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Recent development and investigation of printed polymer based BaTiOa pressure sensors for gait analysis

: Sethu-Madhavan, V.-S.; Knieling, T.; Mitra, K.Y.; Bauman, R.R.

Baumann, R. ; TU Chemnitz, Institut für Print- und Medientechnik:
Printing Future Days 2015. Proceedings : 6th International Scientific Conference on Print and Media Technology for Junior Scientists and PhD Students, October 05 - 07, 2015, Chemnitz, Germany
Berlin: VWB Verlag für Wissen und Bildung, 2015
ISBN: 978-3-86135-626-4
ISBN: 3-86135-626-0
Printing Future Days <6, 2015, Chemnitz>
Fraunhofer ISIT ()

Nowadays pressure or force sensors are applied often for real time analysis of plantar pressure distribution. In this research work, fully printed piezo electric and capacitive sensors which are suitable for human gait analysis are being developed. The sensor design represents the arbitrary layout to distinguish the different shapes between sensing elements. The design may also be suited to replace frequently used MEMS sensors which are moreover only capable of low measurement areas and expensive. In order to develop a printed sensor element, BaTiO3 powder with a particle size mean value of < 2 m was preferred. An innovative polymeric composite with low dielectric loss and high dielectric constant has been developed by binding of polymers with the ferroelectric materials and to be proven with good flexibility. The blended BaTiO3 powder was formulated with different binder ratios (40%, 60%, and 80%) and was processed with magnetic stirrer to disperse the particles, leading to paste suited for screen or stencil printing as well as homogeneity with no particle agglomeration. A sensor matrix composed of different piezoelectric sensing areas was sandwiched by screen printed metallic silver bottom and top electrodes on PET foils. Screen and stencil printing technologies were used for depositing conductive and piezoelectric structures respectively. The samples were cured at optimum temperature which results in good paste wettability and layer adhesion. Printed samples were polarized at different voltages with respect to the thickness of ferroelectric layer at room temperature. Electrical and mechanical characterization was performed by changing the force (120 N/cm) with respect to time which results in a sensitivity factor of about 1 mV/s*N. D33 coefficient was tested for the respective ferroelectric material to examine the piezoelectric charge constant. As a final application, a fully printed flexible shoe inlay was developed with 17 sensors to observe the pressure distribution of human walk.