New-Tech Europe | March 2016 | Digital edition

only be readable in certain directions – or worse still, not at all. A full-wave simulation of the system can calculate the farfi eld of the RFID tag (Figure 11) in order to fi nd the transmission peaks and nulls, to allow the engineer to decide where the best location for the reader antenna is. When compared to Figure 2, it is evident that the environment has altered the tag’s farfi eld drastically. The time domain solver in CST STUDIO SUITE supports GPU computing, which can dramatically speed up the simulation of large or complex models. This makes it possible for big sections of the environment to be simulated and, especially when combined with distributed computing (DC) for solving systems with multiple tags, can be a very useful extension to the simulation tool. Conclusion Traditional RFID design methods can be complemented by EM simulation in order tobetter understand thebehavior of the device. Parameterization and optimization means that multiple design variations can be investigated as part of a what-if analysis, and the antennas can be tuned and matched for better efficiency. The whole system can also be simulated, including the reader, multiple tags, and the device’s surroundings, allowing engineers to examine how the system will behave in a realistic environment. These environmental effects can be very hard to detect without using simulation. Author Marc Rütschlin, Market Development Manager for Microwave and RF Applications, CST AG

Figure 7: Schematic view of a full tag-and-reader simulation, showing the time-domain signals at various points throughout the system. The 3D model is the large block on the center-right. Full sYstEM siMulAtion

simulation is useful is shown in Figure 10. Here, the RFID tag is embedded in a complex metal environment, consisting of several spools of a cable contained in a crate reinforced by a metal cage. All this metal will shield the RFID tag, which means that it may

weakly coupled than the RFID tags located in the center of the pallet, due to constructive interference. This effect would be extremely difficult to calculate without carrying out a fullwave simulation. Another situation where a full

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