DETECTION SYSTEM

• US 3,810,172 A
• Filed: 07/18/1972
• Issued: 05/07/1974
• Est. Priority Date: 07/18/1972
• Status: Expired due to Term

• Current Assignee: Donald A. Paynter, Lee E. Burpee
• Original Assignee: Donald A. Paynter, Lee E. Burpee
• Inventors: Burpee, Lee E., Paynter, Donald A.
• Primary Examiner(s): Tubbesing, T. H.
• Application Number:
  US05/272,831
• Time in Patent Office: 658 Days
• Field of Search: 340/280 343/5PD,6.5R,6.5SS
• US Class Current: 342/27
• CPC Class Codes: G08B 13/2414 using inductive tags
• CPC Class Codes: G08B 13/2471 Antenna signal processing by receiver or emitter
• CPC Class Codes: G08B 13/2474 Antenna or antenna activator geometry, arrangement or layout loop antennae H01Q1/22

Abstract

A system for detecting the presence of resonant circuit targets in a field of electromagnetic radiation. The system includes means for generating a burst of a predetermined single frequency and a detector enabled after the termination of transmission. The detector is sensitive to continued presence of the predetermined frequency indicative of resonant ringing of a target in the field. Time sharing of a common transmitter and detector is accomplished employing a time division multiplex arrangement. Counterfeit target detection is also accomplished employing a test fixture with valid and invalid target indicators controlled by the system. In one embodiment, the antenna means is positioned in obstructions or doors which are moved aside by a person passing through the portal. This provides close coupling of energy and the system is provided with an enabling switch operated by displacement of the obstruction or door.

Claims

1. A system for detecting the presence of a resonant target in a field of interest comprising:

means for generating a signal containing the resonant frequency of the target to be detected;

antenna means coupled to said generating means for radiating the electromagnetic energy in the predetermined resonant frequency into a field of interest;

means for periodically gating said generator on and off;

means for receiving electromagnetic energy in the field as radiated by said antenna means;

detector means coupled to said receiving means for detecting the presence of the predetermined frequency in the field of interest;

means for enabling said detector means at a time interval following the termination of transmission of energy by said generator;

alarm means responsive to the detection of electromagnetic energy in the field of interest after termination of transmission by said generator;

wherein said generator means produces a plurality of discrete frequencies each in timed sequence and including means for sequentially gating those frequencies for introduction into the transmitting antenna.

2. The combination in accordance with claim 1 wherein said system is under the control of a timer and control circuit which in sequence enables the frequency generator, gates the energy from the frequency generator to the transmitting antenna, enables the receiving means and enables the detector and wherein said timing and control circuit performs the foregoing sequence for each frequency generated.

3. A system for detecting the presence of a resonant target in a field of interest comprising;

means for generating a signal containing the resonant frequency of the target to be detected;

antenna means coupled to said generating means for radiating the electromagnetic energy in the predetermined resonant frequency into a field of interest;

means for periodically gating said generator on and off;

means for receiving electromagnetic energy in the field as radiated by said antenna means;

detector means coupled to said receiving means for detecting the presence of the predetermined frequency in the field of interest;

means for enabling said detector means at a time interval following the termination of transmission of energy by said generator;

alarm means responsive to the detection of electromagnetic energy in the field of interest after termination of transmission by said generator; and

switch means responsive to the entrance of a person into a field to be scanned for initiating the operation of the system.

4. The combination in accordance with claim 3 wherein said switch means is responsive to displacement of an obstruction by the person to initiate a system in operation.

5. The combination in accordance with claim 4 wherein said antenna means form a part of said obstruction for closed coupling between the person passing through the area and the energy introduced into the area of search.

6. A system for detecting the presence of a resonant target in a field of interest comprising;

means for generating a signal containing the resonant frequency of the target to be detected;

antenna means coupled to said generating means for radiating the electromagnetic energy in the predetermined resonant frequency into a field of interest;

means for periodically gating said generator on and off;

means for receiving electromagnetic energy in the field as radiated by said antenna means;

detector means coupled to said receiving means for detecting the presence of the predetermined frequency in the field of interest;

means for enabling said detector means at a time interval following the termination of transmission of energy by said generator;

alarm means responsive to the detection of electromagnetic energy in the field of interest after termination of transmission by said generator;

whereby said system is under the control of a timer and control circuit which sequence enables the frequency generator, gates the energy from the frequency generator to the transmitting antenna, and enables the receiving means and the detector;

wherein said timing and control circuit includes a trigger circuit for generating the sequence of pulses to initiate each transmission and to scan the system of the field to be detected; and

a plurality of delay circuits connected between pulse generators for said transmitter, receiver and detector respectively.

7. A system for detecting the presence of a resonant target in a field comprising;

a generator for producing a predetermined frequency corresponding to the resonant frequency of said target;

a receiver responsive to electromagnetic radiation in the frequency of interest;

antenna means having a field encompassing the field to be observed;

switch means for alternately connecting the generator and receiver to the antenna;

detector means responsive to energy in the predetermined frequency above a selected minimum level;

timing means for enabling said detector during each period of time when said receiver is connected to said antenna and said generator is disconnected from said antenna;

alarm means connected to said detector for indicating an alarm condition when said detector detects the presence of a predetermined frequency above the selected level;

wherein said switch means comprises a pair of oppositely poled PIN diodes parallel connected and in series between said generator and said antenna;

a pair of oppositely poled parallel connected PIN diodes connected in shunt between said receiver and ground;

said first and second sets of PIN diodes being responsive to signal energy from said generator to enable the connection between said generator and said antenna and disable the connection between said receiver and said antenna;

said PIN diodes being responsive to the termination of energy from said generator to said antenna for interrupting the conduction path between said generator and said antenna and connecting said receiver to said antenna.

8. The combination in accordance with claim 7 including a pair of antennas each spaced from each other encompassing a substantially common field and means for alternately switching signal path between said generator and said antennas, the transmission of energy from said generator;

and said means operative to alternate the connection between said receiver and said antennas during operation of said receiver.

9. A system for detecting instrumented tokens having a passive resonant circuit therein and means for coupling energy in and out of said circuit;

said system comprising means for generating selected frequencies in a band encompassing the resonant frequency of instrumented tokens to be detected;

first antenna means for radiating said selected frequencies into a predetermined field subject to monitoring for the presence or absence of instrumented tokens;

receiver means responsive to electromagnetic radiation in the band of frequencies transmitted;

second antenna means connected to said receiver and positioned to detect radiation in said predetermined field;

a detector for dEtecting energy in such preselected frequencies above a predetermined threshhold;

gate means for enabling said transmitter to introduce energy in one or more of the preselected frequencies into said field;

second gate means for periodically enabling said receiver after the termination of each transmission by said receiver said detector being operative to detect substantial electromagnetic energy in said field indicative of the presence of the resonant circuit of an instrumented token in said field.

10. The combination in accordance with claim 9 wherein said transmitter and receiver are coupled to a portal area while monitoring the passage of an instrumented token through said portal.

11. The combination in accordance with claim 10 wherein said portal includes at least one door displaced in passing through the portal;

and said antenna means are secured to said door for close coupling between the system and a passerby.

12. The combination in accordance with claim 11 wherein said portal includes a pair by directional swinging doors with said first antenna means secured to one of the doors and said second antenna means secured to the second of said doors.

13. The combination in accordance with claim 12 including switch means responsive to the initial direction of movement of said doors to enable the operation of said system.