GB2348004A - Ultrasonic intrusion detection - Google Patents

Abstract

Intrusion detection apparatus for detecting an intrusion within a space, comprising: transmitter apparatus 20 for transmitting into the space a first acoustic signal at a first frequency and a second acoustic signal at a second frequency; receiver apparatus 22 for receiving and demodulating a first reflected acoustic signal produced by reflection of the first acoustic signal within the space and a second reflected acoustic signal produced by reflection of the second acoustic signal within the space to generate a first in-phase data component and a first quadrature data component for the first received signal and a second in-phase data component and a second quadrature data component for the second received signal; processing apparatus 32 for receiving the first in-phase and first quadrature data components and generating a first deviation value in dependence thereon, receiving the second in-phase and second quadrature data components and generating a second deviation value in dependence thereon, and comparing the first deviation value and the second deviation value and generating an intrusion signal in dependence on that comparison.

Description

INTRUSION DETECTION The present invention relates to an intrusion detection apparatus for detecting an intrusion within a space, such as that defined by a vehicle.

It is known in the prior art to provide an intrusion detection system for use within a vehicle, which is activated each time the vehicle is locked. One known system comprises a transmitter and a receiver. Upon activation, the transmitter transmits an acoustic signal at a single frequency, which is reflected off many different surfaces within the vehicle interior. The reflected signal is received by the receiver. Since the surfaces are situated at different distances from the transmitter and the receiver, the path length from the transmitter to a surface and back to the receiver will be different for each surface. This means that the phase of the original signal will be altered differently by each surface. The receiver calculates the total phase change caused by all the reflections. This can be considered to be a steady phase change which occurs when no intruder is present.

This steady signal is sent to an IQ demodulator. This is a unit which acquires the steady signal to produce an in-phase component and a quadrature component, as known by those skilled in the art. These components are then passed onto a microprocessor, which periodically acquires them.

If there is an intruder within the vehicle, the total phase change calculated by the receiver will be different, due to the transmitted signal being modified differently in certain areas of the vehicle. This means that the in-phase and quadrature components and therefore the signal acquired by the microprocessor are different. Circuitry within the microprocessor monitors this phase change, and if there is seen a certain total phase change with several acquisitions, which represents a certain distance of movement of the intruder, an alarm will be triggered.

The disadvantage of the system is that disturbances other than an intruder can result in a sufficient total phase change to trigger an alarm. An example is low frequency sound waves which might be caused by an exterior disturbance. False triggering of a vehicle alarm is extremely undesirable.

Such a system may be made less sensitive in order that it will ignore any signals presumed to have been caused by anything other than real movement of the object and thus reduce the chance of false alarms. However, there is thus a compromise between sufficient sensitivity to detect the movement and sufficient desensitivity to ignore an interfering signal. Such a compromise is unsatisfactory.

It would be desirable to provide an intrusion detection system which is sensitive to intrusion but which avoids false triggering of an alarm by non-intrusion disturbances.

According to one aspect of the present invention there is provided intrusion detection apparatus for detecting an intrusion within a space, comprising: transmitter apparatus for transmitting into the space a first acoustic signal at a first frequency and a second acoustic signal at a second frequency; receiver apparatus for receiving and demodulating a first reflected acoustic signal produced by reflection of the first acoustic signal within the space and a second reflected acoustic signal produced by reflection of the second acoustic signal within the space to generate a first in-phase data component and a first quadrature data component for the first received signal and a second in-phase data component and a second quadrature data component for the second received signal; processing apparatus for receiving the first in-phase and first quadrature data components and generating a first deviation value in dependence thereon, receiving the second in-phase and second quadrature data components and generating a second deviation value in dependence thereon, and comparing the first deviation value and the second deviation value and generating an intrusion signal in dependence on that comparison.

Preferred features of the invention are set out in the accompanying claims and in the following description.

An embodiment of the present invention will now be described by way of example with reference to the accompanying drawings in which: Figure 1 is a simplified block diagram of an intrusion detection apparatus according to an embodiment of the present invention.

Figure 2 is a block diagram of a software algorithm used in the microprocessor of figure 1 ; and Figure 3 illustrates the vector-based operation of the detector sub-system.

The intrusion detection apparatus of the described embodiment is intended for use within a vehicle, and is most suitable for use within the passenger compartment of a vehicle.

However, it could be used to protect other spaces such as the bonnet area of a vehicle, the boot area of a vehicle or rooms of a building such as a house.

The apparatus is activated each time the vehicle is locked in a manner known to those skilled in the art. This can be done, for example, by a radio transmitter key access device or by a conventional mechanical switch or key. Whilst activated the apparatus monitors the space in order to detect intrusion into the space. If an intrusion is detected that satisfies certain criteria intended to avoid false alarms then the apparatus triggers an alarm such as a siren attached to the vehicle. The apparatus can be deactivated by the key in order to allow the owner access to the vehicle.

The general principle used by the apparatus for detecting an intrusion is the transmission of acoustic signals into the space and the monitoring of the resultant signals as they are reflected within the space. A change in the resultant signals that satisfies certain anti-false-alarm criteria is taken to indicate an intrusion. The acoustic signals are transmitted at at least two frequencies, and the resultant signals of both these transmissions are monitored. This allows considerable accuracy in detecting intrusions. One of the frequencies may be a harmonic frequency of another of the frequencies. One or more of the frequencies may be an ultrasonic frequency, although other frequencies may be used.

When the apparatus is activated it first enters a set-up mode in which it analyses the response of the space under normal conditions. This basic response is used for comparison with subsequent measurements in order to detect intrusions. The set-up mode is important for increasing the accuracy of the system by allowing it to adapt each time it is actuated to the interior layout of the vehicle, which is likely to change each time it is left due to, for example the seats being put in different positions or different objects being left in the vehicle.

However, the set-up mode is not essential-instead a standard response could be stored. After the set-up procedure has been completed the apparatus enters its normal monitoring mode until an intrusion is detected (in which case it triggers an alarm and then returns to the monitoring mode) or it is deactivated by the user. The following describes the apparatus following an activation.

Referring to figure 1, the intrusion detection apparatus for detecting an intrusion within a vehicle provides a first signal generator 2 for generating a signal 1 at a first frequency, fl, which could for example be 70kHz. The signal 1 is generated in the form of a square wave.

This signal 1 is fed to two different locations. The first location is a first divide by two unit 4, which halves the frequency of the signal, so it becomes a square wave signal 3 of frequency f3, where f3 = (f} 12) and is, for example, 35kHz. Generating the signal 3 by division in this way means that a signal at f, is readily available for clocking the sampling of a reflected signal at the f3 frequency, as described below. The sampling is performed by a first IQ demodulator 26, the function of which will be described below, which is clocked by the signal 1 The f3 frequency signal 3 produced by the first divide by two unit 4 is then also sent to two locations. The first location is a first RC filter 6, which converts it into a sawtooth signal 5 of frequency f3. The second location is the first IQ demodulator 26 which will use the signal as described below.

This sawtooth signal 5 produced by first RC filter 6 is sent to a first sawtooth to sinewave converter 8, which smoothes the signal into a sinewave signal 7 of frequency f3. This signal 7 provides a first input to adder/amplifier 18.

A second input to adder/amplifier 18 is produced in the same way by similar components to those described above. There is provided a second signal generator 10 which generates a signal 9 at a second frequency f2, which could, for example, be 92kHz. The signal 9 is also generated in the form of a square wave.

This signal 9 is fed to two different locations. The first location is a second divide by two unit 12, which halves the frequency of the signal, so it becomes a square wave signal 11 of frequency ft, where f4 = (f2/2) and is, for example 46kHz. This is so that a reflected signal can be sampled at 2, as described below. The second location is a second IQ demodulator 30, the function of which will be described below, the purpose of the signal being to provide a clock pulse.

This f4 frequency signal 11 produced by the second divide by two unit 12 is then also sent to two locations. The first location is a second RC filter 14, which converts it into a sawtooth signal 13 of frequency f4. The second location is the second IQ demodulator 30 which will use the signal as described below.

This sawtooth signal 13 produced by second RC filter 14 is sent to a second sawtooth to sinewave converter 16, which smoothes the signal into a sinewave signal 15 of frequency f4.

This signal 15 provides the second input to adder 18.

Adder/amplifier 18 adds signals 7 and 15 to produce a resultant dual frequency sinewave signal. There is provided an amplifier within adder/amplifier 18 which amplifies the resultant signal to produce output signal 17. This signal 17 is passed on to ultrasonic transmitter 20, which transmits it in the form of an acoustic signal into the vehicle interior. It would alternatively be possible to transmit two separate signals each from its own transmitter. The transmitter 20 and receiver 22 are located at a suitable location within the vehicle interior such that the signal is transmitted over as much area as possible of the vehicle interior. One suitable location is on the roof.

The dual frequency signal is radiated broadly from the transmitter so that it reaches many different surfaces within the vehicle interior. The signal is reflected from and between these surfaces and is eventually received by a receiver 22. The receiver 22 could be located close to the transmitter 20, for easy installation, provided the receiver was not swamped by signals received directly from the transmitter without reflection from the vehicle's interior. The reflection from the surfaces modifies the resultant signals in phase and amplitude of each component (f3 and f4) of the dual frequency signal, each surface and each reflection causing a different modification. The resultant signals therefore depend on the path length from the transmitter to the surface (s) and back to the receiver and the nature of the surfaces. The total signal which is received by the receiver 22 is the sum of all the different reflected signals from the different surfaces. Each component, that is original sinewave signals 7,15, can be said to have been modulated by their passage through the vehicle from the transmitter (s) to the receiver (s).

If there is an intrusion into the vehicle then it will be expected to affect the basic response of the space by altering the pattern of reflections. Thus, there is likely to be a change in the received signals. The received signals may also change due to false-alarm factors such as small deflections in the vehicle's windows due to shock waves from passing vehicles, or sources of high frequency acoustic interference outside the vehicle. The received signals are therefore analysed with the aim of determining whether a change from the basic state has occurred, and if so whether that change is likely to represent an intrusion that requires an alarm to be set off.

From the received dual-frequency signal having modulated components, the receiver 22 generates a corresponding data signal 23. This signal 23 is fed into a first filter and a second filter. The first filter is a f3 bandpass filter which filters out all components outside a window (e. g. of around 10kHz) around frequency f3, thus producing a data signal 25 from the modulated f3 signal 7. The second filter is a frequency f4 bandpass filter which filters out all components outside a window (e. g. of around 10kHz), thus producing a data signal 27 from the modulated f4 frequency signal 15. The signals 25,27 can be amplified if necessary.

In the f3 channel data signal 25 is fed into first IQ demodulator 26, where it is sampled at fl in accordance with clock signal 1. Since f3 square wave signal 3 is also fed into first IQ demodulator 26, it is possible to obtain purely the modulation of the original f3 signal by means of transformation of signal 3 with signal 25. This calculated signal is then demodulated to produce a first in-phase component I, and a first quadrature component Ql.

These components Il and Q, can be considered as real and imaginary parts of the modulation of signal 25 respectively. They represent a first steady vector for the vehicle interior, which means they represent the phase modulation of the first transmitted sinewave signal 7 when no intrusion is present within the vehicle interior. They are sent from the first IQ demodulator 26 to the microprocessor 32.

Similarly, in the 44kHz channel data signal 27 is fed into second IQ demodulator 30, where it is sampled at f2 in accordance with clock signal 9. Since f4 square wave signal 11 is also fed into second IQ demodulator 30, it is possible to obtain purely the modulation of the original f4 signal by transformation of signal 11 with signal 27. This calculated signal is then demodulated to produce a second in-phase component 12 and a second quadrature component Q2. These components 12 and Q2 can be considered as real and imaginary parts of the modulation of signal 27 respectively. They represent a second steady vector for the vehicle interior, which means they represent the phase modulation of the second transmitted sinewave signal 15 when no intrusion is present within the vehicle interior. They are also sent from the second IQ demodulator 30 to the microprocessor 32.

If the vehicle interior is altered in any way, such as by an intruder or a false-alarm factor, the first and second steady vectors will have extra perturbation components. This effect can be seen diagrammatically in figure 3, in which a steady vector is indicated S and several perturbation vectors are indicated as P. The function of such perturbation vectors in determining the presence of an intruder will now be described in more detail with reference to the operation of the microprocessor 32.

Turning now to figure 2, it can be seen that signal I, is periodically acquired by a first acquisition unit 34 and signal Q, is periodically acquired by a second acquisition unit 36.

Considering a first acquisition of the signals, a first acquired in-phase signal and a first acquired quadrature signal is sent to a first angle resolver 38. Angle resolver 38 contains a memory which stores the first acquired in-phase signal and the first acquired quadrature signal. These signals represent the steady vector for the vehicle interior. This equivalent to steady state vector 80 in figure 3. These signals are stored during the set-up mode of the apparatus, during which the apparatus waits after activation for a steady state to be attained, or averages the received I, and Q, signals over an initial period, and then stores those I, and Q, signals in the angle resolver 38.

During the operation of the monitoring mode, a pairing of an in-phase signal 11 and a quadrature signal Q, is acquired periodically. These signals together represent a current vector for the vehicle interior. In the angle resolver 38 the memory is accessed to obtain the stored basic acquired in-phase signal and basic acquired quadrature signal. These are subtracted from the corresponding newly acquired signals to determine the deviation vector of the newly acquired signals from the steady state. This is equivalent to the perturbation vector 81 in figure 3. The angle resolver also determines the angular deviation in I-Q space of that deviation vector from the immediately previous deviation vector. A first comparator 40 calculates the angular (phase) difference between the deviation vector and the previous deviation vector. Then the previous deviation vector in the previous angle unit 42 is replaced by the current deviation vector for use in the next cycle.

This process is repeated at the next acquisition, so that a further acquired in-phase signal and a further acquired quadrature signal are stored in the memory, which represent a further vector for the vehicle interior. The memory is accessed to obtain the stored second acquired in-phase signal and second acquired quadrature signal. The comparator 40 calculates the phase difference between the second vector and the third vector.

In general, at each acquisition, the newly-acquired in-phase and quadrature signals represent a vector for the vehicle interior, and the phase difference between this vector and the previous vector (labelled previous angle 42 in figure 2) is calculated by comparator 40. This phase difference is labelled as angle delta 44.

Each time a phase difference is calculated, a counter is incremented by angle delta 44. This operation is labelled 46 in figure 2. The counter can be thought of as a first total angle 48. At the first acquisition it is set to zero, because this value represents the notional phase angle of the steady vector. At each subsequent acquisition, angle delta is added to the previous total angle 50. If there is no intrusion, signals I, and Q, will be the same at each acquisition, which means that the previous angle 42 will be equal to each newly-acquired phase angle. This in turn means that angle delta will be zero and the counter will not be incremented, and hence total angle 48 will remain at zero.

If however, there is an disturbance in the vehicle interior, the f3 component of the dualfrequency acoustic signal will be reflected differently in the area of the disturbance as a result of the disturbance, which means that the modulation caused by that area of the vehicle will be different from the modulation produced when there is no disturbance. This results in the total modulation of the f3 signal being different, so that signal 25 which enters first IQ demodulator 26, will have a different phase angle from the steady signal. This results in components Il and Q, being different, so that when an acquisition is made by the units 34,36, and the signal passed onto angle resolver 38, the phase angle will be different from previous angle 42, and hence angle delta 44 will not be zero. This means that total angle 48 will be incremented by angle delta 44.

The process is repeated at each subsequent acquisition, and each time, angle delta 44 will change and is added to total angle 48. If the disturbance is not a genuine intruder, for example if an object falling from the vehicle's parcel shelf causing an air disturbance, the changes in angle delta 44 are likely to oscillate in sign. In this case the value of total angle 48 will oscillate around zero. If however, the disturbance is caused by a genuine intruder, angle delta will be expected to increase progressively with the same sign as the intrusion moves into the vehicle. However, there are certain types of noise which will cause angle delta to increase as though there were a genuine disturbance, for example a low frequency noise originating from outside the vehicle. In some prior art systems, this would trigger a false alarm.

One advantage of this embodiment of the present invention, is that, as can be seen in figure 2, the same process of acquisition and calculation of angle delta is carried out for the second f4 component of the dual-frequency acoustic signal. For this purpose third and fourth acquisition units 52,54 are provided, which send acquired signals to second angle resolver 56, which contains a memory from which can be retrieved previous angle 60. There is further provided a second comparator 58, which calculates angle delta 62, and adds it to previous angle 68 to produce second total angle 66, this addition process being labelled as 64.

After each acquisition, first total angle 48 and second total angle 66 are supplied to a detection threshold unit 70. This unit decides whether to trigger an intruder alarm, subject to two criteria. The first criterion, which gives an advantage over the prior art, is that the first and second total angles must be related by a predetermined relationship. If a genuine intruder is present, the angle change of the reflected acoustic signal of the first component at f3 will be expected to be different from the angle change of the second reflected acoustic signal of the second component at f4, due to their different wavelengths. If however, a disturbance signal were present in the vehicle, such as a low frequency sound wave caused by a disturbance outside the vehicle, this would be expected to cause the same modulation to both acoustic components and hence, the deviation in angle delta 44,62 would be the same and the total angles 48,66 would be the same. Thus the first criterion may be that the first and second angles differ by greater than a certain threshold such as 1,2 or 3 revolutions.

The second criterion requires the possible intruder to move a certain distance, for example 10cm into the vehicle. This equates to a certain number of revolutions of each angle delta, and would therefore be checked by evaluating each value of total angle against a respective predetermined threshold value held within detection threshold unit 70. This is a second safeguard against a false alarm being triggered by small movements, such as those made by an insect.

If both criteria are satisfied-that is angles 48 and 66 are both greater than a respective threshold and differ by more than another threshold-then an intrusion signal, such as an alarm is triggered. The thresholds may be stored in a memory accessible to the detection threshold unit 70, which contains the apparatus to process its inputs and make the decision to trigger the alarm. The thresholds may be adjustable either by a user or a manufacturer to allow control over the sensitivity of the system. In addition the thresholds may be dynamically adjustable by the apparatus, by the increase of one or more of the thresholds to cope with especially problematic environments-for example next to a busy main road there could be frequent gusts from passing vehicles which might cause too many false alarms if the original settings were maintained.

There are provided two further safeguards against false triggering of an alarm. The first is that there is provided a"zero window"threshold on the values of Il, Q"I2 and Q2. Once the steady vector has been calculated, if further values of these components are below certain threshold values, the calculation of angle delta and subsequent computation is not performed.

This prevents a build-up of tiny disturbance data on the value of total angles 48,66. Again, these thresholds may be adjustable as described above.

The second safeguard is that if an increase in angle delta 44,62 is observed, a second increase must be observed within a certain number of acquisitions, otherwise total angle 48,66 will be reset to zero. This prevents the possibility of a number of non-intruder disturbances building up over time and eventually causing an alarm to be triggered. On way to achieve this is by regular decrementing of the magnitude of the total angle in each channel so that over time each one will return to zero.

The frequencies of the two channels preferably differ by more than 5kHz and more preferably by more than 10kHz. The present invention may include any feature or combination of features disclosed herein either implicitly or explicitly or any generalisation thereof irrespective of whether it relates to the presently claimed invention. In view of the foregoing description it will be evident to a person skilled in the art that various modifications may be made within the scope of the invention.

Claims (22)

1. Intrusion detection apparatus for detecting an intrusion within a space, comprising: transmitter apparatus for transmitting into the space a first acoustic signal at a first frequency and a second acoustic signal at a second frequency; receiver apparatus for receiving and demodulating a first reflected acoustic signal produced by reflection of the first acoustic signal within the space and a second reflected acoustic signal produced by reflection of the second acoustic signal within the space to generate a first in-phase data component and a first quadrature data component for the first received signal and a second in-phase data component and a second quadrature data component for the second received signal; processing apparatus for receiving the first in-phase and first quadrature data components and generating a first deviation value in dependence thereon, receiving the second in-phase and second quadrature data components and generating a second deviation value in dependence thereon, and comparing the first deviation value and the second deviation value and generating an intrusion signal in dependence on that comparison.

2. Intrusion detection apparatus according to claim 1, comprising a memory for storing: a first basic in-phase value representing a basic value of the first in-phase component; a first basic quadrature value representing a basic value of the first in-phase component; a second basic in-phase value representing a basic value of the second in-phase component; and a second basic quadrature value representing a basic value of the second quadrature component.

3. Intrusion detection apparatus according to claim 2, wherein in generating the first and second deviation values the processing apparatus is capable of : accessing the memory to determine the first and second basic in-phase and quadrature values; generating a first in-phase difference value representing the difference between the first in-phase data component and the first basic in-phase value; generating a first quadrature difference value representing the difference between the first quadrature data component and the first basic quadrature value; generating a second in-phase difference value representing the difference between the second in-phase data component and the second basic in-phase value; and generating a second quadrature difference value representing the difference between the second quadrature data component and the second basic quadrature value.

4. Intrusion detection apparatus according to claim 3, wherein the memory is capable of storing previous first and second deviation values, and in generating the first and second deviation values the processing apparatus is capable of : determining a first phase angle represented by the first in-phase and quadrature difference values, and generating the first deviation value by incrementing the stored previous first deviation value by the first phase angle; and determining a second phase angle represented by the second in-phase and quadrature difference values, and generating the second deviation value by incrementing the stored previous second deviation value by the second phase angle.

5. Intrusion detection apparatus according to claim 4, wherein the processor is capable of generating the intrusion signal if the first and second deviation values exceed first and second threshold values.

6. Intrusion detection apparatus according to claim 4 or 5, wherein the processor is capable of generating the intrusion signal if the first and second deviation values differ by less than a third threshold value.

7. Intrusion detection apparatus according to any of claims 4 to 6, wherein the processor generates the first deviation value only if the first in-phase and quadrature data signals are outside a predetermined window about the first in-phase and quadrature basic signals respectively; and the processor generates the second deviation value only if the second in phase and quadrature data signals are outside a predetermined window about the second inphase and quadrature basic signals respectively.

8. Intrusion detection apparatus according to any of claims 4 to 7, wherein the processor is capable of periodically decrementing the stored previous first and second deviation values.

9. An apparatus according to any preceding claim, wherein the transmitter apparatus comprises: a signal generator for generating a third signal at twice the first frequency and a fourth signal at twice the second frequency; a divider for dividing the frequencies of the third and fourth signals by two as a step to generating the first and second acoustic signals; and wherein the receiver is capable of receiving the third and fourth signals for use in demodulating the first and second signals respectively.

10. An apparatus according to any preceding claim, wherein the transmitter apparatus comprises a single acoustic transmitter for transmitting the first and second acoustic signals into the space.

11. An apparatus according to any preceding claim, wherein the space is defined by a vehicle.

12. An apparatus as claimed in claim 11 as dependant directly or indirectly on claim 2, wherein the first and second basic in-phase and quadrature components are determined and stored each time the vehicle is locked.

13. Intrusion detection apparatus substantially as herein described with reference to the accompanying drawings.

14. Apparatus for detecting or measuring motion through analysis of the reflection of two or more acoustic signals at different frequencies.

15. Apparatus according to claim 14 where two frequencies are used, simultaneously, sequentially, or alternatively to achieve the motion sensing.

16. Apparatus according to claim 14 or 15 where one or more of the frequencies used are ultrasonic.

17. Apparatus according to claims 14 to 16 where the area covered by the motion sensing is in the vicinity of, or inside the interior of, a vehicle.

18. Apparatus according to any previous claim where the motion detection is used to diagnose unlawful tampering with, or intrusion into, said vehicle.

19. Apparatus according to claims 14 to 16 where the motion sensing is used to detect the presence of a person or animal inside the vehicle.

20. Apparatus according to claims 14 to 16 where the motion sensing is used to diagnose dangerous objects moving in the vicinity of, or towards said vehicle.

21. Apparatus according to claims 14 to 16 where the motion sensing is used to measure, or react to, the relative motion of the vehicle itself with respect to other fixed or mobile objects in the vicinity of said vehicle.

22. Apparatus according to any previous claim where the motion detection is used to detect unlawful intrusion into a building.