Sensors for Vital Signs: Humidity Sensors

Abstract

In addition to their use in environmental monitoring, chemical and processes industries, the humidity assessment plays important roles in vital signs monitoring as well as general healthcare application. The humidity sensors can be used on the detection of breathing cycles (due to the high humidity associated to human breath) as well as indicators for the microclimate conditions that can be related to pressure ulcers. In wearable technology, humidity assessment also is used on the thermal comfort estimation through the microclimate condition. Following these important applications of humidity sensing, this chapter presents the developments on humidity sensors for on-chip and optical waveguide applications. The operation principles of capacitive, resistive, and optical-based humidity sensors are discussed. However, as the humidity sensor needs a sensitive layer, the properties and humidity dependency of polymers, ceramics, metal-oxides, and composites are discussed. The development of humidity sensing on-chip applications results in an even higher miniaturization of biocompatible sensors with important applications in health care. In addition, the use of photonics waveguides as humidity sensors with multiplexing capabilities and biocompatibility without sensitivity to electromagnetic interferences enables their use in magnetic resonance imaging environments as well as in conjunction with wearable robots.