RF Impedance Research Articles

Spin-torque ferromagnetic resonance based on current-induced impedance

Spin-torque ferromagnetic resonance (ST-FMR) has been widely used for measuring damping-like spin–orbit torques in magnetic bilayers. Typically, the ratio between the damping-like and field-like spin–orbit torques are extrapolated based on the ferromagnetic resonance line shapes. However, when the field-like spin–orbit torque is unknown, the line shape analysis may lead to errors in extrapolating the damping-like spin–orbit torque. Here, we propose a modified version of the ST-FMR that allows extrapolation of both damping-like and field-like torques independently. By introducing an alternating current to the sample, the RF impedance is modulated, allowing detection via the reflected microwave. We show that the extrapolated field-like and damping-like torques in Py/Pt samples are consistent with the technique measuring current-induced linewidth and resonance field change but have much better signal-to-noise ratio. Our proposed method paves a way for more accurate measurement of spin–orbit torques.

Improved impedance matching speed with gradient descent for advanced RF plasma system

Plasma processes are widely used in the fabrication of integrated circuits for the smaller, faster, more powerful circuits demanded by new technology. High-performance semiconductor equipment is required for dynamic random-access memory and three-dimensional NAND flash memory in semiconductor manufacturing. To enhance the speed of RF impedance matching, this paper proposes a method for calculating the load impedance of the plasma chamber. To calculate the target value of the variable components, we employ the input impedance of the impedance-matching unit and the complex impedances of the variable components. In addition, the internal parameters are automatically tuned through the gradient-descent method of machine learning, which improves the accuracy of impedance matching. The new matching method achieved a fast matching time and high efficiency of the matching trajectories. Moreover, it avoids the increase of the reflected power during the matching process, which causes plasma instability, and prohibits significant matching delay in a specific area, which disadvantages the conventional matching algorithm. These advantages are expected to significantly expand the development of new plasma processes from that of conventional impedance matching.

13.56 MHz RF 플라즈마 임피던스 정합기용 전자식 가변 커패시터의 가변 속도 최적화를 위한 인덕터 설계 방법

This study introduces a method for designing an inductor for an electrical variable capacitor for an RF plasma impedance matcher of 13.56 MHz. In the RF impedance matcher, variable capacitors are essentially used for maximum power transfer of loads and sources. Electrical variable capacitors are next-generation variable capacitors. They can shorten the matching time compared with conventional mechanical variable capacitors. The proposed design method determines the inductor value with an optimized variable speed through the inductor design of the diode series-type electrical variable capacitor circuit. This method provides a faster variable speed to the electrical variable capacitor circuit to further shorten the matching time. The proposed design method is validated through simulations and experiments.

Extraction of Graphene's RF Impedance through Thru-Reflect-Line Calibration.

Graphene has unique properties that can be exploited for radiofrequency applications. Its characterization is key for the development of new graphene devices, circuits, and systems. Due to the two-dimensional nature of graphene, there are challenges in the methodology to extract relevant characteristics that are necessary for device design. In this work, the Thru-Reflect-Line (TRL) calibration was evaluated as a solution to extract graphene's electrical characteristics from 1 GHz to 65 GHz, where the calibration structures' requirements were analyzed. It was demonstrated that thick metallic contacts, a low-loss substrate, and a short and thin contact are necessary to characterize graphene. Furthermore, since graphene's properties are dependent on the polarization voltage applied, a backgate has to be included so that graphene can be characterized for different chemical potentials. Such characterization is mandatory for the design of graphene RF electronics and can be used to extract characteristics such as graphene's resistance, quantum capacitance, and kinetic inductance. Finally, the proposed structure was characterized, and graphene's resistance and quantum capacitance were extracted.

A Comprehensive Review on High-efficiency RF-DC Converter for Energy Harvesting Applications

The design of radiofrequency energy harvesting (RFRH) circuit for wearable devices, wireless sensor networks, and IoT applications can be classified mainly into radio frequency to direct current (RF-DC) converter, a transmitter and receiver antenna, an impedance matching network, and a storage device or a load. By scavenging RF energy from the ambient environment, this developing technology allows low-power wireless devices to be self-sustaining and environment friendly. To eliminate the need for batteries, RFEH technology has become a dependable and promising alternative for extending the lifetime of power-constrained wireless networks. This paper mainly focused on the input and output power, Power conversion efficiency (PCE), and sensitivity. Due to the weak and limited signal strength of received RF power, high-efficiency state-of-the-art RF energy harvesters must be designed to provide sufficient DC supply voltage to wireless networks. We provide in-depth information on the system’s parameters. Optimum efficiency and maximum output power are the main concerns of an RFEH system. Therefore, RF Energy harvesting system review, antenna design, impedance matching, and RF-DC converter are presented in this paper to provide a deep insight into the design of the RFEH system. This article may help in identifying new research in the field of RF Energy Harvesting.

Hairpin RF resonators for MR imaging transceiver arrays with high inter-channel isolation and B1 efficiency at ultrahigh field 7 T

Electromagnetic decoupling among a close-fitting or high-density transceiver RF array elements is required to maintain the integrity of the magnetic flux density from individual channel for enhanced performance in detection sensitivity and parallel imaging. High-impedance RF coils have demonstrated to be a prominent design method to circumvent these coupling issues. Yet, inherent characteristics of these coils have ramification on the B1 field efficiency and SNR. In this work, we propose a hairpin high impedance RF resonator design for highly decoupled multichannel transceiver arrays at ultrahigh magnetic fields. Due to the high impedance property of the hairpin resonators, the proposed transceiver array can provide high decoupling performance without using any dedicated decoupling circuit among the resonant elements. Because of elimination of lumped inductors in the resonator circuit, higher B1 field efficiency in imaging subjects can be expected. In order to validate the feasibility of the proposed hairpin RF coils, systematical studies on decoupling performance, field distribution, and SNR are performed, and the results are compared with those obtained from existing high-impedance RF coil, e.g., “self-decoupled RF coil”. To further investigate its performance, an 8-channel head coil array using the proposed hairpin resonators loaded with a cylindrical phantom is designed, demonstrating a 19 % increase of the B1+ field intensity compared to the self-decoupled coils at 7 T. Furthermore, the characteristics of the hairpin RF coils are evaluated using a more realistic human head voxel model numerically. The proposed hairpin RF coil provides excellent decoupling performance and superior RF magnetic field efficiency compared to the “self-decoupled” high impedance coils. Bench test of a pair of fabricated hairpin coils prove to be in good accordance with numerical results.

A 2.4-GHz 10-W Class Bridge Rectifier and Its Efficiency Analysis With the Behavioral Model

This article presents a 2.4-GHz band 10-W class bridge rectifier that achieves a high-measured efficiency of 90.2%. To clarify the mechanism for obtaining high efficiency, a theoretical analysis with the novel behavioral model of bridge rectifiers is demonstrated. The behavior model includes three functional blocks, namely; 1) impedance transform, which defines the RF impedance for the bridge diode; 2) RF impedance matching; and 3) rectification with the ideal current waveform of the bridge diode. Closed-form formulas for the rectification efficiency and the maximum input power are derived using the behavioral model. The RF impedance can be optimized to obtain high efficiency with the derived formulas, similar to source-pull operations in harmonic balance simulations or experiments. The fundamental limitation on the rectification efficiency is obtained for a bridge rectifier with the optimum RF impedance. In the experimental investigation of the 2.4-GHz 10-W class bridge rectifier, the measured efficiency of 90.2% agreed well with the theoretical value of 91.2% with represented formulas. Furthermore, the derived formulas are applied to the 5.8-GHz 1-W rectifier, and its effectiveness can be confirmed. It is evident that the analyzed efficiencies are close to the fundamental limitations.

High‐frequency measurement of dielectric permittivity and antimicrobial properties of polyaniline and graphite oxide nanocomposites

The polyaniline/graphite oxide (PANI/GO) nanocomposite was prepared by the in situ chemical polymerisation method. The synthesis involved the formation of dark green coloured polyaniline/graphite oxide composite. The crystalline structure and morphology of the composite were studied using UV-visible spectroscopy (UV), X-ray diffraction (XRD) and transmission electron microscopy (TEM).The characteristic peaks in XRD and UV-visible spectra confirmed the formation of the PANI/GO nanocomposite. DC conductivity measurements were performed using a two-probe method. Dielectric responses of the composites were investigated in the frequency range100 MHz to 3 GHz by the RF impedance analyser. The dielectric constant ϵ′(w) and dielectric loss ϵ′′(w) were investigated. It was observed that the dielectric constant ϵ′(w) and dielectric loss ϵ′′(w) decreased with an increase in frequencies (for different wt % of GO). The antibacterial activity of this composite was examined.

Impedance Transparency and Performance Metrics of HBT-Based N-Path Mixers for mmWave Applications

MOS N-path mixer-first receivers are capable of providing instantly-reconfigurable RF impedance and bandwidth while achieving moderate noise figure (NF) and high linearity, but their frequency tuning range is limited by both LO (local oscillator) generation and the RF port input capacitance. State-of-the-art mm-wave MOS N-path receivers often compromise performance to cover the mm-wave range, but this paper presents the theory and design considerations for a new topology of N-path mixer which makes use of high f <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">T</sub> HBTs and breaks this trade-off between performance and tuning range. Here, we borrow from a previously derived LTI model for MOS-based N-path mixers to derive an analogous model for the HBT-based counterpart which provides a meaningful comparison between the performance of the two topologies. We show that the HBT-based implementation is capable of operation beyond the frequency limits of MOS-based implementations while maintaining comparable NF and linearity without consuming exorbitant power. Measurements done on a proof-of-concept chip in GlobalFoundries BiCMOS8HP are consistent with our models and simulations. By organizing process parameters and user-selected design variables into dimensionless ratios, we provide expressions for key performance metrics which enable the designer to make informed decisions about trade-offs and optimizations for both LO generation and the mixer core.

Effects of heating rate in thermal debinding on the microstructure and property of sintered NiCuZn ferrite prepared by powder injection molding

NiCuZn ferrite ceramics were prepared by injection molding, debinding and sintering at 1150 °C. The effects of heating rate in thermal debinding on microstructure, bending strength and magnetic properties of sintered samples were investigated by scanning electron microscopy with energy-dispersive X-ray spectroscopy, X-ray diffraction, the Dual Column Tabletop Testing Machine, RF impedance Analyzer and B-H curve analyzer. The results showed the heating rate in thermal debinding played an important role on the sintered NiCuZn ferrite prepared by injection molding. When the heating rate in thermal debinding was quick above 1.2 °C/min in the lager cuboid samples, CuO precipitate was found at the grain boundary of ferrite and the intergranular fracture occurred, which was different from the normal transgranular fracture under the condition of slow heating rate. Furthermore, the density, bending strength, permeability and core loss of the sintered samples were improved with the decrease of heating rate. The influencing mechanism of thermal debinding on the difference was also discussed.

Correlation of RF impedance with Ar plasma parameters in semiconductor etch equipment using inductively coupled plasma

The correlation of RF impedance with Ar plasma parameters was analyzed in semiconductor etch equipment using inductively coupled plasma. Since the impedance measured by a VI probe installed behind the RF bias matcher had information for plasma and structural parts of chamber simultaneously, the impedance was corrected by excluding transmission line and peripheral parts of the bias substrate. The corrected impedance was compared with plasma parameters, such as plasma density and electron temperature. The coefficient of determination between the corrected plasma resistance and the theoretical formula of the resistance for bulk plasma was over 0.9 unlike the resistance measured by the VI probe. It is expected that the corrected RF impedance can assist in monitoring the status of plasma and maintaining the quality of the etch process in semiconductor mass production lines.

Strain mediated enhancement in magnetoelectric properties of sonochemically synthesized piezoelectric and piezomagnetic composites

Materials with magneto-electric (ME) properties are of great importance because of their demand in electronic industries. Three dimensional nano-particles of the ME-composites having the general formula (1-x)CoCr0.3Fe1.7O4(CCFO)+(x)BaTiO3(BTO) (x = 0.0, 0.2, 0.4, 0.6, 0.8 and 1.0) were obtained by comprising the piezoelectric-BTO and piezomagnetic-CCFO phases. The individual phases of CCFO and BTO were synthesized separately by ultrasonic irradiation assisted sonochemical and sol-gel routs. X-ray diffraction patterns (XRD) confirmed the well-crystalline nature of both the phases. BTO and CCFO phases were under tensile strain as confirmed by the variation in lattice constants with varying proportion of BTO and CCFO. An energy-dispersive X-ray spectroscopy spectrum confirmed the phase purity of the samples and stoichiometric concentration of elements. Magnetic properties were investigated by M − H loop measurements and dielectric properties by using RF impedance analyzer. Dielectric constant increased with the increasing percentage of BTO. The maximum value of ME coefficient (24.7 mV/cm⋅Oe) is observed for the 60%CCFO+40%BTO sample. The obtained results were discussed in the light of grain size, strain and the basic properties of the individual phases. The prepared materials can be applicable in electronic devices where high magneto-electric coefficient is desirable.

LTCC-Based Fluidic Tuners for Low Microwave Frequency Reconfigurable Circuits

This article presents a frequency reconfigurable RF impedance tuner using eight cascaded fluidic cells to cover the frequency band [0.9, 2.4] GHz. The tuner is made of eight fluidic fillable cavities on top of a coplanar waveguide transmission line in a single low-temperature cofired ceramic (LTCC) substrate. Each cavity is either kept empty or filled with deionized (DI) water to alter the substrate's permittivity and so change the tuner's response. Closed-form expressions are derived and used to dimension the tuner's individual cells, while 3-D field simulations are used to complete the design of a single cell and an entire eight-cell tuner. Both components are fabricated, and good agreement between simulation and measured is observed. The fabricated tuner is used to build a fluidic reconfigurable RF amplifier.

Frequency- and Time-Domain Modeling and Characterization of PN Phase Shifters in All-Silicon Carrier-Depletion Modulators

We present a systematic study on PN junction phase shifters in silicon Mach–Zehnder modulators (MZMs) in both frequency and time domains, with an emphasis on their impact on MZMs’ RF loss. The RF loss associated with PN phase shifters dominates the overall RF loss of a MZM's transmission line and determines a MZM's bandwidth. The RF loss is also evident in the time domain, which for the first time is investigated. We find that the dielectric loss and conductor loss of a PN-loaded, lossy transmission line result in downhill and uphill features on the instantaneous impedance curve, which features are typically observed on the instantaneous impedance of an inductor and a capacitor, respectively. This is aligned with our model, which shows that the impedance of a PN-loaded lossy line includes an inductor term and a capacitor term and their values are expressed in terms of RF loss. Our model on RF loss and impedance agrees well with experiment in both domains for a variety of doping levels. Finally, we conduct performance test on modulators and discuss the constraints on the baud-rates and BERs in our QAM tests.

사다리형 폴리실세스퀴옥세인과 POSS를 포함하는 하이브리드 폴리이미드 복합체의 합성 및 특성 분석

1,3-bis(4-aminophenoxy)benzene(APB)과 3,3",4,4"-benzophenonetetracarboxylic dianhydride(BTDA)의 조성에 여덟개의 페닐기를 함유한 케이지 구조의 실세스퀴옥세인(octaphenyl-POSS, OPS)과 페닐과 에폭시 그룹이 각각 8대2 비율로 함유된 사다리형 폴리실세스퀴옥세인(LPS)을 혼합하여 내열성 및 절연성이 우수한 하이브리드 폴리이미드 복합체를 제조하였다. 제조된 하이브리드 폴리이미드 필름은 OPS의 중량을 2.5 wt%로 고정시키고, LPS의 중량비를 다양(1.5, 2.5, 3.5 wt%)하게 변화시켜 합성하였다. OPS는 물리적인 결합을 이용하여 poly(amic acid)(PAA) 용액에 균일하게 분산시켰으며, LPS의 경우에는 화학적인 결합을 이용하기 위하여 LPS의 에폭시 그룹과 PAA의 아민 그룹과의 에폭시-아민 반응을 이용하였다. 얻어진 하이브리드 폴리이미드 복합체의 내열 특성, 광학 성질, 유전상수와 모폴로지를 측정하기 위하여 퓨리에 변환 적외선 분광기(FTIR), 열 중량 분석기(TGA), 분광광도계(microspectrometer), 임피던스기(RF impedance) 그리고 전계방사형 주사전자현미경(FE-SEM)과 주사탐침현미경(AFM)을 사용하였다. 또한 제조된 하이브리드 폴리이미드 매트릭스 내에 Si 원소가 균일하게 분산돼 있는 것은 EDS mapping으로 확인하였다. In this study, we used the POSS cage with eight phenyl groups (octaphenyl-POSS, OPS) and ladder-like polysilsesquioxane (LPS) having phenyl and epoxy groups in 8:2 ratio in the composition of 1,3-bis(4-aminophenoxy)benzene (APB) and 3,3",4,4"-benzophenonetetracarboxylic dianhydride (BTDA) to synthesize hybrid polyimide composites with high thermal stability and excellent electrical insulating property. The hybrid polyimide composites had various LPS weight ratios (1.5, 2.5, 3.5 wt%) with the fixed 2.5 wt% of OPS. OPS was homogeneously dispersed in the solution of poly(amic acid) (PAA) via physical bonding interaction and the epoxy groups of LPS were chemically reacted with the residual terminal amines of PAA. The thermal and optical properties, dielectric constant, morphology of the hybrid polyimide composites were determined using infrared spectroscopy (FTIR), thermogravimetric analysis (TGA), microspectrometer, RF Impedance, field emission scanning electron microscope (FE-SEM), and atomic force microscope (AFM). Also, we confirmed that Si atom was uniformly dispersed in polyimide matrix by using EDS mapping.

RF Impedance Sensor for Antenna-Tuning Front Ends

A method for complex RF impedance sensing is proposed. The method is based on using a scalar impedance meter and an impedance tuning network for sensing the complex load impedance. The scalar measurements are conducted three times for different settings of the digitally controlled tuning network after which the load impedance is evaluated based on the scalar outputs from the reflectometer. The measurements of the prototype device are demonstrated. The target application for the presented system and method is the antenna-tuning front end of the multiantenna cellular handheld devices.

Graphene-filled versus ionic liquid-filled poly(vinylidene fluoride-co-hexafluoropropene) electrolytic membranes for high energy devices: thermophysical and electrochemical aspects

The recent developments of membrane technology that requires the composite membrane to work effectively in high energy devices have prompted the inclusion of graphene (GO) and N-butyltrimethylammonium iodide (IL) into a poly(vinylidene fluoride-co-hexafluoropropene) (PVDF-co-HFP) host polymer. From the characterizations that were conducted using FTIR, SEM, TGA, DSC, universal testing machine, Hot Disk Thermal Constants Analyser and the RF impedance spectroscopy, the IL-filled PVDF-co-HFP membrane (1P/IL) was found to have a better dielectric and thermal conductivity, while the decreased porosity of the 1P/GO membrane was discovered to have contributed to its better mechanical performance. Apart from the moieties, which had filled the gaps of the porous architecture and formed a firmer configuration from the chemical junctions with the PVDF-co-HFP, the IL in the membrane was also observed to have increased the density of the accumulated charge carriers and polarization with a better crystallinity control, porosity and ion transportation of the dielectric constant. Based on the above results, the introduction of an ionic liquid (with its plasticizing effect, well-dispersed assembling and diffusional motions) can thus be regarded as significantly improving the properties of the PVDF-co-HFP and particularly in the hi-tech targeted applications of high energy devices such as those of the high-energy Li-ion batteries.

Testing and Validation of Adaptive Impedance Matching System for Broadband Antenna

Broad RF impedance matching is challenging; however, the need for broadband matching is found frequently in modern RF and wireless systems with multiple wireless standards. Moreover, in 5G technology, multiple frequency bands are used, and these systems typically employ a broadband antenna or multiple antennas. Antenna impedances vary from design targets for many reasons including manufacturing process variations or antenna environment changes. An adaptive impedance matching system (AIMS) for testing and validation is introduced, and its implementation is shown in this paper. The AIMS can control impedance matching tuner settings to provide an arbitrary impedance frequency-varying load that meets user-defined conditions. This AIMS provides a testing and validation system for broadband antennas that can be characterized by various settings of the impedance matching tuner. As a device under test (DUT), a three-stub reconfigurable filter was used as the impedance matching tuner on a RT/Duroid 6010 RF board. It was integrated with a control circuit board. This AIMS implementation also included an antenna impedance tuner that can vary the distance between the antenna and the ground plane. This model represents practical antenna impedance variations. The AIMS controls a network analyzer and the impendence matching tuner. The adaptive control program on a PC was developed to perform an effective two-pass tuning strategy. This article presents the successful automated tuned results and their numerical evaluations of three cases that were generated by the antenna impedance tuner.

Adaptive Matching Transmitter With Dual-Band Antenna for Intraoral Tongue Drive System

The intraoral Tongue Drive System (iTDS) is a wireless assistive technology that detects users' voluntary tongue gestures, and converts them to user-defined commands, enabling them to access computers and navigate powered wheelchairs. In this paper, we presented a transmitter (Tx) with adaptive matching and three bands (27, 433, and 915MHz) to create a robust wireless link between iTDS and an external receiver (Rx) by addressing the effects of external RF interference and impedance variations of the Tx antenna in the dynamic mouth environment. The upper two Tx bands share a dual-band antenna, while the lower band drives a coil. The Tx antenna is simulated in a simplified human mouth model in HFSS as well as a real human head model. The adaptive triple-band Tx chip was fabricated in a 0.35-μm 4P2M standard CMOS process. The Tx chip and antenna have been characterized in a human subject as part of an iTDS prototype under open-and closed-mouth scenarios, which present the peak gain of -24.4 and -15.63 dBi at 433 and 915MHz, respectively. Two adaptive matching networks for these bands compensate variations of the Tx antenna impedance via a feedback mechanism. The measured S11 tuning range of the proposed network can cover up to 60 and 75 jΩ at 433 and 915MHz, respectively.

InP series-like transferred electron device for CW submillimeter-wave power sources

The potential of vertical series-like InP transferred electron devices operating in the electron accumulation layer and multiple transit-time mode is investigated at 400 GHz by means of one-dimensional time-domain energy/momentum numerical modeling. The device structure has been optimized at 500 K. The RF operating mode is analyzed. The potential of two- and three-transit series-like TED is compared to the performance of a classical single-transit N+NN+ TED. The series-like TED clearly improves the RF performance and impedance level and consequently is a possible solution to extend the TED frequency limitation at submillimeter wave. The device RF operation stability and thermal consistency of the results are analyzed.