Tunable Impedance Research Articles

Lightweight porous Co3O4 and Co/CoO nanofibers with tunable impedance match and configuration-dependent microwave absorption properties

In this study, we fabricated one-dimensional porous Co3O4 and Co/CoO nanofibers by calcination of cobalt(ii) oxalate dehydrate precursors in an environment filled with air and N2, respectively.

Proximity Coupled Cavity Backed Patch Antenna for Long Range UHF RFID Tag

A novel proximity coupled cavity backed patch antenna for long range Radio Frequency Identification (RFID) tag is proposed in this communication. The RFID tag may sustain fair amount of impact or scratch, since the circuitry is protected inside the metal cavity. The novel feeding structure incorporates a full $\pi $ network for fine impedance tuning. A patch structure with two shorting joints is also proposed, where the shorting joints not only offer mechanical support for the patch but may also serve as a way to tune the resonant frequency of the antenna. A prototype was fabricated and achieved a gain of 5.7 dBi, which gives it a reading range of up to 23 m.

Microwave Imaging Using a Disordered Cavity with a Dynamically Tunable Impedance Surface

When coupled to a tuning mechanism, a disordered medium provides a powerful means for shaping electromagnetic waveforms. The authors leverage this functionality to conduct volumetric computational imaging: A deformed cavity is outfitted with tailored, irregular surfaces, and its microwave resonant modes are projected into an imaging domain to retrieve the scene's spatial information. This approach could be applied to biomedical imaging, security screening, or wireless power transfer or telecommunications.

Linear Voltage Controlled Variable Resistor Using Body Potential in SOI process

A linear voltage controlled variable resistor in partially depleted silicon-on-insulator (PD-SOI) technology is presented. Stacked FET structure is utilized for the variable resistor implementation and the control of gate and body voltage provides wide resistance tuning range. Also, the use of body voltage control of the stacked FET varistor demonstrated improved IP3 and P1dB linearity. This variable resistor can be applicable to tunable load impedance, series and parallel feedback control and variable attenuation, as a part of system or as a discrete component.

A Low-Cost Noise Wave Correlator for Noise Parameters Extraction by Cold Noise Power Measurement

Conventionally, the noise parameters of a Device under Test (DUT) which generally characterize the noise performance of the DUT, are obtained via the impedance tuner technique. The authors have previously presented a technique which eliminates the need for impedance tuner, and rather employs an 8-port network that enables the extraction of the noise correlation matrix of a given DUT and thus its noise parameters. In this paper, we present a further simplification of the 8-port network technique, which also eliminates the need for a conventional external noise source. Cold noise powers emanating from a DUT are measured via a 6-port network with the aid of matched termination. The measured noise powers provide sufficient information for determining the noise wave correlation matrix of a DUT, which are then converted into the conventional 2-port noise parameters. The proposed technique is simple, fast and is verified to give a good estimation of the noise parameters of selected DUTs.

Novel Thin Film Solid State Ionic Device with Electrochemically Tunable Resistance Based on Lithium Plating/Stripping

Electrochemically induced property tuning has recently emerged as a promising pathway to achieve accordable devices and reconfigurable circuits, in most cases making use of the change of one or several material properties with ion exchange or the local electroformation of conducting structures in an insulating material [1–3]. In the present work we report on the electrochemical tuning of a solid state ionic device impedance using lithium ion plating and stripping at a current collector/solid electrolyte interface [4,5]. The device presented a design with two actuation vertical metal electrodes separating a Cu/LiPON/Li multilayer, and two measurement interdigitated electrodes embedded in the LiPON layer. The measurement electrodes were isolated from the bottom actuation electrode by an Al2O3 dielectric layer (Fig1). The devices were microfabricated on silicon substrates with varied architectures including lithium plating surfaces ranging between 1µm² and 3000µm² (Fig.2). Upon chrono-potentiometric stimuli, lithium was plated between the measurement electrodes, thus changing significantly the impedance, and more particulary the electrical resistance. Fully reversible variation of the real part of the impedance (Re Z) over a range of more than 3 decades was observed by electrochemical impedance spectroscopy upon the formation and dissolution of nanometric lithium layer (Fig.3). Particular attention was put on the investigation of the influence of the current density during plating/stripping (plated lithium morphology), and the architecture (interdigitated electrodes design, plating surface) on the device performance.

An Interference Tolerant RF Frontend With Capacitive Feedback for Channel Filtering

In this letter, a reconfigurable RF frontend with 4-path passive mixer is presented. Compared with the conventional method of using passive mixer at LNA output only, this design has further transferred the tunable impedance characteristic of passive mixer to the LNA input with capacitive feedback to achieve reconfigurable impedance matching at target frequency. Furthermore, the negative feedback is also able to free the conventional common base amplifier from 50 Ω impedance matching requirement to achieve better noise figure. The design was implemented with 0.18 μm SiGe BiCMOS technology. Measurement results showed a lowest noise figure of 4.6 dB from 0.6 to 1.1 GHz and an in-band IIP3 of −11 dBm, an out-band IIP3 of +3 dBm respectively.

Ku‐band low side‐lobe level fixed‐frequency electrically scanning leaky‐wave antenna

ABSTRACTA one‐dimensional (1D) Ku‐band electrically scanning leaky‐wave antenna (LWA) is presented. The antenna is based on Fabry‐Perot (FP) cavity leaky‐waveguide, which is composed of a partially reflective surface (PRS) and a tunable high impedance surface (HIS). The PRS consists of a tapered dipole array and the configuration is modulated to reduce the side‐lobe level (SLL). The varactor diodes are loaded on the HIS to achieve the steerable radiation angle. Both simulated and experimental results confirm well that the scanning scope as wide as 30 degree can be obtained and the low SLL can be observed. © 2016 Wiley Periodicals, Inc. Microwave Opt Technol Lett 58:2512–2516, 2016

Tunable Terahertz Filter-Integrated Quasi-Yagi Antenna Based on Graphene

In this paper, a filter-integrated quasi-Yagi antenna (FIQYA) with quasi-independently tunable passband and front-to-back ratio is proposed by using graphene. The graphene at two ends of the coupled-line ring resonator mainly affects the impedance bandwidth while the front-to-back ratio of radiation patterns is attributed to the graphene-implanted open-circuited director. The bandwidth and front-to-back ratio tunability is accomplished by altering the complex conductivity of graphene controlled by chemical potential. For verification, a 2-THz FIQYA using both perfect electric conductor (PEC) and graphene with two different controllable chemical potentials (μ c1 and μ c2) is simulated. The simulated results show that the maximum tunable impedance bandwidth of the FIQYA is varied from 186 to 235 GHz without affecting the radiation patterns when μ c1 changes from 0 to 0.2 eV. The maximum tunable front-to-back ratio is changed from 11.7 to 15.4 dB while μ c2 is altering from 0 to 0.6 eV, maintaining an acceptable matching bandwidth in all cases.

Line-impedance matching and signal conditioning capabilities for high-speed feed-forward voltage-mode transmit drivers

This work presents the design and implementation of a power-efficient 2-tap feed-forward voltage mode driver which has impedance tuning and signal conditioning capabilities. The driver has a robust mechanism to match its impedance to the line impedance even when signal conditioning is enabled which minimizes reflection and improves signal quality. A mixed signal approach that detects and compensates for NMOS and PMOS transistor resistance variation is presented. An analog circuit detects the driver's resistance variation, and a digital circuit controls an analog compensation circuit to maintain line impedance matching for all signal conditioning configurations of the driver. When maximum signal conditioning is enabled, the driver can transmit a 40Gbits/sec PRBS7 signal through a 10 in. FR4 channel. It achieves a differential eye-opening amplitude of 100mVppd and an eye-opening width of 0.8UI consuming 9.7mW of at-speed power. Simulations demonstrate that worst case impedance deviation from 50Ω due to process, voltage and temperature variation is 2.7%. The driver is designed in 28nm CMOS process using a 0.85V nominal supply voltage. It is simulated using HSPICE circuit simulator and mixed mode simulations tools.

On the development of a novel high VSWR programmable impedance tuner

Impedance tuners are key instruments used for load- and source–pull measurements. They are crucial for any active microwave components, circuits, and systems characterization and optimization. This paper reports theoretical, simulated, and experimental results related to the development of a novel programmable impedance tuner offering high-voltage standing wave ratio (VSWR). After presenting the proposed tuner principle, a fabricated prototype operating at microwave frequencies and based on a 3.5 mm coaxial line is introduced with experimental results. Depending on the targeted frequency band, different pairs of slugs, with optimized length and characteristic impedance, can be used to obtain an optimal VSWR. This first prototype allowed us to demonstrate the interest of the proposed impedance synthesis principle and to identify ways forward to further improve its performances and push forward this promising technology.

Experimental Investigation of Adaptive Impedance Matching for a MIMO Terminal With CMOS-SOI Tuners

It is well known that user proximity introduces absorption and impedance mismatch losses (MLs) that severely degrade multiple-input multiple-output (MIMO) performance of handset antennas. In this work, we experimentally verified the potential of adaptive impedance matching (AIM) to mitigate user interaction effects and identified the main AIM gain mechanism in realistic systems. A practical setup including custom-designed CMOS silicon-on-insulator (SOI) impedance tuners implemented on a MIMO handset was measured in three propagation environments and ten real user scenarios. The results indicate that AIM can improve MIMO capacity by up to 42% equivalent to 3.5 dB of multiplexing efficiency (ME) gain. Taking into account the measured losses of 1 dB in the integrated tuners, the maximum net ME gain is 2.5 dB suggesting applicability in practical systems. Variations in ME gains of up to 1.5 dB for different hand-grip styles were mainly due to differences in impedance mismatch and tuner loss distribution. The study also confirmed earlier results on the significant differences in mismatch and absorption between phantoms and real users in which the phantoms underestimated user effects and, therefore, AIM gains. Finally, propagation environments of different angular spreads were found to give only minor ME gain variations.

A Fabry–Pérot Antenna With Two-Dimensional Electronic Beam Scanning

A novel fixed-frequency electronically steerable Fabry–Perot Antenna (FPA) with electronic two-dimensional (2-D) (azimuth and elevation) steering capability is presented. The configuration is based on a centrally fed Fabry–Perot cavity (FPC) loaded with a tunable high impedance surface (HIS). Varactor diodes are used to electronically tune the HIS reflection coefficient, forming four azimuthal sectors that are independently controlled by four control signals, respectively. It is demonstrated that this simple configuration generates a pencil beam that can be pointed to eight discrete azimuthal directions, whereas continuous elevation scanning is also attained simultaneously for each azimuthal direction by controlling the leaky-wave propagation constant. The theory, simulation analysis, and experimental results obtained from a prototype operating at 5.5 GHz are presented to validate the antenna design.

Close Integration of a UHF-RFID Transponder Into a Limb Prosthesis for Tracking and Sensing

The technology of structural radio systems that is well assessed in the avionic and naval communications is here applied to obtain antenna functionality out of a limb prosthesis with minimal changes to the device, in specific, an orthopedic nail. A microchip transponder based on the ultrahigh frequency-radio-frequency identification (RFID) communication standard is connected to the nail by means of a central notch forming a towel-bar-like antenna. The resulting device, called prosthetic structural tag, is such to preserve the mechanical continuity of the original nail, but it is also capable of energy harvesting and RFID. The electrical and geometrical control parameters for impedance tuning were identified using computer simulation and laboratory tests. The radiation performance is mostly dependent on the geometry of the notch, while it is rather unaffected by the length of the nail, so that the proposed layout may also be applied to different kinds of prosthesis. The experimented read distance at 870-960 MHz was more than 35-cm far from the limb surface. The augmented smart prosthesis is, hence, suitable to be monitored using an external non-contacting antenna for application to tracking and, in the near future, to monitor the prosthesis health status.

High‐efficiency CMOS push‐pull power amplifier with multilayer center‐tapped transformer

This paper describes the design of a push‐pull power amplifier (PA) with a center‐tapped transformer for transmitter applications on the 5.2‐GHz band using 0.18μm CMOS technology. The type of the proposed PA is based on a double‐ended push–pull (DEPP) configuration. DEPP has a simple construction with only transistors and transformers. The PA has reverse‐phased cascode‐connected transistors. The proposed transformer has a multilayer structure and was designed using electromagnetic field simulation. To achieve high power added efficiency (PAE), we assumed the optimized output impedance technique with a tunable impedance antenna. The PA has 13.2 dB linearity gain, 14.9 dBm 1‐dB compression point (P1dB), and 27.4% maximum PAE. © 2016 Institute of Electrical Engineers of Japan. Published by John Wiley & Sons, Inc.

Continuously Tunable mm-Wave High Impedance Surface

A continuously tunable high impedance surface (HIS) is presented and experimentally demonstrated at approximately 60 GHz. An optimized phase-shifting HIS consisting of a periodic surface placed over a ground plane is designed and employed to obtain the desired reflection phase. Tuning of the HIS is achieved by virtue of four compact piezoelectric actuators that produce a displacement between the two layers, when voltage is applied to them. This produces a continuous change of the reflection phase response of the structure. Simulated and experimental results are presented, demonstrating a dynamic surface impedance performance with a measured phase shift of over 200 $^\circ$ at about 60 GHz.

Wearable self‐tuning antenna for emergency rescue operations

In this study, the design, hardware implementation and characterisation of a self-tuning 406 MHz antenna of a Cospas-Sarsat personal locator beacon are presented. The realised prototype is able to perform automatic tuning of the antenna under time-varying environmental conditions due to human body movements and sea water proximity. The impedance tuning is performed by tracking the instantaneous value of the reflection coefficient and by modifying an appropriate impedance matching network according to a real-time adaptive algorithm. A resilient default/backup software architecture has been designed to ensure that tuning guarantees a return loss higher than 10 dB for the personal locator beacon in most of impedance mismatching conditions.

Passive Interaction Control With Dynamical Systems

Autonomous dynamical systems (DS) has emerged as an extremely flexible and powerful method for modeling robotic tasks. Task execution of DS models is typically done in an open-loop manner in combination with standard low level controller, e.g. position controller or impedance controller. Such an arrangement has two important drawbacks: 1) it is not passive and 2) the DS model cannot respond to physical perturbations on the robot body. These can imply severe consequences in motion tasks involving expected or unexpected contact with objects whose position is unknown and dynamic. We propose a novel control architecture that closes the loop around the DS, ensures passivity and allows intuitive tuning of the robot impedance. We evaluate our approach in a comparative study in an uncertain manipulation task with unexpected contact.

A SiGe BiCMOS Power Amplifier Using a Lumped Element-Based Impedance Tuner

A dual-path multi-band power amplifier (PA) with a tunable output matching network is presented for long-term- evolution (LTE) handset applications. To optimize output load impedances for various power regions with various frequency bands, an impedance tuner implemented using lumped elements is used. The dual-path multi-band PA fabricated using $0.35{\mathchar702D}\mu{\rm m}$ SiGe BiCMOS process is evaluated for the evolved UMTS terrestrial radio access (E-UTRA) bands 1, 2, 3, 5, and 8 with a 10 MHz bandwidth (BW) LTE 16 quadrature amplitude modulation signal having a peak-to-average ratio of 6.4 dB.

A Highly Efficient Ultralow Photovoltaic Power Harvesting System With MPPT for Internet of Things Smart Nodes

Implementing a monolithic highly efficient ultralow photovoltaic (PV) power harvesting system is pivotal for smart nodes of Internet of things (IOT) networks. This paper proposes a fully integrated harvesting system in 0.18-μm CMOS technology. Utilizing a small commercial solar cell of 2.5 cm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> , the proposed system can provide 0-29 μW of power, which is much higher than the commonly used passive radio-frequency identification devices in IOT application. The hill-climbing maximum power point tracking algorithm is developed in an energy-efficient manner to tune the input impedance of the system and guarantee adaptive maximum power transfer under wide illumination conditions. The detailed impedance tuning approach is implemented with a capacitor value modulation to eliminate the quiescent power consumption as well as to achieve a higher efficiency than the traditional pulse-frequency modulation scheme. A supercapacitor is utilized for buffering, energy storing, and filtering purposes, which enables more functions of the IOT smart nodes such as active sensing and system-on-chip (SOC) signal processing. The output voltage ranges between 3.0 and 3.5 V for different device loads, such as sensors, SOC, or wireless transceivers. The measured results confirm that this PV harvesting system achieves both ultralow operation capability under 20 μW and a selfsustaining efficiency of 89%.