AN2866

Non-contactless (contact) measurement method

19/24

6.1.2

Instructions

Measurements are made with the coil prototype physically connected to the signal

generator.

Generate a signal (sine 13.56 MHz) at a 10 V voltage. Then vary the transmission frequency

(from 12.5 MHz to 15 MHz), in order to obtain as high a signal level as possible on the

reception side. Use the oscilloscope to determine the signal level and thus determine the

resonant frequency (see Figure 19).

Figure 19.

Determining the resonance frequency

6.1.3

Example using an LRI2K device

In this example, the selected device is a long-range RFID tag named LRI2K. The initial

design target for the inlay antenna is:

●

Dimensions: the antenna must fit within an ISO ID1 format credit card

●

Frequency tuning target: 13.6 MHz

Procedure

Follow the steps described below:

1.

Choose the tuning capacitance of the product: 21 pF

2.

Determine the objective Inductance:

3.

Define the antenna’s mechanical dimensions: 45 × 75 (mm)

4.

close values depending on the precision required:

–

–

–

5.

Production of antenna coil samples:

50

150

250

350

450

550

12.5

13

13.5

14

14.5

15

MHz

mV

ai15824

L

ant

1

2

π f

0

⋅

()

2

C

tun

⋅

---------------------------------------------

6.56 µH

==