But the power barrier, Smith says, is rapidly eroding. Advances in sensor chips are delivering predictable, rapid progress in the amount of data processing that can be done per unit of energy. That, he said, expands the potential data workloads that sensors can handle and the distance over which they can communicate — without batteries. 

Smith and a WISP light sensor. In an experiment, Smith hung the sensor on his window and it detected light levels for 12 hours. These sensors take an ordinary RFID tag and increase its functionality.

At Intel, Smith is doing sensor research that builds on commercial RFID technology (for remote identification) and adds an accelerometer and a programmable chip — in a package measured in millimeters.



Its power, he explains, can come from either a radio-frequency reader, as in RFID, or the ambient radio power from television, FM radio and WiFi networks. (For the latter, Intel is developing “power-harvesting circuits,” he adds.)

“The ability to eliminate batteries for these sensors brings the vision of smart dust closer to reality,” he says.

In this model of computing, the sensors are servants. They exist to generate data. And the more sensors there are, the better the data quality should be. When mined and analysed, better data should in turn help people make smarter decisions about things as diverse as energy policy and product marketing.

If sensor-based computing takes off, it will ignite fresh demand for a wide range of hardware and software to store, process and search the new oceans of data for nuggets of useful knowledge. So it could be a boon to business, a foundation for what analysts call “the Internet of Things.”

“It does feel almost like the beginning of the Internet,” says Katharine Frase, (left) vice president for technical and business strategy at I.B.M. Research. “You can see that sensor computing is going to be important and useful, but it’s not possible to see in advance just how it will transform things.”

She is on the record that hardware advances and software programming methods need to be more on the same track.

The recent advances in stand-alone sensors may be impressive, but some researchers are pursuing a different path. “We already have massively distributed wireless sensors — they’re called cellphones,” explains Deborah Estrin, (left) a computer scientist at the University of California, Los Angeles.

She is displaying a sensor for a surveillance camera at the Center for Embedded Networked Sensing, a consortium of six schools headquartered on the UCLA campus.

Estrin envisions a day when the tiny sensors embedded in hard-to-reach places become as commonplace as computers plugged into the Internet.
Several of the projects she has worked on use cellphones and people in data-gathering and analysis.

Cellphones, they say, are versatile data collectors and are becoming more powerful all the time — with cameras, GPS, accelerometers and Internet connectivity. Their work is at the forefront of an emerging field called participatory sensing.

Projects involve collecting travel, time and location data that is fed into Web databases to calculate an individual’s personal environmental impact and exposure to pollutants . Another project, in cooperation with the National Park Service, uses a smartphone application to identify, photograph and track the advance of invasive plants, which can crowd out local species and undermine biodiversity

TheTwitter application for self-reported data on one’s daily life which can be assembled into small graphs that show a person’s behavior over time has as its most common use since the site went up last fall, says (right) Nathan Yau,  a graduate student who created the application, has been to track personal health — eating habits, weight, blood pressure, glucose and sleep times.

The cellphone is a constant companion — immediate and intimate, always there to inform, remind and prompt. “The killer app for this is personalised health and wellness,”says  Estrin. “The potential to help people make behavior changes and lead healthier lives is tremendous.”

Mobiles can also be a lifesaver for solitary workers and in cases that involve such serious illness.

So roll on smart power for sensors and roll on nuclear batteries.  Jae Kwon,  assistant professor in electrical and computer engineering at University of Missouri, is developing a tiny radioisotope battery  - the current model is about the size and thickness of a penny. Kwon is collaborating with J. David Robertson, MU chemistry professor, to build and test the battery at the University of Missouri research reactor (MURR).

Nuclear batteries for MEMS devices are not new, but Kwon's small size battery is and its other unique characteristic - it using a liquid semiconductor rather than a solid-state one.

"The hard part of using radioactive decay is that when you harvest the energy, part of that energy goes towards creating defects that damage a solid-state semiconductor," says Robertson, associate director of the research reactor. "Our hypothesis is that with a liquid-state semiconductor, the same damage won't happen. So we created a battery without that part degrading over time."