Communications: radio wave antennas – Antennas – Having electric space discharge device
Reexamination Certificate
2002-02-05
2004-03-02
Le, Hoanganh (Department: 2821)
Communications: radio wave antennas
Antennas
Having electric space discharge device
C343S742000
Reexamination Certificate
active
06700544
ABSTRACT:
FIELD AND BACKGROUND OF THE INVENTION
The present invention relates generally to the field of plasma sensors operating in near-field conditions and in particular to a new and useful plasma sensor array used to detect the presence of an interactive element.
Near-field readers are generally known for use in scanning systems. Near-field reader systems take advantage of magnetic field interference between a powered transceiver and a powered or passive object to detect the presence of the object by receiving a return signal from the object with the transceiver.
Presently, card and label near-field readers are formed by metal loops which read data in the near electromagnetic field. In the near-field situation, for a loop antenna, the electric field is effectively zero and only the magnetic field is present. Thus, near field loop antennas use mutual inductance between active and passive loop antennas to cause the active loop antenna to receive data from the passive loop antenna. That is, the magnetic flux from one loop antenna induces a current in a second loop antenna having properties dependent on the current and voltage in the first loop. The magnetic flux interaction and induced current can be used to transmit information between the loop antennas because of the dependency. The near-field loop antennas can be more correctly considered loop sensors or loop readers, since there is no electric field interaction between the active source and a passive loop.
A problem with metal loops used in a sensing array is that even when they are not active, several loops arranged in a multiple orientation array still create unavoidable mutual inductance interferences between loops. That is, even if the metal loop sensors are sequentially activated, they still cause mutual interference with other ones of the loops. The interferences result in detuning of the loops in the array and special considerations must be made when forming arrays.
In order to optimize the strength of the mutual inductance field between an active loop sensor and a passive loop antenna, the antennas must be parallel to each other. If the antennas are perpendicular, the magnetic field is zero at the passive loop and there is no mutual induction. The strength of the magnetic field at the passive loop increases as the loops move from a perpendicular to a parallel orientation. For a device to effectively scan a region for a passive loop, a single loop must move through a variety of orientations. The range of effectiveness of an antenna is based on the orientation of the passive and active loops to each other and the diameter of the loop of the active sensor.
Patents describing scanning antenna systems using interaction between active and passive antennas include U.S. Pat. No. 3,707,711, which discloses an electronic surveillance system. The patent generally describes a type of electronic interrogation system having a transmitter for sending energy to a passive label, which processes the energy and retransmits the modified energy as a reply signal to a receiver. The system includes a passive antenna label attached to goods that interacts with transmitters, such as at a security gate, when it is in close proximity to the transmitters. The label has a circuit which processes the two distinct transmitted signals from two separate transmitters to produce a third distinct reply signal. A receiver picks up the reply signal and indicates that the label has passed the transmitters, such as by sounding an alarm.
U.S. Pat. No. 3,852,755 teaches a transponder which can be used as an identification tag in an interrogation system. An identification tag can be encoded using a diode circuit in which some diodes are disabled to produce a unique code. When the identification tag is interrogated by a transponder, energy from the transponder signal activates the electronic circuit in the tag and the code in the diode circuit is transmitted from the tag using dipole antennas. The transponder uses a range of frequencies to send a sufficiently strong signal to activate a nearby identification tag.
A vehicle identification transponder using high and low frequency transmissions is disclosed by U.S. Pat. No. 4,873,531. A transmitting antenna broadcasts both high and low frequency signals that are received through longitudinal slots in a transponder waveguide. Transverse pairs in the waveguide adjacent the longitudinal slots indicate a digital “1”, while the absence of transverse pairs produces a digital “0”. The high and low frequencies are radiated from the transverse pairs to high and low frequency receiving antennas. The transmitting and receiving antennas are fixed relative to each other and move with respect to the transponder.
U.S. Pat. No. 5,465,099 teaches a passive loop antenna used in a detection system. The antenna has a dipole for receiving signals, a diode for changing the frequency of the received signal and a loop antenna for transmitting the frequency-altered signal. The original transmission frequency is changed to a harmonic frequency by the diode.
As discussed above, near-field loop sensors or readers differ from far field loop antennas by the basic difference that in the near-field, the electric field is effectively zero and the magnetic field of an electromagnetic radiant source is controlling, while in the far field, it is the magnetic field that is effectively zero and the electric field controls. As will be appreciated, the relationships between sources and receivers are different as well due to the different distances and fields which affect communication between them.
Plasma antennas are a type of antenna known for use in far field applications. Plasma antennas generally comprise a chamber in which a gas is ionized to form plasma. The plasma radiates at a frequency dictated by characteristics of the chamber and excitation energy, among other elements.
Plasma antennas and their far field applications are disclosed in patents like U.S. Pat. Nos. 5,963,169, 6,118,407 and 6,087,992 among others. Known applications using plasma antennas rely upon the characteristics of electric fields generated by the plasma antenna in far field situations, rather than magnetic fields in near-field conditions.
SUMMARY OF THE INVENTION
It is an object of the present invention to provide a near-field scanning loop sensor array which eliminates interference between adjacent loop sensors in the array.
It is a further object of the invention to provide a near-field loop reader array which can be arranged to scan in multiple directions without concern for interference between array components.
Yet another object of the invention is to provide a near-field scanning array composed of switched plasma loop sensors.
A still further object of the invention is to provide an apparatus and method for scanning a volume for an interactive component containing a data using a plasma reader.
Accordingly, an array of plasma loop sensors which are sequentially made active to scan a space to identify an interactive object comprising a data source based on mutual inductance interaction of the scanning plasma reader with the data source. The data source can be a passive loop of any type.
As used herein, plasma loop sensor and plasma loop reader are intended to both mean a near-field active loop device having at least a section of plasma tube, as will be described further herein. The active loop device is a near-field electromagnetic transducer having a conductive plasma section. That is, the plasma loop reader or sensor can both generate a magnetic field and sense an interfering induction current caused by a nearby passive loop.
The array of plasma loop sensors are connected to a power source, which may include a frequency switching circuit, and to a sensor circuit. The power source provides power to each of the plasma loop sensors as determined by a sequential switch circuit to make the loop sensors active in turn. The sensor circuit is used to interpret signals received from the data source by each plasma loop sensor while it is active.
One or more plasma loop readers can
Le Hoang-anh
Notaro and Michalos P.C.
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