L2 Flashcards
Principle on which RFID systems work
- Mainly magnetic coupling: i.e. Proximity cards, NFC, implanted medical devices
- energy is transferred from circuit to another via magnetic fields
- inductors are present in the reader and tag
Basic component of and RFID system and draw schematic (L2 pag 4)
- Reader/interrogator: DSP, A/D, RF frontend
- Tag/Transponder: matching network, modulator, logic, and memory
- Electromagnetic coupling
- Forward link: interrogating signal + microwave power
- Return link: modulated backscatter
Main function of matching network in the tag
To maximize power got from the reader
Main function of tag, reader, and coupling element in RFID system
- Tag: responds to interrogation signal and sends encoded information
- Reader: initiates channel with the tag and retrieves information
- Coupling: physically exchanges info between reader and tag
Describe RFID communication sequence
- Reader transmits carrier signal, receives modulated signal from tag and initiates communication
- Tag receives signal from reader, powers its electronics, and transmits back modulated signal
- Reader decodes the data and transmit the data to the server
RFID system aspects (design)
- Power the tag by the reader
- Reader must be sensitive to detect weak backscatter signals
- Choose clear protocol for distinguishing different tags
- Choose anti-collision protocols
- Find a way to distinguish by tags
- Antenna design according to application
- Try to miniaturize antennas for easy integration
1 example of communication system for proximity, personal, local and wide range
- Proximity: NFC, RFID
- Personal: Bluetooth, zigbee
- Local: wlan
- wide: 4G, 5G
Types of commercial RFIDs
- Chip-based passive RFID: Near-field (low frequency), far-field (high frequency)
- Chip-based active RFID
- Chip-based battery-assisted (semi-passive) RFID: near-field, far-field
- Chipless RFID
Difference between active and passive RFIDs
- active rely on internal batteries to maintain operation
- passive harvest from external sources of energy (solar, motion)
Compare active and passive RFID systems in terms of power, required signal strength, range, data storage, cost, size, apps
Active|Passive
- Power: battery|no battery
- signal strength: low|high
- range: long range|short range (3m)
- data storage: large|small
- cost: expensive|cheap
- size: various|small
- apps: remote monitoring, laboratories|libraries, items level tracking
draw schematic of inductive coupled system (L2 pag 13)
draw on paper
3 characteristics of antenna coupled system
- operation at high frequency bands (13.56MHz or higher)
- Load modulation for near-fields region
- Backscatter modulation for far-fields region
Draw the schematic of magnetically coupled RFID system (L2 pag 15)
write on paper
define magnetic flux
- magnetic flux is induced around a conductor carrying an electric current
- can be used as medium for transferring magnetic energy to another conductor
- can be intensified increasing turns of the conductor
write Maxwell’s equations in differential and integral form (L2 pag 18)
write on paper
interpret Gauss’s law of magnetism
- summation of magnetic flux B at any closed surface is zero. Amount of field lines entering a closed volume is equal to the number of lines leaving it
- support idea that magnetic monopoles do not exist
- magnetic field can be induced by E fields and currents
- line integral of magnetic field around closed paths is the sum of conduction and displacement currents
Write equations of magnetic flux, electric fields and current density considering medium properties (L2 pag 20)
write on paper
draw an schematic of a coil and magnetic field intensity (L2 21) and list main characteristics
- H decreases as distance x increases
- H is proportional to number of turns
- H is maximum at the center of the coil
write self inductance equation of loop conductor
L = NuHA/I
Main characteristics of mutual inductance
- mutual coupling M exists when two conductors are in proximity
- some magnetic flux B is transferred from coil 1 to coil 2
- this B depends on intensity of the I
- mutual coupling is proportional to number of turns
- mutual coupling decreases with the distance
define coupling coefficient K
- gives an insight of amount of power transferred via mutual coupling
- independent of geometry of coils
- range between 0-1
- k = M/sqrt(L1*L2)
write induced (Maxwell’s) equation and interpret it (L2 26)
write on paper
when does maximum coupling occurs between two loop coils of single turns?
- when coils are parallel to each other (theta=0)
- k is proportional to cosine of theta
draw circuit of basic RFID system whit only resistors and coils (L2 29)
write on paper
how can coupling efficiency be enhanced? draw schematic (L2 32)
- by using resonance phenomenon at tag end
- capacitor is added in parallel to the inductor L2 to form parallel resonant circuit
- should be designed at operating frequency of RFID system (13.56MHz)
- resonant circuit absorbs max power from reader
why is it needed to maximize quality factor?
to maximize transferred power
draw schematic of magnetically coupled RFID system (L2 36) and 1 important consideration
- resonance of reader and tag must be equal for maximum power coupling
write equations of Q-factors for reader and tag, loaded and unloaded (L2 39)
write on paper
write equation of near-field power transfer equation (L2 40)
write on paper
conditions for strong coupling at which max power is coupled between reader and tag and write simplified power equation (L2 41)
- occurs when intrinsic Q factors are much bigger than loaded Q factors
- amount of ohmic losses is small within each coil
define and write equations of capacity performance (L2 44)
- is the max possible data transmission rate over a communication channel
- affected by received power and bandwidth operation
main factors that affect received power and channel capacity in an RFID system
- supplied voltage by the reader
- Q-factors
- Ohmic and induction losses
- mutual coupling
