Transmitter for electronic article surveillance system

Details Transmitter for electronic article surveillance system Transmitter for electronic article surveillance system

1999-08-23

2003-07-22

Tran, Khai (Department: 2631)

Pulse or digital communications

Transmitters

C340S572100

Reexamination Certificate

active

06597744

ABSTRACT:

FIELD OF THE INVENTION
This invention relates generally to electronic article surveillance (EAS) systems and pertains more particularly to improved transmitters for generating magnetic fields for use in EAS systems.
BACKGROUND OF THE INVENTION
Referring to
FIG. 1
, an EAS transmitter
10
placed in present commercial use by the assignee of the subject application comprises an oscillator
12
which generates a continuous output at 58 KHz, a rectangular pulse generator
14
which generates a rectangular pulse with a 1.6 millisecond ON time, a multiplier
16
receiving inputs from oscillator
12
and pulse generator
14
, a linear amplifier
18
which amplifies the output of multiplier
16
and furnishes the amplified output to antenna
20
which radiates energy into a so-called surveillance zone (not shown) to establish a magnetic field in the surveillance zone. EAS tags (markers) entering the surveillance zone and not previously deactivated are activated by the magnetic field and are sensed by an EAS receiver which provides output alarm indication of the presence of the tags in the surveillance zone.
FIG. 2
is a frequency domain plot of the transmitted waveform of the
FIG. 1
transmitter. As is seen, the magnetic field is at its highest strength at the carrier frequency of 58 KHz and has sidelobes at 2K aside the carrier frequency which are down only by approximately 20 dB from the 58 KHz fundamental level.
A prospective specification for EAS systems in Europe looks to a “wide exit” with a 60 KHz guardband. The 2K sidelobe strengths of transmitter
10
, as illustrated in
FIG. 2
, only marginally meet the prospective specification.
SUMMARY OF THE INVENTION
The present invention has as its particular and immediate object the provision of an EAS transmitter meeting the guardband requirements of the prospective European EAS specification.
A more general objective of the invention is to provide method and system for conforming EAS transmitter waveforms to any desired fundamental and sidelobe magnitude relationship as may be required by EAS specifications.
A further object of the invention is to reduce energy in selected “keepout” bands of an EAS transmission waveform without loss of strength of the fundamental and without increasing the length of the transmit burst.
In attaining the foregoing and other objects, the invention provides an EAS transmitter for generating an EAS transmission with a preselected guardband, comprising: means for generating a fundamental frequency pulsed waveform; and means for effecting spectral window shaping of the fundamental frequency waveform on a time basis corresponding with the guardband for reducing sidelobe energy in the guardband.
The transmitter may further include means operative on the spectral window-shaped fundamental frequency waveform for further reducing sidelobe energy of the spectral window-shaped fundamental frequency waveform in frequency correspondence with the guardband.
The means for effecting spectral window shaping of the fundamental frequency waveform preferably includes means for generating a pulsed cosine waveform and means for multiplying the fundamental frequency waveform by the pulsed cosine waveform.
A method for effecting EAS transmission in accordance with the invention comprising the steps of: selecting a fundamental frequency pulsed waveform; identifying a guardband for the fundamental frequency pulsed waveform; and effecting spectral window shaping of the fundamental frequency waveform on a time basis corresponding with the identified guardband for reducing sidelobe energy in the identified guardband.
The method may include the further step of reducing sidelobe energy of the spectral window-shaped fundamental frequency waveform in frequency correspondence with the identified guardband.
The step of effecting spectral window shaping of the fundamental frequency waveform is performed in part through the use of a pulsed cosine waveform.
In a still further aspect, the invention contemplates an EAS transmitter in which a storage device stores a digitized transmission waveform derived from a device separable from the transmitter which inputs the digitized transmission waveform to the storage device. The digitized transmission waveform has a fundamental with a suppressed sidelobe.
These and other objects and features of the invention will be further understood from the following detailed description of preferred embodiments and practices thereof and from the drawings.


REFERENCES:
patent: 5276430 (1994-01-01), Granovsky
patent: 5495229 (1996-02-01), Balch et al.
patent: 5793289 (1998-08-01), Strzelec
patent: 6014407 (2000-01-01), Hunsinger et al.

Affiliated with

Also associated with

Rating

Transmitter for electronic article surveillance system does not yet have a rating. At this time, there are no reviews or comments for this patent.

If you have personal experience with Transmitter for electronic article surveillance system, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Transmitter for electronic article surveillance system will most certainly appreciate the feedback.

Rate now

Comments { 0 }

Profile ID: LFUS-PAI-O-3109883