Non-invasive wood moisture sensing for arthropod infestation prevention using a circularly polarized high-isolation antenna system

Abstract

This paper presents a novel circularly polarized microstrip antenna system for non-invasive detection of moisture in wood, enabling early identification of arthropod infestation areas before structural damage occurs. The proposed system consists of two microstrip antennas with opposite polarization directions (LHCP/RHCP) for transmission and reception. The circular polarization direction difference between the transmitter and the receiver allows long distance measurement and ensures low coupling between the antennas; thus, high isolation is maintained when no moisture is present. Moisture presence alters this condition, increasing the received power by 12.5 dB. The antenna system is fabricated on a low-cost FR4 substrate with compact dimensions of 50 mm × 50 mm × 1.6 mm and operates at 2 GHz. Comprehensive simulations and experiments demonstrate reliable operation across multiple conditions, including moisture levels (0-100%), temperature (- 20 °C to 90 °C), antenna positioning, wood type (Pine, Douglas fir, and Oak), sample thickness (20-30 mm), and subsurface moisture depth (up to 20 mm). A prototype was then fabricated, and experimental repeated measurements confirmed high repeatability, with a standard deviation [Formula: see text] 0.7 dB. Calibration analysis yields an average sensitivity of 0.109 dB/%MC. These results indicate that the proposed system is suitable for wood-protective moisture-sensing applications.