Expected Reading Distance with ST25DV64K / ST25DV04K

[chklemenz]

We are using the NFC Tag Chip ST25DV04K & ST25DV64K for a customer project. The NFC Antenna is on the same PCB as the Tag Chip.

Variant with ST25DV64K, Antenna Size approx 19x44.5mm

Variant with ST25DV04K, Antenna Size approx 66.75x24.5mm

The antenna is well matched to the center of 13.56Mhz (measured in the plastic housing and final installation situation). There is a grounded metal plate around 20mm below the PCB.

Our goal is to reach a reading distance of about 40 – 50mm with commercial Smartphone readers, because the closest distance can be 35mm (the PCB is deep in the housing placed).

With iPhone SE we get a reading distance up to 50mm with smaller Antenna and up to 70mm with the larger Antenna.

We tested with another Smartphone like Samsung Galaxy A14 and A15. With A15 we never get a successful communication at the minimum distance of 35mm. We have to place the Smartphone inside the housing with a distance of approx 10-20mm to get a successful communication.

With A14 it’s a little bit better than with A15. But also there we get only a connection with a distance of around 40mm and lower (even with the larger antenna), and also the communication is not always successful at a reading distance of 40mm.

Our questions are:

• What is the expected reading distance with this antenna sizes and smartphone readers?
• Can you explain this different reading distance with different smartphone ?

We did several tests to improve the reading distance, nothing helped:

• Removing GND Plane around the antenna
• Removing metal plate
• Antenna Matching slightly higher than 13.56Mhz (around 13.6 - 13.8Mhz)

[JL. Lebon]

Hello, 

With such antennas and smartphones, you can expect reading distances between 3 to 6 cm.

It is difficult to be more precise, because it really depends on the smartphone. Every smartphone has a different antenna with different size and different characteristics. They can also transmit at different power level depending on the embedded NFC controller and how the manufacturer has configured it.

Samsung mobiles are usually not providing good performances unfortunately. Moreover, when most smartphones. have their NFC antenna on the top of the case, near the camera, Samsung usually place the antenna in a very different position, sometimes in the middle of the phone's back, sometimes on the bottom, sometimes on the top.
You may try to find the exact position of the NFC antenna on the back of the Samsung phone, and then place the phone's antenna well aligned with your antenna.

Best regards.

[chklemenz]

Thank you for your input. I'm aware of the different positions of antenna in smartphone. Good to know that Samsung smartphones are not known to have particularly good performance. Do you know if there are other Android Phones that performs better than Samsung ?

Beside on that, we would like to optimize the PCB antenna for a better reading distance without increasing the outer dimensions. We found an application note (AN5605), that describes the process to design a 2 Layer antenna. If we transform the existing antenna to a 2 layer antenna, we can reach a higher diameter inner side while the outer dimensions are identical. Do you think that this will help to get a higher reading distance, and if yes, which improvement do you expect ?

[JL. Lebon]

Hello, 

This topic has been opened for quite a time now. 
Where you able to make any progress on this reading distance limit?

Best regards.