Quantifying Initial Contact Resistance Baseline Degradation in High Frequency Sockets
Initial contact resistance degradation in RF test sockets increases insertion loss and alters impedance matching, requiring dry-circuit Kelvin monitoring.
Skin Effect
Meaning
Concentration of alternating current near the outer boundary of a conductor increases with the frequency of the signal. This electrical phenomenon, known as the skin effect, is caused by opposing eddy currents induced by the changing magnetic field. It decreases the effective cross-sectional area of the conductor, which elevates its AC resistance.
Current Distribution
Alternating currents generate internal magnetic fields that oppose current flow in the center of a wire. This behavior, a consequence of the skin effect, forces the current to travel primarily in the outer layers of the metal. At high frequencies, the center of the conductor carries almost no current, making it underutilized.
In coaxial cables and printed circuit traces, this non-uniform distribution becomes a major source of signal loss.
High Frequency Behavior
Signal attenuation rises as frequency increases because the conductive path becomes narrower. In high-speed digital designs, the skin effect limits the rise times of pulses and distorts the waveform as it travels along the transmission line. Engineers calculate skin depth to determine the thickness at which current density drops to about thirty-seven percent of its surface value.
For copper traces at gigahertz frequencies, this depth is less than a micrometer.
Conductor Design
Hollow or plated conductors are used to optimize materials for high-frequency signals. Since the skin effect confines current to the surface, plating a cheap, mechanically strong substrate with a highly conductive metal like silver is cost-effective. Litz wire, composed of many individually insulated strands, is also employed to maximize surface area and minimize losses.