Credit: Nicolle Rager, Zina Deretsky, National Science Foundation

A sensor is any device that can take a stimulus, such as heat, light, magnetism, or exposure to a particular chemical, and convert it to a signal. Sensors have certainly been around for a very long time. Scales–weight sensors–were used by the Sumerians at least 9000 years ago. Thermometers–temperature sensors-were developed in the late 16th century by Galileo and others. Barometers–pressure sensors–were invented a few decades later by Galileo's assistant, Torricelli. More recently, scientists and engineers have come up with devices to sense light (photocells), sound (microphones), ground vibrations (seismometers), and force (accelerometers), as well as sensors for magnetic and electric fields, radiation, strain, acidity, and many other phenomena. From the metal detectors we pass through at airports to the smoke detectors that protect our homes, our modern civilization is utterly dependent on sensors.

While the concept of sensors is nothing new, the technology of sensors is undergoing a rapid transformation. Indeed, the forces that have already revolutionized the computer, electronics, and biotech industries are converging on the world of sensors from at least three different directions:

1. Smaller: Rapid advances in fields such as nanotechnology and (micro electro-mechanical systems (MEMS)) have not only led to ultra-compact versions of traditional sensors, but have inspired the creation of sensors based on entirely new principles. One example is the electronic nose developed by chemist Nathan S. Lewis and his colleagues at the California Institute of Technology. Another is the cantilever molecular sensor. And still others are to be found among the many projects that NSF has funded through its nanotechnology priority area, and through initiatives such as its recent XYZ on a Chip program.

2. Smarter: The exponentially increasing power of microelectronics has made it possible to create sensors with built-in "intelligence." In principle, at least, sensors today can store and process data on the spot, selecting only the most relevant and critical items to report.

3. More Mobile: The rapid proliferation of wireless networking technologies has cut the tether. Today, many sensors send back their data from remote locations, or even while they're in motion.

As these forces converge, however, they pose daunting new challenges for researchers and society alike.