take advantage of scaled technologies. In communications technology, attention is focused on wireless communications technology since this will be an essential part of many EmNets and on wireless geolocation technology since geographic location is a factor in many EmNets. The remaining sections review other components critical to EmNets, namely, the software systems that make EmNets work and MEMS, the new way to build low-cost sensors and actuators. Scattered throughout the chapter are boxes that provide more details on many of the technologies discussed. Readers who are already well versed in these subject areas or who are more interested in understanding the systems-level issues that arise in EmNets should move on to Chapter 3.


Much of the driving force for the technological changes seen in recent years comes from the invention of integrated circuit technology. Using this technology, electronic components are “printed” on a piece of silicon, and over the years this process has been improved so that the printed components have become smaller and smaller. The ability to “scale” the technology simultaneously improves the performance of the components and decreases their cost, both at an exponential rate. This scaling has been taking place for over 40 years, giving rise to eight orders of magnitude change in the size and cost of a simple logic element, from chips with two transistors in the 1960s, to chips with 100 million transistors in 2001. Scaling not only decreases the cost of the devices, it also improves the performance of each device, with respect to both delay and the energy needed to switch the device. During this same 40 years, gates1 have become 1000 times faster, and the power required per gate has dropped more than 10,000-fold. This scaling is predicted to continue for at least another 10 to 20 years before it eventually reaches some fundamental technical and economic limit (Borkar, 1999).

Silicon scaling continues to reduce the size, cost, and power and to improve the performance of electronic components. Reliability of the basic electronics has also improved significantly. Vacuum-tube electronics were limited by the poor reliability of the tubes themselves—filaments burned out regularly and interconnections were generally made by hand-soldering wires to sockets. Transistors were much more reliable due to cooler operation temperatures and the absence of filaments, but there were still huge numbers of soldered interconnects. As integrated circuits


A logic gate (“gate”) is the elementary building block of a digital circuit.

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