Laser-bonding of FEP/FEP interfaces for a flexible manufacturing process of ferroelectrets

This paper presents an optimized laser-bonding process for piezoelectric energy-harvesters based on thin fluorinated-ethylene-propylene (FEP) foils, using an ultra-short-pulse (USP) laser. Due to the minimized thermal stress in the material during bonding, achieved by pulse durations of few picoseconds, we created seams down to 40 µm width without generating holes in the 12.5 µm thick FEP-foils. Using a galvanometer scanning system allowed for fast bonding-speed up to several centimeters per second, making the process also suitable for large structures and areas. The achieved bond strength of the seams under influence of shearing stress was examined using tensile testing, which showed a sufficient strength of about 25 % of the maximum strength of an unbonded, single layer of FEP. (paper)