Bias Lines Research Articles

Media trust and infection mitigating behaviours during the COVID-19 pandemic in the USA

IntroductionThe COVID-19 pandemic is an unprecedented public health crisis. It is becoming increasingly clear that people’s behavioural responses in the USA during this fast-changing pandemic are associated with their preferred...

Design Methodology for Distributed Large-Scale ERSFQ Bias Networks

Rapid single-flux quantum (RSFQ) circuits have recently attracted considerable attention as a promising cryogenic beyond CMOS technology for exascale computing. Energy-efficient RSFQ (ERSFQ) is an energy-efficient, inductive bias scheme for RSFQ circuits, where the power dissipation is drastically lowered by eliminating the bias resistors, while the cell library remains unchanged. An ERSFQ bias scheme requires the introduction of multiple circuit elements—current limiting Josephson junctions, bias inductors, and feeding Josephson transmission lines (FJTLs). In this article, parameter guidelines and design techniques for ERSFQ circuits are presented. The proposed guidelines enable more robust circuits resistant to severe variations in supplied bias currents. Trends are considered, and advantageous tradeoffs are discussed for the different components within a bias network. The guidelines provide a means to decrease the size of an FJTL and, thereby, reduce the physical area, power dissipation, and overall bias currents, supporting further increases in circuit complexity. A distributed approach to ERSFQ FJTL is also presented to simplify placement and minimize the effects of the parasitic inductance of the bias lines. This methodology and related circuit techniques are applicable to automating the synthesis of bias networks to enable large-scale ERSFQ circuits.

SFQ Parallel Encoders Promising for Video Imaging With Superconductor Stripline Detectors

We report demonstration of a readout circuit with high-throughput single flux quantum (SFQ) based encoders for a large-scale video imaging system with a conventional frame rate. The encoders are fully parallel and integrated on the same chip as linear arrays of serially connected superconductor stripline detectors (SSLDs), superconducting quantum interference device (SQUID) based comparators, and SFQ synchronizers. Mutual coupling of parallel SSLDs and SQUID-based comparators allows the use of only one dc bias line; it is possible to use thousands of SSLDs without increasing the bias current or number of bias ports. To achieve crosstalk-free readout, the serially connected SSLDs are separated by low-pass filters or large inductors. We experimentally demonstrated crosstalk-free readout including SFQ parallel encoders from 1-D or 2-D serially connected SSLD arrays.

Bioelectrical impedance analysis and dual x-ray absorptiometry agreement for skeletal muscle mass index evaluation in sarcopenia diagnosis

Background: All definitions for diagnosing sarcopenia include the estimation of muscle mass. This can be made using bioelectrical impedance analysis (BIA) or dual x-ray absorptiometry (DXA). BIA is a portable and inexpensive method suitable for clinical settings, while DXA is cumbersome, more expensive and less available. Objectives: To evaluate the interchangeability of both techniques for skeletal muscle mass index (SMI) estimation, and assess whether the two methods are comparable for the diagnosis of sarcopenia. Approach: Prospective, cross-sectional study. Setting: Faculty for Health Sciences, Universidad de Caldas, Colombia. Participants: Seventy-two subjects aged 65–80 years were recruited. Measurements: BIA and DXA for SMI estimation and sarcopenia diagnoses using the definition of the European Working Group on Sarcopenia in Older People (EWGSOP). Of the 72 patients, 28 were diagnosed with sarcopenia by BIA and corroborated by DXA were included in the study. To establish the agreement between techniques, the intraclass correlation coefficient and the concordance correlation coefficient were calculated. A Bland–Altman plot evaluated the agreement. To evaluate agreement on the diagnosis of sarcopenia, a Cohen’s kappa test was performed. Main results: Agreement between SMI by BIA and DXA was good according to the intraclass correlation coefficient (ICC 0.7 95% CI 0.5 to 0.8) but poor when the concordance correlation coefficient was used (CCC 0.4 was calculated 95% CI 0.3 to 0.5). The Bland–Altman analysis showed a clinically unacceptable discrepancy between the methods; the confidence intervals were too wide; the difference between methods tends to get larger as the average increases and the scatter around the bias line get larger as the average gets higher. Cohen’s kappa test was 0.2 (SEE: 0.1). Significance: The agreement between BIA and DXA was weak. We concluded that, in this studied population, the methods were not interchangeable. Results may improve if a specific formula in a greater sample size is used.

Strong coupling of hybrid system between semiconductor quantum dots and superconducting resonator

<p indent=0mm>Quantum computing is a powerful way of improving computing efficiency. For some specific problems, quantum processor can exponentially reduce computation time compared to the classical computer. Cavity quantum electrodynamics, which studies the coherent interaction between photons in an optical cavity and atoms or other two-level systems, is of enormous significance to quantum computing and quantum information processing. The strong coupling regime where a cavity photon mode and an atom exchange a single quantum energy coherently has attracted extensive interest in varied experimental platforms and systems such as alkali atoms, Rydberg atoms, large spin ensembles, magnons, etc. The semiconductor gate-defined double quantum dot (DQD) system is one of the most promising platforms that possesses advantages of advanced micro-nano processing technology and outstanding scalability. Introducing the concept of cavity QED into superconducting circuits (circuit QED, cQED), provides an opportunity to study interaction between electrons confined in semiconductor DQD and photons trapped in a superconducting resonator. Reaching strong coupling regime in this hybrid system paves the way to large-scale network of quantum computing. Electrons confined in DQD have large electrical dipoles, thus are able to couple to photons with relatively large coupling rate. Whereas, due to the charge noise and other dissipation channels in the hybrid system, the decoherence rate of the system is larger than the coupling rate, leaving the strong coupling a great challenge. In recent years, different methods have been proposed to access the strong coupling regime. Taking advantage of a high-quality heterojunction structure, an overlapping gate architecture and a low-pass LC filter on the DC bias line, the decoherence of the charge qubit and microwave leakage of the resonator can be effectively suppressed. The coupling strength of the hybrid system can be improved utilizing a high impedance resonator which is comprised of high kinetic inductance materials. Spin, which does not interact directly with the electric field, is insensitive to charge noise and has much longer decoherence time than charge qubit. However, the weak interaction results in a small coupling rate between the spin and the photon. To solve this problem, the method of coherent hybridization between the spin and the charge state is proposed to improve the coupling strength. This hybridization can be achieved by applying a non-uniform magnetic field, utilizing spin-orbit interaction or spin exchange interaction. At present, both charge qubits and spin qubits have achieved strong coupling with the cavity and the coupling distance between long-range qubits is greatly expanded as long as millimeters. This review introduces basic ideas about cQED and fundamental elements in semiconductor cQED systems. Recent progress in strong coupling hybrid system and methods for improving coupling structures are discussed. In future research, more efforts will be devoted into long-range transfer of qubit states and photon-mediated two or multi-qubit gates.

Wideband Class-F−1 Power Amplifier With Dual-/Quad-Mode Bandpass Response

Bandpass power amplifiers (PAs) are typically implemented by a cascade of second-order topologies. To achieve a wide and flat passband response, the number of resonators must be increased, which leads to large size, high loss and low efficiency, especially at high frequencies. In this paper, a wideband Class-F−1 PA based on a microstrip multimode bandpass impedance transformer (BPIT) is proposed. The modified quad-mode BPIT operation enables the creation of multiple transmission poles using only a single resonator, thus simultaneously achieving a flat wideband response in a small size. In addition, the drain bias and input feed line of the BPIT are arranged to satisfy the harmonic-impedance requirement of the Class-F−1 amplifier. Two PA prototypes have been designed, fabricated, and measured, which exhibit desirable filtering characteristics centered at 3.5 and 3.6 GHz for 5G applications. The fabricated dual- and quad-mode circuits demonstrate large-signal gains of 11.5 dB and 12.6 dB, maximum power added efficiencies (PAEs) of 67.4% and 66.3%, respectively and, with output powers greater than 38.5 dBm. For operation with a PAE larger than 60%, the PAs achieve bandwidths of 150 and 250 MHz, respectively.

Superconductor-Ferromagnet Tunnel Junction Thermoelectric Bolometer and Calorimeter with a SQUID Readout

The superconductor-ferromagnet thermoelectric detector (SFTED) is a novel ultrasensitive radiation detector based on the giant thermoelectric effect in superconductor-ferromagnet tunnel junctions. This type of detector can be operated without the need of additional bias lines and is predicted to provide a performance rivaling transition-edge sensors and kinetic inductance detectors. Here, we report our numerical studies on the SFTED noise equivalent power, energy resolution and time constant, and the feasibility of a SQUID readout in both bolometric and calorimetric regimes, with the goal to provide practical design parameters for the detector fabrication and the readout circuitry implementation.

Novel planar reconfigurable circularly polarized complementary antenna for unidirectional end‐fire radiation

In this article, a novel planar reconfigurable circular polarization (CP) complementary antenna for unidirectional end-fire radiation is proposed. Its radiator is the combination of a shorted quarter wavelength patch and an electric dipole, which provide the vertical and horizontal polarizations, respectively. By adding a 90° phase delay line, the proposed antenna radiates CP electromagnetic waves in the unidirectional end-fire direction. Four p-i-n diodes are also inserted at joints of the electric dipole and the phase delay lines, and two orthogonal CP states, left-hand (LH) and right-hand (RH) CPs, can be switched. In order to reduce the number of DC bias lines, electric dipole arms on both sides of the substrate are connected by metal via-holes, which simplifies the DC bias lines. The proposed antenna at 2.45 GHz is designed and fabricated. Its measured impedance bandwidth with |S11| < −10 dB and 3-dB axial ratio bandwidth are 2.1% and 10.7%, respectively. Additionally, its maximum half power beamwidth in xoz plane is 196°. Reasonable agreement between the measured and simulated results validates the polarization reconfigurability of the proposed antenna.

MoRe/YBCO Josephson junctions and π-loops

We have developed Josephson junctions between the d-wave superconductor YBa2Cu3O7−x (YBCO) and the s-wave Mo0.6Re0.4 (MoRe) alloy superconductor (ds-JJs). Such ds Josephson junctions are of interest for superconducting electronics making use of incorporated π-phase shifts. The I(V)-characteristics of the ds-JJs demonstrate a twice larger critical current along the [100] axis of the YBCO film compared to similarly-oriented ds-JJs made with a Nb top electrode. The characteristic voltage IcRn of the YBCO–Au–MoRe ds-JJs is 750 μV at 4.2 K. The ds-JJs that are oriented along the [100] or [010] axes of the YBCO film exhibit a 200 times higher critical current than similar ds-JJs oriented along the [110] axis of the same YBCO film. A critical current density Jc = 20 kA cm−2 at 4.2 K was achieved. Different layouts of π-loops based on the novel ds-JJs were arranged in various mutual coupling configurations. Spontaneous persistent currents in the π-loops were investigated using scanning SQUID microscopy. Magnetic states of the π-loops were manipulated by currents in integrated bias lines. Higher flux states up to ±2.5Φ0 were induced and stabilized in the π-loops. Crossover temperatures between thermally activated and quantum tunneling switching processes in the ds-JJs were estimated. The demonstrated ability to stabilise and manipulate states of π-loops paves the way towards new computing concepts such as quantum annealing computing.

Polarization and Frequency-Selective Surface for Vehicular Beamforming Communications Requiring Near-Zero Profile

A polarization-selective and reconfigurable Fresnel zone plate consisting of frequency selective surfaces (FSS) loaded with varactor diodes is devised for compact vehicular wireless communication devices. The unit cell constituting the impedance zone exhibits rapid impedance transitions from 0 ohm (electrically-opaque) to 377 ohm (electrically-transparent). An I-shape configuration is employed for the resonant unit cell structure, featuring high compatibility with DC bias voltage network. In addition, double-sided FSS is employed on the top and bottom faces for polarization-selective beamforming. The FSS comprise of a dielectric with near zero thickness ( λ /250 of 2.40 GHz) resulting in intentionally high mutual coupling between the layers. The devised unit cell is designed using an equivalent circuit model analysis and optimized using finite element solver, achieving over 30 dB impedance switching. The proposed unit cell is experimentally confirmed in both vertical and horizontal polarizations. By configuring the DC voltage bias lines, the unit cells of the FSS are transformed into electrically-driven impedance zones formulating alternating and repetitive gratings. The width and the interval of the grating manipulate the constructive and destructive interference resulting in beam scanning range of 30° in both vertical and horizontal polarizations. The proposed approach can provide concise and compact beamforming solutions for future vehicular communications.

Design of wide-angle metamaterial absorbers based on equivalent medium theory

The performances of metamaterial absorbers can be affected by the incidence angle of electromagnetic wave. It is difficult to design the incidence angle-insensitive metamaterial absorbers. In this paper, we propose a metamaterial absorber with wide-angle incidence based on the equivalent medium theory. The absorber unit consists of a double-sided split resonant ring placed vertically on the ground. The resistors and capacitors are loaded at the opening of the resonant ring. The resistor is used to adjust the equivalent electromagnetic parameters of the metamaterial, and the capacitor is used to control the resonant frequency of the metamaterial and miniaturize the unit. When the transverse electric (TE) plane wave impinges on the surface of the absorber, &lt;i&gt;R&lt;/i&gt; = 4000 Ohm and &lt;i&gt;C&lt;/i&gt; = 1.5 pF, the proposed absorber can achieve an absorptivity greater than 90% at 1.59 GHz up to an incidence angle reaching 70°. Besides, the absorber can achieve an 85% absorptivity under an incidence angle of 75°. when the transverse magnetic (TM) plane wave impinges on the surface of the absorbers, &lt;i&gt;R&lt;/i&gt; = 1200 Ω and &lt;i&gt;C&lt;/i&gt; = 1.5 pF, the proposed absorber can achieve an absorptivity of greater than 90% at 1.59 GHz up to a 70°incidence angle. Besides, the absorber can also achieve an absorptivity of 85% up to 75°. The results show that the measurement results are basically consistent with the simulation results. In addition, when the capacitance is changed while the other parameters are fixed, the metamaterial absorber proposed in this paper still has the same wide-angle absorbing performance at the new resonant frequency. In other words, the proposed absorber has broadband operating characteristics. A frequency-tunable metamaterial absorber with wide-angle incidence can be designed based on the aforementioned results. The results in this paper provide a method of tuning capacitance. The opening is set at the other end of the split ring, and the same fixed-value resistor and variable capacitor are loaded on the left opening, and the corresponding DC bias feeder is designed. One end of the DC bias line is directly connected to the ground, and the other end needs to be separately connected to the other DC bias feeder of each unit to realize the control of the variable capacitors of each unit.

A Wideband Multifunctional Absorber/Reflector With Polarization-Insensitive Performance

A wideband and polarization-insensitive absorber/reflector with multifunctional characteristics is proposed in this communication. The designed structure comprises a switchable layer, an air spacer, and a metal ground. The switchable layer contains active resonant elements, whose switching properties are realized by controlling p-i-n diodes. Bias networks for the p-i-n diodes are integrated into the structures and no dedicated bias lines are required. Thus, the negative effect of extra bias lines can be alleviated. In order to achieve switchable and polarization-insensitive properties simultaneously, a super-element configuration is developed by combining four similar unitary elements. One unique feature of the designed device lies in its real-time and multifunctional capability to switch among multiple working states. In addition, the switchable bandwidth of the proposed structure covers a much wider frequency band compared with previous switchable absorber/reflector designs. Distributions of electric field and surface current as well as an equivalent circuit model are presented to gain the necessary physical insight into the working mechanism of the switchable structure. Finally, a prototype of the proposed design is fabricated and measured for validation.

Electrically tunable miniaturized band-stop frequency selective surface on engineered substrate with embedded permalloy patterns

This paper presents a miniaturized and electrically tunable band-stop frequency selective surface (FSS) with magneto-dielectric engineered substrate which has high and electrically tunable effective permeability. The perspective magneto-dielectric substrate is implemented with multiple layers of 100 nm thick patterned Permalloy (Py) thin film embedded in Roger RT/Duriod 5880 substrate, and each Py thin film layer consists of an array of 15μm×20μm Py patterns with 10 μm gaps among them to suppress the magnetic loss. The tunability of effective permeability for the proposed substrate is achieved by the static magnetic field produced from the applied DC current through the patterned gold bias lines beneath Py patterns. The engineered substrate has been implemented and studied, results show that the substrate embedded with a single layer of patterned Py has an equivalent permeability of 1.14 with tunability of 3.3%, and the substrate embedded with ten layers of patterned Py has an increased equivalent permeability of 2.398 and tunability of 15.8%. A magnetic FSS is designed on the implemented engineered substrate to demonstrate the efficacy of miniaturization and tunability. Compared to non-magnetic FSS on normal dielectric substrate, the size of the designed FSS has been reduced by 16.02%, and the operating frequency of the proposed FSS is continuously tunable from 2.450GHz to 2.672GHz with DC current.

Magnetically-actuated micromechanical nickel patches for a monolithically integrated reconfigurable antenna on printed circuit board

In this paper, we present magnetically-actuated micromechanical Ni patches that have been monolithically integrated on a printed circuit board to demonstrate a reconfigurable pixelated antenna operating within the 5–8 GHz frequency bands. The proposed antenna is based on a monolithically integrated grid structure of movable nickel (Ni) and fixed copper (Cu) patches. The Ni patches are magnetically actuated by means of an array of switchable magnets (SMs) placed behind the ground plane of the antenna. This approach eliminates the need for bias lines, which are generally used in reconfigurable antennas and induce losses. Most importantly, the very low mechanical contact resistance (as low as 200 mΩ) between the Ni and Cu patch ensures the insertion of these devices on the antenna plane without introducing significant losses. The use of a SM for the actuation of the patch makes it such that the antenna can hold the desired configurations without consuming active power. Power is consumed only during the switching operation. To demonstrate the feasibility of the proposed idea, the four most relevant operating modes of this small antenna prototype, centered around 5.55 GHz, 6.44 GHz, and 7.89 GHz, are presented.

Silicon‐based on‐chip four‐channel phased‐array radar transmitter with ferroelectric thin film at 100 GHz

A silicon-based phased-array transmitter working at 100 GHz is proposed in this study. Planar array ferroelectric film phase shifters (FPSs) are realised with patch antennas, DC bias lines, microstrip lines and power dividers on a monolithic silicon substrate. The system enables full process compatibility and avoids loss caused by multichip interconnection. The isolation layer uses benzocyclobutene polymer film with low permittivity and low loss tangent, providing large thickness physical isolation. The FPS has a compact length of 0.45 mm, and simulation results show that its phase shift degree at 100 GHz is 125.7° with 3.95 dB insertion loss and 11.4 dB reflection loss. The patch antenna shows that the maximum simulated radiation gain of the single antenna is 4 dBi and the four-element antenna array is 9.7 dBi at 100 GHz. The beam can be steered to ±10°. The proposed system lays an important foundation for the realisation of silicon-based system-on-chip radar RF front-end system.

Magnetically reconfigurable pixelated antenna

AbstractIn this article, a total of 70 movable nickel (Ni) patches are monolithically integrated with fixed copper (Cu) elements to form a reconfigurable patch antenna. The Ni patches are magnetically actuated by means of an array of permanent magnets (PM) placed behind the ground plane of the antenna. The Ni patches establish low resistance mechanical contact between two fixed Cu patches due to the high contact force generated by the PM. Since the Ni patch is itself part of the radiating element, this approach eliminates the need to insert an external switch on the antenna plane. The PMs, which could be replaced by electronically controlled PMs, are placed behind the ground plane, therefore eliminating losses associated with bias lines generally used in pixelated antennas. The 70 movable element pixelated antenna is capable of reconfiguration in frequency, bandwidth, polarization, and beam steering. Herein, we demonstrate frequency and bandwidth reconfiguration.

Demonstration of Microwave Multiplexed Readout of DC-Biased Superconducting Nanowire Detectors

Superconducting nanowires are widely used as sensitive single photon detectors with wide spectral coverage and high timing resolution. We describe a demonstration of an array of DC biased superconducting nanowire single photon detectors read out with a microwave multiplexing circuit. In this design, each individual nanowire is part of a resonant LC circuit where the inductance is dominated by the kinetic inductance of the nanowire. The circuit also contains two parallel plate capacitors, one of them is in parallel with the inductor and the other is coupled to a microwave transmission line which carries the signals to a cryogenic low noise amplifier. All of the nanowires are connected via resistors to a single DC bias line that enables the nanowires to be current biased close to their critical current. When a photon hits a nanowire it creates a normal hot spot which produces a voltage pulse across the LC circuit. This pulse rings down at the resonant frequency of the LC circuit over a time period that is fixed by the quality factor. We present measurements of an array of these devices and an evaluation of their performance in terms of frequency and time response.

Non-Conventional PJVS Exploiting First and Second Steps to Reduce Junctions and Bias Lines

Quantum digital-to-analog converters (DACs) based on programmable Josephson array [Programmable Josephson Voltage Standard (PJVS)] represent the most widely used quantum standard in ac voltage calibrations. The extension of PJVS frequency above the kilohertz range appears to be arduous; however, some enhancements are still practicable. In this work, we demonstrate the possibility to advantageously operate a conventional binary-divided PJVS array with a reduced number of bias lines. This feature is achieved by exploiting both the first and the second Shapiro steps along with nonconventional DAC codings. Two newly devised bias techniques are described in detail and preliminary experimental tests on waveform synthesis have been carried out and are presented here.

Metasurface-Inspired Low Profile Polarization Reconfigurable Antenna With Simple DC Controlling Circuit

A wide-band metasurface inspired polarization reconfigurable antenna with a low profile and a simple DC controlling circuit is introduced and analyzed in this paper. The proposed antenna consists of three parts, i.e., a coplanar waveguide-fed slot coupling antenna with slot slanted angle of 40 degrees, a metasurface superstrate which is composed of a 3·4 array of metallic rectangular patches, and a simple DC bias controlling circuit including p-i-n diode switches, metallic vias, chip inductors, and bias lines. When all the p-i-n diode switches are in ON state, the antenna will work in linear polarization state and generates linear polarized (LP) wave, the measured operating band ranges from 5.2 to 6.2 GHz (17.5% -10 dB impedance bandwidth), while the measured average realized gain is 6.2 dBi. When all the PIN diode switches are in OFF state, the polarization state of the antenna will alter to left-handed circular polarization and produces left-handed circular polarized wave, the measured -10 dB impedance bandwidth and 3 dB axial ratio bandwidth are 20.7% (ranges from 5.2 to 6.4 GHz) and 15.1% (ranges from 5.5 to 6.4 GHz), respectively, while the average realized gain is 7.1 dBi. Measured results of the reflection coefficients, realized gains at broadside, axial ratio, and radiation patterns are in good agreement with numerical simulations, which verifies the effectiveness and correctness of the proposed design.

High speed flux sampling for tunable superconducting qubits with an embedded cryogenic transducer

We develop a high speed on-chip flux measurement using a capacitively shunted SQUID as an embedded cryogenic transducer and apply this technique to the qualification of a near-term scalable printed circuit board (PCB) package for frequency tunable superconducting qubits. The transducer is a flux-tunable LC resonator where applied flux changes the resonant frequency. We apply a microwave tone to probe this frequency and use a time-domain homodyne measurement to extract the reflected phase as a function of flux applied to the SQUID. The transducer response bandwidth is 2.6 GHz with a maximum gain of 1200°/Φ0 allowing us to study the settling amplitude to better than 0.1%. We use this technique to characterize on-chip bias line routing and a variety of PCB-based packages and demonstrate that step response settling can vary by orders of magnitude in both settling time and amplitude depending on if normal or superconducting materials are used. By plating copper PCBs in aluminum we measure a step response consistent with the packaging used for existing high-fidelity qubits.