Ultrasound Real Time Location Systems

For asset tracking, and particularly for Real Time Location Systems (RTLS), RFID is not always the answer. Ultrasound technology implementations also provide these auto identification benefits.

Ultrasound refers to sound waves that are higher than 20,000 cycles per second, which is beyond what the human ear can hear. The ultrasound used for asset tracking is not the same ultrasound we often first encounter as expectant parents viewing a fetus in the womb, which operate on far higher frequencies.

Like some popular active RFID systems, ultrasound can be cost-effectively deployed over an existing WAN or wi-fi network. For ultrasound, its discrete 35 � 45 kHz frequency provides room-level accuracy, including location accuracy at defined sub-room level zones. There is no interference with electro-magnetic frequencies emitted by other devices and equipment occupying the same space or nearby.

Unlike the radio waves, which are on the electro-magnetic spectrum, acoustic waves have a physical component. They actually push the air, and can be moved by air, just as you have more difficulty hearing someone shout across a field on a windy day. This is one of their advantages in real time location, because ultrasound is contained by walls.

This is a prime factor in assuring asset trackers precisely what room an item is in. Unless you had fire retardant or other materials in the walls or ceilings that contain the radio waves, the RF will act as if the walls are not there. Sound waves, though stopped by physical barriers, are not garbled by other electro-magnetic frequency noise generated by machines or other RF transmissions, an advantage in buildings full of electronic devices.

A site survey for all implementations shows where you have bleed-through of radio waves and where you have reflection. Ultrasound has no similar considerations, although you are certainly better off indoors � as in a hospital � than in open spaces where sound waves can dissipate. Unlike the unlucky resident of an apartment with thin walls, the ultrasound software can filter our amplitude below whatever amount the user calibrates.

Instead of readers, or interrogators, that RFID uses, you have detectors, which are microphones that receive the acoustic waves from the tags. Signal strength tells indicates the relative location of each tag. Louder is closer. Digital Sound Processor (DSP) algorithms determine where the signal came from. The detector converts it from its analog state, so the DSP can do its work. Each detector has its own channel, an IP address, and passes the signal over the network.

Each tag has its own unique identifier, of course, the base ingredient of all auto ID technology. That ID is associated with a database to tell you which tag is on which hardware, and which is on a physician. A tag�s range is up to about 50 feet, since acoustic signal strength, like spoken words, dissipates over distances in the air. There would typically be one detector in each room.

Ultrasound tags are battery powered and comparable in some ways to active RFID tags, with prices ranging from the mid $20�s to the mid-$30�s. They can be set to transmit at certain intervals, when they move, or both, with options like tamper sensors.

Sonitor CEO Terry Aasen believes that ultrasound�s precision data capture capability will enable companies to gain a clear competitive operating advantage. �It provides actionable information for refining processes and performance metrics. Documenting real-time positioning and tracking data enables clients to get an accurate real time audit for assessing people, place, performance, and processes. . . enabling time and motion studies; retooling of processes and productivity; and capturing more accurate billing information, based on personnel and equipment use and duration.�