High-Precision Capacitive Sensors for Intravenous Fluid Monitoring in Hospitals

Automatic detection of the presence of intravenous fluids (IVs) and measuring their drip rates are essential for intelligent health care applications. Conventionally, the drip rate is monitored manually by a gravimetric method that suffers from several drawbacks. Some smart commercial drip systems, which mostly work on the optical technique, have inaccuracy due to external light interference, temperature variation, and misalignment of a photodiode and photodetector. The main motivation of this work is to investigate the usefulness of the capacitive sensors for the noncontact detection and measurement of flow rates of IV fluids. There is no previous work on IV drop detection by the capacitive sensors. This article investigated three types of capacitive sensors, such as a cross capacitive, a semicylindrical, and a planar parallel plate to detect the presence of IV droplets in the fluid pipe nondestructively. The sensors are specially designed to fulfill the application needs, and simulated and fabricated with inexpensive double-sided copper-cladded flexible PCB substrates. Experiments are conducted with the sensors for four IV fluids typically used in hospitals to determine their response parameters, such as precision, drift, and drop rate, when the droplet passes through the inner electric field of the sensors. There is an instantaneous change in the value of capacitance due to a sudden change in the dielectric constant of a partially filled air medium. The distinctive capacitance peak enables to count the droplets, drip rate (0.4-m/s cross capacitive) with highly precise (0.036%), and drift-free readings. All the sensors can be used for the target application, but the cross capacitive sensor has single dimension accuracy.