Development of a free-form piezo-resistive pressure sensor using advanced printing methods

Abstract

The use of printed pressure sensors is becoming a popular alternative to conventionally made silicon-based pressure sensors in niche applications, ranging from automotive and aerospace to the biomedical industry. In this paper, a piezo-resistive pressure sensor is produced onto a free-form Polyamide (PA) substrate, by combining aerosol-based jet printing and screen-printing techniques. The result is a first study towards the implementation of printed piezo-resistive pressure sensors for biomedical applications.The piezo-resistive pressure sensor consists of silver interconnects which are printed onto the substrate and are connected through a layer of piezo-resistive ink. The sensor is printed onto a customized additive manufactured PA substrate, which is produced using Selective Laser Sintering (SLS). First, the interconnects are printed using silver ink, CUR AG-001, from Agfa N.V. Belgium, which is deposited using an aerosol-based jet printer, the Nebula 5X-100s, developed at the Advanced Manufacturing Laboratory (AML) of the KU Leuven. Next, the sensitive elements are printed using a piezo-resistive material, Carbon EMS CI 2050, which is applied across the sensor interconnects using an adapted screen-printing technique. An optimal ink composition for the two-component piezo-resistive ink was found at 40wt% CI-2050LR: 60wt% CI-2050HR, which are respectively low and high resistivity ink components. Both silver ink and printed piezo-resistive elements were sintered in an oven at 150°C for 240 and 45 min, respectively. Finally, a coupling for the sensor readout was provided using a silver conductive epoxy adhesive, which cures at room temperature, so that electrical connections could be attached to the sensor contact pads.Validation of the piezo-resistive pressure sensors was conducted using fingertip actuation, which showed a typical piezo-resistive behavior where the resistance of the sensor decreases in function of the applied pressure, and a maximal decrease in electrical resistance of 30.5Ω has been measured. These results show the feasibility of employing advanced printing techniques to produce piezo-resistive sensing devices onto free-form and additive manufactured substrates, for biomedical applications.