WiEps: Measurement of Dielectric Property with Commodity WiFi Device - An Application to Ethanol/Water Mixture

Hang Song*, Bo Wei, Qun Yu, Xia Xiao, Takamaro Kikkawa

*Corresponding author for this work

Research output: Contribution to journalArticlepeer-review

8 Citations (Scopus)


WiFi signal has become accessible everywhere, providing high-speed data transmission experience. Besides the communication service, channel state information (CSI) of the WiFi signals is widely employed for numerous Internet-of-Things (IoT) applications. Recently, most of these applications are based on the analysis of the microwave reflections caused by the physical movement of the objective. In this article, a novel contactless wireless sensing technique named WiEps is developed to measure the dielectric properties of the material, exploiting the transmission characteristics of the WiFi signals. In WiEps, the material under test is placed between the transmitter antenna and receiver antenna. A theoretical model is proposed to quantitatively describe the relationship between CSI data and dielectric properties of the material. During the experiment, the phase and amplitude of the transmitted WiFi signals are extracted from the measured CSI data. The parameters of the theoretical model are calculated using measured data from the known materials. Then, WiEps is utilized to estimate the dielectric properties of unknown materials. The proposed technique is first applied to the ethanol/water mixtures. Then, additional liquids are measured for further verification. The estimated permittivities and conductivities show good agreement with the actual values, with the average error of 4.0% and 8.9%, respectively, indicating the efficacy of WiEps. By measuring the dielectric property, this technique is promising to be applied to new IoT applications using ubiquitous WiFi signals, such as food engineering, material manufacturing process monitoring, and security check.

Original languageEnglish
Article number9105044
Pages (from-to)11667-11677
Number of pages11
JournalIEEE Internet of Things Journal
Issue number12
Publication statusPublished - 2020 Dec


  • Channel state information (CSI)
  • WiFi signal
  • dielectric property measurement
  • microwave propagation
  • wireless senssing

ASJC Scopus subject areas

  • Signal Processing
  • Information Systems
  • Hardware and Architecture
  • Computer Science Applications
  • Computer Networks and Communications


Dive into the research topics of 'WiEps: Measurement of Dielectric Property with Commodity WiFi Device - An Application to Ethanol/Water Mixture'. Together they form a unique fingerprint.

Cite this