A Study on the Design of A Semi-Cylindrical Capacitive Sensor for Intravenous Drip Detection

This study focuses on the design of a semi-cylindrical capacitive sensor for intravenous (IV) drip detection. A main objective is to explore the capacitance of the semi-cylindrical capacitive sensor in response to drops of the IV fluid inside the drip chamber. The different sizes of semi-cylindrical capacitive sensors made of copper plates were constructed to be the IV drip detectors. They were put on the drip chamber of IV administration sets for detecting drops of the IV fluid appearing inside the drip chamber. Three sizes of the IV set were involved in the investigation: 15, 20, and 60 drops/ml. The sensor capacitances were measured, and the capacitance waveforms were observed. The relationships among the sensor sizes, the drip sizes, and the IV fluid levels inside the drip chamber were explored. The results showed that changes of the sensor capacitances are consistent with the basic principle of capacitor. The larger sensor size can produce the greater changes in capacitance of the semi-cylindrical capacitive sensor in response to the drops of IV fluid. The detected changes in sensor capacitance are approximately in the range of 0.02, 0.03, and 0.04 pF for the drip sizes 60, 20, and 15 drops/ml, respectively. Several factors have influence on the morphology of the capacitance waveform including the sensor size, the drip size, and the IV fluid level inside the drip chamber. In order to obtain the capacitance waveform appropriate for furthering processing, the design of the semi-cylindrical capacitive sensor must make a trade-off between the sensor size and the IV fluid level inside the drip chamber. The semi-cylindrical capacitive sensor would be an alternative effective device for the IV drip detection. The effective processing method is also required for identifying drops of the IV fluid from the detected capacitive waveform.