Last week was relatively slow in comparison to the week before. Due to rain plus other delays, the contractors were not able to make much progress on the house and we were not able to deploy any additional Moos. However, this gave us some time to go over to the house to investigate why the the Moos that we currently have in the wall are not transmitting data back to the readers. Other than one lone tag transmission from the far right Moo on the rear wall, we were not able to get any readings. While it is expected that the concrete mixture will attenuate the signal, we are still hoping that the tag rate might improve as the concrete dries further. This has led us to investigate new approaches to getting around this issue.
Possible solutions to improving Moo penetration as of right now:
1. Adding an air-gap around the Moo antennas (possibly using a straw or other contraption to prevent the concrete from hardening right over the antenna). We found that the tag rate does not suffer nearly as much when the Moo has some air separation.
2. Lengthening/altering the Moo antennas to peak out of the empty cinder blocks. Since the antenna length is inversely proportional to the transmitting frequency, this may pose some issues.
3. Modifying the transmitting frequency to improve tag rate. While we are bound within certain limits and cannot arbitrarily change the frequency (need a new radios), we may find that there is a certain frequency that penetrates through concrete much better. The theory tells us that the lower the frequency the better it will penetrate through certain materials. I will continue to read up on some of the theory behind antenna and RFID design.
Also, it would be nice to know with more certainty if the Moos are not being powered sufficiently or if the problem lies with actually transmitting the data back to the reader. It will be hard to test this, but I think we could perform an experiment with an unpotted Moo that we probe with the Fluke to see how Vdd is affected by the the water. We will need a bag to prevent the equipment from getting wet.
Additionally, last week I made some final revisions to the following two google docs regarding the potting process as well as more info on the concrete and temperature measurement philosophy.
1. read more articles on RF signal basics and their properties. (e.g. http://my.safaribooksonline.com/book/certification/cwna/9780470438909/radio-frequency-fundamentals/radio_frequency_behaviors)
2. perform some experiments with air-gaps and/or metal backing to see how tag rate is affected.