Measurement of Dielectric Constant and Cross-Sectional Variations of a Wire

Omid Hoseini Izadi*, David Pommerenke

*Corresponding author for this work

Research output: Contribution to journalArticlepeer-review


A new measurement method is proposed for identifying small differences between the relative permittivity of data wires of a twisted pair used in high-data-rate USB cables with <1% uncertainty. This method can also detect small variations in the cross section of the insulated wires. Both the variations are the root causes of the differential mode to common-mode conversion, skew, and possibly electromagnetic interference. The method is based on forming a coaxial structure around the insulated wire under test using metals with low melting points, such as Field's metal or mercury. Using time-domain reflectometry and knowing the exact length of the structure, the dielectric constant can be derived from the propagation delay measurement. The local cross-sectional variations are detected by observing local impedance variations. Two examples are provided to verify the method and illustrate how to use the method to determine the dominant sources of skew.

Original languageEnglish
Pages (from-to)1409-1416
Number of pages8
JournalIEEE Transactions on Instrumentation and Measurement
Issue number6
Publication statusPublished - 1 Jun 2018
Externally publishedYes


  • Dielectric constant measurement
  • electromagnetic interference
  • Field's metal
  • radiated emission
  • relative permittivity
  • skew

ASJC Scopus subject areas

  • Instrumentation
  • Electrical and Electronic Engineering


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