METHOD OF AND APPARATUS FOR THE DETECTION OF STOLEN ARTICLES

• US 3,711,848 A
• Filed: 02/10/1971
• Issued: 01/16/1973
• Est. Priority Date: 02/10/1971
• Status: Expired due to Term

• Current Assignee: Henry J. Martens
• Original Assignee: Henry J. Martens
• Inventors: Martens, Henry J.
• Primary Examiner(s): Caldwell, John W.
• Assistant Examiner(s): Slobasky, Michael
• Application Number:
  US05/114,306
• Time in Patent Office: 706 Days
• Field of Search: 340/280,258 325/8
• US Class Current: 340/572.2
• CPC Class Codes: G08B 13/2422 using acoustic or microwave tags
• CPC Class Codes: G08B 13/2431 Tag circuit details
• CPC Class Codes: G08B 13/2474 Antenna or antenna activator geometry, arrangement or layout loop antennae H01Q1/22

Abstract

A system for detecting the unauthorized removal of protected articles from a designated area comprising a harmonic generator circuit made up of a semiconductor diode chip and a pair of antennas adapted to receive a radio frequency signal at a first frequency and transmit a second radio frequency signal at a second, relatively higher frequency. Transmitting and receiving means are positioned adjacent an exit area for actuating the circuit and an alarm when protected articles approach the area, and means are provided for deactivating the circuit when the protected article is legitimately purchased. The generator circuit can be manufactured at very low cost thereby permitting, when a legitimate sale is made, permanent deactivation of the circuit without removing or otherwise handling the tag or label carrying the circuit.

Claims

1. A system for detecting the unauthorized removal of protected articles from a predetermined area comprising a. a semiconductor diode chip having a cathode and an anode, b. first and second antenna means respectively electrically connected to said cathode and said anode of said diode chip, said antennas being shaped and dimensioned to receive radio frequency signals at first predetermined frequency level and to retransmit said signals at a second predetermined, relatively higher radio frequency level, c. carrier means for carrying and embedding said diode chip and said antennas for convenient concealment in or association with the article to be protected, d. at least one reCeiving and transmitting unit positioned near the exit from said area, said unit transmitting radio frequency signals at said first frequency level and receiving radio frequency signals at said second radio frequency level, e. alarm means electrically connected to and actuated by said receiving and transmitting unit when a protected article is in the detectable area around said unit, and f. deactivating means for permanently deactivating the harmonic generator circuit when said protected article has been legitimately purchased and without requiring disassociation of such circuit from said article, said deactivating means comprising a power signal source for transmitting radio frequency signals at a predetermined power level, and antenna means, the power level of said power signal means being substantially higher than the power level of said signal emitted by said receiving and transmitting unit thereby permanently deactivating said harmonic generator circuit.

2. The system of claim 1 wherein said second radio frequency level is approximately twice the frequency of said first frequency level, and the output power of said power signal source is approximately ten times the output power of the transmitted radio frequency signal of said receiving and transmitting unit.

3. The system of claim 2 wherein said receiving and transmitting unit comprises a transmitter including a source of high frequency energy, a filter, and a transmitter antenna, and a receiver comprising a receiving antenna, a band pass filter, a receiver adapted to receive signals of predetermined frequency approximately double the frequency of the signals emitted by said transmitter, and alarm means actuated by said receiver in response to the penetration of a protected article which has not been deactivated into the area of said transmitter.

4. The system of claim 1 wherein said first and second antennas each include a relatively pointed leading end portion adapted to contact and be electrically connected to the cathode and anode, respectively, of said diode chip.