microhm

microhm (μΩ or microohm) is a unit of electrical resistance equal to one millionth of an ohm (1 μΩ = 10−6 Ω). It is a subset of the International System of Units (SI) with the prefix micro (µ) indicating a factor of 10−6. The symbol μΩ is employed in engineering texts and technical specifications to describe resistances that are too small for practical measurement using standard ohmmeters.

In practice, microamperes of current flow through high‑quality conductors and advanced electronic components can produce resistance values in the microohm range. Such low resistances are critical in superconducting circuits, high‑frequency radio frequency (RF) systems, and power‑delivery lines where losses must be minimized. Calculations of power dissipation using P = I²R often require microohm precision to predict heating in interconnects and connector pins that carry large currents.

Measurement of microohms demands specialized instruments. Four‑wire (Kelvin) measurements, hot‑wire methods, and bridge circuits are commonly used to avoid contact resistance errors that would otherwise dominate the reading. In industry, standards such as ASTM G156 and IEC 60255 provide guidelines for measuring low resistances in electrical contacts and printed circuit boards.

The microohm is also relevant in the context of impedance spectroscopy, where the real part of impedance may drop to microohm levels at high frequencies. Knowledge of precise low‑resistance paths allows designers to optimize signal integrity and reduce electromagnetic interference in densely packed electronic assemblies.

Because microohm values typically represent losses rather than inherent resistance, engineers refer to them when assessing the efficiency of power transmission, the quality of contacts, and the stability of superconducting magnets. Consequently, accurate microohm measurements contribute to better energy efficiency, improved electronic reliability, and the advancement of high‑performance electrical systems.