# CR95HF custom antenna current and magnetic field strenght

Question asked by hamalainen.tomi on Jun 14, 2013
Latest reply on Jun 26, 2013 by hamalainen.tomi
Hi,

I am designing a product that uses CR95HF transceiver IC and custom shape flexible antenna.

According to ISO/IEC 15693 standard a vicinity coupling device shall generate a field of at least Hmin (150mA/m) and not exceeding Hmax (5A/m) at manufacturer specified positions (operating volume). It is also defined that a Vicinity Integrated Circuit(s) Card shall continue to operate as intended after exposure to a magnetic field of 12 A/m at 13,56 MHz.

In my mind this specifies the operating conditions my design has to meet. I have been able to build a working system that can read and write tags but I do not have concrete evidence if my system works in boundaries explained by ISO/IEC 15693.

I have studied basics of RFID-technology and read documents like AN3394. In AN3394 equation (III.1) gives us estimate of generated magnetic field. However in that equation there is one varieble that is not explained and that is the rms current in the antenna. My question is how can I calculate or measure that current in real world (with my custom antenna system, our antenna is also rectangular)?

I have some equipment available to me for measurements (Agilent DSO8104A Oscilloscope, HP4282A LCR-meter, R&S ZVA-8 Vector network analyzer) and i have been able to measure the correct component values for the impedance matching network. I have also measured voltage generated between my antenna contacts and between demo boards antenna leads. Below is picture of waveform generated by DEMO-CR95HF-A

Tl;Dr : How can one measure current in custom antenna when using CR95HF (or generated magnetic field)?

Edit: STSW-M24LR015     DEMO-CR95HF-A antenna matching circuit calculation is helpful for estimating the read range and generated magnetic field, but it has fixed value for Irms = 0,106353. How did you get that value?