An inertia based sensor with dynamic PUF

Sensors described in this paper are able to transform parameters like acceleration or tilt, but even so magnetic field strength into electrical signals. They offer a unique PUF (Physical Unclonable Function) characteristic and allow definitely no duplication. The heart of each of these sensors is a variable capacitance. The whole sensor, built on a Printed Circuit Board (PCB), has an InterDigitated Electrode (IDE) structure and a flexible polydimethylsiloxane (PDMS)-membrane filled with conductive steel balls. The distance between the membrane and the board is about 500 μm. External mechanical or magnetically forces can excite the membrane to move. Due to that, the capacitance changes, delivering certain Voltage signals. Since steel balls are randomly distributed, each sensor shows a unique behavior. Possible offset problems solves a differential capacitance arrangement. Therefore, a second IDE-structure is located above the membrane with a distance of about 500 μm. Output-Voltages of this double side capacity arrangement show only the position of the membrane in relation to both IDE's. Sensors having this structure and different steel ball distributions are simulated using the finite element analysis software 'COMSOL'-Multiphysics. Each sensor shows a different output signal at equal excitations. Moreover, experimental investigations show different measured values for different sensors for similar external excitation forces. This unique reaction on changes of excitation is a dynamic behavior, which stands out clearly against known and most static PUF-solutions. It makes the sensors attractive as hardware elements for security solutions. Identity cards, pay-cards or credit cards equipped with one of these sensors will become an unclonable uniqueness. Compared with other security systems, this PUF-sensor shows a great simplicity in design and data collection, a dynamic data acquisition, which completely prevents unauthorized use and it does not require no electrical energy sources.