Feb. 1, 2005—Radio frequency identification is gaining broader acceptance as a robust technology that can be used for many applications. But two Scandinavian companies say there are niche applications where radio waves are a less-than-ideal means of identifying objects.

Sonitor Technologies, a Norwegian startup, has developed an indoor positioning system that uses battery-powered tags that have accelerometers—sensors that respond to movement. When a tagged object moves, its tag emits a series of ultrasound tones that humans can’t hear. A detector picks up the tones from as far away as 45 feet, translates them into a serial number and sends that number along with its own detector identifier to a software system residing on a central server. The software knows which room the detector is in and displays the room where the object was “heard.” When the object stops moving, the tag goes back to sleep.

Sirocco's infrared reader

Ultrasound’s advantage over RFID? It can’t penetrate walls, so when a tag is detected in a room, you can be certain the object is in that room. But it can become a disadvantage when an object can’t be found because it’s in, say, a sealed cabinet.

Ragnar Bo, Sonitor’s CEO, says ultrasound is great for tagging assets, such as wheelchairs, gurneys, pumps and other medical devices and personnel in hospitals. Ultrasound doesn’t interfere with electrical equipment used in hospitals, which could be a concern with RFID.