Multilayer Cavity Research Articles

Multilayer circular SIW cavity differential bandpass filter with wide‐stopband characteristics

AbstractIn this paper, a compact differential bandpass filter with wide‐stopband is presented. The proposed differential filter is designed using two circular substrate‐integrated waveguide (SIW) cavities coupled through a pair of symmetric coupling slots. The filter operates in TM110 mode of the circular SIW cavity. The degenerate TM110 mode is shifted to higher frequency by the introduction of two pairs of perturbation vias. The center frequency of the differential passband can be tuned by changing different design parameters such as location of perturbation vias and length of the slotlines. As a proof of the proposed concept, a second‐order differential bandpass filter is designed, fabricated, and measured. The measured results are in good agreement with the electromagnetic‐simulated ones.

A highly efficient and accurate numerical method for the electromagnetic scattering problem with rectangular cavities

This paper presents a robust numerical solution to the electromagnetic scattering problem involving multiple multi-layered cavities in both transverse magnetic and electric polarizations. A transparent boundary condition is introduced at the open aperture of the cavity to transform the problem from an unbounded domain into that of bounded cavities. By employing Fourier series expansion of the solution, we reduce the original boundary value problem to a two-point boundary value problem, represented as an ordinary differential equation for the Fourier coefficients. The analytical derivation of the connection formula for the solution enables us to construct a small-scale system that includes solely the Fourier coefficients on the aperture, streamlining the solving process. Furthermore, we propose accurate numerical quadrature formulas designed to efficiently handle the weakly singular integrals that arise in the transparent boundary conditions. To demonstrate the effectiveness and versatility of our proposed method, a series of numerical experiments are conducted.

Multilayer circular substrate-integrated waveguide cavity band-pass filters with ultrawide stopband characteristics

AbstractThis paper presents a methodology to design band-pass filters having ultrawide stopband characteristics using multilayer circular substrate-integrated waveguide (SIW) cavities. The orthogonal microstrip feedlines are used as input and output ports that are present at the top and bottom layers, while the middle layers are used to couple the SIW cavities. Higher-order spurious modes of the circular SIW cavity are suppressed by using orthogonal feeding mechanism and properly adjusting the arc-shaped slots between the cavities. To validate the present approach, two filters (second- and fourth-order) have been designed and fabricated and their characteristics are measured. The second-order filter exhibits a stopband rejection below 25 dB up to nearly 5.07f0, while the fourth-order filter has a stopband characteristic of nearly 5.05f0 with 20 dB rejection. The filters allow only TM010 mode propagation and attenuate the higher-order spurious modes of the cavity.

A thermocouple based on wideband hybrid metamaterial absorber for mid-infrared photo-thermoelectric detector

A mid-infrared (MIR) photo-thermoelectric (PTE) detector is proposed based on a hybrid thermocouple consisting of a wideband metamaterial absorber and Seebeck material. When a mid-infrared wave illuminates the detector, the incident energy of the MIR beam is efficiently detected in this process of converting the energy of the light wave into the absorbed heat firstly by the wideband metamaterial absorber, and then outputting a voltage change according to the variation in temperature by a semiconductor material with a high Seebeck coefficient. Because of the existence of the metamaterial absorber, the high absorptions are almost achieved at a wide wavelength range from 3.4μm to 4.8μm with the absorptivity over 80%, and the average absorptivity is 93.6%. Meanwhile, the perfect absorptions appear at the wavelengths of 3.6μm, 4μm and 4.4μm. Comparing with the other reported detectors based on black materials and multilayer resonant cavities, this metamaterial absorber has a high absorptivity as well as a wide bandwidth, facilitating the maximum responsivity of single thermocouple as high as 0.89V/W. This hybrid thermocouple is able to operate at room temperature and has the advantages of angle insensitivity, simple in structure and easy integration, which has good potential applications in mid-infrared detection, sensing and imaging.

Multispectral Imaging with a Planar Cavity-Type Metasurface for Optical Security.

Multispectral imaging refers to capturing images in different wavelength ranges across the electromagnetic spectrum. Despite the potential impact of multispectral imaging, its widespread use has been limited by the poor spectral selectivity of naturally occurring materials beyond the visible range. In this study, we present a multilayered planar cavity structure to simultaneously record mutually independent visible and infrared (IR) images on solid surfaces. The structure consists of a color control unit (CCU) and an emission control unit (ECU). The visible color of the cavity is controlled by varying the thickness of the CCU, whereas its IR emission is spatially tuned by the laser-induced phase change of a Ge2Sb2Te5 layer embedded in the ECU. Because the CCU comprises only IR lossless layers, its thickness variation has negligible influence on the emission profile. This enables different color and thermal images to be printed in a single structure. The cavity structure can be fabricated on flexible substrates (plastic and paper) as well as rigid bodies. Furthermore, the printed images remain stable against bending. This study shows that the proposed multispectral metasurface is highly promising for use in the field of optical security, such as identification, authentication, and anti-counterfeiting.

Highly efficient NbTiN nanostrip single-photon detectors using dielectric multilayer cavities for a 2-µm wavelength band.

We report superconducting nanostrip single-photon detectors (SNSPDs) with dielectric multilayer cavities (DMCs) for a 2-µm wavelength. We designed a DMC composed of periodic SiO2/Si bilayers. Simulation results of finite element analysis showed that the optical absorptance of the NbTiN nanostrips on the DMC exceeded 95% at 2 µm. We fabricated SNSPDs with an active area of 30 µm × 30 µm, which was sufficiently large to couple with a single-mode fiber of 2 µm. The fabricated SNSPDs were evaluated using a sorption-based cryocooler at a controlled temperature. We carefully verified the sensitivity of the power meter and calibrated the optical attenuators to accurately measure the system detection efficiency (SDE) at 2 µm. When the SNSPD was connected to an optical system via a spliced optical fiber, a high SDE of 84.1% was observed at 0.76 K. We also estimated the measurement uncertainty of the SDE as ±5.08% by considering all possible uncertainties in the SDE measurements.

Nanoelectromechanical Temperature Sensor Based on Piezoresistive Properties of Suspended Graphene Film

The substrate impurities scattering will lead to unstable temperature-sensitive behavior and poor linearity in graphene temperature sensors. And this can be weakened by suspending the graphene structure. Herein, we report a graphene temperature sensing structure, with suspended graphene membranes fabricated on the cavity and non-cavity SiO2/Si substrate, using monolayer, few-layer, and multilayer graphene. The results show that the sensor provides direct electrical readout from temperature to resistance transduction by the nano piezoresistive effect in graphene. And the cavity structure can weaken the substrate impurity scattering and thermal resistance effect, which results in better sensitivity and wide-range temperature sensing. In addition, monolayer graphene is almost no temperature sensitivity. And the few-layer graphene temperature sensitivity, lower than that of the multilayer graphene cavity structure (3.50%/°C), is 1.07%/°C. This work demonstrates that piezoresistive in suspended graphene membranes can effectively enhance the sensitivity and widen the temperature sensor range in NEMS temperature sensors.

Numerical and experimental investigations of concrete lined compressed air energy storage system

Compressed air energy storage (CAES) is considered one of the critical technological approaches to bridging the gaps between clean electricity production and electricity demand. An in-situ air storage test in a shallow buried underground cavern was introduced to understand better the connection and mutual influence between aerothermodynamics and cavern safety stability in various aspects of CAES. Moreover, a corresponding finite element model of the multilayer cavity structure considering the multi-field coupling effect and rebar embedding was developed to verify the experimental results. The experimentally measured temperature, air pressure, displacement, and stress are in good agreement with the calculated results, showing the success of the modeling in this paper. The cavern temperature shows large fluctuations for the whole storage phase. The maximum temperature of the air and the cavern walls are 53 °C and 46 °C, respectively. After water circulation heat exchange, the temperature can be regulated within a reasonable range (<40 °C). The cavity walls can reverse the heat output of the air through heat exchange during the discharging phase resulting in a slower temperature drop. The concrete stress is about 1/10 of the reinforcement stress, showing that the deformation between the rebar and concrete is coordinated, and both are in the elastic deformation stage. The sealing layer, reinforced concrete lining, and rock surrounding share the internal air pressure, accounting for 2.07%, 27.55%, and 70.38%, respectively. The surrounding rock is the most important part of bearing the internal pressure, and it is an essential means to improve the safety of the cavity by carrying out anchoring and grouting of the surrounding rock. The thermodynamic processes and stress response are affected by the convection heat transfer coefficient, thermal conductivity, charging time, and leakage rate.

Development of a Wideband Slotted Antenna Array with Low Profile and Low Sidelobe

In this paper, a novel multi-layered waveguide-fed slotted cavity antenna array operating in the K-band (i.e., 18–27 GHz) is presented. The antenna is composed of 64 (8 × 8) groups of 2 × 2 subarrays with low profile, and fed by a 1–64 ways waveguide corporate-feed-network. In order to obtain a low sidelobe level (SLL), the Chebyshev power distribution is introduced into the feeding network to accurately taper the power distribution among the subarrays. To realize the amplitude-tapering network, a simple T-junction, which can provide equal phase but unequal power, is used. The antenna array is analyzed and validated by using the finite element method (FEM). Simulation results demonstrate that the proposed antenna array can achieve a broad bandwidth of 21.9%, and a good gain as 29.1 dBi. Additionally, the first SLL can be as small as −28.3 dB and −20 dB in the E-plane and the H-plane, respectively. The overall size of the slotted cavity antenna array is 169.6 × 169.6 × 7.23 mm3.

Retracted: Design of LoRa Antenna for Wearable Medical Applications

The intraoral Tongue Drive System (iTDS) is a wireless assistive technology (AT) that may be operated using a variety of user-defined voluntary tongue motions. In this study, we introduce a novel arch-shaped iTDS that takes up the buccal shelf space in the mouth without constricting tongue motions. Damage to the central nervous system that causes upper limb paralysis. For instance, severe spinal cord injuries, certain strokes or multiple amputations of the upper limbs can make it very difficult for a lot of individuals to go about their everyday lives since they cause them to lose function, control, and independence. Because its muscles are strong and dexterous and do not quickly tire when not necessary to exert power, the tongue is an excellent choice for controlling an AT. Additionally, through cranial nerves, which are unaffected by a spinal cord damage, the tongue is directly attached to the brain. Furthermore, since the tongue movements may be totally hidden from view, TDS-based AT safeguard users’ privacy. In order to provide an effective solution, this paper proposed a novel antenna design with dual-band and implantability. The antenna is modelled in single-layer human muscle considering the feasibility and computational time. Then, the performance is evaluated through multi-layered human oral cavity model. A protective layer is established to prevent direct contact between the antenna and human body. Simulation results show that the proposed antenna has better reflection coefficient, impedance, and radiation pattern as compared with existing antennas.

Mapping the Optomechanical Coupling Mediated by Light among Mechanical Resonators Including Multilayer Cavity and Molecules

For a wide range of health applications, label-free sensing is essential, and microphotonics offers innovative technical solutions for pursuing important objectives. It has been shown that the strong light/matter coupling formed between a cavity and molecules through light excitation enhances biological and clinical applications by providing deep insights into molecular analysis. The multilayer cavity’s proposed architecture is meant to promote a robust interaction between light and matter. The top layer was made of silver Ag multishape features that, after being synthesized and characterized, were immobilized on the surface of a multilayer system. A layer of indium tin oxide (ITO) was flipped to produce two distinct layouts. An investigation of the mode behavior was conducted to describe the two layouts; experimental and numerical results point to a strong light/matter interaction by the ITO/SiO2/spacer/Ag design. For the characterization of light/matter coupling, a fluorophore was adsorbed on the surface; the anticrossing energy was then examined by integrating the experimental data with a three mechanical oscillator model. To show the system’s sensitivity, the analysis was carried out again using bovine serum albumin (BSA). The protein is water-soluble and exhibits an infrared absorption band (amide I), while also being active in the Raman region. In addition, it may consistently bind to Ag multishape features. The excellent sensitivity was demonstrated, enabling the use of image analysis to capture the surface-enhanced Raman scattering of BSA. In conclusion, the suggested sensing approach raises fresh possibilities for highly sensitive biomolecule detection method and encourages results when used as a fundamental sensing technique to investigate molecular patterns.

Evolutionary design of two-dimensional material Fabry-Perot structures for enhanced second harmonic generation.

The integration of two-dimensional (2D) materials with resonant photonic structures is seen as a promising direction for enhancing its nonlinear optical response. The design of such heterogeneous resonant structures has often relied on multi-parameter sweeps to determine the optimized dimensions of resonant optical structure that results in good resonance characteristics, often in the absence of the 2D material. Such an approach is computationally intensive and may not necessarily result in efficient generation or collection of nonlinear signals from the designed structure. Here, we report hybrid-genetic optimization (HGA) based design and experimental demonstration of second harmonic generation (SHG) enhancement from Fabry-Perot structures of single and double multilayer gallium selenide (GaSe) flakes with bottom silicon dioxide, and index matched polymethyl methacrylate spacer/encapsulation layers. HGA technique utilized here speeds up the multilayer cavity design by 8.8 and 89-times for the single and double GaSe structures when compared to the full parameter-sweep, with measured SHG enhancement of 128- and 400-times, respectively, when compared to a reference sample composed of GaSe layer of optimized thickness on 300nm silicon dioxide layer. SHG conversion efficiencies obtained from the HGA structures are 1-2 orders of magnitude higher than previous reports on 2D material integrated resonant metasurfaces or Bragg cavities.

Symmetric photodetector integrated with multilayer dielectric resonator cavity for 400 Gb/s optical communication system

The Multilayer Dielectric Resonator Cavity Symmetric Photodetector (MDRC-SPD) is designed and characterized. The photodetector possesses an InGaAs/InP symmetrical absorption structure bonded to the resonator cavity with Si/SiO2 reflector. These features alleviate the tradeoff between the 3 dB bandwidth and the quantum efficiency, and the 3 dB bandwidth of 41.3 GHz and the quantum efficiency of 0.92 are achieved. As a result, the optimal bandwidth-efficiency-product (BEP) and figure of merit (FOM) of the MDRC-SPD are 36.7 GHz and 14.6 dB at a reverse bias of 3 V, respectively, satisfies the requirements for the 400 Gb/s optical communication system using PAM4 modulation format.

High Resolution and Stability Self-Reference Plasmonic Sensor With Metallic Grating on Multilayered Dielectric Cavity Substrate

In order to improve the sensing performance of surface plasmon resonance (SPR) refractive index (RI) sensor and avoid the negative effect of various environmental factors, a self-reference plasmonic sensor with high resolution and stability based on the combination of metallic grating and multilayered dielectric cavity is proposed in this article. The sensing mode, based on SPR in the metallic grating, is sensitive to the RI variations of the analyte. The guided mode resonances (GMRs), excited by the multilayered dielectric cavity, can be served as self-references due to the insensitivity to the analyte’s RI variations. It is verified that the sensitivity of 500 nm/RIU is achieved, and the smallest sensitivity of self-reference resonance is 0.83 nm/RIU; thus, the sensitivity ratio (stability) is up to 602. Also, a large figure of merit (FOM) of 238 RIU−1 in the sensor is realized and a high-quality factor of 4668 of self-reference mode with high resolution is achieved, which is much better than that of the previous works. The results provide a theoretical basis to design a highly sensitive self-reference plasmonic sensor and have a potential application in the industrial measuring instruments such as the sensor to measure water content in heavy oil.

Fast design and optimization method for an ultra-wideband perfect absorber based on artificial neural network acceleration

In recent years, ultra-wideband perfect absorbers (UWPAs) based on metamaterial nanostructures have been widely studied due to their excellent performance. However, designing and optimizing the absorber quickly and accurately remains challenging in the broad-band range. In this work, by adopting the genetic algorithm combined with artificial neural network (ANN) acceleration, an effective method with the global search ability and extremely fast optimization speed is developed, which only requires an accurate forward ANN model and offers tremendous controls to the designer. In the context of the optimization of the nano-multilayers absorber, the most of mean absolute errors (MAEs) of ANN between the actual spectral absorptance and the predicted spectral absorptance are less than 1E-2, demonstrating the outstanding consistency. What's more, the optimization speed is four orders of magnitude faster than conventional electromagnetic simulation software, 1.2 × 105 search calculations take only 573 s. Meanwhile, we also show that the hybridization between multilayer cavity plasmonic resonant modes is the main cause of the ultra-wideband absorptance. This method significantly increases the viability of more complex ultra-wideband perfect absorber designs and provides opportunities to manipulate light-matter interactions in the future.

A Study on Dynamic Characteristics of Thin-Walled Cylindrical Cavities with a Large Aspect Ratio

The unstable combustion problem in small-sized solid rocket engines with a large aspect ratio is so complicated that its causes remain unclear. In this study, the coupled vibration between the sound field and shell in the engines was proposed as a possible cause. A solid rocket engine structure was abstracted into a multilayer thin-walled cylindrical cavity in this study, followed by the theoretical calculation and simulation calculation of its inherent frequency. Next, a thin-walled cylindrical cavity fluid-solid coupling experimental platform with the function of modal measurement was established to verify the accuracy of simulated modes for the shell structure and acoustic cavity. Then, the mode of the finite element model (FEM) for the solid rocket engine was theoretically calculated and simulated, accompanied by finite element calculation and experiment of the acoustic mode of the internal acoustic cavity. Subsequently, the engine mode was compared with the acoustic mode of the internal acoustic cavity. On this basis, a new cause for the damage and disintegration of the solid rocket engines in the final working stage was revealed. Moreover, a brand-new idea of inhibiting the pressure oscillation-induced unstable combustion in the solid rocket engines was put forward.

Significant Reduction of Resonant Frequency by Multi-Layered Dielectric Material-Loaded Coaxial Cavity for Microwave Heating

This paper presents a microwave heating method using a cavity whose size is much smaller than the free-space wavelength. The resonant frequency was reduced by inserting multi-layer dielectrics into the cavity, and an appropriate mode was generated in the cavity to heat a specific area inside it. High-permittivity dielectrics were used to make the cavity resonate in the frequency range of a few gigahertz. A formula for the resonant frequency of the multi-layer dielectric material-loaded cylindrical cavity was analytically derived. The frequency reduction by using a dielectric-loaded cylindrical cavity geometry was predicted from the derived formula, from 12.2 GHz to 4.6 GHz, whereas the experiment results showed a reduction from 10.8 GHz to 4.5 GHz. The analytical and the experiment results were compared and analyzed with simulations, which showed good agreement. The heating efficiency at the target in the multi-layered dielectric geometry was analyzed. The electric field inside the target material was measured to prove the temperature response of the microwave heating and was compared with the simulation result. This paper confirms a technical possibility of microwave heating of a smaller-sized cavity with an insertion of low-loss dielectric material in the vicinity of a heating target.

A High-Temperature and Frequency-Reconfigurable Multilayer Frequency Selective Surface Using Liquid Metal

A high-temperature and frequency-reconfigurable multilayer frequency selective surface (FSS) based on liquid metal is proposed in this work. After construction of a multilayer dielectric cavity with specific dielectric-shaped pillars and the injection of liquid metal (EGaIn) into each layer of the cavity, the liquid metal and dielectric pillars form a slot-type bandpass FSS, and frequency reconfiguration is realized by switching the injection layer. A prototype of the proposed FSS was designed, fabricated and measured. The measured results validated the design well. The good conductivity and fluidity of the liquid metal are utilized to realize the reconfigurable electromagnetic performance of the proposed FSS. This works in the C-band (5 GHz) and Ku band (13 GHz) and has a frequency switching time between 13.1 to 14.2 s. Moreover, due to the good thermal conductivity of liquid metal, the flowing liquid metal can take away heat, and the multilayer FSS can work as cooling plate. The heat transfer performance was investigated by numerical simulations. A 1000 ° plane heat source was set on the bottom surface of the double-layer FSS. The average temperature on the top surface was 62.2 °, when the liquid metal fluid in the FSS had a speed of 1 m/s. The proposed multilayer FSS has strong potential for applications in some special application fields involving stealth and hypersonic aircraft.

Enhanced Performance of Multilayer Bandpass Filter Using Slow-Wave Empty Substrate- Integrated Waveguide (SW-ESIW)

In this letter, two compact and high-performance filters based on multilayer slow-wave empty substrate-integrated waveguide (SW-ESIW) are presented. SW-ESIW, which contains the air cavity and a bottom layer including several rows of internal metallized via holes, provides a compromise between insertion loss and footprint. It is the first time that SW-ESIW is used to implement compact filters with multilayer air cavity. The proposed filters are simulated, fabricated, and measured. The measurements are consistent with simulations, indicating that the proposed filters can be reduced more than 35% in dimension compared to the same filters in ESIW. Based on the SW-ESIW technology, the proposed multilayer filters realize the advantages of low insertion loss and miniaturization, and express the tremendous potential on applications to complex and high-performance microwave circuits and systems.

Balanced‐to‐unbalanced and balanced‐to‐balanced filtering rat‐race couplers using multilayer substate integrated waveguide cavities

This study reports a class of balanced-to-unbalanced (BTU) and balanced-to-balanced (BTB) filtering rat-race couplers (FRCs) based on multilayer substrate integrated waveguide (SIW) cavities. Input and output ports can perform the functions of balanced and unbalanced terminals to implement various operating states. The theoretical designs consisting of the mixed-mode scattering matrix and mode analysis are discussed in detail. Good differential-mode (DM) bandpass filtering (BPF) responses are obtained by two pairs of orthogonal degenerate modes in multilayer SIW cavities. Meanwhile, high common-mode (CM) suppression and port-to-port isolation are realized inherently due to mode distributions of the square SIW resonator. Accordingly, to verify the design concept, two types of BTU FRCs and one type of BTB FRC are designed and fabricated, respectively. Moreover, the measured results agree well with the simulated ones, exhibiting high performances in terms of CM suppression, magnitude/phase imbalance as well as port matching/isolation characteristics.