Single photons are elementary particles that are arguably the most tangible, yet some of the most difficult to detect and characterize as single entities. Techniques to count single photons require optical detectors with linear operation, high gain, wide bandwidth and low noise. This article will describe a variety of approaches to detect and count single photons, the key measurement metrics, and potential applications of single photon sensors.

Last month we discussed how IMS and DMS are used for trace chemical detection. Now we consider how the two technologies can be used in tandem to achieve greater selectivity and sensitivity and fewer false positives.

The first installment of this two-part series discusses ion mobility spectroscopy (IMS), the leading contender for fast and reliable detection of trace chemicals, and differential ion mobility spectroscopy (DMS), a related technology that provides faster, smaller and more sensitive sensors capable of detecting chemicals in environments with greater concentrations of interfering substances.

Wildfires, river basins, tsunami alerts, and environmental risk management are just some of the projects using OGC's interoperability framework for Web-based access and control of sensors and sensor data.

Improved noncontact electrodes and noninvasive hybrid biosensors enable fast, reliable readings of hearts and brains, without requiring contact with the skin.

3D image correlation is a general-purpose strain measurement tool that allows us to measure 3D displacement and the true surface strains of any material without contact and without many of the difficulties associated with these measurements.

Autonomous mobile robots rely on sensors to navigate through their environment.

In an increasingly wired world, knitting together data from disparate sources into an interoperable whole can present disaster managers and first responders with critical information during a major emergency or crisis.

The Portsmouth Herald reports that the NH department of transportation has begun deploying sensors to measure atmospheric and road-surface conditions. Scientists at the University of New Hampshire are also using the weather towers to house ozone sensors to detect and measure air pollutants. Data gathered by the sensors allow the state to better plan winter maintenance.

One of the things the FDNY learned during the crisis of 9/11 is the importance of coordinating emergency vehicles without delay," says Asa Yanai, project manager for Motorola, which supplies vehicle-tracking systems to the New York and Chicago fire departments. The company's MDR800 model F5127 system integrates a u-blox GPS receiver with dead-reckoning functionality that, aided by other sensors, provides accurate vehicle location information—even in tunnels and underground parking garages. The systems are responsible, say New York City officials, for reducing response time to 911 calls by 3 minutes. www.sensorsmag.com/0906/SCfire1