Smartphone Integrated Polymer Optical Fiber Humidity Sensor: Towards a Fully Portable Solution for Healthcare

This letter presents a humidity sensor based on the colorimetric change on a silica gel sphere with the increase of the relative humidity, which leads to variations on the optical power transmission in a polymer optical fiber (POF). The sensor setup presented employs a light coupler with two POF ends positioned on a sphere of silica gel. The sensor is characterized with the reflected signal acquired by a spectrometer and the relative fluorescence spectrum of the fibers at different relative humidity is acquired and compared. Then, the sensor is integrated with a smartphone, which is used as the interrogator. In this case, the flashlight and camera are employed as a light source and a photodetector, respectively. Results show the feasibility of the proposed approach, which has some advantageous features such as mechanical robust and compact sensor that presents a linear behavior on the relative humidity range (25%-80%) analyzed. Furthermore, the smartphone integration provides additional advantage for the sensor by increasing its portability and ease to use. Thus, the proposed sensor system can be readily applied in many healthcare applications, including home monitoring, assistive robotics, and medical devices.