Tham khảo tài liệu 'new developments in biomedical engineering 2011 part 17', kỹ thuật - công nghệ, cơ khí - chế tạo máy phục vụ nhu cầu học tập, nghiên cứu và làm việc hiệu quả | 632 New Developments in Biomedical Engineering therefore show that the subterranean burrows of Norway rats are suited to study social networks of animals with wireless sensor network technology. In an underground environment the effective communication range is limited so forwarding of measurement data can be achieved using a technique known as Delay-Tolerant Networking or Pocket-Switched Networking. We exploit the physical meetings of different rats as opportunities to transfer data between their attached sensor nodes. These meetings are also the focus of interest in the effort to understand the social structure of the animals. Data forwarding therefore utilizes the social structure and vice versa the social structure of an animal community can be reconstructed by the routing data of the network. . Radio Propagation in Artificial Rat Burrows A typical rat burrow system consists of a number of segments with a mean diameter of cm see Calhoun 1963 and a mean length of 30 cm. The propagation of electromagnetic waves is very important for the adequate design of an efficient network protocol. Predicting the communication range between two nodes theoretically is difficult as we have to assume the burrow tunnel will act as a lossy wave guide in which the conductivity of the soil depends heavily on the exact composition humidity and surface. As our nodes are based on the CC2420 radio chip we work in the GHz ISM radio band. This chip employs direct sequence spread spectrum DSSS technology which is particularly well-suited for environments suffering from a high degree of multi-path propagation. To be able to better characterize radio propagation in rat burrows we built an artificial burrow system out of drainage pipes depicted in Fig. 2. As a test field we selected a 10 by 10 m field of loose ground consisting of mold small stones and some sand as would be expected for a rat burrow. We selected flexible drainage pipes with a diameter of 8 cm and 10 cm and a stiff
