CONTROLLED WAVE PATTERN ULTRASONIC BURGLAR ALARM

• US 3,781,859 A
• Filed: 04/19/1972
• Issued: 12/25/1973
• Est. Priority Date: 04/19/1972
• Status: Expired due to Term

• Current Assignee: Albert L. Hermans
• Original Assignee: Albert L. Hermans
• Inventors: Hermans, Albert L.
• Primary Examiner(s): Caldwell, John W.
• Assistant Examiner(s): Swann, III, Glen R.
• Application Number:
  US05/245,535
• Time in Patent Office: 615 Days
• Field of Search: 340/258A,1R 343/7.7 310/8.7
• US Class Current: 340/507
• CPC Class Codes: G08B 13/1627 using Doppler shift detection circuits

Abstract

A burglar alarm employs ultrasonic sound to protect a plurality of rooms. Each protected room contains a transmitter which emits an ultrasonic signal in a controlled wave pattern. The signal is received, filtered, and detected to determine if a doppler shift in the ultrasonic signal of a particular amplitude and frequency characteristic of human movement is present. If so, an alarm is given.

Claims

1. A burglar alarm system for detecting intrusion into a protected enclosure comprising:

oscillator means to generate an ultrasonic signal of predetermined frequency;

a directional, wide-beam transmitter means, connected to said oscillator means and located inside said protected enclosure with its transmitting axis directed toward the floor of said enclosure, to emit an ultrasonic sound at said predetermined frequency in a beam toward said floor;

directional receiver means, located inside said protected enclosure, with its sensitive axis directed toward said floor of said enclosure to receive and convert said ultrasonic sound to an electrical signal, the communication path between said transmitter means and said receiver means being other than the line of sight, such that said sound emitted from said transmitter means must be reflected a plurality of times between said floor and the ceiling of said enclosure before it can be received by said receiver means;

decoupler means, connected to said receiver means, to present an input impedance to said electrical signal;

filter means, connected to said decoupler means, to filter extraneous electrical noise from said electrical signal;

phase detector means, connected to said filter means and said oscillator means, to mix said electrical signal and said ultrasonic signal, and to generate a doppler signal from the phase difference between said electrical signal and said ultrasonic signal;

intrusion detection means, connectEd to said phase detector means, to generate an alarm actuating signal upon reception of a doppler signal of predetermined frequency and amplitude indicative of human movement inside the protected enclosure;

alarm means, connected to said intrusion detection means, to render an alarm upon receipt of said alarm actuating signal;

fail safe means, connected to said oscillator means and said alarm means, to generate an alarm actuating signal upon failure of said oscillator means to generate said ultrasonic signal of predetermined frequency;

turbulence circuit means connected to said phase detection means and said intrusion detection means to remove from said doppler signal electrical noise due to random noise and air turbulence in said protected enclosure;

memory logic means to delay rendering of said alarm; and

a walk test switch causing any alarm to be controllably rendered instantly, so that installation and adjustment of said system is facilitated.

2. A burglar alarm system according to claim 1, wherein said turbulence circuit means consists of an integrated circuit amplifier which receives said doppler signal as an input, and whose output is connected to a clipping circuit to remove background noise, said clipping circuit consisting of two parallel diodes of predetermined forward breakdown voltage, each aligned in a conductive direction opposite the other, the output of said clipping circuit being connected in series to a series combination of a resistor, a filter capacitor, and a half-wave rectifier, the output of said half-wave rectifier being connected to said intrusion detection means;

said turbulence circuit further including a feedback circuit to remove voltage peaks connected between said input and said output of said integrated circuit amplifier, said feedback circuit consisting of a plurality of diodes of predetermined forward breakdown voltage, a first number of said plurality of diodes connected in series in the same conductive direction, the remainder of said plurality of diodes connected in series and arranged in parallel connection with said first number of diodes, said remainder of diodes aligned in conductive direction opposite to said first number of diodes.

3. A burglar alarm system according to claim 1, wherein said decoupler means comprises capacitive impedance means, connected between said receiver means and said filter means, to increase the voltages of said electrical signal.

4. A burglar alarm system according to claim 3, wherein said memory logic means comprises a first transistor normally biased in the off condition, with a base connection to said intrusion detection means, and switchable to the on condition when said base connection receives said alarm actuation signal;

a second transistor normally biased in the on condition, with a base connection to the collector of said first transistor and switchable to the off condition when said first transistor switches to the on condition, the emitter of said second transistor being connected in series with the first terminal of the operating coil of an alarm relay, the second terminal of said operating coil being connected to ground;

a diode connected in parallel relationship with said operating coil to protect said second transistor from the inductive surge of said operating coil; and

a timing circuit comprising a charging resistor connected to a first terminal of a capacitor, the second terminal of said capacitor being connected to ground, said timing circuit being connected to said emitter of said second transistor in parallel relationship with said operating coil, and a second resistor connected to said first terminal of said capacitor and to ground, whereby reception of an alarm actuating signal will turn on said first transistor, causing said second transistor to turn off, and causing said capacitor to discharge, through said charging resistor, to a voltage insufficient to operate said operating coil of said alarm relay, thereby rendering a delayed alarm.

5. The Burglar alarm system according to claim 4, wherein said walk test switch is connected between said second terminal of said capacitor and ground, to selectively remove said capacitor from said timing circuit, thereby causing any alarm to be controllably rendered instantly.

6. The burglar alarm system according to claim 5, wherein said receiver means comprises a plurality of ultrasonic receivers, each of said receivers containing a metal plate, each said plate having a resonant frequency equal to said predetermined frequency at which said transmitter means emits said ultrasonic sound.

7. The burglar alarm system according to claim 6, further including a piezoelectric crystal affixed to each said metal plate to convert the vibrations of each said plate to an electrical signal, each said crystal being connected in parallel with the primary winding of a variable transformer, the secondary winding of each said transformer being connected in parallel with a variable potentiometer for adjusting the sensitivity of each said receiver.

8. The burglar alarm system of claim 5 wherein said transmitter means comprises at least one ultrasonic transmitter containing a metal plate having a resonant frequency equal to the predetermined frequency at which said transmitter means emits ultrasonic sound, and a piezoelectric crystal, affixed to said plate, which receives said ultrasonic signal from said oscillator means to vibrate said plate at said resonant frequency.