A Portable Sensor System for Structural Health Monitoring with Printed Sensors on Biodegradable Substrates

This article presents a fully printed paper-based humidity sensor for structural health monitoring of natural fiber composites. The uncoated paper substrate represents 95.6 % of the sensor's mass, making it mostly biodegradable. The sensor measures 73 x 50 mm and consists of a capacitive part that is sensitive to moisture and a printed planar antenna, which allows the system to be read wirelessly via inductive coupling to an external FPGA platform that was specially developed for this purpose. The characterization of the sensor under controlled climatic conditions shows a sensitivity of 4.16 kHz resonance frequency shift per % relative humidity. The lamination of the sensor into composite panels and subsequent tests in a water bath shows that a capillary water absorption of the fibers can be measured with the sensor.