Margit Vallikivi

Turbulence measurements using a nanoscale thermal anemometry probe

A nanoscale thermal anemometry probe (NSTAP) has been developed to measure velocity fluctuations at ultra-small scales. The sensing element is a free-standing platinum nanoscale wire, 100 nm × 2 µm × 60 µm, suspended between two currentcarrying contacts and the sensor is an order of magnitude smaller than presently available commercial hot wires. The probe is constructed using standard semiconductor and MEMS manufacturing methods, which enables many probes to be manufactured simultaneously. Measurements were performed in grid-generated turbulence and compared to conventional hot-wire probes with a range of sensor lengths. The results demonstrate that the NSTAP behaves similarly to conventional hot-wire probes but with better spatial resolution and faster temporal response. The results are used to investigate spatial filtering effects, including the impact of spatial filtering on the probability density of velocity and velocity increment statistics.

Fabrication and Characterization of a Novel Nanoscale Thermal Anemometry Probe

The development, fabrication, and characterization of a novel nanoscale thermal anemometry probe (NSTAP) for measuring velocity fluctuations in turbulent flows are described. This miniature MEMS anemometer consists of a freestanding 30 or 60 × 1 × 0.1 μm platinum filament with electrically conductive pads and a silicon structure. A novel deep reactive ion etching lag-based process for fabricating a 3D silicon support structure is described together with other microfabrication steps. The sensors behave similarly to conventional hotwire anemometers, with an order of magnitude better spatial and temporal resolution. Batch fabrication allows a relatively low-cost high-yield process, which together with its superior frequency response and size, make it an attractive thermal anemometry sensor for velocity measurements in turbulent flows.