Electric-Field-Induced Magnetization Reversal in a Ferromagnet-Multiferroic Heterostructure

The orientation of human red blood cells (RBCs) was controlled by the application of magnetic and electric fields. Because of their anisotropic diamagnetism, RBCs orient parallel to strong magnetic fields. The electric orientation of erythrocytes is also caused by electric dipoles induced by an electric field. The RBCs orientation is parallel to both the electric and magnetic fields. A 4–5 kV/m alternating current (ac) electric field (10–200 kHz, sine wave) was applied to RBCs suspended in a phosphate buffer solution using a pair of platinum black electrodes spaced 200–250 μm apart. An 8 T magnetic field was applied to the RBCs perpendicular to the direction of the electric field. It was observed that all RBCs were oriented in the same direction and parallel to the electric and magnetic fields. By the application of a horizontal 8 T magnetic field and a 4 kV/m ac electric field positioned perpendicular to one another, the RBCs oriented horizontally and their sedimentation rate was decreased by 18%. The flowing rate of the 10% RBCs suspension was decreased by 7.6% with the application of an 8 T magnetic field and a 4 kV/m ac electric field perpendicular to the direction of the suspension flow. It was observed that flowing RBCs were oriented perpendicular to the direction of the flow by the application of the fields, when the velocity of the suspension of RBCs was less than 300 μm/s.

This paper proposes a novel switching strategy for high efficiency of a single-phase three-level inverter. Normally, the conventional unipolar and bipolar switching methods are used in the single-phase three-level inverter. In comparison with two conventional switching methods, the proposed switching method, which keeps switching state of some switches for switching period, is advantageous in efficiency. In this paper, an operation principle of the proposed switching strategy is introduced. It is easy to implement because the operation principle is based on the unipolar switching method. Furthermore, in comparison with the unipolar switching method, the efficiency and the current total harmonic distortion of the proposed switching method are shown by simulations results. bipolar switching methods are the conventional method for the single-phase two-level inverter. These switching methods can be applied in the single-phase three-level inverter. In (10), an optimal switching method is introduced for both the high efficiency and current ripple reduction in the two-level inverter. It is based on analysis of time-domain current ripple. In (11), a flexible switching speed control to reduce the gate driver current is proposed to decrease switching loss. In this paper, the operation principle and characteristic of the unipolar and bipolar switching methods are introduced. Then, this paper proposes a novel switching method for the switching loss reduction in the single-phase three-level NPC inverter. The unipolar switching method, which has performance better than the bipolar switching method (12), is applied to the single-phase three-level inverter. Then, It is compared with the proposed switching strategy. In the proposed switching strategy, reference signals used in the unipolar switching method are changed. As a result, in one leg, one switch is fixed to ON- or OFF-state while another switch is operating. Therefore, it is possible to obtain the advantage of that switching loss is reduced. Simulations are implemented to demonstrate feasibility of the proposed switching method for high efficiency of the single-phase three-level inverter. Additionally, based on simulations, the efficiency and current total harmonic distortion (THD) are shown by comparing the proposed switching method with the unipolar switching method.

We investigate the director reorientation in a nematic liquid crystal confined between two parallel plates and subjected to both a magnetic and an electric field. The permanent magnetic field is used first to align the director and, subsequently, to allow nuclear magnetic resonance (NMR) observation of the director response following the application of the electric field. For sufficiently strong electric fields, the director reorients and aligns parallel to the electric field. In this work we focus on the geometry where the electric and magnetic fields are orthogonal to each other. In this configuration the state of the system, immediately after applying the orthogonal electric field, is steady and unstable, at least in theory, since the director is assumed to be everywhere parallel to the magnetic field. In practice the real state of the system always deviates slightly from the perfect unstable steady state, which induces the start of the director reorientation toward the electric field. The nature and the characteristics of the initial deviation partially determine the reorientation process. In the classical approach, the small deviations from the ideal state are assumed to be due to thermal fluctuations, but this approach fails to account for some recent experimental results. For this reason we were led to investigate slightly non-uniform initial director configurations that are stable under the sole effect of the magnetic field but are sufficient to break the ideal unstable steady state created with the application of the orthogonal electric field. Such non-uniformities must be local or distributed over very small sample volumes, since their effects on the equilibrium NMR spectrum (before the application of the electric field) are not usually observed. In other words, we consider the presence of inversion walls in the bulk of the sample and local misalignments of the director on the boundary plates and investigate the effects of such non-uniformities on the response of the nematic to the application of the electric field, as observed by NMR. The model we propose, including such effects in parallel with thermal fluctuations, is able to account for the recently observed features of the field-induced director dynamics.

This paper presents two interface circuit designs that improve the piezoelectric energy harvesting performance at offresonance. Complex impedance matching at different frequencies is achieved by introducing delay into the conventional switching methods. The proposed techniques can also be used in other applications, such as electromagnetic energy harvesting. The system is analyzed using equivalent impedance at fundamental of operating frequency. Design considerations such as two possible modes of operation, sensitivity to voltage and timing errors, loss due to nonlinear operations, and conduction loss of switches are detailed. As compared with the conventional methods, analytical results show that, with the electromechanical coupling coefficient k2e of 0.076 and the mechanical damping ratio ζm of 0.02, the proposed techniques can improve the 3-dB bandwidth by 76% with a flipping quality factor of 10. Experimental results with a commercially available piezoelectric device show a 23% improvement in 3-dB bandwidth and a 66% improvement in extracted power with 5% of frequency mismatch.

This paper proposes a modulation method to reduce power losses and achieve high efficiency for a single-phase NPC three-level inverter. In conventional switching methods, the bipolar and unipolar pulse width modulation methods are commonly used in a single phase inverter. However, these switching methods have the disadvantages in aspects of the power loss. The several clamp switching methods aggravating the Total Harmonic Distortion (THD) are introduced to solve the loss problem. To overcome these weaknesses in these switching methods, this paper proposes a novel clamp switching method that combines two switching method, unipolar PWM method and clamp switching method. Since the proposed method has all the advantages of both methods, the optimal performance in the power losses and THD can be obtained. The analysis of the power loss reduction and THD is showed through the simulation.

This study proposes a hybrid current controller for a permanent-magnet synchronous motor fed by a two-level inverter. It combines the advantages of model predictive control (MPC) and field-oriented control (FOC), which results in fast dynamics and a zero steady-state error. In addition, space vector pulse width modulation is used to ensure a constant switching frequency and simplify the switching signal generation for the two-level inverter. Two optimal switching methods were proposed to maintain a smooth transition between FOC and MPC and eliminate any undesired bumps or oscillations. These two methods are based on hysteresis average current ripple and artificial neural networks. The proposed switching methods (PSMs) were compared with two recent conventional switching methods (CSMs). Simulation and experimental results were given to validate the effectiveness of the PSMs over the CSMs. The results show that the PSMs have a robust and smooth transition between MPC and FOC in various setups with faster dynamics, minimal overshoot, and zero steady-state error.

This paper proposes a method of switching to improve power loss for the single-phase three-level NPC inverter. The conventional switching methods, which are called as the bipolar and unipolar switching methods, are used for single phase inverters using three-level topology. However, these switching method have disadvantage in the power loss. Because all of the switch are operated. To reduce the power loss of the three-level NPC inverter, clamp switching method is introduced in this paper. This way, one of the lag is fixed that switching loss is reduced. This paper analyzes and compares power losses of unipolar method and clamp method. The validity of the power loss analysis is verified through the simulation and experimental results.

In a droplet transport based on electrowetting on dielectrics, the parallel-plate configuration is more popular than the single-plate one because the droplet transport becomes increasingly difficult without cover plate. In spite of the improved transport performance, the parallel-plate configuration often limits the access to the peripheral components, requesting the removal of the cover plate, the single-plate configuration. We investigated the fundamental features of droplet transport for the single-plate configuration. We compared the performance of several switching methods with respect to maximum speed of successive transport without failure and suggested nonfloating switching method which is inherently free from the charge-residue problem and exerts greater force on a droplet than conventional switching methods. A simple theory is provided to understand the different results for the switching methods.

The Actin Cytoskeleton Has an Active Role in the Electrotransfer of Plasmid DNA in Mammalian Cells

A neuron will fire an action potential when its membrane potential exceeds a certain threshold. In typical activity of the brain, this occurs as a result of chemical inputs to its synapses. However, neurons can also be excited by an imposed electric field. In particular, recent clinical applications activate neurons by creating an electric field externally. It is therefore of interest to investigate how the neuron responds to the external field and what causes the action potential. Fortunately, precise and controlled application of an external electric field is possible for embryonic neuronal cells that are excised, dissociated and grown in cultures. This allows the investigation of these questions in a highly reproducible system. In this paper some of the techniques used for controlled application of external electric field on neuronal cultures are reviewed. The networks can be either one dimensional, i.e. patterned in linear forms or allowed to grow on the whole plane of the substrate, and thus two dimensional. Furthermore, the excitation can be created by the direct application of electric field via electrodes immersed in the fluid (bath electrodes) or by inducing the electric field using the remote creation of magnetic pulses.

A neuron will fire an action potential when its membrane potential exceeds a certain threshold. In typical activity of the brain, this occurs as a result of chemical inputs to its synapses. However, neurons can also be excited by an imposed electric field. In particular, recent clinical applications activate neurons by creating an electric field externally. It is therefore of interest to investigate how the neuron responds to the external field and what causes the action potential. Fortunately, precise and controlled application of an external electric field is possible for embryonic neuronal cells that are excised, dissociated and grown in cultures. This allows the investigation of these questions in a highly reproducible system. In this paper some of the techniques used for controlled application of external electric field on neuronal cultures are reviewed. The networks can be either one dimensional, i.e. patterned in linear forms or allowed to grow on the whole plane of the substrate, and thus two dimensional. Furthermore, the excitation can be created by the direct application of electric field via electrodes immersed in the fluid (bath electrodes) or by inducing the electric field using the remote creation of magnetic pulses.

Photoluminescence of electron donor-acceptor pairs that show photoinduced electron transfer (PIET) has been measured in a polymer film under simultaneous application of electric field and magnetic field. Fluorescence emitted from the locally excited state (LE fluorescence) of 9-methylanthracene (MAnt) and pyrene (Py) is quenched by an electric field in a mixture of 1,3-dicyanobenzene (DCB) with MAnt or Py, indicating that PIET from the excited state of MAnt or Py to DCB is enhanced by an electric field. Simultaneous application of electric and magnetic fields enhances the reverse process from the radical-ion pair produced by PIET to the LE fluorescent state of MAnt or Py. As a result, the electric-field-induced quenching of the LE fluorescence is reduced by application of the magnetic fields. Thus, the synergy effect of electric and magnetic fields is observed on the LE fluorescence of MAnt or Py. Exciplex fluorescence spectra resulting from PIET can be obtained by analyzing the field effects on photoluminescence spectra, even when the exciplex fluorescence is too weak to be determined from the steady-state or time-resolved photoluminescence spectra at zero field.

We propose a new observing method for single-dish millimeter and submillimeter spectroscopy using a heterodyne receiver equipped with a frequency-modulating local oscillator (FMLO). Unlike conventional switching methods, which extract astronomical signals by subtracting the reference spectra of off-sources from those of on-sources, the FMLO method does not need to obtain any off-source spectra; rather, it estimates them from the on-source spectra themselves. The principle uses high-dump-rate (10 Hz) spectroscopy with radio frequency modulation achieved by fast sweeping of a local oscillator of a heterodyne receiver. Because sky emission (i.e., off-source) fluctuates as $1/f$ and is spectrally correlated, it can be estimated and subtracted from time series spectra (a timestream) by principal component analysis. Meanwhile, astronomical signals remain in the timestream since they are modulated to a higher time-frequency domain. The FMLO method therefore achieves (1) a remarkably high observation efficiency, (2) reduced spectral baseline wiggles, and (3) software-based sideband separation. We developed an FMLO system for the Nobeyama $45\:$m telescope and a data reduction procedure for it. Frequency modulation was realized by a tunable and programmable first local oscillator. With observations of Galactic sources, we demonstrate that the observation efficiency of the FMLO method is dramatically improved compared to conventional switching methods. Specifically, we find that the time to achieve the same noise level is reduced by a factor of 3.0 in single-pointed observations and by a factor of 1.2 in mapping observations. The FMLO method can be applied to observations of fainter ($\sim$mK) spectral lines and larger ($\sim$deg$^{2}$) mapping. It offers much more efficient and baseline-stable observations compared to conventional switching methods.

Magnetoelectric coupling at multiferroic interfaces is a promising route toward the nonvolatile electric-field control of magnetization. Here, we use optical measurements to study the static and dynamic variations of the interface magnetization induced by an electric field in Co/PbZr0.2Ti0.8O3 (Co/PZT) bilayers at room temperature. The measurements allow us to identify different coupling mechanisms. We further investigate the local electronic and magnetic structure of the interface by means of transmission electron microscopy, soft X-ray magnetic circular dichroism, and density functional theory to corroborate the coupling mechanism. The measurements demonstrate a mixed linear and quadratic optical response to the electric field, which results from a magneto-electro-optical effect. We propose a decomposition method of the optical signal to discriminate between different components involved in the electric field-induced polarization rotation of the reflected light. This allows us to extract a signal that we can ascribe to interface magnetoelectric coupling. The associated surface magnetization exhibits a clear hysteretic variation of odd symmetry with respect to the electric field and nonzero remanence. The interface coupling is remarkably stable over a wide frequency range (1-50 kHz), and the application of a bias magnetic field is not necessary for the coupling to occur. These results show the potential of exploiting interface coupling with the prospect of optimizing the performance of magnetoelectric memory devices in terms of stability, as well as fast and dissipationless operation.

Cylindrical magnetic nanowires (CNWs) are promising candidates for the building blocks of 3D information technologies such as shift registers, magnetic recording, spintronics and logic gates1-4. Spin-polarized-current is an energy efficient way to excite magnetization dynamics in planar nanostructures. However, in CNWs this research is doing its first steps5. Magnetization dynamics in a CNW of Permalloy, 100 nm diameter and 1 µm length, is investigated under simultaneous application of electric current and magnetic field by micromagnetic simulations. The magnetization reversal process initiates with the creation of open vortex structures with different rotation senses at the nanowire ends. We conclude that the electric current by itself enlarges or reduces the length of these vortex structures according to the rotational sense of the associated Oersted field. Large enough current densities produce a vortex structure which covers the whole nanowire surface. At the same time, the magnetization in the very core of the nanowire remains the same, i.e. no complete magnetization reversal is possible in the absence of external magnetic field. The simultaneous action of the applied electric current and magnetic field allows the complete control of the vortex structures in terms of setting the polarity and vorticity. The resulting diagram of magnetic states obtained after the application of field and electric current showing the values required for the vorticity and axial magnetization switching is presented in Figure 1. This control is essential for future information technologies based on 3D vertical nanostructures. The presented state diagram will become useful for future experiments on current-induced domain wall dynamics in CNWs.