Validate Field Strength of an NFC Antenna at a Given Distance in Seconds
Verify the design intent of an NFC antenna with EMxpert in real-time on your bench-top
What is NFC (Near-Field Communication)?
NFC is the acronym for Near-Field Communications. NFC is a short-range wireless communication between two electronic devices. NFC antennas operate at low frequency centered on 13.56 MHz. Communication range of two devices is several centimetres (typically 10 cm or less).
Some popular NFC applications are contactless transactions (e.g. mobile payment, ticketing, store vouchers) and data exchange (share pictures, files, business cards).
How can EMxpert help design NFC antenna?
Considering the size, frequency and distance, antenna radiation pattern is not a meaningful parameter for NFC designers. Amplitude and distribution of the signal are important. The EMxpert is a fast and effective tool that measure and displays the emissions from an NFC antenna using very-near-field technology. The peak hold mode of the EMxpert can still create a full image of the antenna’s emission in seconds even with a bursty NFC signal.
These results would allow a designer or a tester to verify that the antenna is operating as expected and to validate the antenna’s emission level versus calculated results.
We tested two mobile phones with NFC antenna using EMxpert:
Using the EMxpert the NFC antennas from two mobile phones can be clearly seen. The currents on the antenna element itself can be used to verify the design intent of the antenna. A far-field prediction in this case does not make sense since the antenna is meant to operate in the near-field region only.
The phones were placed directly on the EMxpert scanner and the NFC capability of the phone was turned on. Even without a connection the phones would ‘chirp’ from the antenna intermittently. Once the frequency was identified with a spectral scan, a spatial was run with peak hold so that a complete picture of the emissions could be made.
One of the phones was placed on the scanner as shown in the image below; the spatial scan result is shown next to it.
When the near-field result is overlaid on top of the photograph of the phone itself (left image below), the resulting currents seem to show the antenna is looped around the outside of the phone. An image of the internal circuit board of the phone is shown below right. The NFC antenna is visible in the photograph as the small copper wire at the edge of the board. This confirms what was seen in the near-field plots but of course the near-field measurement confirms that the antenna is transmitting and can verify the transmission level.
The next phone has a back case which comes off and exposes every antenna used for GSM, Wi-Fi, NFC etc. The case is shown below left and the NFC antenna section is highlighted in red. The results from the near-field scan show strong currents in an area similar to the shape of the highlighted antenna (right image below).
When the very-near-field result is overlaid on top of the photograph of the phone case itself, the image clearly shows the strong correlation between the NFC antenna emissions and where the antenna’s physical location is.