Design of Spoke Type CSRR based RF Sensor for Non-Destructive Quality Evaluation of Wood

A spoke type novel complementary split ring resonator (CSRR) based RF sensor for non-destructive qualitative assessment of wood is presented. The novelty of the proposed sensor lies in the creation of many capacitive gaps in the sensing region comparable to that of the dimensions of the micro voids and vessels (0.2 mm to 1.2 mm) present in the wood. This kind of novel CSRR geometry basically facilitates maximum electromagnetic interaction between the sensing region and the test specimen suitable for evaluating the quality of wood samples defined in terms of porosity. The wood samples from Indian barks of Neem, Chir, and Sagwan are specially manufactured for testing in the present scenario. The sensor is fabricated on a 0.8 mm thick Taconic substrate, and all the wood samples are measured using the Vector Network Analyzer. In the next step, these samples are heat treated in a microwave oven for 1 min at 350 watts and are measured once again to determine their porosity in terms of the measured resonant frequency and the corresponding transmission coefficient magnitude. The maximum sensitivity achieved corresponds to the Neem sample, which provides a frequency shift of 23.8 MHz for unity percentage change in the porosity.