Controlled wave pattern ultrasonic burglar alarm

• US 4,172,253 A
• Filed: 09/07/1973
• Issued: 10/23/1979
• 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): Budd, Mark O.
• Application Number:
  US05/395,355
• Time in Patent Office: 2,237 Days
• Field of Search: 179/110 A, 179/115 R, 340/559, 340/560, 310/321, 310/322, 310/324, 310/316-319
• US Class Current: 367/94
• 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. In a burglar alarm system, a low-profile transducer for receiving an ultrasonic signal of predetermined frequency generated by a remote source, said transducer comprising a mounting means, a tuned plate having a characteristic resonant frequency equal to said predetermined frequency and vibrating at said frequency when said signal impinges upon said plate, said plate being spaced from said mounting means by spacer means, a piezoelectric crystal fastened to said plate to provide both electrical and mechanical union therebetween, said crystal vibrating in unison and sympathetically with said plate when said signal impinges upon said plate and thereby generating an electrical signal related to said ultrasonic signal for triggering an external alarm means, said crystal being electrically connected in parallel with the primary winding of a variable transformer, the secondary winding of said transformer being connected in parallel with a variable potentiometer for adjusting the sensitivity of said transformer, said mounting means comprising a rectangular frame means provided with at least one sot extending therethrough, at least one rectangular wall means extending generally normal from said frame means and fixedly attached thereto, said wall means being provided with at least one slot therein;

a cover means fastened to said wall means by at least one fastener which extends through said slot in said wall means, one surface of said cover means being provided with a double-sided foam adhesive tape, said potentiometer and said transformer being fixedly fastened to said frame means by epoxy plastic, said potentiometer being adjustable without removal of said cover means via access through an aperture provided in said wall means, said tuned plate being fixedly attached to a lower surface of said frame means by fastener means which extend through at least one opening in said frame means, and said tuned plate being further spaced from said frame means lower surface by bushing means interposed therebetween.

2. In a burglar alarm system, a low-profile transducer for emitting a wide-beam ultrasonic signal of predetermined frequency comprising a counting means and a tuned plate having a characteristic resonant frequency equal to said predetermined frequency and vibrating said frequency when excited by excitation means comprising a piezoelectric crystal fastened to said plate to provide both electrical and mechanical union therebetween, said crystal being caused to vibrate at said frequency by an electrical signal related to said ultrasonic signal, said crystal thereby causing said plate to vibrate at said frequency in unison and sympathy with said crystal, said mounting means comprising a rectangular frame means provided with at least one slot extending therethrough, at least one rectangular wall means extending generally normally from said frame means and fixedly attached thereto, said wall means being provided with at least one slot therein, a cover means fastened to said wall means by at least one fastener which extends through said slot in said wall means, one surface of said cover means being provided with a double-sided foam adhesive tape, said tuned plate being fixedly attached to a lower surface of said frame means by fastener means which extend through at least one opening in said frame means, and said tuned plate being further spaced from said frame means lower surface by bushing means interposed therebetween.

3. An alarm device comprising a transducer for transmitting ultrasonic signals in an air environment for detection of intruding objects or persons therein, the transducer having a piezoelectric element coupled to a thin, flat, resonant plate substantially larger than said piezoelectric element, the plate having a periphery substantially free and unsupported during operation, said piezoelectric element being excitable at a resonant frequency of said plate when coupled to the piezoelectric element, and, means for detecting variations in ultrasonic signals in an air environment and activating an alarm.