WO2013037399A1

WO2013037399A1 - System and method for detecting a vital-related signal pattern

Info

Publication number: WO2013037399A1
Application number: PCT/EP2011/065790
Authority: WO
Inventors: José María GÓMEZ CAMA; Mireya FERNÁNDEZ CHIMENO; Alan MONTESI; Manuel Carmona Flores; Tomás CARRASCO CARRILLO; Cristian VILAR GIMÉNEZ
Original assignee: Ficomirrors, S.A.
Priority date: 2011-09-12
Filing date: 2011-09-12
Publication date: 2013-03-21

Abstract

System for detecting a vital-related signal pattern of a seated person (10) in a vehicle seat (11), the seat comprising a substantially horizontal base (16) and a substantially vertical backrest (15) having a front surface (12) accommodating the back of the seated person when in use, and a rear surface (19), the system further comprising: at least one Doppler radar (14) arranged behind the front surface of the backrest, in such a way that a main radiation lobe (18) of the emitter/receiver of the Doppler radar is focused towards the front surface of the backrest; and a module for detecting, based on a radar signal obtained by the Doppler radar, a signal pattern related to a vital of the seated person.

Description

System and method for detecting a vital-related signal pattern

The present invention relates to a system for detecting a vital-related signal pattern of a seated person in a vehicle seat. The invention also refers to a method for detecting a vital-related signal pattern of a seated person in a vehicle seat, and to a computer program suitable for carrying out such a method.

BACKGROUND ART

During recent years, security has become a main concern within the automotive industry. Since the early 80's, several passive solutions have been incorporated in vehicles to reduce the impact damage, such as fastening seatbelts, smooth cockpit devices or deformable inner-vehicle structures to avoid damage of passengers in case of collision.

Automotive passive security has evolved into an active security through electronic and digital systems development. These active solutions involve actions to minimize damages of passengers and to avoid collisions, like airbags, assisted breaking systems (ABS) or stability and traction control systems (ESP). These active solutions sense some automotive parameters, process them, and execute an action after collision happens, for example shooting the airbags, or selectively braking some the vehicle's tires to recover a correct trajectory.

The next automotive security objective is to sense mechanicals automotive parameters and combine them with biomedical driver information to minimize collision risk situations. This human state evaluation is a complex field that requires a subjective information processing and the sensing of biometric parameters in a non-invasive way, such as eye movements and blinking, hear rate (HR) or respiration rate (RR). This biomedical driver information needs to be acquired by using a no- invasive measurement instrumentation in order to aavoid disturbing the driver movements and to ease car usage. Regarding driver's bio-signals detection, and more specifically detection by means of radar-based devices, in all the known systems, the radar is typically arranged in front of the driver, since said position is commonly assumed to be the best one for obtaining clear radar signals in a vehicle environment. The main reason is the large displacement of the sternum due to respiratory activity, compared to the back movements.

For example, patent application US2005073424A1 discloses a system and related method for sensing information related to the position and/or movements of the body of a living being, or an inner part of the body. In particular, this patent application describes an embodiment in which the radar is arranged in the steering wheel, as graphically illustrated in Figure 7.

However, such an arrangement of the radar in a frontal position with respect the seated person (e.g. driver) has the drawback of the radar potentially suffering some interferences due to the movements such as the driver's arms, which may result in an unclear radar signal which difficults detecting vital signals in a reliable and efficient way.

SUMMARY OF THE INVENTION

Thus, a need still exists for new systems and related methods for detecting vital-related signal pattern of a seated person in a vehicle seat, to solve the above mentioned drawback. It is an object of the present invention to fulfill such a need.

Said object is achieved by means of a system according to claim 1 , and a method according to claim 12. According to one aspect of the invention a system for detecting a vital-related signal pattern of a seated person in a vehicle seat is provided, the seat comprising a substantially horizontal base and a substantially vertical backrest having a front surface accommodating the back of the seated person when in use, and a rear surface, the system further comprising:

- at least one Doppler radar arranged behind the front surface of the backrest, in such a way that a main radiation lobe of the emitter/receiver of the Doppler radar is focused towards the front surface of the backrest;

- a module for detecting, based on a radar signal obtained by the Doppler radar, a signal pattern related to a vital of the seated person. A vital-related signal of a person, being related to, for example, his heart rate or his respiration rate, is very difficult if not impossible to obtain by means of a Doppler radar being focused directly towards the back of the person. However, when the person is seated on a vehicle seat, the movement related to such vital signals is transmitted to the structure of the backrest of the seat, which has a cushion effect and allows assessing the movement of the body through the surface of the backrest. This way, by focusing a Doppler radar towards said backrest surface, a movement created by a vital of the person can be detected and a vital-related signal can be obtained. Furthermore, by focusing the lobe of the Doppler radar from behind of the vehicle seat, the radar being arranged behind the front surface of the backrest (for example, attached on the rear surface of the backrest, or arranged inside the backrest) noise sources such as the movement of the arms or other persons are avoided, obtaining a vital-related signal with a higher signal-to- noise ratio than a signal obtained by other systems.

By using the system of the present invention, it can be detected in which periods of time a correct or valid vital-related signal is being obtained by the Doppler radar. Thus, such valid vital-related signals may be used to further monitor the status of the driver of the vehicle (for example, a change in the physical status of the driver or a possible heart or respiratory failure can be monitored based on the detected vital-related signal pattern, which may not be normal for a person which is driving a vehicle).

According to another embodiment, the Doppler radar is arranged in such a way that the emitter/receiver of the radar and the surface of the backrest are arranged with a minimum distance between them of 1/4 of the wavelength used by the Doppler radar.

Normally, the emitter/receiver of the radar comprises an antenna which emitts and receives, thus making the emitter and receiver being arranged within the same plane, related to its corresponding emitted and received signals.

According to a further embodiment, the Doppler radar is arranged at a maximum distance of 1/5th of the shoulder breadth for the 5% thinnest women, corresponding to a distance between 0 and 4 cm with respect of a vertical axis of simmetry the backrest, based on the values defined in ISO/TR 7250-2:2010.

According to a further embodiment, the Doppler radar is arranged at a height between 5% of the women height and 95% of the men height, corresponding to 373 mm and 444 mm respectively, referenced to the surface of the seat base, based on the values defined in ISO/TR 7250-2:2010.

According to another embodiment, the system further comprises a mechanism for changing the height of the Doppler radar with respect to the surface of the base of the seat.

According to an embodiment, the Doppler radar is affixed to a support structure arranged in the backrest of the seat, the support structure having a rigidity such that allows a movement of the Doppler radar of less than 0.2mm, in the direction of the main radiation lobe with an acceleration below 3g. According to an embodiment, the system further comprises at least one first inertial sensor arranged with the Doppler radar, for obtaining a parameter related to the inertial movement of the radar; a module for verifying if the parameter obtained by the first sensor is greater than a predetermined threshold, and a module for, in case of positive result of said verification, identifying the detected signal pattern as a non-valid pattern.

The inertial sensor may be, for example, attached to the surface of the radar, or to a support structure of the radar, in such a way that it senses the movements of the radar relative to the vehicle seat. For example, in case that the radar is mounted on the rear surface of the backrest, whenever a movement of the backrest occurs because of the seated person moving it manually, the car movement and vibration during a normal car displacement on the road, or because of the vehicle stopping abruptly, the radar may also move accordingly.

Since the passanger chest is not completely fixed to the backrest of the seat, it may act as an inertial moving mass during car movements, which may cause movements of the backrest. Therefore, the system can detect said unusual movements and, depending on its strength, deeming the vital-related signal pattern unusable because of the noise added by such movement to the obtained Doppler signal. In the case of the backrest, because of the type of movement it may suffer, a gyroscope may be used as the inertial sensor, because of its higher accuracy in the type of motion of the backrest, although an accelerometer or other inertial sensor may also be suitable to be used.

According to a further embodiment, the system also comprises at least one second inertial sensor arranged in the base of the seat, for obtaining a parameter related to the inertial movement of the seat; a module for verifying if the parameter obtained by the second sensor is greater than a predetermined threshold, and a module for, in case of positive result of said verification, identifying the detected signal pattern as a non-valid pattern.

Similarly, the base of the seat may also suffer from movements which may affect the obtained radar signal, such as car movements made by bumps on the road, fast stops, etc. These movements may also add noise to the obtained signal and, in a similar way as in the case of the backrest, a verification of if such a movement deems the signal non-valid to detect a vital- related signal pattern may be performed. Because of the type of movements of the base, the second inertial sensor may preferably be an accelerometer, although a gyroscope or other type of inertial sensors may also be suitable. According to a second aspect of the invention, a method for detecting a vital- related signal pattern of a seated person in a vehicle seat is provided, the seat comprising a substantially vertical backrest and a substantially horizontal base, the method comprising: - obtaining a radar signal by means of a Doppler radar;

- calculating, based on the obtained radar signal, an in-phase signal and a quadrature signal;

- identifying at least one centre of at least one ellipse defined by the calculated in-phase and quadrature signal over a predetermined period of time.

- detecting, based on the obtained radar signal and the identified centre, the vital-related signal pattern of the seated person.

Firstly, a Doppler radar signal is emitted towards the back of the person seated in the vehicle seat, thus reflecting in it and being obtained by the Doppler radar. Afterwards, the in-phase l(t) signal and the quadrature Q(t) signal are extracted by any of the calculations widely known in the state of the art, which can be represented in an l/Q diagram. Then, when sufficient signal measurements have been obtained to form at least one ellipse or circle in the l/Q representation diagram of the obtained radar signal (over a certain period of time), a centre of said ellipse or circle is identified. Such an identification is preferably performed during the accommodation of the person in the seat (i.e., when he is first entering the vehicle and seated in the seat), since during a brief but enough period of time the person is moving in such a way that at least one clear ellipse is defined in the l/Q diagram of the received radar signal.

The position of the identified centre will depend on the position of the radar relative to the back of the person, and the radar components, and will typically not be centred in the representation of the l/Q diagram, and therefore a coordinate in the l/Q representation will be identified related to said centre.

Finally, the detection of the signal related to a vital of the person is performed by taking into account the identified centre and the obtained radar signal. Preferably, this step will be performed when the car is already moving. According to a specific embodiment, identifying at least one centre of at least one ellipse comprises:

- obtaining the maximum value of the calculated in-phase signal and quadrature signal;

- obtaining the minimum value of the calculated in-phase signal and quadrature signal;

- calculating the centre of the ellipse based on the obtained maximum and minimum value of the calculated in-phase signal and quadrature signal;

The obtained maximum and minimum values of I and Q can be used to obtain each axis of the ellipse, and therefore to obtain, by widely known calculations, the centre of the ellipse. Also, the calculation of the centre of the ellipse can be performed by using different techniques, such as, for example, taking into account several ellipses and calculating a mean of all the ellipses' centres, the being ellipses obtained during the period of time when the person is accommodating in the vehicle seat. According to a specific embodiment, detecting the vital-related signal pattern, based on the obtained radar signal and the identified centre, comprises:

- applying a correction to the calculated in-phase signal and quadrature signal of the obtained radar signal, based on the identified centre;

- obtaining a characteristic signal of the corrected in-phase signal and quadrature signal, by demodulating the calculated in-phase and quadrature signals, the characteristic signal being related to at least one of: phase of the corrected in-phase signal and quadrature signal, radius of the corrected in- phase signal and quadrature signal, and frequency shift of the corrected in- phase signal and quadrature signal.

- detecting the vital-related signal pattern by comparing the obtained characteristic signal with a predetermined vital-related pattern.

After the centre has been identified, a correction to further obtained radar signals is applied to be able to obtain the information correctly, since other obtained in-phase and quadrature signals from other obtained radar signals (for example, when the person is driving and movement of the car is occurring), may normally not be forming an ellipse when represented in an l/Q diagram. Therefore, the signals are corrected to be referred to the real centre of the l/Q diagram by subtracting the l/Q diagram position coordinates of the previously identified centre. Afterwards, a demodulation is performed on the corrected l/Q signals in order to obtain information related to the signals which may be useful to subsequently detect a vital-related pattern. Such demodulation will depend on which characteristic signal is wanted to be obtained. For example, if the phase of the l/Q signals is to be obtained, an arctangent demodulation calculation may be applied. The detection is finally performed when, by comparison, at least one predetermined vital-related pattern is identified in the demodulated signal. A number of predetermined patterns may be pre-stored in the system, each one related to a vital of a person while driving, such as the respiration rate or the heart rate, and thus, whenever one of those predetermined patterns matches the demodulated signal, the vital-related pattern is detected, and it is determined that the person is actually having, in this case, such a respiration rate or heart rate.

Furthermore, the method may also comprise obtaining a signal related to the movement of the backrest of the seat, by means of a first inertial sensor, which may be, for example, a gyroscope, and wherein detecting the vital- related signal pattern further comprises taking into account the obtained signal related to the movement. Some external movements such as the movement of the car or the movement of the person due to the inertia when, for example, stopping the car, may introduce noise into the obtained radar signal, and thus, such movements may be sensed in the backrest of the seat and a valid criteria may be established, allowing only a certain amount of movement of the backrest. Therefore, if too much movement is sensed, the obtained radar signal may be considered too noisy, thus making it impossible to detect a vital-related signal pattern.

Similarly, the method may also comprise obtaining a signal related to the movement of the base of the seat, by means of a second inertial sensor, which may, for example, an accelerometer, and wherein detecting the vital- related signal pattern further comprises taking into account the obtained signal related to the movement of the base. In this case, other movements related to the acceleration of the whole vehicle seat may be taken into account, and, in the same way as in the inertial sensor arranged in the backrest of the seat, may be used to consider a signal to be valid or not because of the noise added by, for example, car movements and/or vibrations.

According to a further aspect, the invention provides a computer program product comprising program instructions for causing a computer to perform a method for detecting a vital-related signal pattern of a seated person in a vehicle seat.

According to an embodiment, the computer program product may be embodied on a storage medium.

In some embodiments, the computer program product may be carried on a carrier signal.

Additional objects, advantages and features of embodiments of the invention will become apparent to those skilled in the art upon examination of the description, or may be learned by practice of the invention.

BRIEF DESCRIPTION OF THE DRAWINGS Particular embodiments of the present invention will be described in the following by way of non-limiting examples, with reference to the appended drawings, in which:

Figure 1 is a schematic representation of a first system according to a first embodiment of the invention and of a second system according to a second embodiment of the invention; Figure 2 shows a first graphic reflecting respiration rate data obtained from a system according to an embodiment of the invention under determined conditions, and a second graphic reflecting respiration rate data obtained from a plethysmographic band under the same determined conditions;

Figure 3 shows two different inner views of a system according to an embodiment of the invention;

Figure 4 shows different graphics representing respiration rate data obtained from different vertical positions of the radar of a system according to an embodiment of the invention;

Figure 5 is a schematic representation of some anthropomorphic data for obtaining a suitable range of vertical positions of the radar of a system according to an embodiment of the invention;

Figure 6 shows different graphics representing respiration rate data obtained from different horizontal positions of the radar of a system according to an embodiment of the invention;

Figure 7 is a graphic representing the relation between in-phase l(t) and quadrature Q(t) over time, said l(t) and Q(t) being obtained from a radar of a system according to an embodiment of the invention; Figure 8 shows a two dimensional graphic representing the relation between in-phase l(t) and quadrature Q(t), and a three-dimensional graphic representing the relation between in-phase l(t) and quadrature Q(t) over time, said l(t) and Q(t) being obtained from a radar of a system according to an embodiment of the invention;

Figure 9 is a graphic illustrating some main concepts for identifying at least one centre of at least one ellipse of the obtained l(t)-Q(t) relation in a method according to an embodiment of the invention;

Figure 10 shows a graphic representing data obtained from a radar and data obtained from a gyroscope related to the radar, and how both data are combined to determine a valid vital-related signal pattern, according to an embodiment of the method of the invention;

Figure 1 1 shows a graphic representing data obtained from a radar and data obtained from an accelerometer related to the radar, and how both data are combined to determine a valid vital-related signal pattern, according to an embodiment of the method of the invention; and

Figure 12 shows a graphic representing data obtained from a radar, data obtained from an accelerometer related to the radar and data obtained from a gyroscope related to the radar, and how both data are combined to determine a valid vital-related signal pattern, according to an embodiment of the method of the invention.

DETAILED DESCRIPTION OF EMBODIMENTS

Figure 1 refers to a first system for detecting a vital-related signal pattern of a seated person in a vehicle seat according to a first embodiment of the invention, and to a second system for detecting a vital-related signal pattern of a seated person in a vehicle seat according to a second embodiment of the invention.

Figure 1 a shows a seat 1 1 comprising a substantially horizontal base 16 and a substantially vertical backrest 15 having a front surface 12 accommodating the back of the seated person 10 when in use, and a rear surface 19. This seat 1 1 comprises a system for detecting a vital-related signal pattern of a seated person 10, said system comprising a Doppler radar 14 arranged inside of the backrest 15 in such a way that a main radiation lobe 18 of the emitter/receiver of the Doppler radar 14 is focused towards the front surface 12 of the backrest 15. This system also comprises a module for detecting, based on a radar signal obtained by the Doppler radar 14, a signal pattern related to a vital of the seated person 10.

The system of Figure 1 a also comprises a gyroscope 13 arranged with the Doppler radar 14, for obtaining a parameter related to the inertial movement of the radar; a module (not shown) for verifying if the parameter obtained by the gyroscope 13 is out of a predetermined threshold range; and a module (not shown) for, in case of positive result of said verification, identifying the detected signal pattern as a non-valid pattern. Alternatively to the gyroscope 13, the system could comprise an accelerometer 13 or any other inertial sensor arranged with the radar 14 providing the same or equivalent results. The system of Figure 1 a also comprises an accelerometer 17 arranged in the base 16 of the seat, for obtaining a parameter related to the inertial movement of the seat; a module (not shown) for verifying if the parameter obtained by the accelerometer 17 is out of a predetermined threshold range; and a module (not shown) for, in case of positive result of said verification, identifying the detected signal pattern as a non-valid pattern. Alternatively to the accelerometer 17, the system could comprise a gyroscope 17 or any other inertial sensor arranged in the base 16 of the seat providing the same or equivalent results. The system of Figure 1 b is identical to the system of Figure 1 a, with the only difference of that the radar 14 and its related gyroscope 13 (or accelerometer 13) is attached to the rear surface 19 instead of the Doppler radar 14 being arranged inside of the backrest 15. In both implementations of Figures 1 a and 1 b, the Doppler radar 14 is arranged in such a way that the emitter/receiver of the Doppler radar 14 and the front surface 12 of the backrest are arranged with a minimum distance between them of 1/4 of the wavelength used by the Doppler Radar 14. This minimum distance will make possible to obtain at least one ellipse defined by the calculated in-phase l(t) and quadrature Q(t) signal over a predetermined period of time, as it will be described in detail in later descriptions.

In the systems of Figure 1 , the Doppler radar 14 has the function of measuring the motion over the front surface 12 of the backrest 15. The motion x(t) measured is due to a frequency shift 6(t) between the transmitted and reflected radar 14 electromagnetic continuous waves. It may be assumed that the target movement (of the seated person) is periodic with cero mean velocity, so Doppler shift can be expressed as a phase modulation as follows:

(Expression 1 )

wherein λ is the wavelength of the Doppler radar 14. Therefore, the Doppler radar 14 measures the position of the seated person 10 (e.g. driver), which includes the respiration rate RR(t) (which is typically found within the range of 0.1 Hz and 0.35Hz) , the heart rate HR(t), and all driver movements related to the car displacement, engine vibration and driving motion, such as car steering or gear shifting. The Doppler radar quadrature receiver outputs can be expressed related to the target distance d, heart rate and respiration rate as follows:

(Expression 2)

Before demodulating the radar output and recovering the radar's phase, the centre displacement of the elliptical spiral defined by the representation of the diagram of l(t) and Q(t) (due to e.g. the receiver hardware mismatching or other DC offsets in the electronics instrumentation) may be removed from l(t) and Q(t), in order to obtain more reliable l(t) and Q(t) values. Calculation of elliptical spiral centres will described in detail with reference to Figure 9.

Once centre ellipse values have been subtracted from l(t) and Q(t) signals, an arctangent operation between l(t) and Q(t) is performed to obtain the phase φ(ί) of the obtained signals and information related to the nominal target distance d and respiration rate RR(t). Such operation is performed by applying the following formula:

(Expression 3)

Wherein phase is defined between -π and ττ. If target movements exceed the radar wavelength, a -2π or 2π discontinuity is obtained. The target distance may be calculated by using the Riemann sheets and, therefore linking discontinuous results adding or subtracting 2π phase.

(Expression 4)

Figure 2 shows a first graphic reflecting respiration rate data obtained by a system according to an embodiment of the invention under determined conditions, and a second graphic reflecting respiration rate data obtained by a plethysmographic band under the same determined conditions. The respiration rate data obtained by a system according to an embodiment of the invention is shown in Figure 2a and refers to the variation of the target distance (calculated from radar signals) over time. The respiration rate data obtained by the plethysmographic band is shown in Figure 2b.

Both graphics of Figure 2 have been obtained under optimum conditions, with a static car with its engine being stopped. The respiration rate 20 is perfectly identified and correctly referenced by the plethysmografic band signal 21. It has to be taken into account, when comparing the two graphics, that the respiration rate 20 from the radar presents a delay time with respect to the respiration rate 21 from the plethysmografic band, said delay due to the frequency shift 0(t) between the transmitted and reflected electromagnetic continuous waves emitted by the radar. The experiment was repeated with the car engine on and without movement, and it was checked that car vibration due to engine operation do not affect to the radar respiration rate measure although a noise source is introduced.

Experiments consisting on obtaining target distance variation from radar signals have been carried out without a backrest on which the driver to rest his/her back. These experiments without backrest have produced quite unclear signals that may not be enough to detect vital signals from the driver. Unexpectedly, when the driver rests on a backrest, the target distance variation obtained from radar signals becomes much clearer than without backrest.

Figure 3 shows two different inner views of a system according to an embodiment of the invention. Figure 3a shows a view of a seat comprising an embodiment of the system very similar to the embodiments depicted in Figure 1 , whereas Figure 3b shows a cross section of the embodiment of Figure 3a according to the plane 30 and from the point of view 31 . This cross section shows a typical metallic grid 32 found inside the backrest of the seat, between the radar 14 and the front surface 12. This grid 32 or any other similar element with structural and/or comfort purposes comprises a zone 32a with minimum quantity of metallic composition, which is used to arrange the radar 14, in order to avoid as much as possible interferences negatively affecting the radar operation.

Figure 3c refers to the same view offered by Figure 3a, whereas Figure 3d shows a cross section of the embodiment of Figure 3c according to the plane 33 and from the point of view 34. This cross section shows a rigid H-shaped structure comprising a crossbar or a similar support element to which the radar is fixed. In order to keep the maximum deflection of the crossbar (and also the maximum velocity) below a certain value, it would be needed a minimum rigidity of the structure. The measuring system (the radar) could be placed in a relatively soft support (crossbar or other structure), which could move relative to the seat and the person. For analyzing this structure it can be considered, for example, a bar 37 anchored between two vertical structures 35,36 belonging to the seat back.

When subjected to movements at the edges due to the back seat movements, this structure will bend due its inertia. Assuming an inertia force applied at the center and an oscillatory movement, its maximum value can be approximated by:

where p is the density, V_b is the volume of the support beam (which can be calculated using the product of the length, width and height of the beam), y_max is the maximum bending of the radar support beam related to the seat backrest structure, and T is the maximum allowed period.

A linear rigidity for the support structure may be assumed: F = k_t ^■ x Therefore the minimum ki (ki_min) for a maximum value of displacement (x_max) of the backrest may be obtained. The following characteristic values may be assumed: I = 0.35m, w = 0.01 m, h = 0.01 m, x_max = 0.002m, p = 1000 kg/m³

The Yest_max - 0.0002m, which is 1/10th of the respiratory amplitude and T_max - 0.015 s, which is the period for a 3g acceleration. Therefore:

Therefore, an approximate ki_min of about 600 N/m may be set.

Thus, for a double-clamped beam, the following formula may be applied:

Therefore, minimum values for the rigidity of the material (given by E) for this structure may be estimated. Approximately a minimum young's modulus of this structural material as 0.2GPa may be set. Nevertheless, this result will depend on the exact dimensions of the supporting structure, as can be derived from the applied calculations.

Figure 4 shows different graphics representing respiration rate data obtained from different vertical positions of the radar of a system according to an embodiment of the invention. Figure 4a shows the variation of the phase 40 calculated from radar signals over time when the radar is placed at the height of the T6 vertebra of a middle-sized body. Figure 4b shows the variation of the phase 41 calculated from radar signals over time when the radar is placed at the height of the T7 vertebra a middle-sized body. Figure 4c shows the variation of the phase 42 calculated from radar signals over time when the radar is placed at the height of the T8 vertebra of a middle-sized body. And Figure 4a shows the variation of the phase 43 calculated from radar signals over time when the radar is placed at the height of the T9 vertebra of a middle-sized body.

The clearest variation of the phase calculated from radar signals over time is phase 41 corresponding to the T7 vertebra measurement, and therefore, it is highly preferable to place the radar at a height close as much as possible to the T7 vertebra height. Calculations in accordance with this preferable height will be detailed in following descriptions in reference to Figure 5.

Figure 5 is a schematic representation of some anthropomorphic data for obtaining a suitable range of vertical positions of the radar of a system according to an embodiment of the invention. According to ISO/TR 7250-

2:2010: "Basic human body measurements for technological design - Part 2: Statistical summaries of body measurements from individual ISO populations", the eyes 50 are at a height 53 of 1760 mm for 95% of men and at a height 53 of 1410 mm for 5% of the women, and that the hip 51 is at a height 52 of 1020 mm for 95% of men and at a height 52 of 750 for 5% of women. Assuming that the second cervical vertebra (C2) is at the height 53 of the eyes 50, and the fifth lumbar at the height 52 of the hip 51 , the total spine height between both vertebrae may be calculated as follows:

95% male is: 1760mm-1020mm=740mm

5% female is: 1410mm-750mm=660mm

The T7 position is placed at 59,94% from the Hip point 51 for a high man, so it may be assumed for a high man that the distance between the Hip point 51 and the T7 vertebra is 444mm (=740 x 59,94%). The T7 position is placed at 56,46% from the Hip point 51 for a small woman, so it may be assumed for a small woman that the distance between the Hip point 51 and the T7 vertebra is 373mm (=740 x 56,46%). Therefore, in preferred embodiments of the system, the Doppler radar will be arranged between a minimum height 55 of 373 mm referenced to the surface 54 of the seat base and a maximum height 56 of 444 mm referenced to the surface 54 of the seat base.

This calculus does not take into account the possible cushion compression, and the driver movements that can be associated with a bumped road. For this reason, a second sensor can be embedded inside the cushion, which can provide this information to the system.

Figure 6 shows different graphics representing respiration rate data obtained from different horizontal positions of the radar of a system according to an embodiment of the invention. Figure 6a shows the variation of the phase 60 calculated from radar signals over time when the radar is substantially arranged on a vertical axis of symmetry of the backrest. Figure 6b shows the variation of the phase 61 calculated from radar signals over time when the radar is substantially horizontally arranged 2cm from the vertical axis of symmetry of the backrest. Figure 6c shows the variation of the phase 62 calculated from radar signals over time when the radar is substantially horizontally arranged 4cm from the vertical axis of symmetry of the backrest. And Figure 6b shows the variation of the phase 63 calculated from radar signals over time when the radar is substantially horizontally arranged 6cm from the vertical axis of symmetry of the backrest.

As it can be observed, the phase calculated from radar signals over time is distinguishable in Figures 6a, 6b and 6c, but not in 6d. Therefore, in preferred embodiments of the system, the Doppler radar will be arranged at a distance between 0 and 4 cm with respect of a vertical axis of symmetry of the backrest.

Figure 7 is a graphic diagram representing the relation between in-phase l(t) and quadrature Q(t) over time, said l(t) and Q(t) being obtained from a radar of a system according to an embodiment of the invention. Particularly, Figure 7 shows an l(t)-Q(t) three-dimensional diagram of a person with a medium body mass index versus acquisition time. In this diagram three sections are identified: The first one 70 may be assumed as related to the person accommodation, with movements that exceed the radar wavelength and cause at least one closed spiral ellipse, the second section 72 may be assumed as the motion of the person due to the car movements and respiration, said motion causing an open spiral ellipse, and the last section 71 may be assumed as only representing the chest movements of the person during e.g. a straight line driving and therefore without significant car accelerations. Different experiments with people of different nature may be carried out for empirically obtaining a predetermined vital-related pattern from the different sections 71 (only representing the chest movements) obtained from the experiments. This predetermined vital-related pattern may be used for detecting a vital-related signal pattern during normal operation of the system. Figure 8 shows a two dimensional graphic diagram representing the relation between in-phase l(t) and quadrature Q(t), and a three-dimensional graphic representing the relation between in-phase l(t) and quadrature Q(t) over time, said l(t) and Q(t) being obtained from a radar of a system according to an embodiment of the invention. In particular, Figure 8a shows a two-dimensional view 80 of section 71 shown in Figure 7, and Figure 8b shows the relation between in-phase l(t) and quadrature Q(t) over time with no driving and stopped car engine in order to analyse the respiration movements of the passenger and extract the effects of the moving car. Figure 8b allows concluding that passenger chest movements related to his respiration may be perfectly identified by an open elliptical spiral.

Figure 9 is a graphic diagram illustrating several characteristics for identifying at least one center of at least one ellipse of the obtained relation between l(t) and Q(t), in a method according to an embodiment of the invention. This elliptical spiral center voltage may be determined by using the l(t)-Q(t) diagram data; in particular by measuring the maximum 93 and minimum 94 l(t) voltages and the maximum 91 and minimum 92 Q(t) voltages, and calculating the mean to find the elliptical spiral center 90. Before demodulating the radar output and recovering the radar's phase, it is convenient to subtract said calculated elliptical spiral center from l(t) and Q(t), for compensating receiver hardware mismatching or other DC offsets in the electronic instrumentation. Other center calculation procedures using the l-Q diagram may also be suitable.

The calculation of the elliptical spiral center needs at least one complete substantially closed elliptical spiral and therefore chest movements greater than the operation wavelength of the Radar; in case of using a Doppler radar with a 24GHz frequency signal, movements must be over 1 ,25cm. These calibration procedures may be performed during the passenger seat accommodation or during car initial displacement on a road and detected by an accelerometer fixed inside the back seat. The ellipse center can also be calculated a priory by taking measurements with the Doppler radar focused towards infinite, that is, with no object close to the radar range (in this case, up to 3 meters). This calibration of the radar can be performed before installing the system in the vehicle, but a self-calibration method based on the l-Q diagram data is also possible, which allows correcting small imbalances during operation time due to temperature differences, electronic instrumentation variation offsets or small radar position changes.

Figure 10 shows a graphic diagram representing data obtained from a radar and data obtained from a gyroscope related to the radar, and how both data are combined to determine a valid vital-related signal pattern, according to an embodiment of the method of the invention. In particular, Figure 10a shows how the target distance (calculated from radar signals) changes over time and Figure 10b shows how the angular velocity (calculated from gyroscope signals) changes over time. Figure 10b also shows a predetermined range 103 in which the variation of the angular velocity is assumed as indicating a negligible amount of distorting movements (in this case, different from respiration motion) according to the target distance from the radar; that is to say, a time interval 102 in which the angular velocity does not exceed the range 103 may be understood as a time interval 101 of the target distance from the radar corresponding to a valid signal pattern related to a vital (in this case, respiration) of the seated person.

Figure 1 1 shows a graphic diagram representing data obtained from a radar and data obtained from an accelerometer related to the radar, and how both data are combined to determine a valid vital-related signal pattern, according to an embodiment of the method of the invention. In particular, Figure 10a shows how the target distance (calculated from radar signals) changes over time and Figure 10b shows how acceleration (calculated from accelerometer signals) changes over time. Figure 10b also shows a predetermined range 1 13 in which the variation of the acceleration is assumed as indicating a negligible amount of distorting movements (in this case, different from respiration motion) according to the target distance from the radar; that is to say, a time interval 1 12 in which the acceleration does not exceed the range 1 13 may be understood as a time interval 101 of the target distance from the radar corresponding to a valid signal pattern related to a vital (in this case, respiration) of the seated person.

The same methodology of the invention can be achieved by using substituting the Doppler radar by a plethysmographic band, and by using other sensors different from accelerometers and gyroscopse, achieveing similar results, the sensors being such as the ones described in the following documents:

- Smart seat belt that use smart textiles [C.T. Huang, C. F. Tang, M.C Lee and S.H Chang, "Parametric design of yarn-based piezoresistive sensorsfor smart textiles", Sensors and Actuators A, vol 146, pp.10-15, 2008. Doi: 10.1016/j.sna1008.06.029] to measure the respiration movements

- Sthetoscope based on a microphone that detects the energy related to the movement of the air in the trachea and lungs and the sounds that it produces

[P. Corbishley and E. Rodriguez-Villegas, "Breathing Detection: Towards a Miniaturized, Wearable, Battery Operated Monitoring System", IEEE Transactions on Biomedical Engineering, vol. 55, No. 1 , Jan. 2008.]. Figure 12 shows a graphic diagram representing data obtained from a radar, data obtained from an accelerometer related to the radar and data obtained from a gyroscope related to the radar, and how both data are combined to determine a valid vital-related signal pattern, according to an embodiment of the method of the invention. Figure 12 refers to how a valid signal pattern may be determined by e.g. any of the systems referred by Figure 1 , each of them comprising a gyroscope 13 arranged with the Doppler radar 14 and an accelerometer 17 arranged in the base 16 of the seat. In this embodiment of the method, a time interval 121 corresponding to a valid signal pattern related to a vital (in this case, respiration) of the seated person is obtained from the intersection of the time interval 1 12 in which the acceleration does not exceed the range 1 13 and the time interval 102 in which the angular velocity does not exceed the range 103. This way of determining the valid time interval makes the method more reliable, since any signal from either the gyroscope or the accelerometer indicating distorting motions invalidates the corresponding signal from the radar as part of a vital-related signal pattern. Even though, as commented with reference to Figure 7, vital-related signal patterns may be detected by comparing the values calculated from the radar with an empirically predetermined vital-related pattern, it is more reliable to further use angular velocity measures (from one or more gyroscopes) and acceleration measures (from one or more accelerometers) as described in the three previous paragraphs.

Although only a number of particular embodiments and examples of the invention have been disclosed herein, it will be understood by those skilled in the art that other alternative embodiments and/or uses of the invention and obvious modifications and equivalents thereof are possible. Furthermore, the present invention covers all possible combinations of the particular embodiments described. Thus, the scope of the present invention should not be limited by particular embodiments, but should be determined only by a fair reading of the claims that follow.

Further, although the embodiments of the invention described with reference to the drawings comprise computer apparatus and processes performed in computer apparatus, the invention also extends to computer programs, particularly computer programs on or in a carrier, adapted for putting the invention into practice. The program may be in the form of source code, object code, a code intermediate source and object code such as in partially compiled form, or in any other form suitable for use in the implementation of the processes according to the invention. The carrier may be any entity or device capable of carrying the program.

For example, the carrier may comprise a storage medium, such as a ROM, for example a CD ROM or a semiconductor ROM, or a magnetic recording medium, for example a floppy disc or hard disk. Further, the carrier may be a transmissible carrier such as an electrical or optical signal, which may be conveyed via electrical or optical cable or by radio or other means. When the program is embodied in a signal that may be conveyed directly by a cable or other device or means, the carrier may be constituted by such cable or other device or means.

Alternatively, the carrier may be an integrated circuit in which the program is embedded, the integrated circuit being adapted for performing, or for use in the performance of, the relevant processes.

Claims

1 . System for detecting a vital-related signal pattern of a seated person in a vehicle seat, the seat comprising a substantially horizontal base and a substantially vertical backrest having a front surface accommodating the back of the seated person when in use, and a rear surface, the system further comprising:

- a module for detecting, based on a radar signal obtained by the Doppler radar, a signal pattern related to a vital of the seated person.

2. System for detecting a vital-related signal pattern according to claim 1 , wherein the Doppler radar is at least partially comprised within the backrest of the vehicle seat.

3. System for detecting a vital-related signal pattern according to any of claims 1 or 2, wherein the Doppler radar is arranged in such a way that the emitter/receiver of the radar and the surface of the backrest are arranged with a minimum distance between them of 1/4 of the wavelength used by the Doppler Radar.

4. System for detecting a vital-related signal pattern according to any of claims 1 to 3, wherein the Doppler radar is arranged at a maximum distance of 1/5th of the shoulder breadth for the 5% thinnest women, corresponding to a distance between 0 and 4 cm with respect of a vertical axis of simmetry the backrest, based on the values defined in ISO/TR 7250-2:2010.

5. System for detecting a vital-related signal pattern according to any of claims 1 to 4, wherein the Doppler radar is arranged at a height between 5% of the women height and 95% of the men height, corresponding to 373 mm and 444 mm respectively, referenced to the surface of the seat base, based on the values defined in ISO/TR 7250-2:2010.

6. System for detecting a vital-related signal pattern according to any of claims 1 to 5, further comprising a mechanism for changing the height of the Doppler radar with respect to the surface of the base of the seat.

7. System for detecting a vital-related signal pattern according to any of claims 1 to 5, wherein the Doppler radar is affixed to a support structure arranged in the backrest of the seat, the support structure having a rigidity such that allows a movement of the Doppler radar of less than 0.2mm, in the direction of the main radiation lobe with an acceleration below 3g.

8. System for detecting a vital-related signal pattern according to any of claims 1 to 7, further comprising at least one first inertial sensor arranged with the Doppler radar, for obtaining a parameter related to the inertial movement of the radar; a module for verifying if the parameter obtained by the first sensor is greater than a predetermined threshold, and a module for, in case of positive result of said verification, identifying the detected signal pattern as a non-valid pattern.

9. System for detecting a vital-related signal pattern according to claim 8, wherein the first inertial sensor is a gyroscope.

10. System for detecting a vital-related signal pattern according to any of claims 1 to 9, further comprising at least one second inertial sensor arranged in the base of the seat, for obtaining a parameter related to the inertial movement of the seat; a module for verifying if the parameter obtained by the second sensor is greater than a predetermined threshold, and a module for, in case of positive result of said verification, identifying the detected signal pattern as a non-valid pattern.

1 1 . System for detecting a vital-related signal pattern according to claim 10, wherein the second inertial sensor is an accelerometer.

12. Method for detecting a vital-related signal pattern of a seated person in a vehicle seat, the seat comprising a substantially vertical backrest and a substantially horizontal base, the method comprising:

- obtaining a radar signal by means of a Doppler radar;

- identifying at least one center of at least one ellipse defined by the calculated in-phase and quadrature signal over a predetermined period of time.

- detecting, based on the obtained radar signal and the identified center, the vital-related signal pattern of the seated person.

13. Method according to claim 12, further comprising, wherein identifying at least one center of at least one ellipse comprises:

- calculating the center of the ellipse based on the obtained maximum and minimum value of the calculated in-phase signal and quadrature signal;

14. Method according to any of claims 12 or 13, wherein detecting the vital- related signal pattern, based on the obtained radar signal and the identified center, comprises:

- applying a correction to the calculated in-phase signal and quadrature signal of the obtained radar signal, based on the identified center;

15. Method according to any of claims 12 to 14, further comprising obtaining a signal related to the movement of the backrest of the seat, by means of a first inertial sensor, and wherein detecting the vital-related signal pattern further comprises taking into account the obtained signal related to the movement.

16. Method according to claim 15, wherein the first inertial sensor is a gyroscope.

17. Method according to any of claims 12 to 16, further comprising obtaining a signal related to the movement of the base of the seat, by means of a second inertial sensor, and wherein detecting the vital-related signal pattern further comprises taking into account the obtained signal related to the movement of the base.

18. Method according to claim 17, wherein the second inertial sensor is an accelerometer.

19. A computer program product comprising program instructions for causing a computer to perform a method for detecting a vital-related signal pattern of a seated person in a vehicle seat according to any of claims 12 to 18.

20. A computer program product according to claim 19, embodied on a storage medium.

21 . A computer program product according to claim 19, carried on a carrier signal.