Electronic surveillance system

Claim 2

An electronic surveillance system, comprising transmitter means for transmitting electromagnetic signals, label means adapted for attachment to an article under surveillance for receiving a signal from said transmitter means and for retransmitting a reply, and receiver means for receiving and processing the reply; said label means including signal propagating means responsive to the signal from the transmitter for propagating the transmitted signal along a path at a rate slower than electromagnetic propogation, a plurality of sensing means mounted at coded locations along the path of said propagating means each for sensing the presence of a propagated signal at the location so that said sensing means together sense each signal sequentially in a given coded time order, an energy carrier means coupled to each of said sensing means for retransmitting the sequence of signals in the order they are sensed by said sensing means as the reply, said carrier means forming a signal path between said sensing means so that signals can move faster than the propagation rate of said propagating means.

Claim 3

A system as in claim 1, wherein said carrier means includes a conductive medium.

Claim 4

A system as in claim 1, wherein said sensing means each includes conductive transDucing means coupled to said propagating means.

Claim 5

An apparatus as in claim 3, wherein said carrier means includes a conductive medium.

Claim 6

An apparatus as in claim 1, wherein said propagating medium comprises a piezoelectric material.

Claim 7

A system as in claim 1, wherein said propagating means forms a delay line on part of the path free of sensing means, a plurality of said sensing means being located beyond the delay line along the path.

Claim 8

A system as in claim 6, wherein said sensing means located beyond the delay line are bunched within a distance less than the length of the line, said path beyond the distance being substantially free of sensing means.

Claim 9

A system as in claim 7, wherein one of said sensing means is located at the beginning of the delay line opposite the other of said sensing means.

Claim 10

A system as in claim 6, wherein one of said sensing means is located at the beginning of the delay line opposite the others of said sensing means.

Claim 11

An electronic surveillance system comprising transmitter means for transmitting electromagnetic signals, label means attachable to an article under surveillance for receiving an interrogation from the transmitter and for retransmitting a reply, and receiver means for receiving and processing the reply; said label means including acoustic signal propagating means responsive to the interrogation from the transmitter for acoustically propagating signals corresponding to the interrogation along a path, a plurality of energy return means mounted on said propogating means at coded locations for removing a portion of the energy of each signal as it passes the location and making the removed portion of the signals available for retransmission to said receiver means at the reply, said energy return means including a first plurality of interconnected parallel transducers mounted on said propagating means and a second plurality of interconnected parallel transducers interleaved between said first plurality of transducers, said transducers being spaced so as to correspond with the wave length of the acoustic signals at the frequency of excitation of the signals.

Claim 12

An electronic surveillance system comprising transmitter means for transmitting electromagnetic signals, label means attachable to an article under surveillance for receiving an interrogation from the transmitter and for retransmitting a reply, and receiver means for receiving and processing the reply; said label means including acoustic signal propagating means responsive to the interrogation from the transmitter for acoustically propagating signals corresponding to the interrogation along a path, a plurality of energy return means mounted on said propogating means at coded locations for removing a portion of the energy of each signal as it passes the location and making the removed portion of the signals available for retransmission to said receiver means at the reply, said energy return means including a first plurality of interconnected parallel transducers mounted on said propagating means and a second plurality of interconnected parallel transducers interleaved between said first plurality of transducers, said transducers being spaced so as to correspond with the wave length of the acoustic signals at the frequency of excitation of the signals.

Claim 13

A system as in claim 10, wherein said propagating means includes a piezoelectric crystal.

Claim 14

A system as in claim 11, wherein said energy return means are mounted on the surface of the crystal and the energy is propagated along that surface of the crystal.

Claim 17

An apparatus as in claim 13, wherein said carrier means includes a conductive medium.

Claim 18

An apparatus as in claim 13, further comprising antenna means for responding to the interrogation and applying it to said propagating means, said antenna means being connected to said carrier means for retransmitting the sequence of signals formed as the reply.

Claim 19

An apparatus as in claim 15, wherein said propagating medium comprises a piezoelectric material, said piezoelectric material being connected to said antenna means.

Claim 20

An apparatus as in claim 13, wherein said sensing means each includes conductive transducing means coupled to said propagating means.

Claim 21

An apparatus as in claim 13, wherein said propagating medium compRises a piezoelectric material.

Claim 22

An apparatus as in claim 13, wherein part of said propagating means forms a delay line free of sensing means, a plurality of said sensing means being located beyond the delay line.

Claim 23

An apparatus as in claim 19, wherein said sensing means located beyond the delay line are bunched within a distance less than the length of the line, said path beyond the distance being substantially free of sensing means.

Claim 24

An apparatus as in claim 20, wherein one of said sensing means is located at the beginning of the delay line opposite the other of said sensing means.

Claim 25

An apparatus as in claim 19, wherein one of said sensing means is located at the beginning of the delay line opposite the others of said sensing means.

Claim 26

An apparatus as in claim 13, further comprising antenna means responsive to the interrogation and coupled to said propogating means, said antenna means being connected to said sensing means for transmitting the reply electromagnetically.

Claim 27

An apparatus as in claim 23, wherein said propagating means includes a piezoelectric crystal coupled to said antenna means so as to propagate the signals acoustically, said sensing means each including a first plurality of interconnected electrodes mounted on the surface of said crystal parallel to each other and transverse to the direction of propagation of the signals and a second plurality of interconnected electrodes parallel to each other and extending transverse to the direction of propagation of the signals and interleaved between said first plurality of said electrodes, said crystal being tuned to propagate signals at a predetermined expected received frequency, said electrodes being spaced from each other at one half the wavelength of the predetermined frequency, said carrier means being mounted on said crystal and connecting said sensing means.

Claim 28

An apparatus as in claim 13, wherein each of said sensing means are removable from the locations for changing the coding of the reply.

Claim 31

An apparatus as in claim 26, wherein said propagating means is adapted to respond to signals of a given frequency, said transducers being spaced from each other one half wavelength of the frequency.