Saibal Roy

A micro electromagnetic generator for vibration energy harvesting

Vibration energy harvesting is receiving a considerable amount of interest as a means for powering wireless sensor nodes. This paper presents a small (component volume 0.1 cm3, practical volume 0.15 cm3) electromagnetic generator utilizing discrete components and optimized for a low ambient vibration level based upon real application data. The generator uses four magnets arranged on an etched cantilever with a wound coil located within the moving magnetic field. Magnet size and coil properties were optimized, with the final device producing 46 µW in a resistive load of 4 k? from just 0.59 m s-2 acceleration levels at its resonant frequency of 52 Hz. A voltage of 428 mVrms was obtained from the generator with a 2300 turn coil which has proved sufficient for subsequent rectification and voltage step-up circuitry. The generator delivers 30% of the power supplied from the environment to useful electrical power in the load. This generator compares very favourably with other demonstrated examples in the literature, both in terms of normalized power density and efficiency.

Self-powered autonomous wireless sensor node using vibration energy harvesting

This paper reports the development and implementation of an energy aware autonomous wireless condition monitoring sensor system (ACMS) powered by ambient vibrations. An electromagnetic (EM) generator has been designed to harvest sufficient energy to power a radio-frequency (RF) linked accelerometer-based sensor system. The ACMS is energy aware and will adjust the measurement/transmit duty cycle according to the available energy; this is typically every 3 s at 0.6 m s?2 rms acceleration and can be as low as 0.2 m s?2 rms with a duty cycle around 12 min. The EM generator has a volume of only 150 mm3 producing an average power of 58 ?W at 0.6m s?2 rms acceleration at a frequency of 52 Hz. In addition, a voltage multiplier circuit is shown to increase the electrical damping compared to a purely resistive load; this allows for an average power of 120 ?W to be generated at 1.7 m s?2 rms acceleration. The ACMS has been successfully demonstrated on an industrial air compressor and an office air conditioning unit, continuously monitoring vibration levels and thereby simulating a typical condition monitoring application

Review of Integrated Magnetics for Power Supply on Chip (PwrSoC)

This paper reviews the current state of power supply technology platforms and highlights future trends and challenges toward realizing fully monolithic power converters. This paper presents a detailed survey of relevant power converter technologies, namely power supply in package and power supply on chip (PwrSoC). The performance of different power converter solutions reported in the literature is benchmarked against existing commercial products. This paper presents a detailed review of integrated magnetics technologies, primarily microinductors, a key component in realizing a monolithic power converter. A detailed review and comparison of different microinductor structures and the magnetic materials used as inductor cores is presented. The deposition techniques for integrating the magnetic materials in the microinductor structures are discussed. This paper proposes the use of two performance metrics or figures of merit in order to compare the dc and ac performance of individual microinductor structures. Finally, the authors discuss future trends, key challenges, and potential solutions in the realization of the “holy grail” of monolithically integrated power supplies (PwrSoC).

Alternating-current electrical properties of graphite, carbon-black and carbon-fiber polymeric composites

Abstract Electrical conductivity measurements of graphite, carbon-black and carbon-fiber polymeric composites reported over a broad frequency range covering from d.c. to 109 Hz are comparatively discussed. The d.c. electrical conductivity data from carbon-black and graphite composites exhibit a conducting additive concentration dependence which can be explained on the basis of percolation theory. In both systems, tunneling conduction among particles appears as the predominant mechanism in the concentration range investigated. A frequency-dependent conductivity is observed which is stronger the lower the additive concentration. A modification of the percolation theory which includes the contribution of finite-size clusters is invoked to explain the frequency dependence of the conductivity. In carbon-fiber composites, the high fiber orientation gives rise to materials with higher electrical conductivity levels than those found for particulate composites. The high anisotropic conductivity additionally exhibits an almost absence of frequency dependence. This is explained by assuming the occurrence of a highly interconnected fiber network with almost an absence of electrical barriers.

Microfabricated inductors for 20 MHz Dc-Dc converters

This paper presents the design and measured results for micro-fabricated inductors suitable for use in high frequency (> 10 MHz), low power (1 -2 W) dc-dc converters. The design has focused on maximizing inductor efficiency for a given converter specification. Inductors in the range of 100 nH to 300 nH have been fabricated and tested. The small signal measurements show a relatively flat inductance profile, with a 10% drop in inductance at 30 MHz. Inductance vs. dc bias current measurements show less than 15% decrease in inductance at 500 mA current. The performance of the micro-inductors have also been compared to a conventional wire-wound inductor in a 20 MHz dc-dc converter. The converter efficiency is shown to be approximately 4% lower when the micro-inductor is used compared to the when the wire- wound inductor is used. The peak efficiency of the micro-inductor in the converter is estimated to be approximately 93%.

Vibration based electromagnetic micropower generator on silicon

This paper discusses the theory, design and simulation of electromagnetic micropower generators with electroplated micromagnets. The power generators are fabricated using standard microelectromechanical system processing techniques. Electromagnetic two-dimensional finite element anlysis simulations are used to determine voltage and power that can be generated from different designs. This paper reports a maximum voltage and power of 55 mV and 70 W for the first design, incorporating microfabricated two-layer Cu coils on a Si paddle vibrating between two sets of oppositely polarized electroplated Co50Pt50 face centered tetragonal phase hard magnets. A peak voltage and power of 950 mV and 85 W are obtained for the second design, which includes electroplated Ni45Fe55 as a soft magnetic layer underneath the hard magnets. The volume of the device is about 30 mm3.

Large scale monodisperse hexagonal arrays of superparamagnetic iron oxides nanodots: a facile block copolymer inclusion method.

Highly dense hexagonal ordered arrays of superparamagnetic iron oxides nanodots are fabricated by a simple and cost-effective route. Spectroscopic, microscopic and magnetic measurements show that the nanodots have uniform size, shape and their placement mimics the original self-assembled block copolymer pattern. The nanodots show good thermal stability and strong adherence to the substrate surface, making them useful for practical device applications.

Thin-Film-Integrated Power Inductor on Si and Its Performance in an 8-MHz Buck Converter

This paper presents a microinductor fabricated on silicon using electrochemical techniques that has high efficiency in a low power dc-dc converter. Small signal measurements show a flat frequency response up to 20 MHz with a self resonant frequency of 130 MHz. The inductance at low frequency is approximately 440 nH with a dc resistance of 0.5 Omega , and a high quality factor of 11.7 at 5.5 MHz. The current handling capability test shows less than 10% decrease in inductance at 500-mA current. The performance of the microinductor has been compared to a conventional chip inductor in a commercially available 8-MHz buck converter. The converter maximum efficiency when using the microinductor is shown to be approximately 3% lower than the one using the conventional discrete chip inductor. However, the profile of the microinductor is much lower than that of the discrete chip inductor. The maximum efficiency of the microinductor in the converter is estimated to be approximately 92%.

Microfabricated coupled inductors for DC-DC converters for microprocessor power delivery

High-current, low-voltage power converters with fast transient response are needed for powering digital systems such as microprocessors. Microfabricated coupled inductors for such power converters are discussed. A four-phase microfabricated magnetic structure with 14 nH of inductance per phase has been fabricated for a 5 MHz, 5 V-to-1 V, 10 A dc-dc converter. The first prototype devices have been built with nickel-iron (NiFe) cores and copper conductors on a silicon substrate. Small-signal measurements on the inductors have been performed and predictions have been confirmed. A model for analyzing the performance of coupled inductors is presented. The devices have been implemented in a prototype converter and the measured performance is compared with the predicted results.

MAGNETIC PROPERTIES OF GLASS?METAL NANOCOMPOSITES PREPARED BY THE SOL?GEL ROUTE AND HOT PRESSING

Glass‐metal nanocomposite powders in the systems Fe/SiO2 and Ni/SiO2 have been prepared by the sol‐gel technique followed by reduction treatment. Bulk nanocomposites are then fabricated by hot pressing these powders. The metal particle diameters range from 8.9 to 14.8 nm. The materials show enhanced coercivities, e.g., a maximum of 82 Oe in the case of Ni/SiO2 and a maximum of 474 Oe in the case of Fe/SiO2 systems. The Mossbauer spectra of Fe/SiO2 samples are comprised of a ferromagnetic component superposed on a superparamagnetic doublet.