Effects of Core Air Gap Tolerance on Permeability (PowerPoint).  This article describes the effects of the tolerance of an air gap on core permeability and thus inductance.  A very small gap dictates a large tolerance on inductance as demonstrated here.  A companion spreadsheet allows the reader to evaluate different scenarios with respect to air gaps, their tolerance and the resulting influence on inductance.

Common-mode Choke Inductance – Not Always THE Critical Spec (PowerPoint Show).  While inductance is the most common parameter used to specify a common-mode choke other parameters such as core loss resistance and distributed capacitance play a critical part in CMC performance.  See also the Common-mode Choke Impedance Calculations (Excel spreadsheet) providing a graphical display of both common-mode impedance and attenuation based on CMC parameter elements.  By Dave LeVasseur, VP of Research & Development, Minntronix, Inc.  5/13/2015.

Real-World Inductance Measurement – What you ‘set’ may not always be what you ‘get’  (PowerPoint Show)
Setting the drive level on many inductance bridges doesn’t always guarantee that the level you set will be the same as what is applied to the part under test.
Most if not all core materials (except for “air”) exhibit changes in their permeability at different drive levels.
When tested near its saturation point the inductance of a winding may vary widely causing some bridges to provide erroneous readings or no reading at all.
By Dave LeVasseur, VP of Research & Development, Minntronix, Inc.  12/17/2014

Safety isolation protects users and electronic instruments
Understanding safety-isolation rules and testing requirements enables you to address potential safety-isolation vulnerabilities.
By David Lohbeck, National Instruments, EDN, 9/30/2004

Calculating Creepage and Clearance Early Avoids Design Problems Later
From March/April, 2001 Compliance Engineering, by Homi Ahmadi

Using PSpice to model distributed-gap cores
From EDN Design Ideas, March 17, 2005, by Jeff Fries

Switchmode Power Supply Design
A web site devoted to the design and troubleshooting switchmode power supplies.

Optimal Choice for Number of Strands in a Litz-Wire Transformer Winding
Cost-Constrained Selection of Strand Diameter and Number in a Litz-Wire Transformer Winding From IEEE Transactions on Power Electronics
Vol. 14, No. 2, March 1999, Charles R. Sullivan, Member, IEEE

“What every designer should know about magnetics in switch-mode power supplies”
Power is often an afterthought in system design, but the choice and design of the magnetic elements at the heart of an SMPS are crucial. Acquaint or reacquaint yourself with the fundamentals of this frequently overlooked area.  By Sameer Kelkar, Power Integrations — EDN, 11/26/2009

“A Gallery of Electromagnetic Personalities”
A Vignette History of Electromagnetics: Franklin, Priestley, Coulomb, Galvani, Volta, Laplace, Poisson, Fourier, Ørsted, Ohm, Green, Ampère, Biot, Fresnel, Gauss, Weber, Faraday, Henry, Lenz and many more. University of Maryland EE Dept. web page, by Leonard Taylor.  Also from this site, a photo of Faraday’s ”Induction Coil”, which is presumed to be the very first transformer, and from further background on it.

“Fundamentals of Power Electronics” – textbook on power electronics converters, by Robert W. Erickson, University of Colorado. This book is intended for use in introductory power electronics courses at the senior and first-year graduate level. It is also intended as a source for professionals working in power electronics, power conversion, and analog electronics. It emphasizes the fundamental concepts of power electronics, including averaged modeling of PWM converters and fundamentals of converter circuits and electronics, control systems, magnetics, low-harmonic rectifiers, and resonant converters. Designed for instructors here are accompanying instructional materials for ”Fundamentals of Power Electronics”.

“8 Hints for Successful Impedance Measurements”
Agilent Application Note 346-4, a general guide to making useful and repeatable measurement of impedance.

RF Impedance Measurement Basics”
Greg Amorese, Agilent.  Covers impedance, component value definitions, present typical measurement problems and their solutions along with error correction and compensation.