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

Abstract

The article concerns the electric techniques of moisture detection that are based on the evaluation of the apparent permittivity of the tested medium. The main goal of the research was to evaluate the non-invasive Time Domain Reflectometry (TDR) sensors’ sensitivity by measuring the span of elements and material moisture. To that aim, two non-invasive sensor designs were investigated for their sensitivity in the evaluation of the apparent permittivity value of aerated concrete. Sensors A and B were characterized by the spacing between the measuring elements equal to 30 mm and 70 mm, respectively. The tested samples differed in moisture, ranging between 0 and 0.3 cm3/cm3 volumetric water content. Within the research, it was stated that in the case of the narrower sensor (A), the range of the sensor equals about 30 mm, and in the case of the wider design (B), it equals about 50 mm. Additionally, it was stated that material moisture influences the range of sensor influence. In the case of the dry and low-saturated material, it was not possible to evaluate the range of sensor sensitivity using the adopted method, whereas the range of sensor signal influence was visible for the moist material.

Comparison of the Moist Material Relative Permittivity Readouts Using the Non-Invasive Reflectometric Sensors and Microwave Antenna

“…In the case of the microwave antenna sensor, the signal travels free space and totally penetrates the moist material and the second marker comes from the end of the brick, rather than the end of antenna, which provides more reliable readouts of brick moisture. Moreover, it must be emphasized that the range of TDR signal penetration for the applied sensors equals about 4–5 cm, which was evaluated in the following reference [ 56 ]. The values of relative permittivity measured for dry bricks could be compared to those found in the literature, both for microwave antenna and the TDR investigations.…”

“…For the time domain reflectometry tests, the following elements were utilized: LOM TDR multimeter (ETest, Lublin, Poland), PC computer as controlling station and for data acquisition, as well as TDR surface sensors of own design connected with the TDR multimeter by a coaxial cable. Both applied TDR sensors are widely presented in authors’ article [ 56 ] and they differ in measuring waveguides spacing, where one (Sensor A) has the distance between them equal 40 mm and the other (Sensor B) 80 mm. Both sensors are made of the polyoxymethylene having apparent permittivity value equal 3.8.…”

“…Another approach to moisture evaluation, especially in rigid porous media such as building materials, is presented by surface, non-invasive sensors that are described in many studies [ 36 , 51 , 52 , 53 , 54 , 55 , 56 ]. Surface sensors are utilizable for moisture detection without the necessity of introducing the sensing elements inside the material.…”

Comparison of regression models of linear and polynomial dependencies in moisture detection technique

“…The following materials and equipment were applied for the research: red brick samples (apparent density 1500 kg/m 3 ); TDR multimeter manufactured by ETest, Lublin, Poland; own construction TDR surface sensor [10]; laboratory oven VO-500 manufactured by Memmert, Germany, laboratory scale WPT 6C1 manufactured by Radwag, Poland and PC serving as control station.…”

Estimation of apparent permittivity value of polylactyde polymers using reflectrometric technique

“…These include the group of polylactides, which are classified as aliphatic polyesters. It is worth noting that PLA (polylactide) is obtained from natural raw materials [3,4]. PLA is obtained by lactide ring-opening polymerization or by polycondensation of lactic acid.…”