Transcript
UPDATED
2012
COMPACT DIRECTIONAL PORTALS FOR TRACKING OBJECTS IN RFID SYSTEMS
Seknion T E C H N I C A L
B R I E F
Tracking objects with radio-frequency identification (RFID) can involve the use of awkward physical barriers to partition areas around readers or large, expensive antenna arrays to broadcast narrow beams of power. CONCRETE WALL
Seknion’s solution for tracking RFID tags
PORTAL
works with existing readers and tags and can easily be tailored to fit specific applications and environments.
Tracking objects in RFID systems A common problem for RFID inventory systems is to determine the direction in which tagged items pass through a portal – for example, whether they are entering or leaving a warehouse (Figure 1). Seknion has developed a solution to this problem by turning a standard RFID reader into a directional system with controllable “read zones”. The reverse side of this brochure explains how this patented technology works by limiting the directions in which tags can respond to commands from a reader.* Figure 2 shows how the technology, which can be supplied as an add-on kit, creates directional portals from a standard reader with only two antennas. In STATE 1, the modified reader creates a read zone that sees only those tags on the outside of the portal; in STATE 2, the read zone flips to the opposite side of the portal. By cycling the reader between the two states, and recording time stamps on the information returned by tags, the system easily determines the direction in which tags pass through the portal. Unlike conventional beam steering, Seknion technology for shaping read zones is immune to multi-path scattering off walls and equipment and to interference from other readers and wireless systems.
TAGGED ITEM ENTERING WAREHOUSE
TAGGED ITEM LEAVING WAREHOUSE
RFID READER (TWO-ELEMENT ARRAY)
FIGURE 1
PORTAL STATE 1 READ ZONE OUTSIDE PORTAL
Although wireless power is difficult to control, wireless information can be subject to precise direction. *Hansen, T., and Oristaglio, M., 2006, Method for Controlling the Angular Extent of Interrogation Zones in RFID, IEEE Ant. Wireless Prop. Lett., 5, 134-37.
READER
READER
FIGURE 2
STATE 2 READ ZONE INSIDE PORTAL
READ ZONE
SIGNAL (dB) guard signal
0
reader signal
-10 ANTENNA
ANTENNA
-20
0° SPLITTER
φ1
0° SPLITTER
φ2
0° SPLITTER
180° SPLITTER
RFID READER
GUARD SIGNAL
-30
-40
-90
ADD-ON KIT
-60
-30
0
30
60
90
ANGULAR DIRECTION from antennas
FIGURE 3 | Controlling RFID read zones with two antennas. (LEFT) The command signal from a reader is split into two copies (LEFT), and each copy is mixed with a special auxiliary signal – called the guard or scramble signal – and fed to the antennas. (RIGHT) Adjusting the strength and phase of the signals before mixing creates different patterns for the reader signal and guard signal. In one pattern (STATE 1), the reader signal (blue) exceeds the guard signal (purple) only in a zone to the right of the antennas, which is only where tags will be read. The control system then exchanges the patterns between the two signals (STATE 2), so that the reader picks up tag on left of the antennas.
Simple and robust control Sekion technology uses standard RF components and works with off-the-shelf RFID systems and tags. The photo below shows a demonstration working with an Alien Technology ALR-9780 reader and class I UHF tags in the 902 – 927 MHz band. New components to control the read zone are placed between the reader electronics and the antennas. With the guard beam off, the reader works normally and sees tags on all the bottles. With the guard beam on and set to mix equally at the antennas (to see straight ahead), the reader sees only the tag on the middle bottle directly in front of the antennas.
The technology is simple and robust: it works both in open areas and in narrow enclosed spaces with strong multi-path effects. For example, the demonstration in the figure was done in a small room in the presence of several overlapping Wi-Fi networks. Figure 3 above shows a numerical simulation of the control that can be achieved with a simple two-antenna system operating in an open area and in front of a concrete wall. More sophisticated solutions for applications in which multiple interrogation zones must be shaped and steered from one or more readers can be built from our patented methods for secure wireless broadcasting.
Precision and security in wireless communications Seknion specializes in the design and implementation of new technologies for making wireless systems more precise, efficient, and secure. Our vision is that these features can all be linked in systems that are tailored for your application using smart designs built around a full understanding of your wireless environment. To implement these solutions, Seknion develops both patented broadcasting technologies and a suite of simulation tools for modeling wireless applications in complex indoor and outdoor environments. Contact us for a demonstration of our unique technology working for your wireless applications.
Seknion, Inc.
when precision and security count
GUARD BEAM OFF
GUARD BEAM ON
www.seknion.com •
[email protected]
