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RFID im Blick

UHF RFID Terrestrial Antennas for High Speed Detection at the Opel Test Center

Use Cases | By PR RFID im Blick | 17 December 2013
The UHF terrestrial antenna arrangement allows detection of transponders on vehicles, even at speeds of more than 250 km/h. The UHF terrestrial antenna arrangement allows detection of transponders on vehicles, even at speeds of more than 250 km/h. Photo: Opel

RFID in the automobile industry

In the year 1966, Opel built a completely new test center in Rodgau/Dudenhofen, 50 kilometers from Rüsselsheim. At that time, 33 kilometers of streets and tracks were constructed to test the vehicles' physical limits and durability under extreme conditions. Since the beginning of the first decade of the second millenium, the number of tracks at the test center has been growing by 50 percent so that the area currently includes more than 60 kilometers of test tracks which are going to be expanded to 100 kilometers in the next few years. The track types range from comfort to noise measuring tracks, to torture and mountain routes which are recreations of actually existing streets and serpentines, to high speed tracks.

“Despite the high traffic density, we never had a traffic jam at the entry points to the single tracks“ reports Dr. Matthias Schollmaier, Opel Test Center director, during a site visit by “RFID im Blick“.

Terrestrial antennas for high-speed detection

The UHF license plate version has been tested since 2011, at that time as part of the RAN project in cooperation with Biba from Bremen and was also tested in high speed tests to find out the speed limit for reading UHF transponders. “Up to now, we could not define the limit. Up to 270 km/h the transponders were definitely readable by detection with antennas positioned above the track. In the next step, we carried out tests using antennas which were integrated into asphalt. We noticed in advance that not every antenna is suitable for asphalt integration“, explains Dietmar  who is responsible for IT at the test center. The question that arises has to do with which antenna could resist high temperatures of up to 200 degrees Celsius during the integration into the asphalt layer without taking any damage, and at the same time withstand many tons of pressure when being driven over by road construction machines. “We now use a specifically developed antenna with a housing milled out of one block. Antennas including cabling were integrated into the middle layer on the high speed track; at the same time, we integrated empty pipes made of stainless steel for induction loops and sensors.“

Antenna arrangement for optimal detection

“The antennas we use have an opening angle of 90 degrees. We thus achieve a read range of about one meter. However, the roadway is five meters wide. The solution we're using now is a compromise between the available hardware and the specifications approved by the road constructor without limiting the warranty. This compromise includes a minimum distance of one meter between the antennas to avoid cracks in the roadway. At the same time, it was necessary to calculate which antenna will be integrated into which track in order to “wake up“ the transponders even at high speed via the air interface so they transmit their ID“, Dietmar Terhörst describes the challenges for implementing the antennas into the roadway surface of the high-speed track.

The track types range from comfort to noise measuring tracks, to torture and mountain routes which are recreations of actually existing streets and serpentines, to high speed tracks.

The “three-antenna-trick“

On the high-speed course, vehicles can drive with a speed of up to 250 km/h without lateral forces. At this speed, they drive on the topmost of the three lanes. In order to detect the transponders mounted on the vehicles reliably at this speed, Dietmar Terhörst took advantage of a simple trick: “The more a vehicle drives on top in the lane, the faster it is. As a consequence, our idea was to use three antennas which are integrated consecutively into the roadway. As soon as a vehicle rides over them, the first two antennas send out energy to activate the transponder. The third antenna will receive the data transferred by the transponder at the latest. Of course this construction is not a special new development, but step by step it turned out to be working, even at a speed beyond 250 km/h. Only recently we were able to detect a transponder at almost 270 km/h, yet not reliably. Speed is no problem for us, but the reading procedure is.“

Multiplexers do not help

Usually multiplexers were used when multiple antennas were operated by one reader, activating each of the connected antennas for a few tenths up to a few hundreds of a second and then turning it off again, says Dietmar Terhörst. “If an antenna is inactive right in the moment when a car passes with high speed, it is not detected.“ Dietmar Terhörst is currently working on a solution to meet this challenge cost-efficiently without operating one reader on every antenna.

Clear advantages for test operation

Testing the detection limits is only one reason for Dietmar Terhörst to develop a reliable solution for the high-speed sector together with his colleagues at the Test Center. “From our point of view today, it is globally unique to integrate such a high amount of antennas into the asphalt to provide data for the first time about which vehicle is moving on which track with which round speed. This data is immediately accessible to the testers for evaluation. Of course, a light barrier could also be used for velocity measurement, however it is fascinating that we were not only able to idealize traffic monitoring at the access points but also to determine the round times very exactly using an adhered 5-Cent-Tag, which we already use anyway.

Multiple benefits for refuelling and washing

The responsible developers consider that the RFID solution's added value does not end with speed detection but is expanded to other processes. 18 different types of fuel are kept ready at the fuel station on the test area so that cars can also be tested with diesel or petrol from India, China or South America. “Counting temporarily delivered special fuels, the number rises to about 25 different types at the fuel station. As a consequence, there is the danger of confusion. When a terrestrial antenna detects a vehicle approaching a fuel pump, the right sort of fuel can be released automatically“, reports Dr. Matthias Schollmaier, director at the Opel Test Center. The same applies to the car wash: “For us it is not important that a car is cleaned but we need to know how often a vehicle was washed with which washing program. This data flows into the test analyses. A terrestrial antenna in front of the car wash could detect the vehicle and link the data with the data base automatically“, Dietmar Terhörst adds.

Test Center as “nucleus of innovation“

“To ensure safety at this mixture of enduring tests, tests by foreign companies and events, we needed a control system. Here at the 'Mikrokosmos Test Center' we have the option to design and develop solutions in a small scale. Thus we are pioneers and we can show what moves us ahead and inspire other sites as well, especially regarding the use of RFID technology“, reports Dietmar Terhörst, and glimpsing into the future Dr Schollmaier says: “As soon as all vehicles are equipped with a transponder during the production process, we can use them in the Test Centers, too, which will further optimize processes. Although this development is not yet conceivable with regard to the production of customer vehicles, we see good chances that the transponders are installed at an early stage at the vehicle production for test operation.”

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Last modified on Wednesday, 21 October 2015 17:17