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Description  |
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FIELD OF THE INVENTION
This invention relates to the locating of objects. More particularly, the
invention relates to a locating system for, and to a method of, locating
predetermined labelled objects.
SUMMARY OF THE INVENTION
According to a first aspect of the invention, there is provided a locating
system for locating predetermined labelled objects which includes
a transceiver unit which comprises a narrow beamwidth antenna means for
transmitting an energising signal at a predetermined first frequency and
for receiving a returned signal at a predetermined second frequency from
an object to be located, the energising signal incorporating a
predetermined transponder identification code; and
a plurality of label-like transponders each of which is affixable to an
object to be located, each transponder including logic circuitry in order
that only that transponder to which the said identification code relates
is energised by the energising signal to radiate the returned signal.
Each transponder may be substantially omni-directional in order to operate
effectively irrespective of the orientation of the object to which it is
affixed relative to the transceiver unit. Preferably, the transponder may
be small and flat so as to be easily affixable to the object without
interfering with the object. Further, the transponder should be as cheap
as possible and should operate equally well when affixed to metal,
electrically insulating materials, or when freely suspended.
The above requirements may be satisfied by some form of suitable patch
antenna and, hence, each transponder may include such a patch antenna. The
patch antenna may be substantially C-shaped.
The logic circuitry may comprise a register means for receiving the
predetermined transponder identification code from the transceiver unit
via the energising signal. Additionally, the logic circuitry may include a
comparator for comparing the received transponder identification code with
a code stored in a memory means of the logic circuitry. In use, should the
serial code correspond with the code stored in the memory means of the
transponder, a switching means may be activated to cause the transponder
to transmit the returned signal.
Further, in a development of the system, the system may be operable to
search for and to locate predetermined objects within certain categories
of objects.
In this development of the system, a category code may be stored in the
memory means of the logic circuitry, the category code being comparable by
the comparator with a predetermined encoded energising signal transmitted
by the transceiver unit for facilitating location of predetermined objects
within a predetermined category of objects. The logic circuitry may
further include a time delay means, a different time delay being allocated
to each transponder to delay the transmission of individual identification
codes by the transponders by varying amounts of time such that the codes
are received serially by the transceiver unit.
In this application of the system, the transceiver unit may be operable not
only to "listen" for the acknowledgement of the presence of one
pre-selected identification code, but also to pick up and to store
individual identification codes of all the transponders within a
pre-selected group of transponders.
Each transponder may include a switching means which is controlled by the
logic circuitry, the switching means being activated by the logic
circuitry to cause the returned signal to be radiated or transmitted. The
switching means may be an RF switch.
The transceiver unit may be a portable unit which contains control
electronics including data storage space, signal processing circuitry and
transmitter/receiver circuitry.
The antenna means may comprise a single narrowbeam directional antenna
which is used both for transmitting the energising signal and for
receiving the returned signal or, instead, the antenna means may comprise
two separate antennas.
In order to realise the necessary narrowbeam transmitter and receiver
antennas so as to indicate direction of a response from the transponder,
the said predetermined first frequency of the energising signal may fall
within the UHF range. Then, the said predetermined second frequency of the
returned signal may be an harmonic of the frequency of the energising
signal. Preferably, the frequency of the returned signal is the third
harmonic frequency of the energising signal.
According to a second aspect of the invention, there is provided a method
of locating predetermined labelled objects which includes
modifying an energising signal to incorporate a predetermined transponder
identification code;
transmitting the energising signal via a narrow beamwidth antenna means at
a predetermined first frequency; and
receiving a returned signal at a predetermined second frequency radiated by
a label-like transponder which is energised by the energising signal and
to which the predetermined identification code relates, the said
transponder being one of a plurality of such transponders each of which is
affixed to an object to be located
The method may include transmitting the signal at a frequency in the UHF
range and causing the returned signal to be radiated at a frequency which
is an harmonic of the energising signal. Preferably, the method may
include causing the returned signal to be radiated at a frequency which is
the third harmonic frequency of the energising signal.
Modifying the energising signal may be effected by modulating the
predetermined transponder identification code onto the energising signal.
The modulating of the signal may be effected by digital code modulating
the amplitude or frequency of the energising signal.
Additionally, the method may include further modifying the energising
signal in order to enable a range determination to be made. The further
modifying of the energising signal may be effected by modulating a
predetermined waveform, for example, a sinusoidal waveform onto the
energising signal.
The invention is now described by way of example with reference to the
accompanying diagrammatic drawings.
BRIEF DESCRIPTION OF THE DRAWINGS
In the drawings,
FIG. 1 shows, schematically, a locating system in accordance with the
invention, for locating predetermined labelled objects;
FIGS. 2A, 2B and 2C show waveforms of signals generated by a transceiver
unit of the locating system;
FIG. 3 shows a block diagram of a transponder of the locating system;
FIG. 4 shows a block diagram of a logic circuit of the transponder of FIG.
3;
FIG. 5 shows a block diagram of a development of the logic circuit of the
transponder;
FIG. 6 shows a plan view of the transponder;
FIG. 7 shows a bottom view of the transponder;
FIG. 8 shows a sectional view of the transponder taken along line
VIII--VIII in FIG. 7; and
FIG. 9 shows a block diagram of a transceiver unit of the system.
DETAILED DESCRIPTION OF THE DRAWINGS
Referring firstly to FIG. 1 of the drawings, a locating system, in
accordance with the invention, is shown and is designated generally by the
reference numeral 10. The locating system 10 generally comprises a
portable transceiver unit 12 having an antenna means 14 for transmitting
an energising signal 16 at a first predetermined frequency falling within
the UHF range and preferably having a frequency in the region of between
approximately 100 MHz and 1 GHz.
The system 10 further comprises a plurality of label-like transponders 18,
of which one is shown. Each transponder 18 is affixed to an object such as
a briefcase 20, which is to be located. If the transponder 18 is energised
by the energising signal 16, as will be described in greater detail below,
the transponder 18 is activated and radiates a returned signal 22 which is
received by the antenna means 14 of the transceiver unit 12. The returned
signal 22 is at a significantly different frequency from the energising
signal 16 in order to screen out unwanted reflections and to reduce
crosstalk between the transmitter and receiver of the transceiver unit 12.
Hence, for example, the returned signal 22 is at a frequency which is an
harmonic of the energising signal 16. Preferably, the returned signal 22
is at a frequency which is the third harmonic frequency of the energising
signal 16.
Referring now to FIG. 3 of the drawings, a block diagram of the transponder
18 is illustrated. The transponder 18 comprises a reception antenna 24
tuned to the frequency of the energising signal 16. A signal received by
the antenna 24 is fed by a transmission line or co-axial line 26 to a
non-linear network 28. The non-linear network 28 processes the signal from
the antenna 24 and a signal output from the non-linear network 28 on line
30 is fed to a low-pass filter 32 and to a band-pass filter 34. Outputs of
the low-pass filter 32 and the band-pass filter 34 are fed to a logic
circuit or module 36 which is described in greater detail below. A signal
from the non-linear network 28 which is the third harmonic of the signal
16 is also fed from the non-linear network 28 to an RF switch 38. The RF
switch 38 is controlled by the logic module 36.
The purpose of the low-pass filter 32 is to condition, in conjunction with
the non-linear network 28, the RF energy received by the antenna 24 so as
to serve as a OC power source for the logic module 36.
The purpose of the band-pass filter 34 is to extract, in conjunction with
the non-linear network 28, a digital code modulated on the energising
signal 16, as will be described below.
A signal output from the RF switch 38 is fed via a transmission line or
co-axial line 40 to a transmission antenna 42 from which the returned
signal 22 is transmitted to the antenna means 14 of the transceiver unit
12.
Referring now to FIG. 4 of the drawings, a block diagram of the logic
module 36, in its basic form, is illustrated. The logic module 36
comprises a shift register 44 having a serial input and a parallel output.
The output of the shift register 44 is connected to a digital comparator
46 which, in turn, is connected to a Read Only Memory (ROM) 48.
In this form, the logic module 36 receives a serial code from the
transceiver unit 12 via the non-linear network 28 and the band-pass filter
34. This serial code is shifted into the register 44 and the parallel
output from the register 44 is compared with a permanent identification
code for that particular transponder 18 stored in the ROM 48 by means of
the comparator 46. If a complete match between the serial code and the
identification code stored in the ROM 48 is obtained, an output 50 from
the comparator 46 changes state and switches on the RF switch 38 thereby
allowing the third harmonic wave 22 to be transmitted thus acknowledging
the detection of matching codes.
Referring to FIG. 5 of the drawings, a development of the logic module 36
is illustrated. The purpose of this developed logic module 36 is to
provide uses in application areas where very large numbers of transponders
18 have to be scanned within a limited time period and within a limited
space without causing confusion from a multitude of responses, in order to
identify individual members of a smaller group of labelled objects not
known initially.
In this embodiment, the logic module 36 comprises a ROM 52. A category code
is stored in a first section 54 of the ROM 52, a time-delay code is stored
in a second section 56 of the ROM 52 and an individual identification code
is stored in a third section 58 of the ROM 52. An input signal carrying a
category code is fed serially into a shift register 60 and the parallel
output of the shift register is compared with the category code stored in
the section 54 of the ROM 52 via a digital comparator 62. An output from
the digital comparator 62 is fed via an AND gate 64 where the signal is
summed with a signal from a clock generator 66. The output from the AND
gate 64 is input to a counter 68 and the output from the counter 68 is
compared with a time delay code in the section 56 of the ROM 52 via a
second comparator 70. An output from the comparator 70 is fed via an AND
gate 72, where it is summed with a signal from the clock generator 66, to
a latch or shift register 74. This latch 74 serves to convert the
individual code contained in section 58 of the ROM 52, which is entered
into latch 74 in a parallel mode, into a serial mode, which is fed to the
control terminal of the RF switch 38. This causes the individual code to
be modulated on the returned signal 22 transmitted by antenna 42.
The category code in the ROM 52 serves to activate a small group of
transponders 18 out of a large population and the rest of the transponders
remain de-activated during the scanning process. The "time delay" part of
the ROM 52 serves to generate a time delay which is different for each
individual transponder 18 in the group of transponders 18. This delays the
transmission of the individual codes of each transponder 18 by varying
amounts of time such that codes are received by the transceiver unit 12,
one at a time. Since only a small group of transponders 18, rather than
all the transponders 18, is relevant at any time, the span of time delays
need not be excessively long and the search operation can proceed
relatively briskly.
Referring to FIGS. 6 to 8 of the drawings, the construction of the
transponder 18 is shown in greater detail. The transponder 18 comprises
the receiving antenna 24 in the form of a patch antenna as well as the
transmission antenna 42 which is also in the form of a patch antenna. In
the embodiment illustrated, the patch antennas 24, 42 are in the form of C
patches, but, instead, they may be elliptical. The antennas 24 and 42 are
to be as small as possible and must be relatively thin or flat in one
dimension in order to disturb the surface contours of the marked object
minimally. Further, the antennas 24, 42 are matched to striplines 90 and
91, respectively, which correspond to the transmission lines or co-axial
lines 26, 40, respectively. Further, it is important that the antennas 24
and 42 be as omni-directional as possible in order to operate effectively
despite the orientation of an object to which the transponder 18 is
affixed relative to the transceiver unit 12.
Each transponder 18 is in the form of a label 76. The label 76 consists of
a multi-layer card 78 comprising a first metal layer 80, a second metal
layer 82 and a third metal layer 84. A layer 86 of a dielectric material
is sandwiched between the metal layers 80 and 82 and a further layer 88 of
dielectric material is sandwiched between the metal layers 82 and 84.
The antennas 24, 42 are etched out of the metal layer 80. The middle metal
layer 82 constitutes a continuous ground layer, while the stripline or
microstrip line connections 90 and 91, filters, directional couplers, etc
are etched from the third metal layer, 84. Chip component interconnects 92
are patterned in the metal layer 84 as well. The chips themselves are also
bonded on this side of the card 78 but in clearances where electrical
contact with the ground layer can be made.
Two feed through connections 94 are provided from antenna feed-points 96 to
the microstrip lines 90 and 91 on the opposite side of the card 78.
Finally, FIG. 9 of the drawings shows a block diagram of the transceiver
unit 12. The transceiver unit 12 comprises a control module 98, a
transmitter module 100, a receiver module 102 and a frequency control
module 104.
The control module 98 includes an entering means in the form of a keyboard
106 by means of which instructions are entered into the transceiver unit
12. The keyboard 106 is connected to an embedded microcomputer 108. The
microcomputer 108 controls a visual display unit 110.
For transmitting signals, appropriate signals are sent from the computer
via an interface board 112 to the transmitter module 100. The
microcomputer 108 also receives signals from the receiver module 102 via
the interface board 112.
The microcomputer is connected via a further interface board 114 to the
frequency control module 104.
The transmitter module 100 includes a modulator 116 which is connected via
a UHF amplifier 118 to a transmitting antenna 14.1 of the antenna means 14
(FIG. 1). The modulator 116 is used for modulating the signal 16 as
described below.
The modulator 116 is controlled via a frequency synthesizer 120 of the
frequency control module 104. The frequency synthesizer 120 receives
control signals from the microcomputer 108 via the interface board 114 and
receives a fixed frequency signal from a crystal oscillator 122.
The receiver module 102 comprises a resonant circuit 124 to which a
receiving antenna 14.2 of the antenna means 14 (FIG. 1) is connected. The
resonant circuit 124 is connected to an IF mixer and amplifier 126 which
is controlled by the frequency synthesizer 120 of the frequency control
module 104. An output of the mixer and amplifier 126 is connected to a
demodulator 128 which feeds demodulated signals to the microcomputer 108
via the interface board 112. The frequency synthesizer 120 also controls
the transmit and receive frequencies of the signals 16 and 22. It
functions to obtain a fixed ratio, as described above, typically a ratio
of 1:3, between the frequency of the transmitted signal 16 and the
received signal 22.
It will be appreciated that the components of the transceiver unit 12 as
well as of the transponder 18 are readily realisable to a person skilled
in the art and, as such, are not described any further herein.
In use, data storage space of the microcomputer 108 of the transceiver unit
12 is loaded with identification codes and other relevant information of
all the different transponders 18 of the system 10. A search operation for
any specific transponder 18 can be conducted by selecting such transponder
via the keyboard 106 of the transceiver unit 12. A search operation for
any specific category of transponders can be initiated via the keyboard
106 in a similar way. The visual display unit 110 may display information
on any transponder 18 located during a search operation.
The energising signal 16 is transmitted via antenna 14.1 of the antenna
means 14 of the transceiver unit 12. The energising signal 16 is in the
UHF frequency range to enable narrowbeam transmit and receive antennas
14.1 and 14.2 to be used with the transceiver unit 12. It will be
appreciated that the narrower the beam of the antennas 14.1 and 14.2, the
more directional the antennas 14.1 and 14.2 will be. Hence, by moving the
transceiver unit 12 about on receipt of a response from a transponder 18,
the strength of the signal 22 will vary and an indication of the direction
from which the signal 22 originated can be obtained. It will be
appreciated by those skilled in the art that an antenna with a narrow beam
will need to be sealed inversely proportionally to the frequency of the
signals or the smaller the desired physical size of the antennas 14.1 and
14.2, the higher the frequency of the energizing signal needs to be. In
addition, energy transfer efficiency for powering the electronics of the
transponder 18 can be more readily achieved by means of a signal in the
UHF frequency range.
The energising signal 16 has a waveform substantially as shown in FIG. 2A
of the drawings, i.e. a constant amplitude carrier wave of the desired
frequency.
Thus, the transceiver unit 12 transmits the energising wave 16 having the
waveform shown in FIG. 2A. In the case where transponders 18 are sparsely
distributed, this mode can be used for a walk around type of search. Any
transponder 18 will re-emit a signal, i.e. the returned signal 22 when
within the range and within the beamwidth of the antenna 14.1 of the
transceiver unit 12. The direction of the transponder 18 can be accurately
determined by seeking the direction of maximum response.
In the case where there is a high concentration of transponders 18, the
selected identification code of a particular transponder 18 to be located
is modulated on the energising wave 16 to provide a waveform 130 as shown
in FIG. 2B of the drawings via the operation of the microcomputer 108
controlling the modulator 116. This will first de-activate all
transponders 18 within range of the transceiver unit 12. After the total
identification code has serially been entered into the logic circuitry 36
of the transponder 18 and a complete match with its internal recorded code
has been detected as described above, that particular transponder 18 will
again be activated. All other transponders 18 with non-matching codes
within the range of the transceiver unit 12 will remain de-activated and
will not interfere with any subsequent communication between the
transceiver unit 12 and the specific transponder 18. Thus, it will then be
possible to determine the direction of the specific transponder 18 with
sufficient accuracy without interfering signals arising from elsewhere. In
many applications this will be sufficient to locate the marked object 20.
When it is necessary to make a range determination in respect of a
particular transponder 18, a sinusoidal waveform is modulated on the
energising signal 16 to provide a waveform 132 as shown in FIG. 2C of the
drawings. This step should be taken immediately after the transmission of
the waveform 130 to ensure that all non-selected labels are still
de-activated. By use of the sinusoidal waveform 132, or a sequence of such
waveforms of different frequencies, a range determination in respect of a
particular transponder 18 can be made.
Hence, it is an advantage of the invention, that a low cost locating system
10 and method are provided. The transponders 18 are physically small and
thin and will interfere minimally with the object 20 on which such a
transponder is mounted. Further, the transponders 18 are not
battery-operated and should thus not degrade with time or need maintenance
or adjustment. Also, the system 10 is operable in a cluttered environment
having many reflecting surfaces, etc. In addition, a large number of
transponders 18 can be used in close proximity to one another without
mutual interference. Finally, by means of the system 10, the Applicant
believes that it will be possible to determine the position of a specific
object 20, carrying the necessary transponder 18, from a predetermined
distance. transmitted.
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