Accession Number : ADA327064

Title :   Microfabricated Ice-Detection Sensor.

Descriptive Note : Technical memo.,

Corporate Author : NATIONAL AERONAUTICS AND SPACE ADMINISTRATION CLEVELAND OH LEWIS RESEARCH CEN TER

Personal Author(s) : DeAnna, Russell G. ; Mehregany, Mehran ; Roy, Shuvo

PDF Url : ADA327064

Report Date : JUN 1997

Pagination or Media Count : 12

Abstract : 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 1x1mm to 3x3mm, and the gap between parallel plate capacitors is 2 micrometers. A 200V d.c. was applied to the driving electrode which caused the capacitance to increase approximately 0.6pf from a nominal capacitance of 0.6pf 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. Then a drop of water was placed over the diaphragm and allowed to freeze. This created an approximately 2mm thick ice layer. The applied 200V d.c. produced no change in capacitance, 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.

Descriptors :   *REMOTE DETECTORS, *AVIATION SAFETY, *ICE FORMATION INDICATORS, ICE FORMATION, MICROELECTRONICS, MULTISENSORS, CAPACITANCE, DIAPHRAGMS(MECHANICS), AERODYNAMIC CONTROL SURFACES, VARIABLE CAPACITORS, ICE REPORTING.

Subject Categories : Flight Control and Instrumentation
      Snow, Ice and Permafrost

Distribution Statement : APPROVED FOR PUBLIC RELEASE