Electric-field-induced shift of the magnetic resonance line in ferrite-piezoelectric composites

The electric-field-induced shift of the magnetic resonance line in ferrite-piezoelectric composites has been studied by experimental and theoretical methods. Expressions for the resonance line shift as a function of the field strength and structural parameters are obtained. The shift depends linearly on the field strength and increases with the content of a piezoelectric component in the composite. The results of calculations for a lithium ferrite spinel-lead zirconate titanate composite are in good agreement with the experimental data obtained for this material.     

Ferrite-Piezoelectric Multilayers for Magnetic Field Sensors

A magnetic field sensor based on magnetoelectric effects in a ferrite-piezoelectric layered sample is proposed. Such sensors are passive, provide direct conversion of magnetic fields into an electrical signal, and allow measurements of both ac and dc magnetic fields. A multilayer sample of nickel zinc ferrite-lead zirconate titanate has been used to characterize the sensor response to ac and dc fields, field orientations, frequency, and temperature. The sample shows a linear response for dc fields up to a maximum of 1750 Oe. The sensor output is temperature independent over 273–337 K, but is dependent on frequency of the ac excitation field. Operating at electromechanical resonance for the element enhances the sensor sensitivity by an order of magnitude. For ac magnetic field sensors, the output varies linearly with amplitude.     

Magnetoacoustic resonance in tangentially magnetized ferrite-piezoelectric bilayers

The magnetoelectric (ME) effect in ferrite-piezoelectric bilayers has been theoretically studied at coinciding frequencies of the electromechanical resonance in the electric subsystem and ferromagnetic resonance in tangentially magnetized ferrite. Giant values of the ME voltage coefficient (50–70 V/A at 5 GHz) are predicted for the YIG-PZT system. In contrast to the case of a normally magnetized plate, the magnetoacoustic resonance in a tangentially magnetized sample takes place at a lower value of the magnetic bias field and a smaller ferrite layer thickness. This effect can be used for the development of multifunctional ME nanosensors and transducers operating in the microwave range.     

Magnetoelectric response of a multilayer ferrite-piezoelectric structure to magnetic field pulses

Magnetoelectric (ME) response of a multilayer ferrite-piezoelectric structure to short magnetic field pulses has been measured. The frequency spectrum of the ME coefficient α_E of the structure in the range from several dozen hertz to 1 MHz has been determined by Fourier analysis of the ME response signal. The α_E value shows a general slow monotonic decrease with increasing frequency and exhibits a 7-to 30-fold reso-nance growth at certain frequencies, which is related to the excitation of intrinsic acoustic oscillations of the multilayer structure. In the low-frequency range, the ME coefficient has a maximum in the region of 1 kHz due to relaxation processes in the piezoelectric and ferrite layers.     

Giant magnetoelectric effect in composite materials in the region of electromechanical resonance

The magnetoelectric effect in multilayer ferrite-piezoelectric composites has been theoretically and experimentally studied. Using the method of effective parameters, an expression for the magnetoelectric coefficient is determined and its frequency dependence is analyzed. It is shown that, in the region of electromechanical resonance, the magnitude of the effect exceeds a low-frequency value by more than an order of magnitude. The results of calculations obtained for a nickel ferrite spinel-PZT composite are in good agreement with the experimental data.     

Inverse magnetoelectric effect in ferrite-piezoelectric structures

A theory of the inverse magnetoelectric (ME) effect in bulk ferrite-piezoelectric composite materials is presented. Using the material equations and equations of motion, expressions for the frequency dependence of the inverse ME conversion coefficient and the voltage ratio in an ME transformer are obtained. These dependences exhibit a resonant character, with the ME response magnitude peaking at the resonance frequency. The ME transformer coefficient not only depends on the ME voltage coefficient and the number of turns in the induction coil, but is also influenced by the mutual orientation of the electric and magnetic fields and the sample geometry.     

Magnetic-type resonance in nonmagnetic line wire excited by surface plasmons in microwave range

A magnetic resonance microwave response has been detected and identified in a structure of parallel nonmagnetic wires or a single line wire perpendicular to the electric field of a plane electromagnetic wave in the case where the wires are arranged near an array (grating) of resonant surface-plasmon-generating elements and oriented along the direction of wave propagation. A giant resonance is observed for a definite (resonance) length of the wire(s) in a certain frequency range corresponding to the existence of surface plasmons (below the resonance frequency of the plasmon-generating array). It is suggested that the magnetic response of the wire(s) is due to the excitation of resonance currents by the magnetic field of surface plasmons. Using the observed phenomena, it is possible to obtain new magnetic metamaterials (in particular, those possessing simultaneously negative effective dielectric permittivity and magnetic permeability) tunable in a broad frequency range.     

Frequency dependence of the magnetoelectric effect in ceramic composites based on lead zirconate titanate and nickel ferrite

The magnetoelectric (ME) effect in ferrite-piezoelectric ceramic composites based on a nickel ferrite spinel and lead zirconate titanate (PZT) has been theoretically and experimentally studied. Using the method of effective medium, an expression for the ME coefficient is obtained and its frequency dependence is analyzed. It is shown that, in the region of electromechanical resonance, the magnitude of the ME effect exceeds that in a layered structure of the same components and is more than two orders of magnitude greater than the low-frequency value. The results of calculations for a nickel ferrite spinel-PZT composite are in good agreement with the experimental data.     

The fault current limiting characteristics of a flux-lock type high-Tc superconducting fault current limiter using series resonance

We analyzed the fault current limiting characteristics of a flux-lock type high-T_c superconducting fault current limiter (HTSC-FCL) using series resonance between capacitor for series resonance and magnetic field coil which was installed in coil 3. The capacitor for the series resonance in the flux-lock type HTSC-FCL was inserted in series with the magnetic field coil to apply enough magnetic field into HTSC element, which resulted in higher resistance of HTSC element.However, the impedance of the flux-lock type HTSC-FCL has started to decrease since the current of coil 3 exceeded one of coil 2 after a fault accident. The decrease in the impedance of the FCL causes the line current to increase and, if continues, the capacitor for the series resonance to be destructed. To avoid this operation, the flux-lock type HTSC-FCL requires an additional device such as fault current interrupter or control circuit for magnetic field.This paper investigated the parameter range where the operation as mentioned above for the designed flux-lock type HTSC-FCL using series resonance occurred from the experimental results. In the design of the flux-lock type HTSC-FCL, the some methods to avoid the continuous increase of the line current were suggested and confirmed by the experiments that the suggested methods were available to prevent the continuous increase of the line current after a fault happened.     

Forward electric field calculation using BEM for time-varying magnetic field gradients and motion in strong static fields

A boundary element method for evaluating the electric fields induced in conducting bodies exposed to magnetic fields varying at low frequency has been developed and applied to sources of magnetic field variation that are of relevance in magnetic resonance imaging. An integral formulation based on constant boundary elements which can be used to study the effects of both temporally varying magnetic field gradients and rigid body movement in a static magnetic field is presented. The validity of this approach has been demonstrated for simple geometries with known analytical solutions and it has also been applied to the evaluation of the induced fields in more realistic models of the human head.     

An Iterative Method for Computing the Surface Resistance of YBCO Thin Films in the Nonlinear Regime of RF Power

A numerical method to find, in the nonlinear regime, the quality factor, the surface resistance, and the resonance frequency of YBCO microstrip line resonator, deposited on both sides of an MgO substrate, is presented. The numerical method is based on an iterative self-consistent technique used to find the RF magnetic field in the nonlinear regime of the dissipation mechanisms. The determination of the RF magnetic field yields to the corresponding surface resistance and resonance frequency. The dependence of the geometrical factor of the film on the RF magnetic field is discussed. This latter is usually used as constant in the literature. However, in our calculation this factor has a maximum at a certain RF input power.     

An Iterative Method for Computing the Surface Resistance of YBCO Thin Films in the Nonlinear Regime of RF Power

A numerical method to find, in the nonlinear regime, the quality factor, the surface resistance, and the resonance frequency of YBCO microstrip line resonator, deposited on both sides of an MgO substrate, is presented. The numerical method is based on an iterative self-consistent technique used to find the RF magnetic field in the nonlinear regime of the dissipation mechanisms. The determination of the RF magnetic field yields to the corresponding surface resistance and resonance frequency. The dependence of the geometrical factor of the film on the RF magnetic field is discussed. This latter is usually used as constant in the literature. However, in our calculation this factor has a maximum at a certain RF input power.     

Theory of magnetoelectric effect in ferrite-piezoelectric hybrid composites

A theory of the magnetoelectric (ME) effect in a multilayer ferrite-piezoelectric hybrid composite is presented. Proceeding from the material equations and the equations of motion, an expression for the frequency dependence of the ME voltage coefficient is obtained which involves the parameters of the ferrite and piezoelectric phases. In the region of the electromechanical resonance of the composite, the ME voltage coefficient exhibits a sharp increase. The results of calculations for a Terfenol-D-PZT hybrid composite are in satisfactory agreement with experimental data.     

Flexible visible-infrared metamaterials and their applications in highly sensitive chemical and biological sensing

Flexible electronic and photonic devices have been demonstrated in the past decade, with significant promise in low-cost, light-weighted, transparent, biocompatible, and portable devices for a wide range of applications. Herein, we demonstrate a flexible metamaterial (Metaflex)-based photonic device operating in the visible-IR regime, which shows potential applications in high sensitivity strain, biological and chemical sensing. The metamaterial structure, consisting of split ring resonators (SRRs) of 30 nm thick Au or Ag, has been fabricated on poly(ethylene naphthalate) substrates with the least line width of ～30 nm by electron beam lithography. The absorption resonances can be tuned from middle IR to visible range. The Ag U-shaped SRRs metamaterials exhibit an electric resonance of ～542 nm and a magnetic resonance of ～756 nm. Both the electric and magnetic resonance modes show highly sensitive responses to out-of-plane bending strain, surrounding dielectric media, and surface chemical environment. Due to the electric and magnetic field coupling, the magnetic response gives a sensitivity as high as 436 nm/RIU. Our Metaflex devices show superior responses with a shift of magnetic resonance of 4.5 nm/nM for nonspecific bovine serum albumin protein binding and 65 nm for a self-assembled monolayer of 2-naphthalenethiol, respectively, suggesting considerable promise in flexible and transparent photonic devices for chemical and biological sensing.     

Local magnetic properties of a monolayer of Mn12 single molecule magnets

The magnetic properties of a monolayer of Mn12 single molecule magnets grafted onto a silicon (Si) substrate have been investigated using depth-controlled beta-detected nuclear magnetic resonance. A low-energy beam of spin-polarized radioactive 8Li was used to probe the local static magnetic field distribution near the Mn12 monolayer in the Si substrate. The resonance line width varies strongly as a function of implantation depth as a result of the magnetic dipolar fields generated by the Mn12 electronic magnetic moments. The temperature dependence of the line width indicates that the magnetic properties of the Mn12 moments in this low-dimensional configuration differ from bulk Mn12.     

Josephson plasma resonance in Bi2Sr2CaCu2O8+δ under parallel magnetic field

Josephson plasma resonance in under-doped Bi ₂ Sr ₂ CaCu ₂ O ₈₊ single crystals has been observed when magnetic field is applied parallel to the ab plane and its vicinity. The resonance mode splits into two branches at higher and lower temperature regions, and a definite gap appears in the temperature region between them. As the magnetic field is tilted from the ab plane, these branches come closer and finally merge to a single mode. This leads to a general interpretation that the resonance mode observed in a parallel field may be due to continuous extension of the c axis plasma mode. However, splitting of the mode as well as the peculiar temperature dependence of the resonance field, the line shape, and its intensity strongly imply that these behaviors may originate from the inherent resonance modes in parallel field. In particular, the high temperature mode fields goes even higher in temperature beyond the zero field resonance as the field increases, suggesting that a new explanation may be required for the case of parallel magnetic field.     

Fe基纳米晶粉芯磁致频移特性的研究

测量了Fe基纳米晶粉芯线圈与电容并联成LC回路的共振频率 (fr) ,研究了fr 随外加磁场变化的特性 ,发现fr 随外加磁场有显著变化。在 0— 5 6kA m范围内有很好的线性和灵敏度 ,可以用于磁场测量     

Measurement of dilute 29Si species in solution using a large volume coil and DEFT NMR

A large-sample-volume nuclear magnetic resonance (NMR) spectroscopy probehead has been developed for the detection and characterization of low concentrations of 29Si species in aqueous solution. The approach described entails the use of a large-diameter radio frequency solenoid coil that permits substantially larger sample volumes to be investigated at moderate magnetic field strengths, compared with conventional NMR probehead configurations. In addition, difficulties presented by long 29Si T1 relaxation times have been circumvented by using the DEFT NMR pulse sequence, which permits more rapid signal averaging. Through a combination of these hardware and methodological improvements, high-resolution 29Si NMR spectra have been obtained at 4.2 T (29Si resonance frequency = 36.8 MHz) for an 800 microM solution of 96% 29Si-enriched silicic acid, H4SiO4 (pH approximately 8), with a signal-to-noise ratio of 16 and a line width of 31 Hz after 3 h of total measurement time.     

ESR investigations on polyethylene-single wall carbon nanotube composites

Electron spin resonance investigations on single wall carbon nanotubes dispersed in polyethylene are reported. Three resonance lines were observed; a wide line assigned to magnetic iron clusters (catalyst residues), a broad and intense line originating from uncoupled electrons delocalized over the conducting domains of carbon nanotubes (in interaction with the electronic spins assigned to magnetic impurities), and a faint line superimposed on the broad one, assigned to paramagnetic impurities. The temperature dependence of resonance line parameters (resonance line position, width, and double integral) in the range 150–450 K has been analyzed. It was observed that the parameters of the broad and narrow lines are sensitive to the glass and melting relaxations occurring within the polymeric matrix.     

Stochastic resonance in metal superlattices in the presence of a transverse noise

The stochastic resonance in a metal multilayer system, which is excited by a magnetic field containing a longitudinal harmonic signal and a transverse component oriented in the plane of the structure, has been studied by numerical analysis of the dynamics of the system of coupled magnetic moments. It is established that the resonance can be controlled by changing the amplitude and frequency of the harmonic signal.