IEEE Power Electronics Magazine - March 2017 - 41

Summary

20 nm
(a)

(b)

FIG 7 (a) An artist's rendering of nanoparticles in an encapsulant and (b) an electron micrograph of magnetic nanoparticles
with precisely tailored size and spacing. Arrays like this can
readily be formed in small samples but must be scaled up dramatically to make real inductor materials.

development establishments are rethinking how to fabricate
bulk magnetic materials. One proposed approach is the use
of magnetic nanocomposites [25]. Superparamagnetic
nanoparticles are smaller than the characteristic domain size
of a magnetic material and always have a single magnetic
domain. The moment of each individual superparamagnetic
nanoparticle is therefore always saturated, but the direction
of magnetization can change. An ensemble of superparamagnetic nanoparticles will have zero moment in the absence of
an external field, because of the random direction of the
magnetic moments. If superparamagnetic nanoparticles
could be fashioned into an inductor material without altering
their magnetic properties, they would represent an ideal
material. They have zero magnetic hysteresis and are typically under 25 nm in diameter, which is also too small to support eddy currents. Other loss mechanisms, such as magnetostriction, would still exist but are much lower in magnitude than hysteretic or eddy current losses.
An inductor material could thus be realized by suspending superparamagnetic nanoparticles in a nonconductive
and nonmagnetic material, such as an epoxy encapsulant.
If the nanocrystals are sufficiently small and suspended
without strongly interacting with one another, they could
maintain the lack of magnetic hysteresis and eddy currents. The challenge then is to maximize superparamagnetic nanoparticle loading to maximize energy density
without allowing contact or even strong magnetic interactions. The ideal material would include nanoparticles
of a single size, with uniform spacing between them, with
the nanoparticles as large as possible without losing their
superparamagnetic behavior and with spacing as small as
possible without leading to strong magnetic interactions
(Figure 7). Development of these innovative inductor materials has been hampered by a lack of the requisite control
of the nanoparticle size and spacing. Recent advances in
large-scale nanoparticle synthesis and functionalization
may finally make the preparation of these nanocomposites
practical [26]. This would enable compact, high-frequency,
low-loss inductors for power conversion circuits.

The development and maturation of WBG devices has
already realized incredible improvements in power converter
SWaP. WBG devices enable higher switching frequencies,
higher temperatures, and higher voltage hold-off. On the horizon are UWBG devices, which have the potential to push the
envelope even further, especially for high-voltage applications. These devices may be essential in meeting aggressive
industry and government targets. However, as semiconductor
devices improve in performance, greater burden is placed on
the performance of device packaging and passive components. Luckily, new developments are in progress to complement the capabilities of UWBG devices. These may very well
define generation-after-next power electronics.

Acknowledgments
We thank Prof. Robert Pilawa for providing photos of his
flying capacitor multilevel inverter and the entire UWBG
Grand Challenge team at Sandia National Laboratories. Sandia is a multimission laboratory managed and operated by
Sandia Corporation, a wholly owned subsidiary of Lockheed Martin Corporation, for the U.S. Department of Energy's National Nuclear Security Administration under contract DE-AC04-94AL85000.

About the Authors
Robert J. Kaplar (rjkapla@sandia.gov) received his B.S.
degree in physics from Case Western Reserve University,
Cleveland, Ohio, in 1994 and his M.S. and Ph.D. degrees in
electrical engineering from The Ohio State University,
Columbus, in 1998 and 2002, respectively. In 2002, he joined
Sandia National Laboratories, Albuquerque, New Mexico, as
a postdoctoral researcher, where he is presently a principal
member of the technical staff. His past work has included IIINitride optoelectronics and semiconductor reliability physics, and he is currently focused on wide- and ultrawide-bandgap III-Nitride materials and devices for power electronics.
Jason C. Neely ( jneely@sandia.gov) received his B.S.
and M.S. degrees in electrical engineering from the University of Missouri at Rolla (now Missouri University of Science
and Technology) in 1999 and 2001, respectively. From 2001
to 2007, he worked at Sandia National Laboratories in the
Intelligent Systems and Robotics Center. He received his
Ph.D. in electrical and computer engineering from Purdue
University, West Lafayette, Indiana, in 2010 for the development of new control techniques for power electronics. Since
2010, he has been a researcher at Sandia National Laboratories, Albuquerque, New Mexico, focusing on power electronics, including microgrid systems, grid integration of
renewable energy, energy storage, military power systems,
and circuit design for wide bandgap devices.
Dale L. Huber (dlhuber@sandia.gov) received his
B.A. degree in chemistry from the University of Pennsylvania, Philadelphia, in 1995. He completed his M.S. degree
in 1996 and his Ph.D. degree in 2000, both in polymer science from the University of Connecticut, Storrs, where his
March 2017

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