In this paper, we investigated the effect of humidity on paper substrates and propose a simple and low-cost method for their passivation using ZnO nanoparticles. To this end, we built paper-based microdevices based on an interdigitated electrode (IDE) configuration by means of a mask-less laser patterning method on simple commercial printing papers. Initial resistive measurements indicate that a paper substrate with a porous surface can be used as a cost-effective, sensitive and disposable humidity sensor in the 20% to 70% relative humidity (RH) range. Successive spin-coated layers of ZnO nanoparticles then, control the effect of humidity. Using this approach, the sensors become passive to relative humidity changes, paving the way to the development of ZnO-based gas sensors on paper substrates insensitive to humidity.

This paper describes the fabrication and the characterization of an original example of a miniaturized resistive-type humidity sensor, printed on flexible substrate in a large-scale manner. The fabrication process involves laser ablation for the design of interdigitated electrodes on PET (Poly-Ethylene Terephthalate) substrate and a screen-printing process for the deposition of the sensitive material, which is based on TiO2 nanoparticles. The laser ablation process was carefully optimized to obtain micro-scale and well-resolved electrodes on PET substrate. A functional paste based on cellulose was prepared in order to allow the precise screen-printing of the TiO2 nanoparticles as sensing material on the top of the electrodes. The current against voltage (I–V) characteristic of the sensor showed good linearity and potential for low-power operation. The results of a humidity-sensing investigation and mechanical testing showed that the fabricated miniaturized sensors have excellent mechanical stability, sensing characteristics, good repeatability, and relatively fast response/recovery times operating at room temperature.

A novel UWB bandpass filter based on a grounded square patch resonator with slots is proposed. Owing to this specific geometry, three fundamental resonances of the resonator can be independently controlled and by their even distribution within the UWB range, an UWB passband can be formed. An UWB filter with in-band insertion loss <0.9 dB, group delay variation of 0.25 ns, and very small size of only 0.26λ g × 0.26λ g has been designed and fabricated, and measurement results are in good agreement with simulations.

ZnO nanostructures were grown on patterned Si substrates using a cost-efficient, low-temperature process, for their future exploitation as functional cores of nanopiezotronic applications. Different substrates and growth parameters were examined in order to determine the optimum process window that will constitute a reliable, low-cost method for large-scale ZnO nanorod production. Statistical analysis was performed to assess the size and shape distribution of the nanorods in an effort to determine the energy conversion efficiency of the resulting structures.