Hot-wire anemometers are used to measure turbulent flow variables such as mean and fluctuating velocity components and temperature. Hot-wire anemometry is based on heat transfer through forced convection from a heated wire. The amount of heat transfer caused by an incident flow to maintain the hot-wire at a constant temperature is proportional to the velocity of the fluid. If the fluid material is known, then the fluid velocity can be directly sensed. Autonomous mobile platforms require sensors for navigation, control, positional and situational awareness, as well as for mission-related functions such as detection of personnel and of various threats. Flow sensors can provide valuable information in this regard. These sensors must be lightweight, small, low power and robust when exposed to the environment outside of the lab. They should also have the ability to be integrated with the onboard electronics of the mobile platform with a minimal use of interface circuitry. However, previously reported 3D hot-wire anemometers, resonating, differential pressure, lift-force and piezo-resistive and capacitive hair flow sensors require multiple mask layers and expensive fabrication processes. Therefore, new processes that could eliminate the complexity and costly production of existing technologies comprise a promising area open to research. Furthermore, hot-wires provide signals continuous in time and do not require particles to be added to the flow. This is an additional incentive to pursue developments in hot-wire anemometry, which has already made important contribution to the knowledge of turbulent flows.
A new type of hot-wire hair-sensor for air flow sensing is introduced by the researchers at the University of Michigan that offers high accuracy, high sensitivity and wide dynamic range while consuming a small amount of electrical power, and having a relatively small size and weight. The sensor weighs less than 2.5 grams and its power consumption is less than 100 mW. Researchers were able to achieve a flow speed measurement range from 2.8 cm.s-1 to 5 m.s-1, with an accuracy of 2 mm.s-1 at low flow regime (2 m.s-1). Experiments also showed net sensitivity of 660 mV/(m/s) and 160 ms of response time. The new technology uses a post process technique that is integrated circuit (IC) compatible and simple to fabricate; reducing the cost drastically. The post process technique used also allows the hot-wire to extend above the surface of the substrate. This saves valuable chip area, allowing the possible formation of dense arrays of sensors and other applications such as inertial sensors and accelerometers. The sensor was integrated with a crawler mini-robot and could successfully collect and transmit data through a Bluetooth connection embedded on the robot control board. The system could successfully exhibit an “escape” intelligent behavior using the hair-like air flow sensor. The achieved performance of this lightweight, low-power, high performance and high resolution flow sensor makes it a suitable and functional component to be used for navigation, control, positional and situational awareness on various autonomous mobile platforms.
Applications and Advantages
- Medical equipment
- HVAC systems
- Autonomous mobile platforms
- Integrated circuit compatible and simple to fabricate process
- Applicable to various autonomous mobile platforms