The purpose of this document is to describe the approach to be used when developing a vehicle identification project using S-UHF-WSTKPAP-U technology, to ensure optimal outcomes for the required configuration and installation conditions.
General principles of UHF technology
Operating principle
S-UHF-WSTKPAP-U uses “passive” UHF (Ultra-High Frequency) technology, which means that the chip does not require a battery to operate, because its power is supplied by the reader.
In Europe, the frequency used for this technology is 866 MHz (915 MHz in the USA).
This passive UHF technology can therefore be used to read data from an electronic tag with no integrated power supply within a range of several metres.
Uses, limitations and environmental effects
Various laws of physics apply to this technology and can influence the way it operates. The major factors to bear in mind are as follows:
- The materials the tag is used on or behind will influence reader performance (range and speed). - A tag should be matched to its environment to give the best possible results.
- The same tag will operate very differently on metal or behind glass (windscreen).
- At this frequency, radio waves do not travel well through liquids.
- A human body between the reader/antenna and the tag itself could obstruct tag reading.
- Radio-frequency identification does not work through metal.
- Any tag that is behind this metallic screen would not be read.
Typical example: heat-reflective (or climate comfort) windscreens on modern vehicles have a metallic film that blocks radio waves.
- However, these windscreens have non-treated areas that allow the radio waves through.
- Radio waves emitted by the reader and the tag can bounce off obstacles and be diverted, and therefore the presence of obstacles in the field can influence the results.
- UHF technology can be directional. Some antenna has a fairly directional “reading field”, rather like the area lit up by a spotlight.
- The location of antenna will therefore need to be planned on the basis their reading zone, depending on their characteristics.
Optimum
Given the constraints described above, it is important to identify the conditions that will give the best possible system performance. This means ensuring the optimum antenna and tag positions:
- Performance will depend on the position of the tag relative to the antenna.
- Maximum range and optimised detection will be achieved if the tag is directly opposite the antenna, parallel to it, and with the correct polarisation.
- For optimum performance, the tag should be straight opposite the antenna.
- The range values given in technical specifications for the readers are measured in straight-on distances, with the tag parallel to the antenna.
- When the tag is at an angle from the antenna, the effective range is reduced.
- A UHF tag may have a specific orientation, related to the polarisation of its antenna.
- A “linear” tag will be orientation-sensitive and will not read as well horizontally as it does vertically.
The angle in question may be a horizontal or vertical angle, depending on the comparative height of the antenna compared to the vehicle and the lateral offset of the antenna, compared to the lane of traffic.
Tag Position
Selecting the tag location
S-UHF-WSTKPAP-U performance is influenced by its position on the windscreen, and depends on the windscreen type. The aim is to position the tag to optimise the quality and performance of reading function.
For heat-reflective windscreens, it is essential to place the tag in the non-treated areas (where applicable) as shown in the illustration below.
The location of these non-treated areas will depend on the make and model of the vehicle.
A non-exhaustive list is available in the Appendix. If there isn’t non-treated heat-reflective area, the tag won’t be read.
The angle in question may be a horizontal or vertical angle, depending on the comparative height of the antenna compared to the vehicle and the lateral offset of the antenna, compared to the lane of traffic.
See Appendix: Windscreen types with location of non-treated areas.
Standard private car: the ideal position is near the top of the windscreen, behind the rear-view mirror, if possible on the side the reader antenna is located.
Ensure the tag is not touching the upper edge of the windscreen.
Heavy Goods Vehicle (HGV) / Truck / Bus
For lorries and buses, there are two possible solutions:
- Tag inside vehicle on windscreen (TLT model): same positioning requirements as for a car.
- Tag outside vehicle on bodywork: place the tag so it is as close to parallel as possible with the reader antenna, in the desired reading zone.
Example with a TML model, on a bus radiator grill: approximately 1.10m from the ground, not touching the metal windscreen wiper.
Installing the tag
Once you have decided where to position the tag, install it using the holder provided.
Using the double-sided adhesive tape provided, affix the holder horizontally on the windscreen and insert the tag using the method of your choice:
1. The S-UHF-WSTKPAP-U is removable from its holder to transfer it in an other vehicle.
2 – The S-UHF-WSTKPAP-U is not transferable.
When you choose the location, bear in mind the space you will need to insert the tag into the holder (look at the angle of the windscreen).
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