A security gate and a metal detection method and control detection device for a security gate

Abstract

The application discloses a security door and a metal detection method for the security door. The method comprises the following steps: generating a pulse coding sequence, wherein the code type length of the pulse coding sequence is N, N is an integer greater than 1, the pulse coding sequence is used for controlling the transmitting coil of the security door to emit electromagnetic waves at intervals, and each value in the pulse coding sequence is used for representing a transmitting waveform with a specific phase; acquiring a digital receiving signal corresponding to the pulse coding sequence, and processing the digital receiving signal to focus electromagnetic energy corresponding to the digital receiving signal; and determining a metal detection result based on the processed digital receiving signal. By applying the application, the detection capability of small metal can be effectively improved, and the overall detection performance can be improved.

Description

Technical Field

[0001] This application relates to metal detection technology, and in particular to a security gate and a metal detection method and control detection device for the security gate. Background Technology

[0002] Metal detectors work by using a magnetic field to detect metal objects that pass through them. They are widely used in airports and train stations. However, there are two major problems with the metal detectors currently on the market: First, their detection sensitivity is not high. While they can detect large metals such as mobile phones, they have great difficulty detecting small metals such as paperclips. Second, their anti-interference ability is poor. Neighboring metal detectors may interfere with each other, reducing the accuracy of metal detection.

[0003] To address the two issues mentioned above, most security gates at airports, high-speed rail stations, and subway stations are currently idle, requiring staff to use handheld metal detectors to scan every person's entire body. However, the drawbacks of this method are obvious. Manual scanning not only consumes manpower and increases labor costs, but also increases travel time at airport and train station security checkpoints because security personnel need to scan everyone's entire body, significantly contributing to long queues at station entrances. This detection method urgently needs to be addressed in an environment of continuously increasing traffic pressure. Summary of the Invention

[0004] This application provides a security gate and a metal detection method and control device for the security gate, which can effectively improve the detection capability of small metals and improve the overall detection performance.

[0005] To achieve the above objectives, this application adopts the following technical solution:

[0006] In a first aspect, embodiments of this application provide a metal detection method for a security gate, comprising:

[0007] Generate a pulse code sequence, wherein the code pattern length of the pulse code sequence is N, where N is an integer greater than 1. The pulse code sequence is used to control the transmitting coil of the security gate to transmit electromagnetic waves intermittently. Each value in the pulse code sequence is used to characterize a transmission waveform with a specific phase.

[0008] The digital received signal is obtained by processing the signal received by the receiving coil of the security gate under the action of electromagnetic waves, and the digital received signal is further processed to focus the electromagnetic energy corresponding to the digital received signal.

[0009] The metal detection result is determined based on the processed digital received signal.

[0010] Secondly, embodiments of this application provide a control and detection device for a security gate, comprising: an encoding excitation unit, a digital receiving signal processing unit, and a detection unit;

[0011] The encoding excitation unit is used to generate a pulse coding sequence, wherein the code pattern length of the pulse coding sequence is N, where N is an integer greater than 1. The pulse coding sequence is used to control the transmitting coil of the security gate to transmit electromagnetic waves intermittently. Each value in the pulse coding sequence is used to characterize a transmission waveform with a specific phase.

[0012] The digital receiving signal processing unit is used to acquire the digital receiving signal obtained after processing the signal received by the receiving coil of the security gate under the action of electromagnetic waves, and to process the digital receiving signal to focus the electromagnetic energy corresponding to the digital receiving signal.

[0013] The detection unit is used to determine the metal detection result based on the processed digital received signal.

[0014] Thirdly, embodiments of this application provide a security gate, including: a control and detection device, a digital-to-analog conversion unit, a transmitting circuit, a transmitting coil, a receiving coil, a receiving circuit, and an analog-to-digital conversion unit;

[0015] A control detection device is used to generate a pulse code sequence, wherein the code pattern length of the pulse code sequence is N, where N is an integer greater than 1, and each value in the pulse code sequence is used to characterize a transmission waveform with a specific phase.

[0016] A digital-to-analog converter is used to modulate a pulse-coded sequence into a transmitted signal;

[0017] The transmitting circuit is used to process the transmitted signal to generate the excitation signal for the transmitting coil;

[0018] A transmitting coil is used to intermittently transmit electromagnetic waves under the excitation of an excitation signal;

[0019] A receiving coil is used to receive signals generated by electromagnetic waves.

[0020] The receiving circuit is used to process the signal received by the receiving coil to obtain an analog received signal;

[0021] The analog-to-digital conversion unit is used to demodulate the analog received signal and generate a digital received signal corresponding to the pulse code sequence.

[0022] The control and detection device is also used to acquire digital received signals and process them to focus the electromagnetic energy corresponding to the digital received signals; based on the processed digital received signals, the metal detection result is determined.

[0023] As can be seen from the above technical solution, in this application, a pulse sequence is generated, the pulse sequence code length is greater than 1, and each value is used to characterize a transmission waveform with a specific phase; the pulse sequence is used to control the transmitting coil of the security gate to emit electromagnetic waves intermittently; next, the digital received signal obtained after processing the signal received by the receiving coil of the security gate under the action of electromagnetic waves is acquired, and the digital received signal is further processed to focus the electromagnetic energy corresponding to the digital received signal; here, since the signal controlling the transmitting coil to emit electromagnetic waves is a pulse sequence of a certain code length, and the transmitting coil is controlled to emit electromagnetic waves intermittently, after adaptive processing of the digital received signal, compared with the existing method of continuously emitting electromagnetic waves, the bandwidth corresponding to the processed digital received signal can be narrowed, and the electromagnetic energy corresponding to the digital received signal can be focused accordingly; finally, the metal detection result is determined based on the processed digital received signal. Since the electromagnetic energy corresponding to the processed digital received signal is focused and the amplitude is increased, the sensing and detection capability for small metals can be effectively improved. Attached Figure Description

[0024] Figure 1 A schematic diagram of metal detection using a traditional security gate;

[0025] Figure 2 This is a schematic diagram of the basic process of the metal detection method used in the security gate in this application;

[0026] Figure 3 This is a schematic diagram of the security gate used in the metal detection method of this application;

[0027] Figure 4 This is a schematic diagram illustrating the specific process of electromagnetic wave transmission and reception and metal detection for a security gate in a specific embodiment of this application;

[0028] Figure 5 This is a schematic diagram of a metal detection system used in a security gate in a specific embodiment;

[0029] Figure 6 Example diagram of algorithm structure for convolution processing;

[0030] Figure 7a and Figure 7b These are time-domain diagrams of the emitted signal and echo signal when metal detection is performed according to the method of this application, as shown in the example of this application.

[0031] Figure 8a and Figure 8b The time-domain plots of the transmitted signal and the echo signal are shown for interference scenario 1.

[0032] Figure 9a and Figure 9b The time-domain plots of the transmitted signal and the echo signal are shown for interference scenario 2.

[0033] Figure 10 This is an example diagram of the hardware structure for implementing a security gate. Detailed Implementation

[0034] To make the objectives, technical means, and advantages of this application clearer, the following detailed description is provided in conjunction with the accompanying drawings.

[0035] First, we analyze the problems of traditional security gates: weak small metal detection capability and poor anti-interference ability. A schematic diagram of metal detection using a traditional security gate is shown below. Figure 1 As shown, on the transmitting side of the security gate, a continuous and fixed sine wave is generated. After amplification and filtering by the transmitting circuit, it excites the transmitting coil to continuously emit electromagnetic waves. On the receiving side of the security gate, the receiving coil acquires the signal under the influence of the electromagnetic wave. After filtering and amplification by the receiving circuit, a received signal used for metal detection is obtained. When metal is present inside the security gate, the metal affects the magnetic field distribution inside the gate, causing a change in the amplitude of the received signal. By processing the change in the amplitude of the received signal, metal detection can be achieved. Since the magnitude of the change in magnetic field strength is related to the volume of the metal and the magnetic field strength, under the premise that the magnetic field strength remains constant, small metals have a relatively small volume and a relatively small impact on the magnetic field strength, resulting in a relatively small change in the amplitude of the echo signal. This reduces the accuracy of detection and makes the detection capability for small metals relatively poor.

[0036] To enhance the detection capability of small metals, an obvious approach is to increase the magnetic field strength. Specifically, this can be achieved by increasing the power of the transmitted signal used to excite the transmitting coil on the transmitting side. The greater the transmitted signal power, the stronger the magnetic field emitted by the transmitting coil. However, increasing the transmitted signal power generates severe electromagnetic interference, causing the data received by the receiving coil to be heavily contaminated with circuit board interference, which is detrimental to the detection of small metals. Therefore, increasing the magnetic field strength is not conducive to the detection of small metals.

[0037] Furthermore, in traditional metal detection using security gates, the transmitted signal frequency is usually the same, and the magnetic field emitted by the transmitting coil exists throughout the entire space. When two security gates are close together, the change in the magnetic field of the adjacent gate caused by metal inside can be captured by the receiving coil of the current gate and converted into a received signal for processing. However, because the two gates transmit signals at the same frequency, false metal detections can occur. To avoid this interference, adjacent security gates can be staggered in frequency. However, the suitable frequencies for metal detection are usually within a fixed range, and different security gates using different frequencies will result in differences in metal detection capabilities.

[0038] As can be seen from the above, increasing the power of traditional security gates to improve their ability to detect small metals will generate significant electromagnetic interference, leading to a decrease in the signal-to-noise ratio. The signals of small metals will be submerged in the electromagnetic interference. Therefore, the ability of traditional security gates to detect small metals cannot be improved by increasing the power of the transmitted signal. To avoid mutual interference between different security gates, they need to operate at different operating frequencies. However, there is an optimal detection frequency for security gates to detect metals. Otherwise, the consistency of metal detection by different security gates will deteriorate. Therefore, improving the anti-interference capability cannot be achieved by staggering the frequencies of security gates.

[0039] Based on the above considerations, this application does not change the transmission power and transmission frequency on the transmitting side. Instead, it adopts an encoding excitation scheme and focuses the electromagnetic energy in conjunction with the receiving processing to achieve metal detection. In this way, at the transmitting end, the transmitting coil is excited by the pulse encoding sequence to transmit electromagnetic waves at intervals. At the same time, pulse compression is achieved in conjunction with the processing at the receiving end to focus the electromagnetic energy of the digital received signal, thereby increasing the amplitude of the processed digital received signal and thus improving the detection capability for small metals.

[0040] Figure 2 This is a schematic diagram of the basic flow of the metal detection method in this application. Figure 2 As shown, the method includes:

[0041] Step 201: Generate a pulse-coded sequence.

[0042] In this application, the pulse-coded sequence has a code length of N, where N is an integer greater than 1. Each value in the pulse-coded sequence represents a transmission waveform with a specific phase. The pulse-coded sequence is used to control the transmitting coil of a security gate to intermittently transmit electromagnetic waves.

[0043] As mentioned earlier, in existing metal detection methods for security gates, the excitation signal of the transmitting coil is a continuous sinusoidal signal, which can typically be obtained by modulating a very wide pulse signal to excite the transmitting coil to continuously emit electromagnetic waves. In this application, without changing the transmitting power and frequency, to increase the amplitude of the signal used for metal detection, pulse compression is used. By processing the digital received signal, the pulse width of the processed echo signal is compressed. Since the electromagnetic energy of the digital received signal is constant, the energy of the processed echo signal is also constant. Because the pulse width is compressed, the signal amplitude can be effectively increased accordingly.

[0044] Step 202: Obtain the digital received signal obtained after processing the signal received by the receiving coil of the security gate under the action of electromagnetic waves, and process the digital received signal to focus the electromagnetic energy corresponding to the digital received signal.

[0045] The digital received signal is obtained by processing the signal received by the receiving coil of the security gate under the influence of electromagnetic waves. Specifically, the receiving coil of the security gate receives the signal, and the received signal is processed by the receiving circuit and analog-to-digital converter to obtain the digital received signal. The processing may include amplification and filtering by the receiving circuit, and demodulation by the analog-to-digital converter. The processing of the receiving coil, receiving circuit, and analog-to-digital converter can be the same as in existing metal detection methods.

[0046] This step is used to acquire the digital received signal and process it according to the pulse-coded sequence. For ease of subsequent description, the processed digital received signal will be referred to as the echo signal. Since the pulse-coded sequence excites the transmitting coil to emit electromagnetic waves intermittently—that is, the pulse-coded sequence is emitted intermittently rather than continuously—processing the digital received signal according to the pulse-coded sequence allows the coherent portion of the received signal to be accumulated, while the incoherent portion is suppressed. This focuses the electromagnetic energy corresponding to the digital received signal, thus achieving pulse width compression compared to the wide pulse corresponding to a continuous sine wave, and increasing the amplitude of the echo signal.

[0047] Preferably, when optimal reception processing is used for the digital received signal, electromagnetic energy can be better focused, thereby most effectively increasing the amplitude of the echo signal. Optimal reception processing involves using the result of reversing all values ​​in the pulse-coded sequence as the convolution coefficients.

[0048] Step 203: Determine the metal detection result based on the processed digital received signal.

[0049] After the processing in step 202 above, the amplitude of the processed digital received signal (i.e., the echo signal) can be effectively increased. Because the amplitude of the echo signal is increased, the detection capability of small metals can be effectively improved when performing metal detection based on the echo signal.

[0050] This concludes the basic process of the metal detection method for security gates in this application. Through the above method, on the one hand, a pulse-coded sequence is generated to control the transmitting coil to intermittently emit electromagnetic waves; on the other hand, the digital received signal is processed according to the pulse-coded sequence to focus the electromagnetic energy corresponding to the digital received signal. This synergy achieves pulse compression, effectively increasing the amplitude of the processed digital received signal, thereby improving the detection capability for small metals.

[0051] The metal detection method described in this application can be implemented through a control and detection device in a security gate, which, in conjunction with other modules of the security gate, achieves electromagnetic wave transmission and reception and metal detection. The specific implementation of the metal detection method in this application is illustrated below through specific embodiments. In these embodiments, the complete process of electromagnetic wave transmission and reception and metal detection is described in conjunction with other modules in the security gate. Figure 3 This is a schematic diagram of a security gate using the metal detection method described in this application. Figure 4 This is a schematic diagram illustrating the specific process of electromagnetic wave transmission and reception and metal detection in a particular embodiment. Figure 3 As shown, the security gate in a specific embodiment includes a control and detection device, a digital-to-analog converter, a transmitting circuit, a transmitting coil, a receiving coil, a receiving circuit, and an analog-to-digital converter. The connection between the transmitting coil and the receiving coil represents the magnetic field between them, or can be understood as a connection through a magnetic field. Figure 3 and 4 As shown, the specific process of electromagnetic wave transmission and reception and metal detection includes:

[0052] Step 401: Control the detection device to generate a pulse code sequence.

[0053] The pulse coding sequence can be any sequence, or preferably, to obtain better electromagnetic energy focusing effect, the pulse coding sequence can be a sequence with autocorrelation characteristics, such as the Barker code sequence.

[0054] Step 402: The control detection device controls the digital-to-analog converter to modulate the pulse code sequence into a transmission signal.

[0055] As mentioned earlier, each value in the pulse-coded sequence represents a transmitted waveform with a specific phase. In this step, the pulse-coded sequence is modulated to generate a transmitted signal using phase modulation. The transmitted signal waveforms corresponding to the pulse-coded sequence can be identical. For example, if the pulse-coded sequence is [+1,+1,+1,+1,+1,+1], the corresponding transmitted signal waveforms can all be sine waves with a phase of 0. Alternatively, the transmitted signal waveforms corresponding to the pulse-coded sequence can also include sub-waveforms with phase differences. For example, with a phase difference of 180 degrees, the pulse-coded sequence [+1,-1,-1,+1] could correspond to a sine wave with a phase of 0 + a sine wave with a phase of 180 degrees + a sine wave with a phase of 180 degrees + a sine wave with a phase of 0.

[0056] When controlling the modulation of the pulse code sequence, the digital-to-analog converter can be instructed to modulate the pulse code sequence to a specified frequency, usually the frequency range most suitable for metal detection, such as the transmission frequency of an existing security gate.

[0057] In addition, considering the possibility of security gates being arranged close together, in order to improve the anti-interference between different security gates, adjacent security gates in this embodiment use different pulse code sequences to distinguish them from each other, and preferably, the pulse code sequence of any security gate includes different values.

[0058] Step 403: The transmitting circuit of the security gate processes the transmitted signal and excites the transmitting coil to emit electromagnetic waves intermittently.

[0059] The processing performed by the transmitting circuit in this step can be, for example, filtering or amplification, and can be the same as the processing performed by the transmitting circuit in existing security gates.

[0060] The transmitting coil, excited by the output signal of the transmitting circuit, intermittently transmits electromagnetic waves. To achieve pulse compression in the overall scheme, the generated pulse-coded sequence and the transmission signal need to be intermittently used to control the transmitting coil's electromagnetic wave transmission. Specifically, a complete pulse-coded sequence and transmission signal excite the transmitting coil to transmit one set of electromagnetic waves, then the transmission is paused, and in the next transmission period, the complete pulse-coded sequence and transmission signal excite the transmitting coil to transmit the next set of electromagnetic waves. The specific transmission interval can be set based on practical experience; this application does not impose any limitations on it.

[0061] Step 404: The receiving coil of the security gate acquires the signal under the action of electromagnetic waves, and after processing by the receiving circuit, it obtains an analog received signal.

[0062] In this step, the receiving coil acquires the signal under the influence of electromagnetic waves. The receiving circuit then processes this signal through filtering, amplification, and other methods, outputting a signal referred to as the analog received signal. The processing of the receiving coil and receiving circuit can be the same as that of existing security gates. Furthermore, the processing of the receiving coil and receiving circuit can be symmetrical to that of the transmitting coil and transmitting circuit, and the resulting analog received signal corresponds to the transmitted signal obtained in step 402.

[0063] Step 405: The control and detection device controls the analog-to-digital conversion unit to demodulate the analog received signal to obtain the digital received signal.

[0064] In this step, the control and detection device performs demodulation control, and the analog-to-digital converter (ADC) completes the demodulation operation. Specifically, the control and detection device controls the ADC to perform demodulation in a manner corresponding to that of the aforementioned digital-to-analog converter (DAC). Specifically, based on the correspondence between phase and pulse code sequence in the DAC, the analog received signal input to the ADC is converted into a digital received signal for output. For example, if during modulation processing, the digit 1 in the pulse code sequence represents a phase of 0 degrees, and the digit -1 represents a phase of 180 degrees, then in the ADC, when the phase of the analog received signal is 0 degrees, the corresponding digital received signal is determined to be 1; when the phase of the analog received signal is 180 degrees, the corresponding digital received signal is determined to be -1.

[0065] Step 406: Process the digital received signal to focus the electromagnetic energy corresponding to the digital received signal to obtain the echo signal.

[0066] In this embodiment, the processing of the digital received signal may specifically include:

[0067] a. Determining convolution coefficients based on pulse coding sequences;

[0068] The convolution coefficients can be set according to the pulse code sequence to achieve reception processing adapted to the pulse code sequence. In order to achieve better aggregation of electromagnetic energy corresponding to the digital received signal, preferably, all the values ​​in the pulse code sequence can be arranged in reverse order to obtain the convolution coefficients. Accordingly, the processing of the digital received signal is the optimal reception processing.

[0069] b. Determine the sequence of digital received signals at each receiving moment;

[0070] The code length of the digital received signal sequence is the same as that of the pulse code sequence. Different numerical bits in the digital received signal sequence correspond to the receiving time, and the values ​​of the different numerical bits are determined based on the signals received by the receiving coil at each receiving time. More specifically, the first numerical bit in the digital received signal sequence corresponds to the current receiving time, and the second to Nth numerical bits correspond to the receiving times preceding the current receiving time, respectively. That is, assuming the current receiving time is N, the receiving times corresponding to the first to Nth numerical bits are time N to time 1, respectively.

[0071] For example, if the pulse code sequence is a binary sequence with a code length of 5 [+1,+1,-1,-1,+1], and the receiving coil has a reception delay of 2 seconds, then the signal received by the receiving coil in the first second after the transmitting coil emits the electromagnetic wave is 0, and the signal is not received until the third second. Therefore, the digital received signal sequence corresponding to the first second is [0,0,0,0,0], the second second is [0,0,0,0,0], the third second is [+1,0,0,0,0], the fourth second is [+1,+1,0,0,0], the fifth second is [-1,+1,+1,0,0], and the sixth second is [-1,+1,+1,0,0]. The digital received signal sequence is [-1,-1,+1+1,0]. The digital received signal sequence corresponding to the 7th second is [+1,-1,-1,+1,+1], the digital received signal sequence corresponding to the 8th second is [0,+1,-1,-1,+1], the digital received signal sequence corresponding to the 9th second is [0,0,+1,-1,-1], the digital received signal sequence corresponding to the 10th second is [0,0,0,+1,-1], the digital received signal sequence corresponding to the 11th second is [0,0,0,0,+1], and the digital received signal sequence corresponding to the 11th second is [0,0,0,0,0]. The convolution coefficient sequence is the inverted sequence of the complete pulse code sequence, i.e., [+1,-1,-1,+1,+1].

[0072] c. Perform convolution calculation on the digital received signal sequence at each receiving time with the convolution coefficients, and use the convolution result as the amplitude of the processed received signal at each receiving time.

[0073] For the digital received signal sequence determined in b, the echo signal is obtained through convolution with the convolution coefficients. By generating a pulse-coded sequence and transmitting it intermittently, combined with convolution processing, pulse compression can be achieved, thus focusing the electromagnetic energy corresponding to the digital received signal. The choice of convolution coefficients affects the effectiveness of electromagnetic energy focusing. As mentioned earlier, when the convolution coefficients are the complete inverted sequence of the pulse-coded sequence, optimal reception of the pulse-coded sequence can be achieved through convolution processing, maximizing the focusing of the electromagnetic energy of the digital received signal and maximizing the amplitude of the echo signal at the optimal reception position. Thus, although the amplitude and power of the transmitted signal remain unchanged, the maximum amplitude of the echo signal after convolution processing on the receiving side is still significantly increased.

[0074] Step 407: Determine the metal detection result based on the processed digital received signal.

[0075] This step is used to determine the metal detection result based on the echo signal, and can be performed using various existing methods. In particular, because the maximum amplitude of the echo signal is significantly increased, the changes in small metals reflected in the echo signal are also significantly enhanced. Therefore, metal detection based on such echo signals can effectively improve the accuracy of small metal detection, i.e., improve the detection capability of small metals.

[0076] Meanwhile, the processing in step 406 is for the pulse coding sequence of the current security gate. For other security gates, since the pulse coding sequences differ from each other, the convolution processing of the current security gate can only achieve the maximum amplitude enhancement of the digital received signal sequence B corresponding to the pulse coding sequence A of the current security gate, generating an echo signal C, so that the maximum amplitude of the echo signal C is relatively significantly enhanced. However, for the electromagnetic waves emitted by other security gates through their pulse coding sequence A', even if the receiving coil of the current security gate obtains the corresponding digital received signal through magnetic field induction and processing, the amplitude enhancement effect obtained when the sequences are consistent cannot be obtained because the digital received signal sequence B' is inconsistent with the pulse coding sequence A of the current security gate. Therefore, compared with the case where the digital received signal sequence is consistent with the pulse coding sequence, the amplitude enhancement effect of the echo signal C' generated after processing the digital received signal sequence B' is relatively poor when the two are inconsistent. It can be seen that the amplitude of the echo signal can filter out the interference that is inconsistent with the pulse coding sequence, thereby improving the anti-interference capability and avoiding mutual interference between security gates and false metal detection.

[0077] At this point, Figure 4 The detailed process of the electromagnetic wave transmission and reception and metal detection method shown is now complete.

[0078] Next, a specific implementation example will be given. Figure 5 This is a schematic diagram of a metal detection system used in a security gate, as shown in a specific embodiment. Figure 5 As shown, the specific processing includes:

[0079] S501, generate the pulse coding sequence c(n);

[0080] A pulse code sequence c(n) is generated on the transmitting side, which can be, for example, a 7-bit code sequence (+1+1+1 -1-1+1-1). Each value in this pulse code sequence is used to characterize a transmitted waveform with a specific phase. In this example, the transmitted waveform is a sine wave, where +1 represents a sine wave signal with a phase of 0° and -1 represents a sine wave signal with a phase of 180°.

[0081] Of course, in practical applications, the pulse coding sequence examples given above are not limited to those given above. Appropriate pulse coding sequences can be selected as needed, such as the various sequences shown in Table 1.

[0082] Table 1

[0083] Sequence length N Encoded sequence 5 +1 +1 +1-1+1 7 +1+1 +1-1-1 +1-1 11 +1+1 +1-1 -1-1 +1-1-1 +1-1 13 +1+1+1+1 +1-1-1+1 +1-1 +1-1+1

[0084] S502, the control and detection device controls the digital-to-analog converter to modulate the pulse code sequence onto a specified frequency to generate a transmission signal.

[0085] As mentioned earlier, the amplitude and frequency of the transmitted signal cannot be significantly adjusted. Therefore, phase modulation is used in this embodiment. As described above, +1 represents a phase of 0°, and -1 represents a phase of 180°. The control and detection device controls the digital-to-analog converter (DAC) to perform modulation processing. Specifically, the control and detection device instructs the DAC to perform phase modulation and informs the DAC of the correspondence between the values ​​of the pulse code sequence and the phase.

[0086] S503 uses a transmitting circuit to process the transmitted signal to obtain an excitation signal;

[0087] S504 uses an excitation signal to excite the transmitting coil, causing the transmitting coil to emit electromagnetic waves intermittently;

[0088] S504, the receiving coil receives signals under the action of electromagnetic waves;

[0089] S505, the receiving circuit processes the signal to obtain an analog received signal;

[0090] S506, the control and detection device controls the analog-to-digital conversion unit to demodulate the received signal and obtain a digital received signal;

[0091] S507, the control detection device performs reception processing on the digital received signal corresponding to the pulse code sequence to obtain the echo signal s(n);

[0092] In this example, when processing the digital received signal, the convolution coefficients are the inverted sequence of the complete pulse-coded sequence. Based on the existing transmitting circuit, receiving circuit, transmitting coil, and receiving coil processing, assuming the unit impulse response of the convolution processing unit is d(n) and the transfer function between the transmitting and receiving coils is h(n), the echo signal s(n) obtained after passing through the convolution processing unit can be expressed as:

[0093] s(n)=c(n)*h(n)*d(n)=[c(n)*d(n)]*h(n),

[0094] Where * denotes convolution operation, since the convolution coefficients in the convolution processing unit are the inverted sequence of the complete pulse code sequence, and in this example the pulse code sequence is a sequence with autocorrelation properties, that is, the convolution result of the sequence and its inverted sequence is a unit impulse function, therefore:

[0095] c(n)*d(n)=Nδ(n),

[0096] Where δ(n) is the unit impulse function and N is the length of the pulse code sequence. From the above two equations, it can be seen that s(n) = Nh(n), while in a traditional security gate, s(n) = h(n). Therefore, the maximum amplitude of the echo signal is equivalent to N times the maximum amplitude of the traditional security gate. This clearly demonstrates that the method of this application can obtain an effective echo signal, and the maximum amplitude of the echo signal is significantly improved.

[0097] In this example of convolution processing, the spectrum of the convolution process is the same as the spectrum of the input signal to the convolution processing unit. After convolution processing, the larger the amplitude of the frequency component, the greater the enhancement, and the smaller the amplitude, the weaker the enhancement. In other words, the amplitude of the effective signal in the input signal can be strengthened, while the amplitude of the noise is correspondingly weakened. For example... Figure 6 The diagram shows an example of the convolution processing algorithm structure. The convolution coefficient sequence is formed by reversing the pulse-coded sequence. Under normal receiving conditions, the digital received signal sequence and the pulse-coded sequence are the same. Therefore, the convolution processing of the digital received signal sequence and the convolution coefficient sequence is equivalent to performing an autocorrelation operation on the pulse-coded sequence. For example, assuming the pulse-coded sequence is [+1 +1 +1 -1 -1 +1], then the corresponding convolution coefficients are [+1 -1 -1 +1 +1 +1]. The convolution processing is equivalent to performing an autocorrelation operation on the pulse-coded sequence, that is, convolving [+1 +1 +1 -1 -1 +1] and [+1 -1 -1 +1 +1 +1]. Correspondingly, the maximum amplitude of the convolution result is 6, which can maximize the concentration of the electromagnetic energy corresponding to the received signal, thus significantly increasing the maximum amplitude of the echo signal.

[0098] The following specific example illustrates that, using the pulse-coded inverted sequence method for the above convolution coefficients, under the premise of using the same transmitted signal amplitude as the existing method, an echo signal with maximum amplitude enhancement can be obtained, as shown in 7a and 7b.

[0099] Specifically, when metal detection is performed in the traditional way, the time domain diagram of the signal transmitted by the transmitting side of the security gate is a continuous sine wave signal. Assuming that there is no energy loss in the spatial transmission from the transmitting coil to the receiving coil, and the amplitude of the transmitted signal is 1, then the amplitude of the digital received signal is the same as the amplitude of the transmitted signal, which is also 1.

[0100] Figure 7a and 7bThe following are time-domain plots of the transmitted and echo signals during metal detection according to the method of this application in this example. The pulse coding sequence is [+1+1+1 -1-1+1 -1]. The convolution coefficients of the receiver-side convolution process correspond to the above pulse coding sequence. Assuming there is no energy loss in the spatial transmission from the transmitting coil to the receiving coil, and the amplitude of the transmitted signal on the transmitting side is 1, the time-domain plot of the echo signal obtained after convolution processing is as follows. Figure 7b As shown, the maximum amplitude of the echo signal reaches 7, which is equivalent to 7 times the amplitude of the first signal on the transmitting side. As a result, the amplitude of the echo signal is greatly improved. Therefore, when using this echo signal for metal detection, the detection capability of small metals can be greatly improved.

[0101] The following is a concrete example illustrating the anti-interference effect of adjacent security gates. Assume the current security gate is gate A, and its adjacent security gate is gate B. Gate A uses optimal reception processing for digital signals, i.e., the convolution coefficients are the inverted sequence of the complete pulse code sequence. The following diagram illustrates the reception of interference signals by gate A under the magnetic fields generated by the transmitting coils of adjacent security gates B and C, which are excited by a sine wave of the same frequency and other code patterns of the same frequency, respectively.

[0102] Interference Scenario 1: Assume that the current security gate uses the pulse coding sequence [+1+1+1 -1-1+1 -1] to generate the transmission signal, controlling the transmitting coil to intermittently emit electromagnetic waves. The time-domain diagram of the transmission signal is as follows. Figure 7a As shown, the signal amplitude is 1; the adjacent security gate B generates a sinusoidal signal as the transmission signal, which, after processing by the transmission circuit, is used to excite the transmission coil to intermittently emit electromagnetic waves. The time-domain diagram of the transmission signal is shown below. Figure 8a As shown, the signal amplitude is 1. The magnetic field of security gate B is located throughout the space. The receiving coil of security gate A senses this magnetic field. Therefore, the signal acquired by the receiving coil of security gate A includes signal component B1 under the influence of the electromagnetic wave emitted by security gate B. This signal component B1 is considered an interference signal for security gate A. Next, we will analyze the processing of signal component B1 by security gate A separately. Specifically, signal component B1 is processed by the transmitting circuit and the analog-to-digital converter to obtain the digital received signal B2. Then, B2 is convolved with the pulse code sequence corresponding to that of security gate A (i.e., convolved with the convolution coefficients of security gate A). The result of the convolution is called the echo signal B3. The time domain diagram of echo signal B3 is shown below. Figure 8b As shown; simultaneously, the signal acquired by the receiving coil of security gate A also includes signal component A1 under the influence of the electromagnetic wave emitted by security gate A. The time-domain diagram of the echo signal A3 obtained after processing this signal component A1 is as described above. Figure 7b As shown. Figure 7b and 8b A comparison reveals that, Figure 7b The maximum amplitude of the echo signal A3 shown is 7. Figure 8b The maximum amplitude of echo signal B3 shown is 3, which is nearly 60% lower than that of echo signal A3. This is because the convolution coefficients of security gate A for signal component B1 do not match the transmitted signal of security gate B. Therefore, the maximum amplitude of the convolution output echo signal B3 cannot achieve the same amplitude increase as echo signal A3, and the difference in amplitude increase between the two is significant. It should also be noted that, to characterize the maximum interference, the magnetic field transmission was performed with security gate B and security gate A in overlapping positions. In reality, security gates B and A will not overlap, thus further reducing the magnetic field strength of security gate B, resulting in even greater attenuation of echo signal B3.

[0103] Interference Scenario 2: Assume that the neighboring security gate C of the current security gate A uses a different pulse code sequence than security gate A [+1,-1,+1,-1,-1,+1,+1], and the time domain diagram of the transmitted signal is as follows. Figure 9a As shown, the signal amplitude is 1; the magnetic field of security gate C is located throughout the space, and the receiving coil of security gate A senses this magnetic field. Therefore, the signal acquired by the receiving coil of security gate A includes the signal component C1 under the influence of the electromagnetic wave emitted by security gate C. Next, we will analyze the processing of signal component C1 by security gate A separately. Specifically, signal component C1 is processed by the transmitting circuit and the analog-to-digital conversion unit to obtain the digital received signal C2. Then, C2 is convolved with the pulse code sequence corresponding to that of security gate A (i.e., convolved with C2 using the convolution coefficients of security gate A). The result of the convolution is called the echo signal C3, and the time-domain diagram of the echo signal C3 is shown below. Figure 9b As shown. Meanwhile, as mentioned earlier, the signal acquired by the receiving coil of security gate A also includes a signal component A1 caused by the electromagnetic wave emitted by security gate A. The time-domain diagram of the echo signal A3 obtained after processing this signal component A1 is shown above. Figure 7b As shown. Figure 9b and Figure 7b A comparison reveals that, Figure 7b The maximum amplitude of the echo signal A3 shown is 7. Figure 9bThe maximum amplitude of the echo signal C3 shown is 3, and the maximum amplitude of echo signal C3 is attenuated by nearly 60% compared to echo signal A3. This is because, for signal component C1, the convolution coefficients of the security gate A in the convolution process do not match the transmitted signal of security gate A. Therefore, the maximum amplitude of the echo signal C3 output by convolution cannot achieve the same amplitude increase as echo signal A3, and the difference in amplitude increase between the two is significant. Furthermore, similar to interference case 1 above, in the above signal processing, to characterize the maximum interference, the magnetic field transmission is performed with the positions of security gate C and security gate A overlapping. In other words, in reality, security gate C and security gate A will not overlap, therefore the magnetic field strength of security gate C will be further reduced, resulting in even greater attenuation of the echo signal.

[0104] From the above Figure 8a , 8b As shown in Figures 9a and 9b, for other nearby security gates using the same frequency sine wave or other code patterns, the echo signal B3 / C3 generated after processing the interference signal B1 / C1 of the current security gate is significantly weaker than the correct echo signal A3 of the security gate, and will not be mistaken for the correct echo signal. This shows that by having adjacent security gates use different pulse coding sequences, the mutual interference between adjacent security gates can be effectively reduced.

[0105] The above describes the specific implementation of the metal detection method in this application. As can be seen from the above, the metal detection method for security gates in this application, on the one hand, generates a pulse code sequence at the transmitting end and excites the transmitting coil to emit electromagnetic waves intermittently; on the other hand, through convolution processing corresponding to the pulse code sequence at the receiving end, pulse compression can be effectively achieved, concentrating the electromagnetic energy corresponding to the digital received signal. Therefore, an echo signal with increased signal amplitude can be obtained, thereby improving the detection capability of small metals. Simultaneously, by setting different pulse code sequences for adjacent security gates, mutual interference between security gates can be reduced, false metal detection can be avoided, and anti-interference capability can be enhanced.

[0106] The above describes a specific implementation of the metal detection method for security gates in this application. This application also provides a control and detection device for security gates, which can be used to implement the aforementioned metal detection method. Specifically, the most basic structure of this metal detection device includes: an encoding excitation unit, a digital receiving signal processing unit, and a detection unit.

[0107] The encoding excitation unit is used to generate a pulse coding sequence. The code length of the pulse coding sequence is N, where N is an integer greater than 1. The pulse coding sequence is used to control the transmitting coil of the security gate to transmit electromagnetic waves intermittently. Each value in the pulse coding sequence is used to characterize a transmission waveform with a specific phase.

[0108] A digital receiving signal processing unit is used to acquire a digital receiving signal corresponding to the pulse code sequence and process the digital receiving signal to focus the electromagnetic energy corresponding to the digital receiving signal; wherein, the digital receiving signal is obtained by processing the signal received by the receiving coil of the security gate under the action of electromagnetic waves;

[0109] The detection unit is used to determine the metal detection result based on the processed digital received signal.

[0110] Optionally, in the digital received signal processing unit, the digital received signal is processed to focus the electromagnetic energy corresponding to the digital received signal, which may specifically include:

[0111] Determining convolution coefficients based on pulse coding sequences;

[0112] Determine the digital received signal sequence for each receiving moment, wherein the code length of the digital received signal sequence is the same as the code length of the pulse code sequence, and the different numerical bits in the digital received signal sequence correspond to the receiving moment, and the values ​​of the different numerical bits are determined based on the signals received by the receiving coil at each receiving moment.

[0113] The digital received signal sequence at each receiving moment is convolved with the convolution coefficients, and the convolution result is used as the amplitude of the processed digital received signal at each receiving moment.

[0114] Optionally, in the digital signal receiving processing unit, the process of determining the convolution coefficients based on the pulse coding sequence may specifically include: reversing all the values ​​in the pulse coding sequence to obtain the convolution coefficients.

[0115] Optionally, the first value bit in the digital received signal sequence corresponds to the current reception time, and the second to Nth value bits correspond to the reception times preceding the current reception time.

[0116] Optionally, the encoding excitation unit can be further used to control the digital-to-analog conversion unit of the security gate to modulate the pulse encoding sequence into a transmission signal. The waveform corresponding to the transmission signal includes sub-waveforms with phase differences. The transmission signal is used to excite the transmission coil to transmit electromagnetic waves intermittently.

[0117] Optionally, in scenarios where security gates are arranged in close proximity, the pulse code sequences generated by the encoding excitation units in the control and detection devices of the close proximity security gates are different from each other, and the pulse code sequences generated by the encoding excitation units in the control and detection devices of any security gate include different values.

[0118] Alternatively, the encoding excitation unit and the digital received signal processing unit can be implemented using an FPGA.

[0119] As mentioned above, Figure 3 This is a basic structural diagram of the security gate provided in this application. Figure 3 As shown, the security gate includes: a control and detection device, a digital-to-analog converter, a transmitting circuit, a transmitting coil, a receiving coil, a receiving circuit, and a digital-to-analog converter.

[0120] The control and detection device is used to generate a pulse code sequence. The code length of the pulse code sequence is N, where N is an integer greater than 1. Each value in the pulse code sequence is used to characterize a transmission waveform with a specific phase.

[0121] A digital-to-analog converter is used to modulate a pulse-coded sequence into a transmitted signal;

[0122] The transmitting circuit is used to process the transmitted signal to generate the excitation signal for the transmitting coil;

[0123] A transmitting coil is used to intermittently transmit electromagnetic waves under the excitation of an excitation signal;

[0124] A receiving coil is used to receive signals generated by electromagnetic waves.

[0125] The receiving circuit is used to process the signal received by the receiving coil to obtain an analog received signal;

[0126] An analog-to-digital converter is used to demodulate the analog received signal and generate a digital received signal corresponding to the pulse code sequence.

[0127] The control and detection device is also used to process the digital received signal to focus the electromagnetic energy corresponding to the digital received signal; and to determine the metal detection result based on the processed digital received signal.

[0128] Optionally, in the control and detection device, the process of determining the convolution coefficients based on the pulse code sequence may specifically include: reversing all the values ​​in the pulse code sequence to obtain the convolution coefficients.

[0129] Optionally, the first value bit in the digital received signal sequence corresponds to the current reception time, and the second to Nth value bits correspond to the reception times preceding the current reception time.

[0130] Optionally, the control detection device can be further used to modulate the pulse code sequence into a transmission signal, the waveform of which includes sub-waveforms with phase differences, and the transmission signal is used to excite the transmission coil to transmit electromagnetic waves intermittently.

[0131] Optionally, for scenarios where security gates are arranged adjacent to each other,

[0132] In adjacent security gates, the pulse code sequences generated by the control and detection devices are all different.

[0133] Furthermore, for any given security gate, the pulse code sequence generated by the control and detection device includes different values.

[0134] In the actual implementation of security gates, a schematic diagram of the specific hardware structure can be shown as follows: Figure 10 As shown, the encoding excitation unit in the FPGA generates a pulse code sequence; the digital-to-analog converter modulates the pulse code sequence to a specified frequency using phase modulation, thus converting the digital signal into an analog signal; after processing by the signal amplification circuit and the Class A power amplifier circuit, it is applied to the transmitting coil for intermittent electromagnetic wave transmission; the receiving coil receives the signal under the influence of the electromagnetic wave, and after processing by the amplification circuit and the bandpass filter circuit, a digital received signal is obtained. This digital signal is then demodulated by the analog-to-digital acquisition circuit, converting the analog signal back into a digital signal, which is then input into the FPGA. The digital received signal processing unit in the FPGA receives and processes the signal, obtaining the echo signal, which is then sent to the detection unit for metal detection. The signal amplification circuit and the Class A power amplifier circuit can be considered as the transmitting circuit, and the amplification circuit and the bandpass filter circuit can be considered as the receiving circuit.

[0135] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. A metal detection method for security gates, characterized in that, include: A pulse coding sequence is generated, wherein the code pattern length of the pulse coding sequence is N, where N is an integer greater than 1. The pulse coding sequence is used to control the transmitting coil of the security gate to transmit electromagnetic waves intermittently. Each value in the pulse coding sequence is used to characterize a transmission waveform with a specific phase. The digital received signal is obtained by processing the signal received by the receiving coil of the security gate under the action of the electromagnetic wave, and the digital received signal is further processed to focus the electromagnetic energy corresponding to the digital received signal. The metal detection result is determined based on the processed digital received signal.

2. The metal detection method according to claim 1, characterized in that, Processing the digital received signal to focus the electromagnetic energy corresponding to the digital received signal includes: The convolution coefficients are determined based on the pulse coding sequence; A digital received signal sequence is determined for each receiving moment, wherein the code pattern length of the digital received signal sequence is the same as the code pattern length of the pulse coding sequence, different numerical bits in the digital received signal sequence correspond to the receiving moment, and the values ​​of the different numerical bits are determined based on the signals received by the receiving coil at each receiving moment; The digital received signal sequence at each receiving moment is convolved with the convolution coefficients, and the convolution result is used as the amplitude of the processed digital received signal at each receiving moment.

3. The metal detection method according to claim 2, characterized in that, Determining the convolution coefficients based on the pulse coding sequence includes: reversing all the values ​​in the pulse coding sequence to obtain the convolution coefficients; And / or, The first numerical bit in the digital received signal sequence corresponds to the current receiving time, and the second to Nth numerical bits correspond to the receiving times preceding the current receiving time.

4. The metal detection method according to claim 1, characterized in that, The method further includes: The digital-to-analog converter unit controlling the security gate modulates the pulse code sequence into a transmission signal. The waveform corresponding to the transmission signal includes sub-waveforms with phase differences. The transmission signal is used to excite the transmission coil to transmit electromagnetic waves intermittently.

5. The metal detection method according to claim 1, characterized in that, In scenarios where security gates are arranged in close proximity, the pulse code sequences corresponding to the adjacent security gates are different from each other, and the pulse code sequence of any security gate includes different values.

6. A control and detection device for security gates, characterized in that, include: Encoding excitation unit, digital received signal processing unit, and detection unit; The encoding excitation unit is used to generate a pulse coding sequence, wherein the code pattern length of the pulse coding sequence is N, where N is an integer greater than 1, and the pulse coding sequence is used to control the transmitting coil of the security gate to transmit electromagnetic waves intermittently, and each value in the pulse coding sequence is used to characterize a transmission waveform with a specific phase. The digital receiving signal processing unit is used to acquire a digital receiving signal obtained by processing the signal received by the receiving coil of the security gate under the action of the electromagnetic wave, and to process the digital receiving signal to focus the electromagnetic energy corresponding to the digital receiving signal. The detection unit is used to determine the metal detection result based on the processed digital received signal.

7. The control and detection device according to claim 6, characterized in that, The encoding excitation unit is further used to control the digital-to-analog conversion unit of the security gate to modulate the pulse encoding sequence into a transmission signal. The waveform corresponding to the transmission signal includes sub-waveforms with phase differences. The transmission signal is used to excite the transmission coil to transmit electromagnetic waves intermittently.

8. The control and detection device according to claim 6, characterized in that, The encoding excitation unit and the digital receiving signal processing unit are implemented using an FPGA.

9. A security gate, characterized in that, include: Control and detection device, digital-to-analog converter, transmitting circuit, transmitting coil, receiving coil, receiving circuit and analog-to-digital converter; The control and detection device is used to generate a pulse code sequence, wherein the code pattern length of the pulse code sequence is N, where N is an integer greater than 1, and each value in the pulse code sequence is used to characterize a transmission waveform with a specific phase. The digital-to-analog converter unit is used to modulate the pulse code sequence into a transmission signal; The transmitting circuit is used to process the transmitting signal to generate an excitation signal for the transmitting coil; The transmitting coil is used to periodically transmit electromagnetic waves under the excitation of the excitation signal. The receiving coil is used to receive the signal under the action of the electromagnetic wave; The receiving circuit is used to process the signal received by the receiving coil to obtain an analog received signal; The analog-to-digital conversion unit is used to demodulate the analog received signal and generate a digital received signal corresponding to the pulse code sequence. The control and detection device is further configured to acquire the digital received signal and process the digital received signal to focus the electromagnetic energy corresponding to the digital received signal; and determine the metal detection result based on the processed digital received signal.

10. The security gate according to claim 8, characterized in that, For scenarios where security gates are arranged adjacent to each other, In adjacent security gates, the pulse code sequences generated by the control and detection devices are all different. Furthermore, for any security gate, the pulse code sequence generated by the control and detection device includes different values.

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