Impedance Mismatch Research Articles

Ultralow-content Co decoration on Ti3C2Tx MXene induced electromagnetic characteristic modulation for efficient microwave absorption

Ti3C2Tx MXene has been regarded as a promising candidate for advanced microwave absorption materials. However, the microwave absorbing performance of Ti3C2Tx MXene is suppressed by the single dielectric loss mechanism and impedance mismatch because of the high conductivity. To effectuate a good absorption capability of Ti3C2Tx MXene, this paper constructs a heterostructured Co/Ti3C2Tx hybrid by atomic layer deposition of magnetic Co nanoparticles on Ti3C2Tx nanosheets. The microstructures, magnetism, and microwave absorption behaviors of the Co/Ti3C2Tx hybrids are investigated systematically. The results show that the frequency-dependent electromagnetic parameters of the Ti3C2Tx MXene become tunable by controlling the content of Co decorations, which are conducive to both magnetic loss and impedance matching. The Co/Ti3C2Tx hybrid with ultralow Co decoration content (only 1.52 wt%) achieves the minimum reflect loss of −54.32 dB at a thin matched thickness of 1.29 mm, and the corresponding effective absorption bandwidth with reflection loss below −10 dB reaches 4.29 GHz. The atomic layer deposited magnetic metal nanostructures provides an effective strategy for preparing MXene-based hybrids which not only have high absorption efficiency but also significantly reduce the use of magnetic metals.

Frequency Stability Analysis and Charging Area Expanding Optimal Design for Matrix Coupling Mechanism in Wireless Power Transfer System

The matrix coupling mechanism brings flexibility and reliability to energy supply in the form of multiple transmitting coils and is now favored in most wireless energy transmission applications, such as wireless charging boards for mobile phones, inspection robots, and so on. However, the process of considering the layout of the matrix coupling mechanism and the output performance based on the target in space is very complex, while also taking into account the need to avoid impedance changes caused by cross-interference between each unit, which can lead to frequency inconsistency. This paper proposes a design method based on space charging area expansion for matrix coupling mechanisms, and on this basis, it focuses on analyzing the impedance mismatch phenomenon caused by cross mutual inductance and inconsistent mutual inductance between coil units, in order to obtain the optimal topology to avoid frequency drift as much as possible. Finally, the effectiveness of the method is validated through simulation and experiments.

High-performance electromagnetic wave absorption by two-dimensional mesoporous monolayer Ti3C2Tx MXene

Transition metal carbide MXene, with its unique chemical composition, structure and sizeable particular surface area, is widely applied in wave absorption. However, the high conductivity of MXene resulted in an impedance mismatch that prevented electromagnetic waves from entering the material to achieve dissipation, and thus, tuning the intrinsic properties of pure MXene to obtain excellent electromagnetic wave absorption is still a challenge. Here, we strengthen the absorption of electromagnetic waves by generating titanium vacancies through hydrogen peroxide etching and thus forming micro-sized wrinkles with porous MXene. Porous MXene possesses an excellent microstructure and surface state, abundant porous defects, and moderate electrical conductivity, allowing it to achieve well-matched impedance, dipole polarization, and conduction loss, thus inheriting excellent electromagnetic wave absorption (EWA) properties. Therefore, the porous MXene achieves a strong absorption of − 63.31 dB and an adequate absorption bandwidth (EAB) of 6.88 GHz at a matched thickness of 2.39 mm with a fill ratio of 6 wt%.

Filtenna Designed with Defected Ground Structure (DGS) for Ultra-wideband Applications

In microwave imaging applications, filter and antenna are the key components as front-end devices and function independently. Antenna radiates and receives signals to or from nearby scattered objects while filter is used to suppress unwanted signals noise before and after the required bandwidth. Current antennas suffer from high loss, bandwidth limitation and impedance mismatch and deteriorate their performance near the band-edges if connected as a stand-alone device. Due to the current trend towards simplicity and size reduction, researchers are focusing on integrating the filter and antenna into a single module called integrated filter-antenna (IFA) or filtering antenna (filtenna). These would improve the noise performance of the system and pre-filtering requirements such as complexity algorithm in inverse scattering techniques This paper introduces a novel contribution in the field of UWB antenna design by incorporating Defected Ground Structure (DGS) on both the antenna and filter. Thus, the main aim of this research is to conduct detail parametric studies of the proposed integrated filter-antenna with defected ground structure (DGS) to enhance the performance of imaging system. The proposed IFA will be analysed on Rogers RO4003C dielectric substrate by using EM tool, Computer Simulation Technology (CST) and measured using R&S Vector Network Analyzer (VNA). A compact ultra-wideband (UWB) filter and UWB elliptical antenna are designed and examined in detail before combining the devices. Different types of DGS are designed and act as the ground layer of the proposed filtering antenna. The bandwidth of each design is then compared with and without the existence of DGS. The results show that the proposed IFA with DGS implementation achieve the targeted objective, with compact size, enhanced bandwidth and better performance compared to the conventional design of filter and antenna. By integrating filter and antenna into one subsystem, it can help to reduce the loss and enhancing the bandwidth of the system thus letting the antenna to operate at more different frequencies that fall within the range. Both simulated and measured results prove that by integrating filter and antenna into one module, a low loss and larger bandwidth can be accomplished. High performance compact IFA can act as microwave transceiver to improve the overall performance of the microwave imaging system, MIS.

Regulating the Electronic Structure of MAX Phases Based on Rare Earth Element Sc to Enhance Electromagnetic Wave Absorption.

MAX phases are highly promising materials for electromagnetic (EM) wave absorption because of their specific combination of metal and ceramic properties, making them particularly suitable for harsh environments. However, their higher matching thickness and impedance mismatching can limit their ability to attenuate EM waves. To address this issue, researchers have focused on regulating the electronic structure of MAX phases through structural engineering. In this study, we successfully synthesized a ternary MAX phase known as Sc2GaC MAX with the rare earth element Sc incorporated into the M-site sublayer, resulting in exceptional conductivity and impressive stability at high temperatures. The Sc2GaC demonstrates a strong reflection loss (RL) of -47.7 dB (1.3 mm) and an effective absorption bandwidth (EAB) of 5.28 GHz. It also achieves effective absorption of EM wave energy across a wide frequency range, encompassing the X and Ku bands. This exceptional performance is observed within a thickness range of 1.3 to 2.1 mm, making it significantly superior to other Ga-MAX phases. Furthermore, Sc2GaC exhibited excellent absorption performance even at elevated temperatures. After undergoing oxidation at 800 °C, it achieves a minimum RL of -28.3 dB. Conversely, when treated at 1400 °C under an argon atmosphere, Sc2GaC demonstrates even higher performance, with a minimum RL of -46.1 dB. This study highlights the potential of structural engineering to modify the EM wave absorption performance of the MAX phase by controlling its intrinsic electronic structure.

Phase Engineering on MoS2 to Realize Dielectric Gene Engineering for Enhancing Microwave Absorbing Performance

AbstractPolarization relaxation loss caused by defects and interfaces has become a fascinating electromagnetic wave (EMW) loss mechanism. However, the logical relationship between impedance matching and various loss mechanisms requires further elucidation to facilitate more comprehensive and in‐depth research. Herein, phase engineering on molybdenum disulfide (MoS2) is proposed as the main controller of permittivity, offering a straightforward and highly effective method for regulating permittivity. Through the main control of phase engineering, a small gradient, monotonic change of the permittivity across a substantial area is achieved, leading to the gradual transition of the material system from strong loss but impedance mismatching to weak loss but EMW transparent phase. Thanks to the fundamental regulation of impedance characteristic and attenuation capacity by the dielectric gene engineering controlled by the phase engineering, combined with the ingenious coordination of sulfur vacancy‐induced polarization and interfacial polarization, t‐60 harvests an effective absorption band of 6.8 GHz and a minimum reflection loss of −59.8 dB. This study effectively expands the dielectric gene pool and improves the research logic for various loss mechanisms, offering valuable insights for the development of advanced EMW absorbing materials.

Porous CoZn@NC skeletons supported NiCo2S4 nanorods for efficient electromagnetic wave absorption

Bimetallic sulfides are promising in electromagnetic wave (EMW) absorption due to their moderate permittivity and high dielectric loss. However, the impedance mismatching and insufficient loss mechanism of bimetallic sulfides result in limited EMW absorption performance. Herein, bimetallic sulfide (NiCo2S4) nanorods were loaded onto nitrogen-doped carbon embedded with CoZn nanoparticles (CoZn@NC) derived from CoZn-based metal organic framework (CoZn-MOF) through simple hydrothermal and vulcanization processes. Importantly, during the vulcanization process, CoZn@NC undergoes structural reorganization and evolves into defect-rich porous nanosheets, which promotes dipole polarization and enhance EMW absorption ability. Additionally, the formed NiCo2S4 nanorods are tightly anchored on the porous CoZn@NC skeletons, forming a large number of heterostructures, and promoting interfacial polarization. In addition, the carbon nanotubes (CNTs) formed during the pyrolysis process of CoZn-MOF contribute to the conduction loss of the heterostructure and motivate dielectric loss. Therefore, CoZn@NC/NiCo2S4 heterostructures inherit excellent EMW absorption performance and obtain a reflection loss (RL) value of −32.53 dB at a matching thickness of 2.1 mm, while exhibiting an effective absorption bandwidth (EAB) of 4.1 GHz. Radar cross-sectional area (RCS) simulation shows that the potential of CoZn@NC/NiCo2S4 heterostructure in practical anti radar detection. This work puts up great potential for the development of advanced bimetallic sulfides-based EMW absorbers.

Distributed sliding mode control for reactive power sharing in an islanded microgrid

This paper presents a novel microgrid secondary control method based on distributed sliding mode control, addressing the issue of reactive power sharing in islanded microgrids. Acknowledging the complications posed by feeder impedance mismatch, the traditional droop control mechanism fails to facilitate efficient reactive power sharing. Utilizing a distributed framework, this paper initially introduces a reactive power ratio observer, enabling the observation of global average reactive power without the need for precise reactive power calculation as required in a conventional centralized control setup. Subsequently, employing the devised reactive power ratio observer, sliding mode control is integrated to achieve effective reactive power sharing. Furthermore, this paper broadens its scope to encompass both reactive power sharing and voltage restoration, resulting in the design of a comprehensive controller. Notably, the proposed distributed sliding mode controller not only achieves accurate reactive power sharing but also exhibits significant resilience in the face of load disturbances. The simulation results conducted under various scenarios effectively validate the efficacy of the proposed distributed sliding mode control strategy.

A generic time-frequency analysis-based signal processing and imaging approach for air-coupled ultrasonic testing

The utilization of air-coupled ultrasonic technology is crucial for examining objects that are challenging to establish contact with or cannot endure coupling. Nevertheless, air-coupled ultrasonic is susceptible to various factors such as impedance mismatch, sound wave attenuation, and environmental noise, consequently leading to a diminished signal-to-noise ratio of the received signal. This reduction in signal quality amplifies the complexity of analysis and imaging processes. In this study, a generic air-coupled ultrasonic signal processing and imaging procedure for ultrasonic inspection is proposed, which capitalizes on time-frequency analysis. This methodology attains a heightened level of stability and superior signal-to-noise ratio imaging through a series of procedural steps, encompassing feature extraction, denoising, and the reconstruction of the A-scan signals. The efficacy of the proposed approach is quantitatively assessed in terms of signal-to-noise ratio, probability of detection, robustness, and generality. This innovative method presents a newfangled resolution for automated air-coupled ultrasonic testing.

Simultaneous manipulation of constituent and structure toward MOFs-derived hollow Co3O4/Co/NC@MXene microspheres via pyrolysis strategy for high-performance microwave absorption

The development of microwave absorbing materials with high performance is one of the effective strategies to solve the increasingly serious electromagnetic pollution problem, and has received the attention of researchers. Herein, the structure and composition manipulation of Ti3C2Tx MXene and MOFs derivatives are investigated. It is found that the TiO2 produced by oxidation of Ti3C2Tx MXene, as a low dielectric material, can effectively solve the impedance mismatch caused by the high conductivity of Ti3C2Tx MXene. Additionally, MOFs derivatives with excellent dielectric-magnetic properties are often obtained by high temperature pyrolysis, which also aids in the oxidation of Ti3C2Tx MXene. Here, we successfully synthesized ZIF-67 nanoparticles on the surface of a three-dimensional spherical skeleton supported by Ti3C2TX MXene nanosheets through template method and electrostatic self-assembly, and obtained Co3O4/Co/NC@MXene microspheres with an obvious hollow structure after one-step pyrolysis. This magnetic carbon heterostructure could effectively optimize the impedance matching and achieve efficient microwave absorption. The HCCM-800 sample had a minimum reflection loss value of −71.60 dB with thickness of 2.25 mm and a maximum effective absorption bandwidth achieved 5.14 GHz at 1.85 mm. Meanwhile, the radar cross section (RCS) simulation revealed that the HCCM-800 sample’s RCS reduction value could reach 20.2 dBm2 at 0° incidence angle. It is believed that this research will pave the way for further vigorous development in the field of microwave absorption.

Electrostatic generator enhancements for powering IoT nodes via efficient energy management

Electrostatic generators show great potential for powering widely distributed electronic devices in Internet of Things (IoT) applications. However, a critical issue limiting such generators is their high impedance mismatch when coupled to electronics, which results in very low energy utilization efficiency. Here, we present a high-performance energy management unit (EMU) based on a spark-switch tube and a buck converter with an RF inductor. By optimizing the elements and parameters of the EMU, a maximum direct current output power of 79.2 mW m-2 rps-1 was reached for a rotary electret generator with the EMU, achieving 1.2 times greater power output than without the EMU. Furthermore, the maximum power of the contact-separated triboelectric nanogenerator with an EMU is 1.5 times that without the EMU. This excellent performance is attributed to the various optimizations, including utilizing an ultralow-loss spark-switch tube with a proper breakdown voltage, adding a matched input capacitor to enhance available charge, and incorporating an RF inductor to facilitate the high-speed energy transfer process. Based on this extremely efficient EMU, a compact self-powered wireless temperature sensor node was demonstrated to acquire and transmit data every 3.5 s under a slight wind speed of 0.5 m/s. This work greatly promotes the utilization of electrostatic nanogenerators in practical applications, particularly in IoT nodes.

Broadband ultrasonic transducer based on nested composite structure with gradient acoustic impedance

This study introduces an innovative Broadband Ultrasonic Transducer employing a Nested Composite Structure with Gradient Acoustic Impedance, significantly enhancing the performance in medical diagnostics and non-destructive testing. The developed transducer, based on a unique nested PZT/epoxy composite design, achieves an optimized acoustic impedance gradient from 36.56 MRayls to 4.53 MRayls. This strategic design effectively addresses the impedance mismatch, a long-standing challenge in ultrasonic imaging. Rigorous Finite Element Analysis (FEA) using PZFlex software indicates that the transducer offers a −6 dB bandwidth of 69.31%, a substantial improvement over the existing models. Experimental results corroborate with theoretical predictions, demonstrating enhanced bandwidth (∼71.24%) and transmission efficiency. This advancement highlights the potential of gradient impedance in fabricating high-performance ultrasonic transducers, setting a new benchmark for ultrasonic imaging applications.

Variational study of a model for near-perfect transmission through lossy media with acoustic sources

Complementary acoustic metamaterials have been proposed as a means of compensating for the high impedance mismatches of aberrating layers that disrupt the acoustic field and hence distort acoustic images. Recently, a complementary acoustic metamaterial featuring active components was shown in principle to compensate for both the impedance mismatch and energy attenuation of lossy materials, but a physical realization of the concept has not yet been implemented. Here, we present results from a one-dimensional acoustic model showing how a plane wave incident on a lossy material can be augmented by point monopole and dipole sources to allow for near-perfect transmission, thus rendering the lossy medium acoustically transparent. We present general expressions for source magnitudes that are dimensionless with respect to frequency, material thickness, and the background medium. We explore the sensitivity of the performance to variations in each of the model parameters, considering both theoretical and practical limitations to the proposed method. We show that these findings are consistent with three-dimensional finite element simulations.

Construction of three-dimensional porous network Fe-rGO aerogels with monocrystal magnetic Fe3O4@C core-shell structure nanospheres for enhanced microwave absorption

Single dielectric loss material has defects such as strong dielectric properties and impedance mismatch. Hence, developing electromagnetic wave (EMW) absorption materials with both outstanding EMW absorption and favourable impedance matching performances is still a great challenge. A large number of literature have reported that combining dielectric materials with magnetic materials to enhance microwave absorption. However, there is little literature on the effect of crystal structure on the absorbing properties of materials. Owing to the virtues of light weight, low density and thin thickness of aerogel, which has been widely utilized in EMW absorption materials. Herein, Fe-based metal organic framework-reduced graphene oxide (Fe-rGO) aerogel was synthesized via simple hydrothermal method and freeze-drying. Besides, Polyvinyl Pyrrolidone (PVP) was used as a surfactant to endow Fe3O4 nanospheres with uniform size and smooth morphology. Moreover, Fe3O4 nanospheres with different crystal phase (monocrystal and polycrystal) structure were obtained under different carbonization temperatures (600 and 800 °C). Through comparison, the monocrystal Fe3O4 nanospheres show better microwave absorption and impedance matching performance than that of polycrystal Fe3O4 nanospheres. In addition, the electromagnetic parameters can be adjusted by regulating the mass ratio of Fe-based metal organic framework (Fe-MOF) to GO. As a consequence, the prepared 600Fe-rGO 2:1 aerogel achieves the minimum reflection loss (RLmin) of −64.89 dB and a broad effective absorption bandwidth (EAB) of 6.96 GHz with a low filling content of 5 wt%, showing excellent EMW absorption and impedance matching property. In short, the structural design of single crystal magnetic Fe3O4 nanospheres provides inspiration and guidance for future research of enhanced microwave absorption materials.

Active non-Hermitian complementary acoustic metamaterials for transcranial imaging

High-frequency ultrasound has long been a safe and effective tool for medical imaging, diagnosis, and noninvasive treatments. However, the presence of the porous skull poses a challenge, impeding wave transmission and limiting noninvasive ultrasonic brain imaging due to a significant impedance mismatch and energy attenuation. In this study, we propose an innovative approach by introducing an active non-Hermitian complementary metamaterial (NHCMM) to enhance transcranial imaging. The NHCMM integrates piezoelectric elements, hydrogel materials, and a feedback control circuit. This actively modulates the effective acoustic properties of the metamaterial, ensuring precise tuning to match the impedance of the skull, thereby reducing energy loss and enhancing transmission. This design not only creates a transparent window for high-frequency ultrasound but also significantly improves brain imaging quality. The presented work establishes a foundational framework for non-invasive ultrasound-based brain imaging and high-precision ultrasonic therapies, preserving the structural integrity of the cranial barrier. We anticipate that this research holds immense potential for advancing the fields of brain imaging and ultrasonic treatments, paving the way for future innovations in medical diagnostics and therapeutic interventions.

Regulating the electromagnetic balance of materials by electron transfer for enhanced electromagnetic wave absorption

The fact that single dielectric loss materials have disadvantages of excessive conductivities and impedance mismatches has given rise to a large effort to develop effective strategies to fabricate electromagnetic wave (EMW) absorbing materials comprised of components that bring about a balance between dielectric loss and magnetic loss. Moreover, little is known about the essential features that regulate EMW absorption propensities. This study focused on the development of a new EMW absorbing material and gaining information about factors that govern EMW absorption abilities. The materials at the center of the effort are light weight and porous cobalt sulfonated phthalocyanine-reduced graphene oxide (CoSPc-rGO) aerogels that were synthesized by using a simple hydrothermal method followed by freeze-drying. The properties of these materials that contribute to the electromagnetic balance between dielectric and magnetic loss were elucidated by first formulating a reasonable hypothesis about how the relative orientation of the components in CoSPc-rGO govern p-conjugation and electron transfer from rGO to CoSPc, which is proposed to be a key factor contributing to the regulation of the electromagnetic balance. Polarization relaxation process of materials was analyzed in detail using a variety of approaches including theoretical calculation, spectroscopic measurements, and experimental and simulation studies. The fabricated CoSPc-rGO aerogels that contain an ultra-low content of 4 % were found to exhibit an extraordinary microwave absorption performance associated with a strong reflection loss of -53.23 dB and a broad effective absorption bandwidth of 8.04 GHz. The results of this study should provide an effective guide for new designs of composite materials for EMW absorption.

An ultrasensitive and broadband transparent ultrasound transducer for ultrasound and photoacoustic imaging in-vivo

Transparent ultrasound transducers (TUTs) can seamlessly integrate optical and ultrasound components, but acoustic impedance mismatch prohibits existing TUTs from being practical substitutes for conventional opaque ultrasound transducers. Here, we propose a transparent adhesive based on a silicon dioxide-epoxy composite to fabricate matching and backing layers with acoustic impedances of 7.5 and 4–6 MRayl, respectively. By employing these layers, we develop an ultrasensitive, broadband TUT with 63% bandwidth at a single resonance frequency and high optical transparency ( > 80%), comparable to conventional opaque ultrasound transducers. Our TUT maximises both acoustic power and transfer efficiency with maximal spectrum flatness while minimising ringdowns. This enables high contrast and high-definition dual-modal ultrasound and photoacoustic imaging in live animals and humans. Both modalities reach an imaging depth of > 15 mm, with depth-to-resolution ratios exceeding 500 and 370, respectively. This development sets a new standard for TUTs, advancing the possibilities of sensor fusion.

Enhancing electromagnetic wave absorption with core‐shell structured SiO2@MXene@MoS2 nanospheres

AbstractMaterial composition and structural design are important factors influencing the electromagnetic wave (EMW) absorption performance of materials. To alleviate the impedance mismatch attributed to the high dielectric constant of Ti3C2Tx MXene, we have successfully synthesized core‐shell structured SiO2@MXene@MoS2 nanospheres. This architecture, comprising SiO2 as the core, MXene as the intermediate layer, and MoS2 as the outer shell, is achieved through an electrostatic self‐assembly method combined with a hydrothermal process. This complex core‐shell structure not only provides a variety of loss mechanisms that effectively dissipate electromagnetic energy but also prevents self‐aggregation of MXene and MoS2 nanosheets. Notably, the synergistic combination of SiO2 and MoS2 with highly conductive MXene enables the suitable dielectric constant of the composites, ensuring optimal impedance matching. Therefore, the core‐shell structured SiO2@MXene@MoS2 nanospheres exhibit excellent EMW absorption performance, featuring a remarkable minimum reflection loss (RLmin) of −52.11 dB (2.4 mm). It is noteworthy that these nanospheres achieve an ultra‐wide effective absorption bandwidth (EAB) of 6.72 GHz. This work provides a novel approach for designing and synthesizing high‐performance EMW absorbers characterized by “wide bandwidth and strong reflection loss.”

A perspective on impedance matching and resonance absorption mechanism for electromagnetic wave absorbing

Broadband absorption is urgently desirable for microwave stealth or photothermal conversion, but is a significant challenge in thin layer applications. Impedance mismatch and undesired dielectric relaxation are the main obstacles to realizing simultaneous resonant absorption at multiple frequency bands. In this perspective, the key issues in broadband absorption are briefly reviewed, which must be addressed by the community to enable microwave absorption promoting and widening. Then, impedance matching coefficient used to identify microwave absorbing ability is highlighted. Finally, an ideal model of dielectric dispersion for carbon-based materials is proposed to be used to design broadband absorbing materials, after deducing the inner nature of the typical quarter-wave resonance absorption existing in absorbers.

Fundamental Limits of Few-Layer NbSe2 Microbolometers at Terahertz Frequencies.

The rapid development of infrared spectroscopy, observational astronomy, and scanning near-field microscopy has been enabled by the emergence of sensitive mid- and far-infrared photodetectors. Superconducting hot-electron bolometers (HEBs), known for their exceptional signal-to-noise ratio and fast photoresponse, play a crucial role in these applications. While superconducting HEBs are traditionally crafted from sputtered thin films such as NbN, the potential of layered van der Waals (vdW) superconductors is untapped at THz frequencies. Here, we introduce superconducting HEBs made from few-layer NbSe2 microwires. By improving the interface between NbSe2 and metal leads, we overcome impedance mismatch with RF readout, enabling large responsivity THz detection (0.13 to 2.5 THz) with a minimal noise equivalent power of 7 pW/ and nanosecond-range response time. Our work highlights NbSe2 as a promising platform for HEB technology and presents a reliable vdW assembly protocol for custom bolometer production.