Study on high-order frequency selective surface with interdigital capacitance loading

The application of frequency selection surfaces(FSSs)is limited by large area,narrow bandwidth,low stopband inhibition and large ripple in the passband.A method for designing high-order wide band miniaturized-element frequency selective surface(MEFSS)with capacitance loading is introduced.The proposed structure is composed of multiply sub-wavelength interdigital capacitance layer,sub-wavelength inductive wire grids separated by dielectric substrates.A simple equivalent circuit model,composed of short transmission lines coupled together with shunt inductors and capacitors,is presented for this structure.Using the equivalent circuit model and electromagnetic(EM)model,an analytical synthesis procedure is developed that can be used to synthesize the MEFSS from its desired system-level performance indicators such as the center frequency of operation,bandwidth and stopband inhibition.Using this synthesis procedure,a prototype of the proposed MEFSS with a third-order bandpass response,center frequency of 2.75 GHz,fractional bandwidth of 8%is designed,fabricated,and measured.The measurement results confirm the theoretical predictions and the design procedure of the structure and demonstrate that the proposed MEFSS has a stable frequency response with respect to the angle of incidence of the EM wave in the±30°range incidence,and the in-band return loss is greater than 18 dB,and the rejection in the stopband is greater than 25 dB at the frequency of 3.2 GHz.

A nanoporous thin-film miniature interdigitated capacitive impedance sensor for measuring humidity

This paper presents a development of a low-cost miniature humidity sensor with an interdigitated aluminium electrode connected in parallel on quartz substrate.Interdigitated capacitive device has been fabricated using the photolithography method.The aluminium electrode was covered with sensitive film of a nanoporous thin film of γ-Al_(2)O_(3) made from novel solgel technique.Nanostructured thin film offers very high surface to volume ratio with distribution of micro pores for moisture detection.Pore morphologies of the film have been studied by field emission electron microscope and Xray diffraction methods.Impedance measurement of the miniature capacitive humidity sensor toward relative humidity was investigated at room temperature by Agilent 4294A impedance analyzer(Agilent,Santa Clara,CA,USA).The device exhibits short response and recovery times and good repeatability.