Packaging for a Sensor Platform Embedded in Concrete
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PACKAGING FOR A SENSOR PLATFORM EMBEDDED IN CONCRETE Russell Paul Cain, Bliss G. Carkhuff, R. Srinivasan, Kenneth R. Grossman, and Frank Weiskopf Johns Hopkins University Applied Physics Laboratory 11100 Johns Hopkins Road Laurel, Maryland 20723-6099, U.S.A. http://www.jhuapl.edu ABSTRACT The Johns Hopkins University Applied Physics Laboratory is developing packaging for a sensor platform to be embedded in the harsh environment of concrete structures. The sensors will monitor the corrosive environment of the structure over periods of several decades to aid in scheduling maintenance and repair. The United States has recognized the risks associated with its aging infrastructure and is actively replacing deteriorated/high risk structures as well as simultaneously developing the tools and techniques to monitor new infrastructure as it ages. JHU/APL has reviewed the sensing requirements for infrastructure monitoring, especially bridge decks, and developed a concept based on distributed, embedded sensors. The Wireless, Embedded Sensor Platform (WESP) will implement the concept of a low-cost, customizable sensor platform suitable for long-term field measurements. The WESP is designed to be powered and queried remotely as often as required and can be used to measure the evolution of the corrosive environment over time. The objective of this research and development is to design, implement, and demonstrate packaging techniques for embedded sensor suites commensurate with a 50-year lifetime when embedded in concrete having a pH greater than 13, and exposed to harsh environments of salt, and mechanical and thermal stress. To meet this objective, the WESP construction will use a commercial ceramic IC package and unique manufacturing and assembly techniques. The prototype is expected to provide sensor identification, temperature, pressure, and conductivity data within a package volume less than 2.5 cm3 (0.15 in3). Reliability test results will be reviewed and specialized tests will be performed to evaluate the performance of the packaging design. These include such tests as freeze/thaw cycling, thermal shock, thermal cycling, Highly Accelerated Stress Test (HAST), 85% relative humidity/85ºC, and accelerated life testing. Future developments are expected to reduce size and implement additional sensor types to fully characterize the concrete environment. INTRODUCTION Currently, there are approximately 250,000 bridges and more than a million multistory parking lots in the US. Many built during the 1960’s are reaching their designed life expectancy of 25-50 years as are many roads, buildings, piers, pylons, and other structures. Normal bridge construction costs run approximately $500-1500/m2 and even a small two lane bridge (15m x 30m) can cost in excess of $1,000,000. Construction costs of the Woodrow Wilson Bridge replacement being built in Washington, D.C. are currently at $1.97B. One of the major failure mechanisms of large concrete structures is the corrosion of the construction reinforcement bars (rebar) embedded in the bridge
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