PCB EMI Causes

 

By attaching antennas to a printed circuit board we can analyze the physics of unwanted radiation

Modeling Biconical Antennas

 

The biconical antenna can be modeled using simple and inexpensive software tools

Davis EMC patent

 

Jeffrey Davis’ innovative design for a device driver lowers emissions without compromising performance

PCB EMC and traces

 

As a signal trace is moved towards the edges of a return plane, the inductance of the return plane rises

EMC and Lost Flux

 

Flux from a signal conductor can loop around a return conductor inducing a voltage along it

Shielding and EMC

 

A plane wave impinging on a metal shield with an aperture emerges as a point source

Anechoic Chambers

 

The pyramidal absorbers can be modeled as a sandwich of planes with varying resistivity

Radiation from small wire

 

A map of vector potential from a small wire element

EMC and common mode currents

 

A return plane can develop a voltage along its length causing attached cables to radiate

EMC and slot on PCB

 

A slot cut across a solid return plane can cause havoc because of its affect on return inductance

EMC lost flux and shield

 

“Lost Flux," --the flux created by the center conductor that leaks around a shield -- causes the shield to radiate

EMC unbalanced currents

 

Common mode currents are created when balanced geometries meet unbalanced ones”

Maxwells Equations divergence

 

Divergence -- the flux flowing into and out of a small volume element -- is a key concept in field theory

Field propagation small volume

 

A small change in an electric field over distance creates a changing magnetic field at right angles to it

EMC lost flux and PCB

 

Varying signal and return geometries radiate differently due to varying amounts of "lost flux"

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