What-is-RFID-RFID-Tags-Types-Examples-Analysis-Video

In this video, RFID (Radio Frequency Identification) Technolgy has been explained. What is RFID, what is inside this RFID system, how RFID works, and application of RFID have been explained.

RFID (Radio Frequency Identification) technology, developed in the 1980s, is a new automatic identification technology. And it is a kind of communication technology, which uses radio frequency signal to transmit non-contact information through space coupling (alternating magnetic field or electromagnetic field) and achieve identification through the transmitted information. Therefore, it is also called wireless radio frequency identification.

Background

The radio frequency tag is the physical carrier of the product electronic code (EPC), which is attached to the tracked items and can be circulated globally and read and written. RFID has been paid more and more attention in recent years as the key technology of building the "Internet of Things(IoT)". RFID technology originated in the United Kingdom, and was used in the World War Two to identify the identity of the enemy and become the commercial product in the 1960s.

Terminology

Radio frequency identification (RFID) is a kind of wireless communication technology which can identify a specific target and read and write related data by radio signal without the need to establish mechanical or optical contact between the identification system and a specific target.

The radio signal is transmitted from a label attached to the items by an electromagnetic field modulated to a radio frequency to automatically identify and track them. Some of the tags can be powered in the electromagnetic field emitted from the identifier at the time of identification, without the need for a battery; also the tag itself has a power source and can actively issue a radio wave (an electromagnetic field that is tuned to a radio frequency). The tag contains information stored electronically and can be identified within a few meters. Unlike the bar code, the radio frequency tag doesn’t need within the line of sight of the recognizer or may be embedded within the tracked object.

RFID is used in many industries. Attach a label to a car in production so that the manufacturer can track the progress of the car on the production line. The warehouse can track where the stocks are. Radio-frequency tags can also be attached to livestock and pets to facilitate positive identification of animals and pets (positive identification means preventing multiple livestock from using the same identity). RFID identification cards give employees access to locked buildings, and RF transponders on cars can also be used to collect fees for toll sections and parking lots.

Certain radio-frequency tags are attached to clothing, personal effects, and even implanted into the human body. Therefore the technology may be used to read personal information without permission, which is a action of invading privacy.

Concept

Conceptually, RFID is similar to bar code scanning. For bar code technology, it attaches the coded bar code to the target and uses a special scanning reader to transfer information from bar magnetic to scan reader using optical signal. While RFID uses a dedicated RFID reader and a special RFID tag that can be attached to the target and transmits the information from the RFID tag to the RFID reader using the frequency signal.

1) structure

As for structure, RFID is a simple wireless system with only two basic devices. The system is used to control, detect and track objects. In addition, the system consists of an interrogator and many transponders.

2) development

Initially in the field of technology, transponders refer to electronic modules that can transmit information and reply messages. In recent years, due to the rapid development of radio frequency technology, transponders have new concepts and meanings, that is, smart tags or tags. RFID  readers communicate wirelessly with RFID tags via an antenna, which can read or write tag information codes and memory data. It also can recognize high-speed moving objects and identify multiple tags at the same time. Thus the rapid development of RFID technology is also of great significance to the progress of the Internet of things.

3) constituent part 

A. Basic

Transponder: Generally speaking, the tag is used as the transponder, each tag has a unique electronic code, and it is attached to the object to identify the target object.

Reader: A device consisting of antennas, coupling elements, and chips that reads (and sometimes writes) label information, may be designed as a handheld rfid reader or fixed reader.

Application software system: It is mainly used for further processing the collected data and for people.

B. RFID tags are divided into passive, semi-passive, active three modes.

(1) passive mode

The passive tag does not have an internal power supply. The internal integrated circuit is driven by the electromagnetic waves received, and the electromagnetic waves are emitted by the RFID reader-writer. When the tag receives a sufficient signal, data can be sent to the reader/ writer. These data include not only the ID number (the global unique identification ID), but also the data pre-existing in the EEPROM of the tag.

The passive tag has the advantages of low price, small volume and free of power supply. And the rfid tag of the market is mainly passive.

(2) semi-active mode

Generally speaking, the antenna of the passive tag has two tasks. The first is to receive the electromagnetic wave emitted by the reader so as to drive the tag IC; the second is, when the tag returns the signal, it needs to rely on the impedance of the antenna to switch logic 0 and 1. In addition, there exists a problem that in order to achieve the best return efficiency, antenna impedance must be designed to be "open and short circuit", so that the signal is completely reflected and cannot be received by the tag IC, thus the semi-active tag is designed to solve this problem. The semi-active is similar to the passive, but it has a small battery to drive the tag IC, to keep the IC in a working state. The advantage of it is that the antenna can be used to return signal regardless of the task of receiving electromagnetic waves. Compared to passive, semi-active has faster reaction speed and better efficiency.

(3) active mode

Unlike passive and semi-active labels, the active label itself has an internal power supply that supplies the power needed by the internal IC to generate external signals. In general, active tags have longer read distances and larger memory capacity to store additional messages sent by readers.

Radio frequency identification tag, also known as radio frequency tag, electronic tag, mainly composed of large-scale integrated circuit chip with identification code and receiving antenna, and the driven energy is taken from the radio wave energy received by the antenna; RFID read / write devices and networking with corresponding information service systems, such as stock, inventory and sales systems.

Comparing radio frequency identification technology with bar code technology, RF technology has many advantages, such as: it can accommodate more capacity, communication distance is long, it is difficult to copy, it has higher tolerance to environmental change, and it can read multiple tags at the same time. Also it has drawback, that is, the cost of it is higher. However, through the extensive use of the technology, production costs may be significantly reduced.

C. reader

RFID read-write devices can read or write RFID data, and the card reader connected to the identification system has a key chip, which can achieve good encryption.

Interface Protocol

Air interface 

The air interface communication protocol and specifies the information interaction between readers and electronic tags for the purpose of interconnection and interoperability between different manufacturers’ equipment. ISO/ IEC sets five-band air interface protocol. This idea fully reflects the importance of the unification of standards. One standard is the common demand for a wide range of application systems, but not for all application systems.

ISO/IEC 18000-1, based on unit RF identification, it regulates the communication parameter table of reader and label, the basic rules of intellectual property and so on, which are common to the air interface communication protocol. So that each band corresponding to the standard does not need to repeat the same content.

ISO/IEC 18000-2, based on unit RF identification, applied to intermediate frequency (125KHz~134KHz), prescribes a physical interface between tags and readers, the ability to communicate with Type A (FDX) and Type B (HDX) tags, protocol and instruction, and multi-label communication anti-collision.

ISO/IEC 18000-3, based on unit RF identification, is suitable for the high-frequency (13.56MHz), set physical interfaces, protocols and commands, and anti-collision method between readers and tags. The anti-collision protocol can be divided into two modes, and mode 1 can be divided into one basic and two extended protocols (slot-free non-terminating multiple transponder protocol and slot termination adaptive polling multi-transponder read protocol); mode 2 adopts time-frequency multiplexing FTDMA protocol and has 8 channels, which is suitable for the case of large number of tags.

ISO/IEC 18000-4, based on unit RF identification, it is suitable to the micro-band (2.45GHz), sets the physical interfaces, protocols and commands, plus anti-collision methods between readers and tags. The standard includes two modes, mode 1 is passive tag working mode, mode 2 is active tag.

ISO/IEC 18000-6, based on unit RF identification, it is suitable for ultra-high frequency (860,960MHz), sets the physical interfaces, protocols and commands, plus anti-collision methods between readers and tags. It contains three passive label interface protocols: typeA, typeB and typeC, and the communication distance can reach up to 10m. Among them, typeC was drafted by EPCglobal and approved in July 2006. It had been improved well in recognition speed, reading and writing speed, data capacity, anti-collision, information security, frequency band adaptability, anti-interference and so on. It optimizes the features of electronic tags with auxiliary power and sensors, including label data storage and interactive commands. Active tags with batteries can provide a wide range of read power and greater communication reliability, but its size is larger and more expensive.

ISO/IEC 18000-7 is an active tag for ultra-high band (433.92MHz), sets the physical interfaces, protocols and commands, plus anti-collision methods between readers and tags. Active label can read a wide range, and is suitable for large fixed assets tracking.

Data Protocol

Data content standard mainly specifies the representation of data in label, reader and master (that is, middleware or application program). Because of the limitation of label ability (storage ability and communication ability), the data representation forms in each link must take into account their own characteristics and take different forms of expression. In addition, master access to tags can be independent of readers and air interface protocols, that is, readers and air interface protocols are transparent to applications. RFID data protocol interface is based on ASN.1. It provides a set of independent applications, operating systems, and programming languages, but also is independent from a command structure between the tag reader-writer and the tag drive.

ISO/IEC 15961 fixes the interface protocol between the reader and the application, focusing on the standard way of transmitting data between the application command and the data protocol processor, so that the application can complete the reading, writing, and modification of the tag data. And he protocol also defines error response messages.

ISO/IEC 15962 sets the protocol about data encoding, compression, logical memory mapping format, and the way how to convert the data in the tag. This protocol provides a set of data compression mechanism, which can make full use of the limited data storage space in electronic tags and the air communication capability.

ISO/IEC 24753 extends the data processing capabilities of ISO/IEC 15962 for electronic tags with auxiliary power and sensor capabilities. With the sensor, the amount of data stored in the tag and the management tasks of the sensor are greatly increased. ISO/IEC 24753 provides functions such as battery status monitoring, sensor setup and reset, sensor processing, and so on. ISO/IEC 24753, together with ISO/IEC 15962 regulate data processing and command interaction with auxiliary power and sensor function tags. In addition, their role makes ISO/IEC 15961 independent of electronic tags and air interface protocols.

ISO/IEC 15963 regulates the coding standard for unique identification of electronic tags, which is compatible with ISO/IEC 7816-6, ISO/TS 14816, EAN.UCC standard coding system. 

Note: the difference between the code of the item and the code of the item attached to the label, and the standard identifies of the label itself.

Real-time Position

Real-time position systems can improve the transparency of the supply chain, such as fleet management, logistics and fleet safety, etc. RFID tags can solve short-range position, especially indoor objects positioning, compensating the shortcoming of GPS which is suitable for outdoor large area position. The GPS, mobile phone fix position and RFID short-range position connect with wireless communication used for tracking and monitoring the entire location of objects.

The criteria being developed are:

ISO/IEC 24730-1: API, it regulates the RTLS service function and the access method. The purpose is that the application program can access the RTLS system conveniently. It is independent of the low-level air interface protocol of RTLS.

ISO/IEC 24730-2: RTLS air interface protocol is suitable for 2450MHz. It regulates a network positioning system, which uses a RTLS transmitter to transmit radio beacons, and the receiver calculates the position according to several received beacon signals. In addition, many parameters of the transmitter can be configured remotely and in real time.

ISO/IEC 24730-3: RTLS air interface protocol is suitable for 433MH.

Basic Frame

In 2006, ISO/IEC began to focus on the standardization of RFID applications, adjusting ISO/IEC 24752 to six parts and renaming it ISO/IEC 24791. The purpose of this standard is to provide a framework for RFID application system and to standardize data security and multiple interfaces to facilitate the sharing of information between RFID systems. So that the application program is no longer concerned about the differences between various devices and different types of devices, which is convenient for the design and development of the application program, and can support the distributed coordinated control and centralized management of the equipment, and optimize the performance of dense read /write network. The main purpose of this standard is to solve the problem of sharing data information between readers and applications. With the wide application of RFID technology, the sharing of RFID data information is becoming more and more important.

Technical Norms

As early as the 1990s, ISO/IEC began to fix the container standard ISO 10374, and then the official container electronic standard ISO 18185, animal management standard ISO 11784/5, ISO 14223 and so on. As RFID technology becomes more and more widely used, people recognizes the need to develop common technical standards for common requirements and attributes involved in different application areas, rather than completely independent formulation of each application technology standard.

When formulating the ISO 17367 series standard of logistics and supply chain, the ISO/IEC 18000 series standard was directly cited. The general technical standard provides a basic framework, and the application standard complements and specifies it, so as to ensure the interconnection and interoperability of RFID technology in different application fields, and human also take into account the characteristics of the application field, how to well meet the specific requirements of the application field. The difference between the application technology standard and the user application system: the application technology standard aims at the common attribute of a large class of application system, while the user application system aims at a specific application. If the concept of object-oriented analysis is used as a metaphor, the general technical standard is regarded as a basic class, then the applied technical standard is a derived class.

Logistic Management

In order to enable RFID to play an important role in the whole logistics supply chain field, ISO TC 122 Packaging Technical Committee and ISO TC 104 Freight Container Technical Committee set up a joint working group JWG, in charge of formulating logistics supply chain series standards. According to the application requirements, freight containers, loading units, transport units, product packaging, they developed six application standards.

1)request for ISO 17358 applications

This is the supply chain RFID application requirements standard, chaired by the TC 122 technical committee. The standard defines the parameters of each level of supply chain logistics unit, and defines the environmental identification and data flow.

2) ISO 17363～17367 series standard

Supply chain RFID logistics unit series of standards for freight containers, recyclable transport units, product packaging, product label RFID application specifications. This series of standards is similar in content, such as the air interface protocol using the ISO/IEC 18000 series standard. There are differences in specific provisions, respectively for different objects of use to make supplementary provisions, such as the use of environmental conditions, the size of the label, the location of the label posted, and so on. According to the difference of the object, the carrier frequency of the tag is also different. Freight containers, electronic markers for recyclable transport units and transport units The signature must be reused, the product packaging should be based on the actual situation, and the product label is usually one-off. In addition to consider the integrity of the data, visual identification and so on. Recyclable unit in data capacity, security, communication distance requirements are high.

What should be noted here is the relationship between ISO 10374, ISO 18185 and ISO 17363, which are all for containers. ISO 10374 is for the management of containers themselves; ISO 18185 is for customs to monitor containers; ISO 17363 uses readable and writable RFID label and shipping label on freight containers for supply chain management.

Animal Management

ISO TC 23/SC 19 is the RFID standards for animal management, including ISO 11784, ISO 11785 and ISO 14223.

ISO 11784 coding structure

It sets the 64-bit coding structure of the animal RFID code, which requires the reader and the tag to identify each other. This is usually done by a bit stream containing data and encoded data that is needed to ensure that the data is correct. The code structure is 64-bit, of which 27th to 64th bit can be defined by individual countries.

Application

Logistics and supply management, manufacturing and assembly, air baggage handling, mail/ express package handling, document tracking/ library management, animal identification, movement timing, access control/ e-ticket, road auto-charging, etc.

History

1940-1950: The improvement and application of radar gave birth to radio frequency identification technology, which laid the theoretical foundation of radio frequency identification technology in 1948.

1950-1960: The exploration stage of the early RFID technology was mainly in the laboratory experimental research.

1960-1970: The theory of radio frequency identification technology had been developed, and some application attempts had been started.

1970-1980: RFID technology and product research and development was in a period of great development, and a variety of RF identification technology testing had been accelerated. Some of the earliest RFID applications had emerged.

1980-1990: RFID technology and products entered the commercial application stage, all kinds of scale applications began to appear.

1990-2000: More and more attention had been paid to the standardization of RFID technology. RFID products had been widely used, and RFID products have gradually become a part of people's lives.

2000-: The standardization problem has been paid more and more attention by people. The range of RFID products is more abundant. The active tag, passive tag and semi-passive tag have been developed. The cost of tag has been reduced, and the scale application industry has been expanded.

Different Characteristics

Different bands of RFID products will have different characteristics. The operating frequency of RFID products have low-frequency, high-frequency and ultra-high frequency range in accordance with different standards of different products, and different bands of RFID products will have different characteristics. There are passive and active sensors. The characteristics and main applications of passive sensors in different operating frequencies are described in detail as following.

Low frequency

In fact, RFID technology is first widely used and popularized in low frequency. The frequency is mainly operated by inductor coupling, that is, there is a transformer coupling between the reader coil and the inductor coil. The voltage induced in the inductor antenna is rectified through the action of the reader-writer alternating field, which can be used as a power supply voltage. The magnetic field area can be well defined, but the magnetic field strength drops too quickly.

a. Features

1) The general operating frequency of sensors operating in low frequency ranges from 120KHz to 134 KHz, and that of TI is 134.2KHz. The wavelength of this band is about 2500m.

2) Except the metal materials, the general low frequency can pass through any material without reducing its reading distance.

3) There are no special licensing restrictions for low-frequency readers around the world.

4) Low-frequency products have different packaging forms. A good packaging is always expensive, but it has a long service life of more than 10 years.

5) Although the magnetic-field frequency drops rapidly, it can produce relatively uniform read and write regions.

6) Compared to other frequency bands, the data transmission rate in this band is slower than that of other frequency bands.

7) Sensors are more expensive than other bands.

b. Main application

1) A management system for animals.

2) Application of auto security and keyless door-opening system.

3) Application of the marathon running system.

4) Automatic parking fee and vehicle management system.

5) Application of automatic refueling system.

6) Application of hotel door lock system.

7) Access control and security management systems.

High frequency

Sensors at this frequency no longer require coil winding and the antenna can be fabricated by etching or printing. Sensors usually work through load modulation. In other words, the voltage on the reader antenna is changed by switching on and off of the load resistor on the inductor, and the amplitude modulation of the antenna voltage with the long distance sensor is realized. If people use data to control the load voltage on and off, the data can be transferred from the sensor to the reader.

In the 13.56MHz band, there are mainly two standards, ISO14443 and ISO15693. ISO14443 is commonly known as Mifare 1 series products, and it is often used as a bus card because of its close recognition distance but low price, and confidentiality. The greatest advantage of ISO15693 is its recognition efficiency. The recognition distance can be extended to more than 1.5 meters by a larger power reader, because the penetration of wavelength is better than the UHF reading effect when dealing with dense tags.

a. Features:

1) The operating frequency is 13.56MHz, and the wavelength of this frequency is about 22m.

2) With the exception of metallic materials, the wavelength of this frequency can pass through most materials, but may cause the reading distance reduced. Labels need to be more than 4mm the distance from the metal, its anti-metal effect in several bands is better.

3) There is no special limit to the global recognition of this band.

4) Sensors are generally in the form of electronic tags.

5) Although the magnetic field of this frequency drops rapidly, it can produce relatively uniform read and write regions.

6) The system has anti-collision characteristics and can read multiple electronic tags at the same time.

7) You can write some data information to a label.

8) Data transmission rate is faster than low frequency, and the price is not very expensive.

b. Main application

1) Application of library management system

2) Management and application of gas cylinder

3) Management and application of garment production line and logistics system

4) Three meter pre-charging system

5) Management and application of hotel door lock

6) Personnel access system

7) Management system of fixed assets

8) Management and application of medicine logistics system

9) Management of intelligent shelf

Ultrahigh frequency (UHF)

The UHF system transmits energy through an electric field. The energy of the electric field falls not very quickly, but the read area is not well defined. The reading distance of this frequency band is long, and the passive can reach about 10m. It is mainly realized by capacitive coupling.

a. Features

1) The global definition of this band is not quite the same, in Europe and parts of Asia is 868MHz,  in north America is between 902MHz and 905MHz, and the band proposed by Japan is between 950MHz and 956MHz. The wavelength of the band is about 30cm.

2) There is no uniform definition of the frequency band power output (4W in the United States and 500mW in Europe).

3) Ultra-high frequency (UHF) wave can not pass through many materials, especially metal, liquid, dust, fog and other suspended particulate materials. It can be said that the environment has a great influence on ultra-high frequency band.

4) The antenna of an electronic tag is usually long and tag-shaped. Antenna has linear and circular polarization design to meet the needs of different applications.

5) The frequency band has a good read distance, but it is difficult to define the read area.

6) There is a very high data transmission rate, and in a very short time can read a large number of electronic tags.

b. Main application

1) Management and application of supply chain.

2) Management and application of production line automation.

3) Management and application of air parcel.

4) Container management and application.

5) Management and application of railway parcel.

6) Application of logistics management system.

In the future, UHF products will be widely used. Defense department, supermarket, logistics and so on will apply RFID technology to their supply chains.

Active RFID technology (any frequency band, as long as power is active, there are as common as 433M, 2.4G, and 5.8G ).

Active RFID has the characteristics of low transmission power, long communication distance, large amount of data, high reliability and good compatibility. Compared with passive RFID, its technical advantage is very obvious. It is widely used in highway toll, port freight management and other applications.

Combination

MES lean manufacturing management system, also known as APS+MES system (advanced scheduling system and manufacturing execution system), is a selective integration of system management software and human-machine interface equipment (PLC touch screen), LED manufactures board, LCD board, PDA smart handheld terminal, industrial tablet computer, bar code collector, sensor, I/ O, DCS, RFID, industrial AP, WIFI and other hardware integrated intelligent integrated system according to the manufacturing process of different industries. It consists of a set of shared data programs that can control materials, warehouses, equipment, personnel, quality, processes, anomalies, streams plant resources such as program instructions and other facilities to improve productivity. Its scope of application: manufacturing enterprises.

With the use of RFID technology, the target can be achieved as follows: 35% reduction in production cycle; 36% reduction in data entry time; 32% reduction in-process products; 90% reduction in clerical work; 22% reduction in lead time; 22% reduction in unqualified products; 95% reduction in document loss; information feedback efficiency increased by 3860 times.

Examples

1) Radio frequency access guard

The access control system applies radio frequency identification technology, can carry the effective electronic label, that is, car doesn’t need to stop, which is convenient to pass and save the time, improving the intersection traffic efficiency, more importantly, carrying on the real-time monitoring to the small area or the parking lot vehicle entrance and exit to accurately verify the identity of vehicles and owners, making the security management of residential areas or parking lot more humanized, information-based, intelligent, efficient.

2) Electronic traceability

There are roughly three kinds of traceability technologies: one is RFID radio frequency technology, which places a chip mark to the packaging of the product so that the product can automatically collect and read the relevant information in and out of the warehouse and transportation. The track of the product can be recorded on the chip: for example, the QR code, consumers only need to scan the QR code through a mobile phone with a camera, they can get the relevant information about the product, the records of the inquiry will be kept in the system, achieving accurate recall, in addition, once the product needs to be recalled, it can send a text message directly to the consumer. Another is adding batch information (such as production date, time of production, batch number, etc.) on the bar code, and the production enterprise basically does not increase the production cost by using this way.

Electronic tracing system can achieve all batches of products from raw materials to finished products, or from finished products to raw materials, that is two-way tracing function. This system's biggest advantage is the data security, each manual input action will be recorded in real time as backup.

3) Food trace

The use of RFID technology to trace the origin of food and drugs has begun to pilot in some places. Tracing food and drug mainly solves the problem of food sources, if found a problematic product, you can simply trace it back until you find the root cause of the problem.

4) Product anti-counterfeiting

RFID technology has experienced decades of development and application, and the technology itself has been mature. It can be seen everywhere in our daily life. The application of anti-counterfeiting is actually to add a RFID tag on ordinary goods. The label is equivalent to a commodity identity card to record the commodity information during the commodity production, circulation, use and so on.

Market Development 

RFID has a wide range of applications and great market potential in the future. RFID technology has significant advantages in performance and applications, and can be quickly identified and read. Accurate scan and large storage capacity can meet the requirements of enterprises to improve the goods information management, also enable dealers and manufacturers to quickly connect information, receive and respond to information in time. RFID in financial payment, logistics, retail, manufacturing, clothing industry, medical, identity identification, anti-counterfeiting, asset management, transportation, food, animal identification, libraries, cars, aviation, and other fields will play a more and more important role. 

Related News 

Radio-frequency identification (RFID) tags are designed primarily for inventory control, but researchers at Disney Research and Carnegie Mellon University have found a way to process the tag signals with sufficient speed to make them suitable for use in games, physical interfaces and other interactive objects.

Their technique makes it possible to use RFID tags to sense movement or touch in near real-time. The low-cost tags could thus be incorporated into slider and rotary controls for games and toys or for use in other applications that demand prompt response.

Building interactive objects usually entails circuit boards, wiring and batteries, but passive RFID tags costing as little as a dime apiece make it feasible to add interactivity to a wide variety of objects, even those made from paper or other craft materials, said Alanson Sample, research scientist at Disney Research.

"You can create interactive objects that are essentially disposable and perhaps even recyclable," said Scott Hudson, professor in Carnegie Mellon's Human-Computer Interaction Institute (HCII).

RFID tags also could be incorporated into durable objects, such as interactive pop-up books and toys, in which batteries or wires would be inconvenient or infeasible.

The CMU and Disney researchers will present their method at CHI 2016, the Association for Computing Machinery's Conference on Human Factors in Computing, in San Jose, Calif., May 7-12. Passive RFID tags transmit an identifying code when they are energized by radio frequency waves from an RFID reader that can be several meters away. This method simplifies inventory tasks, but isn't engineered to provide prompt responses.a

"It gets trickier when you're not just trying to get an ID from the tag," said James McCann, associate research scientist at Disney Research. It's possible to infer the trajectory of a tagged object, or whether it is being touched or covered, based on the strength, radio frequency phase and Doppler shift of the tag's signal. But that takes precious time, which has made it difficult to use RFID tags to control games and other real-time apps.

The problem, said Jennifer Mankoff, associate professor in HCII, is that the system is dealing with highly uncertain information - the RFID reader only energizes tags at intervals, tags return signals in random order and tags don't always return signals. Waiting for confirmation through multiple "tag reads" slows response time enough to limit many interactions.

The solution was to develop a framework, called RapID, that interprets the signals by weighing possibilities rather than always waiting on confirmation. For instance, a slider controller might work by moving an object that successively obscures the antennas of a series of RFID tags; if one obscured tag suddenly is uncovered, the system might reason that the next tag in line will be obscured.

RapID reduced typical lag times from two seconds to less than 200 milliseconds, which is similar to other interactive systems.

The researchers demonstrated the capability of RapID by instrumenting a toy spaceship, whose movements would animate an on-screen spaceship; by developing a Tic-Tac-Toe application that uses a physical game board and pieces and congratulates players when they win; and by building an audio control board that enables an interactive music-mixing experience, among other apps.