For the respiration monitor, the team drew the electrode directly on a solution-treated face mask. The sensor easily differentiated mouth breathing from nose breathing and was able to classify three breathing states: deep, regular and rapid. Cheng explained that the data collected could be used to detect the onset of various disease conditions, such as respiratory arrest and shortness of breath and provide opportunities in the smart internet of things and telemedicine.
He added that respiratory rate is a fundamental vital sign and research has shown it to be an early indicator of a variety of pathological conditions such as cardiac events, pneumonia and clinical deterioration. It can also indicate emotional stressors like cognitive load, heat, cold, physical effort and exercise-induced fatigue.
Compared with breath, the human skin exhibits a smaller change in humidity, but the researchers were still able to detect changes using their pencil-on-paper humidity sensor, even after test subjects applied lotion or exercised. Skin is the body’s largest organ, Cheng explained, so if it is not processing moisture correctly, that could indicate that some other health issue is going on.
“Different types of disease conditions result in different rates of water loss on our skin,” he said. “The skin will function differently based on those underlying conditions, which we will be able to flag and possibly characterize using the sensor.”
The team also integrated four humidity sensors between the absorbent layers of a diaper to create a “smart diaper,” capable of detecting wetness and alerting for a change.
“That application was actually born out of personal experience,” said Cheng, who is the father of two young children. “There’s no easy way to know how wet is wet, and that information could be really valuable for parents. The sensor can provide data in the short-term, to alert for diaper changes, but also in the long-term, to show patterns that can inform parents about the overall health of their child.”
The applications of the humidity sensor go beyond “smart diapers” and monitoring for respiration and perspiration, Cheng explained. The team also deployed the sensor as a noncontact switch, which could sense the humidity changes in the air from the presence of a finger without the finger touching the sensor. The team used the noncontact switch to operate a small-scale elevator, play a keyboard and light up an LED array.
“The atoms on the finger don’t need to touch the button, they only need to be near the surface to diffuse the water molecules and trigger the signal,” Cheng said. “When we think about what we learned from the pandemic about the need to limit the body’s contact with shared surfaces, a sensor like this could be an important tool to stop potential contamination.”
Other authors on the study are Penn State doctoral candidate Ankan Dutta as well as Guangyu Niu, Zihan Wang, Ye Xue, Jiayi Yan, Xue Chen, Ya Wang, Chaosai Liu, Shuaijie Du Langang Guo of the Hebei University of Technology. Peng Zhou of Tianjin Tianzhong Yimai Technology Development Co. Ltd. also contributed to the research.
Cheng’s work was funded by the National Institutes of Health, the National Science Foundation and Penn State.