Elastic Filament Velocimetry [EFV]


Leveraging advanced manufacturing to create high-performance probes and new sensing modes

Elastic Filament Velocimetry [EFV] is a novel, highly anisotropic, strain-based method of sensing fluid velocity. It relies on a free-standing, electrically-conductive ribbon with nanoscale thickness. Drag from the passing liquid or gas deflects the nanoribbon, which is fixed at both ends, inducing an axial strain which can be measured as a resistance change. The small dimensions of the sensing element (1 mm long and 100 nanometers thick) mean that the sensitivity to passing fluid flow is viscously dominated, enabling sensitivity to both liquids and gases. The novelty of the EFV lies in the blending of form and function in a simple design. If the aspect ratio (length to thickness) is kept high, the nanoribbon can exhibit deflections of just a few microns, many orders of magnitude larger than the thickness but negligible compared to its length and width. While the circuitry is simple, typical strain gauges need to be mounted onto calibrated cantilevers or membranes giving them a larger footprint and more intricate construction. For EFV, the calibrated member and sensing elements are one and the same. EFV is closer in construction to a hot-wire anemometer, which is a technique that features no moving parts but involves complicated circuitry and lacks robustness. The result is a hybrid design and takes the best aspects of both sensing modes: the simplicity of design of a hotwire anemometer and the robust, inexpensive operation of a strain gauge.

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