Explore the vast range of titles available.

The pH behavior in the μm to cm thick diffusion boundary layer (DBL) surrounding many aquatic species is dependent on light-controlled metabolic activities. This DBL microenvironment exhibits different pH behavior to bulk seawater, which can reduce the exposure of calcifying species to ocean acidification conditions. A low-cost time-domain dual-lifetime referencing (t-DLR) interrogation system and an optical fiber fluorescent pH sensor were developed for pH measurements in the DBL interface. The pH sensor utilized dual-layer sol-gel coatings of pH-sensitive iminocoumarin and pH-insensitive Ru(dpp)3-PAN. The sensor has a dynamic range of 7.41 (±0.20) to 9.42 ± 0.23 pH units (95% CI, T = 20 °C, S = 35), a response time (t90) of 29 to 100 s, and minimal salinity dependency. The pH sensor has a precision of approximately 0.02 pHT units, which meets the Global Ocean Acidification Observing Network (GOA-ON) “weather” measurement quality guideline. The suitability of the t-DLR optical fiber pH sensor was demonstrated through real-time measurements in the DBL of green seaweed Ulva sp. This research highlights the practicability of optical fiber pH sensors by demonstrating real-time pH measurements of metabolic-induced pH changes.

An integrated humidity sensor capable of passive wireless sensing through inductive coupling is presented. The sensor chip consists of two stacked counter-rotating planar aluminium inductors (0.5 μm thick, 100 μm in width, 50 μm space and 6 mm outer diameter) separated by a maskless polyimide film. The two inductors are inductively and capacitively coupled together to form a resonant tank, whose resonant frequency changes with humidity. This topology eliminates the need of a connection bridge or via as used in the usual inductor–capacitor humidity sensors and offers higher sensitivity due to the inner humidity-sensitive parallel-plate capacitor in contrast with the single-layer self-resonant inductor. Three sensor devices with different inductor turns were fabricated and characterised. Measurements show a sensitivity of 45 kHz/%RH with a centre frequency of 50.5 MHz for sensor A (8 turns), 15.8 kHz/%RH, 22 MHz for sensor B (10 turns) and 65 kHz/%RH, 74 MHz for sensor C (4 turns).