M.E.T.I.-System

The Monitoring & Evaluation Technology Integration System (M.E.T.I-System) is a suite of robust damage detection devices that facilitate SHM. Each device shares common component technologies and software, however caters to separate markets in order to offer customized solutions. The two base products, a "wired" and a "wireless" version of the M.E.T.I.-Disk, hold the most comprehensive prognostic capabilities. These small disks (2 to 4cm diameter, approximately 1cm thick) are designed to scan large areas (2m) for the presence, location and type of both surface and subsurface damage. A robust packaging scheme has been designed to withstand typical aircraft hygral, thermal, chemical, mechanical and electrical environments. MDC also plans to develop an "extreme" version to survive temperatures below -55 F and above 250 F. In addition to the packaging, the common components contained in these devices include a concentric piezoelectric actuator and sensor pair, a flexible circuit to connect the actuator, sensor and shield to the PCB, and a PCB containing an integrated datalogger (2 channel, 1 MHz, 16 bit, 2000 data points) and signal generator (2 channel, 1MS/s, 8 bit, 2000 data points). The "wired" version of the M.E.T.I.-Disk also contains a communications driver chip and 2 micro-USB adapters in order to supply power and extract data from the sensors, with the ability to daisy-chain along a communications bus. The "wireless" version of the M.E.T.I.-Disk does not have any physical adaptors, but instead contains a thin-film Lithium polymer battery and a wireless chip integrated into the PCB to provide a communications link. Both devices can function continuously, automatically at fixed intervals, or on demand by an operator to perform mid-air or ground inspections.

There are several competitive advantages to the M.E.T.I.-System over competing technologies. The principal advantage is that MDC has developed a design that allows the SHM hardware to be mass-produced, using flexible software to customize the system to any application. Most rival systems require an actuator/sensor pattern that is custom designed and built for an application, adding significant cost to the system and time and risk to the vehicle manufacturing process. By using a set family of products, the M.E.T.I.-System devices can be added to the vehicle as a final step, and the software constants would be customized and calibrated separately by MDC. Another major advantage is that the M.E.T.I.-System uses Lamb waves, which can efficiently query a much larger area on a vehicle than any other damage detection method using only one sensor and actuator. This allows for full vehicle coverage with a much lower sensor density, reducing cost, weight, complexity and computational requirements. Finally, the M.E.T.I.-System uses surface mounted sensors over embedded technologies, which is seen as a major advantage by most major aerospace manufacturers. Embedded sensors can initiate damage sites themselves, can prohibit repair of the structure if SHM system wires run through the damaged region, and are not able to be replaced if they fail in-situ. By using a surface mounted system that incorporates wireless datalogging and power transmission, the packaged MDC devices are able to survive the operating conditions while not interfering with structural integrity or functionality. The MDC devices can also be retrofitted onto existing and ageing aircraft just as easily as they can be installed on new ones. Surface mounting also allows for easy removal of the devices for structural repair or replacement of faulty sensors without damaging the structure.

Click here for a downloadable design specification for the latest MDC SHM sensors.