ABSTRACT

There is growing interest in the development of autonomous small-scale devices capable of sensing/actuating and performing communication and processing tasks in personnel health-care technology. Such devices form the basis of many novel diagnostic and prosthetic systems and are often networked to form the so-called sensor networks, which constitute a very active field of research. Similarly, autonomous implants within the human body that serve to capture data or to stimulate cells are essentially specialized sensor/actuator nodes, whether or not they are networked. Such implants are typically powered by a battery or through a transdermal inductive link with a device that is external to the body. It is well known that extremely 572low power consumption is a critical feature in order to maximize the operational life expectancy of a node, an implant or an entire network of such devices powered by batteries. Alternatives to batteries generally fall under the energy-scavenging category with the exception of the inductive link discussed earlier. In all such cases, the power available is likely to be very low. Multiple power-saving schemes have been proposed and are in use in several power-conscious devices. Possibly one of the most common is the introduction of inactive or sleep states whenever appropriate. Indeed, an entire electronic device can be shut down when there is no work to perform, or certain components can be turned on and off depending on dynamic demand. The power consumption of devices in sleep or standby modes can be orders of magnitude lower than their active consumption.