A simple breathing rate-sensing method exploiting a temporarily condensed water layer formed on an oxidized surface

Abstract

We describe a very simple breathing rate-sensing method that detects a significant electric current change between two metal electrodes on an oxidized surface. The current change is caused by the formation of a water layer from exhaled breath. We discovered that breathing onto the oxidized surface causes instant water condensation, and it generates 20 times increased current than that measured in the inhalation period. The condensed water quickly evaporates, enabling us to detect dynamic human breathing in real time. We also investigated the breathing rate sensor by varying the relative humidity, temperature, and breathing frequency and confirmed its potential for practical applications.

Fast-Response and Flexible Nanocrystal-Based Humidity Sensor for Monitoring Human Respiration and Water Evaporation on Skin

“…Evaluation of response speed was carried out by using a mechanical chopper and humid N2 gas. Humid N2 gas was chopped and modulated current through the sensor was detected by The conduction is considered to be dominated by Grotthuss mechanism 1,36 and proton transport occurs in water layers as reported in silica gels 37 and oxidized Si surface 38 . In this model, when a physisorbed water-molecule layer is formed, protons are moved by an electric field through hydrogen-bonded water molecules via hopping.…”

Flexible, Stretchable Sensors for Wearable Health Monitoring: Sensing Mechanisms, Materials, Fabrication Strategies and Features

“…The breath can be sensed from nostrils or mouth by the airflow and form chest or abdomen by the cavity volume variation, as seen in Figure 4 . For nostrils or mouth, a face mask is often used to install the sensors, and the breath rate and intensity can be measured from the airflow-induced strain [ 73 ] and the transient difference of moisture in inhaled and exhaled air [ 5 , 76 , 77 , 78 ]. For chest/abdomen, volume variation of cavity can generate an obvious apophysis in our body, inducing a periodic motion that can be detected by the wearable strain sensors [ 7 , 74 ].…”

Silica Nanoparticle-Based Portable Respiration Sensor for Analysis of Respiration Rate, Pattern, and Phase During Exercise

“…The resistance changes three orders of magnitude in the RH range of 10 and 80 %. This tendency is explained by Grotthuss mechanism [12], [25]. Fig.…”

“…Interference fringes are due to the thin film of SiO2 NPs. The sensor chip is flexible, which is an advantage of a NP film as compared to a thermally oxidized SiO2 layer on a silicon substrate [25]. An electrical circuit of the portable respiration sensor is shown in Fig.…”