Portable, batteryless, frequency divider consisting of inductor and diode

• US 4,670,740 A
• Filed: 11/04/1985
• Issued: 06/02/1987
• Est. Priority Date: 11/04/1985
• Status: Expired due to Term

• Current Assignee: Sensormatic Electronics Corporation (Johnson Controls International plc)
• Original Assignee: Security Tag Systems, Inc. (Johnson Controls International plc)
• Inventors: Charlot, Lincoln H. Jr., Herman, Fred W.
• Primary Examiner(s): Swann, III, Glen R.
• Application Number:
  US06/794,552
• Time in Patent Office: 575 Days
• Field of Search: 340/572, 343/895, 343/894, 363/159, 363/158, 363/170, 363/157, 307/271
• US Class Current: 340/572.2
• CPC Class Codes: G08B 13/2425 Tag deactivation
• CPC Class Codes: G08B 13/2431 Tag circuit details

Abstract

A batteryless, portable, frequency divider consists of a single resonant circuit consisting of an inductor and a diode. The resonant circuit detects electromagnetic radiation at a first predetermined frequency and responds to said detection by transmitting electromagnetic radiation at a second frequency that is one-half of the first frequency. The circuit is resonant at the second frequency when the voltage across the diode is zero. The frequency divider is utilized in a presence detection system that uses a tag containing the frequency divider. The system transmits electromagnetic radiation at the first frequency into a surveillance zone, and detects the second frequency to detect the presence of the tag in the surveillance zone.

Claims

1. A batteryless, portable, frequency divider, consisting of a single resonant circuit, consisting of

an inductor;

and

a diode connected in parallel with the inductor to define a resonant circuit that detects electromagnetic radiation at a first predetermined frequency and responds to said detection by transmitting electromagnetic radiation at a second frequency that is one-half of the first frequency, wherein the circuit is resonant at the second frequency when the voltage across the diode is zero.

2. A tag for use in a presence detection system, comprising a batteryless, portable, frequency divider, consisting of

a single resonant circuit, consisting of

an inductor;

and

a diode connected in parallel with the inductor to define a resonant circuit that detects electromagnetic radiation at a first predetermined frequency and responds to said detection by transmitting electromagnetic radiation at a second frequency that is one-half of the first frequency, wherein the circuit is resonant at the second frequency when the voltage across the diode is zero.

3. A presence detection system, comprising

means for transmitting an electromagnetic radiation signal of a first predetermined frequency into a surveillance zone;

a tag for attachment to an article to be detected within the surveillance zone, comprising a batteryless, portable, frequency divider consisting of a single resonant circuit, consisting of an inductor; and

a diode connected in parallel with the inductor to define a resonant circuit that detects electromagnetic radiation at the first predetermined frequency and responds to said detection by transmitting electromagnetic radiation at a second frequency that is one-half of the first frequency, wherein the circuit is resonant at the second frequency when the voltage across the diode is zero; and

means for detecting electromagnetic radiation at the second frequency in the surveillance zone.