The design, development, fabrication, packaging and operating characteristics of two thick film moisture sensors intended for permanent installation in highway, substructures are described. These sensors can be attached to wire leads or connected to special, buried micropower radio transmitters. The first type of sensor is a glass insulated, coplanar, interdigitated thick film capacitor with line widths and spacings of 7 mils. The operation of this sensor depends upon the fact that the dielectric constant of water is about 80 while that of a normal, completely dry soil is about 2.6; the presence of water in the soil causes a change in the effective dielectric constant which can be measured by the capacitor and calibrated in terms of water content by weight. A second type of sensor makes use of the observation that the thermal conductivity of a soil depends upon moisture content. This sensor consists of a thick film heater and thermistor fabricated on opposite sides of an alumina substrate. If a fixed power input is applied to the heater, the temperature of the sensor increases to a steady state value which depends upon the thermal conductivity of the surrounding medium. This temperature increase can then be calibrated in terms of the soil moisture content. /FHWA/

  • Supplemental Notes:
    • Sponsored by Kansas State Highway Commission. Prepared in cooperation with Federal Highway Administration.
  • Corporate Authors:

    Kansas State University, Manhattan

    Manhattan, KS  United States  66506
  • Authors:
    • Lucas, MSP
  • Publication Date: 1974-1

Media Info

  • Pagination: 26 p.

Subject/Index Terms

Filing Info

  • Accession Number: 00261829
  • Record Type: Publication
  • Source Agency: Federal Highway Administration
  • Report/Paper Numbers: Final Rpt
  • Contract Numbers: 22-5001-9-5450
  • Files: TRIS, USDOT
  • Created Date: Oct 22 1974 12:00AM