Nowadays, many retailers and manufacturers use RFID (RFID) tags to track products. The appearance of the RFID tag is like a sticker with antennas and chips. When it is pasted on a milk can or collar, the receiver can read the product name, status and origin stored in the RFID tag. In addition, RFID tags are widely used in logistics management of various products, entertainment flow management and sports management.
Massachusetts Institute of Technology Auto-ID Lab has long been in the forefront of RFID technology research and development. Recently, the laboratory has incorporated sensor functions into the RFID label, developing a RFID tag working at the UHF band, measuring glucose concentration and forwarding information. In the future, the team plans to use the RFID tag to perceive chemicals and gases in the environment, such as carbon monoxide.
Sai Nithin Reddy Kantareddy, a graduate student of mechanical engineering at the Massachusetts Institute of Technology, said that researchers have long been trying to expand the function of RFID, putting a sensor - capable RFID label on every place to form a huge, cheap detection network to detect carbon monoxide or ammonia without electricity. The pool is powered. Kantareddy co developed this new RFID label with research scientist Rahul Bhattacharya, and the vice president of open study at Massachusetts Institute of Technology and Sanjay Sarma, a professor of Daniel Fort Flowers mechanical engineering.
Sarma says that RFID tags are the cheapest and lowest power RF communication tools. Therefore, RFID tag fusion sensing function is a milestone in the research of Internet of things. Antenna centered design is difficult to escape multipath interference .
Before that, there were many types of RFID tags, including active RFID with batteries and passive RFID without batteries. The two tags contain a small antenna. Users can read the information in the microchip of the tag through the reader. Active RFID tags do not require external energy supply, while passive RFID tags acquire energy through the microwave emitted by the reader.
Recently, researchers have been trying to integrate sensing functions into passive RFID tags. The direction of the effort mainly includes developing an antenna that responds to the specific factors in the environment, and then the antenna sends data to the reader at different frequencies or different signal intensities, indicating that a certain substance is detected.
For example, the Sarma team has previously designed a RFID tag antenna that will transmit signals with different waveforms at different humidity levels. They also designed RFID tags that could detect anemia through blood vessels.
However, Kantareddy believes that there is a weakness in this particular reaction antenna, which is multipath interference. That is, the reader receives not only the direct response signal from the RFID tag, but also the direct response signal which reaches the reader's multipath signal through the environmental reflection. Multipath signals interfere with the normal reception of information, resulting in false alarm or missed alarm.
New design based on chip
The Sarma team has another way to make an article on the chip. On the market, they buy RFID chips that work in a semi-active (battery, but not active signal) and passive two modes, and then add a standard antenna to them. Then, they added a new chip to the market chip that enabled the chipset to activate a semi-active RFID mode only under a specific environmental stimulus and launch a set of specific signals. This signal is different from that in passive RFID mode, which can reliably inform the receiver that there is a specific substance in the environment.Kantareddy said that this scheme is more reliable than the sensing RFID technology based on antenna, and users are not susceptible to interference caused by multipath effect. Next, the team will work to further improve the reliability of the transmitted data and reduce the probability of false alarm by studying the new data format and enhancing the power of the transmitting signal.Bhattacharyya emphasizes that the new scheme also addresses a major problem facing antenna based RFID sensing technology - the mutual interference of a large number of RFID tags at the same time. Users who have been puzzled by a large number of short - range passive tags can now put the reader in the distance, and the reader will give an alarm only when the environment does have a specific substance.
Plug and play sensor
In the demonstration experiment, the team demonstrated a RFID glucose sensor based on a commercially available glucose sensor. When glucose is exposed to the label, the electrolyte in the sensor is chemically reacted to generate electricity and provide additional energy for RFID. Next, the RFID tag is switched from passive mode to semi-active mode. The more glucose is added, the longer the semi-active mode will last.
Kantareddy says that once a user receives a semi active mode signal, he knows that the label has found glucose. The user can also further determine the glucose content based on the duration of the semi-active mode.
Of course, the current performance of the new RFID glucose detector is also better than that of the mature glucose detector that is not on sale. The main goal of the team, Kantareddy says, is not to develop a glucose detector, but to show that the new RFID detector can send signals more reliably than the traditional antenna based RFID detectors.
In addition, the new RFID detector is more efficient because, on the one hand, when the target material is not sensed, the RFID tag works in the passive mode and does not consume electricity; on the other hand, the target substance in the environment itself produces energy in contact with the detector, so the process of sending the signal is not much more than the battery. At present, the signal transmitted by the new RFID tag can be received outside 10 meters, while the existing technology can only receive 1-2 meters away.
Next, the team plans to develop a carbon monoxide detector. Kantareddy pointed out that the design of RFID sensors based on antennas should redesign antennas for each specific target material. The new design does not need to change the antenna, it only needs to add the detection chip of target material.
Therefore, the new RFID sensor can be deployed in a low cost and large area to monitor the key systems such as boilers and gas pipes.