Method and acoustic system for measuring surface movements

Abstract

Method for detecting movements of a plurality of points (P) of a surface (21), comprising a measuring step in which an incident ultrasonic wave is emitted into the air towards the surface and an ultrasonic wave reflected in the air by the surface (21) is picked up. The movements of the surface at a measuring point are determined by determining a delay and / or phase shift between two path-forming signals for this measuring point. Before the measuring steps, a topography of the surface (21) is determined by an optical device. During the measuring steps, the path-forming signals are determined from the topography of the surface. Figure for abstract: Figure 1

Description

Title of the invention: Method and acoustic system for measuring surface movements Technical field

[0001] The present invention relates to acoustic methods and systems for detecting surface movements. These movements are in particular the vibrations of various points on this surface. State of the prior art

[0002] Patent application WO-2018 / 015638 proposes a method for detecting movements of a surface, comprising:

[0003] - several successive measurement steps during each of which at least one emits at least one incident ultrasonic wave in the air towards the surface with an ultrasonic wave emitting device and capturing reflected signals representative of at least one ultrasonic wave reflected in the air by said surface from said at least one incident ultrasonic wave, and

[0004] - a movement determination step during which said surface movements.

[0005] During each measurement step:

[0006] - the movements of a plurality of measuring points belonging to the less to said surface by illuminating each measuring point with said at least one incident ultrasonic wave under a multiplicity of angles of incidence,

[0007] - the reflected signals are captured with a network of receiving transducers comprising a plurality of receiving ultrasonic transducers, and

[0008] - a track formation signal is determined for each measurement point, by channel formation at least in reception from said reflected signals.

[0009] During the movement determination step, said movements of the surface at the measurement point considered are determined by determining at least one delay or phase shift between two path-forming signals for this measurement point. Description statement

[0010] The present invention aims in particular to perfect and improve this type of method, in particular in order to allow better efficiency or precision in detecting surface movements.

[0011] A first object of the invention is thus a method as presented above and characterized in that:

[0012] before the measurement steps, a topography of the surface is determined by a optical device, and

[0013] during the measurement steps, the track forming signals are determined from the surface topography.

[0014] Thanks to these provisions of the method, the shape of the surface has less or little influence on the track formation signal for each measuring point. Thus, the movements or vibrations of the surface at the measuring points considered are determined more precisely.

[0015] The topography of the surface makes it possible to know the positions of points on the surface, and possibly to follow their displacements or slow movements, in order to know the distances between the transmission or reception devices, and various measurement points on the surface.

[0016] The accuracy of movement measurement is no longer a function of the location of the measuring point on the surface. The ultrasonic acoustic device and the optical device operate synergistically so that the measurement of movements or vibrations of the surface measuring points is more reliable.

[0017] In preferred embodiments of the method according to the invention, one and / or the other of the following arrangements may optionally be used in addition.

[0018] According to a variant, the topography comprises location points on the surface, the measurement points are determined from the location points.

[0019] According to a variant, the measurement points are determined by choice among the location points, or by interpolation of location points.

[0020] According to a variant:

[0021] all of the steps of measuring and determining movement are repeated,

[0022] the topography determination step is repeated in an interleaved manner with all of the motion measurement and determination steps, and

[0023] the track formation signals calculated in the movement determination step are determined from the last temporally determined topography.

[0024] According to a variant, the step of determining the topographies is carried out at a topography rate lower than the measurement rate of the steps of measuring and determining movement.

[0025] According to one variant, the topography rate is at least ten times lower than the measurement rate.

[0026] According to a variant, the plurality of topographies determined by the optical device is used to determine movements of the surface which are slower than the movements determined by all of the acoustic steps of measurement and determination of movement.

[0027] According to a variant, before the measurement steps, the step of determining to- pography is repeated and the surface is moved until the position of the surface relative to the emitting device is optimal relative to a predetermined optimal position, or conversely the emitting device is moved until the position of the surface relative to the emitting device is optimal relative to a predetermined optimal position.

[0028] According to a variant, while the topography determining step is repeated, a distance is determined between the surface and the transmitting device, and a signal is generated when said distance is less than an optimal distance level.

[0029] According to a variant, the method further comprises a step of calibrating the optical device before the first topography determination.

[0030] According to a variant, the incident ultrasonic wave is a periodic pseudo-random signal.

[0031] A second object of the invention is a system for detecting movements of a surface (21) reflecting ultrasonic waves, comprising:

[0032] a device for emitting ultrasonic waves,

[0033] an ultrasonic wave receiving device,

[0034] a control device controlling the ultrasonic wave emitting device and receiving signals picked up by the ultrasonic wave receiving device,

[0035] in which:

[0036] the control device is adapted to carry out several successive measurement steps during each of which the ultrasonic wave emitting device emits at least one incident ultrasonic wave in the air towards the surface and the ultrasonic wave receiving device picks up reflected signals representative of at least one ultrasonic wave reflected in the air by said surface from said at least one incident ultrasonic wave,

[0037] the ultrasonic wave emission device is adapted to illuminate a plurality of measurement points belonging at least to said surface by said at least one incident ultrasonic wave under a multiplicity of angles of incidence,

[0038] the ultrasonic wave receiving device is a receiving transducer array comprising a plurality of receiving ultrasonic transducers, and the receiving transducer array picks up the reflected signals,

[0039] the control device is adapted to, during each measurement step, determine a channel formation signal for each measurement point, by channel formation at least in reception from said reflected signals,

[0040] the control device is adapted to determine said movements of the surface at the measurement point considered by determining at least one delay or phase shift between two track-forming signals for this measurement point, and characterized in that

[0041] the device for detecting movements of the surface further comprises a optical device suitable for measuring surface topography, and

[0042] the control device is adapted to measure the topography with said optical device at least before the measuring steps, and

[0043] the control device is adapted to determine the track formation signals from the surface topography.

[0044] In preferred embodiments of the system according to the invention, one and / or the other of the following arrangements may optionally be used.

[0045] According to one variant, the optical device is a depth camera or a LiDAR camera.

[0046] According to a variant, the optical device has a spatial resolution of less than X / 10 of the wavelength of the incident ultrasonic waves or of the reflected ultrasonic waves.

[0047] According to a variant, the system is used to detect the movements of a plurality of measurement points of a surface, this surface being the thorax or the back of a person.

[0048] According to a variant, the control device determines a pathology of the person from the movements of the plurality of measurement points of said surface. Brief description of the figures

[0049] Other characteristics and advantages of the invention will appear during the following description of one of its embodiments, given by way of non-limiting example, with reference to the attached drawings.

[0050] In the drawings:

[0051] - [Fig.l] is a schematic overview of an example of a ge device generation of ultrasonic waves implementing the invention,

[0052] - [Fig.2] shows an example of an emission transducer network usable in the present invention,

[0053] - [Fig.3] is a schematic sectional view illustrating an example of a me- langer for one or more ultrasonic emission transducers,

[0054] - [Fig.4] is an example of mapping the movement speeds of a surface measured by the device of figures 1 to 3,

[0055] - [Fig.5] is an example of mapping the movements of a measured surface by the device of figures 1 to 3,

[0056] - [Fig.6] is an example of a curve of the speeds of movement of a point of the surface over time,

[0057] measured by the device of figures 1 to 3, and

[0058] - [Fig.7] is an example of a curve of the displacements of a point on the surface at over time, measured by the device of figures 1 to 3, and

[0059] - [Fig.8] is an example of the implementation of emission transducer networks and receiving, and optical device for an ultrasonic surface motion detection device of the type of figures 1 to 3, and used to measure a surface 21 corresponding to a back or a thorax of a person.

[0060] In the various figures, the same references designate identical or similar elements. Detailed description of the implementation methods

[0061] [Fig.l] represents an ultrasonic system and device 1 for measuring the movements of a surface 21, which can be of any nature, solid or liquid. The surface 21 can for example be the skin of a human or animal being.

[0062] The ultrasonic device 1 comprises an array of emission transducers 2, which may comprise one or more ultrasonic emission transducers 2a numbering M (TE1, TE2, ... TEM), and an array of reception transducers 3, which comprises several ultrasonic reception transducers 3a numbering N (TR1, TR2, ... TRN).

[0063] The two transducer networks 2, 3 can advantageously be two-dimensional networks.

[0064] The two networks 2, 3 can optionally be arranged on the same support and, in this case, the transducers 2a, 3a can be interposed between each other.

[0065] The transducers 2a, 3a may be of any known type. In one embodiment, the transmitting ultrasonic transducers 2a may be high bandwidth loudspeakers and the receiving ultrasonic transducers 3a may be high bandwidth microphones.

[0066] The ultrasonic emission transducer(s) 2a may optionally be arranged to emit ultrasonic waves into a mixing cavity 4 before sending them to the surface 21, as will be described later.

[0067] The network of emission transducers 2 and the network of reception transducers 3 are provided for measuring the movements of a plurality of measurement points P belonging to the surface 21, for example for measuring the movements at substantially any point of the surface 21 over an area greater than 10 cm2 and possibly several tens of cm2.

[0068] For this purpose, the emission transducer array 2 and the reception transducer array 3 are each provided to have a relatively large aperture, so that each measuring point P of the surface 21 is illuminated under a large number of angles of incidence by the incident ultrasonic waves coming from the emission transducer array 2, and so that each point P of the surface 21 is seen by the 3a receiving transducers from a wide range of viewing angles.

[0069] The aperture of the emission transducer array 2 can be defined as the transverse dimensions OEY, OEZ of the array, for example along a vertical axis Z and a transverse horizontal axis Y (see Figures 1, 2). This aperture corresponds to an emission aperture angle a under which the emission transducer array 2 is seen from each measurement point P. Each measurement point P is thus illuminated by the incident ultrasonic waves under a multiplicity of incidence angles forming a range of incidence angles of width a. The aperture angle a can be for example at least equal to 20 degrees.

[0070] The aperture of the receiving transducer array 3 can be defined as the transverse dimensions ORY, ORZ of the array, for example along a vertical axis Z and a transverse horizontal axis Y' (see [Fig.l]). This aperture corresponds to a receiving aperture angle [3 under which the receiving transducer array 3 is seen from each measuring point P. Each measuring point P is thus seen by the receiving ultrasonic transducers 3a under a multiplicity of viewing angles forming a range of viewing angles of width [3. The receiving aperture angle [3 can be for example at least equal to 20 degrees.

[0071] The emission opening angle a can advantageously be greater than the reception opening angle [3.

[0072] More particularly, the opening of the network of emission transducers 2 along at least one axis Y, Z, or both, is advantageously greater than the opening of the network of reception transducers along the corresponding axes Y', Z. This arrangement makes it possible to ensure that at least a portion of the reflected ultrasonic waves always returns to the network of reception transducers 3.

[0073] Optionally, the opening of the network of emission transducers 2 along at least one axis Y, Z, or both, may be greater than 3 times (or even 5 times, or even 7 times) the opening of the network of reception transducers along the corresponding axes Y', Z.

[0074] The ultrasonic device 1 can be controlled by an electronic assembly 11 itself possibly connected to a computer 12 or similar.

[0075] The electronic assembly 11 may comprise:

[0076] - a digital-analog converter 6 (D / A1-D / AM) connected to each transducer emission 2a (El-EM) and associated where appropriate with a buffer memory 9 (Bl-BN),

[0077] - control device 5 such as a controlled electronic central processing unit (CPU) by the computer 12 and controlling each analog-digital converter 6,

[0078] - at least one central memory 7 (MEM) connected to or internal to the device of control 5 or electronic central unit 5,

[0079] - possibly, a specific signal processing circuit 8 (DSP)

[0080] - an analog-digital converter 10 (A / D1-A / DN) connected to each transducer of reception 3a (TR1-TRN)), and associated respectively with a buffer memory 9 (B'I-B'N).

[0081] The control device 5 may optionally be implemented using a computer or the like.

[0082] The computer 12 comprises input means 12a (keyboard, mouse or other) for example so that a user can control and configure the ultrasound system or device 1, and display means 12b such as a screen for displaying results of the ultrasound device 1, i.e. at least the movements of the surface 21.

[0083] The ultrasonic emission transducers 2a can be controlled to emit the incident ultrasonic waves at a frequency of less than 100 kHz, for example between 40 and 70 kHz.

[0084] Advantageously, the control device 5 is adapted to emit the incident ultrasonic waves at a rate greater than 500 shots per second, so as to be able to follow the movements of the surface 21 over time.

[0085] As shown in [Fig.2] in a particular embodiment, the network of emission transducers 2 may be a two-dimensional network of ultrasonic emission transducers 2a carried by a rigid plate 13.

[0086] These ultrasonic transmitting transducers 2a can be controlled to transmit the incident ultrasonic waves either at the same time or sequentially.

[0087] Optionally, the ultrasonic emission transducers 2a can be divided into several groups and all the ultrasonic emission transducers 2a of the same group are controlled to simultaneously emit the same signal. This results in a multiplied network, which artificially increases the emission aperture of the network of emission transducers 2.

[0088] Alternatively or additionally, the emission transducer array 2 may be coupled to a mixing cavity 4, as explained above and as shown in FIGS. 1 and 3. The emission transducer array 2 may possibly in this case be reduced to a single ultrasonic emission transducer 2a, since the aperture OE'Y, OE'Z of the emission transducer array 2 is then defined not by the spatial distribution of the transducers but by the dimensions of the emitting face of the mixing cavity, through which the incident ultrasonic waves exit into the air towards the surface 21.

[0089] The mixing cavity 4 may be a solid object such as a plate or the like, or it may be a housing in which the emission transducer array 2 is mounted, as shown in [Fig. 3]. In this case, the mixing cavity 4 may comprise a bottom 14, side walls 15 and an emission wall parallel to the bottom 14 and held apart from said bottom 14 by the side walls 15. The transducer array emission transducer 2 can be mounted on the bottom 14, in the mixing cavity 4. The emission wall 16 can have holes 17 allowing the incident ultrasonic waves to exit towards the surface 21. These holes 17 constitute as many sources of ultrasound which define the opening of the network of emission transducers 2.

[0090] Inside the mixing cavity, reflective walls may be provided, integral for example with the emission wall 16 and advantageously substantially perpendicular to the bottom 14. The reflective walls are oriented in various ways to promote multiple reflections of the ultrasonic waves in the mixing cavity 4.

[0091] The device which has just been described makes it possible to measure the movements of the surface 21, in particular the displacement and the speed of displacement at any point.

[0092] This measurement is carried out by processing the reflected signals captured by the receiving ultrasonic transducers 3a, by a signal processing method which can for example be one of the three methods described below. Method 1

[0093] In this first signal processing method, the illumination of the surface 21 by the incident ultrasonic waves (the firing of the incident ultrasonic waves) is carried out by simultaneously exciting the M ultrasonic emission transducers 2a.

[0094] At each measurement step k, corresponding to an incident wave shot, the signals captured by the receiving ultrasonic transducers 3a are processed by channel formation in reception, in a conventional manner.

[0095] Thus, for each point P of the observation zone (i.e. the zone likely to be occupied by the surface 21), a channel formation signal in reception Sk(t) is calculated as follows: [00961 (1)

[0097] Where:

[0098] - q is the signal captured by the transducer Rj of the reception network 3,

[0099] -1 is time,

[0100] - dj is the distance between point P and transducer Rj,

[0101] - c is the speed of the ultrasonic wave in air.

[0102] This signal is maximum for the points P belonging to the reflecting surface 21.

[0103] It is thus possible to determine a topography of the surface 21, and therefore an image of the surface 21, which is however most often approximate.

[0104] On the other hand, we can determine very precisely the displacements ô at each point P of the surface between two shots k and k+1, by comparison between the signals Sk(t) corresponding to the different successive shots.

[0105] For a given point P of the surface 21, we compare the successive signals Sk(t) and Sk+i (t) during at least one step of determining movement, which reveals a phase shift q> which is linked to the displacement ô undergone by the point P between shots k and k+1 perpendicular to the surface 21, by the relation:

[0106] JL = (P), 2nf c

[0107] where:

[0108] - c is the speed of the ultrasonic wave in the air,

[0109] - f is the frequency of the ultrasonic wave

[0110] - 0 is the average angle of incidence and reflection of the ultrasonic wave at point P, i.e. the average angle between the surface normal and the reflected beam (determined based on the surface topography 21).

[0111] Given that the surface 21 is reflective for ultrasonic waves, the displacement d of the surface 21 is seen as a displacement 2d.cos0 of a virtual source located behind the surface 21, hence the formula (1') above.

[0112] The displacement ô of point P between shots k and k+1 is therefore calculated by the formula:

[0113] ô = j-^(2).

[0114] Equivalently, we can measure not the phase shift q>, but the delay dt=q> / (2irf) of the signal Sk+i(t) with respect to Sk(t) (t is counted each time from the firing of the incident wave), the calculation of the displacement ô between the firings k and k+1 then being carried out by the formula:

[0115] Ô = ^L(2'). Z.cosu

[0116] In both cases, we can easily return to the normal speed of the surface 21: V = ô / At, where At is the time interval between shots k and k+1.

[0117] This first method is very fast and particularly effective, especially if the surface 21 is illuminated over a wide angular range and therefore if the network of emission transducers 2 has a wide emission aperture.

[0118] The use of a multiplied network or a mixing cavity is therefore particularly desirable in this case for the emission transducer network 2. Method 2

[0119] In this second signal processing method, a mixing cavity is preferably not used for the emission transducer network 2.

[0120] A pulse wave is successively emitted by each ultrasonic emission transducer 2a, which will be considered as punctual and emitting a spherical wave. Each series of successive shots by all the ultrasonic emission transducers 2a constitutes a measurement step k, then the shots are repeated in a following series k+1 of successive shots by all the ultrasonic emission transducers 2a.

[0121] For each series k of shots, we thus determine the impulse response hijk(t) between each transmitting ultrasonic transducer Ei and each receiving ultrasonic transducer TRj.

[0122] For a given point P in the area to be observed, we know the distance to be covered by the ultrasonic wave from the transmitter Ei to the receiver Rj, noted d;j. This distance is known for all the pairs (Ei,Rj).

[0123] A beamforming signal is then calculated in transmission and reception at point P for the receiving ultrasonic transducer TRj. This signal rjk(t) is obtained by summing all the delayed impulse responses so as to compensate for the travel times dij / c. This signal is expressed as follows: 101241 <3)

[0125] The signal S'k(t) corresponding to the point P and to the series k of shots, for all the ultrasonic reception transducers 3a, is the summation of the channel formation signals of all the receivers: 101261 =

[0127] If P is a material point of the surface 21, then the signal S will be a short pulse of maximum amplitude because all the pulses calculated for all the receivers will have the same delay. Otherwise the signal will be more spread out in time and of lower amplitude.

[0128] This method makes it possible, in a first approach, to determine the topography of the surface 21, therefore an image (generally imprecise) of the surface 21.

[0129] For the same point P on the surface, the successive signals S'k(t) corresponding to the different measurement steps k make it possible to determine, with great precision, the displacement ô of the point P between two successive series of shots k and k+1, during at least one movement determination step.

[0130] In all embodiments of the invention, the movement determination steps can be carried out as the measurement steps progress. Of course, this calculation can also be done in a deferred manner.

[0131] If the point P has moved between t and t+dt by a distance ô normal to the surface 21, then the new signal S'k+i(t) will be a pulse shifted in time (counted relative to the firing of the incident waves) relative to S'k(t) by dt = 2ô cosO, with the notations already defined above.

[0132] The time shift dt gives the displacement of the surface 21 at point P:

[0133] ô = dt.c / (2 cosO) (5).

[0134] We can easily return to the normal speed of the surface: V = ô / At, where At is the time interval between the series of shots k and k+1.

[0135] As in method 1, the displacement can be determined in an equivalent manner and the surface speed 21 using the phase shift q> between the signals S'k(t) and S'k+i (t).

[0136] Method 2 is very accurate and can allow surface motion measurements of amplitude much smaller than the wavelength. Parabolic or higher order interpolation or equivalent spectral domain processing can then be implemented to calculate the time shift to the nearest fraction of the sampling period of the acoustic signals. Method 3

[0137] In this third method, the network of emission transducers 2 can be of the multiplied aperture type or comprise a mixing cavity 4.

[0138] The emitted waves reflect on the surface 21 and are collected by the N ultrasonic receiving transducers 3a. The path of the waves from the surface 21 to the receivers will be considered as being direct without any reflection.

[0139] This method 3 comprises at least one calibration step (preliminary, and which can be repeated at regular intervals to recalibrate) where the impulse responses hÿ(t) between the emitting ultrasonic transducers TEi and the receiving ultrasonic transducers TRj are determined. After a Fourier transform, these impulse responses are denoted H;j (the angular pulsation co is omitted to simplify the calculations). This preliminary step can optionally be carried out by having each emitting ultrasonic transducer TEi emit a pulse successively, as in method 2 above.

[0140] This preliminary step is followed by several successive measurement steps, indexed by an index k. During each measurement step k, the incident wave is focused successively on the different points P of the surface 21, which points P have for example been determined during the preliminary step.

[0141] These successive focusings are carried out as follows.

[0142] Following the time reversal process and using the principle of reciprocity, by having transmitter i emit the temporally reversed impulse response (therefore in the frequency domain, H;j*, where the exponent * denotes the complex conjugate) we should obtain the following response: R;j = H;j H;j* = IHJ2. The response R;j is real and corresponds to an impulse centered on the origin of times. Following this observation it is therefore possible to send an impulse to any of the receivers j with a certain delay by simply emitting the temporally reversed and delayed impulse response.

[0143] In fact, it is possible to transmit any wavefront to all receivers from a single transmitter i. This wavefront is simply described by an arrival delay noted Tj at receiver j. To do this, it is sufficient to combine the signals before having them retransmitted by the ultrasonic emission transducer TEi: 101441

[0145] where Ej is the signal emitted by the ultrasonic emission transducer TEi, in the frequency domain.

[0146] It is therefore possible in particular to synthesize a spherical wave front arriving at the level of the receiving ultrasonic transducers TRj, coming from a divergence center constituted by a point P on the surface 21. In other words, the incident ultrasonic wave can be focused at the point P on the surface 21.

[0147] This wavefront synthesis is further reinforced when all the TEi ultrasonic emission transducers emit the signals necessary for the synthesis of the same wavefront. In matrix notation, the signals emitted by all the TEi ultrasonic emission transducers can be written in the following form:

[0148]

[0149] At the level of the receiving ultrasonic transducers TRj, the signals received are: J *^£3-1 * M

[0151] In matrix form this boils down to:

[0152]

[0153] All the signals received by the different ultrasonic reception transducers TRj can be combined after focusing at point P of the surface 21, by carrying out channel formation in reception (beamforming) thanks to the compensation of the delays of the signals received before their summation:

[0154] Sk = ^Rje+jœTl= _ e^T^R^R^

[0155] The index k designates the measurement step, that is to say a succession of shots of incident waves successively focused on the different points P considered on the surface 21.

[0156] In matrix notation, focusing at point P in transmission and channel formation in reception is summed up in the following single signal:

[0157] St = TR = THE = THHT'TT'(ll)

[0158] The superscript T* indicates that the matrix is ​​conjugate transpose.

[0159] The signal Sk mainly represents the information collected at point P.

[0160] When this point moves between measurement step k and measurement step k+1, this results in a phase shift q> between Sk and Sk+i.

[0161] This phase shift q> makes it possible to go back to the displacement ô of the surface 21 at the point P by the aforementioned formula (2), or to the displacement speed V as explained in method 1, during at least one step of movement determination.

[0162] It will be noted that the above calculations of the third method could be done similarly in the time domain rather than in the frequency domain. Conversely, the calculations of methods 1 and 2 could also possibly be done in the frequency domain.

[0163] In the different methods envisaged, depending on the applications, the values ​​of ô and V could be values ​​proportional to the above-mentioned formulas, a. Variant

[0164] The reception channel formation can optionally be carried out with a mixer, as explained in the following documents:

[0165] - Nicolas Quieffin, Stefan Catheline, Ros Kiri Ing and Mathias Fink, “Acoustic source localization model using in-skull reverberation and time reversal", Applied Physics Letters vol. 90, 063902 (2007);

[0166] N. Etaix, M. Fink and RK Ing, “Acoustic imaging device with one transducer”, J. Acoust. Soc. Am. 131 (5), pp. EL395-EL399, 2012;

[0167] N. Etaix, J. Dubois, M. Fink and RK Ing, “Increasing the modal density in plates for mono-element focusing in air”, J. Acoust. Soc. Am., Vol. 134 (2), pp. 1049-1054, 2013.

[0168] Figures 4 and 5 show an example of mapping of the movement speeds and displacements measured by the method according to the invention on the surface 21 of the bottom of the sternum of the human body, vibrated by heartbeats. Figures 6 and 7 show the evolution over time of the movement speeds and displacements measured by the method according to the invention on the same solid surface 21.

[0169] The invention is therefore particularly useful for the analysis of surface movements of the human body, in particular for the study of respiratory movements or the cardiovascular system.

[0170] The invention is particularly advantageous, notably in the study of pulmonary ventilation, since it makes it possible to trace variations in lung volume and therefore the flow rates of inspired / expired air without disturbing the subject, unlike methods involving, for example, a mouthpiece or a face mask.

[0171] The invention also makes it possible to automatically monitor a patient's breathing, for example in intensive care, when waking up from anesthesia, in the emergency room waiting room, or for at-risk infants, etc.

[0172] Outside the medical field, the invention can also make it possible, for example, to to detect early on when a person is falling asleep, to detect when a person is stressed, etc.

[0173] Finally, outside the medical field, the invention can also make it possible to detect objects fixed to the skin and hidden by a fabric. By exciting the subject and more particularly the observed area, the surface movement of the skin will be disturbed by the hidden object(s) and will be observable by the device claimed in this document.

[0174] The system and method according to the present disclosure improves the method described above.

[0175] In particular, the system further comprises an optical device 30 connected to the control device 5, and configured to establish at least one topography of the surface 21. This optical device 30 has a field of vision CV within which it captures a set of location points L situated on the surface 21 (see [Fig.l]).

[0176] By topography, we mean a three-dimensional (3D) representation of the surface 21; that is to say at least the set of location points L of this surface 21 captured by the optical device 30, said points being defined by coordinates in a reference frame, either a reference frame of the optical device 30, or a reference frame of the ultrasound device 1, or any other common reference frame.

[0177] The optical device 30 is for example a camera providing at least one piece of depth or distance information from said camera.

[0178] The optical device 30 operates in an optical wavelength band that can start from infrared (0.1 mm), to the visible band (700 nm to 400 nm), and up to ultraviolet (400 nm to 10 nm), therefore in an extended optical wavelength band.

[0179] The optical device 30 is for example a depth-sensing camera (3D camera), such as the Intel® RealSense™ D415 camera. This type of camera uses two image sensors to obtain stereoscopic vision, with or without infrared projection. It provides:

[0180] - a depth image, i.e. an image whose pixel values ​​cor correspond to a depth distance between the plane of the depth-sensing camera and the considered location point of the space in front of the camera, and

[0181] - an optical image, that is to say an image whose pixels correspond to a light intensity or color of the point considered.

[0182] The optical device 30 is for example a LiDAR camera (LiDAR for “Light Detection And Ranging” in English), such as the Intel® RealSense™ LiDAR Camera L515. This type of camera uses a spatial scanning laser and a photo-detector to obtain a distance between said optical device and location points in the space in front of it. This LiDAR camera operates for example by time-of-flight measurement or by laser beam interferometry. It provides point clouds with 3-dimensional coordinates, and possibly an optical image of the light intensity and / or color of the points in the cloud.

[0183] Therefore, the optical device 30 provides location points with three-dimensional coordinates in a reference frame. This information forms the topography of the surface 21.

[0184] The positions of the transmitting ultrasonic transducers 2a, the positions of the receiving ultrasonic transducers 3a, the positions of the measuring points P, and the positions of the localization points are expressed in a reference frame as mentioned above, such as a reference frame of the ultrasonic device 1, or a reference frame of the optical device 30, or any other predefined common reference frame, and can be easily transformed into coordinates of any reference frame, for example by storing in the central memory 7 the relative positions and relative orientations of the ultrasonic device 1 and the optical device 30. Reference frame change matrices are determined for this task.

[0185] In the case of using the reference frame of the ultrasonic device 1, the control device 5 is able to transform the coordinates of the location points captured by the optical device 30 into coordinates in a reference frame of the ultrasonic device 1, and records them in the central memory 7. In the case of using the reference frame of the optical device 30, the control device 5 is able to transform the coordinates of the measurement points into coordinates in the reference frame of the optical device 30.

[0186] In all cases and for any reference system, this position information allows the control device 5 to calculate the distances (and therefore the delays) necessary for calculating the track formation.

[0187] Optionally, the optical device 30 can be calibrated to determine calibration parameters of said optical device 30, and thus provide precise coordinates of location points of the environment (space) around the optical device 30.

[0188] Optionally, the ultrasonic device 1 is capable of modifying the coordinates of the positions of the ultrasonic transducers stored in the central memory 7, manually by a user or automatically, for example by detecting the material of said transducers.

[0189] Furthermore, the optical device 30 advantageously has a spatial resolution of less than X / 10, where / . is the ultrasonic wavelength (incident or reflected ultrasonic wave) of the ultrasonic device 1. Optionally, this spatial resolution is less than / . / 20. For example, the wavelength / . of the ultrasonic wave is between 1 mm and 10 mm. Thus, in this case, the spatial resolution of the optical device 30 is between 0.1 mm and 1 mm.

[0190] Furthermore, the optical device 30 is capable of providing a number of three-dimensional location points of the order of at least 1000 points, at a rate of at least once per second. The number of location points and the capture rate of the optical device 30 is adapted to the application. The number of location points of the optical device may be greater than 100,000 points. The rate may be greater than 10 Hz, and possibly up to 100 Hz.

[0191] The acquisition rate of the optical device 30 is much lower than the rate of the ultrasonic device 1. The optical device 30 is intended to obtain the topography of the surface 21 and its slow or very slow changes. The ultrasonic device 1 is intended to obtain the movements (vibrations) of the surface 21 at high frequency in a precise manner. For example, the movements, vibrations of the surface can be determined up to 100 Hz or even 600 Hz, with an accuracy of the order of a micrometer (pm).

[0192] For example, the optical device 30 has a resolution of 640x480 points, which corresponds to more than 300,000 acquisition points in three dimensions.

[0193] In contrast, the number of measuring points P of the ultrasonic device 1 is for example 30x40 points, or only 1200 points.

[0194] The number of location points of the optical device 30 is much greater than the number of measurement points P of the ultrasonic device 1. Thus, measurement points P of the ultrasonic device 1 will be chosen corresponding to location points of the optical device 1. The control device 5 will focus each measurement point P on selected location points coming from the optical device 30 or determined from the location points. This focusing is carried out by one of the three methods presented previously. And for which distances or delays are determined. This focusing is obtained by channel formation.

[0195] It should be noted that the incident ultrasonic wave is advantageously a signal of the periodic pseudo-random type, with a wide frequency band. This frequency band is however limited by the frequency capacities of the ultrasonic transducers in emission 2a. Thus, the wavelength X cited above is understood as the longest wavelength of said frequency band, or an average wavelength of this frequency band, or any other definition in this frequency band.

[0196] In particular, each ultrasonic transmitting transducer emits a periodic pseudorandom signal distinct from the other ultrasonic transmitting transducers. In other words, the signals from the ultrasonic transmitting transducers are decorrelated from each other. However, these signals from the ultrasonic transmitting transducers may have equivalent or identical frequency band to each other.

[0197] Alternatively, the incident ultrasonic wave is a sinusoidal signal evolving in frequency, called “chirp” type, which is also of wide frequency band.

[0198] Then, in the method of the present disclosure, the control device 5 further implements the following steps:

[0199] - a topography of the surface 21 is determined by the optical device 30 before the measurement steps, and

[0200] - the track formation signals are determined during the measurement steps from also from the topography of surface 21.

[0201] Thus, the track-forming signal for each measuring point P and the movements (vibrations) of the surface for each measuring point P are determined more precisely. The determined movements have fewer outliers, the accuracy of the movements is no longer a function of the position of the measuring point P on the surface 21. The measured movements of the surface 21 are then more reliable.

[0202] The measurement points P are then determined from the location points of the topography. Thus, the three-dimensional coordinates of the measurement points are defined precisely, and without the assumption that the surface 21 is a plane, or another shape.

[0203] According to a first variant, the measurement points P are determined by choice from among the location points of the topography. Indeed, as already explained, in current applications, the number of measurement points P is much lower than the number of location points on the topography.

[0204] According to a second variant, the measurement points are determined by interpolation of location points of the topography. In particular, a grid or matrix of desired points can be established, for example by projection onto the surface 21, and the coordinates of these projected points are determined by interpolation of the coordinates of neighboring points.

[0205] The control device 5 can then calculate the distance between each determined measuring point P and an emitting and / or receiving ultrasonic transducer thanks to the knowledge of the coordinates of the positions of the transducers. It can also calculate delays by assuming constant speed of the ultrasonic wave.

[0206] More precisely, the various signal processing methods, the control device 5 then calculates:

[0207] - the distance dj between each measuring point P and a transducer Rj, by difference recorded contact details, and / or

[0208] - the arrival delay Tj of the ultrasonic wave at the receiving transducer j by the calculation of the flight time of this ultrasonic wave with a speed c of the ultrasonic wave in the air assumed to be constant, and therefore:

[0209] Tj =dj / c. (12)

[0210] Thus, the track formation parameters, i.e. the delays for track formation are determined from the topography of the surface 21.

[0211] According to one embodiment of the method, the topography of the surface 21 is determined by the optical device 30 repeatedly and possibly periodically during the measurement steps.

[0212] In particular, all of the steps of measuring and determining the movement of the surface 21 are repeated, for example periodically, over time. The system may further comprise a screen 12b configured to display an image or representation or mapping of the movements of the surface 21. Thus, the system may display on this screen the evolution of the mapping over time. This display may also be in real time.

[0213] In this context, the step of determining the topography is also carried out repeatedly, and for example periodically, and in a temporally interlaced manner with the steps of measuring and determining the movement of the surface.

[0214] Thus, the track formation signals can be determined from the last measured topography, temporally.

[0215] The rate of the step of determining the topographies (topography rate) may be lower than the rate of the steps of measuring and determining movement (measurement rate, i.e. acoustic measurement rate). Indeed, the surface 21 does not need to be known too precisely, and in current applications, only slow movements / displacements need to be known to measure the movements (vibrations) of the surface 21.

[0216] The rate of the topographies is for example ten times lower than the rate of the movement maps of the surface 21. Possibly, the rate of the topographies is twenty or thirty times lower than the rate of the movement maps of the surface 2.

[0217] According to one embodiment of the method, the plurality of topographies determined by the optical device 30 is used to determine slow movements of the surface 21, and in particular movements slower than the movements determined by all of the acoustic steps of measurement and determination of movement.

[0218] Very low frequency maps of the movements of the surface 21 can thus be determined from only the repeated successive topographies, and obtained by the optical device 30. Such slow movement information and low frequency maps cannot be obtained by the acoustic device 1, and all of the steps of measuring and determining acoustic movement. Thus, the optical device 30 advantageously completes the device acoustics 1.

[0219] According to one embodiment of the method, before the measuring steps, the topography determination step is repeated and the surface 21 is moved until the position of the surface 21 relative to the emission device 2 is optimal relative to a predetermined optimal position.

[0220] Conversely, the emission device 2 can be moved until the position of the surface 21 relative to the emission device 2 is optimal relative to a predetermined optimal position.

[0221] Thanks to this arrangement, the system is capable of optimally positioning the ultrasonic device 1 relative to the emission device 2, or vice versa, to improve the determination of the movements of the surface 21.

[0222] In particular, the optimal position may be centered relative to the emission device 2, in one or more directions. For example, the surface may be moved in height (Z direction in [Fig.8]) or transversely (Y direction in [Fig.8]) or in depth (X direction in [Fig.8]).

[0223] The system may comprise, for example, a topography model of the expected surface 21 in order to determine the optimal position, by minimizing a distance between the measured topography and the topography model. The topography model is, for example, pre-stored in the central memory 7. Optionally, a library of topography models is stored in the central memory 7 or in any storage system. A particular topography model may be selected from the library, automatically or by a user for this step of optimizing the position of the surface 21.

[0224] The system may further comprise one or more displacement actuators for positioning the surface 21 relative to the emission device 2.

[0225] Optionally, the surface 21 is moved manually relative to the emission device 2. For example, the surface is a part of a human body. The person is possibly seated on a seat whose base is capable of being moved vertically or in another direction. Similarly, the person is possibly lying on a platform capable of being moved.

[0226] Further, the system may include logic to indicate to the person or other user when the optimal position is reached. An optimal distance level may optionally be set in the system to determine that the predetermined optimal position is reached. Thus, when the distance between the surface 21 and the transmitting device 2 is less than the optimal distance level, the system indicates by an acoustic or visual signal that the setting is correct and the method can proceed to the measurement steps.

[0227] This transition to the measuring steps can be operated by the person or another user. lizer, manually or automatically as soon as the optimal position is found.

[0228] By "distance" is meant a measurement of a single distance between the surface 21 and the emission device 2, or a combination of distances between the surface 21 and the emission device 2, or an average or any calculation of distance between the surface 21 and a topography model, i.e. a distance between two surfaces in 3 dimensions (3D).

[0229] The acoustic system and device 1 are particularly useful for analyzing surface movements of the human body, in particular for studying respiratory movements or the cardiovascular system.

[0230] [Fig.8] thus shows an example of use of the acoustic system and device 1 according to the present disclosure, and used to measure the movements (vibrations) of a surface 21 corresponding to a thorax or a back of a person.

[0231] In this three-dimensional figure, emission transducers 2a are distributed in a quasi-cylindrical configuration and at a distance from the person. Reception transducers 3a are located in an area substantially facing the person. The optical device 30 is also facing the person.

[0232] The optical device 30 determines a topography comprising numerous location points L on the surface 21 of the person. These location points L are used by the control device 5 to scan a set of measurement points P acoustically from multiple angles of incidence. The control device 5 then calculates path-forming signals of the measurement points determined from the location points.

[0233] Thanks to this acoustic system and device 1, the movements (vibrations) of the measuring points P on the surface 21 of the person are measured remotely, without contact, precisely and quickly.

[0234] The control device 5 is then able to determine a pathology of the person from the movements of the plurality of measurement points P of this surface 21 by processing these measured movements, and for example by spatial identification of these movements. For example, the system can compare these movements to a library of known movements corresponding to healthy people or people with pathologies. Finally, data processing by classification or by neural network or by artificial intelligence can be carried out to determine the pathology of the person. Partial nomenclature of elements: 1 Ultrasonic system 2 Ultrasonic transmission network 3 Ultrasonic reception network 4 mixing cavity 5 control device 6 digital-to-analog converter 7 main memory 8 signal processing circuit (DSP) 9 buffer memory 10 analog-to-digital converter 11 electronic assembly 12 computer 13 rigid plate 14 bottom 15 side walls 16 emission wall 17 holes 21 surface 30 optical device

Claims

Claims

1. Method for detecting movements of a surface (21) reflecting ultrasonic waves, comprising: several successive measuring steps during each of which at least one incident ultrasonic wave is emitted into the air towards the surface (21) with an ultrasonic wave emitting device (2) and reflected signals representative of at least one ultrasonic wave reflected into the air by said surface (21) from said at least one incident ultrasonic wave are captured, and in which during each measuring step: the movements of a plurality of measuring points (P) belonging at least to said surface are measured by illuminating each measuring point (P) with said at least one incident ultrasonic wave at a multiplicity of angles of incidence, the reflected signals are captured with a receiving transducer array (3) comprising a plurality of receiving ultrasonic transducers (3a),and a path-forming signal is determined for each measuring point (P), by path-forming at least in reception from said reflected signals, a movement determination step during which said movements of the surface (21) are determined at the measuring point (P) in question by determining at least one delay or phase shift between two path-forming signals for this measuring point (P), said method being characterized in that before the measuring steps, a topography of the surface (21) is determined by an optical device, and during the measuring steps, the path-forming signals are determined from the topography of the surface.,

2. Method according to claim 1, wherein the topography comprises location points on the surface (21), the measurement points (P) are determined from the location points.

3. Method according to claim 2, in which the measurement points (P) are determined by choice among the location points, or by interpolation of location points.

4. Method according to one of claims 1 to 3, in which the set of steps of measuring and determining movement is repeated, the topography determination step is repeated in an interleaved manner with all of the measurement and movement determination steps, and the track formation signals calculated in the movement determination step are determined from the last temporally determined topography.

5. The method of claim 4, wherein the step of determining the topographies is performed at a topography rate lower than the measurement rate of the steps of measuring and determining movement.

6. The method of claim 5, wherein the topography rate is at least ten times lower than the measurement rate.

7. A method according to claim 4, wherein the plurality of topographies determined by the optical device (30) is used to determine movements of the surface (21) slower than the movements determined by the set of acoustic steps of measurement and movement determination.

8. Method according to one of claims 1 to 7, wherein before the measuring steps, the topography determining step is repeated and the surface (21) is moved until the position of the surface (21) relative to the transmitting device (2) is optimal relative to a predetermined optimal position, or conversely the transmitting device (2) is moved until the position of the surface (21) relative to the transmitting device (2) is optimal relative to a predetermined optimal position.

9. The method of claim 8, wherein while the topography determining step is repeated, a distance is determined between the surface (21) and the transmitting device (2), and a signal is generated when said distance is less than an optimal distance level.

10. Method according to one of claims 1 to 9, further comprising a step of calibrating the optical device (30) before the first topography determination.

11. The method of claim 1, wherein the incident ultrasonic signal is a periodic pseudo-random signal.

12. System for detecting movements of a surface (21) reflecting ultrasonic waves, comprising: a device (2) for emitting ultrasonic waves, an ultrasonic wave receiving device (3), a control device (5) controlling the ultrasonic wave transmitting device (2) and receiving signals picked up by the ultrasonic wave receiving device (3), and in which: the control device (5) being adapted to carry out several successive measurement steps during each of which the ultrasonic wave emitting device (2) emits at least one incident ultrasonic wave into the air towards the surface (21) and the ultrasonic wave receiving device (3) picks up reflected signals representative of at least one ultrasonic wave reflected into the air by said surface (21) from said at least one incident ultrasonic wave, the ultrasonic wave emitting device (2) is adapted to illuminate a plurality of measurement points (P) belonging at least to said surface (21) by said at least one incident ultrasonic wave under a multiplicity of angles of incidence, the ultrasonic wave receiving device (3) is a receiving transducer array (3) comprising a plurality of receiving ultrasonic transducers (3a), and the receiving transducer array (3) picks up the reflected signals, the control device (5) is adapted to, during each measurement step, determine a channel formation signal for each measurement point (P), by channel formation at least in reception from said reflected signals, the control device (5) is adapted to determine said movements of the surface (21) at the measurement point (P) considered by determining at least one delay or phase shift between two track formation signals for this measurement point (P), and characterized in that the system for detecting movements of the surface (21) further comprises an optical device (30) adapted to measure a topography of the surface (21), and the control device (5) is adapted to measure the topography with said optical device at least before the measuring steps, and the control device (5) is adapted to determine the track-forming signals from the surface topography.

13. The system of claim 12, wherein the optical device (30) is a depth camera or a LiDAR camera.

14. The system of claim 12, wherein the optical device (30) has spatial resolution less than X / 10 of the wavelength of the incident ultrasonic waves or the reflected ultrasonic waves.

15. System according to one of claims 12 to 14, in which the system is used to detect the movements of a plurality of measurement points of a surface, this surface being the thorax or the back of a person.

16. System according to claim 15, wherein the control device (5) determines a pathology of the person from the movements of the plurality of measurement points of said surface.

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