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Design Philosophy of Trolleyponder RFID

New information - Article of the designing of single chip transponders

The Trolleyponder system of tags and readers is an integrated design of an RFID system to produce for the market a transponder system that could be so cost effective and have so many advanced features that it could be seen as a viable replacement technology for the barcode systems even eventually in the retail environment. Although the cost of the transponder will always be higher than the printed cost of a barcode, the productivity enhancements from such a solution are so large that the higher cost is acceptable. The philosophy around Trolleyponders development is to develop a transponder that could eventually be produced for just $0-05US through the optimum choice of the system and components while using the appropriate technologies to make such components.

What would make an ideal transponder system for retail?

  • The system must be safe
  • The transponder must be very cheap
  • The transponders must be read even when inside packaging
  • Multiple transponders in the energising field must be read at the same time
  • Reading accuracy must be very high
  • Good reading ranges for scanning trolleys and stocktaking
  • Numbering systems that are large and can allow many items to have the same number
  • Integrated anti-shoplifting (EAS) features with a good range allowing unmanned checkouts.
  • The use of transponders must benefit all parties from the original manufacturer to the end user.
  • Transponders must be passive so that they do not activate when outside the reading zone and do not cause environmental issues on disposal
  • Transponders must be read irrespective of the geographic orientation to the reader (3D scanning)
  • Fast reading rate is needed and the ability to re-read if needed
  • Transponders must be sourced from many different suppliers.
  • Overcome RF screening problems such as with tin cans
  • Must be compatible with the spectrum planning of the different countries for goods used for international trade.
  • System design
    Feature Implimentation Comments
    System design The Trolleyponder system comprises two parts, namely a reader and a number of tags (also called transponders). The transponders are attached to the goods to be identified and the reader to the computer system that is to process the data.  
    Energising systems In its preferred form the Trolleyponder transponders are passive, that is the reader radiates an energising field which the transponder collects and uses to provide its power requirements. By using the reader to energise the tags, this saves the cost and associated safety issues of onboard batteries on the transponder, and also limits the operating range of the transponders such that only those in the immediate energising field of the reader will be operational and all others will be dormant and not respond to the reader.
    Feature Implimentation Comments
    Simplicity The Trolleyponder transponder comprises a single chip integrated circuit that is attached to a simple antenna. The transponder is packaged according to the requirements of the goods being labelled (e.g. waterproof) By having only a simple design which can be implimented in a single integrated circuit which has all the required circuitry onboard, assembly and component costs can be minimised; meaning that the tag costs the price of the IC, the cost of the antenna; the cost of joining the IC to the antenna and the cost of the chosen packaging around the antenna and the integrated circuit.
    Antenna design Trolleyponder tags can have many different forms of antenna shape depending on the operating frequency and the application. The antenna can be made of simple materials such as wires, foils or even conductive ink. The antenna collects the energising field and converts it to a form where the integrated circuit can extract the energising energy and radiate its response. Any antenna design that is efficient and matches to the circuit would be appropriate.
    Transponder packaging Any packaging that allows the RF energy to penetrate the packaging and be collected by the antenna is suitable  
    Range Trolleyponder can operate over a wide range of frequencies which will give different operating ranges dependent on power and antenna efficiencies. Preferred operating bands are between 200MHz and 1600MHz. Ranges that can be expected in an ideal case are
  • 850-930MHz - 4 to 6 meters
  • 400-450MHz - 6 to 10 meters
  • 1600Mhz - 2 meters
  • 13MHz - 0.5 meters (not preferred)
  • 125Khz - 0.1 meters (not preferred)
  • Range is dependent on the energising fields power and distances quoted here are with a health safety factor of at least 100 times. However local regulations which relate to the local spectrum plan might mean that the regulators need to give special permission to use powers for these ranges.
    Safety In the same way that cell phones use radio energy and must comply to safety guidelines, RFID systems must ensure that the energising fields are well within the safety requirements. Trolleyponder operates at about one percent of the recommended maximum operating levels for radiation of the standards bodies of the US and the EU.
    Multiple items Trolleyponder can read up to about 1000 items that are all illuminated at the same instant by the energising field. Such a large number is not practically likely as usually goods continue to move into and out of fixed reading zones. This feature is a major challenge for any protocol as in practice there is usually only one communications channel (e.g. frequency) for all the tags to communicate with the reader. The tags usually cannot detect the transmissions of the other tags and the reader picks up the garbled sum of all tags that are transmitting at the same time. Trolleyponder protocol solves this problem in a very cost effective manner.
    Operating frequency (chip) Trolleyponder protocol can work from audio frequencies to lightwaves. In order to get good range performance and yet use lowcost manufacturing techniques, the preferred operating frequency range of the transponder integrated circuit is between 200 MHz and 1600MHz.
    Operating frequency (Transponder) Once a transponder has been assembled, it will have an operating frequency that is dependent on the antenna design chosen. As different operating frequencies are used in different countries it is important that the transponder should be frequency agile and be able to respojnd to a wide range of frequencies when used to mark products for international trade. Antenna designs can give operating bandwidths of as high as 10% meaning that the transponder could respond strongly to all readers from say 845MHz to 935MHz in a typical design. This freedom allows regulators to allocate different frequencies in different countries.
    Modulation Trolleyponder uses backscatter modulation to relay information from the tag to the reader. As the backscatter modulated signal is very weak and at the same frequency as the energising signal the transponders are not dependent on having the same operating frequency for each reader. The response signal is very weak and very close to the energising frequency which is generally a relatively powerful transmission. It is virtually impossible for another receiver/reader to detect the responses from the transponders due to them being swamped by the energising transmission. Therefore no addition spectrum needs to be assigned by the regulators for the reply communication as it coexists with the energising signal on the same frequency.
    Electronic Article surveillance EAS features in many RFID systems can be added virtually free as is is a simple extention of the RFID features of the transponder. Trolleyponder features an EAS property that is readable over the full operating range of the transponder, and can be turned on and off by command, as well as having a timeout reactivation feature. Shoplifting losses and investment in antishoplifting equipment in the US alone is estimated as $12billion per annum. In the Trolleyponder system, the EAS feature is not limited to merely indicating a suspect item, but provides the full identity of the item. As the EAS activation is controlled by the reader, all parties that handle the labelled item, from the manufacturer through the logistics and distribution chain to the final retailer can benefit from the EAS features.
    The incorporation of long range EAS features allows for the unattended operation of checkouts by retailers and service providers as the EAS provides a silent check over the correct operation by the client.
    Data range For multiple transponder systems that use a single communication channel between the tags and the reader,the length of the data directly impacts the number of transponders that can be read at a single time by the reader. Despite the very large number of tags that can be read by the system, Trolleyponder has a datalength capable of communicating in excess of 1022 different values. The data carrying capacit of the number system can be further extended by computer data compression techniques.
    Onboard receivers Despite not having onboard receivers, Trolleyponder has unique methods of communicating information from the reader to the tags regarding traffic management and the required status of the EAS features. Most probably the most cost effective design feature of low cost RFID systems is to design the system such that the transponder does not need its own receiver and datadecoder to interpret instructions and data from the reader. Such receivers are in fact highly tuned resonant circuits, which need to be tuned to the operating frequency of the reader to transponder communications. By using such circuitry the designers incur problems of
  • temperature stability of the receiver circuitry,
  • the need to have the same dedicated frequency allocated in all international zones where the transponder might need to operate
  • increased manufacturing costs in tuning the components correctly
  • communmicating data to the transponder reliably over a wide dynamic range experienced by tags that are close to the sourtce versus those that are far away,
  • the need for tags to have a unique identity so that they can be addressed by the reader
  • the need for operating bandwidth due to the energising carrier being modulated with data
  • Onboard tuned circuitry Trolleyponder transponders have no tuned circuitry after the antenna and its matching network on each transponder. The same component can be used for transponders operating over a widely varying operating spectrum by just connecting to the correct antenna. This allows the same chip design to be used by many different clients and applications therefore reducing the costs and simplifing the assembly process.
    Manufacturability /Tolerances The Trolleyponder design allows wide manufacturing tolerances, in some case in excess of 40% When the transponder integrated circuits are manufactured they are produced on a silicon wafer which might each hold as many as a few thousand parts during manufacture. After production the components are tested and those that meet the performance criterea are used and the rest thrown away. The ratio of success to the total made is called the yield. By having a design that allows wide manufacturing tolerances, the yields can be increased and the wastes reduced thereby reducing the manufacturing costs.
    Accuracy The Trolleyponder protocol monitors 6 parameters of the data being received from the transponders continually to verify its integrity. The protocol also has a feature to indicate that all tags in a reading volume have been read, so limiting errors from unread tags being ignored. Reading accuracies of 1 in 100 000 are viable. Two forms of errors are of prime importance in RFID systems, namely:
  • Corruption of the data so that the transferred information is misinterpretted
  • Tags are ignored even though they have not yet been read
  • Read only versus read/write data storage With the exception of the EAS features, the Trolleyponder RFID system is a read only system. The tags can be programmed when applied with the data th user wishes to communicate, but the data cannot be changed by the reader during the reading process. Adding read/write features to a tag can dramatically increase the cost of the tag for the following reasons
  • The memory structure of the tag needs to be altered to have retention properties when power is removed. This can be achieved by means of EEPROM cells, but these need higher energies to program and as energy requirement translates to read range, the reading and writing ranges of such a system might differ with the writing range being often half of the reading range. As ther reader cannot differentiate between close and far ranges for transponders, the reader is not certain that a tag that it is communicating with is within the writing range for changing the memory.
  • Alternative memory structures to EEPROM do exist, such as ferro-electric RAM, but these do not use a standard silicon process.
  • The transponders need to have onboard receivers to decode the data that they need to store
  • The transponders need accurate clocking systems so that they correctly interpret the incoming data, clocks that will not drift with manufacturing tolerances or temperature.
  • The transponders need unique identification data so that the reader can address the specific transponder and indicate that the data is for that transponder
  • The spectrum allocated for the reader needs to be increased to allow for the modulation of the data on the carrier of the energising field
  • The designers have to chose a memory size that will be large enough for all applications.

  • The competitive technology for a read/write tag is a read tag with a good computer network. As the computer interconnectivity of the world increases, the amount od data associated with the product also usually increases such that it is no longer practical to store the information on the tag in read/write memory but to rather transfer the data as a computer file and use the read only information from the transponder to reference the appropriate file (for example the entire service history of a motor vehicle or the pedegree information of a dairy animal).

    Data uniqueness In the Trolleyponder protocol, tags can be uniquely identified or have a common identity - i.e. They can all have the same data in which case the reader can count how many items are present, or they can have unique data differentiating the product. The common identity feature is important for situations such as retailing and where it is used as a barcode replacement technology as consumer items are generally just labelled with a product code. and hence many transponders might all have the same code.
    Transponder energy vs communication requirements The transponders are passive and receive their energy from the energising field Although the energy requirements for the transponders to operate is very small, the energy requirements are still much higher than the communication energy requirements to relay the data. This means that only tags in the immediate vicinity of the reader will be energised and if they are energised their communications with the reader will be good.
    Feature Implimentation Comments
    Reader frequency The reader frequency can be derived from a crystal oscillator and meet the local regulators allocation and stability requirements. The frequency of operation of the reader is the only emmision from the reader. As the tags are intended for use for international trade which might mean that the regulators in the respective countries might wish to allocate different frequencies according to their spectral plans, Trolleyponder is ideally suited to this type of situation as the tags operate at the respective frequencies of the reader that is interrogating them.
    Reader spectrum Trolleyponder uses a carrier wave energising field which occasionally is modulated at a low data rate. Due to the occasional modulation at low switching speeds, the spectrum of the energising field is almost that of a pure carrier wave. The temperature drift and stability of the chosen crystal oscillator needs to be included in the specification when requesting a frequency allocation.
    Reader interfacing Trolleyponder provides a computer compatibl data output for linking to the processing computers in the users network Virtually any computer compatible format can be used, such as RS232, RS485, TC/IP, RFDC etc.
    Reader complexity Because of using a backscatter modulation technique which translates the receiver to operate directly in baseband, the receiver is simple to manufacture. The Trolleyponder reader comprises a crystal oscillator, power amplifier, antennas, mixer and microprocessor. The critical components to meet regulators requirements with regard to emisions are the crystal oscillator and the power amplifier.The mixer is a single component magnetic based quadrature mixer while the microprocessor handles the protocol operation resulting in a very simple receiver. The use of cheaper GSM cell phone components can benefit those systems that will be operating in the 850-930MHz band.
    Technology and implimentation
    Feature Implimentation Comments
    3 Dimension scanning Trolleyponder technology includes features to allow tags to be scanned even when they are randomly orientated or are in situatiosn where the energy transfer might be disrupted during the reading process. Such situations might arise with the random orientation of groceries in a supermarket trolley or where goods are packed in a metal lined truck and the reflected energy wave from the walls of the truck neutralise the direct energy waves. This novel solution is the subject of the second Trolleyponder patent. Particularly with RFID systems it is very important for efficient energy transfer that the antenna system of the reader is correctly aligned with the antenna of the transponder. This orientation is called polarisation. In certain situations where the polarisation is incorrect zero energy transfer can take place. As the requirement is to have all the components of the transponder included in the integrated circuit and to have the integrated circuit produced in a simple manufacturing process, there is a practical limit to the size of any energy storage devices that can be included in the transponder chip to power up the chip in the absence of an energising field.This is where the impact of the Trolleyponder development is felt.
    Patents Presently the Trolleyponder technology is protected by means of two patents that have been filed finally and designated in approximately 102 countries. At final prosecution stages the number of countries might be reduced.
    The purpose of the patents is to ensure that only companies that are licensed by Trolley Scan may make, use or sell the Trolleyponder RFID system.
    Two patents have been filed
  • The first patent details the protocol and system that allows the above features to be realised
  • The second patent details the additional system requirements that allow three dimensional and power interupted scanning to take place
  • Production/licensing Trolley Scan realise that it is not possible for any single company to properly impliment a project of this magnitude. They therefore have implimented a technology transfer process and a licensing process to allow other companies to impliment the design and market their versions of the technology in their markets. The technology transfer process enables even companies that are not necessarily leading electronics companies to become manufacturers of the system. At present companies in USA, Japan, South Korea, Germany and the UK have started to industrialise the Trolleyponder design. Trolley Scan encourage all licensees to produce compatible transponders so that users can have second sources for their projects.
    Use of experts The skilled part of this project is the design of the integrated circuit for the transponder. Most of the other components are within the skills of many subcontractors/engineers.
    Trolley Scan encourage their licensees to use the skills of some of the integrated circuit design houses which have the skills available on contract to design the integrated circuit.
    Trolley Scan provide licensees with a list of design houses that have indicated that they have the skills to design the integrated circuit. Once designed the same design is used for all transponders.
    User Group Trolley Scan have established a user group of companies that wish to sell, make components for, to use the technology or are just interested in following developments.These companies are kept informed about developments via a regular newsletter and are able to be contacted via the potential manufacturers when there developments reach a production stage. One year into the project and 184 companies/ organisations have joined the user group already.
    Ongoing developments Trolley Scan use the skills of the world's leading experts in low cost RFID systems, people who have been involved for the past 9 years in the field and have been responsible for many breakthroughs for this type of technology. This is regarded as a long term project and further improvements are continually expected. The designers were responsible for inventing the Supertag system, the Trolleyponder system and producing the chip design for the Bistar RFID system.

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