Knowledge of ice conditions on important aircraft lift and control surfaces is critical for safe operation. These conditions can be determined with conventional ice-detection sensors, but these sensors are often expensive, require elaborate installation procedures, and interrupt the airflow. A micromachined, silicon-based, flush-mounted sensor which generates no internal heat has been designed, batch fabricated, packaged, and tested. The sensor is capable of distinguishing between an ice-covered and a clean surface. It employs a bulk micromachined wafer with a 7 micrometers -thick, boron-doped, silicon diaphragm which serves as one plate of a parallel-plate capacitor. This is bonded to a second silicon wafer which contains the fixed electrodes-- one to drive the diaphragm by application of a voltage, the other to measure the deflection by a change in capacitance. The diaphragm sizes ranged from 1 X 1 mm to 3 X 3 mm, and the gap between parallel-plate capacitors is 2 micrometers . A 200 d.c. was applied to the driving electrode which caused the capacitance to increase approximately 0.6 pf--from a nominal capacitance of 0.6 pf--when the surface was ice free. After the sensor was cooled below the freezing point of water, the same voltage range was applied to the drive electrode. The capacitance increased by the same amount. When a drop of water was placed over the diaphragm and allowed to freeze, no change in capacitance was measured, confirming that the diaphragm was locked to the ice layer. Since the sensor uses capacitive actuation, it uses very little power and is an ideal candidate for inclusion in a wireless sensing system.

Date Published: 19 June 1997
PDF: 10 pages
Proc. SPIE 3046, Smart Structures and Materials 1997: Smart Electronics and MEMS, (19 June 1997); doi: 10.1117/12.276618

Published in SPIE Proceedings Vol. 3046:
Smart Structures and Materials 1997: Smart Electronics and MEMS
Vijay K. Varadan; Paul J. McWhorter, Editor(s)