Marcus Hultmark: Small, fast and cost-efficient flow sensors

Nov. 10, 2016

Invention Small, fast and cost-efficient flow sensors

Inventor Marcus Hultmark, assistant professor of mechanical and aerospace engineering

What it does The research team led by Marcus Hultmark has invented a suite of nanoscale flow sensors to measure humidity, temperature and velocity. The sensors’ small size and scalable manufacturing could make them valuable for a variety of applications, such as improving comfort levels in “smart homes,” sensing flow parameters in automobile engines to improve performance, or distributed monitoring of atmospheric conditions.

The sensors each consist of a micro-electromechanical system (MEMS) device that can be produced using standard semiconductor manufacturing techniques. Compared to existing sensors, these are faster, smaller, simpler and considerably cheaper. They consist of freestanding nanoscale wire filaments strung across electrically conducting supports.

By incorporating effects of miniaturization both with respect to fluid mechanics and heat transfer, the design of the sensing elements can be tailored to the quantity measured. The sensors are operated in different modes depending on which property is measured. To measure humidity, the heated sensor’s sensitivity to velocity can be decreased by using a wire that is only a fraction of a micrometer in width. This means it loses heat through conduction rather than convection via moving air. Since thermal conductivity can be directly related to humidity, the sensing element gives an accurate measurement of humidity.

Because it is insensitive to convection, the humidity sensor is reliable even under conditions of moving air or fluid flow. If instead the sensor is designed to favor convection, it can be used to measure velocity. In addition to velocity and humidity, these sensors can be operated cold and be used to measure temperature at rates much faster than conventional sensors. Together they form a suite of sensors with unparalleled speed and resolution.

Collaborators Yuyang Fan, Matthew Fu and Clayton Byers, graduate students in mechanical and aerospace engineering; and Gilad Arwatz, who earned his Ph.D. from Princeton in 2015 and is a former postdoctoral researcher in Hultmark’s lab.

Development status InstruMems, a startup venture led by Arwatz, has formed to develop the humidity sensor into a functional prototype.

Funding sources Princeton University and the Fondation pour l’Etude des Eaux du Léman