Communications: electrical – Condition responsive indicating system – Specific condition
Reexamination Certificate
1999-09-02
2001-05-22
Mullen, Thomas (Department: 2632)
Communications: electrical
Condition responsive indicating system
Specific condition
C340S505000, C342S051000, C343S850000
Reexamination Certificate
active
06236314
ABSTRACT:
TECHNICAL FIELD
The present invention relates to transponder modules, a RF tagging system, a method of operating a transponder module and methods of tagging an object having a conductive surface.
BACKGROUND OF THE INVENTION
Electronic identification systems typically include two devices which are configured to communicate with one another. Preferred configurations of the electronic identification systems provide such communications via a wireless medium.
One such configuration is described in U.S. patent application Ser. No. 08/705,043, filed Aug. 29, 1996, assigned to the assignee of the present application, and incorporated herein by reference. This application discloses the use of a radio frequency (RF) communication system
10
including one or more radio frequency transponder modules
12
, as described below with reference to FIG.
1
. The transponder modules
12
are each coupled to an object (not illustrated) that the system
10
recognizes because of signals that the transponder modules
12
emit in response to stimuli. The system
10
includes an interrogator
13
operating in response to commands from a controller
14
. Data and commands are exchanged between the interrogator
13
and the controller
14
through interconnections
15
.
In one mode of operation, a transmitter TX
16
contained in the interrogator
13
supplies RF signals through interconnections
17
to a transmit/receive (T/R) antenna system
18
. The T/R antenna system
18
, in turn, radiates an interrogation signal
20
to one or more of the transponder modules
12
. When the interrogation signal
20
is received by one of the transponder modules
12
, a response signal
24
may be generated and transmitted. The response signal
24
typically includes modulation allowing some property or set of properties of the transponder module
12
to be determined. The property or properties describe the object (not illustrated) to which the transponder module
12
is coupled.
The response signal
24
is received by the T/R antenna system
18
and is coupled to a receiver RX
28
. The receiver RX
28
demodulates the received response signal
24
and supplies information determined from the received response signal
24
to the controller
14
via the interconnections
15
. The controller
14
, in turn, may be able to supply information derived from the response signal
24
to an external processor (not illustrated) via a bus or other data link
30
.
Systems such as the system
10
find wide-ranging application in a broad variety of settings. The IPASS toll collection system presently in use in the Chicago area is one example of such a system. In transponder-based toll collection systems, the presence of an object, such as a moving vehicle (not illustrated), is detected by a detector. In a toll collection system, the detection process may rely on reflection of electromagnetic waves, detection of magnetic anomalies or detection of a large mass.
In response to detection of the presence of the vehicle, the controller
14
causes the transmitter TX
16
to transmit interrogation signals
20
having carefully limited range. The transponder module
12
is typically a dash-mounted unit that has been pre-programmed to identify the vehicle and to provide information regarding a pre-existing account associated with that vehicle.
The transponder module
12
transmits the response signal
24
containing information to the interrogator
13
. The information in the response signal
24
identifies the vehicle and the account associated with that transponder module
12
. The receiver RX
28
receives the response signal
24
, demodulates this information and couples the received information to the controller
14
. The controller
14
may pass the received information to one or more computers (not shown) via the data link
30
, causing the account associated with the vehicle to be appropriately decremented. As a result, the vehicle need not slow for the toll collection process, providing smoother traffic flow, reducing fuel consumption and generally facilitating both vehicular transportation and toll collection.
Similarly, an automated fuel retail system (not illustrated) may use the system
10
including the interrogator
13
. The interrogator
13
exchanges signals with the transponder
12
that is attached to vehicle (not illustrated) to determine whom to bill for fuel dispensed to that vehicle when the vehicle is fueled at the fuel dispensing station.
In these kinds of systems
10
, a range of the interrogation signal
20
is carefully limited to avoid interrogation of more than one transponder module
12
at a time. Additionally, it is often desirable to limit the amount of power that is required by the transponder module
12
in order to provide a stand-alone transponder module
12
that is able to operate without requiring an external source of power and that has long battery life.
Further, it is generally desirable to provide systems
10
that are as simple as possible. One approach to realizing these goals is to receive and transmit the interrogation
20
and response
24
signals in a common frequency band. In some systems, the response signals
24
are derived from the interrogation signals
20
and the transponder module
12
may even be one that simply modulates and re-transmits the received interrogation signal
20
to provide the response signal
24
.
One simple technique for modulating the interrogation signal
20
to form the response signal
24
is to either (i) forward bias a diode that is coupled between ground and an antenna in the transponder module
12
to couple the antenna to ground, corresponding to a first logical state, or (ii) to leave the diode unbiased or reverse biased, decoupling the antenna from ground and corresponding to a second logical state. The antenna re-transmits the interrogation signal
20
in the second logical state but not in the first logical state. The transponder module
12
repeatedly switches between these two logical states according to predetermined patterns while the interrogation signal
20
is present to modulate the response signal
24
with a binary signal. These kinds of systems
10
are known as backscatter systems.
In some backscatter systems, the interrogation signal
20
includes a modulated preamble that carries data identifying which transponder module
12
in a population of such transponder modules
12
is targeted to respond. The preamble of the interrogation signal
20
further may include a request for specific data from the targeted transponder module
12
. In such backscatter systems, the interrogation
20
and reply
24
signals must necessarily use the same frequency band and both the interrogation
20
and response
24
signals are present at the same time.
Backscatter RFID systems
10
are presently of great interest for identifying, sorting, counting and routing in situations where selected objects in a population of objects require individual recognition and treatment. Examples include luggage-handling and routing systems associated with public or private transportation systems, package handling and routing systems, vehicle or other rental or check-out systems and inventory control systems.
Some kinds of systems
10
may interrogate a large number of transponder modules
12
simultaneously. For example, an inventory control system may be used to determine if a specific item coupled to the target transponder module
12
is contained in a warehouse. Typically, each transponder module
12
is associated with an inventory item in the warehouse and vice versa. Various protocols have been developed to facilitate identification of, and communication with, a specific transponder module
12
in a population of similar transponder modules
12
.
In many of these systems
10
, there is need for low cost, compact and rugged transponder modules
12
that are secured to objects, such as vehicles, having metallic, and therefore conductive, surfaces. It is also desirable that the transponder modules
12
provide a compact package that does not protrude from the objec
Khatri Dirgha
Smith Freddie W.
Micro)n Technology, Inc.
Mullen Thomas
Wells, St. John, Roberts, Gregory & Matking PS
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