Micro-condensation sensor for monitoring respiratory rate and breath strength

Human breath monitoring provides a lot of information about the condition of the body. Respiratory rate which is beyond the norm can be a symptom of a serious disease and an indication for hospitalization. This article presents a sensor which enables monitoring of respiratory rate owing to the change of coupling between input and output electrodes caused by the micro-condensation of vapour particles on the sensor surface in the process of exhaling air. The amplitude of a supplying signal (DC or AC in the range of low frequencies) determines the maximum amplitude of the output signal. The micro-condensation sensor (MCBS) was made in PCB technology and its surface was covered with an available antiseptic which increases MCBS sensitivity to breathing to a great extent. With relative humidity exceeding 75%, the change of the sensor capacitance amounts to 0.5 nF/%RH.The sensor was tested within the frequency range of several to 240 breaths per minute. Such a wide range of frequencies was chosen in order to determine the sensor sensitivity and the speed of its operation in widely different circumstances.

► Covering the sensor with an antiseptic greatly increases its sensitivity to breath.
► A significant increase in capacitance, 0.5 nF/% RH, with relative humidity over 75%.
► The sensor was tested within the frequency range of several to 240 breaths per min.
► Low production costs enable to treat the sensor as a disposable product.