequency domain characteristics of low-frequency magnetic fields, comprising:

[0120] The low-frequency magnetic field transmitting unit 001 is used to transmit a set low-frequency magnetic field by activating the magnetic field transmitting module; the set low-frequency magnetic field is a low-frequency signal that is not an integer multiple of the power frequency and is superimposed with a unique regional identity code.

[0121] The three-dimensional AC magnetic field data acquisition unit 002 is used to acquire raw three-axis magnetic field data through a dual-mode sensing receiver based on the set low-frequency magnetic field; and to perform high-pass filtering on the raw three-axis magnetic field data to remove the DC component of the geomagnetic field and obtain three-dimensional AC magnetic field data.

[0122] The three-dimensional AC magnetic field data conversion unit 003 is used to calculate the Euclidean norm based on the three-dimensional AC magnetic field data; and to convert the three-dimensional AC magnetic field data into a one-dimensional scalar signal based on the Euclidean norm.

[0123] The magnetic field energy value acquisition and regional identity code verification unit 004 is used to extract the magnetic field energy value corresponding to the target frequency in the set low-frequency magnetic field based on the one-dimensional scalar signal and through the Gosser algorithm; demodulate the regional identity code in the set low-frequency magnetic field and complete the regional identity code verification to obtain the verification result.

[0124] The safety status determination and processing unit 005 is used to determine the safety status of the protected object based on the magnetic field energy value and the verification result by setting hysteresis comparison and multi-level decision logic, and to execute the corresponding alarm operation when the alarm triggering condition is met.

[0125] In this embodiment, in the low-frequency magnetic field transmitting unit 001, the carrier frequency of the set low-frequency magnetic field is 15Hz to 30Hz; the set low-frequency magnetic field drives the H-bridge circuit through bipolar pulse width modulation, and in conjunction with the LC series resonant circuit, the driving signal is shaped into a quasi-sine wave; the regional identity code is superimposed through frequency shift keying or amplitude shift keying.

[0126] In this embodiment, the calculation formula for the three-dimensional AC magnetic field data in the three-dimensional AC magnetic field data acquisition unit 002 is as follows:

[0127]

[0128] In the formula, This represents the three-dimensional alternating magnetic field data at time n. This represents the three-dimensional alternating magnetic field data at time n-1; This represents the original three-dimensional magnetic field data at time n; This represents the original three-dimensional magnetic field data at time n-1; These are the filter coefficients.

[0129] In this embodiment, the Euclidean norm is calculated using the following formula in the three-dimensional AC magnetic field data conversion unit 003:

[0130]

[0131] In the formula, The signal is a one-dimensional scalar signal at time n. , , These represent the components of the three-dimensional AC magnetic field data at time n in the x-axis, y-axis, and z-axis directions, respectively.

[0132] In this embodiment, in the magnetic field energy value acquisition and area identity coding verification unit 004, during the process of extracting the magnetic field energy value corresponding to the target frequency in the set low-frequency magnetic field using the Gossel algorithm, the calculation formula for the magnetic field energy value is as follows:

[0133]

[0134]

[0135]

[0136]

[0137] In the formula, The angular frequency corresponding to the target frequency; To set the carrier frequency for the low-frequency magnetic field; This represents the sampling rate of the original triaxial magnetic field data; These are the iteration coefficients; This is the result of the iterative calculation at time n. N represents the total number of sampling points in a single energy extraction. This represents the magnetic field energy value corresponding to the target frequency.

[0138] In this embodiment, the security status determination and processing unit 005 presets a high threshold during the process of determining the security status of the protected object by setting hysteresis comparison and multi-level decision logic. and low threshold ,and > ;when When, the protected object is determined to be in a safe state; when And the duration exceeds the detection time. When this condition is met, it is determined to be an alarm trigger condition.

[0139] In this embodiment, the specific configuration structure of the mobile terminal contactless anti-theft system provided by the present invention is as follows: Figure 7 As shown, it includes a magnetic field transmitter and a mobile receiver. The magnetic field transmitter includes an MCU main controller, a drive circuit, and a coil load; the mobile receiver includes a magnetic sensor, a data processing unit, and an anti-theft APP.

[0140] It should be noted that the information interaction and execution process between the modules of the above system are based on the same concept as the method embodiment in Embodiment 1 of this application, and the resulting technical effects are the same as those in the method embodiment of this application. For details, please refer to the description in the method embodiment shown above in this application, and it will not be repeated here.

[0141] Example 3

[0142] Embodiment 3 of the present invention provides a non-transitory computer-readable storage medium storing program code for a mobile terminal contactless anti-theft method based on low-frequency magnetic field frequency domain characteristics. The program code includes instructions for executing the mobile terminal contactless anti-theft method based on low-frequency magnetic field frequency domain characteristics of Embodiment 1 or any possible implementation thereof.

[0143] Computer-readable storage media can be any available medium that a computer can access, or a data storage device such as a server or data center that integrates one or more available media. The available medium can be magnetic media (e.g., floppy disks, hard disks, magnetic tapes), optical media (e.g., DVDs), or semiconductor media (e.g., solid-state drives (SSDs)).

[0144] Example 4

[0145] Embodiment 4 of the present invention provides an electronic device, including: a memory and a processor;

[0146] The processor and the memory communicate with each other via a bus; the memory stores program instructions that can be executed by the processor, and the processor can call the program instructions to execute a mobile terminal contactless anti-theft method based on low-frequency magnetic field frequency domain characteristics according to Embodiment 1 or any possible implementation thereof.

[0147] Specifically, a processor can be implemented in hardware or software. When implemented in hardware, the processor can be a logic circuit, an integrated circuit, etc. When implemented in software, the processor can be a general-purpose processor that reads software code stored in memory. This memory can be integrated into the processor or located outside the processor and exist independently.

[0148] In the above embodiments, implementation can be achieved, in whole or in part, through software, hardware, firmware, or any combination thereof. When implemented in software, it can be implemented, in whole or in part, as a computer program product. The computer program product includes one or more computer instructions. When the computer program instructions are loaded and executed on a computer, all or part of the processes or functions described in the embodiments of the present invention are generated. The computer can be a general-purpose computer, a special-purpose computer, a computer network, or other programmable system. The computer instructions can be stored in a computer-readable storage medium or transmitted from one computer-readable storage medium to another. For example, the computer instructions can be transmitted from one website, computer, server, or data center to another via wired (e.g., coaxial cable, fiber optic, digital subscriber line (DSL)) or wireless (e.g., infrared, wireless, microwave, etc.) means.

[0149] It is obvious to those skilled in the art that the modules or steps of the present invention described above can be implemented using general-purpose computing systems. They can be centralized on a single computing system or distributed across a network of multiple computing systems. Optionally, they can be implemented using program code executable by a computing system, thereby storing them in a storage system for execution by the computing system. In some cases, the steps shown or described can be performed in a different order than those presented herein, or they can be fabricated as separate integrated circuit modules, or multiple modules or steps can be fabricated as a single integrated circuit module. Thus, the present invention is not limited to any particular combination of hardware and software.

[0150] Although the present invention has been described in detail above with general descriptions and specific embodiments, modifications or improvements can be made to it, which will be obvious to those skilled in the art. Therefore, all such modifications or improvements made without departing from the spirit of the present invention fall within the scope of protection claimed by the present invention.

Claims

1. A non-intrusive anti-theft method for mobile terminals based on the frequency domain characteristics of low-frequency magnetic fields, characterized in that, include: By activating the magnetic field transmission module, a set low-frequency magnetic field is emitted; the set low-frequency magnetic field is a low-frequency signal that is not an integer multiple of the power frequency and is superimposed with a unique regional identity code. Based on the aforementioned low-frequency magnetic field, raw triaxial magnetic field data is acquired through a dual-mode sensing receiver; the raw triaxial magnetic field data is then subjected to high-pass filtering to remove the DC component of the Earth's magnetic field, thereby obtaining three-dimensional AC magnetic field data. Based on the three-dimensional AC magnetic field data, the Euclidean norm is calculated; based on the Euclidean norm, the three-dimensional AC magnetic field data is converted into a one-dimensional scalar signal. Based on the one-dimensional scalar signal, the magnetic field energy value corresponding to the target frequency in the set low-frequency magnetic field is extracted by the Gosser algorithm; the area identity code in the set low-frequency magnetic field is demodulated and the area identity code is verified to obtain the verification result. Based on the magnetic field energy value and the verification result, the safety status of the protected object is determined by setting hysteresis comparison and multi-level decision logic, and the corresponding alarm operation is executed when the alarm triggering condition is met.

2. The mobile terminal contactless anti-theft method based on low-frequency magnetic field frequency domain characteristics according to claim 1, characterized in that, The carrier frequency of the set low-frequency magnetic field is 15Hz to 30Hz; the set low-frequency magnetic field drives the H-bridge circuit through bipolar pulse width modulation, and in conjunction with the LC series resonant circuit, the driving signal is shaped into a quasi-sine wave; the regional identity code is superimposed through frequency shift keying or amplitude shift keying.

3. The mobile terminal contactless anti-theft method based on low-frequency magnetic field frequency domain characteristics according to claim 2, characterized in that, The formula for calculating the three-dimensional AC magnetic field data is: In the formula, This represents the three-dimensional alternating magnetic field data at time n. This represents the three-dimensional alternating magnetic field data at time n-1; This represents the original three-dimensional magnetic field data at time n; This represents the original three-dimensional magnetic field data at time n-1; These are the filter coefficients.

4. The mobile terminal contactless anti-theft method based on low-frequency magnetic field frequency domain characteristics according to claim 3, characterized in that, The formula for calculating the Euclidean norm is as follows: In the formula, The signal is a one-dimensional scalar signal at time n. , , These represent the components of the three-dimensional AC magnetic field data at time n in the x-axis, y-axis, and z-axis directions, respectively.

5. The mobile terminal contactless anti-theft method based on low-frequency magnetic field frequency domain characteristics according to claim 4, characterized in that, In the process of extracting the magnetic field energy value corresponding to the target frequency in the set low-frequency magnetic field using the Gossel algorithm, the formula for calculating the magnetic field energy value is as follows: In the formula, The angular frequency corresponding to the target frequency; To set the carrier frequency for the low-frequency magnetic field; This represents the sampling rate of the original triaxial magnetic field data; These are the iteration coefficients; This is the result of the iterative calculation at time n. N represents the total number of sampling points in a single energy extraction. This represents the magnetic field energy value corresponding to the target frequency.

6. The mobile terminal contactless anti-theft method based on low-frequency magnetic field frequency domain characteristics according to claim 5, characterized in that, In the process of determining the security status of the protected object by setting hysteresis comparison and multi-level decision logic, a high threshold is preset. and low threshold ,and > ;when When, the protected object is determined to be in a safe state; when And the duration exceeds the detection time. When this condition is met, it is determined to be an alarm trigger condition.

7. A mobile terminal contactless anti-theft system based on low-frequency magnetic field frequency domain characteristics, employing the mobile terminal contactless anti-theft method based on low-frequency magnetic field frequency domain characteristics as described in any one of claims 1-6, characterized in that, include: The low-frequency magnetic field transmitting unit is used to transmit a set low-frequency magnetic field by activating the magnetic field transmitting module; the set low-frequency magnetic field is a low-frequency signal that is not an integer multiple of the power frequency and is superimposed with a unique regional identification code. A three-dimensional AC magnetic field data acquisition unit is used to acquire raw three-axis magnetic field data through a dual-mode sensing receiver based on the set low-frequency magnetic field. The original triaxial magnetic field data is subjected to high-pass filtering to remove the DC component of the geomagnetic field and obtain three-dimensional AC magnetic field data. A three-dimensional AC magnetic field data conversion unit is used to calculate the Euclidean norm based on the three-dimensional AC magnetic field data; and to convert the three-dimensional AC magnetic field data into a one-dimensional scalar signal based on the Euclidean norm. The magnetic field energy value acquisition and regional identity code verification unit is used to extract the magnetic field energy value corresponding to the target frequency in the set low-frequency magnetic field based on the one-dimensional scalar signal using the Gosser algorithm; demodulate the regional identity code in the set low-frequency magnetic field and complete the regional identity code verification to obtain the verification result. The safety status determination and processing unit is used to determine the safety status of the protected object based on the magnetic field energy value and the verification result by setting hysteresis comparison and multi-level decision logic, and to execute the corresponding alarm operation when the alarm triggering condition is met.

8. The mobile terminal contactless anti-theft system based on low-frequency magnetic field frequency domain characteristics according to claim 7, characterized in that, In the low-frequency magnetic field transmitting unit, the carrier frequency of the set low-frequency magnetic field is 15Hz to 30Hz; the set low-frequency magnetic field drives the H-bridge circuit through bipolar pulse width modulation, and in conjunction with the LC series resonant circuit, shapes the driving signal into a quasi-sine wave; and the regional identity code is superimposed through frequency shift keying or amplitude shift keying.

9. A mobile terminal contactless anti-theft system based on low-frequency magnetic field frequency domain characteristics according to claim 8, characterized in that, In the three-dimensional AC magnetic field data acquisition unit, the calculation formula for the three-dimensional AC magnetic field data is as follows: In the formula, This represents the three-dimensional alternating magnetic field data at time n. This represents the three-dimensional alternating magnetic field data at time n-1; This represents the original three-dimensional magnetic field data at time n; This represents the original three-dimensional magnetic field data at time n-1; These are the filter coefficients.

10. A mobile terminal contactless anti-theft system based on low-frequency magnetic field frequency domain characteristics according to claim 9, characterized in that, In the three-dimensional AC magnetic field data conversion unit, the Euclidean norm is calculated using the following formula: In the formula, The signal is a one-dimensional scalar signal at time n. , , These represent the components of the three-dimensional AC magnetic field data at time n in the x-axis, y-axis, and z-axis directions, respectively. In the magnetic field energy value acquisition and regional identity coding verification unit, during the process of extracting the magnetic field energy value corresponding to the target frequency in the set low-frequency magnetic field using the Goser algorithm, the calculation formula for the magnetic field energy value is as follows: In the formula, The angular frequency corresponding to the target frequency; To set the carrier frequency for the low-frequency magnetic field; This represents the sampling rate of the original triaxial magnetic field data; These are the iteration coefficients; This is the result of the iterative calculation at time n. N represents the total number of sampling points in a single energy extraction. This represents the magnetic field energy value corresponding to the target frequency. In the security status determination and processing unit, during the process of determining the security status of the protected object by setting hysteresis comparison and multi-level decision logic, a high threshold is preset. and low threshold ,and > ;when When, the protected object is determined to be in a safe state; when And the duration exceeds the detection time. When this condition is met, it is determined to be an alarm trigger condition.

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