Plan

Our goal in pursuing a project with NFC devices was to further understand the technology and to see if we could amplify the signal of NFC devices to boost the range of data transfers. We planned to do this by inserting thin sheets of metal with high magnetic permeability between the NFC device and a regular metal object, which under normal circumstances grounds the magnetic field and makes data transfers impossible. When we were unable to acquire the appropriate materials to do this testing, we pivoted our focus to testing how placing an NFC chip (tag) on materials of varying electromagnetic permeability affected the range of NFC transfers. We predicted that when placed on an object with high permeability like ferrite, an NFC tag would be capable of transferring data at greater distances than when placed on objects of lower permeability.

Testing

To test the effect of a material’s permeability on the range of the transfer, we first looked at the range at which data transfer was possible without backing. Using a ruler, we measured the distance between the NFC tag and the NFC reader device. The NFC reader reader device was a NFC tag powered by the battery of a smart phone. We did several trials to establish an average distance for data transfers when the standalone NFC tag had no backing. In each test, we moved the NFC reader from out of transfer range towar the NFC tag until the rader device registerd the NFC tag, signifying a data transfer was successful. We then measured the distance between the reader device and the NFC tag when transfer was established. This operation was then repeated with different backing materials.

Results

We found an average of 3.645 cm for data transfer to be possible when the NFC tag had no backing. Data transfer between the NFC tag and the reader was impossible when the tag had a stainless steel backing. Trials with a 10 cm iron backing showed a smaller range of data transfer with an average of 1.72 cm.  We then found an average of 4.115 cm for a 1.2 cm glass backing, 1.98 cm for a 16 mm ferrite backing and 3.325 cm for wood backing. Interpretation We hoped that our testing would show a positive correlation between permeability and range of data transfer. These hopes were burned to the ground after several rounds of testing with different materials, when it became clear that our data was inconsistent with average permeabilities of our materials.

We hypothesized that greater permeability would ad to greater transfer distance, but as the test results show, our data was completely unpredictable. For example, when testing with the permeable metals iron and ferrite, we expected to see a greater transfer distance when the NFC tag was placed on ferrite, the permeability of which is on average far higher than most iron. Additionally, though non-magnetic materials like wood, glass, and air would normally be expected to achieve similar averages, tests with glass produced a surprisingly higher average of data transfers than the other nonmetal materials. Austenitic stainless steel backing didn’t allow data transfer because it is non-magnetic.

Analysis

What can account for these inconsistencies in our results? Unfortunately, there were too many uncontrolled and unknown variables that could have affected our tests to provide any one specific explanation. The quality and composition of metals used in the tests are unknown; ferrite, for example, has a wide range of permeability depending on the ratio of its components. Purity of iron affects its permeability as well, and there are a variety of stainless steels with variable permeability. Permeability is also affected by temperature, and our inability to control the temperature of the test area could have accounted for statistical discrepancies. Human error in the form of misreading a taken value or changes in how the NFC tag was held are also possible sources of confusing data.

Science

We were able to learn about the technology that powers NFC transfers in our research and experimentation, as well as the differences between NFC and similar wireless transfer technology like RFID. We also learned about electromagnetic permeability. Unfortunately, we did not find that in specific cases permeability affected the electromagnetic field of the NFC chips in a meaningful way.

Next Time

If we were to conduct this experiment again, we would acquire materials from sources that provided details on the composition of said materials in order to properly ascertain their actual permeabilities. Ideally we would be able to acquire thin foils of permeable metal so we could follow up on our original plan of adding a thin layer between the NFC tag and a grounding metal object. If we had another 6 weeks, we could attempt to build a rudimentary signal amplifier by altering a ham radio (suggestion courtesy of Larry Doe).

References

1.  Definition of permeabilty in a vacuum
2.  B. D. Cullity and C. D. Graham (2008), Introduction to Magnetic Materials, 2nd edition, 568 pp., p.16
3.  Richard A. Clarke. “Clarke, R. ”Magnetic properties of materials”, surrey.ac.uk”. Ee.surrey.ac.uk.