Can the ST25R3916B reliably power NFC sensors via energy harvesting?

[MERSI]

Hi everyone,

I'm currently working on a project involving batteryless NFC sensors that rely on energy harvesting for their power supply. In this setup, the ST25R3916B is used as the NFC reader and is responsible for generating the RF field.

The idea:

• The ST25R3916B actively emits the RF field

• A passive NFC sensor harvests energy from this field via its VOUT

• The sensor performs lightweight tasks such as measurements or data transmission, powered entirely by the harvested energy

My questions:

1. Is the ST25R3916B suitable for providing enough energy via RF for passive NFC sensors in such harvesting applications?

2. Does the antenna design need special tuning to support stable energy transfer over 1–2 cm distance?

3. Has anyone successfully powered NFC sensors drawing 5–10 mA continuously via the ST25R3916B field?

4. Does this also work with a single-ended antenna design (e.g., using just TX1), or is a differential (TX1+TX2) configuration required for energy harvesting?

5. Can this work with a 50 Ohm matched antenna circuit, or does the energy transfer efficiency suffer significantly in such setups?

6. Any NFC (dynamic) Tag recommendations?

The goal is to create a fully passive, batteryless sensor setup, where the RF field from the reader not only enables communication but also powers the tag reliably.

Any insights, real-world experiences, or recommended antenna setups are highly appreciated!

Thanks and best regards,

[Marcel Rossignol · Accepted solution]

Hi Mersi,

basically what you want to do is in the context of NFC Wireless Charging (NFC). Here we have experience regarding energy transfer/harvesting.

To your questions:

1. Is the ST25R3916B suitable for providing enough energy via RF for passive NFC sensors in such harvesting applications?--> Yes, this reader IC is suitable and should fulfill your needs (according to you next questions :-))

2. Does the antenna design need special tuning to support stable energy transfer over 1–2 cm distance?--> This depends on the distance between reader and tag antenna. In your case (1- 2 cm distance) the mutual coupling of the antenna coils is already relatively weak and it could be sufficient enough to tune the reader matching network without the tag (receiver). This makes the antenna impedance measurement for your reader matching network design much easier.

3. Has anyone successfully powered NFC sensors drawing 5–10 mA continuously via the ST25R3916B field?--> This is the most crucial question: How much power do you want to transfer at which distance? I assume you would need a voltage of ~5V with max. 10mA  (max. 50mW)?! This should be feasible for your target distance (max. 2cm). Please be aware that the antenna designs play a significant role as well. (dimensions, Q-factors, coupling factor, surrounding environment,...)

4. Does this also work with a single-ended antenna design (e.g., using just TX1), or is a differential (TX1+TX2) configuration required for energy harvesting?--> Basically you can create more output power with a differential configuration. I don´t have any experience with a single-ended design. All comments before refer to the differential design.

5. Can this work with a 50 Ohm matched antenna circuit, or does the energy transfer efficiency suffer significantly in such setups?--> Similar answer as in point 4: 50 Ohm antenna --> single ended configuration. And yes, I assume you would lose energy.

6. Any NFC (dynamic) Tag recommendations? --> We did our studies with this tag: ST25DV + external bridge rectifier in parallel

I hope this helps you :)

Best regards,

Marcel

[Henry Crane]

Hi Mersi,

We developed a demo board called SMART TAG (https://www.st.com/en/evaluation-tools/steval-smartag1.html), based on our ST25DV NFC tag IC family with NFC, I²C and Energy Harvesting features, an STM32 and various sensors. . Documentation like BOM and schematics is available at the link above, and it can buy it at different distributors.

best regards,

Henry Crane, NFC/RFID support team