Registers – Coded record sensors – Particular sensor structure
Reexamination Certificate
2003-10-27
2004-11-30
Tremblay, Mark (Department: 2876)
Registers
Coded record sensors
Particular sensor structure
C235S449000
Reexamination Certificate
active
06824054
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to apparatus and methods enabling simultaneous reading out of transponders, and in particular such methods and apparatus enabling simultaneous reading out, or reading, of passive inductive transponders arranged in a stack, so that the coils of the transponders are closely magnetically coupled to each other.
2. Description of Prior Art
With reference to
FIG. 3
, a conventional transponder system will be described below which consists of a base station
10
and a transponder
12
, depicted schematically in FIG.
3
. In the simplified representation, the base station
10
includes a power source
14
, a resistor
16
serially connected to the power source, and a capacitor
18
connected in parallel to the serious connection consisting of the power source
14
and the resistor
16
. Connected in parallel to the capacitor
18
is a transmitter coil
20
. Along with the capacitor
18
, the coil
20
thus represents a parallel resonant circuit loaded, in the simplified example, by the resistor
16
and the power source
14
, and in reality by the power output stage.
The transponder
12
includes a transponder coil
22
and a tuning capacitor
24
. The transponder coil
22
and the tuning capacitor
24
define a parallel resonant circuit. In addition, in the simplified schematic representation of the transponder
12
, a rectifier diode
26
is connected between the parallel resonant circuit and a capacitor
28
for storing energy. A variable load, consisting of a resistor
30
and a switch
32
, is arranged in parallel with the capacitor
28
. Further, a transponder ASIC
34
(ASIC=application-specific integrated circuit) is provided which is connected to the switch
32
in the manner represented.
The base station
10
inductively supplies the transponder
12
with energy
36
, whereas the transponder returns transponder data
38
by means of the load modulation method. Here, the transponder is a passive transponder not requiring any additional source of energy.
In the base station
10
, a current in the transmitter coil
20
generates an alternating magnetic field
40
at an operating frequency f
B
. The transponder coil
22
of the transponder
12
is arranged in the near-field region of the transmitter coil
20
, so that the alternating magnetic field
40
impinges upon the transponder coil
22
and induces an electrical voltage there. The voltage induced serves the transponder ASIC
34
as an operating voltage obtained via the rectifier
26
and the capacitor
28
.
To send data, the transponder ASIC
34
, controlled by means of a data signal
42
, switches the resistor
30
to be parallel with the capacitor
28
via the switch
32
, i.e. the transponder ASIC
34
switches on the variable load. This leads to an increase in the power consumption of the transponder. Due to this power consumption of the transponder, the field generated by the transmitter coil
20
is weakened. As a consequence, the voltage applied at the resistor which exists between the transmitter coil and the power output stage and is shown schematically as a resistor
16
in
FIG. 3
, increases in the base station
10
. These voltage changes in the base station
10
may be detected to reconstruct the data signal
42
sent by the transponder
12
, such a method being referred to as load modulation.
In a transponder system as has been explained above with reference to
FIG. 3
, the voltage induced in the transponder coil
22
must be higher than the operating voltage of the transponder ASIC. To enable this, the tuning capacitor
24
is connected in parallel with the transponder coil
22
, the tuning capacitor forming a resonant circuit with the transponder coil
22
. In the transponder system shown, the resonant frequency of the transponder resonant circuit is the operating frequency f
B
, so that the voltage induced has a local maximum at the operating frequency f
B
depending on the frequency.
If several transponders exist in the field of the transmitter coil of a base station, and if these transponders are closely magnetically coupled to each other, the transponders mutually influence each other. In addition to affecting the quality of the respective transponder resonant circuits, this influence also relates to the resonant frequency of the transponder resonant circuits, so that same no longer matches the operating frequency. So far it has not been possible to power and read out a stack of passive inductive transponders which are arranged, in relation to each other, such that the coils of same are closely magnetically coupled.
SUMMARY OF THE INVENTION
The present invention is based on the object of providing apparatus and methods enabling transponders arranged in a stack to be powered and read out.
In accordance with a first aspect, the present invention provides a transponder reading device for reading out a plurality of inductive passive transponders having a resonant circuit, the device comprising:
a transmitter coil for generating an alternating magnetic field having an operating frequency f
B
, in which the plurality of transponders may be placed such that they are magnetically coupled to each other; and
a retuning means arranged in the alternating magnetic field and having such a frequency-dependent impedance that a voltage induced in the resonant circuits of the transponders by the alternating magnetic field has a maximum in the range of the operating frequency f
B
.
In accordance with a further aspect, the present invention provides a method for reading out a plurality of inductive passive transponders having a resonant circuit, the method comprising:
generating an alternating magnetic field at/with/having an operating frequency f
B
;
placing the plurality of transponders in the alternating magnetic field such that the transponders are magnetically coupled to each other;
placing a retuning means in the alternating magnetic field, the retuning means having such a frequency-dependent impedance that a voltage induced in the resonant circuits of the transponders by the alternating magnetic field has a maximum in the range of the operating frequency f
B
; and
receiving data created by the transponders in response to the voltage induced.
The present invention is first of all based on the findings that, if several transponders are arranged in the field of the transmitter coil and if same are closely magnetically coupled to each other, the circuit elements at the terminals of each transponder coil are mapped at the terminals of every other transponder coil. This leads to an electrical network containing coupled coils. This network is no longer a simple resonant circuit. The voltage induced no longer takes on a maximum at the operating frequency and is therefore no longer high enough to power the transponder ASIC.
Instead, in a plurality of transponders arranged in close magnetic coupling to each other in the alternating magnetic field of the transmitter coil, a maximum of the voltage or the current, respectively, induced in the transponder coils is caused by each transponder coil, i.e. by each transponder oscillating circuit. These maximums occur at various frequencies, the frequency positions of all maximums changing as soon as a further transponder is added in the alternating magnetic field. If the transmitter coil is also part of an oscillating circuit, as in the example described above with reference to
FIG. 3
, a maximum of the voltage induced in the transponder coils is caused also by the oscillating circuit of the transmitter coil.
As has been mentioned above, the various oscillating circuits influence each other, so that, depending on the number and the nature of the transponder coils stacked, the voltage maximums have frequency positions deviating from the resonant frequencies to which the individual transponder resonant circuits are tuned. The transponders thus cannot be read out. Since the transponders have fixed device variables, for example a transponder coil inductance of 5 &mgr;H and a tuning capacitance o
Christoffers Niels
Hammerschmidt Dirk
Niederholz Juergen
Vom Boegel Gerd
Fraunhofer-Gesellschaft zur Foerderung der angewandten Forshcung
Glenn Michael A.
Glenn Patent Group
Tremblay Mark
LandOfFree
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