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Evaluation of Magnetic Materials for Very High Frequency Power Applications Yehui Han, Member, IEEE, Grace Cheung, An Li, Charles R. Sullivan, Member, IEEE, and David J. Perreault, Senior Member, IEEE
Abstract—This paper investigates the loss characteristics of rf
magnetic materials for power conversion applications in the 10
MHz to 100 MHz range. A measurement method is proposed
that provides a direct measurement of inductor quality factor
QL as a function of inductor current at rf frequencies, and
enables indirect calculation of core loss as a function of flux
density. Possible sources of error in measurement and calculation
are evaluated and addressed. The proposed method is used to
identify loss characteristics of several commercial rf magnetic
core materials. The loss characteristics of these materials, which
have not previously been available, are illustrated and compared
in tables and figures. The use of the method and data are
demonstrated in the design of a magnetic-core inductor, which is
applied in a 30 MHz inverter. The results of this paper are thus
useful for design of magnetic components for very high frequency
(VHF) applications.
Index Terms—Magnetic materials, resonant inductor, very high
frequency (VHF), Steinmetz parameters.
I. INTRODUCTION
There is a growing interest in switched-mode power electronics
capable of efficient operation at very high switching
frequencies (e.g., 10 – 100 MHz). Power electronics operating
at such frequencies include resonant inverters [1]–[10] (e.g.,
for heating, plasma generation, imaging, and communications)
and resonant dc-dc converters [1], [3], [11]–[20] (which utilize
high frequency operation to achieve small size and fast transient
response.) These designs utilize magnetic components
operating at high flux levels, and often under large flux
swings. Moreover, it would be desirable to have improved
magnetic components for rf circuits such as matching networks
[21]–[25]. There is thus a need for magnetic materials and
components suitable for operation under high flux swings at
frequencies above 10 MHz.
Unfortunately, most magnetic materials exhibit unacceptably
high losses at frequencies above a few megahertz. Moreover,
the few available bulk magnetic materials, which are
potentially suitable for frequencies above 10 MHz, are typically
only characterized for small-signal drive conditions, and
Y. Han is with the University of Wisconsin-Madison, 2559C Engineering
Hall, 1415 Engineering Drive, Madison, WI 53706 USA (e-mail:
yehui@engr.wisc.edu).
G. Cheung is with Intersil Corp (e-mail: gmcheung@gmail.com).
A. Li is with Massachusetts Institute of Technology, MA 02139 USA (email:
anli@mit.edu).
C. R.
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