Aplicabilidade do método da reflectometria no Domínio do Tempo (TDR) em amostras de rocha

Abstract

The Time Domain Reflectometry (TDR) method has its greatest applicability in studies carried out in soils, due to this factor, TDR sensors are already idealized for this purpose. Due to the ability of the method to measure dielectric properties in different materials and in a wide range of frequency values, it can also be tested to measure the dielectric constant in different types of rocks. For this work, the TDR sensor model TDR315H from Acclima was used, having three waveguides with 15 cm each and the SDI-12 reading sensor from the same company. With the TDR used, it was possible to obtain temperature values in degrees Celsius (°C), water content in percentage, conductivity in Microsiemens per centimeter (μS/cm) and permittivity (dielectric constant), where it is worth mentioning that the TDR measures only the real part of the complex relative dielectric permittivity, known as the dielectric constant. The equipment is configured to carry out measurements in different types of soils, also allowing it to be calibrated for a different material by the operator. Two rock samples were used, one sandstone and one steatite (soapstone) and a container with water, in which the first tests with the equipment were carried out. The tests carried out on the two samples showed that the measurements carried out with the equipment are only reliable after a depth of 7 cm from the waveguides. For the first measurements on the soapstone sample, a 6mm diameter drill was used to make the holes for fitting the TDR probes. depths of the rod, it was possible to obtain for the water content in the sample, values that varied from 0.33% to 3.64%, (Graph 3) temperature values that varied between 29.4°c to 30.3°c, and permittivity values ranging from 1 to 3.3 (Graph 4). In another point of the same rock, the values for water content varied between 0.56% and 2.43% (Graph 5), and for permittivity varied from 1 to 2.8 (Graph 6). Measurements performed on the sandstone sample showed values for water content (Graph 7) of 0.56% (at a depth of 12 cm) and 1.57% (at a depth of 12.7 cm); for permissiveness, the values varied between 1 and 2.5 (Graph 8).