Electrical Impedance Matching Research Articles

High-speed, low-voltage, low-bit-energy silicon photonic crystal slow-light modulator with impedance-engineered distributed electrodes

Silicon modulators in optical transceivers feature high-density integration and low manufacturing cost, but they also need to deliver high speed and low power consumption to meet the demands of future data centers and high-performance computing. This paper demonstrates a significantly improved 64 Gbps silicon Mach–Zehnder modulator incorporating photonic crystal slow-light phase shifters. By employing distributed electrodes and engineering their impedance, electro-optic phase matching and electrical impedance matching were obtained simultaneously, and the driving voltage was reduced to 0.87 V, which is compatible with fin-type field effect transistors and eliminates the need for additional electrical amplifiers. The bit energy of as low as 59 fJ/bit is comparable to that of microring modulators, while this modulator does not require temperature control like that used for microring modulators, due to its wide working spectrum of 6 nm. These results indicate the potential for addressing power issues in next-generation data infrastructures.

Accretion of SiO2/doped-Si cuboid for terahertz absorber and impedance matching

This paper presents an ultra-broadband polarization-insensitive terahertz absorber that consists of a doped Si substrate and a triple-layer of doped Si covered with a SiO2 anti-reflective coating. The finite element method is used to investigate the absorption of the absorber. The absorber exhibits high absorption rates of over 95 % between frequencies of 0.9 THz and 9.2 THz, with a center frequency of 5.05 THz and a relative bandwidth ratio of 164 %. Moreover, it exhibits outstanding wide-angle absorption properties, achieving over 90 % absorption at angles of incidence ranging from 0 to 55° and frequencies spanning from 1.1 to 10 THz. Furthermore, the underlying mechanisms behind broadband absorption and high absorption rates are studied by analyzing the electric field distribution and impedance matching theory. Additionally, this absorber showcases excellent fabrication tolerance. Therefore, the proposed terahertz absorber featuring doped silicon triple-layer stacked arrays has significant potential in applications such as sensing, stealth technology, and biomedicine.

Reversible Switching Between Microwave Absorption and EMI Shielding of VO2 Composite Foam.

Developing lightweight composite with reversible switching between microwave (MW) absorption and electromagnetic interference (EMI) shielding is promising yet remains highly challenging due to the completely inconsistent attenuation mechanism for electromagnetic (EM) radiation. Here, a lightweight vanadium dioxide/expanded polymer microsphere composites foam (VO2/EPM) is designed and fabricated with porous structures and 3D VO2 interconnection, which possesses reversible switching function between MW absorption and EMI shielding under thermal stimulation. The VO2/EPM exhibits MW absorption with a broad effective absorption bandwidth of 3.25GHz at room temperature (25 °C), while provides EMI shielding of 23.1dB at moderately high temperature (100 °C). This reversible switching performance relies on the porous structure and tunability of electrical conductivity, complex permittivity, and impedance matching, which are substantially induced by the convertible crystal structure and electronic structure of VO2. Finite element simulation is employed to qualitatively investigate the change in interaction between EM waves and VO2/EPM before and after the phase transition. Moreover, the application of VO2/EPM is demonstrated with a reversible switching function in controlling wireless transmission on/off, showcasing its excellent cycling stability. This kind of smart material with a reversible switching function shows great potential in next-generation electronic devices.

Dual-polarization small-angle strong nonreciprocal thermal radiator with Weyl semimetal

The development of dual-polarization irreversible radiators that can operate without external magnetic field is an arduous task. To avoid the need of strong magnetic field, a dual-polarization nonreciprocal thermal radiator with the introduction of Weyl semimetal is demonstrated. It consists of cross-shaped silicon nanopores, Weyl semimetal, and Ag reflective layer. The simulation results show that the proposed radiator offers both TE- and TM-polarized strong irreversible radiation with an incident angle of 1.6°. The TE-polarized absorptivity and TM-polarized emissivity are 98.8% and 97.6%, respectively. The dual-polarization nonreciprocity exceeds 80%. The physical principle is explained by the electric field energy distribution and impedance matching theory. The demonstrated scheme and radiator have potential application in dual-polarization multi-band irreversible radiation and thermal management.

Dynamically tunable terahertz quadruple-function absorber based on a hybrid configuration of graphene and vanadium dioxide

A quadruple-function dynamically tunable terahertz absorber that uses a hybrid configuration of graphene and vanadium dioxide is proposed in this paper. The absorber achieves dynamic conversion of four functions in one structure: ultra-broadband, broadband, single-frequency narrowband and dual-frequency narrowband, by utilizing the electrical control properties of graphene and the phase-shifting properties of vanadium dioxide. Furthermore, the paper also reveals the physical mechanism of the proposed absorber through the electric field distribution and impedance matching theory. In addition, the influences of the Fermi energy level of graphene and the electrical conductivity of vanadium dioxide on the absorption spectra are investigated, demonstrating the structure’s dynamic tunability. Due to the above features, the designed absorber is expected to have potential applications in terahertz imaging, modulation and filtering.

Broadband electrical impedance matching of sandwiched piezoelectric ultrasonic transducers for structural health monitoring of the rail in-service

To achieve high power transmission efficiency and high signal-to-noise ratio of sandwiched piezoelectric ultrasonic transducers (SPUTs) over a wide bandwidth, broadband electrical impedance matching (EIM) is investigated in-depth. Firstly, L type, T type, III type, IV type and V type EIM networks are designed and the corresponding component parameters are determined by the Smith chart with a quality factor Q constraint. Secondly, the above EIM networks are compared by reflection coefficient S11, transducer power gain (TPG) and active power. It is shown that they can effectively improve the TPG, and active power by two times and greatly reduce S11. Then the emitted voltage and received voltage under different excitation frequencies and EIM networks are analyzed. It is shown that the III type network presents optimal performance, which can make the aforementioned voltage values increase by two times over entire frequency range of interest. Finally, the effect of III type and IV type networks on electromechanical characteristics is studied by using the PSpice model of SPUTs. Compared to non-matching, the electro-acoustical gain ratio is improved almost two times, while the electro-acoustical power ratio is greatly reduced.

Study on nonreciprocal radiation and photothermal conversion of VO2-based tunable inverse opal thermal emitter

In this work, a novel tunable nonreciprocal thermal emitter, consisting of an InAs magneto-optic inverse opal film and a VO2 film, is designed to achieve strong and tunable nonreciprocal radiation in the mid-infrared band of 6.8–7.8 μm. A more appropriate Lorentz-Drude model is used to describe the material properties of InAs, and the nonreciprocal band in the mid-infrared range for doped InAs is obtained through the Lorentz-Drude model. The effect of different middle layers on the structure of films and inverse opals is investigated under a magnetic field at an incident angle of 26° The inverse opal structure is found to have better nonreciprocal properties, while VO2 has the role of replacing noble metals in the tuning of nonreciprocal radiation. In addition, the strengthening mechanism of the inverse opal structure and the physical mechanism of the nonreciprocal radiation are further analysed and revealed through electric field energy distribution plots and impedance matching theory. A comparison of the nonreciprocal radiation and the photothermal effect of three inverse opal structures with different pore distributions and porosities for different parameters shows that the simple cubic structure has the strongest nonreciprocal radiation performance and a relatively high photothermal conversion effect, which can further increase the radiation capacity of the thermal emitter over a range. Therefore, the designed inverse opal composite structure can be used for the fabrication of tunable thermal emitters with nonreciprocal effects, where the amount of light absorbed in one channel of the thermal emitter can be controlled to tune the radiation capacity of the other channel. Providing a degree of assistance in the development and application of nonreciprocal thermal radiation devices in the mid-infrared wavelength band.

An electrical impedance matching method of dual-frequency transducers for ultrasound internal imaging

A micro single transducer with two resonant frequencies can solve the inherent contradiction between detection depth and resolution by simultaneously emitting two frequency bands of ultrasonic waves. But the difference of impedance values in the two resonant frequency bands seriously affects dual-frequency echo signal efficiency. In order to improve the quality of transducer sensitivity, a dual-frequency electrical impedance matching method is proposed in the study. By selecting a specific matching structure to match one frequency without messing up the impedance of another frequency, the two frequencies can be designed independently to achieve preliminary impedance matching. The matching networks for single frequency are combined to form a complete dual-frequency matching circuit, and adjust the initial matching value to obtain a suitable matching state. The performances of the matching network have been tested and verified by experiments. After matching, the low-frequency and high-frequency sensitivities of the transducer increased 1.86 times and 2.26 times, respectively. In addition, system noise was also reduced by 29.6% after adding the matching network. The results demonstrate that this dual-frequency matching network can simultaneously increase the amplitude of high-frequency and low-frequency echoes to obtain better quality images.

Machine learning in design of broadband terahertz absorbers based on composite structures

Metasurface absorbers have gained increasing attention in the field of electromagnetic (EM) absorption in recent years. The conventional design method often involves designing various structures and comparing absorption bandwidth and intensity to determine the absorber's structural parameters. The absorption of EM waves by absorbers involves a complicated process of electric field excitation and impedance matching. Although design experience can reduce the number of design iterations, the selection of artificial parameters is often imprecise and can result in design bias. Fortunately, machine learning (ML) algorithms offer the possibility of automating the design of critical parameters for metasurfaces, which can effectively reduce the laborious design process and the high cost of trial and error. In this study, a pyramid-based metasurface absorber (PMA) and an inverted pyramid-based metasurface absorber (IPMA) were designed and optimized using the random forest (RF) algorithm. The results show that the absorption bandwidths of the two absorber models are 2.68 THz and 2.42 THz, respectively, and the mean absolute percentage error (MAPE) is only 0.60%, which is significantly better than other classical ML and deep learning (DL) algorithms. This study offers a new approach for designing complex systems related to EM wave absorption, reflection, and transmission propagation.

Tunable, polarization-dependent multi-band perfect metamaterial absorber based on single layer mickey-like patterned graphene

This paper proposes and investigates a polarization-dependent multi-band perfect absorber composed of mickey-like patterned graphene. Simulation results demonstrate three perfect absorption peaks at 24.62 μm, 31.16 μm, and 65.12 μm with maximal absorbance of 96.6%, 98.8%, and 99.1% respectively, for instance, when an incident y-polarized wave is taken. A hybrid combination of the two ear and face structures effectively enhances and improves the absorption performance. This is evidenced by a step-by-step spectrum analysis of each decomposed and synthesized component, as well as an analysis of electric field coupling and impedance matching theory. Further investigation of the device's performance reveals that it is largely insensitive to incident angles (up to 30°), but is significantly affected by polarization angles due to the characteristic asymmetric properties of the structure along the x axis. The absorption peaks can be dynamically tuned by adjusting the effective parameters of graphene, the permittivity of the dielectric material, and the refractive index of its surroundings. Based on polarization related modulation mechanism, such graphene surface plasmon resonance (GSPR) induced device has potential applications in polarized light filtering, differentiation of dielectric materials, and sensing of surrounding refractive indices.

Two-Port Antenna Based on Shorting Pins and Open-Ended Slots with T-Shaped Stub for Isolation Enhancement

In this paper, a compact two-port antenna consisting of an open-ended slot loaded with shorting pins and a T-shaped stub is presented. The beak-shaped two-port antenna radiators enhance the antenna bandwidth and electrical length. The two inverted L-shaped open-ended slots form an effective capacitance and an inductance, resulting in a dual-operating band. The T-shaped stub improves electrical height and impedance matching to ground, while the combination of the T-shape and open-ended slots provides a dual-band response and improves isolation by up to 8 dB. Shorting pins connected to the ground show inductive behavior that improves isolation by up to 6 and 4 dB for the low- and high-frequency bands. The two-port antenna exhibits more than 20 dB of isolation with only 2 mm of edge-to-edge distance of the antenna element. The two-port antenna operates in dual frequencies from 4.1 GHz to 4.6 GHz and from 5.55 GHz to 6 GHz, and the 32 mm × 26.5 mm size makes it suitable for 5G and WLAN/ISM applications.

Thermoelectric device performance beyond average ZT: Holistic consideration of materials and design

In the current era where many renewable energy technologies are commercially mature and optimized, thermoelectrics remain relatively under-utilized. This can be partly attributed to their limited device efficiencies despite their high materials performances. On the materials level, the performance of thermoelectrics can be defined by zT or average zT, which is directly correlated to device power conversion efficiency. Due to this direct correlation, it is a longstanding assumption that maximizing average zT will result in higher efficiency. Although this practice holds true for many cases, it does not provide a complete picture due to the complex interplay between electronic and thermal transport properties. In this work, we surveyed the literature to find that high average zT does not always translate to high efficiency. Instead, it was found that compatibility factor, which dictates the optimal ratio of electrical and heat current passing through the material, is equally important in determining the device efficiency. Other factors such as electrical and thermal impedance matching, as well as contact resistance are also discussed. This review concludes with food for thought on future thermoelectric research beyond average zT to realize the untapped potential in this special class of materials.

Optimizing wireless acoustic energy harvesting and communication with passive markers underwater

To enhance functionality of Acoustic Identification Tags (AID), passive markers designed as landmarks for Autonomous Underwater Vehicles (AUVs) [Satish et al., JASA 149 (2021)], the development of an accompanying battery free active communication platform was explored [Bhardwaj et al., JASA 152, 4 (2022)]. This platform utilizes custom piezoelectric transducers impedance matched for broadband operation, enabling concurrent acoustic energy harvesting and fast backscatter communication [Allam et al., SPIE 31, 9 (2022)]. The combination of these active and passive devices can improve AUV localization and information transfer for specific applications such as short-range search missions or AUV homing and docking. The design of this platform for underwater operations requires a balance of parameters such as center frequency and piezoelectric element dimensions to achieve a high range of operation, power efficiency and data rates, while minimizing attenuation and spreading losses challenges. The design process for piezo selection, acoustic and electrical impedance matching, transducer casing design, and the experimental evaluation of the chosen 350 kHz design will be discussed. This approach was validated experimentally to quantify performance metrics such as the maximal range, data rates using various standard communication such as Frequency Shift Keying (FSK) and Amplitude Modulation (AM).

Individually frequency and amplitude tunable metamaterial absorber with sensing functions based on strontium titanate and graphene

A terahertz metamaterial absorber with sensing function based on strontium titanate (STO) and graphene is designed. The optical characteristics of the designed structures are simulated and numerically calculated by the finite difference time domain (FDTD) and coupled mode theory (CMT) method. The results show that the temperature of STO is 300 K and Fermi level of graphene is 1.0 eV, the absorptance achieves 99.8 % and 92.7 % at 0.36 THz and 2.18 THz, respectively. When the temperature of the STO is set from 250 K to 400 K, the center frequency is moved from 0.32 THz and 1.96 THz to 0.43 THz and 2.54 THz. When the temperature is stable at 300 K, the dual narrow band absorption can be converted to single narrow band absorption by tuning the Fermi level from 1.0 eV to 0 eV. The physical mechanism of the dual narrow band absorptions and active tuning is analyzed by electric field distribution and impedance matching theory. The effect of polarization direction and incident angle on the absorber performance is also investigated. In addition, we also investigated the sensing characteristics of the absorber when the Fermi level of graphene is 0 eV, and the sensitivity and figure of meritis of the structure for detecting different refractive indices is 50 GHz/RIU and 0.33/RIU. The proposed structure provides new ideas for future multifunctional terahertz device design.

An ultrasound-induced wireless power supply based on AlN piezoelectric micromachined ultrasonic transducers

Wireless power transfer is one of the enabling technologies for powering implantable biomedical devices. Biocompatibility and CMOS compatibility of wireless power transfer devices are highly desired due to safety and footprint concerns. Toward implantable applications, this paper presents an ultrasound-induced wireless power supply based on AlN piezoelectric micromachined ultrasonic transducer (PMUT). The wireless power supply integrates wireless power transfer, power management and energy storage functions. The PMUT array is used as a passive wireless power receiver, followed by electrical impedance matching networks and a voltage multiplier for efficient power transmission and rectification. The output power intensity of the wireless receiver reaches 7.36 μW/mm2 with an incident ultrasound power below the FDA safety limit. The output power of the wireless power supply reaches 18.8 μW and a 100-μF capacitor is fully charged to 3.19 V after power management, which are sufficient to power many low-power implantable biomedical devices such as for neural electrical stimulation, biosensors and intrabody communication applications. The wireless power supply is implemented in a PCB with a diameter of 1 cm. With biocompatibility and CMOS compatibility of AlN thin film compared to commonly used PZT, the proposed solution paves the way for safer and ultraminiaturized wireless power supplies with further development incorporating all the functions on a monolithic chip in the future.

A Lamb waves-based wireless power transmission system for powering IoT sensor nodes

Sensor nodes (SNs) are widely deployed for condition monitoring within closed thin-walled structures. Conventional wired power supply using cables will affect the structural integrity, and wireless power supply based on inductive coupling will be shielded by metal structures, therefore, neither is desirable. Motivated by these issues, this article presents a Lamb waves wireless power transmission (WPT) technology based on piezoelectric wafer active sensors (PWASs). A PWAS with a diameter of 7 mm was used to excite A0 single-mode Lamb waves on a 1.6 mm aluminum plate at a frequency of 150 kHz for power transmission. Two optimization strategies for the Lamb waves-based WPT system were proposed and designed, including electrical impedance matching and beamforming with a linear PWAS array. The optimization effects of these two methods were analyzed experimentally. By combining these two approaches, the maximum received power is 1.537 mW, which is 384.25 times higher than that without the optimization method. The corresponding transmission efficiency is 0.217%, which is 43.4 times higher than that without the optimization method. A power management circuit was built with a maximum output power of 1.41 mW and a corresponding conversion efficiency of 77.5%. Finally, an internet-of-things (IoT) SN is designed, and a test proves that the proposed WPT system can power IoT SNs.

Piezoelectric transducer design for simultaneous ultrasonic power transfer and backscatter communication

Ultrasonic waves can transfer power and data to sensors and devices deployed to traditionally inaccessible locations, such as inside the human body or deep in the ocean, eliminating the need for battery replacement. In ultrasonic power and data transfer systems, a piezoelectric transducer converts incident ultrasonic waves to useful electric power while transmitting data by modulating its reflected signal through backscatter communication. Existing approaches rely on reflecting a portion of the incident power to communicate, reducing the harvested power. This work realizes uninterrupted power harvesting with simultaneous backscatter communication through frequency multiplexing. A piezoelectric transducer is first designed and tested experimentally for high sensitivity and high bandwidth operation through low-loss broadband acoustic and electrical impedance matching. The transducer achieved 70% bandwidth at 1 MHz with a 10 dB difference between reflecting and absorbing incident ultrasonic waves. A frequency multiplexing technique is then developed to separate power and data into different frequency bands achieving simultaneous operation. The technique extends the range and bandwidth of ultrasonically powered devices such as biomedical implants and ocean monitoring sensors.

EM waves absorption properties of nitrogenous porous carbon derived from PANI fiber clusters carbonization

The carbon source, graphitization degree and microstructure of pure carbon materials have strong effects on their electrical conductivity, impedance matching and electromagnetic (EM) waves absorption properties. A novel microstructure nitrogenous porous carbon (NPC) material with excellent EM waves absorption properties was synthesized by carbonizing polyaniline (PANI) fiber clusters. When the filler loading is only 30 wt%, the widest effective absorption bandwidth (EAB) reached 5.5 GHz from 12.41 GHz to 17.91 GHz (almost the entire Ku band) with a thickness of only 1.5 mm and the EAB/thickness was up to 3.67 GHz/mm, which is not inferior or even better than many composites with complex structure. The nitrogen atoms in NPC lattice reduced its graphitization degree. The synergistic effect of optimized impedance matching and enhanced dielectric loss improved EM waves absorption of NPC. The EM waves dissipation mechanisms of NPC material mainly include dipole polarization, interface polarization and conductance loss. The synthesized NPC is a potential EM waves absorption material.

Exploration of the mechanisms enabling high performance in relaxor ferroelectric crystals

<p indent="0mm">Relaxor ferroelectric single crystals, exhibiting excellent dielectric, piezoelectric, electro-optic, and pyroelectric properties, are important functional dielectric materials in electronic technology. Since the 1990s, relaxor ferroelectric crystals have attracted considerable attention in the ferroelectric and piezoelectric research fields and improved the performance of numerous piezoelectric devices, especially medical ultrasonic imaging transducers. In this paper, we briefly introduce the history of relaxor ferroelectric crystals and then focus on the research progress of our group in recent years, as listed below. (1) To elucidate the contribution of polar nanoregions (PNRs)<italic> </italic>to piezoelectricity, we performed closely integrated experimental and computational studies on relaxor ferroelectric crystals. In this work, we obtained key experimental evidence (low-temperature dielectric relaxation) for the contribution of PNRs to the piezoelectric activity in relaxor-PbTiO₃ (PT) crystals via cryogenic measurements, and more importantly, for the first time, we quantified the contribution of PNRs accounting for 50%–80% of the room-temperature dielectric and piezoelectric properties. Based on the phase-field simulations, we proposed a mesoscale mechanism wherein the PNRs are aligned in a ferroelectric matrix facilitating the polarization rotation, which successfully explains the contribution of PNRs to dielectric/piezoelectric properties. This work opens up a new material design paradigm that introduces local heterogeneities to achieve enhanced macroscopic responses. (2) Based on the origin of high piezoelectric activity in relaxor ferroelectric crystals, we proposed a theoretical approach, i.e., judiciously introducing local structure heterogeneity, to engineer the interfacial energies, thereby increasing the piezoelectricity of ferroelectric materials. According to this method, we designed and fabricated a series of rare earth element-doped relaxor ferroelectric crystals with piezoelectric coefficients <italic>d</italic>₃₃ in the 3400–4100 pC/N, double the values of the undoped counterparts. The newly developed piezoelectric materials offer potential benefits for piezoelectric devices, especially high-frequency medical transducers, where ultrahigh clamped dielectric constant (~3000) improves the electrical impedance matching of the transducers, thereby increasing the sensitivity and decreasing the insertion loss in the ultracompact transducers. (3) Using phase-field simulations and experimental measurements, we transformed the originally opaque [001]-poled rhombohedral PMN-PT crystals into a transparent one by using an AC electric field to engineer the domain structure. These crystals possess ultrahigh piezoelectric coefficient <italic>d</italic>₃₃ (&gt;2100 pC/N), outstanding electromechanical coupling factor <italic>k</italic>₃₃ (~94%), and large electro-optical coefficient <italic>γ</italic>₃₃<sc>(~220 pm/V),</sc> far beyond the performance of the state-of-the-art transparent ferroelectric crystal LiNbO₃, showing great potential in various hybrid device applications, including photoacoustic medical transducers and self-energy-harvesting touchscreens. Furthermore, we discovered that the larger domain sizes lead to higher piezoelectricity in [001]-poled rhombohedral perovskite ferroelectric crystals, opposing the long-standing belief that a smaller domain size always results in higher piezoelectricity in ferroelectric crystals. This observation may benefit the future design of piezoelectric materials. Finally, the applications of our newly designed relaxor ferroelectric crystals in electromechanical and electro-optical devices are introduced, and the future perspectives of relaxor ferroelectric crystals are discussed.

Broadband Electrical Impedance Matching of Transmitter Transducer for Acoustic Logging While Drilling Tool

Broadband Electrical Impedance Matching of Transmitter Transducer for Acoustic Logging While Drilling Tool