We have organized these FAQs sequentially, so as to walk the potential and current users through the selection process. We are confident that the ensuing Q&A discussions, would set or re-set the user-expectations at the right level about the overall promise of this technology, while making the user-experience a rewarding one.

Is an RFID system the appropriate solution for my needs?

What type of RFID systems is suitable for me?

How do I achieve FCC/PTT regulatory compliance?

How do I choose the operating tag RF frequency?

How do I select the proper tag size, shape & package?

How do I decide on reader or module packaging?

How do I choose the proper antennas?

When and how do I use multiplexers?

How do firmware and software affect system performance?

Is an RFID system the appropriate solution for my needs?

One of the first and foremost question users face is whether the problem at hand can be adequately and cost-effectively solved by deploying RFID. While RFID has a lot of promise, it is not, at least currently, meant to replace existing barcode solutions. Some applications are perfectly suited for a bar code, due to its low cost, and in those instances, the generally higher cost of a RFID tag is not fully justified.

A good example, at this time, is the barcodes used to ID the relatively low-value items in supermarkets and retail outlets. RFID tags need to be disposable and be around $0.05 to reach that penetration threshold, which is expected to happen over the next five to eight years. Barcodes and RFID are expected to co-exist until then and they each shall exploit their unique strengths and suffer from any weaknesses.

BAR-CODE vs. RFID

In general, RFID is readily suitable where the following constraints prohibit barcode usage:

* Line-of-sight is not available
* Harsh use environment where barcodes can get mutilated, dirty, faded, smudged or become un-readable
* High-Value (> $100) of items to be tagged
* Need to ID item as well as write dynamic, user-data to tag (intelligence needed)
* User-data retention on tag or in database for audit trail/transaction audits
* Business Process Automation is envisioned for data collection.

TOTAL COST OF OWNERSHIP

One of the most common mistakes is to evaluate the two technologies strictly on the basis of tag vs. barcode costs. RFID systems, being wireless and hands-free, offer the best case for significant cost avoidance, labor avoidance and productivity improvement opportunities. Barcode reading is very labor intensive and, generally, less accuracte.

Hence, a total cost-of-ownership computation at the systems level is essential to highlight the overall benefits and shorter payback advantages. Then you can compare the entire process costs using barcode vs. RFID; a fast payback and ROI is possible, in spite of the initial higher tag cost.

Sentinel provides consultancy services in helping you make such critical investment decisions.

CUSTOMER SATISFACTION

One of the key attractions of RFID is that it enables total supply-chain automation by providing complete visibility of the enterprises’ most productive and critical assets. It can pinpoint enterprise inventory and people in terms of thier status, location, and/or current value in real-time. RFID, along with wireless data collection and communication network elements, can let you ID, locate and track movement of these critical assets throughout the extended supply-chain and take timely corrective actions.

What type of RFID systems is appropriate for me?

Once RFID is deemed to be the correct technology, then the next critical issue is whether you need a passive or an active tag system. This is a function of the read-range and read-speed needed for your application.

How do I achieve/control the required read-range?

For passive tags:

The current state-of-the-art for passive tags achieves a reliable read range from sub-inch to up to 20 feet, with dual antennas. The commonly available tags are in the 125 kHz to 2.4 GHz frequency range.

The range achieved for passive (battery-free) tags is a function of the following key system parameters:

* RF Power: burst, average, instantaneous & pulse duty-cycle
* Pulse-width and data modulation/demodulation schema (AM, FM, HDX, FDX)
* RF conversion efficiency between tag & read antenna
* Tag and read antenna sizes
* Charge capacitor and voltage generated on tag for reliable data transfer
* Overall duty-cycle and power management techniques

For active tag:

The current state-of-the art for active tags achieves a read range of between 20 to 100+ feet, depending on the frequency and protocol/standard supported. Typically, a 3 to 5 VDC long-life, lithium battery is provided to power the tag.

A back-scatter, reflected energy management scheme is typically used to initiate data transfer between the tag and the reader. Reader-talk-first vs. tag-talk-first are two approaches used, as for the tag protocol, with the latter becoming more common among fielded systems (13.56 MHz, 900 MHz). These are propagation systems, as opposed to inductive or capacitive coupling systems.

All of the other issues discussed above also apply to the active tags. Currently, toll-tags and yard/fleet management and warehouse management systems are deploying active tags.

How do I optimize the write range?

The write range for a read/write tag can sometimes be up to 70 % of the read range, especially in the lower frequency range (kHz). Power management techniques and the robustness of the anti-collision algorithms can also dictate the tag write range and the read/second rate achieved.

How do I achieve FCC/PTT regulatory compliance?

In general, higher the tag RF power level, the longer the read range. However, in order to still be compliant with the local RF interference, \RF emissions limitations set by the FCC and PTT in the country of operation, one has to actively manage RF power levels, duty-cycles and emissions during operation. One has to also seek to dynamiccally balance the trade off between RF power, read/write range and read/write speed.

The majority of the readers provide on-board adjustment for RF power and duty cycle so local compliance is achieved. In some cases, a systems integrator like Sentinel can provide proprietary firmware to control and maximize the range or speed of operation while maintaining local regulatory compliance.

Sentinel can provide consulting in all of the above areas.

How do I choose the operating tag RF frequency?

The optimum frequency of operation for RFID systems has to do with the items to be tagged, range needed, space constraints and RF power/emission constraints. Currently available frequencies for RFID applications around the world are: 125/134 KHz, 13.56 MHz, 433 MHz, 872 to 915 MHz, and 2.4 or 5.8 GHz (approved for unlicensed operation). For each of these frequencies, there may be a totally different allowed RF energy emission standards from country to country. Hence, a similar RFID system may offer higher read range, speed performance in Europe vs. North America. This is currently true for the 13.56 MHz spectrum smart label systems. The US is currently evaluating higher RF emissions standards for this and other RFID frequency bands.

Within the frequencies where ISO standard(s) and/or protocol(s) exist, there are ample choices of OEM suppliers, and their pricing is very competitive for both tags and the readers.

However, at present, there is no standardization above the 13.56 MHz (smart label, smart card domain), and hence most of the systems have proprietary architectures and protocol. This drives the cost of the system up. But the advantages of such systems are, at this time, a longer read range feasibility (900 MHz & 2.4 GHz systems), smaller read antennas and higher read/write speeds.

For example, if tags have to be read through human or animal flesh, then the only frequency that would work would be a low frequency (125 or 134 kHz). HF (13.56 MHz) and UHF (> 900 MHz) systems will not work for such applications due to the RF energy absorption, reflection in proximity of body fluids, tissues and multi-path, shading, or skin effects.

Metal proximity is another critical issue. In general, the tag has to be at least ¾ to 1 inch away from any metal surfaces for proper operation and to avoid any detuning situations. This is true for both the tag and the interrogating antenna's metal proximity.

Wood, plastics, hybrid materials, ferrous metals, aluminum, and titanium, which all have different properties, present unique problems and need special considerations.

The effects of antenna shape, RF signal shading, multi-path, bouncing, and absorption/reflection effects have to be modeled and corrected for achieving a robust system design. Dynamic, auto-tuning or re-tuning algorithms as well as hardware schema are deployed to maximize performance for the selected frequency domain.

In general, the higher the frequency, the longer the read range and the smaller the antenna sizes. Achieving FCC/PTT compliance at each operating frequency needs special attention during the design of the system architecture, partitioning, RF front-end, RF components and the embedded or application support software/firmware.

Again, Sentinel offers design assistance for FCC compliance, RF site surveys, FCC, PTT testing itself and/or overall consulting on designing for FCC/PTT or regulatory compliance.

How do I select the proper tag size, shape & package?

The tag type, RF modulation type, size, and material are all dictated by the item to be tracked, and then mainly on the read-write range required and any air-borne noise strength for the application at hand. Smaller tags have a small range. Amplitude Modulation (AM) is less robust than Frequency Modulation (FM) techniques. Full vs. half-duplex (FDX vs. HDX) affects the tag read performance, operation speed (duty cycle), data rates and noise immunity levels.

Currently the smallest, fully packaged tag available is 1.5 mm square, which has an integrated silicon antenna and can provide a range of up to a quarter inch. They come in round and elliptical shapes as well or as long strips. The largest tag Sentinel has supplied to date is a 5 in x 5 in square x ¼ in thick, to give a range of up to 10-12 feet at 900 MHz. With dual, active antennas, one can achieve 20+ feet range at 4 watts RF power.

The tag antenna has to have the correct impedence or capacitance/inductance so as to match it to the RFID IC chip's internal capacitance and achieve resonance at the operating frequency. It should be readily tunable using laser beams. At some frequencies, it presents a limitation on how small a tag can get. Charging and/or tuning capacitors are built into the tag and/or the chip itself for initial tuning using laser beams. Some tags incorporate dynamic re-tuning algorithms to compensate for operating environment and RF variations.

Tag inlays can have either a ferrite core or air-coil version tag antenna in copper or aluminum traces on a suitable PCB (FR-4) or a rugged plastic substrate. Ferrite core is usually necessary for longer range tags.

Tags can be designed to be especially effective in metal proximity. Either a stand-off is provided so as to maintain ¾ in clearance from metal surfaces or the addition of proprietary surface treatments and material coating will allow for operation near metal. Screened-on tuning circuitry, coatings or ground planes can actually enhance the read range for metal proximity or within metal applications. These tags operate up to ¼ inch deep under metal skins. In these instances, the metal itself helps with the tuning process and is used to achieve a higher range.

Tags can be secondarily packaged (basic inlets above) to achieve resistance to temperature, humidity, liquid spray exposure, chemical exposure, EMI, IR, or any RF exposure. Tags can also be hermetically sealed in glass.

Tags and boxed reader assemblies can achieve Industrial Protection ratings up to IP-68, or Intrinsically Safe (IS) ratings for harsh, explosive and hazardous environments.

Please visit our tags page to get a sampling of available tag shapes, sizes and material versions that support all frequency domains, from LF to HF to UHF/microwave bands. We also provide custom packaging development services.

How do I decide on reader or module packaging?

Once the frequency is decided upon, the next issue is selection of appropriate reader components.

For read-ranges below six inches, we recommend a Pico- or Micro- module, typically the size of a PCMCIA plug-in card. These modules have an RF front end for RF processing stages, such as down converters, op-amps, gain control, oscillator (VCXO or TCXO), and microprocessor controller elements for data decoding and processing for communication with the 8-, 16- or 32-bit host micro-controllers. Typically, these come with either TTL output or RS-232/USB serial interfaces. Optionally, some modules support RS-422, 485 multi-drop, or other custom protocols for networked and addressed mode operation. These units operate in the 50 to 150 mA range at either 5, 9 or 12 VDC.

The mid- and long-range modules typically have a higher RF power input capability (in the one to four watts range) and varying duty-cycles. With a single antenna, they deliver a range of up to six feet for the LF category (kHz) with large tags (3 in. diameter or 6 in. long cylinders). With dual panel tuned active antennas at HF (13.56 MHz), one can get 5 to 6 feet range and at UHF/MW (> 433 MHZ). They can deliver up to 10 feet range in a passive tag system. These are typically 12 or 24 VDC systems.

Please watch the DC power polarity carefully during installations, since some modules do not have any reverse-polarity protection circuitry. We recommend use of ferrules around power and communication cables to get rid of conducted noise interference. Baluns are also suggested.

Many reader modules provide antenna tuning bridges or capacitor banks to achieve tuning in-place. Additionally, some have LEDs that brighten with the pick-up of noise interference signals (usually a yellow LED). On-board jumpers allow dynamic and in-situ resonance tuning to maximize reader performance.

Some recent 900 MHz systems have boasted ranges up to 25 feet with dual active gate antennas.

With active tags, you can typically get > 30 feet range (maximum range of a few hundred feet).

Please refer to the reader module section of the Sentinel web site for more detailed specs and product offerings.

How do I choose the proper antennas?

Read/write antenna shape, polarization scheme and RF power level determine the effective RF field strength and field patterns. This, in turn, determines the read range, write range, read zones, and dead spots of an antenna. These parameters are also influenced by the RF energy transfer/conversion efficiency of the coupling between the tag antenna and the interrogating antenna. The coupling can be inductive, capacitive, propogation or hybrid.

The majority of the RFID antennas need to be tuned to the resonance at the operating frequency. Dynamic auto-tuning is feasible using feedback loops to correct for RF variations, environemental variations, skin-effects, harmonic effects, and losses due to metal proximity or other interference, such as RF, EMI from conducted or emitted sources, antenna cabling losses, eddy fields, signal fading, shading, and bouncing.

Please note that there is a very high DC voltage across all active antenna terminals, (> 700 VDC at times). Hence, always provide adequate insulated terminations to avoid shock!!

Typical sources of interference in field installations are AC or DC brushed motors, ballasts, switching power supplies, CRT monitors, CRT tubes, and transformers. Baluns (balanced-unbalanced coils), pickup coils, ferrite cores, donuts, filters and other special RF devices are used to compensate and correct for these undesirable elements.

Higher frequency antennas are smaller in size. Antenna arrays that can be adaptively tuned are used in tunnel reader systems, providing 3-D coverage. Beam-forming, null or adaptive array antennas offer higher dB gains and higher performance. Phased-array elements can be used in systems needing diverse, zoned and remote coverage.

RFID and RF communications antennas used in the Automatic Data Collection (ADC) systems, fall in the following major categories:

* Gate antennas (orthogonal use)
* Stick antennas (directional)
* Patch antennas
* Di-pole or multi-pole antennas
* Circularly polarized
* Linearly polarized
* Omni directional antennas
* Yagi antennas
* Adaptive, beam-forming or phased-array element antennas

In multi-array antenna systems or with multiplexed antenna systems, one can choose which antenna would be active and does read/write functions and then keep the others in inactive or sleep mode selectively to avoid any interference or cross-talk. Firmware or configuration options allow you to select the operating mode and antenna selection addresses or criteria.

Excessive multiple-antenna panel proximity leads to undesirable cross-talk, mis-reads, and de-tuning; system design should arrive at the minimum separation distances and/or corrective algorithms to overcome these issues.

Sentinel provides full antenna and other accessory development consulting services. Please use our contact page to send your inquiries.

When and how do I use multiplexers?

A multiplexer, used to drive multiple antenna elements from a common reader, is essentially a RF multi-pole switch, where one antenna becomes active for a pre-specified or programmable duration and the other connected antennas are shunted out to avoid interference.

This is typically achieved by pulling-down the unused antennas to ground through proper pull-down discrete components.

Individual antennas or array elements can be either run in the addressed mode or sequenced mode or by some digital addressing or timing scheme, based on events or pre-set parametric conditions. Manual mode-switch is also available in some systems to achieve individual, in-use antenna tuning, with the use of a LED bar graph indicator or LED antenna-tuning indicator. This LED brightens as the system approaches full-resonance.

Currently, we have developed 2, 4 and 8 multiplexer units, and if they are additionally used with master/slave configurations, then one can essentially control up to 8x8 (i.e. up to 64 remote antennas from one reader).

Please visit our multiplexer accessory section for Sentinel offerings in this area. In addition to MUXes, we also offer protocol-converters such as ASCII to WEIGAND format converters and ISO converters that are used widely in access control applications for people as well as autos.

Multiplexers can, however, slow down the read-speed. Thus, syncronization and timing becomes critical. Hence, MUXes may not be suitable for all applications, especially where real-time control and a minimum system throughput are critical. Sentinel can also develop custom multiplexers or protocol converters.

How do firmware and software affect system performance?

The majority of the RFID reader modules, and data communication devices/modules, such as ADC modems and wireless LAN controllers, all have embedded software or application software that allow full control of the RFID reader to perform an optimum ID function. The ADC device (modem) allows control of how and in what format the ID or transaction data (i.e. time/date/location stamped data), can be transferred to the host device, such as a PC, server, or PLC.

The reader configuration software is either embedded or resides in a EEPROM module. This allows the setup of protocol & frequency (in Multi-Protocol, Multi-frequency Sentinel offerings), RF power levels, duty cycles, power burst modes, and if any, power clamping, dynamic filtering, dynamic antenna tuning parameter setups, communication protocol setup (RS-232, 422 or 485, USB, Bluetooth), redundancy checks (CRC/LRC), data integrity tests, data rates (baud), rrror management modes, and/or error rate limits.

This type of firmware control allows you to set up the teader functionality/personality to suit your exacting application needs. They can have a significant impact on the system performance envelope and system reliability.

Other factors controlled under application software are tag polling period and frequency, anti-collision algorithms for simultaneous, multi-tag reads, selective and addressable tag reading, sleep and wake-up commands, broadcast commands, encryption, challenge-response algorithms, and firewall control.

Sentinel systems offer a firmware download option for remote control of multiple reader or scanner units and multiple antenna elements within a given networked RFID system. This minimizes system reconfiguration downtime and offers extreme flexibility to arrive at desirable system performance levels, data rates, reliability and feature-set.

Our customized Application Software modules can consist of re-usable and re-configurable cores if the application is to cover similar use environments across multiple enterprise functions. Our software solutions enable totally secure manufacturing, R&D, process-control, warehousing, security operations, inventory, and supply-chain control.

Sentinel specializes in Software Defined Radios (SDR), software-controlled antennas, and tuning circuits.