METHOD AND APPARATUS FOR DETECTING MOTION

• US 3,803,539 A
• Filed: 07/20/1972
• Issued: 04/09/1974
• Est. Priority Date: 07/20/1972
• Status: Expired due to Term

• Current Assignee: Richard L. Mcmaster
• Original Assignee: Richard L. Mcmaster
• Inventors: McMaster, Richard L.
• Primary Examiner(s): Farley, Richard A.
• Application Number:
  US05/273,472
• Time in Patent Office: 628 Days
• Field of Search: 340/3D,258A,1R 343/7.7
• US Class Current: 367/94
• CPC Class Codes: G01S 15/523 for presence detection burglar, theft or intruder alarms G08B13/00, e.g. G08B13/16

Abstract

A unique signal injection technique is employed to stabilize the range and sensitivity of motion-detection devices of the Doppler type. A signal of substantially constant amplitude is algebraically added to the received signal prior to detection of the Doppler frequency to substantially eliminate the adverse effects on range and sensitivity produced by both null and excessively large signal conditions.

Claims

1. An acoustic motion-detecting device comprising:

means for transmitting acoustic energy waves of predefined frequency into a region wherein motion is to be detected, said transmitting means comprising means for generating a first electrical signal having a frequency proportional to said predefined frequency;

means for receiving said transmitted acoustic energy waves upon being reflected and/or modified by objects within said region, said receiving means comprising acusto-electrical transducing means for converting the acoustic energy waves received by said receiving means into a second electrical signal having a frequency, phase and amplitude proportional to the algebraic sum of all energy waves arriving at said receiving means, said frequency phase and amplitude being proportional to the rate of motion of objects in said region;

summing means electrically coupled to said generating means and said acousto-electrical transducing means for linearly adding said first and second electrical signals to provide a summed signal; and

means, operatively coupled to said summing means, for converting said summed signal to an analog signal having a frequency proportional to the instantaneous difference in frequency between said first and second electrical signals and proportional to the rate at which the amplitude and/or phase of said second signal varies.

2. The invention according to claim 1 further comprising means for activating an indicator when the frequency of said analog signal is within a predefined frequency range.

3. The invention according to claim 1 wherein said converting means comprises an envelope detector which linearly detects amplitude variations of said summed signal.

4. The invention according to claim 3 wherein said envelope detector comprises a nonlinear amplifier biased in a Class B or Class C mode.

5. The invention according to claim 1 wherein said first electrical signal has a peak-to-peak amplitude substantially equal to or larger than the maximum peak-to-peak amplitude of said second electrical signal.

6. A method for detecting motion comprising transmitting acoustic energy waves of predefined frequency into a region wherein intrusion is anticipated;

deriving a first electrical signal having a substantially constant amplitude and a frequency proportional to said predefined frequency;

deriving a second electrical signal having a frequency and amplitude proportional to said transmitted energy waves upon being reflected and/or modified by objects in said region;

summing said first and second electrical signals to provide a summed signal; and

deriving an analog signal from said summed signal having a frequency proportional to the difference in frequency between said first and second electrical signals and proportional to the rate of change in amplitude of said received signal.

7. The invention according to claim 5 further comprising the step of activating and indicator when the frequency of said analog signal is within a predefined frequency range.