ie3d rfid hf
But when I used it to calculate the near field distribution of a small size HF(13MHz) spiral antenna for RFID, there seems to be some problems in the magnetic field H calculation.
My spiral antenna is only 45mm X 75 mm large, and the operation frequency is at 13.56MHz. And in order to satisfy the FCC requirement, I need to examize the near-field distribution of both E and H.
In IE3D, I used the current distribution to calculate the near field along X and Y axis, and the distance is about 2400mm (2.4 meter) far from the antenna. The E field distribution is pretty reasonable and smoothy, but the H field has some convergency problem since it is like a random noise add to the Field.
I know that in IE3D, the near field are calculated from poynting vector, so the E field and H field are less accurate. But even though I decreased the step size for near field calculation, the non-convergency problem of H field still exists.
Are there anyone here good at IE3D near field display can help me to solve this problem? Thanks in advance.
Hi, antenna_abc:
The near field calculation on IE3D is based upon solving the PHI and A numerically. E and H are solved using finite differences on PHI and A.
Also, the near field calculation on IE3D is not supposed to be used for the E and H fields at far distances. The calculation involves numerical calculation of Sommerfeld integrals and the integrals are harder to solve when the distance is large. Your structure's electrical distance is not large while its physical distance is not small. Also, the distance is significantly larger than the size of your antenna. I do suggest you to use the far field calculation to predict the field in medium and far zones. The far field calculation is based upon asymptotic formulas and they are accurate and stable for far distances. What you can do is to solve the radiation pattern of the antenna on IE3D and add it into the Pattern List in PATTERNVIEW. Then, you can select it and select EDIT->PATTERN MANIPULATION AND WAVE PROPAGATION to solve the field values using the far field pattern.
Regards.
Thank you very much, Jian. Your explanation make sense to me.
So as you mentioned, by using the PATTERNVIEW in IE3D, the fields are calculated using the radiation pattern information. So basically it will be accurate in far-field region.
But if we calculate it by using radiation pattern, is it assumed fields decays with rate 1/r?
Actually, our measurement shows that the field in 3 meter range decays between the rate of 1/r^3 and 1/r, that is why we want to know what is the criterion distance between the near field dominant and far field dominant.
The other question is that I am using current source with 1E8 ohm parallel impedance as excitation in IE3D, can the PATTERNVIEW take into account for the source setting like the current view?
Thanks.
Hi, antenna_abc:
Yes. The distannce is not electrically very large. However, as I mentioned before, at this time, we are calculating the A and Phi instead of E and H directly. We will calculate the E and H using finite differences. It will degrade the accuracy. Also, for the near field calculation part, it is less critical than the EM simulation part and we have not put some much effort in improving the stability on it, even though we do plan to improve it in the near future. Using the far field pattern to predict the field distribution is a good way. Far field radiation pattern on IE3D is extensively used and its accuracy and stability is proven. The formula is very stable and accurate for far zone. The field is assumed to be inversely proportional to R. It should give you some good estimate of the field from the antenna. Regards.