Determination of Time Domain Reflectometry Surface Sensors Sensitivity Depending on Geometry and Material Moisture

Area of Science:

• Electrical Engineering
• Materials Science
• Geophysics

Background:

• Moisture detection is crucial in various fields, including construction and agriculture.
• Electrical techniques, particularly those measuring apparent permittivity, offer non-invasive solutions.
• Time Domain Reflectometry (TDR) is a promising electrical method for subsurface moisture assessment.

Purpose of the Study:

• To evaluate the sensitivity of non-invasive Time Domain Reflectometry (TDR) sensors.
• To determine the influence of sensor design (element spacing) on sensitivity.
• To assess the impact of material moisture content on sensor performance and range.

Main Methods:

• Investigated two non-invasive TDR sensor designs (30 mm and 70 mm element spacing) for aerated concrete.
• Measured apparent permittivity across a range of volumetric water content (0–0.3 cm³/cm³).
• Analyzed the relationship between sensor spacing, material moisture, and effective sensing range.

Main Results:

• The narrower sensor (30 mm spacing) had an effective range of approximately 30 mm.
• The wider sensor (70 mm spacing) exhibited an effective range of approximately 50 mm.
• Material moisture significantly affected the sensor's effective range, with clear influence observed only in moist materials.

Conclusions:

• Sensor element spacing is a key factor determining the effective range of non-invasive TDR moisture sensors.
• The sensitivity and effective range of TDR sensors are dependent on the moisture content of the tested material.
• Accurate non-invasive moisture detection using TDR requires careful consideration of sensor design and material saturation levels.