Development of permittivity sensor for advanced in situ testing and evaluation of building material

In recent years, numerous electromagnetic sensors have been devised to measure the dielectric properties of building materials and correlate them with their physical and mechanical characteristics. Many of these sensors require access to materials from both sides, while others are restricted to laboratory settings. This paper introduces a novel radio wave permittivity sensor (RWPS) alongside its theoretical framework for application. The RWPS is engineered and produced to assess the in situ permittivity of building materials across a low frequency radio wave spectrum ranging from 1 kHz to 300 MHz. Structurally, the RWPS resoles a capacitive electrode, comprising two conducting plates separated by a known distance. These plates are smooth and flat, facilitating conformity to the surface of the material being tested. To validate the system, preliminary tests were conducted on specimens with known dielectric properties such as Teflon, PVC, and deionized water. A robust calibration and validation procedure was established for the RWPS. Subsequently, a prototype RWPS device was developed as a surface sensor, characterized by its lightweight, portability, affordability, and user-friendly design. The RWPS can glide across material surfaces, providing data from various points. Mounted on a circular plate, the RWPS can rotate, enabling data collection from different angles by altering the polarization of the electromagnetic signal. The proposed sensor has the potential to be used to estimate the strength, moisture content, and water-to-cement ratio of construction materials, as demonstrated by the results of measurements of the dielectric constant of wood and concrete.