A micromachined flow sensor for measuring small liquid flows

A flow sensor for measuring small liquid flows in chemical measurement systems has been fabricated using bulk silicon micromachining techniques. The liquid flow sensor utilizes the measurement principle of thermal transit time, where a heat pulse is injected into the liquid and the velocity of the heat pulse is measured. The sensor consists of a silicon wafer mounted between two glass plates. A flow channel is anisotropically etched into the front side of the wafer, and on the back side electrical components for heat delivery and temperature detection are made. The flow sensor shows excellent accuracy, speed, and long-term stability. Due to the well-defined geometry easily obtainable in this technology, the mechanical, thermal, and flow properties of the flow sensor are very reproducible. There is firm mechanical insulation between the fluid system and the electrical parts of the sensor. Good thermal coupling between the fluid and the temperature controlling components is ensured, since silicon is an excellent heat conductor.<<ETX>>