Dual-band wave-absorbing waveguide integrated with Helmholtz resonant cavity array

Abstract

The invention provides a dual-band wave-absorbing waveguide integrated with a Helmholtz resonant cavity array, which comprises a low-frequency wave-absorbing body and a high-frequency wave-absorbing body which are nested on a rectangular waveguide body and formed by splicing a plurality of rectangular annular wave-absorbing units, and is characterized in that a plurality of wave-absorbing Helmholtz resonators which are periodically arranged are arranged on two groups of opposite sides of each wave-absorbing unit respectively; the resonant frequency of the wave-absorbing Helmholtz resonator is determined by the size of the Helmholtz resonant cavity and the relative dielectric constant of the filling medium. The high-frequency wave absorber and the low-frequency wave absorber achieve the broadband wave absorbing characteristic in a target frequency band, provide total reflection in other frequency bands, and achieve waveguide efficient wave guiding. By means of the design, the limitation that only narrow single-band band elimination characteristics can be achieved in the prior art is avoided, and dual-band broadband absorption of main-mode electromagnetic waves in the rectangular waveguide is achieved.

Description

Technical Field

[0001] The invention belongs to the technical field of artificial electromagnetic absorber materials, and in particular relates to a dual-band absorber for rectangular waveguides, which can be applied to fields such as high-density electronic components and integrated circuit absorbers. Background Art

[0002] Electromagnetic waves are prone to interference during transmission, especially in high-density electronic components and integrated circuits, where electromagnetic compatibility requirements are becoming increasingly stringent. Waveguide band-stop filters are widely used in various communication systems to suppress signals outside the passband. These filters achieve band-stop effects by coupling resonant cavities or transmission lines on the side walls of rectangular waveguides, but the large size of the resonant structure and the generally narrow stopband limit their broadband performance. For example, the patent application publication number CN114008852A discloses a design that achieves a single-band band-stop characteristic with a transmission coefficient lower than -18dB in the 6.206GHz-6.242GHz frequency band by connecting a cavity resonant structure on the narrow side of the waveguide, but its reflection coefficient is close to 0dB. Due to the high-order modes and physical size of the resonant structure, the design cannot achieve broadband dual-band band-stop characteristics. In addition, the cavity resonant structure of the invention is relatively high and complex in structure, which limits its flexibility and efficiency in practical applications.

[0003] Unlike band-stop filters, absorbing waveguide technology not only does not transmit signals within a limited frequency band, but also avoids reflections. This technology can eliminate reflections and reduce electromagnetic interference by introducing absorbing materials or structures into the waveguide, and is particularly suitable for use in high-density electronic systems. Compared with the reflection characteristics of band-stop filters, absorbing waveguides provide a cleaner signal transmission environment. However, existing absorbing waveguide technology faces some challenges. The performance of traditional absorbing materials is limited in waveguide structures, which is mainly reflected in the following aspects: First, the loading of absorbers often reduces the waveguide efficiency of the waveguide, because these materials usually have higher losses, which may cause additional signal attenuation in other waveguide working frequency bands. Secondly, it is difficult for absorbers to effectively suppress high-order mode responses in high-frequency applications, which may lead to poor absorbing effects and unnecessary electromagnetic interference. Summary of the invention

[0004] The purpose of the present invention is to overcome the defects existing in the above-mentioned prior art and propose a dual-band absorbing waveguide with an integrated Helmholtz resonant cavity array, aiming to achieve stopband characteristics without generating redundant reflections and improve electromagnetic compatibility.

[0005] To achieve the above purpose, the technical solution adopted by the present invention includes a low-frequency absorber 1 and a high-frequency absorber 2 nested on a rectangular waveguide body, both of which are composed of K rectangular ring-shaped absorber units 3, K ≥ 8; M and N absorber Helmholtz resonators 31 arranged in a period p are respectively arranged on the long side and the short side of the absorber unit to just completely cover the waveguide, M ≥ 4, N ≥ 2. Each absorber Helmholtz resonator 31 is composed of a metal cavity 311 and a filling medium 312 in the cavity.

[0006] The wave-absorbing Helmholtz resonator is tightly wrapped around the waveguide body, with the rectangular gap facing one side of the waveguide body, and the FR-4 medium filled in the middle of the Helmholtz resonant cavity in contact with the waveguide needs to have a corresponding gap space opened on the corresponding metal wall of the waveguide to allow the resonator to function.

[0007] The resonant frequency f of the wave-absorbing Helmholtz resonator is determined by the size of the Helmholtz resonant cavity and the relative dielectric constant ε of the filling medium. r Decide:

[0008]

[0009] Where c is the speed of light in vacuum, w1 and h1 are the width and height of the rectangular gap, w2 and h2 are the width and height of the rectangular cavity, respectively.

[0010] As an optimization, the wave-absorbing Helmholtz resonator 31 includes a rectangular metal block with a square cross-section and a Helmholtz resonant cavity. The Helmholtz resonant cavity is composed of a cross-shaped composite cavity arranged in the rectangular metal block and a dielectric material filled in the cavity.

[0011] As an optimization, the cross-shaped composite cavity includes a cross-shaped cavity composed of two rectangular cavities that penetrate two sets of side surfaces of the rectangular metal block and cross each other. A rectangular gap distributed along the length direction and penetrating the rectangular cavity is provided on the bottom surface of each rectangular cavity.

[0012] As an optimization, the two rectangular cavities constituting the cross-shaped cavity cross vertically, and the intersection point is located on the center normal line of the cross section of the rectangular metal block.

[0013] As an optimization, the rectangular gap is located at the center of the rectangular cavity in the width direction.

[0014] As an optimization, the widths of the rectangular gaps in the low-frequency wave-absorbing Helmholtz resonator and the high-frequency wave-absorbing Helmholtz resonator are equal.

[0015] As an optimization, the cross section of the absorbing unit is perpendicular to the propagation direction of the waveguide.

[0016] Compared with the prior art, the present invention has the following advantages:

[0017] 1. A low-frequency absorber and a high-frequency absorber formed by splicing a plurality of absorber units are embedded on the rectangular waveguide of the present invention, and a plurality of absorber Helmholtz resonators are arranged on the sides of the absorber units. The high-frequency and low-frequency absorbers realize broadband absorber characteristics in the target frequency band, and provide total reflection in other frequency bands, and realize efficient waveguide waveguiding, avoiding the limitation of the prior art that only narrow single-band band-stop characteristics can be realized, and realizing dual-band broadband absorption of main mode electromagnetic waves in the rectangular waveguide.

[0018] 2. The absorption frequency of the present invention is determined by the size of the Helmholtz resonant cavity and the relative dielectric constant of the filling medium, and is related to the number of rings around the waveguide. It has more adjustable degrees of freedom and will not produce high-order resonant absorption effects.

[0019] 3. The low-frequency broadband absorption structure and the high-frequency broadband absorption structure adopted in the present invention will not affect each other, showing independent adjustability, and the loss material used is single, the design is simple, and it is easy to prepare. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] Figure 1 It is a structural schematic diagram of the present invention.

[0021] Figure 2 It is a side view of the wave absorbing unit in the present invention.

[0022] Figure 3 It is a schematic diagram of the structure of the wave-absorbing Helmholtz resonator in the present invention.

[0023] Figure 4 Schematic diagram of the S parameters of the rectangular waveguide in the present invention.

[0024] Figure 5 It is a schematic diagram of wave absorption of the present invention.

[0025] Figure 6 This is a schematic diagram of the internal field distribution of the waveguide structure in the wave absorbing state of the present invention.

[0026] Figure 7 This is a diagram of the wave absorbing performance of the Helmholtz resonant wave absorbing unit of the present invention.

[0027] Figure 8 Graphs showing the wave absorbing performance of the waveguide when the present invention only includes a low-frequency absorber and a high-frequency absorber.

[0028] Fig. 9 This is a schematic diagram of the S parameters after the dual-band Helmholtz resonant absorbing structure is loaded in the present invention. DETAILED DESCRIPTION

[0029] The present invention is further described in detail below in conjunction with the accompanying drawings and specific embodiments.

[0030] Reference Figure 1 The present invention comprises a low-frequency absorbing body 1 and a high-frequency absorbing body 2 nested on a rectangular waveguide body, the two absorbing bodies are both formed by splicing K rectangular ring-shaped absorbing units 3, K≥8, the long side and the short side of the absorbing unit are respectively provided with M and N periodically arranged absorbing Helmholtz resonators 31, the rectangular gap in the absorbing Helmholtz resonator faces one side of the waveguide body, and the area of ​​the rectangular cavity cross section in the low-frequency absorbing Helmholtz resonator is greater than the area of ​​the rectangular cavity cross section in the high-frequency absorbing Helmholtz resonator, and the resonant frequency f of the absorbing Helmholtz resonator is determined by the size of the Helmholtz resonant cavity and the relative dielectric constant ε of the filling medium. r Decide:

[0031]

[0032] Where c is the speed of light in vacuum, w1 and h1 are the width and height of the rectangular gap, w2 and h2 are the width and height of the rectangular cavity, respectively.

[0033] The rectangular waveguide used in the present invention has a width a of 20 mm, a height b of 10 mm and a length z of 300 mm. The number K of the absorbing units 3 constituting the low-frequency absorbing body 1 and the high-frequency absorbing body 2 is 18.

[0034] Reference Figure 2 The wave-absorbing Helmholtz resonator 3 includes M wave-absorbing Helmholtz resonators 31 periodically arranged above and below and perpendicular to the propagation direction of the waveguide signal, and N wave-absorbing Helmholtz resonators 31 periodically arranged left and right and perpendicular to the propagation direction of the waveguide signal, the arrangement period p is 5 mm, and the rectangular gap on the wave-absorbing Helmholtz resonator faces one side of the waveguide body.

[0035] Reference Figure 3 The wave absorbing Helmholtz resonator 31 comprises a rectangular metal block with a square cross section and a Helmholtz resonant cavity. The Helmholtz resonant cavity is composed of a cross-shaped composite cavity arranged in the rectangular metal block and a dielectric material filled in the cavity. The dielectric material is FR4, with a dielectric constant ε r is 4.3, and the loss tangent is 0.25. The slit width w1 is 0.1 mm, the slit height h1 is 0.6 mm, the cavity width w2 is 1.2 mm, the cavity height h2 is 0.5 mm, and the entire Helmholtz resonant cavity height is 2.5 mm.

[0036] The working principle of the present invention is that, when electromagnetic waves are incident in free space, the Helmholtz resonant cavity only allows the electromagnetic waves of the specific frequency to enter the resonant cavity and be absorbed by the lossy medium. In a rectangular waveguide, the Helmholtz resonant cavity bends the electric field lines, causing the waveguide transmission phase to change, so the continuous arrangement of the Helmholtz resonant cavities will widen the absorption band, resulting in a broadband absorption effect.

[0037] The present invention includes two working frequency Helmholtz resonant cavity wave absorbing structures consisting of an empty rectangular waveguide working at 8-15GHz and a surrounding rectangular waveguide. The distance between the Helmholtz resonant cavity array working at low frequency and the waveguide port 1 is l1=40mm, the distance between the Helmholtz resonant cavity array working at high frequency and the waveguide port 2 is l2=62mm, and the distance between the two Helmholtz resonant cavity arrays is 20mm. An array of two annular Helmholtz resonators with different working frequencies is embedded in the four metal walls of the rectangular waveguide. The rectangular metal device composed of the Helmholtz cavity array can be used as a connecting device for the metal waveguide, because the resonant cavity body itself is a metal structure, which can replace part of the waveguide, and only absorbs waves at the resonant frequency, and will not absorb at other frequencies. The outer material of the rectangular waveguide also adopts an aluminum metal skin closed structure, and the filling medium in the waveguide is air. The Helmholtz resonator is outside the aluminum metal skin, and the part where the FR4 medium in the middle of the Helmholtz resonator contacts the waveguide needs to have a corresponding space dug out on the metal wall of the waveguide so that the resonator can function.

[0038] When electromagnetic waves are incident on the Helmholtz resonant cavity in free space, only electromagnetic waves with the same resonant frequency as the resonant cavity are allowed to converge through the narrow slit into the cavity, and then all other electromagnetic energy is reflected. When resonating, the narrow slit of the Helmholtz resonant cavity can be equivalent to a flat plate capacitor, and its equivalent capacitance of the gap is:

[0039]

[0040] Where ε0 is the dielectric constant of vacuum, ε r is the relative dielectric constant, w1 is the slit width, and h1 is the slit height. Its resonant cavity can be equivalent to an inductor, and the equivalent inductance can be expressed as:

[0041]

[0042] Where μ0 is the vacuum magnetic permeability, w2 is the width of the cavity, and h2 is the height of the cavity. At this time, the resonant frequency of the Helmholtz resonant cavity can be approximately determined by the following formula:

[0043]

[0044] Here, c is the speed of light in vacuum.

[0045] The following is a further description of the technical effects of the present invention in conjunction with the simulation results:

[0046] 1. Simulation conditions and contents:

[0047] The simulation software CST Microwave Studio 2022 simulates the performance of the present invention:

[0048] Experiment 1: The empty rectangular waveguide in the present invention is simulated, and the frequency is set to 7.5-15 GHz. In this frequency range, the waveguide only propagates TE 10 The waveguide is simulated using the finite-difference time-domain solver. The simulation results are shown in Figure 4 shown.

[0049] Experiment 2: The dual-band rectangular waveguide broadband absorber of the present invention is simulated. The frequency is set to 8-16 GHz. The waveguide is simulated using the finite difference time domain method solver. The simulation results are as follows: Figure 5 shown.

[0050] Experiment 3: The electric field distribution of the dual-band rectangular waveguide broadband absorber in the present invention is calculated. The frequency is set to 10.65 GHz. The electric field distribution of the waveguide at port 1 is as follows: Figure 6 As shown in (a), the electric field distribution of the dual-band rectangular waveguide broadband absorber on the xoz cross section is as follows: Figure 6 As shown in (b), the magnetic field distribution of the dual-band rectangular waveguide broadband absorber on the xoz cross section is as follows: Figure 6 As shown in (c), the power loss distribution of the dual-band rectangular waveguide broadband absorber on the xoz cross section is as follows: Figure 6 As shown in (d), the power loss distribution of the rectangular waveguide dual-band broadband absorber on the yoz cross section is as follows: Figure 6 (e) as shown.

[0051] Experiment 4: For the two Helmholtz resonant cavity units used in the present invention, the frequency domain finite element method solver is used to simulate the two, and the frequencies are set to 0-13 GHz and 13-18 GHz respectively. The simulation results are as follows: Figure 7 shown.

[0052] Experiment 5: The low-frequency broadband and high-frequency broadband Helmholtz resonant cavity wave absorbing structures in the present invention are combined with waveguides respectively, and the frequencies are set to 8-15 GHz and 10-18 GHz respectively. The waveguide is simulated using the finite difference time domain method solver. The simulation results are shown in the figure. Figure 8 shown.

[0053] Experiment 6: The two Helmholtz resonant cavity structures in the present invention are combined with the waveguide, and the waveguide is simulated using the finite difference time domain method solver, and compared with the simulation results of the empty rectangular waveguide without the two Helmholtz resonant cavity structures. The frequency is set to 8-16GHz. The simulation results are as follows: Fig. 9 shown.

[0054] 2. Experimental results analysis:

[0055] Reference Figure 4 , Figure 4 It shows that the empty rectangular waveguide in TE10 When the main mode electromagnetic wave propagates along the waveguide, the S parameter of the waveguide port changes. 21 It starts to increase at 7.5-8GHz and starts at 8GHz. 11 Below -60dB, the transmission coefficient S 21 It is about 0dB, indicating that the rectangular waveguide works well.

[0056] Reference Figure 5 , the rectangular waveguide loaded with dual-frequency Helmholtz resonant cavity array has an absorption rate of 90% or more at low frequencies from 9.6GHz to 11.1GHz, and the relative absorption bandwidth is 14.5%. At high frequencies from 14.1GHz to 15.8GHz, the absorption rate is more than 90%, and the relative absorption bandwidth is 11%. Among them, the absorption rate at 10.65GHz in the low-frequency broadband absorption range is as high as 98.5%, and the absorption rate at 14.35GHz in the high-frequency broadband absorption range is as high as 98%, realizing the dual-frequency broadband absorption characteristics of the main mode electromagnetic wave transmitted in the rectangular waveguide.

[0057] Reference Figure 6 , given in TE 10 The electromagnetic field energy distribution diagram at different positions and cross sections of a rectangular waveguide at a frequency of 10.65 GHz during wave propagation along the waveguide. Figure 6 (a) shows the electric field density at waveguide port 1. It is found that the electric field energy is the largest in the middle of the wide side a of the rectangular waveguide, and there is almost no electric field energy on both sides of the wide side a near the narrow side b, which indicates that the feed source generates TE 10 Master mode. TE 10 The main mode electric field is only E y The component does not change along the y-axis, but it changes sinusoidally along the x-axis. 10 The wave of the mode moves along the waveguide in the z-axis direction, and the electric field energy is always kept at the maximum in the center of the broadside. When the electric field vector is vertically irradiated on the upper and lower rows of Helmholtz resonant cavities on the broadside, the electric field vector is converged to the narrow slit of the middle Helmholtz resonant cavity, while the electric field is almost not converged in the cavities at both ends of the broadside due to the energy distribution, such as Figure 6 (b) is shown. And there is a weak electric field in the four Helmholtz resonant cavities on the narrow side of the waveguide. Because the vector direction of the electric field in the waveguide is along the y-axis direction, parallel to the yoz plane, it is equivalent to incident on the Helmholtz resonant cavities on the left and right sides at 90°, and the electric field density on the left and right sides of the waveguide itself is almost zero. However, because the Helmholtz resonant cavity can bend the electric field parallel to itself and close to the middle of the waveguide into the narrow slit, it can also produce lossy electromagnetic waves. Figure 6As shown in (c), in the cavity of the Helmholtz resonant cavity, the magnetic field energy is also concentrated in the cavity at the center of the upper and lower sides. The concentration of the magnetic field energy depends on the induced magnetic field strength generated after the narrow slit of the resonant cavity gathers the electric field energy. There is almost no magnetic field energy in the cavity at both ends of the wide side, and there is a weak magnetic field in the narrow side Helmholtz resonant cavity. The Helmholtz resonant cavity is equivalent to an LC resonator, the narrow slit is equivalent to a capacitor, and the cavity is equivalent to an inductor. When the magnetic field vector is perpendicular to the four Helmholtz resonant cavities on the yoz plane, because the narrow slit of the cavity only allows current to enter, it is equivalent to a metal wall at this time. Figure 6 The power loss shown in (d) mainly occurs in the wide-side Helmholtz resonant cavity, which focuses the vertically incident electric field into the narrow gap and consumes electromagnetic waves by relying on the loss of the FR4 medium. Figure 6 (e) shows the TE at the yoz section in the waveguide at a certain time. 10 Electric field density diagram of a Helmholtz resonator operating at a low frequency during wave propagation from left to right. The electric field vector E y During the propagation process, the electric field vector provided by port 1 changes, and E y The peaks and valleys of the electric field intensity. At the peak, the electric field intensity is the largest, so the Helmholtz resonant cavity has the strongest ability to converge the electric field. At the valley, the electric field intensity is the smallest, so the Helmholtz resonant cavity has the weakest ability to converge the electric field. And the loss capacity of electromagnetic waves is the strongest within the half-wavelength range at the beginning of the Helmholtz resonant cavity array, because the electromagnetic wave energy in the waveguide is the strongest at this time, and the propagation energy is weakened after being consumed by the front-end Helmholtz resonant cavity, and the energy that can be resonated and absorbed by the subsequent Helmholtz resonant cavity becomes less.

[0058] Reference Figure 7 , the result obtained when the frequency domain simulation is performed with a plane wave in free space at vertical incidence. Figure 7 As shown in (a), the low-frequency Helmholtz cavity has perfect absorption at 10.4 GHz, as Figure 7 As shown in (b), after changing the parameters of the Helmholtz cavity, the high-frequency Helmholtz cavity absorbs perfectly at 15.4 GHz.

[0059] Reference Figure 8 When the 18-row ring array consisting of 12 Helmholtz resonant cavities operating at 10.4 GHz is embedded in the waveguide system, the S parameter results and wave absorption are shown in Figure 2. Figure 8 (a)-(b) shows that the absorption rate is 90% or above from 9.78 GHz to 11.23 GHz, and the relative bandwidth is 13.8%. Figure 5Compared with the absorption band of the medium and low frequencies in the dual-band absorbing waveguide between 9.6 GHz and 11.1 GHz, the center frequency moves toward the high frequency. The Helmholtz resonant cavity unit working at 15.4 GHz is assembled in the waveguide system in the same way, and the S parameter results and absorption conditions are as follows: Figure 8 (c)-(d) It can be seen that the absorption rate is 90% or above from 13.65 GHz to 14.82 GHz, and the relative bandwidth is 8.2%. Figure 5 Compared with the absorption band of 14.1GHz to 15.8GHz in the medium- and high-frequency dual-band absorbing waveguide, the center frequency moves toward the low frequency. After the two Helmholtz arrays are embedded in the waveguide system, the relative bandwidth is reduced because the absorption rates of the two in their respective ineffective absorption bands are not zero. When the two are combined in a waveguide system, their respective absorption bandwidths will be increased, thus achieving a better broadband absorption effect.

[0060] Reference Fig. 9 , when no absorber is loaded, the reflection coefficient S of the empty waveguide 11 From 8 to 16 GHz, the transmission coefficient is lower than -45 dB. 21 Close to 0dB, with good transmission characteristics. After loading the absorber, the low-frequency absorption transmission coefficient S 21 In the broadband absorption range from 9.9GHz to 10.3GHz, the attenuation is below -40dB, and the reflection coefficient S 11 Increased to a maximum of -10dB, the transmission coefficient S in the high-frequency broadband absorption range 21 From 14.4GHz to 15GHz, it is -40dB, and the reflection coefficient S 11 The maximum is -11dB.

Claims

1. A dual-band absorbing waveguide with an integrated Helmholtz resonant cavity array, characterized in that: The invention comprises a low-frequency wave absorbing body (1) and a high-frequency wave absorbing body (2) nested on a rectangular waveguide body, wherein the two wave absorbing bodies are both formed by splicing K rectangular ring-shaped wave absorbing units (3), where K is greater than or equal to 8, and M and N wave absorbing Helmholtz resonators (31) arranged periodically are respectively arranged on the long side and the short side of the wave absorbing unit, wherein the rectangular gap in the wave absorbing Helmholtz resonator faces the side of the waveguide body, and the resonance frequency f of the wave absorbing Helmholtz resonator is determined by the size of the Helmholtz resonance cavity and the relative dielectric constant ε of the filling medium. r Decide: Where c is the speed of light in vacuum, w1 and h1 are the width and height of the rectangular gap, w2 and h2 are the width and height of the rectangular cavity, respectively.

2. The absorber according to claim 1, characterized in that: The wave-absorbing Helmholtz resonator (31) comprises a rectangular metal block with a square cross section and a Helmholtz resonant cavity, wherein the Helmholtz resonant cavity is composed of a cross-shaped composite cavity arranged in the rectangular metal block and a dielectric material filled in the cavity.

3. The absorber according to claim 2, characterized in that: The cross-shaped composite cavity comprises a cross-shaped cavity composed of two rectangular cavities penetrating two sets of side surfaces of a rectangular metal block and intersecting in a cross shape, and a rectangular gap distributed along the length direction and penetrating the rectangular cavity is arranged on the bottom surface of each rectangular cavity.

4. The absorber according to claim 3, characterized in that: The two rectangular cavities constituting the cross-shaped cavity intersect vertically, and the intersection point is located on the central normal line of the cross section of the rectangular metal block.

5. The absorber according to claim 3, characterized in that: The rectangular gap is located at the center of the rectangular cavity in the width direction.

6. The absorber according to claim 5, characterized in that: The widths of the rectangular gaps in the low-frequency wave-absorbing Helmholtz resonator and the high-frequency wave-absorbing Helmholtz resonator are equal.

7. The wave absorbing body according to any one of claims 2 to 6, characterized in that: The cross section of the wave absorbing unit is perpendicular to the propagation direction of the waveguide.

Images