Frequency Characteristics Of Impedance Research Articles

Full-Differential Folded-Cascode Front-End Receiver Amplifier Integrated Circuit for Capacitive Micromachined Ultrasonic Transducers.

This paper describes the design of a front-end receiver amplifier for capacitive micromachined ultrasonic transducer (CMUT). The proposed operational amplifier (op amp) consists of a full differential folded-cascode amplifier stage followed by a class AB output stage. A feedback resistor is applied between the input and the output of the op amp to make a transimpedance amplifier. We analyzed the equivalent circuit model of the CMUT element operating in the receiving mode and obtained the static output impedance and center frequency characteristics of the CMUT. The op amp gain, bandwidth, noise, and power consumption trade-offs are discussed in detail. The amplifier was fabricated using GlobalFoundries 0.18-μm complementary metal-oxide-semiconductor (CMOS) technology. The open loop gain of the amplifier is approximately 65 dB, and its gain bandwidth product is approximately 29.5 MHz. The measured input reference noise current was 56 nA/√Hz@3 MHz. The amplifier chip area is 325 μm × 150 μm and the op amp is powered by ±3.3 V, the static power consumption is 11 mW. We verified the correct operation of our amplifier with CMUT and echo-pulse shown that the CMUT center frequency is 3 MHz with 92% fractional bandwidth.

The Research on Mechanical Impedance of the Base for Some Ships’ Pump Group

In order to assess the vibration characteristics of the base system for some ships’ pump group, this paper studies in terms of mechanical impedance characteristics at two aspects of simulation and experiment. With the finite element method, firstly, this research adopted modal analysis module to analyze the base and got its natural frequency and principal mode, and then used harmonic response analysis module to obtain the frequency characteristics of mechanical impedance in a specific excitation. With the experiment, the mechanical impedance of corresponding frequency can be obtained directly. Finally, by comparing those two results, this research shows that the base meets the requirements of use within the application range.

Analysis and mitigation of low-frequency resonance in a long-distance UHVDC ±1100 kV system

Low-frequency resonance may seriously threaten the stable operation of a long-distance ultra-high-voltage-direct-current (UHVDC) system. In this paper, the impedance model of long-distance UHVDC systems was analyzed for various disturbances. For different disturbances, the positions of voltage sources in the simulated DC loop are different. Taking the first ±1100-kV DC power transmission project with a length of 2688km as an example, the frequency characteristics of the DC-loop impedance were studied using the PSCAD/EMTDC simulation platform. The effects of various operating modes and the firing angle of the converters on impedance–frequency characteristics of the DC loop were discussed. The effect of the length of DC transmission lines on the DC-loop resonant frequency was studied. The distance is the most important factor determining the system low-frequency resonance. Faults in an AC grid, such as phase-to-phase short-circuit and single-phase faults, are shown to produce 50-Hz positive sequence harmonics on the AC side and 100-Hz disturbances in the DC loop. Two methods of mitigating low-frequency resonance were proposed and the effects simulated. Installation of the blocking filter in the neutral bus of the converter station can reduce the amplitude of the resonance overvoltage.

Impedance analysis and stabilization control of the LCL-type wind power inverter under weak grid conditions

To address the instability issues of LCL-type wind power inverter's operation under weak grid conditions, stability control methods are investigated in this paper. Based on an inverter impedance model that considers an inner current control loop, a precise impedance model that considers dynamic characteristics of dc bus voltage and a reactive power outer loop is created in this paper. The phasor diagram method and an analytical method are used to interpret frequency characteristics of the inverter output impedance. The impedance analysis results show that the instability of the inverter in a weak grid has a weak correlation with the LCL filter parameter and a strong correlation with the inner and outer control loops. Phase-locked loop bandwidth reduction improves inverter's operation stability to some extent. However, it also reduces the inverter's tracking and anti-interference performance. Therefore, a capacitor current-feedback-based stability control method is proposed in this paper. The feasibility of the proposed control method is proven via general Nyquist-criteria-based impedance analysis. Finally, an RT-LAB hardware loop test platform is created to verify the validity of impedance modeling proposed in this paper and the effectiveness of the stability control strategy.

Temperature and frequency dependent dielectric and impedance characteristics of double perovskite Bi2MnCoO6 electronic material

The temperature and field dependent capacitive as well as conducting characteristics of double perovskite electronic material (Bi2MnCoO6) have been investigated using dielectric and impedance spectroscopy techniques. The electronic material has been formulated by applying a high temperature solid state reaction based ceramic processing route. The formation of the desired sample material is confirmed with a monoclinic crystal system using room temperature X-ray diffraction analysis. The uniform grain distribution is predicted from the micrograph, and the stoichiometric chemical content of the solid solution is determined from energy dispersive X-ray technique. The acquaintance between micro structural study and frequency–temperature dependent electrical properties of the compound has revealed negative temperature coefficient of resistance behaviour. The prepared compound unveils non-Debye type relaxation. The studied compound presents important dielectric properties which substantiate the material propensity for formulation of electronic devices.

A Simple Method to Determine Synchronous Machine Quantities Using Frequency Characteristics of Operational Impedances

SUMMARYThis paper presents a simple method for determining synchronous machine quantities: d‐ and q‐axes time constants and reactances. This method determines them only by drawing additional lines in the frequency characteristics of operational impedances. A new systematic drawing strategy for determining transient/subtransient open‐circuit time constants and the d‐axis transient reactance is proposed. The frequency characteristics of operational impedances are obtained by the standstill dc test using a small dc power supply. Since the rotational test becomes unnecessary, the proposed method is suitable for tests in a factory. The validity of the proposed method was demonstrated with a numerical calculation example on a large‐capacity machine (800 MVA, 25 kV, two poles, 60 Hz) and an implementation test on a small‐capacity machine (10 kVA, 200 V, 31.9 A, four poles, 50 Hz).

演算子インピーダンスの周波数特性を利用した同期機の等価回路定数算出法とブラシレス機への適用

演算子インピーダンスの周波数特性を利用した同期機の等価回路定数算出法とブラシレス機への適用

Investigation Into the Effects of Nucleotide Content on the Electrical Characteristics of DNA Plasmid Molecular Wires.

In this study, we investigate the effect of nucleotide content on the conductivity of plasmid length DNA molecular wires covalently bound to high aspect-ratio gold electrodes. The DNA wires were all between [Formula: see text] in length (>6000bp), and contained either 39%, 53%, or 64% GC base-pairs. We compared the current-voltage (I-V) and frequency-impedance characteristics of the DNA wires with varying GC content, and observed statistically significantly higher conductivity in DNA wires containing higher GC content in both AC and DC measurement methods. Additionally, we noted that the conductivity decreased as a function of time for all DNA wires, with the impedance at 100 Hz nearly doubling over a period of seven days. All readings were taken in humidity and temperature controlled environments on DNA wires suspended above an insulative substrate, thus minimizing the effect of experimental and environmental factors as well as potential for nonlinear alternate DNA confirmations. While other groups have studied the effect of GC content on the conductivity of nanoscale DNA molecules (<50bp), we were able to demonstrate that nucleotide content can affect the conductivity of micrometer length DNA wires at scales that may be required during the fabrication of DNA-based electronics. Furthermore, our results provide further evidence that many of the charge transfer theories developed from experiments using nanoscale DNA molecules may still be applicable for DNA wires at the micro scale.

On DC-Side Impedance Frequency Characteristics Analysis and DC Voltage Ripple Prediction under Unbalanced Conditions for MMC-HVDC System Based on Maximum Modulation Index

In this study, we first briefly introduce the effect of circulating current control on the modulation signal of a modular multilevel converter (MMC). The maximum modulation index is also theoretically derived. According to the optimal modulation index analysis and the model in the continuous domain, different DC-side output impedance equivalent models of MMC with/without compensating component are derived. The DC-side impedance of MMC inverter station can be regarded as a series xR + yL + zC branch in both cases. The compensating component of the maximum modulation index is also related to the DC equivalent impedance with circulating current control. The frequency characteristic of impedance for MMC, which is observed from its DC side, is analyzed. Finally, this study investigates the prediction of the DC voltage ripple transfer between two-terminal MMC high-voltage direct current systems under unbalanced conditions. The rationality and accuracy of the impedance model are verified through MATLAB/Simulink simulations and experimental results.

An MRI-readable wireless flexible pressure sensor.

We developed a magnetic resonance imaging (MRI) -detectable wireless flexible pressure sensor with pressure-sensitive LC resonator fabricated on a flexible film substrate. Measuring pressures in the body such as blood vessels and cardiac ventricle are very important in making diagnoses and in postoperative observation. However, conventional wired pressure sensors have difficulty in maintaining their connections to external readout equipment, and they also increase the risk of infection during and after implantation. In this study, to read the pressure wirelessly using an MRI system, an LC resonator consisting of a spiral coil and a pressure-sensitive capacitor was designed resonate at 300 MHz which corresponds to the Larmor frequency in an external magnetic field of 7-T. In order to validate the operating principle of the fabricated device, the frequency-impedance characteristics were measured by changing the pressure. The resonance frequencies of complemented LC circuits were lower by approximately 10% than those of nonpressured conditions. After implanting these devices in a 1% agarose gel, MR images were acquired by inducing pressures close to blood pressures of 20 kPa. As a result, contrast changes in the MR images were observed around the integrated spiral coils. This result indicated that the developed flexible pressure sensor has sufficient sensitivity to measure physiological pressure such as blood pressure of 20 kPa wirelessly in the body. In the future, quantitative pressure sensing will be evaluated by comparing it to the contrast changes in MR images with flip angle mapping.

Assessment of Electric Impedance Varieties of Grain, Treated in Magnetic Field

enlarge in some ways: chemical way, influence of electrical and magnetic field treatment. The aim of our research is not to research the growth of germination power after influence of seed on adequate magnetic flux density, but estimate what influence to biological signs has magnetic field. It was done by measuring electrical impedance frequency characteristics of seeds by using electronic equipment. Our research showed that grain ITF image PFCh has larger change character in compare to AFCh changes. It shows that magnetic field more influence reactance elements of grain equivalent electrical circuit elements.

Frequency, Impedance Characteristics and HF Converters of Two-Coil and Four-Coil Wireless Power Transfer

Magnetically coupled wireless power transfer (WPT) can be roughly divided into two kinds of inductively coupled and strongly coupled magnetic resonances. In this paper, the frequency characteristics, impedance characteristics and high frequency (HF) converters of two-coil and four-coil magnetically coupled WPT are outlined between inductively coupled power transfer (ICPT) and resonant coupling WPT. First, the frequency bifurcation in ICPT and frequency splitting in resonant coupling WPT are analyzed, and the natural similarities are explained, which have not been pointed out before. Second, the differences of the conventional two-coil (often used in ICPT) and four-coil WPT are analyzed by their input impedance characteristics. The results show that the two-coil WPT is appropriate for short-range and the four-coil WPT suitable for mid-range applications. In the end, as one of the most important parts of magnetically coupled WPT systems, HF converters used in WPT systems are summarized and a new soft-switched converter is put forward, which has 70% efficiency though it is not precisely designed.

演算子インピーダンスの周波数特性を利用した同期機諸定数の簡易算出法

This paper presents a simple method for determining synchronous machine quantities: d- and q-axes time constants and reactances. This method determines them only by drawing additional lines in the frequency characteristics of operational impedances. A new systematic drawing strategy for determining transient/subtransient open-circuit time constants and the d-axis transient reactance is proposed. The frequency characteristics of operational impedances are obtained by the standstill DC test using a small DC power supply. Since the rotational test becomes unnecessary, the proposed method is suitable for tests in a factory. The validity of the proposed method was demonstrated with a numerical calculation example on a large-capacity machine (800MVA, 25kV, 2 poles, 60Hz) and an implementation test on a small-capacity machine (10kVA, 200V, 31.9A, 4 poles, 50Hz).

Suppression of High-Frequency Interference in Signal Loop

With the deep and promotion of unattended work in substations, the correct rate of remote signal becomes an important index in automation scheduling system. For remote signal false caused by high-frequency interferences in substation, we propose the use of Ni-Zn ferrite ring to suppress high-frequency interferences. The frequency-impedance characteristics of ferrite ring with different turns are tested. And the inhibitory effect of ferrite ring on interferences below and above 100MHz is measured separately. We installed ferrite rings in remote signal loops, and compared the voltage waveforms before and after installation. Experimental results provide some references to suppress high-frequency interferences by Ni-Zn ferrite ring.

Modeling of lung's electrical impedance using fractional calculus for analysis of heat generation during RF-ablation.

Recently, Radio Frequency Ablation (RFA) is becoming a popular therapy for various cancers such as liver, breast, or lung cancer. RFA is one kinds of thermal therapy. However, it has been often reported about excessive ablation or non-ablation due to difficult control of ablation energy. In order to solve these difficulties, we have been proposed robotized RF-ablation system for precise cancer treatment. We have been tried to control heat energy by control of electromagnetic-wave frequency. In this paper, we reported about relation among electrical impedance of lung, lung's internal air volumes, and heat energy by use of electromagnetic-wave. In case of RFA for lung cancer, heat energy depends on electrical impedance and lung's internal air volumes. Electrical impedance has the dependence of electromagnetic-wave frequency and the dependence of lung's internal air volumes. Therefore, firstly we considered about fractional calculus model between lung's internal air volumes and electrical impedance. Secondly, we measured electric impedance frequency characteristic of lung with change of lung's internal air volumes. The measured and modeled results showed that use of fractional calculus realized high accurate model for electrical impedance of lung. And, from the results of numerical analysis of heat energy, it is supposed that control of electromagnetic-wave frequency has a small effectiveness for lung tissue ablation even if lung includes abundant air.

Frequency Characteristics of the Input Impedance of Meander Slow-wave System with Additional Shields

A method for determination of input impedance of meander slow-wave system with additional shields is presented. It is based on a technique used for a calculation of frequency characteristics of helical slow-wave systems. The input impedance was determined at two ports: on the edge and in the centre of a system. S11 parameter is known as the input reflection coefficient, so system‘s input impedance in the lower frequencies can be determined by changing the signal source and load resistances until minimum value of S11 parameter is obtained. Using proposed method frequency characteristics of input impedance and S11 parameter of a meander slow-wave system with additional shields is analysed in Sonnet software. DOI: http://dx.doi.org/10.5755/j01.eee.20.3.6678

The Measurement System of Partial Discharge under Impulse Voltage

Partial discharge (PD) is the important detection parameter for power equipment, with the development of high voltage test technology, PD detection under impulse voltage is more attention. In order to detect the partial discharge signal under the impulse voltage, this paper designs a high-frequency current sensor and broadband measurement impedance. A set of partial discharge measurement system under impulse voltage is built up. The frequency characteristics of current sensor and measurement impedance are detected. In order to test the measurement system, the PD signals of a needle defect under impulse voltage is detected, the test results show that the PD measurement system can detect the PD signals effectively.

J2410105 ラジオ波焼灼療法における電磁波周波数特性に基づく発熱量のモデル化([J241-01]医工学テクノロジーによる医療福祉機器開発(1))

Radio Frequency Ablation (RFA) is one kinds of hyperthermia treatment for cancer. Advantages of RFA are mainly low impact operations and shorter hospital stay. Disadvantage of RFA is difficult to get coagulation information for operator. Therefore, it needs to control ablation energy precisely. Thus, we have been proposed a method control of ablation energy. A feature of RFA, it uses electromagnetic-wave for ablation. RFA is related as not only thermal physics but also electrical physics. And, Heat generation from RF-electrode depends on frequency of electromagnetic-wave frequency. Therefore, in this study, we modeled heat generation based on electric impedance frequency characteristic during RFA. Firstly, it measured electric impedance frequency characteristic of pig liver samples. Secondly, it measured temperature distribution of the samples during RFA. Finally, it modeled electric impedance frequency characteristic of pig liver samples based on equivalent circuit model which was considered about fractional calculus. And, we evaluated a value of electrical impedance. From results, Model value of heat generation was matched with actual measurement value by using a coefficient of electrical impedance.

Measurement System for Parameter Estimation and Diagnostic of Ultrasonic Transducers

The paper presents an architecture and design of measurement system and methods for parameter estimation and diagnostic of ultrasonic transducers used in ultrasonic welding and cutting systems manufactured by Tele and Radio Research Institute. The key element of the ultrasonic welding and cutting system is a high power ultrasonic transducer implemented as a sandwich transducer consisting of a stack of piezoelectric ceramic rings mounted between two masses. High quality welding and cutting demand predetermined frequency characteristic of transducer impedance. Also important are: high energy e ciency, high coupling coe cient, low dielectric loss, and the optimal radiation pattern. In order to manufacture high quality and long-life transducers the piezoelectric rings must be selected and the sandwich transducers diagnosed on the basis of their measured parameters. Presented measurement system takes advantage of the virtual instrument technique in the NI LabVIEW environment. It uses Agilent U2761A Function Generator, U2531A Data Acquisition Unit, and the linear ampli er to measure impedance frequency characteristic in the frequency range of 10 kHz to 100 kHz. Moreover, the system can measure the vibration amplitude in the range of 1 μm up to 100 μm, using an optical sensor, and the temperature of the transducer using a pyrometer sensor.

Impedance Spectroscopy Studies of DCM Doped Alq&lt;sub&gt;3&lt;/sub&gt; Organic Material

In this work, we report on the frequency-impedance characteristics of dye-doped organic material. The device structure is glass substrate/indium tin oxide/DCM:Alq3/Aluminum 100 nm. The influence of doping concentraion has been investigated by impedance spectroscopy. The impedance characteristics of the dye-doped organic material can be modelled by simply adopting the conventional equivalent circuit with the simple combination of resistors and capacitor network. The variation of bulk resistance with applied bias voltage as a result of the Space Charge Limited Conduction (SCLC) mechanism for charge conduction.