Inductive Head Research Articles

Ultra-efficient localized induction heating by dual-ferrite synchronous magnetic field focusing

Induction heating is widely used in aviation, communication, and new energy fields due to its advantages of non-contact, high-power, and controllable heating depth. However, it is still challenging to achieve high energy utilization efficiency of traditional induction heating, mainly due to the magnetic dispersion effect. Herein, a dual-ferrite synchronous focused (DFSF) induction heating method is first proposed by simultaneously placing ferrites inside and outside the induction coil. Meanwhile, an electromagnetic-thermal coupling numerical model was also built to predict the magnetic and temperature fields around the DFSF induction heating system. A conventional induction heating head and two DFSF induction heating heads (cone-type DFSF head and pot-type DFSF head) are compared on soldering the high-power devices. The results show a significant enhancement in magnetic flux density (MFD) with the pot-type DFSF head, exhibiting a remarkable 12-fold increase from 0.02 T to 0.24 T compared to the conventional induction head. Additionally, the pot-type DFSF head generates a substantial 22.3-fold surge in energy within the solder joint, escalating from 0.6 J to 13.4 J, surpassing the traditional induction head. Moreover, the influence mechanism of six external ferrite structural parameters on the heating efficiency was analysed to optimize the pot-type DFSF. It is found that the inner diameter of the ferrite tip has the most significant effect, which can induce a remarkable temperature variation of 310 °C. As a result of optimization, the pot-type DFSF demonstrated an impressive surge of 26% in heating efficiency. Finally, the agreement between the numerical and the experimental temperature proves the accuracy of the model, and the solder joint without defect has been achieved through the pot-type DFSF. This work effectively minimizes the magnetic dispersion and increases the energy utilization efficiency for induction heating, providing new approaches for localized soldering of high-performance power electronic devices.

Detecting Magnetic Ink Barcodes With Handheld Magnetoresistive Sensors

Information encoding in barcodes using magnetic-based technology is a unique strategy to read data buried underneath non-transparent surfaces since a direct line-of-sight between the code and the reader is not required. This technology is of particular interest in secure labelling and recyclable packaging applications. However, current magnetic reading heads, such as those employed for magnetic ink character recognition, need to be placed in contact with the magnetic structures, limiting the depths at which the information can be read. This paper describes a strategy to overcome that limitation by replacing the traditional inductive heads with tunnel magnetoresistive (TMR) sensors. Soft-magnetic codes can be printed using conventional LaserJet toners and, by having their magnetisation set with a permanent magnet included in the device, the resulting magnetic field can be read using a TMR sensor. We demonstrate that such a device can read barcodes at depths of at least 1 mm. It can also resolve individual structures as thin as 200 {\mu}m when used in contact.

Compact UV Nitrogen Laser Pumped by a Pulsed Longitudinal Inductive Discharge

The creation of a compact emitter for an inductive nitrogen laser (λ = 337.1 nm) with the active medium pumped by a pulsed inductive longitudinal discharge of the transformer type is reported for the first time. In the inductive laser head created, the lasing energy attains 0.35 mJ and the lasing pulse length is (25 ± 5) ns (FWHM) depending on the cavity Q-factor. The use of a semiconfocal cavity provides for a near-Gaussian beam profile.

A High-Sensitivity MFL Method for Tiny Cracks in Bearing Rings

In order to detect tiny cracks in bearing rings, a high-sensitivity magnetic flux leakage (MFL) method based on magnetic induction head is proposed and investigated in this paper. First, the MFL sensing method based on magnetic induction head is theoretically illustrated. A magnetic core with an open gap is applied to guide leaked magnetic flux into a detection magnetic circuit, where an induction coil is placed to detect the change of the magnetic flux. To obtain an optimal gap width for higher sensitivity, its influence on MFL sensitivity is analyzed by building magnetic circuits. Then, to realize automatic inspection for bearing rings, a U-shape magnetizer is proposed and 3-D numerical simulations are conducted to investigate the signal characteristics of the proposed method and the sensitivity affected by gap width. Furthermore, MFL experiments for bearing rings were performed and it was found that the proposed method has high sensitivity for tiny cracks and when the gap width is approximately equal to the width of the crack, the greatest sensitivity will be obtained. Finally, the automatic MFL testing system for bearing rings is designed and employed in the production line. In-line tests show that the novel MFL system can fulfill the inspection requirement for bearing rings.

Using Film Flux Detectors to Determine Properties of Conducting and Magnetic Objects

The optical images of magnetic fields recorded with flux detectors are provided as well as the distributions of electric voltage U(t) across an inductive magnetic head as it scans a discrete magnetic carrier that contains recordings of residual magnetic fields resulting from a pulsed magnetic field acting upon the magnetic carrier with a test object. Procedures have been developed that make it possible to measure the distributions of magnetic fields and inspect objects made of conducting or magnetic materials, while enhancing the accuracy of measuring conductivity σ, magnetic permeability μ, the homogeneity of distributions of σ and μ, thickness, and the parameters of solidity flaws in these materials.

Computer-assisted methods for finding pulsed magnetic-field distributions near current-conducting objects

Time dependences are given for an electric voltage U(t) that is recorded across an inductive magnetic head when scanning a discontinuous magnetic carrier that has been subjected to pulsed magnetic fields of a linear inductor. The value of U(t) at each point of the carrier is determined by the amplitude of each pulse, the pulse direction, and the sequence of exposures. If a current-conducting object is present, this value also depends on the field pulse rise time. The phenomenon of hysteretic interference of a pulsed magnetic field (HI) is used. Digital images of pulsed magnetic fields, as well as computer-assisted methods for measuring these fields, finding their distributions, and processing observation results are presented.

A Titan exits stage left: Summary of the Waun Ki Hong Festschrift.

On August 15, 2014, at The University of Texas MD Anderson Cancer Center in Houston, Dr. Fadlo Khuri, along with co‐chairs Drs. James Abbruzzese, Patrick Hwu, Roy Herbst, and Scott Lippman, chaired a Festschrift celebrating the lifetime of accomplishments of Dr. Waun Ki Hong. A series of lectures celebrating Dr. Hong's legacy ensued, highlighting his accomplishments in the areas of induction chemotherapy, organ preservation, head and neck biology, carcinogenesis, and chemoprevention, as well as his leadership in the biological interrogation of biomarker‐driven pathways in lung and head and neck cancer and his transformation of the culture of mentorship and multidisciplinary science at The University of Texas MD Anderson Cancer Center.

Toward Wafer Scale Inductive Characterization of Spin-Transfer Torque Critical Current Density of Magnetic Tunnel Junction Stacks

We explore the prospects of wafer scale inductive probing of the critical current density $j^{c0}$ for spin transfer torque switching of a CoFeB/MgO/CoFeB magnetic tunnel junction with varying MgO thickness. From inductive measurements magnetostatic parameters and the effective damping are derived and $j^{c0}$ is calculated based on spin transfer torque equations. The inductive values compare well to the values derived from current induced switching measurements on individual nanopillars. Using a wafer scale inductive probe head could in the future enable wafer probe station based metrology of $j^{c0}$.

Inductive displacement sensors with a notch filter for an active magnetic bearing system.

Active magnetic bearing (AMB) systems support rotating shafts without any physical contact, using electromagnetic forces. Each radial AMB uses two pairs of electromagnets at opposite sides of the rotor. This allows the rotor to float in the air gap, and the machine to operate without frictional losses. In active magnetic suspension, displacement sensors are necessary to detect the radial and axial movement of the suspended object. In a high-speed rotating machine equipped with an AMB, the rotor bending modes may be limited to the operating range. The natural frequencies of the rotor can cause instability. Thus, notch filters are a useful circuit for stabilizing the system. In addition, commercial displacement sensors are sometimes not suitable for AMB design, and cannot filter the noise caused by the natural frequencies of rotor. Hence, implementing displacement sensors based on the AMB structure is necessary to eliminate noises caused by natural frequency disturbances. The displacement sensor must be highly sensitive in the desired working range, and also exhibit a low interference noise, high stability, and low cost. In this study, we used the differential inductive sensor head and lock-in amplifier for synchronous demodulation. In addition, an active low-pass filter and a notch filter were used to eliminate disturbances, which caused by natural frequencies. As a consequence, the inductive displacement sensor achieved satisfactory linearity, high sensitivity, and disturbance elimination. This sensor can be easily produced for AMB applications. A prototype of these displacement sensors was built and tested.

A Research on Automatic Detection Device for the Missing of the Roller Chain's Rollers and Sleeves

The set of automatic detection device for the parts missing of the roller chains rollers and sleeves is based on the displacement transfer theory of the lever mechanism and combined with the integration of PLC control. The levers one end is the detection head close to the roller chain and the other end is the induction head, its support is placed on the base. Sensor puts the induction information into the PLC, and then the PLC make the Synthetic judgment to control the chains drive mechanism to slow down and marking on the places that have missing some parts on time. Its a device has high reliability and high efficiency, which can realize auto-running to replace manual check perfectly.

Towards Wafer Scale Inductive Determination of Magnetostatic and Dynamic Parameters of Magnetic Thin Films and Multilayers

We investigate an inductive probe head suitable for non-invasive characterization of the magnetostatic and dynamic parameters of magnetic thin films and multilayers on the wafer scale. The probe is based on a planar waveguide with rearward high frequency connectors that can be brought in close contact to the wafer surface. Inductive characterization of the magnetic material is carried out by vector network analyzer ferromagnetic resonance. Analysis of the field dispersion of the resonance allows the determination of key material parameters such as the saturation magnetization MS or the effective damping parameter Meff. Three waveguide designs are tested. The broadband frequency response is characterized and the suitability for inductive determination of MS and Meff is compared. Integration of such probes in a wafer prober could in the future allow wafer scale in-line testing of magnetostatic and dynamic key material parameters of magnetic thin films and multilayers.

Magnetic actuators and sensors

Preface. PART I MAGNETICS. 1. Introduction. 1.1 Overview of Magnetic Actuators. 1.2 Overview of Magnetic Sensors. 1.3 Actuators and Sensors in Motion Control Systems. References. 2. Basic Electromagnetics. 2.1 Vectors. 2.1.1 Gradient. 2.1.2 Divergence. 2.1.3 Curl. 2.2 Ampere's Law. 2.3 Magnetic Materials. 2.4 Faraday's Law. 2.5 Potentials. 2.6 Maxwell's Equations. Problems. References. 3. Reluctance Method. 3.1 Simplifying Ampere's Law. 3.2 Applications. 3.3 Fringing Flux. 3.4 Complex Reluctance. 3.5 Limitations. Problems. References. 4. Finite-Element Method. 4.1 Energy Conservation and Functional Minimization. 4.2 Triangular Elements for Magnetostatics. 4.3 Matrix Equation. 4.4 Finite-Element Models. Problems. References. 5. Magnetic Force. 5.1 Magnetic Flux Line Plots. 5.2 Magnetic Energy. 5.3 Magnetic Force on Steel. 5.4 Magnetic Pressure on Steel. 5.5 Lorentz Force. 5.6 Permanent Magnets. 5.7 Magnetic Torque. Problems. References. 6. Other Magnetic Performance Parameters. 6.1 Magnetic Flux and Flux Linkage. 6.1.1 Definition and Evaluation. 6.1.2 Relation to Force and Other Parameters. 6.2 Inductance. 6.2.1 Definition and Evaluation. 6.2.2 Relation to Force and Other Parameters. 6.3 Capacitance. 6.3.1 Definition. 6.3.2 Relation to Energy and Force. 6.4 Impedance. Problems. References. PART II ACTUATORS. 7. Magnetic Actuators Operated by Direct Current. 7.1 Solenoid Actuators. 7.1.1 Clapper Armature. 7.1.2 Plunger Armature. 7.2 Voice Coil Actuators. 7.3 Other Actuators Using Coils and Permanent Magnets. 7.4 Proportional Actuators. 7.5 Rotary Actuators. Problems. References. 8. Magnetic Actuators Operated by Alternating Current. 8.1 Skin Depth. 8.2 Power Losses in Steel. 8.2.1 Laminated Steel. 8.2.2 Equivalent Circuit. 8.2.3 Solid Steel. 8.3 Force Pulsations. 8.3.1 Force with Single AC Coil. 8.3.2 Force with Added Shading Coil. 8.4 Cuts In Steel. 8.4.1 Special Finite-Element Formulation. 8.4.2 Loss and Reluctance Computations. Problems. References. 9. Magnetic Actuator Transient Operation. 9.1 Basic Timeline. 9.2 Size, Force, and Acceleration. 9.3 Linear Magnetic Diffusion Times. 9.3.1 Steel Slab Turnon and Turnoff. 9.3.2 Steel Cylinder. 9.4 Nonlinear Magnetic Diffusion Time. 9.4.1 Simple Equation for Steel Slab with B-H. 9.4.2 Transient Finite-Element Computations for Steel Slabs. 9.4.3 Simple Equation for Steel Cylinder with B-H. 9.4.4 Transient Finite-Element Computations for Steel Cylinders. Problems. References. PART III SENSORS. 10. Hall Effect and Magnetoresistive Sensors. 10.1 Simple Hall Voltage Equation. 10.2 Hall Effect Conductivity Tensor. 10.3 Finite-Element Computation of Hall Fields. 10.3.1 Unsymmetric Matrix Equation. 10.3.2 2D Results. 10.3.3 3D Results. 10.4 Toothed Wheel Hall Sensors for Position. 10.5 Magnetoresistance. 10.5.1 Classical Magnetoresistance. 10.5.2 Giant Magnetoresistance. 10.5.3 Newest Forms of Magnetoresistance. 10.6 Magnetoresistive Heads for Hard-Disk Drives. Problems. References. 11. Other Magnetic Sensors. 11.1 Speed Sensors Based on Faraday's Law. 11.2 Inductive Recording Heads. 11.3 Proximity Sensors Using Impedance. 11.3.1 Stationary Eddy Current Sensors. 11.3.2 Moving Eddy Current Sensors. 11.4 Linear Variable Differential Transformers. 11.5 Magnetostrictive Sensors. 11.6 Flux Gate Sensors. 11.7 Magnetometers and Motes. Problems. References. PART IV SYSTEMS. 12. Coil Design and Temperature Calculations. 12.1 Wire Size Determination for DC Currents. 12.2 Coil Time Constant and Impedance. 12.3 Skin Effects and Proximity Effects for AC Currents. 12.4 Finite-Element Computations of Temperatures. 12.4.1 Thermal Conduction. 12.4.2 Thermal Convection and Thermal Radiation. 12.4.3 AC Magnetic Device Cooled by Conduction, Convection, and Radiation. Problems. References. 13. Electromagnetic Compatibility. 13.1 Signal-to-Noise Ratio. 13.2 Shields and Apertures. 13.3 Test Chambers. 13.3.1 TEM Transmission Lines. 13.3.2 TEM Cells. 13.3.3 Triplate Cells. Problems. References. 14. Electromechanical Finite Elements. 14.1 Electromagnetic Finite-Element Matrix Equation. 14.2 0D and 1D Finite Elements for Coupling Electric Circuits. 14.3 Structural Finite-Element Matrix Equation. 14.4 Force and Motion Computation by Timestepping. 14.5 Typical Electromechanical Applications. 14.5.1 DC Solenoid with Slowly Rising Input Current. 14.5.2 DC Solenoid with Step Input Voltage. 14.5.3 AC Clapper Solenoid Motion and Stress. 14.5.4 Transformers with Switches or Sensors. Problems. References. 15. Electromechanical Analysis Using Systems Models. 15.1 Electric Circuit Models of Magnetic Devices. 15.1.1 Electric Circuit Software Including SPICE. 15.1.2 Simple LR Circuits. 15.1.3 Tables of Nonlinear Flux Linkage and Force. 15.1.4 Analogies for Rigid Armature Motion. 15.1.5 Maxwell SPICE Model of Bessho Actuator. 15.1.6 Simplorer Model of Bessho Actuator. 15.2 VHDL-AMS/Simplorer Models. 15.2.1 VHDL-AMS Standard IEEE Language. 15.2.2 Model of Solenoid Actuator. 15.3 MATLAB/Simulink Models. 15.3.1 Software. 15.3.2 MATLAB Model of Voice Coil Actuator. 15.4 Including Eddy Current Diffusion Using a Resistor. 15.4.1 Resistor for Planar Devices. 15.4.2 Resistor for Axisymmetric Devices. Problems. References. 16. Coupled Electrohydraulic Analysis Using Systems Models. 16.1 Comparing Hydraulics and Magnetics. 16.2 Hydraulic Basics and Electrical Analogies. 16.3 Modeling Hydraulic Circuits in SPICE. 16.4 Electrohydraulic Models in SPICE and Simplorer. 16.5 Hydraulic Valves and Cylinders in Systems Models. 16.5.1 Valves and Cylinders. 16.5.2 Use in SPICE Systems Models. 16.6 Magnetic Diffusion Resistor in Electrohydraulic Models. Problems. References. Appendix: Symbols, Dimensions, and Units. Index.

Microfluidic MEMS-based light modulator using magnetic fluid suitable for flat panel display applications

A new microfluidic MEMS-based light modulator using magnetic fluid is introduced. The device has a planar structure that makes it suitable for being produced with conventional thin-film processes and for being used in flat-panel displays (FPDs). The optical reflectance from the device is modulated by applying an electric current into an electrode. The magnetic field produced by the current exerts a magnetic force on the magnetic fluid and drives it to cover the cell surface. The surface tension of the fluid provides a restoring force when the field is reduced. A permalloy based thin-film process developed for the manufacturing of inductive head for magnetic data storage devices was used for the device fabrication. The actuation of the fluid is completed in about 12 ms for both thin-to-thick and thick-to-thin fluid film switching by magnetic forces and surface tension forces, respectively. It was observed that the switching speed was almost independent of the driving current, and no considerable thermal effect has been observed when driven by a current up to 100 mA.

Technique to obtain head-medium magnetic spacing in a disk drive

A technique is presented to determine the head-medium magnetic spacing utilizing square wave recording spectral measurements. Because spectral analysis does not give a unique separation of the spacing and the transition parameter, the transition parameter is first determined at low densities using time domain transition noise analysis. The total noise power versus density is utilized to determine the transition parameter variation with density due to record process nonlinearities. Spectral fitting gives both the spacing and the giant magnetoresistance gap length. It is shown this technique is robust by analysis of data on perpendicular media with both inductive and single pole heads.

Reduction of field through read element using shorter read shield

Values for field through the read element (Hread) in longitudinal and perpendicular magnetic recording are compared with the aid of three-dimensional (3d) finite element models. We show that the Hread of the single-pole-type head used in perpendicular magnetic recording (PMR) was larger than that of the inductive ring head used in longitudinal magnetic recording (LMR). This is because that the medium for a PMR system includes a soft under layer (SUL). The Hread of PMR is affected by the permeability and thickness of SUL. The characteristic length of the upper and lower shield layers at which the Hread starts to decrease is found to be roughly equal to the length of the return pole. Decreasing the length of the upper and lower shield is shown to be the most practicable and effective way to realize the reduction of Hread.

Correlation of domain pattern and high-frequency response in pole-tip of inductive thin film head

The high frequency response of the soft magnetic pole tip in the thin film inductive head is crucial for the noise analysis of computer hard disk. A micromagnetic model is established in a mesoscopic soft magnetic thin film to analyze the domain pattern as well as the initial permeability in a wide frequency range from 10MHz to 18GHz. The simulated domain patterns in the pole tip, a vortex- and ladder-type, are chosen as the initial conditions for the high-frequency response studies. The scaling law of the permeability is analyzed at different amplitudes of the alternating external magnetic field. It is found that in the ladder-type domains the high frequency response is much better than that in the vortex-type domains, which agrees with experiment. A simplified explanation of the simulation result is discussed based on the analysis of the nonlinear Landau–Liftshitz equation.

Studies of Deep-Submicrometer Ultranarrow-Track Recording by Composite Simulation Models

This paper presents an analysis of the signal and noise in deep-submicrometer ultranarrow-track disk recording by composite simulation models, including the micromagnetics in longitudinal media and giant magnetoresistive (GMR) multilayers and the surface finite-element methods for inductive thin film heads and GMR head shields. The analysis assumes that the linear density of the recording process is in a range of 57 to 1200 kilo-flux changes per inch (kfci) and the width/gap ratio of the write head is between 4 and 2, corresponding to current industry practice. The first to fifth harmonics of all-one signals are found by the simulated spectrum. The signal and noise at different track densities and linear densities are analyzed by the harmonics in the spectrum. The composite heads in the disk recording system with widths 160, 240, and 320 nm are evaluated by the signal-to-noise ratio at a linear density around 1000 kfci.

Superposition in Inductive and Magnetoresistive Readback

This letter demonstrates that the physics of linear readback in various recording-reproducing systems is different from that of communication systems and conventional linear filters, in which superposition is described by the convolution integral. In a linear system of magnetic readback with inductive heads, superposition is described by the correlation (not convolution) between two vector entities-the derivative of media magnetization and the sensitivity function of the readback head. More generally, superposition in all linear magnetic readback with heads of any type is described by the correlation between two scalar entities-the distribution of magnetic charges in the recorded media and the scalar sensitivity function of the readback head with respect to moving charges.

Analysis of Heat Production in Induction Heating Irons

The eddy currents in heating irons induced from ferrite-core induction coils are calculated using a theoretical approach and the results are compared with experimental data. Optimizations of components and materials for constructing the induction head are investigated to develop new type induction heating irons. Formulations in our theory are based on the magneto-resistance calculations. The self- and mutual- inductances are estimated precisely using these magneto-resistances. Induction heating phenomena are analyzed theoretically using the eddy currents. Finally, the heated iron is shown in good agreement of parameters.

The Effect of Phosphazene additives to passivate and stabilize lubricants at the head/disk interface

There have been a number of applications for lubricant additives in the disk drive media area, the first of which was for pseudo-contact recording with inductive heads (tri-pad sliders) in an effort to stabilize the head/disk interface and minimize lube decomposition under hot/wet conditions. A number of additives have been tried which include antioxidants as well as Lewis bases, the latter in an effort to passivate the catalytic activity of the Lewis Acid sites on the slider which results in the decomposition of the perfluoropolyether (PFPE) lubricants such as Z-Dol, AM and Z-Tetraol. In addition to this passivation action of the phosphazene toward catalytic decomposition of the lubricant, it has recently been reported that the use of X-1P (a cyclic phosphazene) also enhances reflow of the lube, increasing the durability of the head disk interface. In this regard there are still a number of unanswered questions that pertain to the mechanism of the interaction of the X-1P with the lubricant and/or carbon to cause this increase in mobility of the lubricant resulting in the enhanced durability. There are numerous technical issues associated with the use of the various additives with the main one being compatibility between the additive and the PFPEs as well as the carbon surfaces on which they are coated. These issues include bonding, phase separation of the components, and the transfer mechanism for the additive to the slider where the passivation is required. In this paper, we will look at the interaction of the X-1P with the carbon overcoat on the media in an effort to try to better understand the mechanism of such an interaction and its effect on the mobility of the lubricant as well as the amount of bonded lube on the disks.