Meaning
Electrical opposition that occurs at the physical junction of two conducting surfaces. Constriction resistance arises because current cannot flow across the entire surface area of a joint. The flow is instead forced through microscopic peaks called asperities where the two metals actually touch.
Mechanical Pressure
Normal force applied to the junction increases the number of contact spots. As the pressure rises, the asperities undergo deformation and the total area available for current flow expands. This expansion causes the constriction resistance to drop as more paths open for electrons.
Harder materials require more force to achieve the same reduction in resistance as softer metals. The contact area grows until the material can support the load.
Current Density
Narrow paths through the contact points cause the local temperature to rise. This heating can alter the material properties of the interface. High current density at these spots sometimes leads to localized melting or welding of the contact surfaces.
Interface Contamination
Oxides and films on the metal surface block the flow of current. These layers force the electrons to tunnel through or find gaps in the coating. The presence of such films adds to the measured constriction resistance and can lead to intermittent signal failure.
