Novel Wearable Sensors for Body Area Network Applications
16.1 Body Area Networks
In free space, electromagnetic waves emitted by isotropic radiators are transmitted as spherical waves. Spherical transmission is effective for multicasting services. On the other hand, to realize point-to-point links by radio in areas where cables were previously used, a precisely directed antenna transmitting a narrow beam is necessary to focus the energy emitted by a given base station to certain receive antenna.
It is also essential to reduce the output power of the transmitter and to limit interference with other systems in order to separate the coverage area of one radio system from another. Bluetooth or ZigBee have been developed to provide power control by protocol when using free-space transmission. In addition, low-power radios with a modest transmission capacity are available for unlicensed use.
Many wireless devices are currently used, so controlling the propagation of the electromagnetic waves so as to limit the cell covered by one device is expected to be the challenge in many applications. Body area networks (BANs) have to confine the coverage area to the human body, for example. As a result, the potential use of a subsidiary waveguide is being considered as a new method of focusing the transmitted energy, lowering transmission loss, and controlling the transmission power of wireless devices. The coverage ...