Column: EMC
Magnetic-field loops By Dr Min Zhang, EMC consultant at Mach One Design, and design engineers at REO UK M = M dI1 /dt.
agnetic field coupling or inductive coupling occurs when energy is coupled from one
circuit to another through a magnetic field. In most applications there’s no convenient closed-form equation for calculating the mutual inductance – EMC engineers often deermine the mutual inductance by estimating the percentage of the total magnetic flux generated by the first loop that couples the second loop.
The theory behind it A transformer consists of a pair of closely placed wires. When an electric current, I1
, flows through the first
conductor, it induces a voltage in the second conductor, assuming the second conductor is an open circuit. This induced voltage, V2
Figure 1: A homemade magnetic field loop , is determined
by the mutual inductance, M, between the two conductors. Mathematically, the induced voltage can be expressed as V2
Therefore, a square magnetic field
loop shown in Figure 1 is ideal for measuring the induced voltage on one side of the loop, which is proportional
to the rate of change of flux generated by rapidly changing current in the wire under test. Such a loop is called a “magnetic field loop” or “H-field loop”,
Figure 2: Frequency response of a magnetic field loop
12 July/August 2023
www.electronicsworld.com
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