RFID Systems
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Project Objective
The objective of this project was to research RFID for use in lost-item location and retrieval in assisted living and healthcare environments. RFID in the healthcare environment is not a new idea and it has been explored many times. In an article titled, "Leveraging RFID in Hospitals: Patient Life Cycle and Mobility Perspectives" [1], it was explored how RFID could be used in patient and mobile object tracking in hospitals. The specific goal of our project was to determine if a system could be developed which would allow a patient's important items(eyeglasses, medication bottles, etc.) to be located, if lost. Many hours are currently spent looking for lost items in healthcare environments. Developing a location system by writing RFID tags for specific items and locating them with a handheld device would alleviate some of the work that healthcare professionals and assistants have to perform on a daily basis. The need for this product arose from a discussion with the nursing and support staff at Phoebe Home in Allentown.
To accomplish this goal, we looked for a long-range, passive RFID solution. The reason we chose passive RFID tags is because the solution should be as discrete as possible. An active or even semi-passive solution would involve tags much too large for the items we would expect to tag. The device would also need to be of a small form factor, so that someone could hold it in their hand, point to an area, and it would return if anything tagged was located.
RFID Technology
Three current RFID solutions were researched for this project. Passive RFID, which was the technology chosen, relies on the reader's signal to power the antenna to return the data on the tag. This is the cheapest and most discrete solution because the tags do not require the use of battery power. Semi-passive RFID tags require the use of a battery to give more power to the return signal. Active RFID tags are fully battery powered and act as beacons, constantly sending out a signal to readers which are listening. The tags used in semi and active RFID solutions are also much larger than their paper-thin, passive, proponents, making them less suitable for this particular project.
RFID Reader
The M9 can be connected to a computer via USB or serial, and it was chosen for it's performance and interoperability with both Windows and the Linux Operating System. The device comes with software and libraries that allow it to be configured for different needs and environments. The reader can read and write to passive UHF tags using different power levels that allow greater distance between the tag and the reader. For the purposes of measuring the following tags' characteristics the reader was set to its maximum power level of 27 dBM.
Testing Approach
For testing the tags were held at varying distances from the reader to determine the varying maximum distances that we could expect. The tags were then affixed to various objects to determine where each tag performed better than the others. Maximum distances were considered the maximum distance that the tag could travel away from the reader and not backscatter a signal from the reader. When tags are close to the reader, they perform more strongly by returning the signal at a higher frequency. At further distances the tags would return a signal more sporadically. The maximum distance is the distance of lowest frequency of returned signal.
RFID Tags
- A total of 12 tags were evaluated for use, with some of the tags being less useful as they either have short distance reads of 5cm, or are intended for more industrial applications such as being affixed to steel. The 5 tags were selected below as being the tags with highest relevance to the assisted living project. They are fairly discrete as they are slightly thicker than a piece of paper and are generally small in size. The distance measurements were taken with the tag not affixed to any object. When the tag is affixed to an object, the read distance declines, sometimes dramatically.
"2x2"
- Dimensions: 4.7x4.2 (cm)
- Distance:
- Normal - 50cm
- Angled(45) - 40cm
- Angled(90) - 20cm
- Distance:
"Squiggle"
- Dimensions: 9.7x1.1 (cm)
- Distance:
- Normal - 260cm
- Angled(45) - 260cm
- Angled(90) - 60cm
- Distance:
"Mini-Squiggle"
- Dimensions: 2.7x1.0 (cm)
- Distance:
- Normal - 50cm
- Angled(45) - 50cm
- Angled(90) - 10cm
- Distance:
"Ad-612"
- Dimensions: 13x2.5 (cm)
- Distance:
- Normal - 260cm
- Angled(45) - 260cm
- Angled(90) - 1cm
- Distance:
- Note: This also comes packaged in a plastic housing to provide weathering protection and increase readability when affixed to objects.
"TTF-Label 12x180-PH46"
- Dimensions:1.2x18.0 (cm)
- Distance:
- Normal - 190cm
- Angled(45) - 190cm
- Angled(90) - 5cm
- Distance:
Readability
General Problems
- There are a couple notable problems with the tags which would apply to the PATCI project
- Placing tags on rounded surfaces reduces the strength of the antenna. The tag will only be readable at contact if at all. This will have an effect on the readability of the tag if it is placed on a prescription bottle, as would be practical in the case of this project.
- Liquids and metals greatly interfere with the strength of the antenna. The tags perform better when placed away from the metallic object and some tags come pre-equipped with a standoff to enforce this.
Specific Cases
Application to Eyeglasses
- The above distance values were recorded without any item attached. A logical use of the 12x180 tag would be to place them on a pair of glasses. When affixed to the side of the glasses, the read distance of this tag drops to approximately 5cm. The metal in the rims interfere with the antenna of the rfid tag. The length of the tag was also of concern as it is longer than most standard eyeglass rims. Tests were done to cut the tag in half and judge the effect this would have on the reception. The tag performed more poorly and would not make a good tag to discretely affix to eyeglasses as it is too large and it does not have the necessary reception qualities unless a standoff is in place between the eyeglasses and the tag. The stand-off would have to be approximately 1 cm to begin reading better.
Application to Plastic Objects
- The tags perform differently depending on the content and size of the plastic. The Mini-squiggle when affixed to an ID card performs similarly to when it is not affixed to anything. The tags could be used on plastic objects that do not hold metal or liquids. The direction that the object is pointing becomes an issue with distance.
Application to Containers
- The tags do not lose as much of their signal when they are placed inside of plastic containers as compared to when they were placed on items. As an example, when the Ad-612 is placed inside of a trashcan it's readability distance only decreases to 220cm. Tests were done affixing tags to objects and placing them in containers. When affixed to a scientific calculator, the squiggle would read at 90cm outside of a bin, and 60cm inside of a bin. This proves that in cases with certain ideal objects, that the detector would function at finding the object buried in bins and under clothes. However, this is also dependent on the environment inside of the container. When the same item was places in a bag with other objects of different compositions(metal, paper, plastic, etc) the tag performed very poorly, only getting a good read at about 1cm from the bag.
Conclusions
- In the assisted living environment, objects that would be tracked would be of high value, and complex in nature. For flat objects that contain little metal or liquid and have a solid plastic standoff from them, any of the tags would work within the given ranges supplied from above. However, as can be seen, the readability changes depending on the orientation, the object affixed to, and the environment. When looking for an object, it is obviously not always going to be in an ideal place and position. At this time no one of the studied tags would provide all the benefits that are being sought after in this project.
Future Work
- Future work can be done by further exploring ideal objects that could be potentially lost and found with this technology in the assisted living environment. For larger objects such as boxes and books, or large bottles where a tag could be placed on a flat region, there may be more room for exploration. But the smaller objects which are lost more often will prove to be difficult to track until the technology advances. Semi-passive and active tags would perform better, and exploration into larger objects that could benefit from being tracked less discretely in the healthcare environment may provide some opportunity.
Notes
[1] Cangialosi,Andrea, Monaly,Jr,Joseph E, Yang,Samuel C (September 2007), "Leveraging RFID in Hospitals: Patient Life Cycle and Mobility Perspectives", IEEE Applications and Practice,45(9):18-23
