On the analysis of second-harmonic modulators

Analysis of magnetic modulators, which includes low-level transducer amplifiers and magnetometers, usually is based on control-signal displacement of fixed hysteresis loops of some particular shape. Experience shows, however, that many qualitative aspects of the device operation do not agree with the analysis. In this paper, an analysis is based on thedphi/dtwidening of the hysteresis loop, which is applicable to metal alloy tape cores. The analysis makes possible the comparison of amplifiers using different magnetic materials by relating small-signal gain and output waveform to measurable properties of the material.     

A magnetic sense amplifier

A new mode of operation of a balanced magnetic circuit is described. With this new mode of operation, which utilizes pulsed current excitation, the detection sensitivity of the magnetic modulator circuit is combined with the high-speed amplification of parametric buildup. This combination permits detection of low-level current pulses applied during a specified time interval of the excitation sequence and provides subsequent amplification of the detected signal. Matched square-loop toroids are used. Signal currents which are a small fraction of the coercive MMF have been successfully detected. The limit of detection sensitivity depends upon the matching of the two cores. The parametric buildup has been made to occur for pump cycle times of 30 μs to 120 μs, depending upon the magnetic material used. The signal information is retained when the pulse excitation sequence is interrupted during buildup because the signal information is stored as a flux unbalance in the two cores during the time interval between excitation pulses. The use of this circuit mode as a sense amplifier for the detection and amplification of sense winding currents in magnetic memories is suggested.     

High Tc superconducting quick responsenonlinear inductances and magnetic modulators

Remarkable nonlinear inductances due to the soft magnetic BH hysteresis characteristics are obtained for YBa₂Cu₃O_7-x disk-shaped cores at 77 K which are tightly wound with polyester-coated copper coils. The inductance changes from nearly zero due to the Meissner effect to that of an equivalent coreless coil as a result of the flux penetration effect due to increasing the exciting current or the applied external magnetic field. Values of inductances are almost constant from low frequency to at least 20 MHz, indicating that the high-T_c superconductor is a fast-response nonlinear inductor material. Fast-response magnetic modulators use one toroidal core or one pair of disk cores with a carrier frequency of more than 10 MHz and a signal frequency of 0 to 500 kHz     

High-resolution of rotary encoder analog quadrature signals

The paper describes a software technique to provide high-resolution absolute angular measurements from the analog quadrature signals of a rotary encoder. The method uses digitized samples of the sinusoidal quadrature signals and the output of a divide-by-four counter circuit. Dynamic measurements on an external trigger signal are possible allowing instantaneous up-to-date angular readings even at high speed. The resolution and hysteresis errors are only dependent on the encoder itself and the bandwidth and resolution of the sampling circuitry. The scheme allows up to 135 degrees of counter hysteresis and delay without loss of precision, thus also affording excellent noise immunity. The theoretical resolution for a 12-bit digital conversion of the analog signals is 1/3360 of a pitch. Experimental results on an encoder built into a laser-tracking measurement system and using 81000 pitches show a unidirectional precision of 0.3 arcsec (rms), a mean bidirectional hysteresis of about 1 arcsec and a worst case variation for a stationary encoder shaft of 0.06 arcsec     

A system for measuring magnetic core noise as a function of themagnetization level

The problem of magnetic core noise is considered in terms of non-repeatability of the hysteresis loop trace for any repetition of the magnetization process. The examination condition is that the effect of eddy currents is reduced to as low a level as possible. Based on such premises, this paper presents a system which periodically extracts the fluctuation voltage, induced at an arbitrary but specified point of the impressed magnetic field, as an instantaneous value. The minimum extraction interval is mainly determined by the integration time of the digital voltmeter used to measure the voltage and by the time required for transferring the extracted data to a personal computer. Therefore, the upper limit of the repetition frequency for the magnetization is restricted to less than 1 Hz. The serially extracted time data is dealt with in a statistical manner and is arranged in order as a magnitude distribution. Two kinds of cores are tested, one is a Fe-Ni-based amorphous core and the other a supermalloy. The results reveal that each core has distinctive noise features     

Effect of magnetic relaxation times on electromagnetic pulseshielding

The penetration of an electromagnetic pulse (EMP) through a ferromagnetic conducting thin film is investigated for the case in which the magnetization of the material has a characteristic time delay τ. Both saturation and hysteresis effects of he magnetization are considered and the susceptibility is defined in the nonlinear region as dM/dh. It is found that the response time τ has a significant effect on the shielding factor with optimum shielding when τ is on the order of twice the rise time of the pulse     

A Digital Interpolation Technique in Time Measurement

The problem of measuring a time interval using a crystal oscillator as a time base is discussed. A statistical analysis is made of the free-running oscillator and gated counter when the time interval to be measured is repetitive. Using the equivalent circuit of a quartz crystal, the difficulties involved in using a pulsed crystal oscillator as a time base are investigated. A method is described to measure, at a random instant, the instantaneous phase of a free-running oscillator and use this information as the last significant figure in a time interval or pulse delay method. The method consists of sensing the coincidence between oppositely-traveling pulses on a delay line. A digital-delay generator was constructed using this technique. The accuracy of the delay was measured as ±0.01 us ±crystal time-base accuracy. The construction and testing of this device is discussed.     

Viscosity-based magnetodynamic model of soft magnetic materials

A time-stepping method based on the concept of magnetic viscosity developed to reproduce the excess loss in electrical steel is proposed. A numerical scheme for simultaneous solution of Maxwell equations and equations describing the magnetic viscosity has been developed. The method is suitable for describing arbitrary magnetization regimes such as waveforms associated with pulsewidth modulation (PWM) voltage excitation, and the model differential equations can be conveniently combined with equations of an external electric circuit. The accuracy of the proposed dynamic model is shown using three nonoriented electrical steel as examples. Fitting of the magnetic viscosity parameters for one sinusoidal flux regime enables dynamic hysteresis loops and losses to be predicted with high accuracy over a wide range of frequencies and amplitudes of sinusoidal or nonsinusoidal flux densities.     

Variation of the instantaneous luminous flux of fluorescent lamps fed by dimmable electronic ballasts with frequency control

Effects of hysteresis and inertial processes on the instantaneous luminous flux of fluorescent lamps (FLs) are experimentally investigated, which are fed by frequency controlled, dimmable, electronic ballasts. Other phenomena are also examined, such as the time displacement between the light ripple and the waveform of the electrical power of the lamp, the 'modulation' of the instantaneous luminous flux waveform and generally, the behaviour of the lamp at varying high frequency (HF) levels. For a typical FL, fed by dimmable electronic ballast with frequency control, inertial processes are reduced, as the operating frequency of the lamp decreases. The time displacement between the instantaneous luminous flux and the lamp power has maximal and minimal as frequency varies. As frequency of the FL increases, the diffusion of the metastable states of the Hg atoms is enhanced and the 'modulation' of the instantaneous luminous flux decreases. The hysteresis and the looping of lamp's voltage-current and luminous flux- current characteristics at various frequency levels indicate that it is necessary to add an inductance and a capacitance to the equivalent electrical circuit of a FL at HFs.     

Self-consistently computed magnetization patterns in thin magnetic recording media

A model involving head motion is given for self-consistently computing magnetic recording medium magnetization patterns. The reduction in demagnetizing field due to the presence of the high-permeability head structure is included, as is record head removal, read head replacement, and computation of the readback voltage. The model is capable of handling an arbitrary record current waveform. Optimum record-current amplitude for nonreturn to zero (NRZ) digital recording is first determined, and then single-, double-, and quadruple-transition computations are performed using two different values of hysteresis loop squarenessM_{r}/M_{s}and both linear and exponential current reversals. Results are primarily for the Karlquist fringe field, but the recording properties of a head exhibiting regions in which the fringe field reverses sign are also briefly investigated.     

Use of a voltage follower to ensure sinusoidal flux in a core

A circuit employing a voltage follower is given for obtaining a sinusoidal flux in a ferromagnetic core. The amplifier just supplies the copper loss of the exciting winding.     

Propagation of reversible magnetization changes along ferromagnetic amorphous ribbons

Local reversible magnetization changes are produced in a region of a long ferromagnetic amorphous ribbon, and their amplitude decay versus the distance from this region is measured. The amplitude decay is analyzed as a function of the reversible permeability on as-cast and annealed ribbons of various widths and thickness at different points of the hysteresis loop. The results are discussed on the basis of the theoretical flux conduction of a magnetically homogeneous cylindrical sample. The results agree with the theoretical model of the magnetic flux conduction on homogeneous materials only for low values of the reversible permeability. The larger deviation, occurring at high values of permeability, are ascribed to both the sample shape and the nonhomogeneous magnetic structure due to magnetic domains.     

Viscous flux motion in anisotropic magnetic superconductors

Magnetic field penetrates in the form of flux lines or vortex thread into type-II magnetic superconductors (MSC) and induces magnetization of magnetic subsystem over a distance of an order of the London penetration depth surrounding the normal cores. When a flux line moves by, surrounding magnetization moves as a whole through the sample and a free motion of vortices is subjected to magnetic viscous drag, giving rise to dissipation. The flux flow resistance in the mixed state of anisotropic MSC has been studied on the basis of the London theory. Expressions for the dissipation and viscosity coefficient associated with the change of the magnetic subsystem as a vortex moves about are derived.     

Single-pulse time-resolved comparative study on the performance of a master-oscillator,power-amplifier copper-vapor-laser system with generalized diffraction-filtered and unstable resonators as master oscillators

We present results of comparative time-resolved coherence studies on a single pulse from amaster oscillator power amplifier (MOPA) copper vapor laser with generalized diffraction-filtered and unstable resonators as master oscillators. It is shown that, unlike the conventionally used unstable-resonator MOPA reported in literature, the coherence of a generalized diffraction-filtered resonator MOPA pulse is fairly independent of the delay between the oscillator and the amplifier. It also remains constant throughout the pulse, with the result that the flux is constant over a large range of the delay.     

Magnetic core model

The paper presents a nonlinear electric circuit to describe the behaviour of magnetic cores in low-frequency applications. A method of hysteresis modelling is proposed, which is able to reproduce minor loops and remanent flux. Classic eddy-current losses and anomalous losses are represented by a linear resistor and a non linear resistor, respectively. The obtained results are compared with those calculated by the models of Hodgdon and Preisach. Comparisons with experimental results are also accomplished. This model is useful for transformer transient phenomena studies, such as inrush currents and ferroresonance     

Effect of various pulse wave forms for pulse-type magnetic flux pump

The excitation current of magnetic pole windings in magnetic flux pump needs to be generated by a control system. In this paper, the control system of pulse-type high temperature superconducting magnetic flux pump is discussed in detail. The control system consists of a control circuit and a drive circuit. A direct current power supply is the unique power supply of the drive circuit. The control circuit is powered by a computer through a USB interface of the computer. The control circuit receives commands from the computer and controls the drive circuit to generate different pulse waves. Each pulse wave generates a unique pulse-type traveling magnetic field and will pump magnetic flux into the superconducting loop. Experiments have been performed to examine the pumping effect of different pulse waves on both MgB₂ and Bi-2223 superconducting loops using the proposed control system, and the best pulse wave has been found. The experimental results show that the magnetic flux pump can compensate current decay up to 32.5 A for MgB₂ loop and 129 A for Bi-2223 loop. It indicates that the control system of the pulse-type magnetic flux pump is effective and feasible.     

Eddy current loss in saturated solid magnetic plates, rods, and conductors

Included in this paper is a procedure which utilizes the digital computer to solve eddy current loss problems when the magnetization process extends into the nonlinear region of the magnetization curve. The values of permeability used in the equations are obtained from the actual magnetization curve, thus eliminating the approximations employed in most previous investigations. The nonlinear partial differential equations are replaced by finite difference equations and solved by numerical methods on an IBM 7070 digital computer. The investigation covers cases of both rectangular plates and cylindrical rods. For the cylindrical rods, cases involving piecewise homogeneous material as well as cases involving homogeneous material are considered. The material is said to be of a homogeneous nature, as the term is used here, when it satisfies the requirements that 1) resistivity be constant throughout the material; and 2) flux density and magnetic intensity be related by the same magnetization curve throughout the material. A cylindrical rod, composed of two concentric cylinders of different magnetic and electrical properties, is the piecewise homogeneous case covered in the present paper. Throughout the investigation, it is assumed that flux density and magnetic intensity are related by a single valued curve; hence, hysteresis effects are neglected.     

磁流变液减振器的磁路设计方法研究

针对传统的磁流变减振器磁场利用率不高的问题,提出了一种基于多级径向流动模式的磁流变减振器。以磁流变液作为控制介质,研究其流变学特性与磁化特性;选择相应的软磁材料,利用多项式描述其磁化特性,并辨识相应的参数。根据动态磁路设计理论,建立磁路分析模型,确定工作间隙内磁感应强度与励磁线圈激励电流的理论关系。为了验证理论推导的正确性,利用有限元分析软件对阻尼调节器内的磁路进行仿真,并按照轨道车辆抗蛇行减振器的技术要求,设计制作了基于多级径向流动模式的磁流变减振器,利用型号为A1322ELHLT-T3的霍尔传感器对其工作间隙的磁感应强度进行检测,与理论结果进行对比分析。     

Effects of relaxation in levitating superconductors

The effect of the magnetic flux creep on the levitation stability of high-temperature superconductors was studied. It was shown experimentally that under a unipolar magnetization the levitation force decreased at a logarithmic velocity characteristic of the creep process. If the current structure was bi- or multi-polar one, which was formed in a sample exposed to a reversing external magnetic field, the force remained unchanged during a certain period of time. The theory of relaxation of magnetization and force for a partial and full penetration of the critical state was considered. It was shown that relaxation decelerated sharply if the region with a current producing the main magnetization was far from the superconductor surface. A concept of an open and internal magnetic relaxation was introduced. The time of the internal relaxation for different reverse depths was estimated. The calculated values approached the experimental values of the levitation stabilization time.     

Allowing for hysteresis in the calculation of fields in the elements of accelerator magnetic systems

Iron magnetic circuit residual magnetization may contribute as much as several Gs to the magnetic field in charged-particle accelerators. This contribution depends on the magnetization “history.” It is not taken into account in most of the existing software that uses the main magnetization curve. Therefore, an error in field calculations usually exceeds 1%, which is unacceptable for accelerators. In this article, a simple phenomenological magnetic-hysteresis model that is suitable for numerical computations is suggested. Approximations based on the proposed model are compared to the results of measurements on partial hysteresis cycles in a steel ring.