Proceedings Article | 19 April 2007
Jerry Jones, Valerie Rhoades, Radford Arner, Timothy Clem, Adam Cuneo
KEYWORDS: Sensors, Telecommunications, Composites, Control systems, Nondestructive evaluation, Standards development, Wireless communications, Digital signal processing, Sensor networks, Data communications
NDE measurements, monitoring, and control of smart and adaptive composite structures requires that the central
knowledge system have an awareness of the entire structure. Achieving this goal necessitates the implementation of an
integrated network of significant numbers of sensors. Additionally, in order to temporally coordinate the data from
specially distributed sensors, the data must be time relevant. Early adoption precludes development of sensor
technology specifically for this application, instead it will depend on the ability to utilize legacy systems. Partially
supported by the U.S. Department of Commerce, National Institute of Standards and Technology, Advanced
Technology Development Program (NIST-ATP), a scalable integrated system has been developed to implement
monitoring of structural integrity and the control of adaptive/intelligent structures. The project, called SHIELD
(Structural Health Identification and Electronic Life Determination), was jointly undertaken by: Caterpillar, N.A. Tech.,
Motorola, and Microstrain. SHIELD is capable of operation with composite structures, metallic structures, or hybrid
structures. SHIELD consists of a real-time processing core on a Motorola MPC5200 using a C language based real-time
operating system (RTOS). The RTOS kernel was customized to include a virtual backplane which makes the system
completely scalable. This architecture provides for multiple processes to be operating simultaneously. They may be
embedded as multiple threads on the core hardware or as separate independent processors connected to the core using a
software driver called a NAT-Network Integrator (NATNI). NATNI's can be created for any communications
application. In it's current embodiment, NATNI's have been created for CAN bus, TCP/IP (Ethernet) - both wired and
802.11 b and g, and serial communications using RS485 and RS232. Since SHIELD uses standard C language, it is easy
to port any monitoring or control algorithm, thus providing for legacy technology which may use other hardware
processors and various communications means. For example, two demonstrations of SHIELD have been completed, in
January and May 2005 respectively. One demonstration used algorithms in C running in multiple threads in the
SHIELD core and utilizing two different sensor networks, one CAN bus and one wireless. The second had algorithms
operating in C on the SHIELD core and other algorithms running on multiple Texas Instruments DSP processors using a
NATNI that communicated via wired TCP/IP. A key feature of SHIELD is the implementation of a wireless ZIGBEE
(802.15.4) network for implementing large numbers of small, low cost, low power sensors communication via a meshstar
wireless network. While SHIELD was designed to integrate with a wide variety of existing communications
protocols, a ZIGBEE network capability was implemented specifically for SHIELD. This will facilitate the monitoring
of medium to very large structures including marine applications, utility scale multi-megawatt wind energy systems, and
aircraft/spacecraft. The SHIELD wireless network will facilitate large numbers of sensors (up to 32000), accommodate
sensors embedded into the composite material, can communicate to both sensors and actuators, and prevents
obsolescence by providing for re-programming of the nodes via remote RF communications. The wireless network
provides for ultra-low energy use, spatial location, and accurate timestamping, utilizing the beaconing feature of
ZIGBEE.
