UHF RFID SOLUTION FOR AUTOMATIC WEIGHTING PROJECT

There is many in-and-out transport vehicles in the power plant, coal yard dump area and mining area. There are some procedures such as parking registration and weighting required.

If the operators input the data into the computer or register by hand writing, it will waste a lot of time and may cause many errors and human cheatings, so usually a huge economic loss may occur to the enterprise.

The intelligent weighing system has integrated the UHF RFID technology, electronic automobile scale technology, communication technology, automatic control technology, database technology and computer network technology.

It automatically records the weight and time information of in-and-out vehicles that tagged with an electronic tag, the information store into the database of the host computer.

The system can get rid of the human errors effectively, prevents the weighing cheating and other unfavorable cases, and make sure the accuracy of the data collection and reduces economic loss.

Workflow
* Green signal lights on, the vehicle to be weighed enters the lane and then the red signal lamp turns on to prohibit the entrance of next vehicle into the lane.
* The vehicle passes the entrance-sensing coil, and then the sensing coil will generates inductive signals and the UHF RFID Reader begin to read the card information which stick on the windshield. Compare the card information with the database of the host computer .Register the vehicle information at the same time.
* the vehicle drives onto the balance for weighing and the screen displays the weight information and the camera will capture the vehicle photo and store to the system at the same time.
* After weighing, the vehicle leave the balance and passes the ground-sensing coil and then the barrier rises up and left the vehicle go.
* after the vehicle pass the barrier puts down then the green signal light turn on, the next vehicle is allowed for entrance.

*when the vehicle finish the uploading. it will pass the system again and get the vehicle weight and store the information to the system, then the software will know the goods weight.

Benefits
* it is suitable for the application under various extremely terrible environments such as wind, snow and rain weather
* the tag data is specially encoded and the electronic tags (electronic vehicle plate) cannot be faked or copied

* the vehicle tag with long life and no maintenance required;
* High-speed data collection enables the rapid weighing, improves the efficiency of the weighing and gets rid of the phenomenon of queue-up for Vehicles
*Avoid human operation errors, Due to the adoption of automatic data collection, all vehicles to be weighed will be recorded by the computer automatically
* Long distance identification with 5-8m identification distance

RFID tag cloning

There are many other issues associated with RFID security, one of which is RFID tag cloning. RFID security systems need to be able to prevent cloning as this would open the overall system to a variety of forms of security attack.

Typically when RFID tag cloning occurs, the responses of RFID tags are received by rogue monitors. Information received can then be used to replicate tags.

To enable RFID security to overcome this vulnerability, cryptographic techniques are used and embedded into the chips used. A number of approaches may be adopted:

Rolling code approach: This approach to RFID security uses a scheme where the identifier given by the RFID tag changes after each read action. This reduces the usefulness of any responses that may be observed. It requires the RFID reader and RFID tag to have the same algorithm for changing the identifier. If multiple readers are used, they must be linked so that tracking can occur.

Challenge response authentications: These systems use cryptographic principles. Here the reader issues an enquiry to the tag which results in a response, but as secret tag information is never sent over the interface between the RFID reader and tag the system cannot be compromised. Both reader and tag compute information from internal cryptographic algorithms, and the results are sent and the correct responses required for a successful information interchange. The system is essentially the same as encrypting data to send over a normal radio link.

In view of the additional processing required, the tags have a very much higher cost, and they are also far more power hungry. As a result deployment of these RFID secure tags is limited to areas where the cost can be justified.

RFID security and RFID privacy both remain as issues. In many cases the limited range provides the level of security required by many. Also there is often not a direct gain that can be made by criminals, so RFID security is not an issue in the same way as that for credit cards.

RFID frequency band allocations

There is a total of four different RFID frequency bands or RFID frequencies that are used around the globe. These are placed widely different areas within the radio frequency spectrum and this enables RFID to choose frequencies that will enable the right system parameters to be obtained.

RFID FREQUENCY BAND / SPECTRUM ALLOCATIONS
RFID FREQUENCY
BAND
FREQUENCY BAND
DESCRIPTION
TYPICAL RANGE TYPICAL RFID APPLICATIONS
125-134.2 kHz and 140-148.5 kHz Low frequency Up to ~ 1/2 metre These frequencies can be used globally without a license. Often used for vehicle identification. Sometimes referred to as LowFID.
6.765 – 6.795 MHz Medium frequency Inductive coupling is used on these RFID frequencies.
13.553 – 13.567 MHz High Frequency
HF
Often called 13.56 MHz
Up to ~ 1 metre These RFID frequencies are typically used for electronic ticketing, contactless payment, access control, garment tracking, etc
26.957 – 27.283 MHz Medium frequency Up to ~ 1 metre Inductive coupling only, and used for special applications.
433 MHz UHF These RFID frequencies are used with backscatter coupling, for applications such as remote car keys in Europe
858 – 930 MHz Ultra High Frequency
UHF
1 to 10 metres These RFID frequencies cannot be accessed globally and there are significant restrictions on their use. When they are used, it is often used for asset management, container tracking, baggage tracking, work in progress tracking, etc. and often in conjunction with Wi-Fi systems.
For further information on its use see the paragraph below.
2.400 – 2.483 GHz SHF Backscatter coupling, but only available in USA / Canada
2.446 – 2.454GHz SHF 3 metres upwards These RFID frequencies are used for long range tracking and with active tags, RFID and AVI (Automatic Vehicle Identification). Backscatter coupling is generally used.
5.725 – 5.875 GHz SHF Backscatter coupling. Not widely used for RFID.

858-930 MHz UHF RFID Frequencies

As the UHF RFID frequencies are not a global allocation, these frequencies cannot be used internationally. Where access is allowed, it may be found that there are different restrictions in different countries.

UHF RFID FREQUENCY BAND DETAILS
COUNTRY COMMENTS
North America Here the UHF RFID band can be used unlicensed within the limits of 915 MHz ± 15MHz (i.e. 902 – 928 MHz). There are restrictions on transmission power.
Europe (less exclusions) Within this region, the RFID frequencies (and other low-power radio applications) specified ETSI recommendations EN 300 220 and EN 302 208, and ERO recommendation 70 03. These allow RFID operation within the band 865-868 MHz, but with some involved restrictions. RFID readers must to monitor a channel before transmitting – “Listen Before Talk”.
France The North American standard is not accepted within France as it interferes with frequencies allocated to the military.
China and Japan There are no licence free RFID bands or frequencies. However it is possible to request a licence for UHF RFID which is granted in a site basis.
Australia & New Zealand Within this area the RFID band exists between 918-926 MHz as these frequencies are unlicensed, but there are restrictions on the transmission power.

When looking at using, developing or setting up an RFID system it is necessary to consider the frequencies that are to be used as spectrum allocations and general regulations vary from country to country. This is particularly true for UHF RFID usage.

NFC Antenna basics

As with any antenna, and NFC antenna follows the basic rules of any antenna system. The antenna is basically a form of tuned circuit. Power is fed into the antenna and much of it is radiated. As all passive antennas are perform in an equivalent manner in reception as they do in transmission, it is often easier to look at them as a radiating element as it is often easier to look at the concepts in terms of radiation.

There are a number of parameters and definitions for antennas that are useful when looking at NFC antennas:

Radiation resistance: The resistance that equates to that which would be required to dissipate any power that is radiated.

Resistive losses: The losses that occur as a result of the resistance of the antenna elements – these losses plus the radiated power equate to the total input power.

Bandwidth: The band over which the antenna will operate satisfactorily. Normally antennas operate as resonant elements and therefore their performance falls either side of the centre frequency. This must be accounted for in the design of the NFC antenna, or any other antenna for that matter.

Feed impedance: The current and voltage will vary along the length of the antenna element. Voltage rises towards the ends and the current falls and is also dependent upon the length of the antenna, etc. As impedance is the ratio of current and voltage this means that the feed impedance varies. TO ensure the maximum power transfer the source and load impedances must match, and therefore the feed impedance of the antenna is particularly important to ensure efficient operation.

These and many other parameters are used when designing antennas and in this case NFC antennas.

RFID reader elements

The RFID reader can be broken down into a number of major elements or sub-systems:

Antenna:The antenna is an integral element within the RFID reader. The antenna must obviously be tuned to the frequency of operation. It must also be mechanically incorporated into the overall packaging or case design for the RFID reader. For lower frequencies, the RFID reader antenna may comprise a coil, whereas for higher frequencies it may be a form of dipole element. With RFID up to 30 MHz typically using inductive coupling this means that most antennas would comprise a coil, but above this where radiative systems are used and the wavelengths are much shorter, then forms of dipole offer good performance.

Controller:The controller is the area within the RFID reader that provides the control for the system. It will enable the read or read-write processes to be actioned correctly and any protocols that need to be observed will be initiated in this area.

The complexity of the controllers for RFID readers varies considerably dependent upon the application and the system. Some are particularly simple, whereas others will be considerably more complicated.

Network interface: Once information has been gained from a tag, the RFID reader needs to ensure that the required actions are taken. To achieve this, the RFID reader will normally need to communicate with a central controller. Traditionally RS232 or RS422 interfaces have been used, but now there is much greater use of Ethernet, or wireless systems including Wi-Fi, Bluetooth, or Zigbee.

In addition to these elements there is also software as most items these days have processors which are software driven.

RFID tag storage and processing

One important area and function of the RFID tag is the area that handles the information storage and processing. RFID tags range vastly in their capabilities as some do not have their own power, relying on the received signals to provide any power and this limits their abilities. Other RFID tags with their own battery power are able to carry out far more sophisticated tasks.

There are several types of RFID tag that may be used:
One-bit EAS RFID tags: EAS (Electronic Article Surveillance) tags are commonly found in shops and stores to prevent theft. EAS tags are often termed “1 bit” tags. The reason for this is simply that they are only designed to communicate one bit of information, i.e. their presence. They are widely used in anti-theft measures in shops and stores. If the RFID tag is present and active, then it means that the item has not been through the checkout. If they have been passed through the checkout the RFID tag is either deactivated or removed.

Because of their use, EAS tags are used in their millions and possibly the most widely used form of RFID tag. They do not have any memory or other chips as these would make them too expensive. Coupling used for these tags is generally inductive or backscatter. The tags simply consist of a resonant circuit, and the reader is able to detect their presence. A further point to note about EAS tags is that the readers have to sweep across a small frequency band, because the manufacturing tolerances of these RFID tags is such that there is a spread in the resonant frequencies of the different tags.

RFID smart labels : Smart labels are simple RFID tags that are embedded in a an adhesive paper label. The advantage of this form of tag is that they can be used by RFID and barcode readers as well as having the option for human readable characters. They can be used in areas where the end product may enter one of a number of scenarios where the form of reader is not known – for example retail outlets a product may be shipped to may have either a barcode reader or an RFID reader, and outlets will have different options. Therefore to cover all eventualities a combined RFID and barcode tag is printed.

SAW RFID tag: SAW – Surface Acoustic Wave tags form a half way house between the very basic 1-bit RFID tags and the more advanced tags that are available. The SAW RFID tags operate in the microwave region using backscatter techniques, and although they do not have a processor, they can be encoded at point of manufacture with a number. This number is limited by the technology but may be up to 32 or 64 bits.

Smart card tags: Smart card tags are different to smart labels. Advanced smart card tags are used for many applications, and in particular where secure communications is required, for example for transactions involving finance. These cards may have complicated processors on board along with sufficient memory. When using these cards there is a balance to be made between functionality and cost – this needs to be taken at the outset of the design and needs to be carefully balanced.

Although RFID tags may appear to be the more straightforward or simple element within an RFID system, this may not be the case as considerable ingenuity and careful design is required to ensure the RFID tags perform correctly while being capable of being manufactured to a very low cost and within constraints of size, weight, form factor and also reliability. While most RFID tags are very cheap to manufacture, this hides the design behind them.

Read only and read-write RFID tags

RFID tags may be able to either perform as a read only RFID tag, or they may be a read-write Radio Frequency Identification tag. In view of the cost of manufacturing different types against the quantities made and the differences between the two, most RFID tags today are the read-write variety, and for applications where only a read function is required, the write ability is not used.

Read only radio frequency identification tags are typically programmed either in the factory. Data included will be a unique identifier and other specified data that cannot be changed.

Read-write RFID tags normally contain an area where data cannot be altered – this is often a segregated secure read-only area in the memory. Again this will include a unique identifier, and other data that may be required. The writeable area can then be used to contain data that may be required. For example if the RFID tag is used with a container, it can contain details of the container contents, etc. This area of memory within the RFID tag can be re-written many times.

RFID backscatter coupling

RFID backscatter coupling or RFID backscattering uses the RF power transmitter by the tag reader to energise the tag. Essentially they “reflect” back some of the power transmitted by the reader, but change some of the properties, and in this way send back information to the reader.

Using RFID backscatter or RFID backscattering, some tags achieve their data transmission by changing the properties of the tags themselves, while others switch a load resistor in and out of the antenna circuit.

RFID backscatter coupling operates outside the near field region, and the radio signal propagates away from the RFID reader. When the signal reaches the RFID tag, this interacts with the ingoing signal and some energy is reflected back towards the RFID reader. The way in which the signal is reflected back depends upon the properties of the tag (or any other object for that matter). Factors such as the cross sectional area, and the antenna properties etc within the tag all have an effect. In particular the antenna will pick-up and re-radiate energy, and the way this energy is re-radiated is dependent upon the antenna properties – by changing factors such as adding or subtracting a load resistor across the antenna, the re-radiated signal properties can be changed.

Over short ranges, the amount of power reaching the tag from the reader is sufficient to allow operation of small low current circuits within the tag. This can be used to drive an electronic switch, e.g. a FET that can switch an antenna load resistor in and out of circuit. This will effectively modulate the returned signal and allow data to be passed back to the reader.

In order to allow transmission and reception of a signal at the same time, a directional coupler is often used to allow the received signal to be separated from the transmitted on. Additionally the reader must be able to detect the modulation in the presence of a host of other reflections, although these will normally be stable and not modulated in any way.

Active RFID

The original tags that were used in the shopping electronic surveillance tags was purely passive – the next step in the RFID history was to develop active tags.

As happens in the development of technology, several people were working on similar types of development around the same time, each with their own approach or result. In one development a US patent was granted for an active RFID tag with a rewritable memory in January 1973.

Also in the 1970s the Los Alamos National Laboratories started to develop a system to track the transportation of nuclear materials securely and safely. The system included a variety of readers and transponders attached to the vehicles carrying the materials. These would then enable the truck to be identified at various points along its route.

In another development in the RFID history, again at Los Alamos, but in the agricultural department needed to devise a system that would allow individual cows to be identified. A system was devised that enabled a passive transponder was injected under the skin of the cow. The RFID was based at a frequency of around 125 kHz transponder drew power from the reader, reflecting back a “backscatter” signal that was modulated with the cow identification information.

While the low frequencies of 125 kHz were initially used, systems around the 13.56 MHz license free frequencies were also developed. The use of the higher frequency allowed for higher data rates and longer ranges to be achieved.