Preliminary study on wireless passive resistive sensor applied for smart objects

Smart objects are capable of measuring the surrounding environment or internal status through their sensors. A viable solution to implement sensors in objects is to print them directly on the object. Printed electronics enables customization in the design and in the choice of the materials according to the final application. Aerosol jet printing (AJP) is a technology for the fabrication of electronic components directly onto objects. In combination with AJP, passive telemetric systems can represent a valid solution to interrogate sensors, reducing the number of electronic components integrated into the object. An example of a scenario on Industry 4.0 is smart packaging, which supports the control of the production process and of the transportation chain. In this work, we propose a manufacturing process based on AJP for fabricating simultaneously the sensing coil and the tuning capacitor to be used in a passive telemetric system for the measurement of a resistive sensor at a fixed frequency. The printed devices were characterized by electrical and geometrical points of view. The printed capacitance can be tuned from 13.95 pF to 31 pF, by changing the number of depositions. Capacitors with the same characteristics differ 1.28% at maximum. For validation, printed coil and printed capacitor were then used in a telemetric system for measuring resistive loads; known commercial resistors were used and the maximum error between the nominal value and the measured value obtained by the telemetric system was lower than 6% in the range 2.2k Ω and 560kΩ.