Lecture 7 - The Urban Landscape Flashcards
What does the acronym RFID stand for?
Radio Frequency Identification: A technology that uses radio-frequency electromagnetic fields to identify and track transponders (tags) containing electronically stored information.
Describe (in a short sentence or two) a method by which the security of an RFID system/tag may be compromised.
(1) Unauthorized scanning of tages for spying on a person. The encryption system needs to be known or hacked.
(2) Reprogramming an RFID chip. Make an expensive item much cheaper in a shop. The encryption system needs to be known or hacked.
(3) Replay. The intercept and record modulated backscatter signal.
(4) DoS. RFID frequencies use well-known and use of interfering signals to jam signals to make communication with the reader impossible.
(5) Kill command. Some RFID tags have a useful Kill command that kills the cheap electronic component.
Explain how a modulated backscatter signal is generated in a passive RFID tag through electromagnetic induction.
- The RFID reader sends a radio-frequency signal through its antenna
- The EM field of the propagating signal induces a voltage in the tags antenna resulting in a small current.
- The current charges up a capacitor which powers the tags IC
- The IC sends out a unique digital code as a series of 1’s (high volt) and 0’s (low volt)
- The original radio-frequency signal goes full circle and gets transmitted back to the reader. However, before transmission it is modified by a transistor.
- The transistor switches the signal on + off according to the high and low voltages sent to the IC
- Reader decodes signal and tag is then identified (or not)
A new high-frequency (HF) RFID reader is being installed to allow secure access to a facility containing restricted documents. The loop antenna in the RFID reader has a radius of a=4cm and a current of I=20 mA.
What is the minimum number of turns in the loop antenna to ensure access cards can be read from 10 cm away?
: A magnetic field of 1x10-6 Wbm-2
(minimum)
50 turns
A high-frequency (HF) RFID reader at an airport is used to allow certain employees access to restricted areas. Its loop antenna carries 25mA of current, has radius of 5cm and is made up of 75 turns. What is the magnetic field strength at a distance of 10cm away from the center of the loop antenna? Give your answer in Wbm-2
to 2 decimal places
2.95 x 10-6 Wbm-2
Provide an example application of the use of RFID technology for increasing security and reducing crime
(1) Access control and person identification - Biometric passports, secure and private locations, public car and bike sharing
(2) Transport flow monitoring - New York’s Intelligent transport systems
(3) Payment systems - Oyster cards and contactless payment
(4) Loss prevention - retail (item tagging)
Locate the sub-sections within the radio band of the electromagnetic spectrum which RFID tags/readers operate, and the associated operational read-range for each
Low Frequency (LF) RFID
– 125 to 134 kHz
High Frequency (HF) RFID
– 13.56 MHz
Ultra-High Frequency (UHF) RFID – latest technology
– 433 MHz
– 865 to 960 MHz
Explain the differences between passive, active and semi-active RFID tags
Passive RFID tags are powered by the reader’s signal, have the shortest read range but are the most economical.
Active RFID tags have their own battery, have the longest read range but are the most expensive.
Semi-passive RFID tags have a small battery that powers the tag’s circuitry, improving read range and data storage but still requiring reader activation.
What is Ampere’s law?
A current flowing through a conductor produces a magnetic field around the conductor.
What is the Faraday’s law of induction?
A change in flux of one weber per second will induce an EMF of one volt
What is a limiting factor of RFID?
The rapid decay in the magnetic field is the main limiting factor in the read ranges of RFID devices.
Pros and Cons of RFID tags
Pros:
Can be as low as <1 pence per stage
No requirement for expensive batteries
Simultaneous tag reading
Replace only if coil or IC gets damaged
Cons:
LF RFID: 10cm
Does have some infrastructure costs (fixed readers)
How is the EMMIE Framework used to assess the evidence generated from systematic reviews related to crime prevention? (3)
(1) Determine whether tags are Effective at reducing theft
(2) Articulate the Mechanisms through which tags are expected to reduce
theft and the conditions that Moderate tag effectiveness
(3) Identify the Implementation considerations and Economics of tagging
What does EMMIE stand for?
E → Effect (mixed result for efficacy use of tagging)
M → Mechanisms/Mediators (risk perceived of being caught)
M → Moderators (shop layout/product/tag type)
I → Implementation (proper and consistent application of tags and removes staff time to attach in-store)
E → Economic Costs (infrastructure costs and cost of tag varies)
