All posts by: andrew@rfidtiming.com

Tech Talk – The Great Spacer Debate

There is sometimes confusion over the performance of RFID tags placed on wet objects. This is not a problem for low frequency passive tags used by our HDD System, but for the newer UHF passive tags this can present challenges. Unless race timers use Battery Assisted Passive (BAP) tags, they will need to make allowances for proximity of a passive UHF tag directly next to the liquid-filled, moist human body.

There is no ‘black magic’ here. Even when high performing, industry leading Monza 4 or Higgs 3 ICs are used with the very best dipole designs, passive UHF tags suffer performance problems when directly placed on the human skin. Simply put, it is just physics and the result of detuning and signal loss due to water.

The solution is to space the tag away from the skin with the cheapest electrically inert substance: closed cell foam. Our testing has shown that the spacer needs to be only 2-3 mm thick to guarantee excellent read rates, even when the runner’s race bib is stretched tight against the body – and the singlet dripping wet with sweat.

Some of our competitors claim they don’t need a spacer, yet they have to employ two tags per bib. Even a 1 mm thin PET spacer will help things, but we believe that to get near 100% read rates, some type of thin foam spacer is required to guarantee performance in all racing conditions. Using two tags is also a good insurance policy given that each tag costs less than $0.15 each*. Yes, that’s 15 US pennies, not the exorbitant $1.00 per tag that our competitors are charging!

* Approximate cost of the passive tags that we recommend: Alien Squiggle and UPM Raflatac Dogbone. Adding a spacer adds about $0.04 per tag.

Tech Talk – Remote Timing

Many large events require real-time scoring from sometimes distant timing points along the course. These times are often shown on a live scoreboard both on the web and at the finish line. While it may sound high-tech to some, it is really not too complex to put timing systems onto an inexpensive and reliable network using the Internet.

The most common way to accomplish this is to use a built-in GPRS modem that utilizes the GSM mobile phone network to send data over the Internet to a remote server which receives this data. An external 3G modem can also be used.  Some savvy timers can even use a 3G Modem Router to use “The Cloud” to send data over the Internet, and many places in Europe have free Wifi connectivity within the area of a timing point. Data can be sent over the Internet to a server that accepts, deciphers, and stores them in a database. This server can then be accessed by any computer via the Internet to pull down this timing data to scoring software at the race finish line. The whole process takes only one or two seconds, so the results effectively appear in real-time.

Some other timing operators have set up a virtual private network (VPN) where the remote modem is connected directly to the finish line as if it were on the same local area network. The setup of a VPN can be complicated, but essentially eliminates the need for a central or ‘repeater’ server saving the data.
We, at RFID Race Timing Systems, offer all of the above solutions to our customers. The Ultra System even has an optional built-in GPRS as well as an HTTP post request, using an external modem.

Tech Talk – Not all tags are equal

Of the passive transponders on the market there are advantages and disadvantages between types for sports timing. We are often asked to provide a solution that can time everything from running to kayaking and even windsurfing. Each sport has its own requirements in terms of athlete speed, density and where you can put the actual transponder. Some timers wish they could surgically implant a tag in the athlete negating the old complaint, “I left my chip back home”.

Basically there are three frequencies that the bulk of RFID transponders work in, these being low frequency (120 to 140 KHz), high frequency (13.56 MHz) and ultra high frequency (860 to 950 MHz).

The low and high frequency transponders (or tags, as known in the RFID industry) work well in close proximity to water or the human body. They work in the electromagnetic energy region and these waves can pass through water but not metal. This makes these tags ideal for events where the athlete has to wear a tag on the ankle (ie. Triathlon).

On the other hand, UHF uses electrical coupling and these waves can be blocked or detuned by both liquids and metal. A huge investment has been made on UHF tag design to overcome these problems with the best solutions using a small battery to improve backscatter signal, or mechanical means like using a spacer to separate the tag from the offending material. So why do we want to use UHF tags? There are two primary reasons being low cost and huge read rates.

Firstly the UHF tag has the lower cost due to its light weight and ease of manufacture in large quantities. The UHF tags available today pretty much follow the Generation 2 Class 1 EPC protocol which is an industry wide platform adopted by almost all reader and tag manufacturers. Despite some differences in frequency regulations between countries, UHF tags can be read in Europe (866Mhz) as well as in the USA (902-928MHz). This uniformity across the industry has resulted in small passive UHF tags being available for less than 15c each. However high performance tags like the PowerT that RFID Race Timing Systems recommends will cost more due to the added battery and size, but still be lower in cost than the lower frequency transponders.

The second reason UHF is so attractive is the ability to transfer large amounts of information between tag and reader in a given time. This means advanced anti-collision algorithms can be employed to allow one reader to interrogate hundreds of tags in a second using just one antenna.

So, do we think UHF tags will dominate sports timing in the next 5 years? The answer is an emphatic yes with a footnote. We do not see UHF being an alternative in the near future for timing triathlon. Even a battery assisted passive tag like the PowerT has trouble being read on the ankle underneath a wetsuit! We think that timers will continue to use low frequency or active tags for triathlon for a long time to come and that is why our HDD and Dual Antenna Systems continue to sell strongly.

But we will make a bold statement and declare that 95% of the worlds running events will be using some form of UHF disposable tag in 2 years time

Tech Talk – The gap between Active and Passive Transponders

It can be confusing these days deciding on a technology to adopt for timing your next race. Some technologies have come and gone whilst others like the Texas Instruments half duplex low frequency transponders developed in the mid 90s continue to live on. Active tags use an internal battery to transmit their signal when woken up by a signal from the RFID reader. The transmitted signal from the tag is strong and thus read performance tends to be very close to, if not 100%. The drawback with active tags is their cost – ranging from USD $25-$100 – and their limited lifespan based on the coin cell battery used. The passive tag uses no battery to transmit the return tag code but uses the energy sent from the reader to either charge up a little on board capacitor for power, or reflect the energy in the form of a modulated signal. The first instance is used in many low and high frequency passive tags. The second instance is used in Gen 2 Ultra High Frequency systems and is called backscatter. The read performance of a well designed passive RFID system approaches 100% but there is always the odd chance that a tag is not energised in the short time it is in the read field. The big advantage of passive tags is the cost factor which is many times less than for active tags. This is because the circuitry is simpler and there is no need for a relatively large power source on board the actual tag. These tags can cost as little as USD $0.50 in volume.

A hybrid passive tag is the Battery Assisted Passive (BAP) tag developed by the company PowerID. The thin film battery only has a small amount of energy stored relative to a coin cell but is cheap to manufacture and has no harmful chemicals to the environment. The BAP tag uses this energy source to wake the tiny integrated circuit onboard the tag so that almost 100% of the energy sent from the reader is backscattered back to the reader from the tag. The improvement in performance is clear both in read range and readability next to bad substances like water and metal. RFID Race Timing Systems decided to adopt the new PowerID tags because the BAP significantly narrows the gap between active and passive RFID tags used in sports timing keeping.