S Figure 3-2 Sensors use the strength and direction of radio signals from their neighbors to map their locations. flow through the membrane and creating an electrical signal detected by the underlying circuit. The other sensor under development contains antibodies placed between tiny electric contacts. When an agent such as a virus, bacteria, or spore binds to the antibody, the current flowing between the contacts is altered. To keep size and power requirements small, the devices will communicate using very-low-power radio signals, allowing each device to reach only a few others in its immediate neighborhood. Rather than using global positioning system (GPS) technology, which would add weight and power requirements, the sensors will use the strength and direction of radio signals from their neigh- bors to map their locations. The signals will be relayed from one device to another until they reach a human operator at the edge of the territory. In theory, the "reachout point" could be a van, a low-flying aircraft, or even a satellite (Fig. 3-2). The engineers will also draw on game theory-which deals with how a group of individuals interacts and competes for resources-to program the devices to work together. The devices will decide, for example, the order and direction in which messages should be relayed, avoiding redundant signals. If the coverage mapping shows that some areas are not covered, the network will be able to call for the deployment of additional sensors. Additionally, the researchers will draw on case histories of earthquake effects, accidents in crowded urban environments, and the aftermath of the World Trade Center attack to develop prototype applications, which in turn will determine the design of the sensors and networks. This work will draw on a database developed by the Multidisciplinary Center for Earthquake Engineering Research at the University of Buffalo as well as on interviews with experienced rescue workers, including some who worked in the wreck- age of the World Trade Center. WIRELESS S