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A Digital Mems-based Strain Gage for Structural Health Monitoring

Published online by Cambridge University Press:  10 February 2011

B. J. Maclean ,
M. G. Mladejovsky ,
M. R. Whitaker ,
M. Olivier  and
S. C. Jacobsen
B. J. Maclean
Affiliation:
Sarcos Research Corp., 360 Wakara Way, Salt Lake City, UT 84108, b.maclean@sarcos.com
M. G. Mladejovsky
Affiliation:
Center for Engineering Design, University of Utah, 3176 MEB, Salt Lake City, UT 84112
M. R. Whitaker
Affiliation:
Sarcos Research Corp., 360 Wakara Way, Salt Lake City, UT 84108, b.maclean@sarcos.com
M. Olivier
Affiliation:
Sarcos Research Corp., 360 Wakara Way, Salt Lake City, UT 84108, b.maclean@sarcos.com
S. C. Jacobsen
Affiliation:
Sarcos Research Corp., 360 Wakara Way, Salt Lake City, UT 84108, b.maclean@sarcos.com
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Abstract

One approach for structural health monitoring of aging aircraft is to take discrete airframe strain measurements and record the flight loads history. A complementary method consists of measuring changes in dynamic response due to fatigue crack growth. The challenge in implementing such methods is the need for inexpensive networks of distributed strain sensors which possess high resolution with no drift over time. The Uni-Axial Strain Transducer (UAST) has been developed as a digital, absolute encoding device to address these very issues. The UAST is a micro-electromechanical system (MEMS) which exploits the capacitive coupling between an array of electrostatic field emitters and an array of 64 field detectors on a CMOS IC chip. The slightly different array element spacings form a vernier scale and digital signal processing of the detector outputs is used to calculate the absolute translational displacement of the emitter array relative to the CMOS detector chip. The UAST provides a dynamic range of 11,500 μ-strain and displacements of 2.5 nm are easily resolved. The sensor sampling rate is dynamically configurable for 150, 290, 540, 1000, 1600 or 2500 Hz, providing 15, 14, 13, 12, 11, or 10 bits of resolution (equal to 0.35, 0.7, 1.4, 2.8, 5.6, or 11.4 μ-strain), respectively. The sensor network can communicate with up to 128 UASTs on a common 5-wire digital bus, eliminating the need for shielding and considerably reducing the number of wires which will have to be routed through the airframe. A network technology demonstration is being conducted on a 1/2 scale F-I 8 vertical tail where dynamic loads are applied to evaluate network performance related to monitoring of fatigue crack growth or rivet-line failures. Application of the UAST in a helicopter rotor health usage and monitoring system, and the design of a bi-axial transducer under development, are also mentioned.

Type
Research Article
Information
MRS Online Proceedings Library (OPL) , Volume 503: Symposium JJ – Nondestructive Characterization of Materials in Aging Systems , 1997 , 309
Copyright
Copyright © Materials Research Society 1998

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References

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