MICROWAVE RING-RESONATOR AS A NOVEL BIO-MATERIAL MOISTURE SENSOR

A novel miniature microwave microstrip sensor for the study of moistur e in bio-materials (paper and leaves) is suggested. The leaf-drying pr ocess (time-variation) exhibits the leaf-specific nature. The paper-mo isture estimation using f(r) and Q(r) variations are the two complemen tary moisture sensing methods. The Q(r) variations are useful to sense low moisture level, less than 10% M-ww, with sensitivity of the order of 300% M-ww(-1), with an error of 1.57% M-ww in the estimated moistu re. The f(r) variations are useful to sense moisture in the wider rang e 0-40% M-ww, with sensitivity of the order of 25 MHz % M-ww(-1), with an error of 2.2% M-ww in the estimated moisture. The trend of f(r) va riations with percentage M-ww for both types of bio-materials, could b e divided broadly in two regions with an additional region shown by th e high moisture containing leaves. A preliminary explanation of the re lated dominant phenomena is attempted. (C) 1998 Elsevier Science S.A. All rights reserved.