Day 1 - 20 July
- Sara Faour
Trends in the design of RFID tags and sensors
Prof. Smail Tedjini
Agenda
INTRODUCTION & HISTORICAL FACTS
BACKSCATTER SYSTEM : RFID
CONVENTIONAL RFID TAGS
TAG ANTENNA DESIGN
RFID CHIP CHOICE
RFID COMMUNICATION SIGNALS : REGULATIONS
TAG DESIGN & SELECTED EXAMPLES
AUGMENTED RFID TAGS
SENSING TAGS
HARMONIC COMMUNICATION
HARVESTING TAG
CHIPLESS RFID SOLUTIONS
CONCLUDING REMARKS
Highlights
RFID tags are based on ultra high frequency bands.
The difference between different tags is the design of the antenna.
RFID tags are passive, they don’t have any internal power source, they need to be powered by external antenna.
RFID is chipless, the good substrate of the RFID is the device to be detected is self, most of times the tag is fixed into a paper, paper is considered as a good substrate
Augmented tags: RFID tags can be used for sensing also, and not just for identification
The Radar Cross Section (RCS) of a target is the equivalent area seen by a radar. It is the fictitious area intercepting that amount of power which, when scattered equally in all directions, produces an echo at the radar equal to that from the target.
RFID is not more than the reflectivity of these elements.
Any target have a backscatter signal with certain frequency response including specific resonances and anti-resonances that can be exploited for target recognition as in radar application or identification like in RFID.
The tag use these two impedance to modulate the incident RF signal.
The transmission process is based on the propagation of an EM wave between two antennas.
Today, the communication is possible for up to 20 meters away.
Larger the surface, larger the distance can be covered.
for UHF, we don’t have a loop, but we have antenna, similar to:
All RFID tags have 512 bits of on-chip memory (to be compatible with UFH EPC G2 standard)
RFID chip sensitivity: the minimum power required to activate this chip.
Aloha protocol: we have one reader and multiple tags → multi-access procedure. The data is sent to the reader in a cyclical sequence.
Applications of RFID tags:
measuring the displacement based on the change of phase
symbols and texts as RFID tags
Barcode tag: RFID+QR at the same time
New Directions in RFID Reader and Tag Design
Prof. Nicolas Bardot
Designing a RFID reader starts by buying a RFID module (100 euros in avg)
The objective of this work is to design a low-cost, low-power, simple and flexible RFID reader.
The main idea is to implement all the RFID functionalities using software.
Simplest architecture (costing almost 20 dollars) is obtained after removing all the hardware components replaced by software, a local oscillator is used, no power amplifier:
The receiver tracks the envelope of the carrier (simple circuit made of two diodes and a capacitor).
This reader is very sensitive to noise.
In this technique the tag is semi-passive, it require external power (battery) to be powered.
This design allows the user to view lots of parameters which are hidden in COTS RFID readers. → more flexible.
Chipless Technology:
Each design is characterized by a resonance frequency:
All chipless tags are linear time-invariant systems:
Note that every (static) object present in the environment is also a LTI sytem!
The read range in chipless does not depend on the transmitted power. Very different from classical communication systems.
A read is possible only if the tag has the dominant power.
How could we break this limitation? → we need to break either the linearity or the time-invariance
UHF RFID Tags are LTV transponders, because a filter is used
Integrated circuits and architectures for Industrial IoT applications: communication aspects
Prof. Sergio Saponara
The frequencies that cannot be used for free, are those who need a service provider and an infrastructure like in cellular communication. However Bluetooth in a free service.
Each country has a different value of maximum allowed transmitted power.
The hardware is not different, only the software configuration differs.
These differences refer to cultural differences:
EU: if something is dangerous it cannot be sold
US: if something is dangerous its up to you
60 GHz wireless networks exist:
wigig
“google soli” uses EM to check whether there is a human and if there is movement https://atap.google.com/soli/
IoT is a part of communication but different from cellular, people look for free spectrum bands,
For remote sensing applications at mm-waves the 24 GHz and the 77 GHz spectrum bands are preferred due to lower attenuation than 60 GHz
Simplex RF system: system allowing one direction communication, i.e. FM radio, TV, smartmeters… There is a high demand on more complex RF systems allowing for interaction.
Half-duplex RF Systems: each end can transmit and receive but not simultaneously. → one frequency is allocated. Applies to most TDD and TDMA systems.
Full-duplex RF Systems: each end can transmit and receive simultaneously → two frequencies are used. Applies to Frequency Division Duplex (FDD) systems. (similar to two persons speaking different languages at the same time)
ESP32 is an example
Increasing the power due to high noise is not the correct choice always since this leads to increasing the noise too for other devices, game theory explains this problem, increasing power depends on the application and how much they are critical (i.e. remote surgery)
Signal modulation:
Amplitude Shift Keying (ASK)
pros: simple
cons: not power efficient, susceptible to attenuation
On-Off Keying
pros: simple, lower-power comsumption
cons: lack of synchronization
Frequency Shift Keying (FSK)
pros: less susceptible to noise (the envelope is constant)
cons: require larger bandwidth
Phase Shift Keying (PSK)
pros: less susceptible to noise, bandwidth efficient
cons: requires synchronization in frequency and phase → complicated transmitter and receiver
used by IEEE 802.15.4 and Zigbee
Quadrature Amplitude Modulation (QAM)
mix of phase and amplitude modulation
pros: bandwidth effiecient
cons: non constant envelope → complex scheme
Baud: transmitted symbol, 1 Baud may include multiple bits
→ The optimal solution depends on the application
Spread Spectrum:
Data sent using Spread Spectrum is intentionally spread over a wide frequency range, Since it appears as noise, the signal is difficult to detect and jam. Thanks to spread spectrum the communication is resistant to noise and interference thus increasing the probability that the signal will be received correctly. Moreover, it is unlike to have interference with other signals.
2 types of Spread Spectrum techniques are common in ISM bands: direct sequence spread spectrum (DSSS) and frequency hopping spread spectrum (FHSS).
Direct Sequence Spread Spectrum (DSSS)
each bit represented by multiple bits using spreading code
The signals sent by wireless can be captured by anyone → open the door to attacks
example of attack was already done on a car: jeep hack, tesla hack
different fabrication process can be seen at: https://europractice-ic.com/technologies/ (this company offer silicon services for small companies and uni)
Inductors need certain properties, silicon do not have them
the second figure follows the concept of dividing the problems into small chunks to be able to save it.
But more components → more expensive but better performance
LNA is also a power amplifier, but for weak signals. (low noise amplifier)
https://dras.in/the-internet-of-battlefield-things-iobt/
If I uses silicon for everything so I am saving money → heterogeneity raises the cost
the frequency of the radar does not depend on the technology fabrication but on the length
all analog parts of the design depend on the wavelength and not on the fabrication process
when multiple amplifiers are cascaded, the noise figure is mainly determined by the first amplifier
The relation between distance and power is not linear: