Abstract:
A method for detecting an intrusion in a confined space is provided. The method includes the steps of detecting an ultrasonic acoustic signal with a Doppler shift and a low frequency acoustic signal, said signals being indicative of an intrusion, and generating an alarm if the ultrasonic acoustic signal with a Doppler shift and the low frequency acoustic signal were detected within an assigned timeframe.

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
       [0001]    This application claims the benefit of Israeli patent application No. 214575 filed on 9 Aug. 2011 which is incorporated herein by reference. 
       FIELD OF THE INVENTION 
       [0002]    The present invention relates to method and system for detecting an intrusion in a confined space and the implementation thereof. 
       BACKGROUND OF THE INVENTION 
       [0003]    It is known in the art to apply the Doppler principle in alarm systems for detection of intrusion. In devices of this type, radiation is emitted by a transmitter and is reflected by objects, including people. The reflected radiation is picked up by a receiver and evaluated. If the reflection results from an object at rest, the frequency of the received radiation coincides with the frequency of the transmitted radiation. If, however, the reflection results from an object which is moving with a velocity component in the direction of the transmitter and/or the receiver, or away from the transmitter or receiver, then a Doppler frequency shift occurs in the received radiation. 
         [0004]    It is also known that an intrusion into a confined space, for example by breaking a window or a wall, generates a low frequency signal along with a Doppler frequency shift. 
         [0005]    Known alarm systems utilize ultrasonic radiation in a frequency range of about 40 kHz, for example. However, ultrasonic devices have special disadvantages. One particular disadvantage is that the transmitted ultrasonic radiation is also influenced, for example, by moving air, for instance by attenuation fluctuations. Particularly in heated areas, however, air turbulence cannot be precluded. 
         [0006]    In order to avoid false alarms, there is provided an alarm system in which one section that operates with low frequency radiation and another section that operates with ultrasonic waves. In this system it has been found that false alarms can be reduced or even totally avoided, if an alarm is given only when there is a coincidence, namely when an occurrence which is to be reported is detected by both sections; or even more preferably, if an alarm is given only when an occurrence which is to be reported is first detected by a section which operates with low frequency radiation and if said occurrence is detected by both sections. 
       SUMMARY OF THE INVENTION 
       [0007]    In accordance with a first aspect of the present invention, there is provided a method for determining an alarm condition, the method characterized by the steps of: 
         [0008]    generating an ultrasonic acoustic signal and transmitting it into a confined space; and 
         [0009]    detecting a LF acoustic signal and an ultrasonic acoustic signal with a Doppler shift, said signals being indicative of the intrusion; and 
         [0010]    determining whether said LF acoustic signal and said ultrasonic acoustic signal with a Doppler shift were detected within an assigned timeframe; and 
         [0011]    generating an alarm signal, if said LF acoustic signal and said ultrasonic acoustic signal with a Doppler shift were detected within an assigned timeframe. 
         [0012]    In accordance with a second aspect of the present invention, there is provided a method for determining an alarm condition, the method characterized by the steps of: 
         [0013]    generating an ultrasonic acoustic signal and transmitting it into a confined space; and 
         [0014]    detecting a LF acoustic signal and an ultrasonic acoustic signal with a Doppler shift, said signals being indicative of the intrusion; and 
         [0015]    determining whether said LF acoustic signal was detected before said ultrasonic acoustic signal with a Doppler shift; and 
         [0016]    determining whether said LF acoustic signal and said ultrasonic acoustic signal with a Doppler shift were detected within an assigned timeframe; and 
         [0017]    generating an alarm signal, if said LF acoustic signal was detected before said ultrasonic acoustic signal with a Doppler shift and said LF acoustic signal and said ultrasonic acoustic signal with a Doppler shift were detected within an assigned timeframe. 
         [0018]    In accordance with a third aspect of the present invention, there is provided a detection system, the detection system is characterized by: 
         [0019]    an ultrasonic transmitting unit arranged to generate and to transmit an ultrasonic acoustic signal into a confined space; and 
         [0020]    an ultrasonic receiving unit arranged to receive and to detect an ultrasonic acoustic signal having a Doppler shift and to generate an electrical signal indicative of said Doppler shift; and a LF unit arranged to detect a LF acoustic signal and to generate an electrical signal indicative of said LF acoustic signal; and 
         [0021]    a processing unit arranged to receive from said ultrasonic receiving unit an electrical signal indicative of the acoustic signal with a Doppler shift and from said LF unit an electrical signal indicative of the LF acoustic signal, said processing unit is configured to generate an alarm signal if said electrical signal indicative of the LF acoustic signal and said electrical signal indicative of the acoustic signal with a Doppler shift were received within an assigned time frame. 
         [0022]    In accordance with a fourth aspect of the present invention, there is provided a detection system, the detection system is characterized by: 
         [0023]    an ultrasonic transmitting unit arranged to generate and to transmit an ultrasonic acoustic signal into a confined space; and 
         [0024]    an ultrasonic receiving unit arranged to receive and to detect an ultrasonic acoustic signal with a Doppler shift and to generate an electrical signal indicative of said Doppler shift; and 
         [0025]    a LF unit arranged to detect a LF acoustic signal and to generate an electrical signal indicative of said LF acoustic signal; and 
         [0026]    a processing unit arranged to receive from said ultrasonic receiving unit an electrical signal indicative of the acoustic signal with a Doppler shift and from said LF unit an electrical signal indicative of the LF acoustic signal, said processing unit is configured to generate an alarm signal if said electrical signal indicative of the LF acoustic signal was received before said electrical signal indicative of the acoustic signal with a Doppler shift and said electrical signal indicative of the LF acoustic signal and said electrical signal indicative of the acoustic signal with a Doppler shift were received within an assigned timeframe 
         [0027]    Further aspects and advantageous features of the present invention are as described in the appended claims. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0028]    Exemplary embodiments of the present invention will now be described, by way of example only, with reference to the accompanying drawings, in which: 
           [0029]      FIG. 1  illustrates a block diagram of a motion detection system in accordance with the preferred embodiment of the present invention; 
           [0030]      FIG. 2  illustrates a flowchart of a motion detection operation in accordance with the preferred embodiment of the present invention; 
           [0031]      FIG. 3  illustrates a flowchart of the motion detection operation in accordance with another preferred embodiment of the present invention. 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       [0032]      FIG. 1  illustrates a functional block diagram of a detection system  100 , in accordance with a preferred embodiment of the present invention. The system  100  comprises an ultrasonic transmitting unit  20  which transmits an ultrasonic acoustic signal into the confined space that is to be monitored by the detection system  100 , this space being known as the protected space. The ultrasonic transmitting unit  20  of the preferred embodiment of the present invention comprises a frequency generator  23  (which may be a quartz generator) that provides an ultrasonic signal, preferably of 40 kHz, for an ultrasonic acoustic transmitter  21 , the signal first being amplified by an amplifier  22 . 
         [0033]    The ultrasonic acoustic signal is reflected by objects within the protected space and its frequency is shifted by objects within the space that are in motion, i.e. intruders (Doppler shift). An ultrasonic receiving unit  10  detects any reflected and frequency shifted ultrasonic acoustic signals and generates an electrical signal which is indicative of the Doppler shift of these signals. The ultrasonic receiving unit  10  of the preferred embodiment of the present invention comprises an ultrasonic acoustic receiver  11  that receives a reflected and frequency shifted ultrasonic acoustic signal. The output of said receiver  11  is then further amplified by a selective amplifier  12 . The amplified signal is then inputted into a phase detector  13 , that also receives an input from the frequency generator  23 . The subtracted signal from the phase detector  13  is further filtered by a low pass filter  14 , preferably with a cut-off frequency of 1 kHz. The filtered signal is actually a signal having the Doppler Effect frequency. This signal is then amplified by a low frequency amplifier  15  and digitized by means of an AID converter  16  prior to being further processed by a processing unit  40 . 
         [0034]    The system  100  also comprises a low frequency (LF) unit  30  which detects low frequency acoustic signals generated by intruders, for example low frequency acoustic signals generated by breaking a window or a wall, and generates an electrical signal that is further processed by the processing unit  40 . The LF unit  30  of the preferred embodiment of the present invention comprises a low frequency acoustic microphone  31  that receives low frequency acoustic signals, indicative of an intrusion into the protected space. The output of said LF microphone  31  is then amplified by an amplifier  32  and further filtered by a low pass filter  33 , preferably having a cut-off frequency of 100 Hz. This signal is then amplified by a low frequency amplifier  34  and digitized by means of an A/D converter  35  prior to being further processed by the processing unit  40 . 
         [0035]    The processing unit  40  comprises a programmable microcontroller  41  which is connected to the A/D converter  16  of said ultrasonic receiving unit  10  and to the A/D converter  35  of said LF unit  30 . Said processing unit  40  receives input signals from the ultrasonic receiving unit  10  and from the low frequency unit  30 . The microcontroller  41  is configured according to the preferred embodiment of the present invention to determine whether said input signals were detected within an assigned time period and to generate an alarm signal  42 , only if both of said received input signals were received within an assigned time period, wherein said time period is preferably less than 2 seconds, and more preferably is less than 1 second, and even more preferably is less than 0.5 second. 
         [0036]    According to another preferred embodiment of the present invention, the microcontroller  41  is configured to determine if an input signal from the low frequency unit  30  was received before an input signal from the ultrasonic receiving unit  10  and to determine if both of said received input signals were detected within an assigned time period, and to generate the alarm signal  42  only if the input signal from said low frequency unit  30  was received before the input signal from said ultrasonic receiving unit  10  and both of said received input signals were detected within an assigned time period, wherein said time period is preferably less than 2 seconds, and more preferably is less than 1 second, and even more preferably is less than 0.5 second. 
         [0037]    Referring now to  FIG. 2 , a flowchart  200  illustrates intrusion detection in accordance with the preferred embodiment of the present invention. The flowchart  200  commences with a protected space being monitored for an intrusion of foreign objects, as shown in step  201 . In the case of the intrusion, a LF acoustic signal and a Doppler signal (i.e. an ultrasonic acoustic signal with a Doppler shift) are generated (step  202 ) and if both of them are detected within an assigned timeframe (step  203 ), the alarm is generated (step  204 ). 
         [0038]    Referring now to  FIG. 3 , a flowchart  300  illustrates intrusion detection in accordance with another preferred embodiment of the present invention. The flowchart  300  commences with a protected space being monitored for an intrusion of foreign objects, as shown in step  301 . In the case of the intrusion, a LF acoustic signal and a Doppler signal are generated (step  302 ) and if the LF signal is detected before the Doppler signal (step  303 ) and also if the LF and the Doppler signals are detected within an assigned timeframe (step  304 ), the alarm is generated (step  305 ). 
         [0039]    Having thus described the present invention by reference to certain of its preferred embodiments, it is noted that the embodiments disclosed are illustrative rather than limiting in nature and that a wide range of variations, modifications, changes, and substitutions are contemplated in the foregoing disclosure and, in some instances, some features of the present invention may be employed without a corresponding use of the other features. Accordingly, it is appropriate that the appended claims be construed broadly and in a manner consistent with the scope of the invention.