Capacitively-Coupled SQUID Bias for Time Division Multiplexing

The multiplexing scheme presented in this paper is part of the readout chain of the QUBIC instrument devoted to cosmic microwave background polarization observations. It is based on time domain multiplexing using superconducting quantum interference devices (SQUIDs) to read out a large array of superconducting bolometers. The originality of the multiplexer presented here lies in the use of capacitors for the SQUID addressing. Capacitive coupling allows us to bias many SQUIDs in parallel (in a 2D topology), with low crosstalk and low power dissipation of the cryogenic front-end readout. However, capacitors in series with the SQUID require a modification of the addressing strategy. This paper presents a bias reversal technique adopted to sequentially address the SQUIDs through capacitors using a cryogenic SiGe integrated circuit. We further present the different limitations of this technique and how to choose the proper capacitance for a given multiplexing frequency and current source compliance.     

Flux-Ramp Modulation for SQUID Multiplexing

SQUIDs are typically operated in a flux-locked loop to linearize their response to input flux. However, a flux-locked loop is not possible with a microwave SQUID multiplexer. We describe an alternative technique called flux-ramp modulation and report its successful implementation.     

Integrated Planar HTS SQUID Gradiometer for NDE Application

The performance of a SQUID NDE probe with integrated planar SQUID gradiometers was compared to that with an electronic axial SQUID gradiometer. A circular excitation coil was used for the SQUID NDE probe with the planar gradiometer, whereas a differential excitation coil was adopted for the one with the axial gradiometer. These NDE systems are used to detect a buried flaw in aluminum plates, and the phase-depth relations of the buried flaw were found to show similar linear dependences. Overall, the SQUID NDE system with the planar gradiometer is relatively simple and practical for unshielded operations.     

Integrated niobium DC SQUID gradiometers for non-destructive evaluation and biomagnetism

We describe the design and fabrication of thin-film Nb gradiometers with integrated DC SQUIDs for use in non-destructive evaluation (NDE) and biomagnetism. Issues of sensitivity, imbalance and field response are considered. Results are presented from eddy-current NDE in an unshielded environment of aluminium plates with sub-surface flaws, and from biomagnetic measurements of spinal and peripheral nerve evoked fields.     

A Low-Power Algorithm for Baseband Feedback Used with Frequency Domain Multiplexing

SRON is developing an electronic read-out system for an array of transition edge sensors (TES), which combines the techniques of frequency domain multiplexing (FDM) with base-band feedback (BBFB). An important part of this technique is implemented in digital electronics. This paper describes how a significant reduction of the power consumption of the digital electronics is realized by down-sampling to much lower frequencies using channelization and a poly-phase filter design adapted to BBFB.     

Optical Efficiency and R(T,I) Measurements of ACTPol TESes Using Time Domain Multiplexing Electronics

We present new data on feedhorn-coupled transition-edge sensor devices fabricated for the second-generation receiver (ACTPol) for the Atacama cosmology telescope (ACT). First, we describe optical efficiency measurements of the latest ACTPol detector wafer, which has a \(86\,\pm 15\,\%\) average optical efficiency. Next, we discuss measurements of the TES resistance as a function of temperature and bias current ( \(R(T,I)\) ) using the ACTPol time-domain multiplexing electronics. Qualitative agreement between \(R(T,I)\) data at low bias current and the two-fluid model prediction is shown. Using the two-fluid model and low bias current \(R(T,I)\) data, \(\alpha \) and \(\beta \) at our operating bias current are calculated.     

Design, Fabrication, and Multiplexing of Magnetic Calorimeter X-ray Detectors with High-Efficiency SQUID Readout

Metallic magnetic calorimeters, where deposited energy is detected by measuring a temperature-dependent magnetization with a low-noise SQUID, remain a promising potential route to X-ray spectrometers with energy resolution approaching 1 eV. In this paper we describe our recent work toward array-compatible, high-resolution MMCs fabricated entirely using thin-film techniques. We describe a meander-style pickup loop designed for good coupling to high-efficiency, low noise SQUIDs, as well as considering various routes to a thin-film paramagnetic sensor. We also briefly overview the most promising technology for multiplexing arrays of non-dissipative metallic magnetic calorimeters.      

网络时间服务器的NTP同步偏差性能评估

针对网络时间服务器的溯源问题,对其展开NTP同步偏差的性能评估.通过两种不同测量方法得到的NTP同步偏差分别进行评估,完善了网络时间服务器的溯源方法.实验结果表明,采用直接测量法测量NTP同步偏差的扩展不确定度为322.88μs(k=2),采用比较法测量NTP同步偏差的扩展不确定度为2.48ms(k=2).     

Low-Noise Readout of TES Detectors with Baseband Feedback Frequency Domain Multiplexing

SRON is developing an electronic read-out system for an array of transition edge sensors (TES) based on the techniques of frequency domain multiplexing (FDM) and base-band feedback (BBFB). The astronomical applications of our system are the read-out of soft X-ray micro-calorimeters in a potential instrument on the European X-ray mission-under-study Athena and far-IR bolometers for the SAFARI instrument on the Japanese mission SPICA. In this paper we demonstrate the simultaneous locking of up to 51 BBFB loops. While locked, the in-band read-out noise of the loops is shown to reach the $\mbox{10~pA/}\sqrt{\mathrm{Hz}}$ level required for these missions.     

Cryostats for SQUID magnetometers

A non-metallic and non-magnetic cryostat, with a very low thermal budget and a container type autonomy was developed, to condition SQUID magnetometers whose maximum sensitivity reaches 10^?14$\text{T Hz}{}^{\mathrm{<mtext>?</mtext><mtext>1</mtext><mtext>2</mtext>}}$. This instrumentation uses composite materials, thermal shock and vibration resistant, multilayer thermal radiative insulation, to detect vibrations with thermal equivalent emissivity lower than 10^?3.     

PWM逆变器死区效应在线补偿

为了减小控制系统中由PWM逆变器死区效应引起的电流波形失真,在分析了死区效应产生的机理及谐波影响基础上,提出了一种死区在线补偿的新方法。该方法结合两相静止坐标系下误差电压的线性特点,估计出误差电压幅值,再在两相同步坐标系下利用误差电压幅值和转子角度的关系对死区效应进行前馈补偿,补偿方法考虑了逆变器的非线性误差,无需额外硬件电路支持或离线测量,避免了电流极性检测,能够摆脱误差电压突变带来补偿不利的缺陷,简单且易于实现。仿真及实验结果表明,该方法能够有效地抑制高次谐波电流分量,改善电流波形质量。     

胶印机输墨系统响应时间的研究

利用复数矢量法和图论的理论对胶印机榆墨系统响应时间进行建模,构建了胶印机输墨系统响应时间的教学模型.根据这一新的模型可以计算任意的给定参数的胶印机输墨系统响应时间,为胶印机输墨系统的设计者提供理论依据,具有一定的理论和实际应用价值.     

Time Domain Reflectometer Return Loss Measurements

Equations are derived for the exact identification of a transmission line discontinuity that can be represented by an equivalent circuit consisting of one or more cascaded, series-inductive, parallel-capacitive, and series-transmission-line elements. Equations are presented for determining frequency domain return loss from time domain reflectometer data and the frequency limitations for this method of discontinuity evaluation are discussed.     

DC SQUID Spectrometers for NMR

We report experiments in which we have used DC SQUIDs in pulsed NMR spectrometers to observe directly the free precession of nuclear spins. A broadband spectrometer, which operates in flux-locked loop mode with a bandwidth of 3.4 MHz using a SQUID with additional positive feedback and an untuned superconducting input circuit, has been used to observe NMR signals from platinum powder at frequencies of 38, 65, 85, 240 and 513 kHz. The performance is compared with a second system in which a DC SQUID is operated open loop as a small signal rf amplifier with a series tank input circuit tuned at 1 MHz.     

由相位噪声间接测量阿伦方差的研究

振荡器的频率稳定度在时域一般用阿伦方差表征,在频域一般用相位噪声谱密度函数表征,两者存在一定的数学转换关系,即可以由频域测量的相位噪声谱密度函数转换为时域的阿伦方差.t<0.1 ms时短期频率稳定度的时域测量非常困难.利用两者之间的转换关系对振荡器的时域稳定度进行了间接测量,并用实测数据进行了验证.     

SQUID magnetometers for low-frequency applications

We present a novel formulation for SQUID operation, which enables us to evaluate and compare the sensitivity and applicability of different devices. SQUID magnetometers for low-frequency applications are analyzed, taking into account the coupling circuits and electronics. We discuss nonhysteretic and hysteretic single-junction rf SQUIDs, but the main emphasis is on the dynamics, sensitivity, and coupling considerations of dc-SQUID magnetometers. A short review of current ideas on thin-film, dc-SQUID design presents the problems in coupling and the basic limits of sensitivity. The fabrication technology of tunnel-junction devices is discussed with emphasis on how it limits critical current densities, specific capacitances of junctions, minimum linewidths, conductor separations, etc. Properties of high-temperature superconductors are evaluated on the basis of recently published results on increased flux creep, low density of current carriers, and problems in fabricating reliable junctions. The optimization of electronics for different types of SQUIDs is presented. Finally, the most important low-frequency applications of SQUIDs in biomagnetism, metrology, geomagnetism, and some physics experiments demonstrate the various possibilities that state-of-the-art SQUIDs can provide.     

Return-flux corrections for SQUID susceptometry

A temperature controlled sample in a SQUID magnetometer or susceptometer cannot fill the cross-section of the gradiometer pickup due to the requirement of a cryogenic insulating space between the sample and the superconducting pickup. Return-flux corrections beyond those accounted for by the ordinary demagnetizing factor are thus required. Such corrections as applicable to spheroidal samples are calculated herein, and some of their applications and consequences discussed.     

Two-Stage SQUID Multiplexers for TES Readout

SQUID multiplexers (SQMUX) are essential components for large arrays of TES-based detectors. This paper presents the analysis of multiplexers with two SQUID-stages (2-stage SQMUX) that allows for improved noise performance compared to existing SQMUX configurations. In the 2-stage SQMUX configurations here discussed, each TES is associated with its front-end SQUID. Flux-actuated, SQUID-based switches are used to encode the output current of the front-end SQUIDs. This encoding can be done such that code division (CD) or time division (TD) multiplexing is realized. The encoded output signals of all front-end SQUIDs are then coupled via a superconducting intermediate loop to a second-stage SQUID. We discuss the expected noise and dynamic performance of 2-stage CD-SQMUX and 2-stage TD-SQMUX based on measured parameters of existing switches and SQUID current sensors.     

医学超声内窥成像系统的数字增益补偿

为了补偿医学超声内窥镜中超声信号的传输衰减,设计了由AD8065、AD8331和现场可编程门阵列（FPGA）组成的前置放大与增益补偿电路．电路采用AD8065实现超声换能器与增益补偿电路间的阻抗变换,然后,根据超声信号在人体组织中的衰减规律,由FPGA输出补偿控制电压,控制AD8331实现对回波信号的补偿放大．对实际超声回波进行的补偿实验表明,该电路能够有效地补偿超声信号的传输衰减,而且,利用FPGA的可编程性,该电路可根据不同的衰减曲线进行灵活配置.