Flexible self-compensation time-varying Doppler metasurface system and radar detection deception method thereof

Abstract

The invention discloses a flexible self-compensation time-varying Doppler metasurface system and a radar detection deception method thereof, and relates to the technical field of flexible electronics, and the system comprises a plurality of flexible multi-layer metasurface units and a dynamic regulation and control module. The flexible multilayer metasurface unit is provided with a stretchable conductive patch layer, a flexible substrate layer, a positive electrode layer, a piezoelectric composite layer and a negative electrode layer from top to bottom, the patch layer is provided with a variable capacitance diode and a strain sensor, and the phase of a reflected wave is regulated and controlled by adjusting the bias voltage of the variable capacitance diode; the dynamic regulation and control module is composed of a signal processing unit, a resistance monitoring circuit and a bias network and achieves signal receiving, phase calculation and regulation and control. Meanwhile, a radar detection deception method is provided, a strain sensor and a resistance monitoring circuit are used for collecting data, a compensation phase is calculated in combination with a deformation quantity-resistance-phase model pre-stored in a signal processing unit, a variable capacitance diode is driven through signal conversion, and 0-360-degree phase continuous regulation and control are achieved.

Description

Technical Field

[0001] This invention relates to the field of flexible electronics technology, and in particular to a flexible self-compensating time-varying Doppler metasurface system and its radar detection deception method. Background Technology

[0002] Radar is an electronic device that uses electromagnetic waves to detect targets and is widely used in military, aviation, meteorology, and traffic management fields. Its basic principle is to emit electromagnetic waves and receive the echoes reflected from targets, analyzing information such as the time delay and frequency changes of the echoes to determine the target's position and speed.

[0003] The basic principle formula for radar to detect the position information of an object is:

[0004]

[0005] Where R is the distance between the target and the radar, and c is the speed of electromagnetic waves in air (approximately 3 × 10⁻⁶). 8 (m / s), where Δt is the time delay between the radar transmitted wave and the received echo.

[0006] The principle behind radar detection of object velocity involves the Doppler effect, which states that when there is relative motion between the target and the radar, the frequency of the reflected wave changes. The formula is:

[0007]

[0008] Δf is the Doppler frequency shift (the difference between the frequency of the reflected wave and the frequency of the transmitted wave), v is the relative velocity between the target and the radar, and f0 is the frequency of the radar transmitted wave. The target velocity can be calculated by measuring the Doppler frequency shift Δf.

[0009] If we consider the angle θ between the target's direction of motion and the radar beam direction, then the actual velocity and the radial velocity v measured by the radar... r The relationship between them is: v r = v·cosθ. r Let v be the radial velocity measured by radar (the component along the radar beam direction), v be the actual velocity of the target, and θ be the angle between the target's direction of motion and the radar beam direction. The corrected Doppler frequency shift formula is:

[0010]

[0011] With the continuous advancement of radar technology, modern radar systems possess high resolution, multi-band operation, and anti-jamming capabilities, placing higher demands on target detection accuracy and stealth. To counter radar detection, stealth technology has emerged. Traditional stealth technologies mainly include:

[0012] 1. The radar cross section (RCS) can be reduced through shape design, but the stealth effect is only effective at a specific incident angle. The RCS increases significantly when the incident angle is not designed, and the complex shape affects aerodynamic performance.

[0013] Second, radar wave energy is absorbed by using radar absorbing materials (RAM), which converts radar wave energy into heat energy. However, it is only optimized for specific frequency bands, making it difficult to cover a wide frequency band. It also has poor environmental adaptability and high maintenance costs.

[0014] Third, the frequency selective surface (FSS) selectively reflects or transmits electromagnetic waves of a specific frequency, but its filtering characteristics are determined by the structural design and cannot be dynamically adjusted, resulting in insufficient ability to counter multi-band radar.

[0015] These traditional technologies are all static responses and cannot actively eliminate or fake the Doppler shift caused by target motion, resulting in poor stealth effectiveness against new radars. Metasurfaces are two-dimensional materials composed of subwavelength unit structures, capable of precisely controlling the phase, amplitude, and polarization characteristics of electromagnetic waves. Compared to traditional stealth technologies, metasurfaces offer advantages such as thinness, flexibility, dynamic adjustability, and versatility. However, metasurfaces are typically composed of metals and dielectric materials, and the rigid metal substrate prevents them from perfectly fitting curved platforms, such as drone wings and wearable devices, and deformation leads to a significant performance degradation. Summary of the Invention

[0016] The purpose of this invention is to provide a flexible self-compensating time-varying Doppler metasurface system and its radar detection deception method. By adjusting the phase of the reflected wave in real time, it simulates the radar scattering characteristics of stationary or falsely moving targets, thereby interfering with or deceiving radar detection. It has advantages such as dynamic adjustability, strong multi-band adaptability, and low power consumption, and can be applied to military stealth, civilian anti-tracking and other fields.

[0017] To achieve the above objectives, the present invention provides a flexible self-compensating time-varying Doppler metasurface system, comprising:

[0018] Several flexible multilayer metasurface units, each unit including a stretchable conductive patch layer, a flexible substrate layer, a positive electrode layer, a piezoelectric composite layer, and a negative electrode layer arranged from top to bottom. Positive conductive copper pillars and negative conductive copper pillars are disposed in the flexible substrate layer and the piezoelectric composite layer. The stretchable conductive patch layer includes symmetrical silver nanowire sub-units, varactor diodes, and strain sensors. By changing the bias voltage of the varactor diodes, their capacitance value is adjusted, thereby causing the silver nanowire sub-units to deform and change the phase of the reflected wave.

[0019] The dynamic control module, connected to the flexible multilayer metasurface unit, includes:

[0020] A resistance monitoring circuit is used to measure the resistance of each flexible metasurface unit and transmit the result to the signal processing unit.

[0021] The signal processing unit is used to receive the deformation and resistance changes of the silver nanowire subunit and radar parameter signals. Based on the pre-stored deformation-resistance-phase model and deception mode, it generates the target phase compensation amount corresponding to the radar parameter signals. Based on the pre-stored resistance-curvature-voltage-phase model, it calculates the voltage corresponding to the varactor diode at different curvature positions. Then, it controls the capacitance of the varactor diode through the bias network.

[0022] The bias network, connected to the signal processing unit, is used to transmit the analog bias voltage to the varactor diode at the corresponding curvature position, forming a phase-controlled signal path.

[0023] Preferably, the bias network includes a rectification and filtering module, a low-voltage regulator (LDO), a digital-to-analog converter (DAC), a current limiting protection module, and a multiplexer.

[0024] The rectification and filtering module includes a full-bridge rectifier circuit composed of four BAT545 chips and a filter capacitor. The full-bridge rectifier circuit is connected to the piezoelectric composite layer, which serves as a voltage source, through the positive electrode layer. The unstable AC voltage generated by the piezoelectric composite layer is rectified by the full-bridge rectifier current and filtered by the filter capacitor, and then outputs a DC voltage with high-frequency noise removed to the voltage regulator module.

[0025] The low-voltage regulator (LDO) provides a stable DC voltage to the digital-to-analog converter (DAC) after voltage regulation.

[0026] A digital-to-analog converter (DAC) converts the digital signal output from the signal processing unit into an analog signal.

[0027] Current limiting protection circuit, including current limiting resistor and resettable fuse, is used to protect the circuit;

[0028] Multiplexer 1 is used to receive instructions from the signal processing unit to transmit the analog DC voltage generated by the digital-to-analog converter (DAC) to the varactor diode through the silver nanowire sub-unit.

[0029] Preferably, the resistance monitoring circuit includes a constant current source, a multiplexer, a differential amplifier, a low-pass filter, and an ADC.

[0030] A constant current source provides power to the resistance monitoring resistor;

[0031] Multiplexer 2, connected to the metasurface unit, enables multi-channel resistance measurement;

[0032] The differential amplifier amplifies the measurement results from multiplexer two and transmits them to the low-pass filter.

[0033] A low-pass filter suppresses noise in the measurement results and transmits them to the analog-to-digital converter (ADC).

[0034] An analog-to-digital converter (ADC) converts measurement results from analog signals to digital signals and transmits them to a signal processing unit.

[0035] Preferably, the flexible substrate layer is made of polyimide with a bending radius of not less than 5 mm; the piezoelectric composite layer is made of PDMS-ZnO piezoelectric material with an open circuit voltage ≥10V and a power density ≥0.05mW / cm2; the silver nanowire sub-units are made of silver nanowire mesh material with an elongation ≥30% and a sheet resistance ≤2Ω / sq.

[0036] Preferably, the silver nanowire sub-units are symmetrically arranged along the longitudinal central axis of the stretchable conductive patch layer. The silver nanowire sub-units include longitudinal arms and vertical arms disposed at both ends of the longitudinal arms. The vertical arms are perpendicularly connected to the longitudinal arms and are away from the longitudinal central axis. A varactor diode is disposed between the two longitudinal arms and is connected across the two longitudinal arms.

[0037] Preferably, the two ends of the positive conductive copper pillar are connected to the positive electrode layer and the positive terminal of the varactor diode, respectively, and the two ends of the negative conductive copper pillar are connected to the negative electrode layer and the negative terminal of the varactor diode, respectively.

[0038] Preferably, two strain sensors are respectively disposed in the middle of the two longitudinal arms on the side away from the longitudinal central axis, for monitoring the curvature change near the varactor diode. The strain sensors are made of silver nanowire strain grating material, the resistance change rate is proportional to the curvature, and the sensitivity is 5ppm / με.

[0039] Preferably, the signal processing unit uses an FPGA or MCU, the digital-to-analog conversion module uses a 16-bit high-precision DAC, the output analog bias voltage range is 0-5V, and the resolution is ≤10mV.

[0040] Preferably, the deception modes pre-stored in the control algorithm module include:

[0041] The stationary target simulation mode outputs a uniform phase distribution to compensate for the Doppler frequency shift caused by motion, and is suitable for scenarios where the target needs to be disguised as stationary.

[0042] The virtual velocity generation mode generates a linear phase gradient to simulate the radar scattering characteristics of a false moving target, which is suitable for scenarios where false moving targets are created to interfere with radar detection.

[0043] Preferably, the dynamic control module achieves continuous 0-360° phase control of the reflected wave in the X-Ku band of 8-18 GHz through a resistance monitoring circuit and a bias network.

[0044] A radar detection deception method for flexible, self-compensating, time-varying Doppler metasurface systems includes the following steps:

[0045] The resistance change of the silver nanowire subunit is monitored by a resistance monitoring circuit and the monitoring result is converted into a digital signal. The deformation of the silver nanowire subunit is monitored by a strain sensor and output as a digital signal. The strain sensor and the resistance monitoring circuit transmit the digital signal to the signal processing unit.

[0046] Input the radar's preset parameters into the system, and calculate the compensated phase using the signal processing unit based on the deformation-resistance-phase model;

[0047] The digital voltage signal calculated by the signal processing unit is converted into an analog signal by a bias network, which drives the varactor diode to adjust the capacitance value. Phase modulation is achieved by using the symmetrical silver nanowire sub-units on the surface of the stretchable conductive patch layer.

[0048] The preferred method for constructing the deformation-resistance-phase model is as follows:

[0049] Experiments were conducted to obtain phase data of reflected waves from metasurfaces in the operating frequency band under different deformation and resistance variations.

[0050] A linear model was used to initially fit the relationship between deformation, resistance change and phase compensation.

[0051] By using neural networks to perform nonlinear optimization on the initial fitting results, the fitting accuracy of the model under complex conditions can be improved.

[0052] According to specific embodiments provided by the present invention, the present invention discloses the following technical effects:

[0053] Dynamic Doppler compensation and deception capability: The signal processing unit calculates the phase error caused by the target's motion state and deformation in real time, and adjusts the reflection phase of the metasurface unit by combining the varactor diode to accurately cancel the real Doppler frequency shift, causing the radar to mistakenly judge the target as stationary; it can also preset false velocity parameters and generate Doppler frequency shift by superimposing phase gradients to interfere with the radar's velocity measurement accuracy and improve stealth.

[0054] Flexible materials and deformation-adaptive design: Employing a flexible polyimide (PI) substrate and silver nanowire mesh patches, the bending radius can be as low as 5 mm, making it suitable for complex curved platforms. Curvature changes are monitored in real time using strain sensors, and a pre-calibrated model dynamically compensates for path differences and conductivity changes caused by bending, ensuring phase control accuracy (error ≤ 5°).

[0055] Self-powered module and low power consumption: Integrated piezoelectric material (PDMS-ZnO) converts mechanical vibration energy into electrical energy, with an output power density ≥0.1mW / cm². 2 This design meets the microwatt-level driving requirements of varactor diodes, reducing reliance on external power supplies. The self-powered module and conformal metasurface design adapt to complex environments, enhancing system usability.

[0056] Multi-band compatibility and high-precision control: The silver nanowire mesh patch supports the X-Ku band (8-18GHz) with a phase control range of 0-360°, making it suitable for multi-band radar detection scenarios. A 16-bit DAC outputs a bias voltage with a phase resolution ≤1°, and combined with a closed-loop feedback algorithm (PID control), it ensures the real-time performance and stability of dynamic control.

[0057] The technical solution of the present invention will be further described in detail below with reference to the accompanying drawings and embodiments. Attached Figure Description

[0058] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the following briefly introduces the drawings required for use in the embodiments. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying any creative work.

[0059] Figure 1 This is a cross-sectional view of the side structure of the flexible multilayer metasurface unit according to Embodiment 1 of the present invention;

[0060] Figure 2 This is a schematic diagram of the top surface structure of the flexible metasurface unit in Embodiment 1 of the present invention;

[0061] Figure 3 This is a schematic diagram of the flexible metasurface unit structure parameters of Embodiment 1 of the present invention;

[0062] Figure 4 This is a schematic diagram of the dynamic control module workflow in Embodiment 2 of the present invention;

[0063] Figure 5 This is a comparison diagram of the effects of a bare object and a flexible multilayer metasurface object in Embodiment 3 of the present invention;

[0064] Figure 6 These are radar echo intensity diagrams of an exposed object and an object covered with a flexible multilayer metasurface in Embodiment 3 of the present invention, respectively, under static, distance, and proximity conditions.

[0065] Figure Labels

[0066] 1. Stretchable conductive patch layer; 1-1. Silver nanowire sub-unit; 1-1-1. Vertical arm; 1-1-2. Longitudinal arm; 1-2. Varactor diode; 1-3. Strain sensor; 2. Flexible substrate layer; 3. Positive electrode layer; 4. Piezoelectric composite layer; 5. Negative electrode layer; 6. Positive conductive copper pillar; 7. Negative conductive copper pillar. Detailed Implementation

[0067] The following will clearly and completely describe the technical solutions in the embodiments of the present invention in conjunction with the accompanying drawings. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative efforts are within the scope of protection of the present invention.

[0068] To make the above-mentioned objects, features and advantages of the present invention more apparent and understandable, the present invention will be further described in detail below with reference to the accompanying drawings and specific embodiments.

[0069] Example 1

[0070] like Figure 1 As shown, the flexible self-compensating time-varying Doppler metasurface system includes:

[0071] Several flexible multilayer metasurface units, each unit comprising, from top to bottom: a stretchable conductive patch layer 1, a flexible substrate layer 2, a positive electrode layer 3, a piezoelectric composite layer 4, and a negative electrode layer 5.

[0072] like Figure 2 As shown, the stretchable conductive patch layer 1 has a thickness of 0.1 μm and includes symmetrical silver nanowire sub-units 1-1, varactor diodes 1-2, and strain sensors 1-31-3. The silver nanowire sub-units 1-1 are made of silver nanowire mesh material with a stretchability ≥30% and a sheet resistance ≤2Ω / sq. The period P = 6 mm, suitable for the 8–18 GHz X-Ku band. The silver nanowire sub-units 1-1 are symmetrically arranged along the longitudinal central axis of the stretchable conductive patch layer 1. Each silver nanowire sub-unit 1-1 includes a longitudinal arm 1-1-2 and vertical arms 1-1-1 disposed at both ends of the longitudinal arm 1-1-2. The vertical arms 1-1-1 are perpendicularly connected to the longitudinal arm 1-1-2 and located away from the longitudinal central axis.

[0073] A varactor diode 1-2 is positioned between and across the two longitudinal arms 1-1-2. The varactor diode 1-2 is a Skyworks SMV1405 with a capacitance range of C = 0.63pF to 2.67pF.

[0074] Two strain sensors 1-31-3 are respectively disposed on the side away from the longitudinal central axis in the middle of the two longitudinal arms 1-1-2, and are used to monitor the curvature and resistance changes of the silver nanowire subunit 1-1. The strain sensors 1-31-3 are made of silver nanowire strain grating material, whose resistance change rate is proportional to the curvature, and whose sensitivity is 5ppm / με.

[0075] The flexible substrate 2 is made of polyimide (PI) material with a thickness of 50μm and a bending radius of not less than 5mm.

[0076] The positive electrode layer 3 is made of aluminum and has a thickness of 0.1μm.

[0077] The piezoelectric composite layer 4, made of PDMS-ZnO piezoelectric material, has a thickness of 100 μm and a power density of ≥0.05 mW / cm² when the open-circuit voltage is ≥10V. 2 It converts mechanical vibration energy into electrical energy to power the system.

[0078] The negative electrode layer 5 is made of aluminum and has a thickness of 0.1μm.

[0079] A positively conductive copper pillar 6 and a negatively conductive copper pillar 7, each with a diameter of 0.15 mm, are disposed within the flexible substrate layer 2 and the piezoelectric composite layer 4 to supply power to the varactor diode 1-2. The two ends of the positively conductive copper pillar 6 are connected to the positive electrode layer 3 and the positive terminal of the varactor diode 1-2, respectively. The two ends of the negatively conductive copper pillar 7 are connected to the negative electrode layer 5 and the negative terminal of the varactor diode 1-2, respectively.

[0080] Figure 3 The figure illustrates one possible structural parameter for a flexible metasurface unit:

[0081] The flexible multilayer metasurface unit has a length a: 6 mm, a width b: 6 mm, and a height h: 150.2 μm.

[0082] The longitudinal arm 1-1-2 has a length L2 of 3mm and a width w2 of 0.4mm.

[0083] Vertical arm 1-1-1: Length L1: 2mm, Width w1: 0.4mm.

[0084] The gap width e between the two longitudinal arms 1-1-2 is 0.2mm.

[0085] Strain sensor 1-3 diameter d: 1mm.

[0086] The dynamic control module, connected to the flexible multilayer metasurface unit, includes:

[0087] The signal processing unit receives the deformation, resistance change, and radar parameter signals of the silver nanowire subunit 1-11-2. Based on a pre-stored deformation-resistance-phase model and deception mode, it generates the target phase compensation amount corresponding to the radar parameter signals. It also calculates the voltage corresponding to the varactor diode 1-2 at different curvature positions based on a pre-stored resistance-curvature-voltage-phase model, and then adjusts the capacitance of the varactor diode 1-2 through a bias network. The signal processing unit uses an FPGA or MCU.

[0088] The bias network, connected to the signal processing unit, transmits the analog bias voltage to the varactor diodes 1-2 at the corresponding curvature positions, forming a phase-controlled signal path. The bias network includes a rectification and filtering module, a low-voltage regulator (LDO), a digital-to-analog converter (DAC), a current-limiting protection module, and a multiplexer.

[0089] The rectification and filtering module includes a full-bridge rectifier circuit composed of four BAT545 chips and a filter capacitor. The full-bridge rectifier circuit is connected to the piezoelectric composite layer, which serves as a voltage source, through the positive electrode layer. The unstable AC voltage generated by the piezoelectric composite layer is rectified by the full-bridge rectifier current and filtered by the filter capacitor before being output to the voltage regulator module.

[0090] The low-voltage regulator (LDO) provides a stable DC voltage to the digital-to-analog converter (DAC) after voltage regulation.

[0091] The digital-to-analog converter (DAC) converts the digital signal output from the signal processing unit into an analog signal; the TIDAC8760 model is selected, with an output analog bias voltage range of 0-5V and a resolution of ≤10mV.

[0092] Current limiting protection circuit, including current limiting resistor and resettable fuse, is used to protect the circuit;

[0093] Multiplexer 1 is used to receive instructions from the FPGA to transmit the DC voltage generated by the digital-to-analog converter (DAC) to the varactor diode 1-2 through the silver nanowire sub-unit and strain sensor 1-3.

[0094] A resistance monitoring circuit is used to measure the resistance of each flexible metasurface unit and transmit the data to the signal processing unit. The resistance monitoring circuit includes a constant current source, a multiplexer, a differential amplifier, a low-pass filter, and an ADC.

[0095] A constant current source provides power to the resistance monitoring resistor;

[0096] Multiplexer 2, connected to the metasurface unit, enables multi-channel resistance measurement;

[0097] The differential amplifier amplifies the measurement results from multiplexer two and transmits them to the low-pass filter.

[0098] A low-pass filter suppresses noise in the measurement results and transmits them to the analog-to-digital converter (ADC).

[0099] An analog-to-digital converter (ADC) converts measurement results from analog signals to digital signals and transmits them to a signal processing unit.

[0100] The spoofing patterns pre-stored in the signal processing unit include:

[0101] The stationary target simulation mode outputs a uniform phase distribution to compensate for the Doppler frequency shift caused by motion, and is suitable for scenarios where the target needs to be disguised as stationary.

[0102] The virtual velocity generation mode generates a linear phase gradient to simulate the radar scattering characteristics of a false moving target, which is suitable for scenarios where false moving targets are created to interfere with radar detection.

[0103] Example 2

[0104] Radar detection deception methods for flexible, self-compensating, time-varying Doppler metasurface systems, such as Figure 4 As shown, it includes the following steps:

[0105] The resistance change of silver nanowire subunit 1-1 is monitored by a resistance monitoring circuit and the monitoring result is converted into a digital signal. The deformation of silver nanowire subunit 1-1-1 is monitored by a strain sensor 1-3 and output as a digital signal. The analog signals output by strain sensor 1-3 and resistance monitoring circuit are converted into digital signals by ADC and then transmitted to the signal processing unit.

[0106] Input the radar's preset parameters, and calculate the compensated phase using the signal processing unit based on the deformation-resistance-phase model;

[0107] The bias network converts the digital voltage signal calculated by the signal processing unit into an analog signal, which drives the varactor diodes 1-2 to adjust the capacitance value, thereby achieving phase modulation.

[0108] The theoretical derivation process of electromagnetic wave control by the dynamic control module is as follows:

[0109] The signal strength detected by the receiver after the electromagnetic waves emitted by the radar are reflected by an object at a distance Z is:

[0110]

[0111] Where cos(w·t-kZ): represents the value at time point t. i The instantaneous amplitude of a radar wave reflects the signal strength and phase information, and is determined by factors such as the radar wave frequency w, time t, and the distance Z between the target and the radar. The wave vector k depends only on the wavelength. δ(tt) i ): is the impulse function, used to apply the impulse at time point t. i The signal is sampled at a certain point, indicating that the radar wave has an instantaneous intensity contribution at that moment; Z = (v - v0)t, where v is the propagation speed of the electromagnetic wave in the medium and v0 is the velocity of the object, therefore:

[0112]

[0113] After metasurface phase modulation:

[0114]

[0115] Where Δφ=w0t is the phase added to the reflected wave by the metasurface, and -kvt is the Doppler frequency shift caused by the motion of the object relative to the detector. When the two cancel each other out, the Doppler frequency shift can be eliminated, that is:

[0116] w0 = kv

[0117] At this moment, the radar detects that the object is stationary. Also, w0 = 2πf0. but:

[0118]

[0119] Currently, military radars generally use millimeter waves, assuming the target's velocity is 10. 3 Given a radar wave speed of m / s and a wavelength of 1 mm, the required metasurface voltage conversion frequency is 10. 6 HZ, while the maximum voltage conversion frequency of current signal generators is generally around 10 Hz. 9 HZ can be easily achieved.

[0120] By approximating the metasurface as a plane, the Doppler shift can be eliminated using the above theory. However, since real-world scenarios often involve more complex curved surface conditions, the phase shift caused by the curved surface also needs to be considered.

[0121] Assuming the additional displacement of an electromagnetic wave relative to the center point at a point on the curved surface is ΔZ, then:

[0122]

[0123] The compensated phase of the surface should be:

[0124] Δφ1=k(vt+ΔZ)

[0125] The conductivity of silver nanowire meshes changes when they are bent. To take into account this property, a mapping model of silver nanowire mesh deformation-resistance-phase is established to accurately obtain the specific value of the phase that the metasurface needs to compensate for. The deformation involves curvature and distance from the center point.

[0126] When silver nanowire meshes are bent, phase errors caused by changes in resistance need to be compensated. The compensation formula is as follows:

[0127]

[0128] Where ΔR is the change in resistance and k is the calibration coefficient, which is determined experimentally.

[0129] The method for constructing the deformation-resistance-phase model is as follows:

[0130] 1) Experimental calibration: The phase data of reflected waves in the working frequency band of the metasurface under different deformation and resistance changes are obtained through experiments.

[0131] The silver nanowire metasurface sample was fixed on an adjustable curvature fixture with a bending radius R = 5–50 mm.

[0132] Using a vector network analyzer, the resistance R(κ) and reflection phase φ(k,f) under different curvatures were measured in the frequency band of 8-18 GHz.

[0133] 2) A linear model is used to initially fit the relationship between deformation, resistance change, and phase compensation, as shown in the formula:

[0134] Δφ(κ,f)=α(f)·ΔR(κ)+β(f)·κ

[0135] Where α(f) is the resistance-phase coefficient, obtained by fitting experimental data through linear regression. β(f) is the phase shift directly caused by curvature, which is due to path difference.

[0136] 3) Use a neural network to perform nonlinear optimization on the initial fitting results:

[0137] A neural network is used to establish a nonlinear mapping from κ,f to Δφ, with curvature and frequency as inputs and phase compensation as outputs. This improves the model's fitting accuracy under complex conditions.

[0138] Example 3

[0139] The manufacturing process of flexible multilayer metasurface units is as follows:

[0140] 1) Spin-coat a 10cm×10cm PI film onto a glass substrate to form a flexible substrate layer 2.

[0141] 2) A periodically arranged stretchable conductive patch layer 1 is coated onto the PI film using a template mask to spray a silver nanowire mesh, with a period p = 6 mm. To ensure the uniform conductivity of the silver nanowires and the accuracy of the pattern, laser annealing is performed after spraying.

[0142] An aluminum film is deposited beneath the flexible substrate layer 2 to serve as the positive electrode layer 3.

[0143] 3) A piezoelectric composite layer 4 of PDMS-ZnO material is screen-printed below the flexible substrate layer 2 and the positive electrode layer 3.

[0144] An aluminum mold is vapor-deposited below the piezoelectric composite layer 4 to serve as the negative electrode layer 5.

[0145] 4) Use a femtosecond laser to micro-drill holes and fill the holes with positively conductive copper pillars 6 and negatively conductive copper pillars 7.

[0146] 5) Implant varactor diode 1-2 and strain sensor 1-31-3, and connect them to the dynamic control module.

[0147] Precision control:

[0148] The phase modulation accuracy (error ≤ 5°) and insertion loss (< 0.5 dB @ 15 GHz) in the 8–18 GHz range were verified using a vector network analyzer.

[0149] The target motion (velocity 0-100m / s) was simulated in a microwave anechoic chamber to verify that the radar velocity measurement error is ≤2m / s.

[0150] Verification of mechanical deformation stability: with a bending radius of 5mm, the phase consistency error is ≤3°.

[0151] Temperature stability verification: In an environment ranging from -40℃ to 85℃, the output fluctuation of the self-powered module is ≤5%.

[0152] To verify the effectiveness of the flexible self-compensating time-varying Doppler metasurface system, a flexible multilayer metasurface was coated on the surface of an object, and the radar echo intensity was measured under stationary, distant, and close conditions.

[0153] Figure 5 The diagrams are for comparison and simulation. In the diagrams, (a) represents a stationary exposed object, with the radar returning a phase of φ0; (b) represents a moving exposed object, with the radar returning a phase of φ0+φ. dopler (c) represents a moving object covered by a flexible multilayer metasurface, whose phase returned by radar detection is φ0.

[0154] Figure 6 The diagram shows a comparison of radar echo intensity, reflecting the phase change of the electromagnetic waves received by the detector over the same distance (1.5m). (a) represents the radar echo intensity of a stationary, bare object; when the object is stationary, the phase changes by 10π (5 cycles). (b) represents the radar echo intensity of a bare object moving away from the wave source; due to the Doppler shift, the phase changes by only 9π. (c) represents the radar echo intensity of a bare object moving closer to the wave source; the phase changes by 11π. (d) represents the radar echo intensity of a stationary object covered with a flexible multilayer metasurface; the phase changes by 10π. (e) represents the radar echo intensity of an object covered with a flexible multilayer metasurface moving away from the wave source; the phase changes by 10π. (f) represents the radar echo intensity of an object covered with a flexible multilayer metasurface moving closer to the wave source; the phase changes by 10π. It can be seen that the metasurface-covered object eliminates the Doppler shift, simulating the effect of a stationary object's reflected phase.

[0155] The remaining technical features in the above embodiments can be flexibly selected by those skilled in the art to meet different specific practical needs. However, it is obvious to those skilled in the art that these specific details are not necessary to implement the present invention. In other instances, to avoid obscuring the present invention, well-known components, structures, or parts are not specifically described, and all are within the scope of technical protection defined by the claims of the present invention.

[0156] Modifications and variations made by those skilled in the art that do not depart from the spirit and scope of this invention should be within the protection scope of the appended claims. In the above description, numerous specific details have been set forth to provide a thorough understanding of the invention. However, it will be apparent to those skilled in the art that these specific details are not necessary to practice the invention. In other instances, to avoid obscuring the invention, well-known techniques, such as specific construction details, operating conditions, and other technical conditions, have not been specifically described.

[0157] This document uses specific examples to illustrate the principles and implementation methods of the present invention. The above examples are only intended to help understand the method and core concept of the present invention. At the same time, those skilled in the art will find that the specific implementation methods and application scopes may vary based on the concept of the present invention. In summary, the contents of this specification should not be construed as limiting the present invention.

Claims

1. A flexible, self-compensating, time-varying Doppler metasurface system, characterized in that, include: Several flexible multilayer metasurface units, each unit including a stretchable conductive patch layer, a flexible substrate layer, a positive electrode layer, a piezoelectric composite layer, and a negative electrode layer arranged from top to bottom. Positive conductive copper pillars and negative conductive copper pillars are disposed in the flexible substrate layer and the piezoelectric composite layer. The stretchable conductive patch layer includes symmetrical silver nanowire sub-units, varactor diodes and strain sensors. The phase of the reflected wave is changed by adjusting the capacitance value of the varactor diode by changing the bias voltage of the varactor diode. The dynamic control module, connected to the flexible multilayer metasurface unit, includes: A resistance monitoring circuit is used to measure the resistance of each flexible metasurface unit and transmit the result to the signal processing unit. The signal processing unit is used to receive the deformation and resistance changes of the silver nanowire subunit and radar parameter signals. Based on the pre-stored deformation-resistance-phase model and deception mode, it generates the target phase compensation amount corresponding to the radar parameter signals. Based on the pre-stored resistance-curvature-voltage-phase model, it calculates the voltage corresponding to the varactor diode at different curvature positions. Then, it controls the capacitance of the varactor diode through the bias network. The bias network, connected to the signal processing unit, is used to transmit the analog bias voltage to the varactor diode at the corresponding curvature position, forming a phase-controlled signal path.

2. The flexible self-compensating time-varying Doppler metasurface system according to claim 1, characterized in that: The bias network includes a rectification and filtering module, a low-voltage regulator (LDO), a digital-to-analog converter (DAC), a current limiting protection module, and a multiplexer. The rectification and filtering module includes a full-bridge rectifier circuit composed of four BAT545 chips and a filter capacitor. The full-bridge rectifier circuit is connected to the piezoelectric composite layer, which serves as a voltage source, through the positive electrode layer. The unstable AC voltage generated by the piezoelectric composite layer is rectified by the full-bridge rectifier current and filtered by the filter capacitor, and then outputs a DC voltage that filters out high-frequency noise to the voltage regulator module. The low-voltage regulator (LDO) provides a stable DC voltage to the digital-to-analog converter (DAC) after voltage regulation. A digital-to-analog converter (DAC) converts the digital signal output from the signal processing unit into an analog signal. Current limiting protection circuit, including current limiting resistor and resettable fuse, is used to protect the circuit; Multiplexer 1 is used to receive instructions from the signal processing unit to transmit the analog signal generated by the digital-to-analog converter (DAC) to the varactor diode through the silver nanowire sub-unit.

3. The flexible self-compensating time-varying Doppler metasurface system according to claim 2, characterized in that: The resistance monitoring circuit includes a constant current source, a multiplexer, a differential amplifier, a low-pass filter, and an analog-to-digital converter (ADC). A constant current source provides power to the resistance monitoring resistor; Multiplexer 2, connected to the metasurface unit, enables multi-channel resistance measurement; The differential amplifier amplifies the measurement results from multiplexer two and transmits them to the low-pass filter. A low-pass filter suppresses noise in the measurement results and transmits them to the analog-to-digital converter (ADC). An analog-to-digital converter (ADC) converts measurement results from analog signals to digital signals and transmits them to a signal processing unit.

4. The flexible self-compensating time-varying Doppler metasurface system according to claim 3, characterized in that: The silver nanowire sub-units are symmetrically arranged along the longitudinal central axis of the stretchable conductive patch layer. Each silver nanowire sub-unit includes a longitudinal arm and vertical arms disposed at both ends of the longitudinal arm. The vertical arms are perpendicularly connected to the longitudinal arms and are away from the longitudinal central axis. A varactor diode is disposed between the two longitudinal arms and is connected across the two longitudinal arms.

5. The flexible self-compensating time-varying Doppler metasurface system according to claim 2, characterized in that: The two ends of the positive conductive copper pillar are connected to the positive electrode layer and the positive terminal of the varactor diode, respectively, and the two ends of the negative conductive copper pillar are connected to the negative electrode layer and the negative terminal of the varactor diode, respectively.

6. The flexible self-compensating time-varying Doppler metasurface system according to claim 4, characterized in that: Two strain sensors are respectively set in the middle of the two longitudinal arms on the side away from the longitudinal central axis to monitor the curvature change of the silver nanowire subunit. The strain sensors use silver nanowire strain grating material, and the resistance change rate is proportional to the curvature, with a sensitivity of 5ppm / με.

7. The flexible self-compensating time-varying Doppler metasurface system according to claim 1, characterized in that: The spoofing modes pre-stored by the signal processing unit include: The stationary target simulation mode outputs a uniform phase distribution to compensate for the Doppler frequency shift caused by motion, and is suitable for scenarios where the target needs to be disguised as stationary. The virtual velocity generation mode generates a linear phase gradient to simulate the radar scattering characteristics of a false moving target, which is suitable for scenarios where false moving targets are created to interfere with radar detection.

8. The flexible self-compensating time-varying Doppler metasurface system according to claim 1, characterized in that: The dynamic control module achieves continuous 0-360° phase control of the reflected wave in the X-Ku band of 8-18 GHz through a resistance monitoring circuit and a bias network.

9. A radar detection deception method based on the flexible self-compensating time-varying Doppler metasurface system according to any one of claims 1-8, characterized in that, Includes the following steps: The resistance change of the silver nanowire subunit is monitored by a resistance monitoring circuit and the monitoring result is converted into a digital signal. The deformation of the silver nanowire subunit is monitored by a strain sensor and output as a digital signal. The analog signals output by the strain sensor and the resistance monitoring circuit are converted into digital signals by an ADC and then transmitted to the signal processing unit. Input the radar's preset parameters into the system, and calculate the compensated phase using the signal processing unit based on the deformation-resistance-phase model; The digital voltage signal calculated by the signal processing unit is converted into an analog signal by a bias network, which drives the varactor diode to adjust the capacitance value. Phase modulation is achieved by using the symmetrical silver nanowire sub-units on the surface of the stretchable conductive patch layer.

10. The radar detection deception method for a flexible self-compensating time-varying Doppler metasurface system according to claim 9, characterized in that, The method for constructing the deformation-resistance-phase model is as follows: Experiments were conducted to obtain phase data of reflected waves from metasurfaces in the operating frequency band under different deformation and resistance variations. A linear model was used to initially fit the relationship between deformation, resistance change and phase compensation. By using neural networks to perform nonlinear optimization on the initial fitting results, the fitting accuracy of the model under complex conditions can be improved.

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