Abstract—The paper describes a sensor that offers a unique characteristic. It is impossible to duplicate the sensor because it belongs to devices with a Physical Unclonable Function (PUF). The sensor detects mechanical parameters. It has a capacitive electrode structure (dual electrode configuration) and can transform the movement of a membrane filled with conductive steel balls into a capacity change. Since the steel balls are randomly distributed, the sensor is unique and unclonable. The sensor has a large offset (fixed) capacity along with a variable capacity. Only the variable capacity varies with measured quantity. This paper presents an electrical equivalent model of the sensor. Detailed analysis of the model shows, the ground plane introduced to reduce the offset capacity degrades the sensitivity. Therefore, a new differential capacitive electrode structure is proposed. It nullifies the unwanted offset capacity and provides a sensor output of only the variable capacity. The new sensor design is verified using finite element analysis software COMSOL Multiphysics. Different steel ball distributions (i.e. sensors) have been assumed to study their influence on the sensor output. It was possible to prove the uniqueness of each senor by different output signals for the same excitation. Results are very promising in view of the application of such sensors in Identity-systems (ID-systems).