On chip droplet characterization: a practical, high-sensitivity measurement of droplet impedance in digital microfluidics

We demonstrate a new approach to impedance measurement on digital microfluidics chips for the purpose of simple, sensitive, and accurate volume and liquid composition measurement. Adding only a single series resistor to existing AC droplet actuation circuits, the platform is simple to implement and has negligible effect on actuation voltage. To accurately measure the complex voltage across the resistor (and hence current through the device and droplet), the designed system is based on software-implemented lock-in amplification detection of the voltage drop across the resistor which filters out noise, enabling high-resolution and low-limit signal recovery. We observe picoliter sensitivity with linear correlation of voltage to volume extending to the microliter volumes that can be handled by digital microfluidic devices. Due to the minimal hardware, the system is robust and measurements are highly repeatable. The detection technique provides both phase and magnitude information of the real-time current flowing through the droplet for a full impedance measurement. The sensitivity and resolution of this platform enables it to distinguish between various liquids which, as demonstrated in this paper, could potentially be extended to quantify solute concentrations, liquid mixtures, and presence of analytes.     

Analyses of power output of piezoelectric energy-harvesting devices directly connected to a load resistor using a coupled piezoelectric-circuit finite element method

This paper presents, for the first time, a coupled piezoelectric-circuit finite element model (CPC-FEM) to analyze the power output of a vibration-based piezoelectric energy-harvesting device (EHD) when it is connected to a load resistor. Special focus is given to the effect of the load resistor value on the vibrational amplitude of the piezoelectric EHD, and thus on the current, voltage, and power generated by the device, which are normally assumed to be independent of the load resistor value to reduce the complexity of modeling and simulation. The presented CPC-FEM uses a cantilever with a sandwich structure and a seismic mass attached to the tip to study the following characteristics of the EHD as a result of changing the load resistor value: 1) the electric outputs: the current through and voltage across the load resistor; 2) the power dissipated by the load resistor; 3) the displacement amplitude of the tip of the cantilever; and 4) the shift in the resonant frequency of the device. It is found that these characteristics of the EHD have a significant dependence on the load resistor value, rather than being independent of it as is assumed in most literature. The CPC-FEM is capable of predicting the generated output power of the EHD with different load resistor values while simultaneously calculating the effect of the load resistor value on the displacement amplitude of the tip of the cantilever. This makes the CPC-FEM invaluable for validating the performance of a designed EHD before it is fabricated and tested, thereby reducing the recurring costs associated with repeat fabrication and trials. In addition, the proposed CPC-FEM can also be used for producing an optimized design for maximum power output.     

交流注入式电池内阻测试仪电阻参数的校准方法

分析了基于交流注入式电池内阻测试仪电阻参数的测量原理,研究了采用标准交流电阻和感应分压器对其进行校准的方法,利用多位双级感应分压器对标准交流电阻的电压进行分压,模拟产生多值高准确度交流电阻箱,解决了电池内阻测试仪校准缺乏高准确度标准器的问题,分析了标准交流电阻的时间常数和感应分压器的相位误差对测量结果的影响。将该方法校准结果与采用实物标准电阻的校准结果进行了比较,在全量程范围内相差小于0.02%,表明该方法具有较高准确度。     

电机定子匝间绝缘测量用冲击分压器性能试验研究

在研究电机定子电气性能检验装置校准方法项目过程中,研制了一种采用高压无感电阻、等电位屏蔽措施、二级分压结构和分布电容调节技术的冲击分压器,它被用于电机定子匝间绝缘项目的冲击电压峰值和波前时间的测量。经过试验,该电阻分压器的分压比误差小于0.5%;上升时间小于100ns,满足测量指标要求。     

脉冲偏压下电弧离子镀等离子体负载的等效电路模型及其定量表征

为了解决电弧离子镀(AIP)工艺中脉冲偏压电源与AIP等离子体负载间的匹配问题,结合脉冲偏压下AIP工艺实验,运用等离子体鞘层理论、电路理论和仿真模拟技术,得到AIP等离子体负载本质上是由鞘层引起的容性负载,在电路中可以等效为电容和电阻相并联的单元;根据AIP等离子体鞘层演化的特性,将AIP等离子体负载的等效电容表征为与时间无关而只与脉冲偏压幅度和等离子体相关参数有关的量,AIP等离子体负载的等效电阻,可以在直流偏压下通过测量与脉冲偏压幅值对应的AIP等离子体负载电流来确定.经验证,本文建立的AIP等离子体负载的等效电路模型及其定量表征是有效性的.     

Wide-Range Low Current Measurements of Diode Reverse Currents with Automatic Ranging Features

This paper describes a method used successfully by the author in measuring silicon diode reverse leakage currents. The technique used is straightforward and provides wide-range, low current measurements with improved accuracies and automatic ranging features. The full-scale indications extend from 10-3 through 10-10 amperes in eight decade ranges. The full-scale accuracies achieved are better than ±0.5 per cent on ranges 10-3 through 10-8 amperes, ±1 per cent on the 10-9 ampere range, and ±10 per cent on the 10-10 ampere range. The automatic ranging feature exhibits a response of 10 msec per range. The method used is based on sensing the voltage drop (ES) across a sensing resistor (RS). This sensing resistor is in series with the reverse biased diode, as shown in Fig. 1. The sensing voltage is then amplified to an appropriate level (Eo) which can be more easily and accurately measured and/or digitized, depending upon the type of output display and storage method used.     

Practical voltage/current-controlled grounded resistor with dynamic range extension

A novel voltage- or current-controlled grounded resistor is proposed. The circuit makes use of bisection of the drain-to-source voltage of a field effect transistor to produce a practical linear resistor with dynamic range extension. A second generation positive current conveyor is used with three resistors to extend the linearity of the variable resistor, and the resistance can be controlled by a variety of methods. Experimental and PSPICE simulation results, using an AD844 current feedback amplifier and a 2N5485 N-channel JFET, are presented which verify the theoretical derivations. In one experiment, the measured input resistance of the grounded resistor was observed to vary from 1.8 to 18 kOmega or by a factor often.     

1/f Electrical Noise in Planar Resistors: The Joint Effect of a Backgating Noise and an Instrumental Disturbance

Any planar resistor (channel) close to a conducting layer left floating (gate) forms a capacitor C whose thermal voltage noise (kT/C noise) has a backgating effect on the sheet resistance of the channel that is a powerful source of 1/f resistance noise in planar resistors and, hence, in planar devices. This 1/f spectrum is created by the bias voltage V _DS applied to the resistor, which is a disturbance that takes it out of thermal equilibrium and changes the resistance noise that existed in the unbiased device. This theory, which gives the first electrical explanation for 1/f electrical noise, not only gives a theoretical basis for the Hooge's formula but also allows the design of proper shields to reduce 1/f noise.     

Stochastic-flash analog-to-digital conversion

Flash-type analog-to-digital converters (ADC's) presenting a nonlinear behavior, i.e., having nonequally spaced threshold levels, may introduce harmonic distortion that can be reduced by employing large-amplitude dither-based conversion techniques. However, large-scale dithering is difficult to implement and, in addition, severely reduces the ADC input dynamic range. In this paper, a new ADC architecture is presented based on ordinary flash conversion and dynamic element matching, that strongly reduces nonlinear distortion. It eliminates the need for large-scale dither signals by randomizing the resistor positions in the resistor string used to generate the voltage references. Some properties of this architecture are analyzed and simulation results that validate the theoretical assumptions are presented     

组合式高阻箱及高压表检定装置

介绍一种既是高压分压箱 ,又是高值电阻器的装置。它与通用型的 QJ36电桥、检流计、高压电源一起组成了一台高阻箱、高压表检定装置 ,适合于省、局级计量机构及大型企业计量机构使用。     

Effects of a parallel resistor on electrical characteristics of a piezoelectric transformer in open-circuit transient state

This paper investigates electrical transient characteristics of a Rosen-type piezoelectric transformer (PT), including maximum voltages, time constants, energy losses and average powers, and their improvements immediately after turning OFF. A parallel resistor connected to both input terminals of the PT is needed to improve the transient characteristics. An equivalent circuit for the PT is first given. Then, an open-circuit voltage, involving a direct current (DC) component and an alternating current (AC) component, and its related energy losses are derived from the equivalent circuit with initial conditions. Moreover, an AC power control system, including a DC-to-AC resonant inverter, a control switch and electronic instruments, is constructed to determine the electrical characteristics of the OFF transient state. Furthermore, the effects of the parallel resistor on the transient characteristics at different parallel resistances are measured. The advantages of adding the parallel resistor also are discussed. From the measured results, the DC time constant is greatly decreased from 9 to 0.04 ms by a 10 k(omega) parallel resistance under open output.     

Demultiplexers for Nanoelectronics Constructed From Nonlinear Tunneling Resistors

When using linear resistors to implement nanoelectronic resistor-logic demultiplexers, codes can be used to improve the voltage margins of these circuits. However, the resistors which have been fabricated in nanoscale crossbars are observed to be nonlinear in their current versus voltage (I-V) characteristics, showing an exponential dependence of current on voltage; we call these devices tunneling resistors. The introduction of nonlinearity can either improve or degrade the voltage margin of a demultiplexer circuit, depending on the particular code used. Therefore, the criterion for choosing codes must be redefined for demultiplexer circuits built from this type of nonlinear resistor. We show that for well-chosen codes, the nonlinearity of the resistors can be advantageous, producing a better voltage margin than can be achieved with linear resistors     

A square-rooting current-to-frequency converter

A square-rooting current-to-frequency converter is presented in this paper. It has been designed by using one relaxation oscillator where a current-controlled resistor in CMOS technology with bisection of the input voltage is used instead of the ordinary resistor. In this way, the time constant of the relaxation oscillator is current-controlled. There is no need for a high stable voltage or current references in the proposed circuit. By appropriate setting of the process parameters of the MOSFETs used, the temperature variations of the output frequency can be made smaller than 7.6/spl times/10/sup -3/%/K. Experimental results confirm that the behavior of the proposed square-rooting CFC is in good agreement with the predictions of the analysis performed. According to these results, relative errors are less than 1% for the input current range from 35 /spl mu/A to 15 mA, and for the output frequency range from 1.45 kHz to 9.80 kHz.     

Realization of the kilogram by measuring at 100 kV with the voltagebalance ETF

The possibilities for adapting the existing electrostatic device known as the voltage balance ETF-84, to work with a voltage of 100 kV and a weight of 1 kg, are considered. A few theoretical analyses, experiments, and computer simulations have been carried out to define the measurement procedure needed at the required level of uncertainty of 1 part in 10⁸. These analyses identified which parts of the balance itself and of the high voltage electrode isolation have to be reconstructed, as well as how the associated high voltage resistor has to be designed for this purpose     

Digital Impedance Measurement by Generating Two Waves

A digital measurement system is described which measures the voltages across a voltage divider consisting of a reference resistor and the unknown impedance. The voltages across reference and unknown are converted so that their magnitude and phase are digitally determined.     

直流高压电阻分压器泄漏电流测量研究

介绍了一种测量直流高压电阻分压器泄漏电流的装置。该装置采用ZigBee无线通信技术,通过独立电源供电的方式,避免了因高压电场导致测量仪器损坏的风险,解决了分压器在高电压工作状态下难以测量泄漏电流的问题。通过采用同步采样的方法,有效克服了高压电源纹波和漂移对测量精度的影响,泄漏电流测量不确定度优于9.8×10^-6 V,k=2。     

Improvement of the Voltage Dependence of High-Voltage AC–DC Transfer Differences at the NMIJ

A new ac–dc comparator system of 20–1000 V has been developed at the National Metrology Institute of Japan (NMIJ) for the calibration of ac–dc thermal voltage converters (TVCs), which are used as national ac–dc transfer standards. The ac–dc transfer differences of high-voltage transfer standards were evaluated by a traditional step-up procedure. The voltage dependence of the ac–dc transfer difference was observed in the earlier step-up procedures over 300 V, as reported by the latest international intercomparison. The experimental results for high-voltage TVCs with several different range resistors at the NMIJ suggest that the voltage dependence may primarily be caused by input connectors of range resistors and the change in the resistance value of the resistor and TVC modules due to heating from resistors. This paper describes the voltage dependence improvement of ac–dc transfer differences over 300 V at the NMIJ.      

A new piezoelectric energy harvesting design concept: multimodal energy harvesting skin

This paper presents an advanced design concept for a piezoelectric energy harvesting (EH), referred to as multimodal EH skin. This EH design facilitates the use of multimodal vibration and enhances power harvesting efficiency. The multimodal EH skin is an extension of our previous work, EH skin, which was an innovative design paradigm for a piezoelectric energy harvester: a vibrating skin structure and an additional thin piezoelectric layer in one device. A computational (finite element) model of the multilayered assembly - the vibrating skin structure and piezoelectric layer - is constructed and the optimal topology and/or shape of the piezoelectric layer is found for maximum power generation from multiple vibration modes. A design rationale for the multimodal EH skin was proposed: designing a piezoelectric material distribution and external resistors. In the material design step, the piezoelectric material is segmented by inflection lines from multiple vibration modes of interests to minimize voltage cancellation. The inflection lines are detected using the voltage phase. In the external resistor design step, the resistor values are found for each segment to maximize power output. The presented design concept, which can be applied to any engineering system with multimodal harmonic-vibrating skins, was applied to two case studies: an aircraft skin and a power transformer panel. The excellent performance of multimodal EH skin was demonstrated, showing larger power generation than EH skin without segmentation or unimodal EH skin.     

A new method of absolute temperature measurements

Summary Preliminary experimental data shows the possibility of measuring temperature by the number of voltage noise pulses. In theory, this method provides absolute and comparative temperature measurements over a wide range: the upper limit being that at which the resistor is destroyed; the lower boundary, in theory, is limited by the superconductivity temperature of the resistor material. The sensitivity of the method rises with decreasing temperatures.There are reasons to believe that by counting pulses over a longer period of time with highly stable temperature fields and amplifier gain with an adjustable threshold of discrimination, it will be possible to raise the absolute accuracy of temperature measurements as compared with other existing methods.