A micro-structured optical fiber negative hydraulic pressure sensor

Negative hydraulic pressure measurement finds broad applications across various industries and sciences, including biomedicine, food and beverage, liquid storage and transportation, as well as geotechnical engineering and agriculture. This talk introduces, for the first time, a novel optical fiber interferometric sensor designed for direct local measurement of negative hydraulic pressure. The sensor incorporates a dual-micro-cavity structure consisting of a hollow airgap Fabry-Perot interferometer (FPI) cavity and a liquid reservoir, separated by a thin silica diaphragm. A partially fusion-collapsed photonic crystal fiber serves as the entry channel to the liquid reservoir, facilitating the transfer of negative hydraulic pressures to the liquid reservoir. This pressure transfer causes slight deflection of the silica diaphragm, which is precisely measured by the FPI. The prototype device demonstrates the capability to measure both positive and negative pressures across a wide range of pressures from -1000 kPa to 1000 kPa with a resolution of 0.8 kPa.