This article presents a new method to synthesize the Cauer-equivalent circuit for inductors that can represent the hysteresis, eddy current, anomalous core losses, dc and ac winding losses as well as inductance. Only the measurement of inductor loss under the sinusoidal excitation is required to synthesize the SPICE loss model. The proposed circuit model can be used to evaluate the loss under arbitrary voltage/current excitations. In the proposed approach, the measured loss is subdivided into the ac and hysteresis losses. Then, the Cauer-equivalent circuit for SPICE simulation is synthesized from the loss model. It is shown that the losses evaluated by the proposed model are in good agreement with the measured results under the condition of the sinusoidal and triangular cases with and without dc bias current.

As today's small portable electronics (smartphones, tablets, e-readers, etc.) becomes lighter, thinner, quicker, and smarter, the voltage regulator for the processor is expected to be efficient, miniaturized, integrated, and placed closer to the processor. In this paper, a concept of a very high frequency [tens of megahertz (MHz)] three-dimensional integrated voltage regulator (IVR) for small portable electronics is proposed. The magnetic characterization technique at tens of MHz is investigated, and the issues of and solutions for permeability and loss measurement are demonstrated. The LTCC and NEC flake materials are characterized and compared for the IVR inductor development. Both single-phase and five-phase integrated inductors are designed, fabricated, and experimentally tested at 20 MHz, featuring a simple single-via winding structure, small size, ultralow profile, ultralow DC resistance (DCR), high current-handling ability, air-gap-free magnetics, multiphase integration within one magnetic core, and lateral nonuniform flux distribution.

The volume compressibility of natural oligoclase (Na0.86K0.02Ca0.12Mg0.01(Fe0.01Al1.12Si2.87O8)) was investigated by in situ powder synchrotron X-ray diffraction (XRD) methods at pressure up to 27 GPa, and the equations of state (EoS) of the oligoclase were obtained. The experimental data indicate that the oligoclase specimen underwent triclinic to monoclinic phase transition (P (1) over bar to C2) at about 3. 5 GPa and a further phase transition from C2 to C2/m in monoclinic symmetry at about 10 GPa with increasing pressure. The bulk modulus of the triclinic phase was calculated to be K-0 =73. 8 GPa, and those of monoclinic phases with C2 symmetry and C2/m symmetry to be K-(C2) =124 GPa and K-(C2/m) = 272 GPa, respectively. The stiffness of the T-O-T angle, the strength of the M-O bond and bending of Si-O-Al angle are as a function of the chemical compositions of feldspars. The substitution of mingled ions for main ions in the crystal structure of the oligoclase modified T-O-T angle and the strength of the M-O bonds, resulting in variation of high pressure behavior of the oligoclase. Unit cell compression of triclinic phase oligoclase is obviously anisotropic. The results indicate that oligoclase may probably contribute to the deep recycle of alkali and alkaline-earth elements in the cool subduction zone.

As an essential part in a power converter, the magnetic cores and their design play an important role in achieving high efficiency and high power density. Accurate measurement of the core loss is important to their optimization. To improve the measurement accuracy (especially at high frequencies), previous methods proposed to cancel the reactive voltage of the testing core by using a cancellation capacitor or inductor. However, the value of the cancellation component is critical, and a small variation can induce a big measurement error, so extra effort is required to fine-tune the cancellation component value, which is a very time-consuming process and makes the standardization of the measurement instrument almost impossible. This paper presents a new measurement method with a partial cancellation concept that enables accurate core loss measurement for arbitrary wave excitation without the requirement to fine-tune the cancellation component value. The proposed method is experimentally verified up to 10 MHz.

As today's small portable devices (smartphones, tablets, etc.) becomes lighter, thinner, quicker, and smarter, the voltage regulator for the processor is expected to be efficient, miniaturized, integrated, and placed closer to the processor. In this paper, a concept of very high frequency (tens of MHz) 3D integrated voltage regulator for small portable devices is proposed. Both single-phase and 5-phase integrated inductor with NEC flake magnetic material is designed, fabricated and experimentally tested at 20MHz, featuring simple single-via winding structure, small size, ultra-low profile, ultra-low DCR, air-gap-free magnetic core, and lateral non-uniform flux.

To efficiently power multi-core processors in today's computing devices, integrated voltage regulator (IVR) shows significant energy saving ability by dynamic voltage and frequency scaling. One key aspect in developing IVR is to design power inductors with small size and small loss at very high frequency. However, the challenge in very high frequency magnetic characterization is a major obstacle to accurately design and test the IVR inductors. In this work, the magnetic characterization technique at tens of MHz is investigated, and the issue and solution in permeability and loss measurement are demonstrated. The LTCC and NEC flake materials are characterized and compared at very high frequency for IVR inductor design.

The alloy flake composite magnetic material has been justified to be compatible with the conventional PCB manufacturing process. By embedding the layerwise core into multilayer PCB, a single-phase 3D integrated POL module achieves 700W/in3 power density and more than 85% efficiency. More important, the application of standard PCB process reduces the cost for manufacturing such integrated modules due to the easy automation and low temperature process. This paper tries to extend the same technology to multiphase POL module with coupled inductor. Combining the advanced control strategy, the high density and cost-effective two-phase POL modules are demonstrated for laptop VR application. The old low profile coupled inductor structure is modified slightly to improve its transient response. The air slots are added to reduce the transient inductance and enhance the coupling at light load condition. The non-linear inductance of the coupled inductor can be well controlled by using different slot structures. With the proposed coupled inductor structure, both low profile design and fast transient speed can be realized simultaneously.

The 3-Dimensional (3D) integrated non-uniform flux inductor has shown good performance in achieving high power density and high efficiency in Point of Load (POL) module design. In this work, both single-phase and two-phase coupled non-uniform flux inductors are designed to build an 18A POL module with a QFN package. The non-uniform flux inductor's unique property of varying core loss at different load conditions is analyzed, and the two-phase coupled inductor design that considers both efficiency and dynamics is demonstrated. The module evaluation shows improvement in efficiency and power density in comparison to conventional design.

The planar inductor with lateral flux pattern has been successfully demonstrated as a substrate for the high density 3D integrated point-of-load (POL) module. By decoupling the flux distribution from the thickness of the core, both an ultrathin core structure and a high power density can be achieved simultaneously. However, the flux distribution in the lateral flux core is very non-uniform, which is totally against the conventional sense of the inductor design, namely the flux should be as uniform as possible. This paper reveals the DC flux and AC flux counterbalance phenomenon, by which the AC flux and core loss in the saturated core are essentially limited. The comparison between the core with variable flux and the core with relatively constant flux is presented, based on a specific high current POL application. The inductance density and the performance factor are proposed as the criteria to evaluate the utilization of the core for different magnetic structures. The variable flux core with multiple DC bias safely extended the operating points into saturation region, which gives better utilization of the core. The FEA simulation and measurement also prove that the core temperature is almost uniform for this planar core with variable flux, despite of 2∼3 times difference in core loss density distribution. Because of the better thermal management capability, the planar core can be pushed to higher core loss density level than the core with relatively uniform flux, to realize lower total core loss and smaller core volume. In addition, the planar core saves more core loss at light load, due to the AC flux and core loss density redistributions.

In an effort to find a magnetic material for making low-loss magnetic components for high-power-density converters, we investigated the magnetic core-loss characteristics of a commercial NiCuZn ferrite (LSF 50) at 5 MHz as a function of the sintering temperature of the ferrite powder. The ferrite powder was compacted into toroid cores and then sintered at 850°C, 900°C, 950°C, 1000°C, and 1050°C for 2 h. The sintered densities of the cores increased at higher sintering temperatures. The magnetic properties of the sintered cores—complex permeability and core-loss density—were measured. We found that both the real and imaginary parts of the relative permeability increased with sintering temperature. The core-loss results at 5 MHz showed that the cores sintered at 950°C and 1000°C had the lowest core-loss densities, being two to three times lower than that of a commercial NiZn ferrite (4F1) core. Microstructures of the sintered cores were examined by scanning electron microscopy; the grains grew significantly at higher sintering temperatures.

All electric devices are built to operate with a certain type and amount of electrical energy, but this is often not the same type or amount of electrical energy that comes out of the outlet in your wall. Power converters modify electrical energy from the outlet to a useable current, voltage, and frequency for an electronic device. Power stations also use power converters on a larger scale to modify electrical energy so it can be efficiently transmitted. Today’s power converters are inefficient because they are based on decades-old technologies and rely on expensive, bulky, and failure-prone components. Within the next 20 years, 80% of the electricity used in the U.S. will flow through these devices, so there is a critical need to improve their power density and efficiency. The Center for Power Electronics Systems (CPES) at Virginia Tech is finding ways to save real estate on a computer’s motherboard that could be used for other critical functions. Every computer processor today contains a voltage regulator that automatically maintains a constant level of electricity entering the device. The current voltage regulator solution is embedded in the mother board employing discrete components, thus occupying a significant portion of the valuable motherboard space. In this project CPES successfully developed a voltage regulator that uses semiconductors made of gallium nitride and high-frequency soft magnetic material. These materials are integrated on a small, three-dimensional (3D) chip that can handle same amount power of traditional voltage regulators with 1/10 of its size and with improved efficiency. The proposed power supplies on a chip (PSOC) frees up to 90% of the motherboard space occupied by current voltage regulators. With the ever increasing demand of size/weight reduction and functionality improvement of all forms of portable battery operated electronics equipment and the trend of increasing use of cloud computing, the proposed PSOC will have profound impact in future generations of IT equipment.

The high power density Point-of-Load (POL) converter with high operating frequency has gained increasing interest in the growing market for portable communications and handheld electronics. Low profile magnetic components and associated integration techniques are desired for design and fabrication of highly integrated POL converters. Low fired ferrite tapes for multilayer chip inductors and high frequency applications have been developed and used in hybrid integration of power modules. The inductor made of multilayer ferrites can be fabricated as the magnetic substrate in an integrated POL converter with active components on top. The developed 3-D integration approach is applied to reduce footprint and increase power density for the high frequency POL converter. The current work reports the characterization of magnetic properties, microstructures, and chemical compositions of commercially available low-fire Ni-Cu-Zn ferrite materials (ESL 40010, 40011, and 40012) and their mixed laminates. Permeability and core loss density are measured on toroidal shaped samples sintered at 885 °C for 3.5 hrs. Because high DC current is always applied to bias the core for the inductors used in high frequency POL converters, the influence of superimposed DC bias on the magnetic properties of ferrite laminates has also been evaluated. The microstructures and chemical compositions of low temperature sintered ferrite laminates are observed and analyzed in order to explain the difference of magnetic properties among samples. The mixed laminate with alternating layers of ESL 40010 and ESL 40012 in 1:1 ratio presents the highest permeability and the lowest core loss density among all examined samples when DC bias is above 1000 A/m. Finally, a 12 V to 1.2 V, 15 A, high frequency (1.5–5 MHz) integrated POL converter with laminated ferrite inductor has been fabricated and demonstrated working at high efficiency with power density as high as 1000 W/in3.

The phase analysis of sodium azide (NaN3) has been investigated by in situ synchrotron X-ray diffraction measurements in a diamond anvil cell up to 52.0 GPa at room temperature. Three pressure-induced phase transitions were observed. The phase transition pressures were determined to be 0.3, 17.3, and 28.7 GPa verified by three different pressure transmitting media. The first high pressure phase, α-NaN3 (0.3 ∼ 17.3 GPa), was identified to be monoclinic with a C2/m space group. The β-NaN3 to α-NaN3 transition is a second-order phase transition, accompanied by the shearing of the Na-layers and the tilting of the azide chains. The second high pressure phase, γ-NaN3 (18.4 ∼ 28.7 GPa), has a lower symmetry than the α-NaN3. A further phase transition of γ-NaN3 to δ-NaN3 at 28.7 GPa was observed.

Potassium azide was investigated by Raman scattering spectroscopy up to a pressure of 55.0 GPa by use of diamond anvil cell at room temperature. A pressure-induced reversible phase transition was revealed. The onset of the phase transition was characterized by the hardening of a previously soft lattice mode at 13.6 GPa. This transition is considered a structural phase transition. Compression induces a symmetry reduction, which is indicated by the splitting of the librational modes, the development of infrared active vibrational modes, and the appearance of other new modes in the external mode region. The new high-pressure phase, with azide ions still in a molecular state, can be preserved down to 1.2 GPa. The Grüneisen parameters for the parent phase were calculated.

The high pressure properties of icosahedral boron arsenide (B12As2) were studied by in situ X-ray diffraction measurements at pressures up to 25.5GPa at room temperature. B12As2 retains its rhombohedral structure; no phase transition was observed in the pressure range. The bulk modulus was determined to be 216GPa with the pressure derivative 2.2. Anisotropy was observed in the compressibility of B12As2—c-axis was 16.2% more compressible than a-axis. The boron icosahedron plays a dominant role in the compressibility of boron-rich compounds.

Silver azide (AgN3) was compressed up to 51.3 GPa. The results reveal a reversible second-order orthorhombic-to-tetragonal phase transformation starting from ambient pressure and completing at 2.7 GPa. The phase transition is accompanied by a proximity of cell parameters a and b, a 3° rotation of azide anions, and a change of coordination number from 4-4 (four short, four long) to eight fold. The crystal structure of the high pressure phase is determined to be in I4/mcm space group, with Ag at 4a, N1 at 4d, and N2 at 8h Wyckoff positions. Both of the two phases have anisotropic compressibility: the orthorhombic phase exhibits an anomalous expansion under compression along a-axis and is more compressive along b-axis than c-axis; the tetragonal phase is more compressive along the interlayer direction than the intralayer directions. The bulk moduli of the orthorhombic and tetragonal phases are determined to be KOT = 39 ± 5 GPa with KOT’ = 10 ± 7 and KOT = 57 ± 2 GPa with KOT’ = 6.6 ± 0.2, respectively.

In situ x-ray diffraction measurements of cesium azide (CsN(3)) were performed at high pressures of up to 55.4 GPa at room temperature. Three phase transitions were revealed as follows: tetragonal (I4/mcm, Phase II) -> monoclinic (C2/m, Phase III) -> monoclinic (P2(1)/m or P2(1), Phase IV) -> triclinic (P1 or P (1) over bar 1, Phase V), at 0.5, 4.4, and 15.4 GPa, respectively. During the II-III phase transition, CsN3 keeps its layered structure and the azide anions rotate obviously. The compressibility of Phase II is dominated by the repulsions between azide anions. The deformation of unit cell is isotropic in Phases II and IV and anisotropic in Phase III. With increasing pressures, the monoclinic angle increases in Phase III and then becomes stable in Phase IV. The bulk moduli of Phases II, III, IV, and V are determined to be 18 +/- 4, 20 +/- 1, 27 +/- 1 and 34 +/- 1 GPa, respectively. The ionic character of alkali azides is found to play a key role in their pressure-induced phase transitions.

Crystal structure and compressibility of potassium azide was investigated by in-situ synchrotron powder X-ray diffraction in a diamond anvil cell at room temperature up to 37.7GPa. In the body-centered tetragonal (bct) phase, an anisotropic compressibility was observed with greater compressibility in the direction perpendicular to the plane containing N3− ions than directions within that plane. The bulk modulus of the bct phase was determined to be 18.6(7)GPa. A pressure-induced phase transition may occur at 15.5GPa.

Phase transition and bulk moduli of bulk and nanocrystalline γ-Fe2O3 were studied using synchrotron X-ray diffraction under high pressure. Contrary to most other nanomaterials, nanocrystalline γ-Fe2O3 begins to transform into α-Fe2O3 at the same pressure as bulk γ-Fe2O3, which is caused by a special structure of γ-Fe2O3, in which there exist vacancies of crystal. It is believed that phase transition starts from a certain site of vacancy because of the stress concentration at vacancy sites. Compared to bulk material, nanocrystalline γ-Fe2O3 has a larger bulk modulus, which is ascribed to the large ratio of surface to volume.