News and New Products

Conference: RFID struggles while smart sensors animate intelligent buildings

By Bill Schweber, Executive Editor -- EDN, 4/21/2005

RFID technology is having difficulty gaining wide acceptance despite all the attention it receives, but smart sensors are finding use in diverse and substantive applications, according to speakers at yesterday's Smart RFID Briefing, organized by the Boston University School of Management and Information Gatekeepers.

Smart sensors, which combine a sensor, local intelligence, and a wireless link more versatile than an RFID approach, are finding success because they offer more flexibility than simple RFID tags, said leadoff speaker Mark Gaynor, assistant professor in the Information Systems Department of BU's School of Management. An RFID tag is primarily just an ID, and provides no context, while a smart sensor can be programmed and reprogrammed, can implement local decisions, can communicate effectively, and can be re-tasked when you have project uncertainty, he said.

Smart sensors provide a value proposition and a return on infrastructure investment that plain RFID tags cannot match, and "allow you to capture the value of design options," Gaynor noted. Linking the sensor to a network provides a basis for value-added analysis and overview, which are strong benefits.

Mark Pacelle, vice president of marketing at Millennial Net, said that sensors provide tangible, immediate opportunities with short and justifiable paybacks, notably in the building-management area. Buildings have a large number of points that need monitoring, including doors, windows, temperatures, room air flows, fire zones, elevators, stairs, HVAC systems, and water systems. "The challenge is getting all the trickle of data from the pervasive sensors back to one spot," Pacelle said.

In general, the application requirements divide into handling event-driven signals like fire alarms, periodically sampled sensors for signals like room temperature, and even store-and-forward data for applications such as "cold-chain management," which assesses the integrity of freight shipments that must be kept below a specified temperature, he said. Sensor networks have found their greatest success to date in building-management applications because that is where the requirements are most clear and the overall project situation is bounded and definable, he noted.

Sounding a note of caution, Pacelle emphasized that "the RF environment is fundamentally unstable, but a mesh network can overcome this problem."

Underscoring that point, Michael Newman, principal engineer of Sensicast Systems, described his company's learning curve in installing an alarm system in a small, local museum. The application watches for intruders, but also includes touch sensors that, for example, respond to someone handling a picture frame by automatically alerting guards, directing a camera to swing to the source of the alarm, and feeding the picture to security video monitors. The mesh network Sensicast installed used nodes approximately every 100 m, and had to work around RF dead spots, interference sources, and other impediments to the application's 0.5-sec latency goals.

The company found that "multipath is the biggest problem in these installations—bigger than interference," Newman noted. The best frequency within the overall band of the spread-spectrum modulation Sensicast used turned out to be different between different node pairs and was heavily dependant on interior location.

Newman does not believe that any variation of the IEEE 802.11 standard is a good choice for this type of installation. "The tacit assumption in 802.11 is that the node is always on—which is not the case," he said. "Also, it is too complex to manage, and it is overkill and a poor fit in terms of bandwidth and power consumption." Instead, he believes that the IEEE 802.15.4 standard represents a much better choice for smart-building applications.