Ultrasonic intrusion detection system
First Claim
1. An intrusion detection system for detecting the presence of moving objects in a protected area, comprising:
- transmitter means for transmitting waves into the protected area, including means, responsive to a modulation frequency, for alternately transmitting waves of a first frequency and waves of a second frequency, the transmitter alternating between the first and second frequency at a rate determined by the modulation frequency;
receiving means for receiving echoes resulting from reflection of the transmitted waves by objects in the protected area and for providing an output signal representative of the received signal; and
processing means responsive to the receiving means output signal for detecting frequency components in the receiving means output signal representative of doppler-shifted echoes from moving objects in the area, and for providing an alarm signal only in response to the detection of frequency components which are substantially either all above or all below the transmitted frequencies and further selectively responsive to the modulation frequency, thereby detecting objects having a net movement with respect to the receiving means which reflect said alternating first and second frequencies.
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Accused Products
Abstract
Apparatus and method of processing in an ultrasonic alarm system to detect the doppler-shifted components which indicate the presence of an intruder. A master control applies to each of the transmitter transducers a signal which alternates between two frequencies at a modulation frequency. The output signal from the receiving transducer is synchronously detected and low pass filtered. The filtered signal is applied to electronics which respond to the presence of modulation frequency components in the filter output signal. A first embodiment utilizes a high-Q bandpass filter having a resonance frequency equal to the modulation frequency. In a second embodiment, the modulation frequency is used to effectively perform a correlation between the received signal and the modulation frequency.
42 Citations
30 Claims
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1. An intrusion detection system for detecting the presence of moving objects in a protected area, comprising:
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transmitter means for transmitting waves into the protected area, including means, responsive to a modulation frequency, for alternately transmitting waves of a first frequency and waves of a second frequency, the transmitter alternating between the first and second frequency at a rate determined by the modulation frequency; receiving means for receiving echoes resulting from reflection of the transmitted waves by objects in the protected area and for providing an output signal representative of the received signal; and processing means responsive to the receiving means output signal for detecting frequency components in the receiving means output signal representative of doppler-shifted echoes from moving objects in the area, and for providing an alarm signal only in response to the detection of frequency components which are substantially either all above or all below the transmitted frequencies and further selectively responsive to the modulation frequency, thereby detecting objects having a net movement with respect to the receiving means which reflect said alternating first and second frequencies. - View Dependent Claims (2)
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3. An intrusion detection system for detecting the presence of moving objects in a protected area, comprising:
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transmitter means for the transmitting waves into the protected area, including means, responsive to a modulation frequency, for alternately transmitting waves of a first frequency and waves of a second frequency, the transmitter alternating between the first and second frequency at a rate determined by the modulation frequency; receiving means for receiving echoes resulting from reflection of the transmitted waves by objects in the protected area and for providing an output signal representative of the received signal; and processing means responsive to the receiving means output signal for detecting signal components in the receiving means output signal representative of echoes from moving objects in the area, and for providing an alarm signal in response to echoes representative of an object having a net movement with respect to the receiving means, wherein the processing means includes; doppler frequency sensing means for sensing the presence in the receiving means output signal of signal components representative of doppler-shifted echoes produced by moving objects in the protected area, and for producing an output signal representative of the doppler-shifted echoes; and modulation frequency sensing means for monitoring the doppler frequency sensing means output signal to detect the presence therein of frequency components at the modulation frequency and for producing an alarm signal in response to the presence of such modulation frequency components. - View Dependent Claims (4, 5, 6, 7, 8, 9, 10, 11, 24, 25, 26, 27, 28, 29, 30)
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12. A receiver for use with an ultrasonic intrusion detection system having a transmitter which alternately transmits acoustic signals of first and second frequencies into a protected area, said transmitter alternating between the first and second frequencies at a modulation frequency, the receiver for receiving echoes resulting from reflections of the transmitted signal by objects in the protected area and for providing an alarm signal in response to echoes representative of a moving object with the protected area, said receiver comprising:
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a receiving transducer for receiving echoes resulting from reflections of the transmitted signal by objects in the area and for producing an electrical output signal representative of the received echoes; doppler frequency sensing means for sensing the presence of signal components in the receiving transducer output signal representative of doppler-shifted echoes produced by moving objects in the protected area and for producing an output signal representative of such doppler-shifted echoes; and modulation frequency sensing means for monitoring the doppler frequency sensing means output signal to sense the presence therein of frequency components equal to the modulation frequency, and for producing an alarm signal in response to the presence of modulation frequency components in the doppler frequency sensing means output signal. - View Dependent Claims (13, 14, 15)
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16. In an intrusion detection system of the type having a transmitter for transmitting acoustic waves into a protected area and a receiver for receiving echoes resulting from reflections of the transmitted waves by objects in the protected area and for detecting doppler-shifted frequency components in the received echoes representative of the presence in the protected area of a moving object, the improvement comprising:
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means in the transmitter for producing a first frequency; means in the transmitter for producing a second frequency; means in the transmitter for producing a modulation frequency; means in the transmitter for causing the transmitter to alternately transmit acoustic waves into the protected area at the first and second frequencies, alternating therebetween at a rate determined by the modulation frequencies; and means in the receiver for detecting doppler-shifted frequency components and for discriminating against false alarm conditions, including; doppler-frequency sensing means for demodulating the received echoes with a frequency intermediate the first and second frequencies to produce a demodulated output signal; modulation frequency sensing means responsive to the demodulated output signal for detecting frequency components therein equal to the modulation frequency and for producing an alarm signal in response to the detection of such modulation frequency components. - View Dependent Claims (17)
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18. A method of detecting the presence of moving objects in a protected area comprising the steps of:
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transmitting acoustic waves into the protected area in a repetitive time sequence of first and second frequencies at a predetermined rate; receiving reflections of the transmitted waves from objects in the protected area and producing an input signal representative thereof; detecting the presence in the input signal of doppler-shifted frequency components resulting from reflections from moving objects in the protected area to produce an intermediate signal representative thereof; detecting the presence in the intermediate signal of variations therein occurring at the predetermined rate corresponding to the transmitted sequence, and producing an alarm signal in response to a positive detection of the presence of such variations.
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19. A method of detecting the presence of moving objects in a protected area comprising the steps of:
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alternately transmitting acoustic waves into the protected area in a sequence of first and second frequencies; receiving reflections of the transmitted waves from objects in the protected area and producing an input signal representative thereof; detecting the presence in the input signal of doppler-shifted frequency components resulting from reflections from moving objects in the protected area to produce an intermediate signal representative thereof, wherein said step of detecting includes the steps of; producing a reference frequency intermediate the first and second frequency; demodulating the input signal with the reference signal to produce a demodulated output signal representative of the presence in the input signal of doppler-shifted frequency components; and detecting the presence in the intermediate signal of variations therein corresponding to the transmitted sequence, and producing an alarm signal in response to a positive detection of the presence of such variations. - View Dependent Claims (20, 21, 22)
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23. An ultrasonic intrusion detection system for detecting the presence of moving objects in a projected area, comprising:
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transmitter means for transmitting acoustic waves into the protected area, including; means, responsive to a modulation frequency, for producing a transmitter signal which alternates between a first frequency and a second frequency at a rate determined by the modulation frequency; a plurality of transmitting transducers, responsive to the transmitter signal, for alternately transmitting acoustic waves at said first and second frequencies into the protected area; a plurality of receiving transducers, each for receiving acoustic waves from the protected area, and for producing an electrical output signal representative thereof; and a plurality of processing means, equal in number to the plurality of receiving transducers, each processing means being associated with and connected to a respective one of the receiving transducers, each processing means being responsive to the associated receiving transducer output signal for detecting signal components in the receiving means output signal representative of echoes from moving objects in the protected area, and for providing an alarm signal in response to echoes representative of an object having a net movement with respect to the receiving transducer, each of the processing means including; doppler frequency sensing means for sensing the presence in the receiving means output signal of signal components representative of doppler shifted echoes produced by moving objects in the protected area, and for producing an output signal representative of the doppler shifted echoes; and modulation frequency sensing means for monitoring the doppler frequency sensing means output signal to detect the presence therein of frequency components at the modulation frequency and for producing an alarm signal in response to the presence of such modulation frequency components.
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Specification