Capacitance measurement applied to the medical injection pen

Many drugs need to be injected frequently by the patient himself, e.g. insulin for diabetes treatment. Disposable injection pens comprise the most popular delivery devices for ease of use and discretion. However, these devices do not provide any tracking capability. In this paper we present a method to measure automatically the injected dose based on a capacitive measurement. A typical dose of e.g. 2 IU insulin (volume of 20.8μl) can be accurately detected corresponding to a capacitance change of 11.82fF at a standard deviation of 4.89 fF for 5 consecutive injections. This paper will focus on the design of the electrodes and the feasibility of the capacitive tracking method.