New-Tech Europe | March 2016 | Digital edition

across a wider range of frequencies, and the effect of the optimized circuits can be included directly in a new 3D simulation. The inclusion of circuit simulation tools means that the analysis can be more detailed than a simple S-parameter calculation. The electronic components of the chip and reader can be combined with a 3D model of the system (Figure 7), and using the AC Task, a realistic data transmission can be simulated. This will take into account distortions to the signal caused by modulation and demodulation, refl ection within the system, and unwanted parasitic eff ects such as interference from other tags. Full system simulation It is not enough for an RFID tag to work in isolation. Any practical RFID application also needs to take into account the effect of the environment, including detuning, shielding, and coupling between tags. These effects can have many different possible sources, including other tags, metal structures, nearby people and animals, and the tagged object itself. Simulation is the only way to calculate these complex effects before the prototyping phase begins. Figure 8 shows one example: sixteen pill boxes marked with RFID tags, all located in close proximity. These tags are interrogated by a reader located some distance away. Figure 9 shows the S-parameters for one tag on each row, ordered from those nearest to the antenna to those furthest away. The simulation reveals that the RFID tag in the first row, which is closest to the antenna, are actually more

Figure 6: The eff ect of diff erent possible alignment problems in a 13.56 MHz RFID-based near-fi eld communication (NFC) system.

For this, the OptenniLab tool is ideal. Optenni Lab shares a close two- way link with CST STUDIO SUITE, allowing simulation results and circuit models to be shared between the two products. The matching circuits can then be optimized to get a good match

broadband optimization is required. In addition, matching the coils at a single position will cause as many problems as it solves – strong mismatches will occur when the antennas are moved. Together, these two factors make effective matching difficult.

New-Tech Magazine Europe l 55