"METHOD AND DEVICE FOR DETECTION OF INTRUSIONS IN CLOSED VOLUMES, IN PARTICULAR FOR PASSENGER COMPARTMENTS OF VEHICLES"

D e s c r i p t i o n

The present invention relates to a device for detecting intrusions in closed volumes, in particular for passenger compartments of vehicles.

The present invention also relates to a method of carrying out said detection.

It is known that different systems for detecting intrusions in the passenger compartments of vehicles, in particular motor-vehicles, are presently available on the market.

These systems generally contemplate radiation emissions to a predetermined freguency (e.g. in the microwave range) and subsequent detection of the radiation reflected by the elements constituting the volume or space to be monitored.

In more detail, in order to detect the presence and movement of objects or persons in the driver and passenger compartment of a vehicle, a series of microwave pulses is generated (every lOμs, for example) and the phase of the corresponding received pulses is then determined.

If the phase relating to the received pulses is constant, it means that the surface on which the generated pulses strike and from which they are reflected is substantially stationary and therefore no

danger situation is occurring.

If on the contrary the step relating to the received pulses varies in time, then something is likely to be moving on board the vehicle and an intrusion could be in progress.

The phase of the reflected pulses is determined by sampling these pulses at precise time instants, within windows having a time amplitude greatly smaller than the time duration of the pulses themselves; for instance, if a pulse has a duration of some nanoseconds, the sampling window can be of some tens of picoseconds.

In more detail, the sampling window is activated with some delay (of a few nanoseconds, for example) relative to the instant . at which each microwave pulse is generated, to sample the signal reflected by the object to a well-defined certain distance.

It is to be noted that in order to enable detection of objects that are to a smaller distance relative to that defined by the delay time of the sampler with respect to the pulse generator, the microwave pulse is required to have a duration at least as long as the delay time of the sampler.

However, in case of a longer duration the sampler, due to the non-ideality of the insulation between the transmitting section and receiving .section of the circuit, will also detect part of the "direct" signal (i.e. of the generated pulse) coming from the microwave oscillator.

In addition, still in the hypothesis of a duration of the microwave pulse longer than the sampler delay, it may happen that this pulse be mixed, in the sampler circuit, with the reflected pulse, thus creating a further Doppler signal due to reflection of moving objects to a greater distance than that defined by the delay imposed to the sampler, therefore altering correct' operation of the system.

Given some fixed duration of^ the microwave pulse, it is substantially impossible to go below a certain value with the minimum detection distance.

If on the contrary the microwave pulse duration is reduced while being however maintained fixed, a system is obtained that is not able to detect the presence of movement in the objects that are to smaller distances than that imposed by the sampler delay.

Therefore, the devices of known type are able to operate in a correct manner only in volumes of predetermined sizes and, even if attempts are made to adapt the operation parameters to the external operating conditions, it is impossible to obtain reliable detections of moving objects or intrusions.

Accordingly, the present invention aims at providing a device and a method for detection of intrusions in closed volumes, in particular for passenger compartments of vehicles, that can be easily made suitable for situations that are different from each other.

In particular, it is an aim of the present invention to provide a device and a method that can be easily made

suitable for correct operation with reference to detection areas having different sizes.

Another aim of the invention is to provide a device and a method enabling the detection distance to be varied and avoiding false alarms due to a poor insulation between the transmitting section and receiving section, while at the same time maintaining covering of the regions located to smaller distances.

It is an auxiliary aim of the invention to make available a device and a method that are precise and reliable, and adapted to correctly detect intrusions into areas of predetermined sizes.

The foregoing and further aims are substantially achieved by a device and a method for detection of intrusions in closed volumes, in particular for passenger compartments of vehicles, in accordance with the features recited in the appended claims.

Further features and advantages will become more apparent from the detailed description of a preferred embodiment of a device and a method according to the invention, given by way of non-limiting example. This description is taken with reference to the accompanying drawings, which too have purposes of illustration but not of limitation, in which:

- Fig. 1 shows a block diagram of a device in accordance with the invention;

- Fig. 2 shows time diagrams of signals used by the device seen in Fig. 1. ^' -

With reference to Fig. 1, a device in accordance with the invention and through which the method of the

invention is put into practice, has been generally identified with reference numeral 1.

Device 1 applies to detection of intrusions in closed volumes or spaces and in particular for passenger compartments of vehicles, such as cars and motor- vehicles in general.

Device 1 (Fig. 1) first of all comprises a pulse generator 100, to generate a plurality of main pulses 10, 11.

Preferably, the main pulses 10, 11 are microwave pulses, each being defined by few sine cycles of a frequency included between 1 GHz and 10 GHz, and equal to 6 GHz (diagram 2b in Fig. 2), for example.

The time duration of the main pulses 10, 11 is in the order of nanoseconds; how this duration is defined will be described in detail in the following.

The pulse generator 100 may comprise a low-frequency oscillator 110, preferably of a frequency included between 10 KHz and 1000 KHz, and equal to 100 KHz for example, and a microwave oscillator 120 operating at the above specified frequency for the main pulses 10, 11.

At a first leading edge 110b of the wave 110a generated by the low-frequency oscillator 110 (diagram 2a in Fig. 2), the microwave oscillator 120 is activated for generation of a first main pulse 10.

At a second leading edge 110c of the wave 110a generated by the low-frequency oscillator 110, the

microwave oscillator 120 is activated for generation of a second main pulse 11. Preferably the main pulses 10, 11 have the same time duration. Preferably the main pulses 10, 11' have the same starting phase.

As explained in more detail in the following, operation of device 1 may also need thousands of main pulses; however, in the- present specification and in the drawings, for the sake of exposition simplicity, reference is made to two main pulses 10, 11 alone.

In the preferred embodiment, a band-pass filter 125 is connected downstream of the microwave oscillator 120; this band-pass filter 125 has a passband of an amplitude included between 100 MHz and 800 MHz, and in particular equal to 500 MHz.

Preferably the passband of the band-pass filter 125 is centred on the frequency of the first main pulse 10.

An antenna 126 is connected downstream of the band-pass filter 125 for propagation of pulses generated by generator 100.

Propagation of the main pulses 10, 11 is caused in the closed volume to be monitored; depending, on the interaction between the main pulses 10, 11 and this closed volume it is possible to establish whether there are moving objects or not and therefore to detect possible intrusions.

In fact, device 1 also comprises a detector 130 for detecting auxiliary pulses 20, 21 (diagram 2d in Fig.

2) obtained by an interaction between the main pulses 10, 11 and at least one surface or object 2 present in

the volume under examination. In other words, the main pulses 10, 11 strike on an object or surface 2 present in the driver and passenger compartment of the vehicle in which device 1 is installed; under regular non- intrusion conditions, this surface 2 can be any wall of the driver and passenger compartment itself.

The auxiliary pulses 20, 21 obtained following a reflection phenomenon for example, are received by receiver 130 with some delay with respect to generation of the respective main pulses 10, 11; this delay is a function of the distance between device 1 and surface 2 on which the first main pulse 10 strikes.

If this surface 2 remains stationary, the delay between generation of the main pulses 10, 11 and reception of the respective auxiliary pulses 20, 21 keeps constant in time .

Vice versa, if the surface 2 on which the main pulses 10, 11 strike varies its position in time, then the delay between generation and reception will change in time.

Preferably, the receiver is provided with a sample-and- hold circuit 131 that is activated with some delay relative to generation of each main pulse 10, 11 so as to intercept the respective auxiliary pulse 20, 21.

The sampling window of the sample-and-hold circuit 131 can have a time duration included between 10 ps and 100 ps, equal to 50 ps for example (diagram 2c in Fig. 2) .

In the preferred embodiment, the receiver 130 further comprises one or more of the following elements:

- a first band-pass filter 132, interposed between an antenna 133 and the sample-and-hold circuit 131 and having a passband of an amplitude included between 100 MHz and 800 MHz, and preferably equal to 500 MHz; - a second band-pass filter 134 connected downstream of said sample-and-hold circuit 131 and having a passband of an amplitude included between 2 Hz and 200 Hz, and preferably between 5 Hz and 50 Hz;

- an amplifier 135 connected downstream of said second band-pass filter 134.

Device 1 further comprises a comparison module 140 to compare values of a parameter characteristic of said auxiliary pulses 20, 21 with each other. Depending on this comparison, the comparison module generates a notification signal 30.

Preferably, said notification signal 30 is an alarm signal and is generated to inform the vehicle's proprietor and/or a person in charge of the security that an intrusion within the vehicle has been detected.

The comparison module 140 can be incorporated into a microcontroller 140a designed for operation control of device l/

Preferably the characteristic parameter taken into account can be the phase variation ^s' of the auxiliary pulses 20, 21, as better clarified in the following; the values of the characteristic parameter considered are therefore the phases of the auxiliary pulses 20, 21 evaluated at the sampling instants.

The possible phase variation of the different auxiliary pulses 20, 21 is representative of the variation of the

delay with, which said pulses are received by receiver 130; if the auxiliary pulses are always received with the same delay relative to the generation instant of the respective main pulses (i.e. if the auxiliary pulses all have the same phase at the sampling instants) , then surface 2 is substantially stationary.

If, on the contrary, the delay with which the auxiliary pulses are received varies in time (i.e. if phase variations between the different auxiliary pulses received occurs), then surface 2 is moving.

Practically, the sample-and-hold circuit 131 of receiver 130 detects, at the frequency dictated by the low-frequency oscillator 110, the amplitudes of the auxiliary pulses that are received in succession, at the sampling instants.

Integration of these amplitudes preferably represented by respective voltages supplies a substantially sine wave (at the so-called "Doppler frequency"), should surface 2 be in movement.

The sampling period of receiver 130 is equal to the generation period of the main pulses defined by the frequency of the low-frequency oscillator 110.

Practically, in order to be able to detect a movement of surface 2 between 0.15 m/s and 1.5 m/s, it will be necessary to observe a high number of pulses; in particular an observation over a time interval of at least 200ms corresponding to 20,000 puTses is required.

Advantageously, device 1 further comprises an adjustment module 150 to adjust the time duration of

the main pulses 10, 11.

This is represented in Fig. 1 by the fact that a first output of the low-frequency oscillator 110 is directly connected to a first input of the microwave oscillator 120 for activation of the latter, while a second output of the low-frequency oscillator 110 is connected to a second input of the microwave oscillator 120 through the adjustment module 150, to deactivate the microwave oscillator 120 after the interval dictated by the adjustment module 150, thus defining the time duration of the main pulses.

In more detail, the adjustment module 150 adjusts the time duration of the main pulses 10, 11 as a function of a maximum detection distance of device 1.

Practically, the adjustment module 150 can be provided with a delay network RC in which resistor R and/or capacitor C are varying to determine the desired delay.

In one embodiment, the adjustment module 150 may comprise a digital potentiometer or a digital capacitor .

Device 1 further comprises a processing unit 170 operatively active on the adjustment module 150 to vary the delay that the latter introduces between the beginning and end of each main pulse 10, 11, i.e. to adjust the time duration of these pulses.

In more detail, the processing unit is designed to send a control signal 40 to the adjustment module 150 to set the desired duration for the main pulses.

The control signal 40 is representative of the maximum detection distance required for device 1; through a pre-stored table or a suitable conversion algorithm, from the maximum detection distance it is obtained the corresponding time duration for the main pulses.

By way of example, it is possible to consider that for each 25 cm variation of the maximum detection distance of device 1, the main pulse duration is varied by about 1 ns.

Depending on the features of the single embodiment, conversion from detection distance to time duration of the pulses can be carried out by the processing unit 170 or the adjustment module 150.

Preferably, the processing unit 170 is provided to receive a setting signal introduced by a user which is an indication of the desired detection distance.

Due to the above described structure, the adjustment module 150 is suitably set by virtue of this distance.

Advantageously, the processing unit 170 is incorporated into microcontroller 140a.

It will be appreciated that the processing unit 170 and comparison module 140 have been illustrated separately only for the purpose of better clarifying the functional characters of device 1; clearly these elements must' not necessarily be distinct from a hardware point of view, but can be formed of a single processor that is suitably programmed to perform both functions .

Receiver 130 and in particular the sample-and-hold circuit 131 present therein, is activated with a fixed delay δt relative to the transmission end of each main pulse 10, 11. This delay is introduced by the delay module 160 operatively interposed between an output of the adjustment module 150 and an input of the sample- and-hold circuit 131.

Therefore, on varying of the time duration of the main pulses 10, 11 also the activation instant of receiver

130 is varied. Therefore, on increasing of the time duration of the main pulses 10, 11, the maximum detection distance of device 1 increases in a corresponding manner and, on decreasing of the duration of the main pulses 10, 11 there is a corresponding decrease of the maximum detection distance of device 1.

This occurs because, as specified above, the activation delay of receiver 130 varies on varying of the duration of the main pulses 10, 11, and the activation instant of receiver 130 directly defines the maximum detection distance of device 1.

As above stated, the first and second main pulses 10, 11 preferably have the same time duration.

Practically, the generation frequency of the main pulses 10, 11 is defined by said low-frequency oscillator 100.

The same frequency is preferably used for activation of receiver 130, however with introduction of a delay between the beginning of generation of each main pulse 10, 11 and each activation of receiver 130, equal to the sum of the duration of each (adjustable) main pulse and said fixed delay δt.

This fixed delay δt is in particular introduced to avoid the possibility that a tail of the main pulse 10, 11 be detected, i.e. sampled, by receiver 130.

The fixed delay is further useful to avoid mixing of tails of the main pulse 10, 11, due to poor insulation, with the echo signal received and creation of a spurious beat signal at the sampler output.

This type of operation is represented in Fig. 1 by the fact that the adjustment module 150 (varying delay) and delay module 160 are connected in cascade between the low-frequency oscillator 110 and receiver 130 (sample- and-hold circuit 131) .

Practically, the possibility of varying the duration of the main pulses allows the maximum detection distance to be varied, while the fixed delay δt between the end of each main pulse and the subsequent activation of receiver 130 prevents part of the main pulse (or a tail of same) from being sampled by the receiver, and avoids a spurious beat signal being created at the sampler output .

The invention achieves important advantages.

First of all, the device and method of the invention can be easily made suitable for situations that are different from each other.

In particular, the device and method can be easily made suitable for correct operation with reference to detection areas having different sizes.

In addition, the device and method of the invention

allow the detection distance to be varied while avoiding false alarms due to a poor insulation between the transmitting section and receiving section, and at the same time maintaining covering of the regions located to a smaller distance.

It will be also recognised that the device and method of the invention are precise and reliable and adapted to correctly detect intrusions within areas of predetermined sizes.