This paper presents design, fabrication, and characterization of flexible capacitive graphene oxide (GO) based humidity sensors, which can be used in many applications, such as environmental protection, civil engineering, and agriculture. They consist of interdigitated electrodes ink-jet printed on a polyimide flexible substrate and GO based sensing layer. Measurement setup for testing and characterization was developed in laboratory conditions. The dependence of the capacitance and resistance of the GO based humidity sensors on the percentage of the applied humidity is presented. The main advantage of developed GO based capacitive humidity sensors is very large variation of capacitance, almost five orders of magnitude, compared with the previously demonstrated sensors. The other advantages of the sensors are fast response-recovery time, excellent reproducibility of the measurement results, and use of cost-effective additive ink-jet technology.

This paper describes the design, simulation and fabrication of an inductive angular position sensor on a flexible substrate. The sensor is composed of meandering silver coils printed on a flexible substrate (Kapton film) using inkjet technology. The flexibility enables that after printing in the plane, the coils could be rolled and put inside each other. By changing the angular position of the internal coil (rotor) related to the external one (stator), the mutual inductance is changed and consequently the impedance. It is possible to determine the angular position from the measured real and imaginary part of the impedance, in our case in the frequency range from 1 MHz to 10 MHz. Experimental results were compared with simulation results obtained by in-house developed software tool, and very good agreement has been achieved. Thanks to the simple design and fabrication, smaller package space requirements and weight, the presented sensor represents a cost-effective alternative to the other sensors currently used in series production applications.

Polycrystalline samples of NaCo_2−xCu_xO₄ (x = 0, 0.01, 0.03, 0.05) were obtained from powder precursors synthesized by a mechanochemically assisted solid-state reaction method (MASSR) and a citric acid complex method (CAC). Ceramic samples were prepared by pressing into disc-shaped pellets and subsequently sintering at 880 °C in an argon atmosphere. Effects of low concentrations of Cu doping and the above-mentioned synthesis procedures on the thermoelectric and mechanical properties were observed. The electrical resistivity (ρ), the thermal conductivity (κ) and the Seebeck coefficient (S) were measured simultaneously in the temperature gradient (ΔT) between the hot and cold side of the sample, and the figure of merit (ZT) was subsequently calculated. The ZT of the CAC samples was higher compared with the MASSR samples. The highest ZT value of 0.061 at ΔT = 473 K was obtained for the sample with 5 mol% of Cu prepared by the CAC method. The CAC samples showed better mechanical properties compared to the MASSR samples due to the higher hardness of the CAC samples which is a consequence of homogeneous microstructure and higher density obtained during sintering of these samples. The results confirmed that, besides the concentration of Cu, the synthesis procedure considerably affected the thermoelectric and mechanical properties of NaCo₂O₄ (NCO) ceramics.

The force is one of the parameters very often measured in our life. Force sensing resistors (FSRs) can be successfully used for measuring force, especially that they can be applied in dentistry for measuring bite forces. However, it is very difficult to apply commercial FSRs for accurate measurement of bite forces and to ensure personalized approach to each patient. Because of that, design, fabrication, and characterization of tailor-made force sensing resistors intended for application in dental medicine are presented in this paper. We designed two FSRs, one with two active areas and one with four active areas (for teeth of higher volume–molars). Two different fabrication processes were applied: first additive, using inkjet printer and silver as material for conductive segments, and second subtractive, using cutter, and gold as a material for manufacturing of interdigitated structure of FSR. Performances of these FSRs have been compared, measuring resistance as a function of applied force, using in-house developed experimental set-up with an articulator.

This paper compares performances of two wireless sensors for measuring water concentration in building materials, one manufactured by the printed circuit board (PCB) technology and another one using the low temperature co-fired ceramics (LTCC) process. The fabricated sensors consist of inductive part (L) and interdigitated capacitive part (C) in one metal layer, connected in parallel. Inductance of inductive part was kept constant, whereas capacitance of capacitive part was changed by exposing the sensor to different moisture concentration, changing its resonant frequency. The variation of resonant frequency as a function of different water concentration was measured, using antenna coil and impedance analyser, in two widely used construction materials: clay brick and autoclaved aerated concrete block. Surface analysis for two sensors was performed by means of 3D profilometer. Mechanical properties of the sensors were measured for both conductive segments (copper and silver) and substrates materials (PCB and ceramics substrates) using nanoindenter. Comparative characteristics of the sensors are presented from their application point of view.