A Slotted-Patch Antenna Sensor With Higher Sensitivity for Detecting Setting Time of Cement Paste

Abstract

A patch antenna can be applied to determine the setting time of cement paste by using resonant frequency as a sensing parameter to obtain real-time change of moisture content. However, for the traditional patch antenna sensor, the variation of its resonant frequency caused by moisture change is often interfered by environmental factors, especially the temperature effect. Based on the edge effect theory of the patch antenna, the extent of resonant frequency effects due to nearby material highly depends on the edge size of the radiation patch. To widen the variation range of the resonant frequency, we propose a slotted-patch antenna with multiple rectangular openings, which will consequently increase the edge area of a traditional patch antenna sensor. The proposed antenna sensor has enhanced sensitivity to the surrounding water ratio based on the electric flux theory and a numerical simulation by the Ansoft High Frequency Structure Simulator (Ansoft HFSS). The topological shape and dimension of the slotted-antenna sensor are determined numerically. The proposed sensor was fabricated and tested by wired interrogation. The results show that its variation ranges of resonant frequency increased 2.5 times over that of a rectangular patch antenna sensor. This improves the usability of a slotted patch antenna for detecting the setting time of cement paste.