Fundamental Operating Principles - RFID: Fundamentals and Applications in Contactless Smart Cards and Identification - page 32

Tags:

Coil

Stick on tag
(Back of barcode)

Column

PVC hard tag

Figure 3.4 Left, typical frame antenna of an RF system (height 1.20 - 1.60 m); right, tag designs

Table 3.1 Typical system parameters for RF systems (VDI 4471)

Quality factor Q of the security element > 60-80

Minimum deactivation field strength H D 1.5 A/m

Maximum field strength in the deactivation range 0.9 A/m

Table 3.2 Frequency range of different RF security systems (Plotzke et al. , 1994)

System 1 System 2 System 3 System 4

Frequency (MHz) 1.86 - 2.18 7.44 - 8.73 7.30 - 8.70 7.40 - 8.60

Sweep frequency (Hz) 141 141 85 85

The range of products that have their own resonant frequencies (e.g. cable drums)
presents a great challenge for system manufacturers. If these resonant frequencies lie
within the sweep frequency 8 . 2MHz

± 10% they will always trigger false alarms.

3.1.2 Microwaves

EAS systems in the microwave range exploit the generation of harmonics at compo-
nents with nonlinear characteristic lines (e.g. diodes). The harmonic of a sinusoidal
voltage A with a defined frequency f A is a sinusoidal voltage B , whose frequency
f B is an integer multiple of the frequency f A . The subharmonics of the frequency f A
are thus the frequencies 2 f A ,3 f A ,4 f A etc. The N th multiple of the output frequency
is termed the N th harmonic ( N th harmonic wave) in radio-engineering; the output
frequency itself is termed the carrier wave or first harmonic.
In principle, every two-terminal network with a nonlinear characteristic generates
harmonics at the first harmonic. In the case of nonlinear resistances , however, energy
is consumed, so that only a small part of the first harmonic power is converted into the
harmonic oscillation. Under favourable conditions, the multiplication of f to n × f