EVGENIJ BARSOUKOV, PhD, is a Senior Application Engineer at Texas Instruments, Inc. His current research focuses on the application of impedance spectroscopy-based modeling to improve battery monitoring technology.J. ROSS MACDONALD, DSc, is the William Rand Kenan, Jr., Professor Emeritus of Physics at The University of North Carolina. He has published more than 200 papers in the fields of physics, chemistry, applied mathematics, and electrical engineering, and he was the editor of the First Edition of Impedance Spectroscopy (Wiley). His current research uses impedance spectroscopy to help analyze the electrical response of high-resistivity ionically conducting solid materials.