Wireless sensor nodes

Highly miniaturized and autonomous sensor systems or in short wireless sensor nodes can serve many application domains in an ambient intelligent future such as health and comfort, industrial processes, automotive etc. Ultra-low power consumption and energy scavenging from the environment are essential for their commercial success. This paper reviews the technologies necessary to develop these systems, with focus on micropower generation and low-power design. The potential of wireless sensor nodes and the challenges related to their development are illustrated by a test case on body area network technology. I. CONCEPT AND APPLICATION AREAS OF WIRELESS SENSOR NODES Our future is evolving towards a world where compact and inexpensive microsystems will add intelligence to almost every object that surrounds us. Sensing and actuating functionalities will be ‘hidden’ in the environment. They will be aware of the context and be able to interact wirelessly with people and with each other. These miniaturized sensor systems are configured into a wireless network and work autonomously, based on their low power consumption and energy scavenging from the environment. Hence they are referred to as highly miniaturized and autonomous sensor systems or, in short, wireless sensor nodes. Each node can be imagined as a small computer, extremely basic in terms of interfaces and components. They usually consist of sensors, a radio unit for wireless communication, a logic circuit for basic calculations and a power supply unit. Size and cost constraints result in corresponding constraints on resources such as energy, memory, computational speed and bandwidth. These wireless sensor nodes are being developed for integration in all possible objects, hence serving applications in a large number of domains. For instance, a variety of state-of-the-art devices for sport, comfort and entertainment applications (such as gaming) will make use of sensors and actuator systems in and around the body. They will be developed to be worn as easily as a digital wristwatch. Equally, wireless sensor nodes will be used to scan, sense and interpret data from the human body, enabling people to better control their healthcare and potentially reduce medical costs. Ultimately, the technology will lead to the development of a personal body area network (BAN) which provides medical, sports or entertainment functions to the user. But also in automotive electronics, the demand for wireless sensor nodes is growing rapidly. They will be used to scan the car and its exterior environment, sense relevant information, collect it, interpret it, record it and communicate it so the driver can respond accordingly. Networks of distributed sensor nodes will as well be used to enhance industrial process control, or to assist farmers in efficiently cultivating large crops. Construction workers and engineers will rely on the data that are collected by miniaturized pressure sensors built into buildings, roads, bridges and railways. It’s almost easier to come up with examples than to find areas of our civilization that will not be affected. In the next section, we will illustrate what today’s technology is capable of in the area of healthcare. Ambulatory multiparameter monitoring as an example of a BAN was chosen as a driving application. The features of the first demonstrators have been translated into challenges that need to be solved in order to enable a widespread deployment of BANs. In the remainder of the paper, we will show how advances in generic technologies, with focus on micropower generation and low-power design, can enable such systems in the near future. II. TEST CASE ON HEALTHCARE: AMBULATORY MULTIPARAMETER MONITORING A. Body area networks, a component of e-Health technology It is a common trend especially in wealthier nations that people spend increasingly more money on healthcare. Statistics show that the cost lowering effect of technology and automation is more than offset by the impact of an ageing society, consumerism, biotechnology and medical breakthroughs. This results in an overall increase in cost between 2-3% per year. As a result, alternative ways to increase efficiency, productivity and usability while controlling cost are being sought. One strategy consists of offloading healthcare institutions by shifting the health management outside the expensive formal medical institutions. E.g., in the field of chronic diseases, the provision of real-time data from and to the patient anywhere and at any time may hold significant potential for cost reduction. In all this, the supporting role of an adequate technology platform such as an ‘e-Health technology platform’ is critical. E-Health refers to the use in the health sector of digital data transmitted, stored and retrieved electronically for clinical, educational and administrative purposes, both at the local site and at a distance. Driven by demographics (the ageing society), an increased incidence of chronic diseases and the ever rising patient expectations e-Health technology is increasingly coined as the revolutionizing enabler for the next decades to come.