驱动信号对电容式传感器特性的影响分析

在电容检测中,交流电压驱动常常是测量电容变化的必要手段。驱动电压引起作用于可动电极上的静电力,从而影响到可动电极的运动。因此,交流电压的静电驱动势必影响测量的范围和精度。本文详细地分析了由交流电压引起的静电驱动力对微机械结构表态位移特性的影响,并以电容式加速度传感器为例,分单边驱动和双边驱动两种情况,推导出可动电极的运动微分方程。运用近似和图解的方法分另在特殊和一般的情况下求解方程,得到静电驱动电     

基于钼酸铅晶体电致旋光效应的光学电压传感器

研究了基于晶体电致旋光效应的光学电压传感器,电压传感元件采用了国产钼酸铅(PbMoO4)晶体。光学电压传感头仅由两块棱镜偏振器和一块钼酸铅晶体组成。实验结果表明此电压传感器具有较大的线性测量范围,例如对50-5000V工频电压测量的非线性误差低于0.2%;当测量100kHz的高频电压并利用锁相放大器检测传感信号时,最小可测量电压幅值为0.5V。此外,实验测量了所用钼酸铅晶体在635nm光波长及工频电压作用时的电致旋光系数,其数值为1.03pm/V。     

交流电沉积制备纳米枝晶拉曼基底

使用交流电沉积方法在预定的微区域内制备了纳米枝晶表面增强拉曼散射基底。通过调节交流和偏置直流电压可以控制基底的形貌、位置以及生长方向。从电化学过程、液电耦合场2个角度对拉曼基底的生长机理进行了阐述。激光共焦显微拉曼实验进一步表明：使用四巯基吡啶作为指针分子,该基底具有良好的拉曼活性。     

压电驱动器的电致振动特性研究

旨在分析压电驱动器的电激励振动特性。以双晶压电悬臂梁为对象,基于能量法和热力学平衡方程推导了压电悬臂梁在电压激励下的强迫振动微分方程。利用自行搭建的电激励振动试验系统,测试了不同幅值交流电压激励下压电梁的谐响应和瞬态响应。通过试验验证了理论分析的合理性,讨论了激励电压和阻尼对谐响应和瞬态响应的影响。结果表明：压电悬臂梁的谐响应呈非线性,具有弹簧渐软特性;压电梁的共振频率随激励电压幅值的增大而减小,在6V、9V、12V交流电压激励下,压电梁的共振频率分别为55.6Hz、54.8Hz、54.4Hz;当激励电压频率等于压电梁的固有频率时,其横向振幅达到峰值;当激励电压频率逐渐远离压电梁的固有频率时,其振幅则迅速降低;激励电压频率接近共振频率时梁会发生“拍振”现象;阻尼对压电梁的共振抑振作用最为明显。     

基于单片机的电力监控系统交流采样技术的实现

系统采用8031单片机实现电力参数的交流采样,通过LED显示器显示频率、电压、电流的实时值,在过压30％、欠压30％时进行声光报警,并能定时打印电压、电流及频率值。实践证明,采用交流采样方法进行数据采集,通过算法运算后获得的电压、电流、有功功率、功率因数等电力参数有较好的精确度和稳定性。     

交流畸变频谱分析中的幅值和频率修正方法

在交流畸变频谱分析中,因电压频率调制和离散傅立叶变换(DFT)的栅栏效应,会导致分析结果产生较大的幅值和频率误差。笔者给出了一种电压幅值和频率修正方法,该方法依据DFT频谱中幅值最大的两个相邻谱线幅值,计算出交流电压谐波的准确幅值和频率,仿真结果表明其幅值精度优于0.01%,频率误差小于0.001 Hz。     

电活性聚合物致动器机电响应特性研究

电活性聚合物(EAP)致动器是一类极具发展潜力的智能材料。通过对尺寸为10 mm×2 mm离子型聚吡咯致动器施加阶跃电压、方波、正弦波、斜波电压,研究分析致动器位移响应与驱动电压波形、幅值和频率的关系。阶跃电压下,致动器位移响应经过5s左右达到稳定状态,仅1 V驱动电压就可使致动器稳态弯曲位移变化值达2. 22 mm。在幅值为±1 V方波驱动电压下,致动器稳定状态位移变化值则为1. 96 mm。试验结果表明:驱动电压增加,迁进迁出致动聚合物层的离子增多引起聚合物层的氧化还原加剧,致动器位移响应滞后于驱动电压变化;其位移响应幅值随驱动电压增加而增大,呈线性关系。当驱动电压波形与幅值相同时,致动器位移变化幅值随驱电压频率的增高而减小,且呈非线性关系。该致动器机电响应特性试验为微阀、微型机器人、生物医学设备、人工肌肉、电化学传感器、贮能材料等领域的实际应用提供了理论参考。     

一种实用的交流电量参数测量方法

系统采用89C51单片机实现电力参数的交流采样,通过液晶显示器显示频率、相位差、电压和电流的实时值,在过压20%、欠压20%时进行报警,并能定时打印电压,电流、频率及相位差值。实践证明,采用交流采样方法进行数据采集,通过运算获得的电压、电流有功功率,功率因数等电力参数有很好的精确度和稳定性。     

基于单片机的电力监控系统交流采样技术的实现

系统采用8031单片机实现电力参数的交流采样,通过LED显示器显示频率、电压、电流的实时值,在过压30%、欠压30%时进行声光报警,并能定时打印电压、电流及频率值.实践证明,采用交流采样方法进行数据采集,通过算法运算后获得的电压、电流、有功功率、功率因数等电力参数有较好的精确度和稳定性.     

电力监控补充交流采样技术

系统采用AT89C52单片机实现电力参数的补充交流采样,通过LED显示器显示频率、电压、电流的实时值,在过压10%、欠压10%时进行声光报警,并能定时打印电压、电流及频率值.实践证明,采用交流采样方法进行数据采集,通过算法运算后获得的电压、电流、有功功率、功率因数等电力参数有较好的精确度和稳定性.     

AC electrokinetic pumping on symmetric electrode arrays

AC electro-osmotic (ACEO) pumping is experimentally demonstrated on a symmetric gold electrode array. Using asymmetric connection of electrodes to the applied AC voltage, spatial asymmetry along the array is created, which produces unidirectional flow of electrolyte. An aqueous solution of 100 μM KCl is selected as the pumping fluid. The liquid velocity obtained as a function of voltage and frequency is compared to that generated using travelling-wave electroosmosis (TWEO) with the same electrode array. The expected velocities from the linear electrokinetic models of ACEO and TWEO are computed numerically. The comparison shows that TWEO generates greater velocity amplitudes and the streamlines are smoother than those generated by ACEO.     

Radio‐frequency plasma‐display cell

Abstract— This paper demonstrates that it is possible to improve the basic parameters of plasma displays (efficiency, primarily) using AC voltages with frequencies so high that the amplitude of the electron‐drift oscillations is smaller than the inter‐electrode gap. In this case, the voltage drop on sheaths is much smaller than that in the low frequency or DC discharge and, correspondingly, the energy losses in ion heating are also small. Electron losses in the RF discharge are of the diffusion character and sufficiently lower than the losses in a typical AC plasma‐display panel (AC PDP), in which the electron drift to the electrodes is predominant. Hence, the energy cost of gas ionization in the cells of radio‐frequency PDPs (RF PDPs) is also rather low. In the long run, about 80% of the energy absorbed in the RF discharge goes into excitation of the energy level of a Xe atom, yielding UV radiation. The experiments performed show that efficiency of a RF PDP is five times higher than the efficiency of existing AC PDPs and DC PDPs and can exceed 5 lm/W.     

Design of a relaying electroosmosis pump driven by low-voltage DC

Electroosmosis pumps (EOPs) have been widely used for manipulating small amounts of reagents for chemical and biological analysis. Traditionally, a high-voltage DC has to be applied in order to achieve the required flow rate. One alternative is to use low AC voltage. Here we propose another solution, which, instead of using a high-voltage DC or low AC voltage, adds a low-voltage DC to an array of electrodes. This design of EOP is called a relaying EOP or cascade EOP. In this study, we intend to push the limit of the low-voltage further down to 2 V by patterning a dense electrode array in a straight microchannel. Two patterns of interdigitated electrodes, symmetric with equal size electrodes and asymmetric with unequal size electrodes, are proposed. Simulations are performed to optimize the distribution and geometrical parameters of the electrode array in order to achieve the maximum flow rate. The proposed low-voltage DC electroosmosis pump shows an advantage in integrating EOP into portable Lab-on-a-chip devices. In addition, the low-voltage DC EOP shows a good promise for in vivo biomedical applications such as drug delivery.     

Influence of electrode array parameters used in electrotherapy on tumor growth kinetics: A mathematical simulation

Evaluation of the distance between the electrodes, voltage applied to them, and number of electrodes in tumor growth kinetics is very useful for effective tumor destruction when electrotherapy is used. However, a study of this type has not yet been proposed. The aim of this paper is to simulate the influence of such parameters and the point–point electrode configuration on the tumor growth kinetics through a Modified Gompertz Equation. The results show a good agreement between the simulations performed in this study and the experimental results reported by our group and other authors. A critical distance between electrodes and a threshold ratio between the applied electric field and that distributed in the tumor are revealed, for which higher electrotherapy antitumor effectiveness is reached. In conclusion, electrotherapy antitumor effectiveness not only depends on the distance between the electrodes, voltage applied to them, and number of electrodes, but also on the ratio between the applied electric field and that distributed in the tumor. In addition, the results of these simulations may be used to help physicians choose the most appropriate treatment for patients with malignant solid tumors, as we have implemented in a current clinical trial.     

Performance optimization of current focusing and virtual electrode strategies in retinal implants

The electrode configuration in an implanted visual prosthesis array affects the spatial electric field distribution within the retina, contributing to current focusing and virtual electrode (VE) stimulation strategies. In this paper, a finite element model incorporating various electrode configurations was used to study the interaction between electrode size and electrode-to-cell distance in current focusing and VE stimulation paradigms. The electrode array unit comprises an active electrode, six flanking return electrodes and a distant monopolar return. A quasi-monopolar (QMP) fraction is defined as the proportion of current which can be preferentially returned through the distant return, in comparison with the more adjacent flanking electrodes. The simulation results indicate that current focusing and VE strategies can be optimized by tuning the QMP fraction. The QMP fraction is adjusted to optimize the electric field spread based on retinal ganglion cell (RGC) density in the degenerate retina, thereby offsetting the effect of inhomogeneous distribution of surviving RGCs and leading to a uniform stimulation paradigm across electrodes. Importantly, there is negligible difference in functional performance across electrode configurations for distances less than the electrode diameter, implying that the stimulation mode does not significantly affect activation threshold or activated retinal area for electrode diameters greater than the retinal thickness. Furthermore, the QMP fraction has a significant effect on VE performance, defined by activation threshold and activated retinal area, when threshold current is evenly divided between two adjacent active electrodes.     

Measurement of contact potential difference in head disk interface by readback signal spectrum

The contact potential difference leads to electrostatic interaction between the slider and disk in a hard disk drive. The effect of electrostatic force on slider’s flying height and flying stability becomes more significant with the decrease of flying height. A method of measurement of contact potential difference in head disk interface by readback signal spectrum is demonstrated in this paper. When a voltage with DC and AC was applied in the head disk interface, the amplitude of readback signal at the first harmonic frequency of applied AC voltage is proportional to the sum of contact potential difference and applied DC voltage. The contact potential difference in head disk interface is equal to the negative of DC voltage when the amplitude of readback signal at the first harmonic frequency is minimal.     

Performance improvement of an AC electroosmotic micropump by hydrophobic surface modification

This paper describes the improvement of bi-directional micropump velocity by deposition of a hydrophobic nanocomposite monolayer. A polymer base nanocomposite coating consisting of a homogeneous mixture of silicon nanoparticles in polydimethylsiloxane (PDMS) is used to improve the hydrophobicity of the micropump surfaces. For hydrophobic nature of PDMS and the monolayer coating with nanoscale surface roughness, the hydrophilic surface of a biased AC electroosmotic micropump will transform to a hydrophobic surface. In our previous research the applied AC voltage, frequency, channel dimension, and electrode width were optimized (Islam and Reyna, Electrophoresis 33(7), 2012). Based on the prior results obtained for the biased AC electroosmotic micropump, the pumping velocity was 300 micron/s in 100-μm channel thickness for applied voltage of 4.4 V at 1 kHz frequency. Here in this work, improvement of the micropump velocity is investigated through a surface modification process. The highest velocity of 450 micron/s is observed by modifying the surface characteristics. This paper will also discuss the synthesis process and characteristics of the polymer base nanocomposite monolayer. In addition to hydrophobicity improvement, adding a thin nanocomposite monolayer will physically separate the electrodes from the pumping liquid, thus eliminating their reaction, which is usually observed due to the application of voltage. As a result, higher voltages can be applied to the electrodes and higher pumping rates are achievable.     

Two-phase AC electrothermal fluidic pumping in a coplanar asymmetric electrode array

The ability to achieve fast fluid flow yet maintain a relatively low temperature rise is important for AC electrothermal (ACET) micropumping, especially in applications such as bioMEMS and lab-on-a-chip systems. In this paper, we propose a two-phase ACET fluidic micropump using a coplanar asymmetric electrode array. The proposed structure applies a two-phase AC voltage, i.e., voltage of phase 0°/180°, to the narrow electrodes while the wide electrodes are at ground potential. Numerical simulation demonstrates that this simple coplanar electrode configuration can achieve at least 25% faster fluid flow rates than using a single AC signal. By selecting certain design parameters, a two-phase ACET structure can achieve up to 50% faster fluid flow rates than a corresponding single-phase structure. The simple two-phase AC signal sources are easily produced by using inverter buffers, which is a considerable improvement compared to the multi-phase AC signals required by other electrokinetic micropumping methods, such as traveling wave structures.     

Electric current density distribution in planar solid tumor and its surrounding healthy tissue generated by an electrode elliptic array used in electrotherapy

The knowledge of the electric current density distribution generated by an electrode array is very useful in electrotherapy for tumor treatment. We propose an innovative mathematical approach that takes into account planar solid tumor elliptic geometry, electrical differences between it and its surrounding healthy tissue, and positioning of the electrodes with respect to tumor-surrounding healthy tissue interface. We show the distributions of the electric current density in leading order and first correction terms in a heterogeneous planar medium formed by two regions (tumor and its surrounding healthy tissue) in function of these parameters. The results show that when electrodes are completely inserted in tumor and/or its conductivity is higher than that of its surrounding healthy tissue, the electric current density lines concentrate more in tumor and its tumor-surrounding healthy tissue interface. No significant differences are reported between the electric current density distributions in leading-order and first-order correction for each parameter investigated. However, norm of this physical magnitude reveals that these distributions are different when the ratio between radius of the electrodes and radius of the tumor is less than 0.8. We conclude that the analytical modeling presented in this study is of practical interest because it provides a convenient way to visualize the electric current density distributions generated by an electrode elliptic array in order to efficiently destroy the localized planar tumors with the minimum damage to organism, through an increase of the potential applied to the electrodes, the tumor conductivity with respect to its surrounding healthy tissue and insertion of all electrodes into tumor.