A 2D micro-fluxgate earth magnetic field measurement systems with fully automated acquisition setup

In this paper we present an Earth magnetic field measurement system and an automated acquisition setup to characterize it. The measurement system consists of a fluxgate sensor and an integrated front-end circuit, both realized in CMOS technology. The couple of orthogonal axes of the sensor makes the system suitable for realizing an electronic compass device. Indeed, we can measure not only the amplitude of the Earth magnetic field (whose full-scale value is of the order of 60 μT), but also its direction. The complete measurement system achieves a maximum angular error of 1.5° in the measurement of the Earth magnetic field direction. Furthermore, an acquisition setup was developed to evaluate the measurement system performance. It consists of a precision mechanical plastic structure, in tower form, a microcontroller-based interface circuit, that provides a digital output through an RS232 serial interface, a PC software suitably developed to post-process the data from the acquisition system and a couple of Helmholtz coils to evaluate the linearity of the system. This setup allows us to perform a completely automated and numerically controlled characterization of the measurement system.     

Quasi-omnidirectional electrical spectrometer for studying spin dynamics in magnetic tunnel junctions

We report an omnidirectional electrical spectroscopy setup for studying the spin dynamics in a nanoscale magnet. It has a measureable solid angle range comprising about 50% of the total range and allows the magnetoresistance and spin-torque diode signal to be measured simultaneously at any angle to the magnetization. This setup can provide detailed information about the spin-wave resonance modes excited in a nanoscale magnet.     

Torque detected broad band electron spin resonance

We present a novel technique to measure high frequency electron spin resonance spectra in a broad frequency range (30-1440 GHz) with high sensitivity. We use a quasioptical setup with tunable frequency sources to induce magnetic resonance transitions. These transitions are detected by measuring the change in the magnetic torque signal by means of cantilever torque magnetometry. The setup allows tuning of the frequency, magnetic field, polarization, and the angle between the sample and the external magnetic field. We demonstrate the capabilities of this technique by showing preliminary results obtained on a single crystal of an Fe(4) molecular nanomagnet.     

Investigating the effect of magnetic pipes connected to electromagnetic flowmeters using experimentally validated finite element models

This paper describes a finite element model for computing the magnetic field distribution in commercial electromagnetic flowmeter designs. The model is validated through an experimental setup, measuring the magnetic flux density in the radial direction at the inner perimeter of the flowmeter wall. The predicted flux densities are in overall good agreement with experimental obtained data. The model is used to evaluate the effect of having magnetic pipes connected to flowmeters of two different designs. Using analytic models, the flowmeter sensitivity is computed both with magnetic and non-magnetic pipes connected.     

Noise reduction of ultrasonic Doppler velocimetry in liquid metal experiments with high magnetic fields

The last decades have seen a number of liquid metal experiments on the interaction of magnetic fields with the flow of electrically conducting fluids. The opaqueness of liquid metals requires non-optical methods for inferring the velocity structure of the flow. Quite often, such experiments are carried out in the presence of high electrical currents to generate the necessary magnetic fields. Depending on the specific purpose, these currents can reach several kiloamperes. The utilized switching mode power supply can then influence seriously the measurement system by electromagnetic interference. A recent experiment on the azimuthal magnetorotational instability (AMRI) has shown that a hydrodynamically stable Taylor–Couette flow becomes unstable under the influence of a high azimuthal magnetic field. An electrical current along the axis of the experiment with up to 20 kA generates the necessary field to destabilize the flow. We present experimental results of this AMRI experiment carried out at the PROMISE facility with an enhanced power supply. For this setup, we discuss the elaborate measures that were needed to obtain a reasonable signal-to-noise ratio of the ultrasonic Doppler velocimetry (UDV) system. In dependence on various parameter variations, some typical features of the observed instability, such as the energy content, the wavelength, and the frequency are analyzed and compared with theoretical predictions.     

Two-dimensional higher order noise spectroscopy up to radio frequencies

Going beyond the usual determination of the frequency-resolved power spectrum of an electrical noise signal, we implement a setup for the determination of a frequency-resolved two-dimensional correlation spectrum. We demonstrate measurements of two-dimensional correlation spectra with sampling rates up to 180 MSamples/s and real-time numerical evaluation with up to 100% data coverage. As an example, the purely Gaussian behavior of 1/f resistor noise is demonstrated with unprecedented sensitivity by verifying the absence of correlations between different frequencies. Unlike the usual power spectrum, the correlation spectrum is shown to contain information on both the homogeneous and inhomogeneous linewidths of a signal, suggesting applications in spin noise spectroscopy and signal analysis in general.     

Complex magnetic susceptibility setup for spectroscopy in the extremely low-frequency range

A sensitive balanced differential transformer was built to measure complex initial parallel magnetic susceptibility spectra in the 0.01-1000 Hz range. The alternating magnetic field can be chosen sufficiently weak that the magnetic structure of the samples is only slightly perturbed and the low frequencies make it possible to study the rotational dynamics of large magnetic colloidal particles or aggregates dispersed in a liquid. The distinguishing features of the setup are the novel multilayered cylindrical coils with a large sample volume and a large number of secondary turns (55 000) to measure induced voltages with a good signal-to-noise ratio, the use of a dual channel function generator to provide an ac current to the primary coils and an amplitude- and phase-adjusted compensation voltage to the dual phase differential lock-in amplifier, and the measurement of several vector quantities at each frequency. We present the electrical impedance characteristics of the coils, and we demonstrate the performance of the setup by measurement on magnetic colloidal dispersions covering a wide range of characteristic relaxation frequencies and magnetic susceptibilities, from chi approximately -10(-5) for pure water to chi>1 for concentrated ferrofluids.     

不锈钢物流管道内表面磁力研磨的回转磁场设计

分析了不锈钢物流管道内表面磁力研磨运动轨迹和速度的要求,研究了各种励磁方法及其研磨运动轨迹, 提出了同时产生回转磁场和往复磁场的励磁方法,设计了能实现复杂研磨轨迹的一种新型回转磁场装置,该回转 磁场通过磁极轴向分布产生波浪形研磨条纹,同时完成磁性磨料对工件的周向回转和轴向往复运动,最后用316L 管道进行了回转磁场的材料去除试验。     

Coplanar stripline antenna design for optically detected magnetic resonance on semiconductor quantum dots

We report on the development and testing of a coplanar stripline antenna that is designed for integration in a magneto-photoluminescence experiment to allow coherent control of individual electron spins confined in single self-assembled semiconductor quantum dots. We discuss the design criteria for such a structure which is multi-functional in the sense that it serves not only as microwave delivery but also as electrical top gate and shadow mask for the single quantum dot spectroscopy. We present test measurements on hydrogenated amorphous silicon, demonstrating electrically detected magnetic resonance using the in-plane component of the oscillating magnetic field created by the coplanar stripline antenna necessary due to the particular geometry of the quantum dot spectroscopy. From reference measurements using a commercial electron spin resonance setup in combination with finite element calculations simulating the field distribution in the structure, we obtain a magnetic field of 0.12 mT at the position where the quantum dots would be integrated into the device. The corresponding π-pulse time of ≈0.5?μs meets the requirements set by the high sensitivity optical spin read-out scheme developed for the quantum dot.     

A versatile low-temperature setup for the electrical characterization of single-molecule junctions

We present a modular high-vacuum setup for the electrical characterization of single molecules down to liquid helium temperatures. The experimental design is based on microfabricated mechanically controllable break junctions, which offer control over the distance of two electrodes via the bending of a flexible substrate. The actuator part of the setup is divided into two stages. The slow stage is based on a differential screw drive with a large bending range. An amplified piezoceramic actuator forms the fast stage of the setup, which can operate at bending speeds of up to 800 μm/s. In our microfabricated break junctions this is translated into breaking speeds of several 10 nm/s, sufficient for the fast acquisition of large statistical datasets. The bandwidth of the measurement electronics has been optimized to enable fast dI/dV spectroscopy on molecular junctions with resistances up to 100 MΩ. The performance of the setup is demonstrated for a π-conjugated oligo(phenylene-ethynylene)-dithiol molecule.     

Large atom number Bose-Einstein condensate of sodium

We describe the setup to create a large Bose-Einstein condensate containing more than 120 x 10(6) atoms. In the experiment a thermal beam is slowed by a Zeeman slower and captured in a dark-spot magneto-optical trap (MOT). A typical dark-spot MOT in our experiments contains 2.0 x 10(10) atoms with a temperature of 320 microK and a density of about 1.0 x 10(11) atoms/cm(3). The sample is spin polarized in a high magnetic field before the atoms are loaded in the magnetic trap. Spin polarizing in a high magnetic field results in an increase in the transfer efficiency by a factor of 2 compared to experiments without spin polarizing. In the magnetic trap the cloud is cooled to degeneracy in 50 s by evaporative cooling. To suppress the three-body losses at the end of the evaporation, the magnetic trap is decompressed in the axial direction.     

Synchronized time- and high-field-resolved all-optical pump-probe magneto-optical setup based on a strong alternating magnetic field and its application in magnetization dynamics of high coercivity magnetic medium

An alternating magnetic field (AMF) apparatus is developed and composed of an electromagnet and driving power supply. The structure of the electromagnet and configuration of the driving supply are described in detail. The apparatus can produce a peak magnetic field up to 9000 Oe and above under a small driving power at its resonance frequency of 1.14 kHz. Based on synchronization between the AMF and the femtosecond laser pulse train, a photomagnetic synchronized time- and high-field-resolved all-optical pump-probe magnetic-optical setup is developed. This setup has the ability to reinitialize any magnetic states between two successive laser pulses so that irreversible magnetization reversal dynamics can be studied. Dynamic Kerr hysteresis loops and magnetization reversal dynamics of high coercivity ferromagnetic TbFeCo and FePt films are demonstrated using this setup, showing importance of this synchronized time- and high-field-resolved all-optical pump-probe magnetic-optical setup in the research of ultrafast magnetization dynamics.     

Experimental setup for non-destructive measurement of tunneling currents in semiconductor devices

A new experimental setup used to perform non-destructive measurement of electrical quantities on semiconductor devices is described in this paper. The particular case of tunneling current measurement in n-type semiconductor–oxide–semiconductor (SOS) capacitors, whose dielectrics play a crucial role in non-volatile memories, has been investigated. When the gates of such devices are polarized with a sufficient bias voltage while the other terminals are grounded, tunnel conduction of electrons through the thin oxide layer is allowed. Typical tunneling current measurements obtained with this advanced setup are presented and compared to the results yielded by older standard experimental protocols. An application to the experimental observation of the temperature dependence of the tunneling current is proposed. Conclusions about the benefits of this kind of electrical measurements are then drawn.     

城轨车辆并行走线的串扰耦合分析

利用CST软件对城轨车辆多根电缆并行走线进行仿真及分析,分析了四线共面和长方体布线形式以及四线中不同的电流方向对敏感电缆中串扰电压的影响.通过仿真分析发现,改变布线形式以及电流流向能够显著降低敏感电缆中的串扰电平,为工程实际提供了一种易于实现的低串扰布线形式.     

A high-vacuum deposition system for in situ and real-time electrical characterization of organic thin-film transistors

We present a home-built high-vacuum system for performing organic semiconductor thin-film growth and its electrical characterization during deposition (real-time) or after deposition (in situ). Since the environment conditions remain unchanged during the deposition and electrical characterization process, a direct correlation between growth mode and electrical properties of thin film can be obtained. Deposition rate and substrate temperature can be systematically set in the range 0.1-10 ML∕min and RT-150 °C, respectively. The sample-holder configuration allows the simultaneous electrical monitoring of up to five organic thin-film transistors (OTFTs). The OTFTs parameters such as charge carrier mobility μ, threshold voltage V(TH), and the on-off ratio I(on)∕I(off) are studied as a function of the semiconductor thickness, with a submonolayer accuracy. Design, operation, and performance of the setup are detailed. As an example, the in situ and real-time electrical characterization of pentacene TFTs is reported.     

Torsional bridge setup for the characterization of integrated circuits and microsensors under mechanical shear stress

We present a torsional bridge setup for the electro-mechanical characterization of devices integrated in the surface of silicon beams under mechanical in-plane shear stress. It is based on the application of a torsional moment to the longitudinal axis of the silicon beams, which results in a homogeneous in-plane shear stress in the beam surface. The safely applicable shear stresses span the range of ±50 MPa. Thanks to a specially designed clamping mechanism, the unintended normal stress typically stays below 2.5% of the applied shear stress. An analytical model is presented to compute the induced shear stress. Numerical computations verify the analytical results and show that the homogeneity of the shear stress is very high on the beam surface in the region of interest. Measurements with piezoresistive microsensors fabricated using a complementary metal-oxide-semiconductor process show an excellent agreement with both the computational results and comparative measurements performed on a four-point bending bridge. The electrical connection to the silicon beam is performed with standard bond wires. This ensures that minimal forces are applied to the beam by the electrical interconnection to the external instrumentation and that devices with arbitrary bond pad layout can be inserted into the setup.     

Magnetic pulser and sample holder for time- and spin-resolved photoemission spectroscopy on magnetic materials

A compact coil setup, in conjunction with a high power current pulser, is presented; developed especially for time- and spin-resolved photoemission spectroscopy measuring the sample in magnetic remanence at room temperature. A novel approach is presented where the sample is switched in the stray field of a coil pair. This enables the electrical biasing of the sample without altering the electron trajectories due to field gradients introduced by the coils. The pulser driving the coils reaches a peak power of 1 MW at 1 kA with a switching frequency up to 10 kHz suitable for experiments, for example, with state of the art repetition rates of femtosecond laser systems.     

An approach to the systematic distortion correction in aberration-corrected HAADF images

Systematic distortion has been analysed in high‐angle annular dark‐field (HAADF) images which may be caused by electrical interference. Strain mapping techniques have been applied to a strain‐free GaAs substrate in order to provide a broad analysis of the influence of this distortion on the determination of local strain in the heterostructure. We have developed a methodology for estimating the systematic distortion, and we correct the original images by using an algorithm that removes this systematic distortion.     

A simple and accurate method for calibrating the oscillation amplitude of tuning-fork based AFM sensors

We have developed a simple and accurate method for calibrating the amplitude of vibration of quartz tuning fork sensors commonly used in atomic force- and near field optical-microscopy. Unlike interferometric methods, which require a complex optical setup, the method we present requires only a simple measurement of the electro-mechanical properties of the tuning-fork oscillator and can be performed in a matter of minutes without disturbing the experimental setup. Comparison with interferometric methods shows that an accuracy of better than few percent can be routinely achieved.