Since the start of the war in Iraq, soldiers have returned home at an alarming rate with a highly complex battlefield injury: traumatic brain injury (TBI). The injury, which is frequently caused by the blast from an improvised explosive device (IED) or rocket-propelled grenade, can be difficult to detect and diagnose. The difficulty is made worse because the number and severity of the blasts to which a soldier has been exposed are often unknown.

In an effort to understand brain injuries, the U.S. Defense Advanced Research Project Agency (DARPA) has awarded a $5 million, three-year contract to the Palo Alto Research Center (PARC) to develop a strip of plastic that can be "taped" onto a soldier's helmet to measure his or her exposure to explosions. The tape, which will cost less than a dollar per strip, is a flexible plastic substrate that will contain printed electronics, analog memory, and sensors. It will record seven days' worth of information, which will then be transferred to a soldier's medical record. The disposable tape will be replaced.

IEDs emit shock waves--waves of air pressure--that travel at around a thousand feet per second, or close to the speed of sound. Such an explosion can cause severe brain damage, which often goes undiagnosed until weeks after a soldier's return home. "TBI is going to be the signature injury of the war, but to understand it, we need the data," says Kevin "Kit" Parker, an assistant professor of biomedical engineering at Harvard University and a U.S. Army Reserve captain who served in southern Afghanistan from 2002 to 2003.

Last year, the U.S. Army awarded a million-dollar contract to Simbex, of Lebanon, NH, to build sensor-studded helmets, but the technology is cost prohibitive and has not made it to the battlefield.

The sensor tape being developed by PARC will be fabricated using its ink-jet printing technology, a patterning technique developed for large-area electronics, such as flexible, flat-panel displays, RFID tags, solar cells, and electronic paper. To print the components--electronics, memory, and sensors--on the tape, the ink-jet printer will deposit solution-processed materials, including organic semiconductors, polymer dielectrics, and metal nanoparticles, on a plastic substrate.