A low profile energy selective surface with ultra-wideband protection

Abstract

This invention belongs to the field of electromagnetic protection technology and provides a low-profile energy selective surface with ultra-wideband protection to solve electromagnetic protection problems. This invention improves the equivalent circuit design of a cascaded energy selective surface and a frequency selective surface, resulting in a low-profile energy selective surface with ultra-wideband protection. Under low power density incidence, the energy selective surface generates a passband in the S-band, ensuring normal signal reception and transmission for the protected antenna. Under high power density incidence, the energy selective surface can totally reflect electromagnetic waves across the entire frequency band. Furthermore, this invention employs a rotationally symmetric structure, exhibiting polarization insensitivity. Compared with existing technologies, the energy selective surface proposed in this invention has a simpler structure, a lower profile, higher shielding effectiveness, and provides wider bandwidth protection, achieving ultra-wideband protection.

Description

Technical Field

[0001] This invention belongs to the field of electromagnetic protection technology, specifically providing a low-profile energy selective surface with ultra-wideband protection. Background Technology

[0002] With the rapid development of electronic information technology, various electronic information devices have been widely used in both military and civilian fields. However, this has also greatly increased the possibility of interference from strong electromagnetic pulses (ESPs), which may originate from nature or from electromagnetic weapons. In the military field, radar systems require high sensitivity to enhance their detection and information acquisition capabilities, but this also significantly increases the likelihood of electromagnetic damage. In the civilian sector, areas with dense concentrations of electronic equipment, such as financial centers, command and control centers, and power supply control centers, also face multifaceted strong electromagnetic threats.

[0003] Electromagnetic pulse (EMP) protection can be broadly categorized into backdoor protection and frontdoor protection. Backdoor protection refers to the openings, gaps, and cables within the electronic device's casing, primarily achieved through shielding, grounding, and filtering techniques. Frontdoor protection, on the other hand, refers to the system's antennas and sensors, currently primarily protected using limiters and frequency selective surfaces. While limiters can significantly attenuate the current flowing into the circuit, they also impede the passage of normal signals. Frequency selective surfaces, while isolating high-power out-of-band signals, cannot protect against strong in-band electromagnetic threats. Therefore, researching an effective frontdoor EMP protection method is of significant practical importance.

[0004] Energy selective surfaces (ESS) are a novel type of electromagnetic surface proposed in recent years, and are a typical adaptive strong electromagnetic protection device. Currently, most ESSs can provide protection against high-power electromagnetic pulses within their operating frequency band. However, on the one hand, high-power microwaves outside the passband can still pass through the ESS and couple into the electronic system through the protected antenna; on the other hand, electromagnetic waves outside the passband can pass through the ESS and be totally reflected by the antenna, resulting in a significant increase in the radar cross-section. To increase the protection bandwidth, the literature "D. Qin, R. Ma, J. Su, X. Chen, R. Yang and W. Zhang, Ultra-Wideband Strong Field Protection Device Based on Metasurface, in IEEE Transactions on Electromagnetic Compatibility, vol. 62, no. 6, pp. 2842-2848, Dec. 2020, doi:10.1109 / TEMC.2020.3020840." proposes an ultra-wideband strong field protection device based on a metasurface, which superimposes a frequency-selective surface and an energy-selective surface to achieve ultra-wideband strong field protection. However, to maintain the independent operation of the two surfaces, this method requires a sufficient height separation between them, making it impossible to achieve a low profile. Therefore, how to achieve an energy-selective surface with ultra-wideband protection using a lower profile and a simpler structure remains an unsolved problem. Summary of the Invention

[0005] The purpose of this invention is to address the aforementioned electromagnetic protection problems by proposing a low-profile energy selective surface with ultra-wideband protection, which has a simpler structure, a lower profile, higher shielding effectiveness, and achieves ultra-wideband protection.

[0006] To achieve the above objectives, the technical solution adopted by the present invention is as follows:

[0007] A low-profile energy selective surface with ultra-wideband protection is composed of a number of periodic units arranged in a periodic pattern. Each periodic unit has a square structure and includes, from bottom to top, a bottom metal structure 6, a second dielectric substrate layer 4, a metal mesh structure 5, a first dielectric substrate layer 1, and an energy selective structure 2; characterized in that:

[0008] The energy selection structure is a 90° rotationally symmetrical structure around the center, consisting of a cross-shaped metal structure and four PIN diodes 3. The cross-shaped metal structure is arranged along the centerline of the upper surface of the first dielectric substrate layer, and a top cross-shaped slot is opened in the cross-shaped metal structure along the centerline of the upper surface of the first dielectric substrate layer. The four PIN diodes are loaded in the top cross-shaped slot and are respectively located on the four metal arms of the cross-shaped metal structure.

[0009] The metal mesh structure has a 90° rotational symmetry structure along the center and adopts a grid-shaped metal structure;

[0010] The bottom metal structure has a 90° rotational symmetry structure along the center and adopts a metal layer covering the lower surface of the second dielectric substrate layer. The metal layer has a bottom cross-shaped slit 7 along the center line of the lower surface of the second dielectric substrate layer.

[0011] Furthermore, the width of the central metal line in the grid-shaped metal structure is twice that of the border metal line.

[0012] Furthermore, the bottom cross-shaped gap adopts a bent structure.

[0013] Furthermore, the first dielectric substrate layer 1 and the second dielectric substrate layer 4 use the same dielectric substrate and have the same thickness.

[0014] In terms of working principle:

[0015] Energy selective surfaces (ESS) are implemented by loading PIN diodes onto a metal structure. At low power densities, the diodes are in the off state, which can be approximated as a small capacitor; at high power densities, the diodes are in the on state, which can be approximated as a small inductor in series with a small resistor. Changing the diode's operating state causes a significant difference in the ESS's surface impedance, thus enabling both transmission and shielding operation. To further illustrate the principle, an equivalent circuit is constructed to analyze the energy selective surface.

[0016] like Figure 5 The diagram shows the equivalent circuit of a metasurface-based ultrawideband strong field protection device in the background art. The air layer between the energy-selective surface and the frequency-selective surface is considered as a transmission line, which means adding a series inductor and a parallel capacitor between the energy-selective surface and the frequency-selective surface. The equivalent parallel capacitance is very small and can be ignored. Therefore, Figure 1 The energy selective surface and the frequency selective surface are coupled through a series inductor L0. The thicker the air layer between the two surfaces, the larger the inductance value, and the smaller the coupling between the energy selective surface and the frequency selective surface. Therefore, in order to ensure the independent operation of the two surfaces, weak coupling between the two surfaces is required, that is, a certain air layer thickness is required.

[0017] like Figure 6 The diagram shows the equivalent circuit of the low-profile energy selective surface with ultra-wideband protection in this invention. A metal mesh structure 5 is added between the energy selective structure A (energy selective structure 2) and the frequency selective structure B (bottom metal structure 6), which is equivalent to a parallel inductor L3. Similarly, the first dielectric substrate layer 1 and the second dielectric substrate layer 4 can also be regarded as a transmission line. Furthermore, the thickness and dielectric constant of the two dielectric substrate layers are the same, which is equivalent to a series inductor L2 in the equivalent circuit. Thus, the two inductors L2 and L3 form a T-shaped network. Through transformation, the T-shaped network is changed into a PAI-shaped network, as shown below. Figure 7 As shown; the two parallel inductors L after transformation 31 These structures are combined with energy selection structure A and frequency selection structure B respectively, resulting in energy selection structure C and frequency selection structure D. Energy selection structure C and frequency selection structure D are then connected through inductor L. 21 Coupled, and series inductor L 21 The value of is much larger than the value of the series inductance L2 before the transformation. Therefore, it can be seen that... Figure 7 The equivalent circuit form shown is the same as Figure 5 Similarly, the same effect is achieved; however, in this invention, due to the addition of the metal mesh structure 5, the effect of cascading the energy selective surface and the frequency selective surface can be achieved even with a small series inductance L2 value, i.e., a low profile. Furthermore, after the transformation, the inductance L... 31 It can be combined with energy selection structure 2 to form a resonator E, thereby reducing the design complexity of the energy selection structure; similarly, inductor L 31 It can be combined with the underlying metal structure 6 to form a resonator F, thereby reducing the design complexity of the underlying metal structure.

[0018] To further illustrate the working principle of the ultra-wideband protection of this invention, a more detailed equivalent circuit is given below, such as... Figure 8 The diagram shown is an equivalent circuit diagram of the energy selective surface in the transmission state in this invention. Figure 9 The diagram shows the equivalent circuit of the energy selection surface in the shielded state in this invention. Due to the impedance characteristics of inductors, the frequency response of parallel inductors exhibits low impedance and high pass characteristics. Therefore, parallel inductors suppress low-frequency frequencies, and the smaller the value of the parallel inductor, the stronger the suppression effect on low-frequency frequencies. Similarly, due to the impedance characteristics of capacitors, the frequency response of parallel capacitors exhibits low pass and high impedance. Therefore, parallel capacitors suppress high-frequency frequencies, and the larger the value of the parallel capacitor, the stronger the suppression effect on high-frequency frequencies. Thus, the inductor L in the circuit... 21 It suppresses low frequencies, and to suppress high frequencies, capacitor C2 is added to the circuit. Specifically:

[0019] When the energy selective surface is in a transmission state, two resonators can be clearly seen in the transformed circuit. The resonator E consists of the diode equivalent capacitance C1, inductance L1, and inductance L... 31 The resonator F is composed of capacitor C2 and inductor L. 31 The two resonators are composed solely of inductor L. 21 Coupling; when the resonant points of the two resonators are the same, this equivalent circuit is a typical second-order coupled resonant circuit, which can produce second-order resonance; furthermore, since there is also a series resonance in resonator E, a transmission zero will also be formed; inductance L 21 The capacitor C1 suppresses the low-frequency band outside the passband, and the capacitor C1 suppresses the high-frequency band outside the passband, thereby achieving ultra-wideband out-of-band suppression.

[0020] When the energy-selective surface is shielded, the diode's operating state changes, and the diode becomes equivalent to an inductor. Only one resonator remains in the circuit, and the second-order resonant point disappears. Simultaneously, the diode's equivalent inductances L4, L1, and L... 21 It can be equivalent to a specific inductance L 21 A smaller inductance value enhances the suppression of low-frequency bands, thus suppressing the passband formed by the retained resonator; the presence of the parallel capacitor C2 also leads to the suppression of high-frequency electromagnetic waves, thereby forming an ultra-wideband stopband across the entire frequency range.

[0021] In summary, the beneficial effects of the present invention are as follows:

[0022] This invention improves the equivalent circuit design of a cascaded energy selective surface and a frequency selective surface, resulting in a low-profile energy selective surface with ultra-wideband protection. Under low power density incidence, the low-profile energy selective surface generates a passband in the S-band, ensuring normal signal reception and transmission for the protected antenna. Under high power density incidence, the energy selective surface can totally reflect electromagnetic waves across the entire frequency band. Furthermore, this invention employs a rotationally symmetric structure, exhibiting polarization insensitivity. Compared to existing technologies, the energy selective surface proposed in this invention has a simpler structure, a lower profile, higher shielding effectiveness, and provides wider bandwidth protection, achieving ultra-wideband protection. Attached Figure Description

[0023] Figure 1 This is a side view of the periodic unit of the low-profile energy selective surface with ultra-wideband protection in this invention; wherein, 1 is the first dielectric substrate layer, 2 is the energy selective structure, 3 is the PIN diode, 4 is the second dielectric substrate layer, 5 is the metal mesh structure, and 6 is the bottom metal junction structure.

[0024] Figure 2This is a top view of the energy selection structure of the low-profile energy selection surface with ultra-wideband protection in this invention.

[0025] Figure 3 This is a top view of the metal mesh structure of the low-profile energy selective surface with ultra-wideband protection in this invention.

[0026] Figure 4 This is a top view of the underlying metal structure of the low-profile energy selective surface with ultra-wideband protection in this invention; wherein, 7 is a cross-shaped slit with a bent structure.

[0027] Figure 5 This is an equivalent circuit diagram of an ultrawideband strong field protection device based on metasurfaces in the prior art.

[0028] Figure 6 This is an equivalent circuit diagram of the low-profile energy selective surface with ultra-wideband protection in this invention.

[0029] Figure 7 This is the equivalent circuit diagram of the low-profile energy selective surface transformation with ultra-wideband protection in this invention.

[0030] Figure 8 This is the equivalent circuit diagram of the low-profile energy selective surface with ultra-wideband protection in the transmission state of the present invention.

[0031] Figure 9 This is the equivalent circuit diagram of the low-profile energy selective surface with ultra-wideband protection in the shielded state in this invention.

[0032] Figure 10 This is a frequency response curve of a low-profile energy selective surface with ultra-wideband protection in two states in the frequency range of 1 GHz to 10 GHz, according to an embodiment of the present invention.

[0033] Figure 11 Frequency response curves of the low-profile energy selective surface with ultra-wideband protection provided by the present invention in two states in the frequency range of 10 GHz to 35 GHz. Detailed Implementation

[0034] To make the objectives, technical solutions, and beneficial effects of this invention clearer, the invention will be further described in detail below with reference to the accompanying drawings and embodiments.

[0035] This embodiment provides a low-profile energy selective surface with ultra-wideband protection, composed of a number of periodic units arranged in a periodic pattern. These periodic units have a square structure, such as... Figure 1 As shown, it includes, from bottom to top, a bottom metal structure 6, a second dielectric substrate layer 4, a metal mesh structure 5, a first dielectric substrate layer 1, and a power selection structure 2; specifically:

[0036] The energy selection structure 2 is located on the upper surface of the first dielectric substrate layer 1, such as... Figure 2 As shown, the energy selection structure has a 90° rotational symmetry structure around the center and is composed of a cross-shaped metal structure and four PIN diodes 3. The cross-shaped metal structure is arranged along the centerline of the upper surface of the first dielectric substrate layer, and a top-level cross-shaped slot is opened in the cross-shaped metal structure along the centerline of the upper surface of the first dielectric substrate layer. The four PIN diodes are loaded in the top-level cross-shaped slot and are respectively located on the four metal arms of the cross-shaped metal structure. The cross-shaped metal structures of adjacent periodic units are connected accordingly.

[0037] The metal mesh structure 5 is located between the first dielectric substrate layer 1 and the second dielectric substrate layer 4, such as Figure 3 As shown, the metal mesh structure has a 90° rotational symmetry around the center and adopts a grid-shaped metal structure. The width of the metal line in the middle of the grid-shaped metal structure is twice that of the border metal line; the border metal lines of the grid-shaped metal structure are connected to each other between adjacent periodic units.

[0038] The underlying metal structure 6 is located on the lower surface of the second dielectric substrate layer 4, such as... Figure 4 As shown, the bottom metal structure has a 90° rotational symmetry structure along the center and adopts a metal layer covering the lower surface of the second dielectric substrate layer. The metal layer has a bottom cross-shaped slot 7 along the center line of the lower surface of the second dielectric substrate layer, and the bottom cross-shaped slot adopts a bent structure.

[0039] Furthermore, in this embodiment, the period of the periodic unit is p, that is, the unit size is p×p, p=8mm; in the energy selection structure, the width of the metal arm of the cross-shaped metal structure is we, we=3.2mm, and the gap width of the top cross-shaped gap is ge, ge=0.7mm. The magnitude of we controls L1 in the equivalent circuit (e.g., Figure 8 , Figure 9 The size of the metal mesh structure (as shown); in the metal mesh structure, the width of the middle metal line of the grid-shaped metal structure is wf, wf = 0.4mm, and the size of wf controls the L3 in the equivalent circuit (as shown). Figure 6 The size of the cross-shaped gap in the bottom metal structure is gf, where gf = 0.1 mm. The size of gf and the degree of bending of the gap control the value of C2 in the equivalent circuit (as shown). Figure 8 , Figure 9 The size of the first dielectric substrate layer 1 and the second dielectric substrate layer 4 is shown; the first dielectric substrate layer 1 and the second dielectric substrate layer 4 are made of the same dielectric substrate, specifically using F4B board with a dielectric constant of 2.65, and the thickness of the two dielectric substrate layers is the same, both being 2.1 mm. The thickness controls the L2 in the equivalent circuit (as shown). Figure 6 The size is shown; the PIN diode is an NXP BAP-70-03.

[0040] Based on the above structural parameters, the total thickness of the low-profile energy selective surface with ultra-wideband protection in this embodiment is approximately 4.2 mm, which is 0.047 wavelengths of the center frequency, less than one-twentieth of the wavelength of the center frequency, and meets the requirements of low profile.

[0041] Furthermore, simulation tests were conducted on the low-profile energy selective surface with ultra-wideband protection in this embodiment, and the results are as follows: Figure 10 and Figure 11 As shown; Figure 10 , Figure 11 The response curves of the energy selective surface in the frequency ranges of 1 GHz to 35 GHz and 10 GHz to 35 GHz under low power density and high power density electromagnetic wave incident conditions are shown. As can be seen from the figure, under the low power density electromagnetic wave incident condition, the insertion loss is less than 1 dB in the range of 2.83 GHz to 3.89 GHz, the relative bandwidth is 31.5%, and the shielding effectiveness is greater than 10 dB in the ranges of 0-2.32 GHz and 4.29 GHz to 33 GHz, exhibiting good out-of-band suppression. Under the high power density electromagnetic wave incident condition, the shielding effectiveness is greater than 16 dB in the range of 0 to 25 GHz and greater than 10 dB in the range of 0 to 33 GHz. In summary, the low profile energy selective surface in this embodiment achieves ultra-wideband out-of-band suppression under the low power density electromagnetic wave incident condition and ultra-wideband bandwidth suppression under the high power density electromagnetic wave incident condition.

[0042] Furthermore, to more intuitively illustrate the beneficial effects of the present invention, the ultra-wideband strong field protection device based on a metasurface from the literature "D. Qin, R. Ma, J. Su, X. Chen, R. Yang and W. Zhang, Ultra-Wideband Strong Field Protection Device Based on Metasurface, in IEEE Transactions on Electromagnetic Compatibility, vol. 62, no. 6, pp. 2842-2848, Dec. 2020, doi:10.1109 / TEMC.2020.3020840." is used as Comparative Example 1, and the high-frequency ultra-wideband energy selective surface from the patent with publication number "CN 115458984B" is used as Comparative Example 2. The performance parameters of Comparative Example 1 and Comparative Example 2 are shown in the table below:

[0043] profile Protected frequency band Shielding effectiveness Transmittance radio frequency band Insertion loss Comparative Example 1 0.149λ 0-20GHz >13dB 3.38-4.33GHz <1.5dB Comparative Example 2 0.122λ 0-16.2GHz >10dB 4.3-14GHz <1dB

[0044] Compared with Comparative Examples 1 and 2, the profile of the energy selective surface in this invention is significantly reduced, reaching less than one-twentieth of the center frequency wavelength; and in the transmission state, it has ultra-wideband out-of-band suppression, the protection frequency band is significantly extended, and the shielding effectiveness is further improved, providing shielding effectiveness of more than 16dB in the 0-25GHz range and shielding effectiveness of more than 10dB in the 0-33GHz range.

[0045] The above description is merely a specific embodiment of the present invention. Any feature disclosed in this specification may be replaced by other equivalent or similar features unless otherwise specified. All disclosed features, or steps in all methods or processes, may be combined in any way except for mutually exclusive features and / or steps.

Claims

1. A low-profile energy selective surface with ultra-wideband protection, comprising a plurality of periodic units arranged in a periodic pattern, wherein the periodic units are square in structure, including: The following layers are arranged sequentially from bottom to top: a bottom metal structure (6), a second dielectric substrate layer (4), a metal mesh structure (5), a first dielectric substrate layer (1), and an energy selection structure (2); characterized in that: The energy selection structure is a 90° rotationally symmetrical structure along the center, consisting of a cross-shaped metal structure and four PIN diodes (3). The cross-shaped metal structure is set along the centerline of the upper surface of the first dielectric substrate layer, and a top cross-shaped slot is opened in the cross-shaped metal structure along the centerline of the upper surface of the first dielectric substrate layer. The four PIN diodes are loaded in the top cross-shaped slot and are respectively located on the four metal arms of the cross-shaped metal structure. The metal mesh structure has a 90° rotational symmetry structure along the center and adopts a grid-shaped metal structure; The bottom metal structure has a 90° rotational symmetry structure along the center and adopts a metal layer covering the lower surface of the second dielectric substrate layer. The metal layer has a bottom cross-shaped slit (7) along the center line of the lower surface of the second dielectric substrate layer. The width of the metal line in the middle of the grid-shaped metal structure is twice that of the border metal line; the bottom cross-shaped gap adopts a bent structure; the cross-shaped metal structures of adjacent periodic units are connected accordingly; the border metal lines of the grid-shaped metal structures of adjacent periodic units are connected accordingly.

2. The low-profile energy selective surface with ultra-wideband protection as described in claim 1, characterized in that, The first dielectric substrate layer and the second dielectric substrate layer use the same dielectric substrate and have the same thickness.

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