Impedance Matching Layer Research Articles

Construction of hierarchical yolk-shell Fe@SiO2@NC composites with dual impedance matching layers and dual built-in electric fields for efficient electromagnetic wave absorption

Construction of hierarchical yolk-shell Fe@SiO2@NC composites with dual impedance matching layers and dual built-in electric fields for efficient electromagnetic wave absorption

Enhanced microwave absorption in organogels: The synergy of polar molecules and magnetic particles

Herein, wideband microwave absorbing materials with high flexibility are developed by creating a novel layered organogel composite consisting of carbonyl iron particles (CIP) and polyacrylamide (PAM), employing ethylene glycol (EG) as the solvent. The microwave absorbing properties of layered absorbers with different CIP contents are investigated over the 1–18 GHz range. An integrated stratified architecture was obtained using polar EG molecules and magnetic CIP particles, which were the main contributors to magnetic and dielectric losses in the PAM matrix. The results indicated that the minimum reflection loss reaches a value of −48.0 dB at a thickness of 2 mm and a frequency of 15.5 GHz; meanwhile, an effective absorption bandwidth of 3.2 GHz in the C-band can also be obtained. An analysis of the absorption mechanism shows that the combination of an impedance-matching layer composed of CIP magnetic particles and an absorption layer composed of EG polar molecules in the PAM matrix provides strong broadband absorption in the C-band. Overall, the CIP/EG@PAM organogel composites have simple preparation, high flexibility, and it has adhesion. This study provides a new strategy for designing wideband microwave absorbing materials.

Non-invasive ultrasonic sensing of internal conditions on a partial full-scale spent nuclear fuel canister mock-up

The safe storage of spent nuclear fuel (SNF) in dry cask storage systems (DCSSs) is critical to the nuclear fuel cycle and the future of nuclear energy. A critical component of DCSSs is the SNF canister. The canister is a sealed stainless-steel structure, which is first vacuum dried and then backfilled with helium. The structural deterioration within a canister can be monitored through its internal gas properties. This monitoring serves as the driving force behind the non-invasive ultrasonic sensing approach in this paper. A major challenge in collecting gas-borne signals using ultrasonic sensing is the impedance mismatch between the stainless-steel canister and the helium gas inside. Only a small fraction of the ultrasonic signal makes its way from the transmitter to the receiver through the gas medium. In this paper, experimental studies on a partial full-scale canister mock-up were carried out to capture the gas-borne signals. Damping materials were applied on the outside, and blocking and unblocking tests were conducted to identify the gas-borne signal. The research results showed that the excitation frequency played an important role in maximizing the gas-borne signals. The gas-borne signal was successfully detected at around the theoretical time-of-flight (TOF) at 225 kHz. A high signal-to-noise ratio (SNR) was achieved in the measurements. Next, acoustic impedance matching (AIM) layers were added, and it was found that the gas signal energy was improved by 160.4% compared with that of no AIM layers. Subsequently, the relative humidity (RH) level and temperature of the gas were varied to simulate abnormal internal conditions of the canister. The non-invasive testing system demonstrated reliability and sensitivity in detecting gas temperature and RH variations. Theoretical calculations demonstrated the potential for detecting low-level xenon and air within an actual SNF canister filled with helium. Last, an active noise cancellation (ANC) method, previously developed by the authors, was verified on the canister mock-up for the first time. The results showed that the SNR of the gas signal was improved by 213.6% compared with that of no ANC.

Multivariate gradient structure design of flexible thermoplastic polyurethane based composite foam for enhanced electromagnetic interference shielding performance

Flexible and efficient electromagnetic interference (EMI) shielding polymer composite foams are rapidly developing, but it is difficult to avoid the deterioration of shielding properties after foaming. To solve the issue, in this work, composite foams with multivariate gradient structure of thermoplastic polyurethane (TPU) mixed with multiwalled carbon nanotubes (MWCNTs) were constructed by combining the soft-hard domains proportional gradient of TPU with filler content gradient. Gradient-structured TPU/MWCNTs foams with impedance matching layer and high reflector layer were obtained and impedance matching layer with large cells significantly reduced the density while high reflector layer with a few cells maintained relatively perfect conductive network, whose shielding efficiency was 38.2 % higher than that of unfoamed sample. Furthermore, TPU/MWCNTs composite foams presented great stability even after 1000 times bending. This special multivariate gradient structure shows potential applications in microelectronic devices and aerospace fields and is critical to the development of high-performance EMI shielding polymer foams.

Synergistic Layered Design of Aerogel Nanocomposite of Graphene Nanoribbon/MXene with Tunable Absorption Dominated Electromagnetic Interference Shielding.

Electromagnetic pollution presents growing challenges due to the rapid expansion of portable electronic and communication systems, necessitating lightweight materials with superior shielding capabilities. While prior studies focused on enhancing electromagnetic interference (EMI) shielding effectiveness (SE), less attention is given to absorption-dominant shielding mechanisms, which mitigate secondary pollution. By leveraging material science and engineering design, a layered structure is developed comprising rGOnR/MXene-PDMS nanocomposite and a MXene film, demonstrating exceptional EMI shielding and ultra-high electromagnetic wave absorption. The 3D interconnected network of the nanocomposite, with lower conductivity (10-3-10-2 S/cm), facilitates a tuned impedance matching layer with effective dielectric permittivity, and high attenuation capability through conduction loss, polarization loss at heterogeneous interfaces, and multiple scattering and reflections. Additionally, the higher conductivity MXene layer exhibits superior SE, reflecting passed electromagnetic waves back to the nanocomposite for further attenuation due to a π/2 phase shift between incident and back-surface reflected electromagnetic waves. The synergistic effect of the layered structures markedly enhances total SE to 54.1 dB over the Ku-band at a 2.5 mm thickness. Furthermore, the study investigates the impact of hybridized layered structure on reducing the minimum required thickness to achieve a peak absorption (A) power of 0.88 at a 2.5 mm thickness.

Absorption-dominant electromagnetic interference shielding material using MXene-coated polyvinylidene fluoride foam

MXene (Ti3C2Tx), known for its exceptional electrical conductivity, unique two-dimensional structure, extensive surface functionality, and hydrophilicity, has emerged as a leading candidate for electromagnetic interference (EMI) shielding applications. Despite these excellent characteristics, EMI shielding materials based on MXene mostly utilize the reflection mechanism, which may cause secondary interferences. This study introduces an approach to utilize MXene as absorption-dominant EMI shielding materials. By engineering a porous layer of polyvinylidene fluoride (PVDF) atop MXene nanoflakes, we achieved a synergistic enhancement in EMI shielding effectiveness (SE) and absorptivity. The PVDF foam serves as an effective impedance matching layer, substantially enhancing the absorption of electromagnetic waves into the shielding material. Incorporating electrically conductive MXene nanoflakes to form a thin film creates a robust conductive network, fully leveraging its inherent performance. This network efficiently dissipates EM waves, thereby significantly enhancing the EMI SE. The shielding performance of this composite was thoroughly evaluated across both the X-band (8.2 GHz–12.4 GHz) and the Ka-band (26.5 GHz–40 GHz) frequencies. It demonstrated high EMI SE, attributed to mechanisms predominantly based on absorption. Specifically, it achieved an EMI SE of approximately 63.3 dB with high absorptivity (0.74) in the X-band and approximately 73.3 dB with high absorptivity (0.85) in the Ka-band. These findings underscore its potential as a route to develop absorption-dominant EMI shielding materials.

Micromechanical piezoelectric micromachined ultrasonic transducer array package enhancement with integrated frontliners

In order to improve the susceptibility of ultrasonic transducers to damage and the mismatch in acoustic impedance with test specimens, an impedance-matching layer is introduced between the transducer and the specimen. The impact of the matching layer on acoustic propagation of transducer was analyzed through acoustic field simulation. The performance of the improved transducer was experimentally evaluated by using a dedicated echo testing system for transducers. The matching layer was optimized by considering different materials. The results show that for non-metallic materials, only a layer of acoustic matching layer (organic silicone gel) can be added to achieve acoustic impedance matching and avoid wear. For metal materials, two acoustic matching layers (organic silicone gel and epoxy resin) need to be added to achieve acoustic impedance matching. The propagation efficiency of sound waves is increased by 30% as a result of this process.

PMUT-Based System for Continuous Monitoring of Bolted Joints Preload.

In this paper, we present a bolt preload monitoring system, including the system architecture and algorithms. We show how Finite Element Method (FEM) simulations aided the design and how we processed signals to achieve experimental validation. The preload is measured using a Piezoelectric Micromachined Ultrasonic Transducer (PMUT) in pulse-echo mode, by detecting the Change in Time-of-Flight (CTOF) of the acoustic wave generated by the PMUT, between no-load and load conditions. We performed FEM simulations to analyze the wave propagation inside the bolt and understand the effect of different configurations and parameters, such as transducer bandwidth, transducer position (head/tip), presence or absence of threads, as well as the frequency of the acoustic waves. In order to couple the PMUT to the bolt, a novel assembly process involving the deposition of an elastomeric acoustic impedance matching layer was developed. We achieved, for the first time with PMUTs, an experimental measure of bolt preload from the CTOF, with a good signal-to-noise ratio. Due to its low cost and small size, this system has great potential for use in the field for continuous monitoring throughout the operative life of the bolt.

Study on microwave absorption performance of the skin‐core dual‐domain structure constructed with thin‐ply laminate and honeycomb

AbstractThis study introduces an innovative approach to enhance the absorption capabilities of skin‐core dual‐domain structure radar‐absorbing materials (SDSRAM) composed of thin‐ply laminates and honeycomb. The upper skin laminates consist of transmissive skin and impedance matching layer. The impedance matching layer was hot‐pressed using functionalized absorbed thin‐ply glass fibers prepregs, flaked carbonyl iron powder (FCIP) and multi‐walled carbon nanotubes (MWCNTs) as the absorber. The lower skin was manufactured using carbon fiber‐plated nickel. The core is prepared by honeycomb modified (HCM). The permittivity and permeability of the skin laminates and the HCM were measured by wave‐guide method. The impact of FCIP/MWCNT on the electromagnetic (EM) parameters of the thin‐ply laminates and the influence of MWCNTs on the permittivity of the honeycomb were investigated. Microwave absorption properties of SDSRAM were assessed through the measurement of reflection loss (RL) using the arch method and simulated using the microwave simulation software CST studio suite 2020. Experimental verification was conducted to confirm the absorbing performance. The results show that the effective absorption bandwidth (RL < 10 dB) of SDSRAM covers the frequency range of 2.2–18 GHz, with a maximum absorption intensity of −42.5 dB. The introduction of the thin‐ply laminates caused a shift in the peak of the reflectance curve toward lower frequencies.Highlights Functionalized absorbed glass fibers were prepared using fiber spreading functional sizing integrated process. A new skin‐core dual‐domain synergistic modulation absorbed structure was developed with thin‐ply laminates and modified honeycomb. Its broadband absorption mechanism was discussed. Desired broadband absorption performance was acquired with thin thickness.

Barium titanate–silicon elastomer based body coupled antenna for wearable microwave head imaging applications

This paper presents a flexible monopole antenna fed by a coplanar waveguide (CPW) feeding line with a barium titanate (BaTiO3) silicon-elastomer impedance matching layer for microwave head imaging applications. The operating frequency bandwidth of the proposed antenna is 614 MHz which is from 0.475 GHz to 1.089 GHz. In biomedical microwave sensing and imaging applications, the major challenge is the high power loss due to reflection between the BaTiO3 and the antenna due to impedance mismatch. Therefore, the proposed BaTiO3 silicon-elastomer composite is designed to have dielectric property of 20 which acts as an impedance matching layer for the monopole antenna. The proposed antenna has dimensions of 70×30×6 mm. The flexibility of the antenna is provided by the use of the silicon elastomer. It has been shown that the power radiated into an artificial head phantom improved by almost 160% as compared to antenna without impedance matching layer. Moreover, the SAR level is 0.0286 W/kg when 1 mW of power is transmitted, which is well below the limit set by the regulation. This makes the antenna suitable for wearable biomedical applications due to its wideband characteristic and improved power penetration into human head.

On the Cross-Polarization Levels of Arrays With Wide Angle Impedance Matching Layers

On the Cross-Polarization Levels of Arrays With Wide Angle Impedance Matching Layers

Multistage microcellular waterborne polyurethane composite with optionally low-reflection behavior for ultra-efficient electromagnetic interference shielding

Electromagnetic interference (EMI) shielding materials with superior shielding efficiency and low-reflection properties hold promising potential for utilization across electronic components, precision instruments, and fifth-generation communication equipment. In this study, multistage microcellular waterborne polyurethane (WPU) composites were constructed via gradient induction, layer-by-layer casting, and supercritical carbon dioxide foaming. The gradient-structured WPU/iron-cobalt loaded reduced graphene oxide (FeCo@rGO) foam serves as an impedance-matched absorption layer, while the highly conductive WPU/silver loaded glass microspheres (Ag@GM) layer is employed as a reflection layer. Thanks to the incorporation of an asymmetric structure, as well as the introduction of gradient and porous configurations, the composite foam demonstrates excellent conductivity, outstanding EMI SE (74.9 dB), and minimal reflection characteristics (35.28 %) in 8.2–12.4 GHz, implying that more than 99.99999 % of electromagnetic (EM) waves were blocked and only 35.28 % were reflected to the external environment. Interestingly, the reflectivity of the composite foam is reduced to 0.41 % at 10.88 GHz due to the resonance for incident and reflected EM waves. Beyond that, the composite foam is characterized by low density (0.47 g/cm3) and great stability of EMI shielding properties. This work offers a viable approach for crafting lightweight, highly shielding, and minimally reflective EMI shielding composites.

Utilizing Shear Piezoelectricity of Chiral Lead‐Free Metal Halides for Electromechanical Sensing

AbstractChiral hybrid metal halides have emerged as a promising class of piezoelectric materials owing to their ease of synthesis, low acoustic impedance, and solution processibility. However, many known chiral halides crystalize in structures with only shear piezoelectricity which is less facile to be utilized compared with the longitudinal piezoelectricity, largely preventing their practical utility. In addressing this problem, chiral lead‐free S‐MPBiCl5 and R‐MPBiCl5 (MP = 2‐methylpiperazinium) with shear piezoelectricity are synthesized and the thin films orientating along the polarization direction are fabricated. These orientated films, characterized by numerous grains and compact grain boundaries, can effectively facilitate the grain boundary sliding to convert normal stress into shear stress, thus facilely activating the shear piezoelectricity. The resulting devices can accurately identify the position and type of ultrasound sources without the need for a complex acoustic impedance matching layer. Moreover, these devices can successfully sense delicate variations in momentum caused by table tennis balls. The findings open up a new pathway to utilize shear piezoelectricity that is normally considered unuseful of metal halides and other molecular piezoelectrics.

Lithium Niobate Electro-Optic Modulation Device without an Overlay Layer Based on Bound States in the Continuum.

Electro-optic modulation devices are essential components in the field of integrated optical chips. High-speed, low-loss electro-optic modulation devices represent a key focus for future developments in integrated optical chip technology, and they have seen significant advancements in both commercial and laboratory settings in recent years. Current electro-optic modulation devices typically employ architectures based on thin-film lithium niobate (TFLN), traveling-wave electrodes, and impedance-matching layers, which still suffer from transmission losses and overall design limitations. In this paper, we demonstrate a lithium niobate electro-optic modulation device based on bound states in the continuum, featuring a non-overlay structure. This device exhibits a transmission loss of approximately 1.3 dB/cm, a modulation bandwidth of up to 9.2 GHz, and a minimum half-wave voltage of only 3.3 V.

Broadband tunable acoustic impedance matching using gradient-distributed piezoelectric structure

In this paper, we propose a broadband tunable acoustic matching layer (BTAML) comprising an array of piezoelectric elements with non-uniform gradient shunt circuits (NGSCs). The effective impedance of the BTAML can be controlled in real time by regulating the parameters of NGSCs. The theoretical results demonstrate that BTAML is capable of adjusting impedance from 1.5 to 20 MRayl and has a broad bandwidth compared with the traditional matching layer. Furthermore, we experimentally verified the acoustic transmission property of the BTAML, and good agreement was achieved with numerical simulations. The approach can significantly promote research on tunable acoustic matching and offer effective impedance matching layers with a broad bandwidth in industrial applications.

Durable and sustainable CoFe2O4@MXene-silver nanowires/cellulose nanofibers composite films with controllable electric–magnetic gradient towards high-efficiency electromagnetic interference shielding and Joule heating capacity

Exploring electromagnetic waves (EMW) absorption-dominated high-performance electromagnetic interference (EMI) shielding materials with robust mechanical properties and remarkable Joule heating capability is highly desired but remains a daunting challenge for the development of modern electronic equipment. Herein, durable and multifunctional cellulose nanofiber-based composite films with elaborate electric–magnetic dual gradient structure were successfully fabricated through highly controllable vacuum-assisted filtration technology. The electric–magnetic dual gradient network consists of CoFe2O4@MXene hybrids with electric–magnetic cooperative loss concentrated on the top region as impedance matching layer and silver nanowires (AgNWs) with high conductivity placed on the bottom as high-efficiency shielding layer. Benefiting from the construction of dual gradient network with rational arrangement of the impedance matching layer and conductive shielding layer, the synergy of electric–magnetic loss, polarization loss induced by the numerous heterointerfaces and “absorption-reflection-reabsorption” shielding mechanism, the resultant composite films simultaneously reveal ultraefficient EMI shielding effectiveness (SE) and low EMW reflectivity. The prepared composite films (0.1 mm in thickness) achieve an extraordinary EMI SE of 84.3 dB and a satisfactory reflection coefficient of 0.42, realizing EMW absorption-dominated shielding feature. Moreover, the mechanical properties and Joule heating capacity of the prepared composite films are outstanding, which mainly benefits from the construction of hierarchically layered structure. This work paves a novel route for designing and fabricating absorption-dominated high-performance EMI shielding composite films with durable mechanical performance and outstanding Joule heating capability, which are potentially suitable for new-generation advanced electronics.

Bioinspired Fano-like resonant transmission: frequency selective impedance matching

The study of the impedance mismatch between the device and its surroundings is crucial when building an acoustic device to obtain optimal performance. In reality, a high impedance mismatch would prohibit energy from being transmitted over the interface, limiting the amount of energy that the device could treat. In general, this is solved by using acoustic impedance matching layers, such as gradients, similar to what is done in optical coatings. The simplest form of such a gradient can be considered as an intermediate layer with certain qualities resting between the two media to impedance match, and requiring a minimum thickness of at least one quarter wavelength of the lowest frequency under consideration. The desired combination(s) of the (limited) available elastic characteristics and densities has traditionally determined material selection. Nature, which is likewise limited by the use of a limited number of materials in the construction of biological structures, demonstrates a distinct approach in which the design space is swept by modifying certain geometrical and/or material parameters. The middle ear of mammals and the lateral line of fishes are both instances of this method, with the latter already incorporating an architecture of distributed impedance matched underwater layers. In this paper, we develop a resonant mechanism whose properties can be modified to give impedance matching at different frequencies by adjusting a small set of geometrical parameters. The mechanism in question, like the lateral line organ, is intended to serve as the foundation for the creation of an impedance matching meta-surface. A computational study and parameter optimization show that it can match the impedance of water and air in a deeply sub-wavelength zone.

Enhanced electromagnetic absorption properties of the double-layer Ti3C2Tx MXene absorber with orthogonal microstructures

A double-layer MXene absorber with orthogonal microstructures was designed unidirectional freeze-casting method, which yielded favorable electromagnetic wave absorption properties by tuning the thickness ratio of the parallel ends when the parallel sample was used as an impedance matching layer.

Multifunctional phase-change composites for green electromagnetic interference shielding and thermal response prepared under the guidance of an impedance matching strategy.

With the advent of the information age, electromagnetic hazards are becoming more serious. In view of environmental protection, green electromagnetic interference (EMI) shielding materials with little or no secondary reflection have become the ideal choice. In this paper, by freeze-drying, high-temperature carbonization, coating and impregnation backfilling, we prepared carbonized Ni-MOF/reduced graphene oxide/silver nanowire-polyimide@polyethylene glycol composites (Ni@C/r-GO/AgNW-PI@PEG) with gradient conductivity based on impedance matching. The impedance matching layer Ni@C/r-GO-300 reduces the reflection of electromagnetic waves from the surface of the material, the dissipation layer Ni@C/r-GO-600 provides excellent electromagnetic wave dissipation capability, and the reflection layer AgNW-PI ensures that the electromagnetic waves are reflected back into the material. Meanwhile, the EMI shielding performance value of Ni@C/r-GO/AgNW-PI@PEG reaches 62.3 dB with an ultra-low reflectivity (R) of 0.04. In CST simulations, the intrinsic mechanism of electromagnetic energy loss within the material is revealed by energy loss density cloud maps. In addition, heat from high-temperature objects is transferred through the highly thermally conductive AgNW-PI membrane to the long-channel Ni@C/r-GO backbone. Therefore, the composites prepared on the basis of impedance matching will accelerate the use of EMI shielding materials for the thermal management of portable electronic devices and battery heat dissipation packaging.

Hydrophobic Composite Foams with Asymmetric Gradient Sandwich Structure for Excellent Electromagnetic Interference Shielding and Photothermal Response.

The evolution of contemporary electronics urgently requires the use of versatile electromagnetic interference (EMI) shielding materials in complex environments. Interlayer polydimethylsiloxane (PDMS)/Fe3O4@multiwalled carbon nanotubes (MWCNTs) foams were prepared by a simple physical foaming method with excellent flexibility and electromagnetic wave absorption. The bottom nickel aramid paper (NiP) layer creates a dense conductive network by chemical plating technology, which ensures excellent EMI effectiveness. The upper carbon black (CB)/Fe3O4 layer further improves the absorption performance via conductive loss and magnetic loss. With the effective layout of the impedance matching layer, absorbing layer, and conductive shielding layer, the CB/Fe3O4-PDMS/Fe3O4@MWCNTs-NiP composite material achieves an EMI shielding effectiveness (EMI SE) of 61.7 dB and an absorption coefficient of 0.58 at X-band. In addition, the composite foam provides photothermal conversion and hydrophobicity due to the effective stacking of PDMS and CB/Fe3O4. Thus, the multifunctional composite foam presents a broad range of possible applications, benefiting EMI shielding as well as other specific areas.