A study on fine detection of moisture content in stone cultura relics by high-sensitivity wireless sensing.

As moisture is the main factor that causes weathering of stone cultural relics, probing their corresponding contents is the basis for all conservation work. In this work, the moisture content of stone cultural relics was examined using the non-Hermitian exceptional points in the second-order parity-time (PT) symmetric system. Tiny moisture changes inside the samples were determined through the resonant frequency difference. Using the difference in dielectric constants between moisture and sandstone, the database of dielectric constants of stone cultural relics with differing moisture contents can be established. Meanwhile, the fine detection of small changes in moisture contents of stone cultural relics can be realised. Compared with conventional passive wireless sensors, the second-order PT symmetric system has improved detection sensitivity and a smaller error, of less than 0.07% compared with the drying method. Furthermore, compared with other kinds of nondestructive testing technology, this system exhibits many advantages in detecting the moisture content of stone cultural relics, including compact size, high sensitivity, and low detection cost, and is thus of great significance for the protection and restoration of cultural relics.