tailieunhanh - MEMS Mechanical Sensors - Stephen Beeby Part 14

Tham khảo tài liệu 'mems mechanical sensors - stephen beeby part 14', kỹ thuật - công nghệ, cơ khí - chế tạo máy phục vụ nhu cầu học tập, nghiên cứu và làm việc hiệu quả | 250 Flow Sensors ultrasonic waves and it has the potential to measure liquid flow rates. However the idea of this novel MEMS flow sensing principle has not been picked up by future researchers and thus it was not discussed above. Ultrasonic wave sensors to measure liquid density and viscosity have also been described 129 130 . Ultrasound enables instruments to be noninvasive because the acoustic wave can often penetrate the walls of channels. Other sensing principles that have gained little attention so far are the fluid flow detection via a pyroelectric element 131 and resonant flow sensing mechanism 132 133 . Turbulent flow studies with considerable impact from micromachining may open a new area. In the future an aircraft wing could be covered with wall shear stress sensors and actuators to actively influence the flow profile. A first step in this direction is the micromachined flexible shear stress sensor skin applied to an unmanned aerial vehicle presented recently by Xu et al. 134 . Here an array of 36 shear stress sensors was mounted over the 180 surface of the leading edge of a wing and data during flight was collected for an aerodynamic study. Flow sensors have made the jump from the MEMS into the NEMS world nanoelectro mechanical systems . Ghosh et al. 36 measured flow rates for various liquids using carbon nanotubes. They reported that the flow of a liquid on single walled carbon nanotube bundles induces a voltage in the sample along the direction of the flow. The magnitude of the voltage depends on the ionic conductivity and on the polar nature of the liquid. Nanotube bundles with an average tube diameter of nm were densely packed between two metal electrodes. The dimensions of the sensor were 1 X X 2 mm3. Flow rates between micrometers per second and millimeters per second were measured. This approach using carbon nanotubes may have the potential to measure extremely low flow rates. Lerch et al. 135 writes The research is often technology driven