DEVICE FOR CONTACTLESS ELEMENT DETECTION

Description

TECHNICAL FIELD AND PREVIOUS ART

[0001] The invention relates to the field of remote, contactless detection and interaction with one or more elements. More particularly, the invention relates to a device enabling one or more elements to interact with this device without the need for contact between the device and the element(s), as well as a method for controlling such a device.

[0002] A non-contact element detection device determines or characterizes the presence, position, or movement of one or more elements, such as the fingers or hands of one or more users, located at a certain distance from the device. Based on the detection, interaction then becomes possible between the detected element(s) and the device.

[0003] Several technologies exist for creating such a device.

[0004] For example, it is possible to create a non-contact element detection device using the principle of optical capture, employing one or more cameras, lasers, or infrared sensors. However, such a device is highly sensitive to the optical conditions of its environment. Furthermore, when such a device is used to allow the user to interact with virtual 3D objects, the computing power required for its operation is substantial due to the analysis of the captured images. In addition, using lasers for optical capture is an expensive solution. Finally, using infrared sensors for optical capture also presents several drawbacks: significant size, a small detection range, and the need for a large number of sensors to obtain a sufficient representation of the observed area.Privacy concerns may also arise with such a device because optical capture acquires everything around the element(s) to be detected, such as the user's face.

[0005] It is also possible to create a non-contact object detection device using miniature radar. However, the performance obtained is not satisfactory, especially if the object to be detected is not metallic (such as a hand or a finger).

[0006] Non-contact object detection devices using Wi-Fi or shorter electromagnetic waves have also been proposed. However, these solutions require complex external components that could overload the communication network with which the device communicates.

[0007] It has also been proposed to create contactless element detection devices using capacitive matrices. However, these matrices are not very effective beyond a few centimeters between the matrix and the element(s) to be detected, and can be affected by surrounding electric fields.

[0008] Contactless detection and interaction techniques implemented using the microphones and speakers of mobile phones, or smartphones, have also been proposed. Some of these techniques detect gestures by measuring frequency shifts and phase perturbations induced by movement on acoustic waves emitted by the phone's microphone(s). Prior training allows different gestures to be associated with the perturbations induced by the user's actions on the emitted acoustic waves. However, these techniques do not allow for precise localization of the element(s) to be detected if they are stationary, and therefore cannot, for example, detect the manipulation of virtual 3D objects or the movement of a virtual cursor. Furthermore, the detected gestures must necessarily be predefined by the device manufacturer.Other techniques allow tracking the movement of a detected element and locating it in space through triangulation, time-of-flight tracking, phase shift analysis, or impulse response analysis. However, the resulting measurements are not very precise, and trajectory reconstruction generally requires correction using the Doppler effect or phase-change tracking, which allows for determining the direction, speed of movement, and distance traveled. These techniques do not improve the detection of quasi-static interactions (i.e., those with low-amplitude movement), making such movements difficult to measure, and they cannot distinguish between multiple elements detected simultaneously, such as several fingers of a user.

[0009] Compared to the systems previously listed, ultrasonic remote sensing technology has many advantages: compactness of the components used, insensitivity to optical conditions of use, ability to operate through opaque surfaces, limited computing power required, no privacy issues, ability to detect many materials (few materials do not reflect acoustic waves), insensitivity to electromagnetic interference.

[0010] The paper by Yun, S. et al., "Strata: Fine-grained acoustic-based device-free tracking," 2017, Proceedings of the 15th Annual International Conference on Mobile Systems, Applications, and Services, pp. 15-28, describes an algorithm that allows a smartphone to detect the position and trajectory of a finger without contact, in real time. By using the smartphone's two microphones, this algorithm can track the trajectory of a finger in a two-dimensional plane at a certain distance from the smartphone.However, this solution has several drawbacks: the need to define in advance a range of possible interaction distance between the finger to be detected and the smartphone, the need for finger movement, the impossibility of detecting and distinguishing between several fingers, the unrobustness of the solution because the determination of the finger's position is obtained by performing an optimization involving the phase shift, itself dependent on the choice of the reflection path which depends on the absolute position of the finger, the tracking of the finger's trajectory is only possible in the chosen two-dimensional plane.

[0011] The document Etaix, N. et al., "Acoustic imaging device with one transducer", The Journal of the Acoustical Society of America 131, 2012, EL395-EL399, describes a detection technique using a time-reversal process for 3D imaging. Several piezoelectric actuators are arranged on a so-called "chaotic" metal plate with randomly drilled cavities. A known signal is generated by each actuator, and the corresponding step response at each point on the plate's surface is measured with a vibrometer. The time-reversal process is applied to the signals, which are then modified by a mathematical function. By applying these new signals to the actuators, acoustic waves are focused onto a chosen point in space. A plane is then scanned at a chosen altitude, and the echo is observed using a microphone.A time window corresponding to the theoretical time it would take for a potential echo to return to the microphone after reflection at a distance D from the plate is chosen. By measuring the maximum amplitude of the sound within this time window, the presence or absence of an object at distance D, located at the chosen focus coordinates, is determined. In this document, the plane located at distance D from the plate is scanned by focusing the acoustic waves point by point and then analyzing each time window. Furthermore, several planes must be fully scanned point by point to obtain a complete 3D image of the environment. This results in a very long acquisition time. DESCRIPTION OF THE INVENTION

[0012] One aim of the present invention is to propose a non-contact detection device based on the use of ultrasonic acoustic waves and not presenting the disadvantages mentioned above, that is to say, which is capable of interacting via a detection of the position and / or movement of one or more elements simultaneously, these elements being able or not to be in planes located at different distances from the device, and this with a short acquisition time.

[0013] To this end, the present invention proposes a contactless detection device, comprising at least: a detection surface; several actuators, for example piezoelectric, acoustically coupled to the detection surface and configured to emit ultrasonic acoustic waves; an ultrasonic acoustic wave detector; an electronic and / or computer processor; the device being configured to perform a detection of one or more elements by implementing several times the following steps: focusing ultrasonic detection acoustic waves emitted by the actuators via the detection surface into a focal region belonging to a plane opposite the detection surface, by applying to the actuators control signals calculated by the electronic and / or computer from a measurement of an audio impulse response and / or a vibrational impulse response of the detection surface, generated by an emission of calibration ultrasonic acoustic waves by each of the actuators, and the application of a first time-reversal process to the audio impulse response and / or the vibrational impulse response of the detection surface,then measurement of the time interval between the emission of ultrasonic detection waves and the reception of an echo of the ultrasonic detection waves by the ultrasonic wave detector; wherein the electronic and / or computer system is configured to calculate the control signals such that the ultrasonic detection waves are successively focused into focal regions of different shapes and / or dimensions.

[0014] This device proposes to perform a detection of one or more elements based on the use of acoustic focusing obtained through the principle of time reversal applied to ultrasonic acoustic waves (wavelengths between 16 kHz and 10 MHz) emitted from a detection surface, flat or not, in order to locate the element(s), for example at least one finger or hand of a user, in the space in front of this detection surface.

[0015] Determining the position of the element(s) is based on measuring the time it takes for focused acoustic waves to be emitted and then return as an echo. Estimating the position of the element(s) is done in three dimensions using the echo of the focused waves, which allows us to determine the presence of the element(s) to be detected within the focal region (which lies in a two-dimensional plane), and by measuring the time delay between wave emission and echo reception, which allows us to determine the distance between the detected element and the ultrasonic acoustic wave detector, which is advantageously located in the same plane as the detection surface.

[0016] Thanks to the focusing of ultrasonic acoustic waves in several different focusing regions, several fingers can be detected independently.

[0017] This location can then be used to enrich the ways of interacting with the device, without contact with it.

[0018] By judiciously choosing the characteristics (dimensions and / or shapes) of successive focal regions of ultrasonic acoustic waves, it is possible to considerably reduce the acquisition time by judiciously traversing different regions of the space in which the element(s) to be detected are located, by varying for example the size of the focal regions and the distance reached by the focused ultrasonic acoustic waves, and by performing dynamic target tracking.

[0019] The term "focal point" refers to the point where ultrasonic acoustic waves are focused and converge.

[0020] The detection performed by the device can be static because it does not involve comparing signals between two distinct moments. It can also be quasi-static (slight movement of the element(s) to be detected) or dynamic.

[0021] This device can be advantageously used to increase the capabilities of interactive systems by going beyond touch interaction, to enable gestural and contactless interaction.

[0022] The device can be advantageously used to perform multi-finger detection of a user.

[0023] This device can allow real-time interaction from a user.

[0024] This device is not sensitive to optical conditions of use and is robust against electrical disturbances.

[0025] This device is capable of performing detection at a significant distance, for example up to approximately 1 meter from the detection surface.

[0026] This device also has the advantage of being able to operate with low electronic or computer processing power because it does not use image processing methods to locate the object(s) to be detected. This device directly retrieves the position of the nearest object(s) that have reflected an echo of the ultrasonic acoustic waves.

[0027] This device also has the advantage of preserving privacy, because it does not capture images, it operates at ultrasonic frequencies and the acquired data is processed locally.

[0028] This device can be advantageously used for low-dynamic-range multi-finger interaction. Indeed, the device generates virtual audio sources by focusing ultrasonic acoustic waves. The number of virtual ultrasonic sources generated can be significant, thus increasing the accuracy of locating the elements to be detected. Furthermore, thanks to the focusing, the energy of all actuators is concentrated in the focal region, which increases the amplitude of the reflected signal (echo) and therefore simplifies detection. By focusing the waves in the focal region, the area under study is isolated from all unwanted reflections, whose amplitude will be much lower. The detection performed by the device in the focal region is therefore not disturbed by elements outside this region.

[0029] Each finger can, for example, be detected independently. Furthermore, even if these fingers are stationary, the device knows the position of the region on which it is focusing. If it receives a response, it associates a precise position with the detected finger. The distance to the finger can be measured even more accurately by measuring the time between the emission of the ultrasonic detection waves and the reception of their echo.

[0030] Focusing ultrasonic acoustic waves from multiple piezoelectric actuators increases the amplitude of the received echo, making it easier to detect and distinguish from any spurious echoes.

[0031] This device therefore forms an easily integrated and inexpensive solution allowing interaction with a large workspace.

[0032] The potential applications of such a device are advantageously related to human-machine interfaces (HMIs), such as contactless interactive displays, vehicle dashboards, building switches, and interactive tables. The device can also be used for contactless interaction with computers, tablets, or smartphones. Possible functions include manipulating virtual 3D objects, using contactless interactive displays (which is beneficial from a health and hygiene perspective), and interacting with a dashboard in a confined space.

[0033] This device can also be used for other types of applications, such as in industrial fields of 3D object localization for robotic control or geometry control of parts, or for system applications such as vehicle reversing radars or adjusting the orientation of a vehicle relative to targets.

[0034] For example, this device can allow for the simple, compact, and inexpensive integration of control buttons into a vehicle dashboard or a piece of audio equipment. The proposed device allows for the integration of a large number of virtual buttons and toggles within a small, reconfigurable space, creating an interactive volume in front of the dashboard.

[0035] The device can allow perceptual functions to be added to a robot, in the case of difficult environments (for example low or poorly controlled lighting, or observation of poorly textured or transparent objects, or presence of many obstructions).

[0036] The element(s) detected by the device can be of any shape and composed of any material that does not absorb ultrasonic acoustic waves.

[0037] In the fields of mobile phones and computing, contactless detection can be used to add a dimension of interaction, facilitate 3D manipulation, or enable interactions through user gestures. Examples of applications for this technology include: interact with a background application (e.g., music, camera) or activate brief functions (e.g., flashlight, volume); interact with the usual user interface but without contact (e.g., when hands are wet or dirty, or the device is not within the user's reach); enhance application interaction functions (e.g., zoom, rotate, tilt, translate an image, drag and drop files, copy and paste text, etc.); enhance interactivity in video games.

[0038] A smartphone or a computer device equipped with such a device can also be used directly as a 3D measurement system during a virtual or augmented reality activity, to scan objects in 3D, or any other 3D imaging application.

[0039] In the automotive sector, the device can be used to replace buttons and touchscreens, or to enable interaction via gestures. The interactive device can be integrated directly into a vehicle's dashboard.

[0040] In the field of industrial robotics, this device can be used to allow an industrial robot arm to 3D scan its approach area as close as possible to obstacles (sensor placed on the end effector) while avoiding obstructions if the sensor is centralized.

[0041] In the field of construction / agricultural machinery, this device can improve the functionalities of a reversing / approach radar to take into account the context surrounding the machine (geometry of objects approached to better position itself).

[0042] The calibration process, which allows the calculation of the actuator control signals to emit the ultrasonic acoustic detection waves, can be done in several ways: measurement, near or at a certain distance from the detection surface, of the audio impulse response generated by the emission of the ultrasonic calibration acoustic waves, then application of the first time reversal process to this measured audio impulse response, and / or measurement of the vibrational impulse response of the detection surface generated by the emission of the ultrasonic calibration acoustic waves, then application of the first time reversal process to this measured vibrational impulse response.

[0043] The closer the audio impulse response is measured to the detection surface, the more precisely the radiating part of the calibration ultrasonic acoustic waves is measured (which results in less information loss), and the more precise the focusing of the subsequent detection ultrasonic acoustic waves.

[0044] The vibrational impulse response of the sensing surface can be measured by a vibrometer, for example a laser vibrometer.

[0045] The actuators can be piezoelectric actuators. Alternatively, the actuators can be of a different type than piezoelectric if they have a broadband frequency response, such as electrostatic actuators.

[0046] The detection surface can correspond to one face of a material plate, and the actuators can be attached to a second face, opposite the first, of the material plate. This configuration facilitates the integration of the detection device, as the actuators are attached behind the surface to be instrumented.

[0047] The plate forming the detection surface may be made of glass and / or plastic and / or metal. The material(s) of the plate may be transparent or opaque. The plate may be flat or curved, for example.

[0048] The material plate may have a thickness between 0.1 mm and 3 mm and / or may comprise a material whose Young's modulus is between 50 GPa and 300 GPa, and / or may be such that a ratio of its density to the Young's modulus of the plate material is between 20.10 -8< kg / mN and 50.10 -8< kg / mN. Such characteristics make it possible in particular to guarantee good transmission of ultrasonic acoustic waves through the plate to the air.

[0049] The ultrasonic acoustic wave detector may include at least one microphone and / or acoustic transducers arranged on the detection surface. The acoustic transducers may be piezoelectric actuators separate from the actuators configured to emit the ultrasonic acoustic waves for detection.

[0050] Alternatively, the ultrasonic acoustic wave detector can be formed by actuators, for example piezoelectric ones, configured to emit ultrasonic acoustic waves and which are also capable of performing acoustic transduction. This variant is advantageous because it allows for very good integration of the device.

[0051] Furthermore, in this variant, the electronic and / or computer system can be configured to apply a second time-reversal process to the echo of the ultrasonic acoustic detection waves received by each of the actuators. In this case, the element to be detected, on which the focused wave is reflected, is considered a sound source. The system, knowing the signal emitted by this virtual source as well as the impulse response linking the vibrations in the plate to all points within the observable volume, can therefore locate the virtual source by measuring the vibrations in the plate and applying the time-reversal principle. The application of this second time-reversal process allows for the addition of location information to the data regarding the presence or absence of a reflector in the focusing zone.This variant can be advantageously used when the size of the acoustic focal spot—that is, the area where the acoustic waves converge—is large during preliminary detection. This allows for a more precise selection of the future detection zone in which the acoustic waves will be focused. Consequently, this improves the localization accuracy and detection speed of the device.

[0052] The actuators can be configured to emit ultrasonic acoustic waves with frequencies ranging from 20 kHz to 100 kHz. This range is sufficiently far removed from the range of frequencies audible to humans, thus preventing any discomfort for the device's user.

[0053] The electronic and / or computer-based system can be configured to measure the frequency shift between the emitted ultrasonic detection waves and their echoes, and to calculate the velocity of the detected element(s) based on this measured frequency shift. This velocity is determined along the direction between the detected element(s) and the ultrasonic wave detector using the Doppler effect.

[0054] The electronic and / or computer-based system can be configured to encode the control signals prior to the emission of ultrasonic acoustic waves. This encoding can be performed so that the focused wave has a known frequency content, a discrete phase or frequency variation, or a frequency modulation. In this case, the detection device is more robust thanks to the decoding of the echo waves, which allows it to verify that this signal is indeed correlated with the emitted signal and that it is not generated by ambient noise.

[0055] The invention also relates to a contactless interaction device, comprising at least one contactless detection device as described above, and configured to perform one or more actions based on a result of the detection performed by the contactless detection device.

[0056] The contactless interaction device can form a human-machine interface comprising a display surface to which the detection surface of the contactless detection device is attached.

[0057] The invention also relates to a method for controlling a contactless detection device as described above, comprising the implementation of the following steps: calculation, by the electronic and / or computer computer, of the control signals from a measurement of an audio impulse response and / or a vibrational impulse response of the detection surface, generated by an emission of the calibration ultrasonic acoustic waves emitted by each of the actuators, and the application of a first time-reversal process to the audio impulse response and / or the vibrational impulse response of the detection surface, then application of the calculated control signals on the piezoelectric actuators, focusing the ultrasonic detection acoustic waves emitted by the piezoelectric actuators into a focusing region belonging to a plane opposite the detection surface,then measurement of the time between the emission of the ultrasonic detection waves and the reception of an echo of the ultrasonic detection waves by the ultrasonic wave detector; and in which these steps are repeated several times such that the calculated control signals focus the ultrasonic acoustic detection waves successively into focusing regions of different shapes and / or dimensions.

[0058] The process may also include calibration of the non-contact detection device involving the implementation of the following steps: emission of ultrasonic calibration acoustic waves by each of the piezoelectric actuators; measurement of an audio impulse response and / or a vibrational impulse response of the detection surface generated by the emission of the ultrasonic calibration acoustic waves; application of the first time-reversal process to the audio impulse response and / or the vibrational impulse response of the detection surface; storage of the signals obtained by applying the first time-reversal process to the audio impulse response and / or the vibrational impulse response of the detection surface.

[0059] The method can advantageously be implemented to detect a position or movement of one or more fingers of a user of the detection device. BRIEF DESCRIPTION OF THE DRAWINGS

[0060] The present invention will be better understood upon reading the description of exemplary embodiments given by way of illustration only and in no way limiting, with reference to the accompanying drawings in which: there figure 1 schematically represents a non-contact detection device according to a particular embodiment; the figure 2 schematically represents the operating principle of the contactless detection device according to the specific embodiment; figure 3 represents the spatial distribution of the focusing obtained at different distances from the detection surface of the non-contact detection device, for the same emission of acoustic waves focused at the same focal point; the figure 4 represents several echoes of ultrasonic acoustic waves obtained for the same wave emission, when these waves are reflected by objects located at different distances; the figure 5represents a contactless interaction device according to a particular embodiment.

[0061] Identical, similar or equivalent parts of the different figures described below bear the same numerical references in order to facilitate the transition from one figure to another.

[0062] The different parts represented in the figures are not necessarily shown on a uniform scale, in order to make the figures more legible.

[0063] The different possibilities (variants and modes of implementation) should be understood as not being mutually exclusive and can be combined with each other. DETAILED DESCRIPTION OF SPECIFIC METHODS OF IMPLEMENTATION

[0064] A non-contact detection device 100 according to a particular embodiment is described below in connection with the figure 1 .

[0065] The device 100 comprises a plate of material 102, a first face 104 of which forms a detection surface for the device 100. The plate 102 is, for example, made of glass, plastic, or metal. The plate 102 has, for example, a thickness between 0.1 mm and 3 mm and / or is made of a material with a Young's modulus between 50 GPa and 300 GPa and / or is such that the ratio of its density to the Young's modulus of the material of the plate 102 is between 20 × 10⁻⁸ kg / mN and 50 × 10⁻⁸ kg / mN

[0066] The plate 102 is here fixed to a frame 103. When the device 100 is intended to be fitted to the front face of a screen, the plate 102 may include a transparent material so that the screen remains visible through it, when the piezoelectric actuators 106 described later are arranged around the periphery of the plate 102,

[0067] According to a particular example of implementation, the dimensions of plate 102 are, for example, equal to 156 mm x 76 mm, with a thickness equal to 0.5 mm.

[0068] Plate 102 can be flat or not, for example curved.

[0069] The device 100 also includes several actuators 106 acoustically coupled to the sensing surface and configured to emit ultrasonic acoustic waves. Advantageously, the actuators 106 are piezoelectric actuators. Alternatively, the actuators 106 can be electrostatic.

[0070] In the particular embodiment described here, the actuators 106 are attached, for example by gluing, to a second face, opposite the first face 104, of the plate 102. Furthermore, in the particular embodiment described here, the actuators 106 are attached to the plate 102 near its edges. Alternatively, the actuators 106 may be positioned at any point on the second face of the plate 102. In another variant, the actuators 106 may be positioned on the side of the first face 104 of the plate 102, that is, on the side of the sensing surface.

[0071] According to one embodiment, each piezoelectric actuator 106 comprises a portion of piezoelectric material, for example PZT, arranged between at least two control electrodes for applying a potential difference to the portion of piezoelectric material. For example, each piezoelectric actuator 106 may comprise a portion of PZT in the form of a strip measuring 70 mm x 10 mm x 0.2 mm, to which 16 electrodes are coupled for actuating this PZT strip.

[0072] In general, the number of first actuators 106 acoustically coupled to the detection surface of the device 100 is, for example, between 1 and 32, or even more depending on the actuation electronics of the device 100. The greater the number and dimensions of the actuators 106, the greater the power of the signal emitted by the device 100, and the better the focusing resolution obtained.

[0073] The piezoelectric actuators 106 are configured to emit ultrasonic acoustic waves with frequencies advantageously between 20 kHz and 100 kHz.

[0074] Device 100 also includes an electronic and / or computer calculator 108, symbolically represented on the figure 1 by a rectangle designated by reference 108. One of the functions of this calculator 108 is to calculate control signals intended to be applied to the piezoelectric actuators 106.

[0075] The device 100 also includes an ultrasonic acoustic wave detector 110. This detector 110 is intended to capture the echo of the ultrasonic acoustic waves that will be emitted by the piezoelectric actuators 106 through the plate 102. In the particular embodiment described here, the detector 110 includes at least one microphone disposed near the plate 102.

[0076] Alternatively, the detector 110 can correspond to additional piezoelectric actuators distinct from the actuators 106 and arranged on the detection surface of the device 100, on the side of the first face 104 of the plate 102 or on the second face opposite to the first face 104. According to another variant, the detector 110 can be formed by the piezoelectric actuators 106 which ensure both the emission of ultrasonic acoustic waves and the reception of the echo of these waves.

[0077] The operating principle of device 100 is described below in relation to the figure 2 .

[0078] Prior to the detection of one or more elements by device 100, a calibration of device 100 is implemented.

[0079] For this calibration, according to a first example of embodiment, an ultrasonic acoustic wave measurement device 150 is placed at a non-zero distance from the detection surface of device 100. The plane in which device 150 is located during calibration is, for example, spaced from the detection surface by a distance between 0 and 50 cm.

[0080] Each of the actuators 106 then emits calibration ultrasonic acoustic waves. These calibration ultrasonic acoustic waves correspond, for example, to periodic or pseudo-periodic signals whose instantaneous frequency varies within at least part of the frequency range used for the operation of the device 100. These signals are commonly called "chirps." Reference numeral 152 designates an example of a pseudo-periodic control signal applied to the control electrodes of one of the piezoelectric actuators 106.

[0081] The ultrasonic calibration acoustic wave emitted by each of the piezoelectric actuators 106, propagated and reflected in the plate 102, is measured by the device 150. On the figure 2 , the reference 154 symbolically designates one of the ultrasonic calibration acoustic waves measured by the device 150. Each of the acoustic waves measured at a point, resulting from the emission of each of the piezoelectric actuators 106, are recorded as calibration data for that point.

[0082] A time-reversal process is then applied to each of the ultrasonic calibration acoustic waves measured by device 150. The signals obtained after applying this process correspond to the waves intended to be emitted by each of the piezoelectric actuators 106 to achieve focusing of these waves at the focal point corresponding to the location of device 150. On the figure 2The reference 156 symbolically designates the signals obtained after application of the time reversal process. Details of the implementation of the time reversal process are described, for example, in the document by Fink M., "Time Reversal of Ultrasonic Fields - Part I: Basic Principles", IEEE Transactions on Ultrasonics, Ferroelectrics, and Frequency Control, vol. 39, no. 5, pages 555-566, September 1992.

[0083] This time-reversal calibration process is then repeated for a large number of locations on device 150 opposite plate 102. For example, in the variant shown in figure 2 , this calibration is repeated so that the locations of device 150 form a mesh covering the entire surface of the first face 104 and having a spacing of 10 mm between two neighboring locations of device 150.

[0084] The signals obtained after applying the time reversal process to each of the ultrasonic acoustic calibration waves measured by device 150 are then stored in a memory or database of device 100, for example part of computer 108.

[0085] According to a second embodiment, this calibration can be performed not by measuring the audio impulse response generated by the emission of the ultrasonic calibration waves, but by measuring the vibrational impulse response on the detection surface generated by the emission of the ultrasonic calibration waves. In this case, device 150 is replaced by a vibrometer, for example a laser vibrometer, placed against plate 102, which allows this vibrational impulse response to be measured.

[0086] At the end of this calibration phase, device 100 is used to detect one or more elements seeking, for example, to interact with device 100.

[0087] To this end, the actuators 106 are controlled to simultaneously emit focused ultrasonic detection waves in a region of space where the presence of the element(s) seeking to interact with the device 100 is being sought. The control signals enabling the focusing of the ultrasonic waves in the desired focal region are calculated by the computer 108 by applying a transformation and filtering to the signals previously stored at the end of the calibration phase. figure 2, reference 158 symbolically designates the calculated control signals which enable the focusing of ultrasonic acoustic waves at a desired focal point designated by reference 160.

[0088] The signal emitted and focused by the actuators 106 is chosen so as to excite only ultrasonic frequencies, for example filtering out frequencies below 20 kHz. It is possible to filter the emitted waves at the point of emission.

[0089] Filtering the signals before their emission serves several functions. The first is to adapt vibration signals recorded on the surface of plate 102 during calibration, so that focusing occurs at a chosen distance from the surface of plate 102. The calculations performed, for example, are based on solving the Kirchhoff-Helmholtz integral, which can be simplified. This integral determines the acoustic pressure at a point in the volume when the acoustic pressure and the velocity of movement are known at all points of plate 102. It also assumes that the environment in which device 100 operates does not contain any acoustic source other than plate 102, in which case the system's performance will be reduced. Additional assumptions made to solve the integral include that the boundary conditions of plate 102 are known.The edges of plate 102 are either rigidly or flexibly embedded. In both cases, the computer 108 can solve a simple integral involving all the signals recorded during the calibration of a transmitter. Thus, the computer 108 makes it possible to determine the theoretical impulse response between this transmitter and the point in the volume under study. By time-reversing this theoretical signal and performing this procedure for all transmitters, the signals to be emitted to focus an acoustic wave at this point are known. All of these calculations can be performed in real time before emission, or can be pre-recorded following the calibration phase. Details relating to this procedure can be found in the document by Nicolas Etaix, "Acoustic Imaging with a Low Number of Transducers Using an Acoustic Cavity." Acoustics [physics.class-ph].Paris-Diderot University - Paris VII, 2012, Chapter II: Acoustic plate radiation and focusing.

[0090] The second role of filtering is to limit the frequencies emitted by device 100 to a chosen frequency band: these frequencies must remain within the ultrasonic range, and a high-pass filter can therefore be used for this purpose. The chosen frequency band must also allow for adjusting the size of the acoustic focal spot formed by the emitted waves. A low-pass filter can therefore also be implemented to eliminate high frequencies and thus widen the acoustic focal spot.

[0091] The third role of filtering can be to add frequency or phase coding so that the measured echoes can be well correlated with the emitted signals.

[0092] By achieving such focusing, the energy of the waves emitted by the actuators 106 accumulates in the focusing region, which makes it possible to obtain a stronger signal in this region.

[0093] There figure 3 represents the spatial distribution of the focusing obtained at different distances from the detection surface for the same emission of acoustic waves focused at a focal point located at a distance of 183 mm from the detection surface. In the three diagrams of this figure 3The power of the focused waves obtained in a plane parallel to the detection surface, as a function of the position in this plane, is represented. In diagram a), the plane considered is at a distance of 168 mm, while in diagram b), the plane considered is at a distance of 183 mm (equal to the distance between the detection surface and the focal point), and in diagram c), the plane considered is at a distance of 198 mm.

[0094] If the emitted ultrasonic acoustic waves encounter an element, designated by reference 162 on the figure 2These waves are then reflected in the form of an echo. This echo is detected by the detection means 110 of the device 100. The device 100 then measures the time between the emission of the ultrasonic acoustic waves and the reception of the echo of these ultrasonic acoustic waves by the detector 110, which makes it possible to determine the distance between the device 100 and the detected element.

[0095] There figure 4This represents several echoes of ultrasonic acoustic waves obtained for the same wave emission, when these waves are reflected by objects located at different distances. Curve 164 corresponds to the echo measured for waves emitted and focused at a focal point 200 mm from the detection surface, and reflected off an object placed 185 mm from the detection surface. Curve 166 corresponds to the echo measured for waves emitted and focused at a focal point 200 mm from the detection surface, and reflected off an object placed 200 mm from the detection surface. Curve 168 corresponds to the echo measured for waves emitted and focused at a focal point 200 mm from the detection surface, and reflected off an object placed 215 mm from the detection surface.

[0096] To reduce the measurement time for the position of the element(s) to be detected, the calculator 108 is configured to calculate the control signals so that the ultrasonic acoustic waves emitted by the piezoelectric actuators 106 are successively focused onto regions of different shapes and / or sizes. Thus, the dimensions and / or shape of the regions into which the ultrasonic acoustic waves are successively focused are judiciously adjusted to reduce the time required to detect the element(s).

[0097] For example, it is possible to begin the detection of the element(s) to be detected with a rough overview of the environment, that is, by defining an initial, relatively large focal region. Then, the emitted acoustic waves can be focused into one or more smaller regions to increase the spatial resolution of the measurement performed by device 100 and thus precisely determine the position of the element(s) to be detected. This does not require additional calibration, but rather a different filtering of the emitted signals to calculate different control signals. Subsequently, device 100 can emit focused waves into small regions around the measured points.Having previously determined the distance between the detection surface and the detected element by measuring the echo reception time, subsequent focal regions can be chosen at a distance from the detection surface equal to the distance between the detected object and the detection surface. This helps to limit the reception of unwanted echoes.

[0098] To improve the detection speed of elements, the device 100 can select relevant observation areas and adjust its field of view accordingly. Technically, modifying the field of view can be achieved by widening or narrowing the size of the acoustic focal spot, that is, by extending or narrowing the area where the acoustic waves converge. This is accomplished by filtering the high frequencies of the signal emitted by each actuator 106. Indeed, the fewer high frequencies the emitted signal contains, the wider the resulting acoustic focal spot. Thus, even if an element is located far from the center of the focal spot, it will send back an echo, indicating to the device 100 that it should search this area more thoroughly. In this case, the spot will be in the shape of an ellipsoid with a variable diameter of its horizontal cross-section.By dichotomy, by varying the size of the ellipsoid, the device 100 can determine the precise position of the detected element.

[0099] To obtain an initial image of the elements present in the observed scene, the 100 device can emit detection waves that form several large-diameter ellipsoids at various altitudes. Since the distance of the element from the detection surface can always be precisely determined using the time of flight, this determination is faster if the focal spot is more elongated, like a beam. Unfortunately, the technology does not allow control over the elongation of these ellipsoids. However, it is possible to control the distance of the bottom of this geometry from the emission surface, and thus maximize the acoustic energy focused above this point.

[0100] The dimensions of the chosen focal spots depend on the size of the space to be scanned, the required spatial accuracy, and the desired response time of the device 100. The diameter at half maximum intensity (HMI) of a focal spot tends towards half the acoustic wavelength. This means that the frequency used by the emission signals directly impacts the size of the focal spot. For example, in air, this corresponds to a frequency of 40 kHz and a focal spot diameter of 4 mm. However, this dimension also increases with the distance of the focal point from the detection surface, an effect that is compensated for by the equivalent emission aperture of the device 100. This aperture corresponds to the dimensions of the plate 102, plus a correction related to the quality of the reflections in the plate 102 and the number of actuators 106.Thus, for a plate 102 of 150x150mm 2< , the detection resolution at 50 cm is theoretically 14 mm, this resolution can be improved by the embedding conditions and the number of actuators 106 of the device 100.

[0101] On the other hand, the choice of the frequency at which detections are performed for large focal regions depends on the application. If the action performed during the interaction only requires a finger, the device 100 can be configured to decide to track only that detected finger without performing detections in large focal regions.

[0102] Algorithmic work can be implemented to choose the optimal area to scan.

[0103] When device 100 is configured to detect one or more moving elements, it can be configured to measure at least one frequency shift between the emitted acoustic detection waves and their echoes, and to calculate the velocity of the detected element(s) from this measured frequency shift. Thus, by measuring the Doppler effect (corresponding to the measured frequency shift), it is possible to determine the velocity of the detected element(s). It is then possible to determine other information about the movement of the detected element(s), such as predicting its future distance from the detection surface after a certain time and anticipating the positions of the focal points to which the ultrasonic acoustic waves will be focused during subsequent detections.In parallel with these displacement tracking phases, device 100 can focus ultrasonic acoustic waves into wide focal regions, in order for example to detect the appearance of new elements seeking to interact with device 100.

[0104] On the other hand, the geometry of the focus region can also be modified. For example, it is possible to generate a kind of ray that allows an object to be detected over a wide range of altitudes, without having to scan each distinct altitude.

[0105] To improve the robustness of observation and echo measurement, focused ultrasonic acoustic waves can be coded. This coding can be achieved by alternating the phase of the signals and / or the frequency content of the control signals applied to the first piezoelectric actuators 106. Indeed, even if the wave focusing performed by device 100 prevents detection from being disturbed by obstacles further away or located outside the considered focusing region, it is possible that some of the emitted ultrasonic acoustic waves may be detected with a certain delay by detector 110, after reflection from the focal point. Coding the emitted ultrasonic acoustic waves makes it possible to verify, by comparing whether the received echo has the same coding as that applied to the emission, that the echoes captured by the detection means correspond to the waves initially emitted.

[0106] In one embodiment of the device 100, the piezoelectric actuators 106 can be used to cancel or attenuate residual vibrations of the plate 102, thereby accelerating the detection process or increasing the signal-to-noise ratio of the measurement. Indeed, vibrations in the plate 102 continue after the focusing signal is emitted, due to numerous reflections occurring before the waves naturally dissipate. This unintentional lengthening of the emitted signal also leads to a lengthening of the received echo signal, necessitating waiting for the entire system to stabilize before generating a new pulse or accepting a loss of signal quality. Attenuating the vibrations of the plate 102 thus prevents the new reception from being interfered with by the previous one.

[0107] To achieve a brief and controlled emission, residual vibrations can be actively attenuated. Indeed, thanks to calibration, the response of plate 102 following the emission of focusing signals is known. Since the actuators 106 cover a large area traversed by these waves, they can be controlled with a signal of opposite amplitude to the residual vibration signal, which is known at each of their positions. These active attenuation signals can be applied directly following the focusing signals by time reversal.

[0108] According to another approach, these residual vibrations can be digitally eliminated because they are known, as they result from the emission of calculated ultrasonic acoustic waves. Their effect at the focal point is calculated digitally. Since the residual vibration of plate 102 is known following calibration, it is possible to calculate the acoustic field it generates within the volume. Knowing this signal, if an object has been detected in the focal zone, it is possible to directly suppress this signal in the acoustic measurement following the next focusing operation. Thus, it is possible to perform a detection at a new point before the echo from the previous measurement is completely attenuated, without disrupting the measurement.

[0109] These variants make it possible to recover an echo of ultrasonic acoustic waves that is not or only slightly disturbed by these residual vibrations.

[0110] According to one embodiment, when the detection means 110 used correspond to the piezoelectric actuators 106, it is possible to apply a second time-reversal process to the received waves, thereby improving the localization accuracy of the detected element(s). Indeed, the element to be detected, on which the focused wave is reflected, is considered a sound source. The computer 108, knowing the signal emitted by this virtual source as well as the impulse response linking the vibrations in the plate 102 to all points of the observable volume, can, by measuring the vibrations in the plate 102 and applying the time-reversal principle, locate the virtual source. The application of this second time-reversal process adds localization information to the data on the presence or absence of a reflector in the focal zone.This can be advantageously used when the focal spot size is large during preliminary detection, allowing for a more precise selection of the future focal region. This can therefore improve the localization accuracy and detection speed of the device.

[0111] According to another embodiment, in addition to all these acoustic localization techniques, the electrodes of the piezoelectric actuators 106 can be used as mutual capacitive sensors. In this case, disturbances in the electric field near the detection surface can be measured and associated with the presence of an element to be detected. This advantageously increases the near-field interaction accuracy of the device 100.

[0112] In this alternative variant, the upper electrodes of the piezoelectric actuators 106, which are bonded to the sensing surface, can be connected to an electronic capacitive measurement system, for example, the computer 108. This computer can measure the capacitance formed by the upper electrodes of two adjacent actuators 106. When an object with an electrical permittivity different from that of air is present, it distorts the electric field lines, and therefore the mutual capacitance between these electrodes. For example, in the presence of a finger, which has a permittivity higher than that of air, this mutual capacitance increases.This increase in mutual capacitance depends on the size of the finger and its distance from the detection surface. However, by using multiple pairs of electrodes, it is possible to retrieve this information and thus precisely locate the finger, both in terms of distance from the detection surface and within the plane in which it lies. This technique can improve interaction accuracy near the surface, but also when the object touches the surface because, in this case, time reversal no longer applies as the object attenuates the focusing waves and there is no echo. Nevertheless, the accuracy decreases very rapidly with distance (a few centimeters), whereas this is not the case in acoustics (up to a few decimeters). This variant has the advantage of using a single system to exploit several complementary physical principles for the purpose of interaction detection.

[0113] For all the variants and embodiments described above, the physical principle of ultrasonic acoustic detection used by device 100 does not require any particular characteristics for forming the detection surface. However, certain parameters can improve detection performance, and a compromise on these parameters can maximize the focusing contrast, focusing resolution, and echo signal amplitude obtained. These parameters of the plate 102 forming the detection surface are: the surface mass ρ s and Young's modulus Y associated with the Poisson coefficient v the material of plate 102, the thickness e of plate 102 and the sensing surface S, the number Q of actuators 106, the frequency bandwidth used B, the minimum frequency of the signals f and the emission time T of the signals.

[0114] A first element to consider is the frequency of coincidence. FC This corresponds to the fact that the acoustic wavelength in plate 102 is equal to that of air. At this frequency and slightly above, the plate-air coupling is maximized, resulting in maximum radiation from plate 102 and thus increasing the amplitude and richness of the emitted signals for ideal focusing. This frequency can be chosen at 20 kHz to achieve good coupling up to 100 kHz. This coincidence frequency is expressed by the following formula: f c = 1 2 . π . c 0 2 . 12 . ρ s . 1 − ν 2 Y . e 3 , with c 0 is the speed of sound in air. Y, v And ρ s Since they are related to the material of plate 102, adjusting the thickness e of plate 102 is preferred to define a plate stiffness D = Y . e 3 12 . 1 − ν 2 , such as f c = 1 2 . π . c 0 2 . ρ s D . When e, and therefore D, is increased, the low-frequency coupling of plate 102 improves. But it is necessary to avoid that FCeither too weak to avoid radiation in the audible range.

[0115] For good focus contrast It's ideal It is preferable to have numerous vibration modes within the frequency band used, which are related to the stiffness, frequencies, and surface area of ​​plate 102. This focus contrast is expressed by the relation C id éal 2 = B . S 2 D ρ s Thus, by increasing the stiffness, the surface area of ​​plate 102, and the bandwidth of the emitted signal, ideal contrast is achieved. However, this assumes that the product QT be tall in front S 2 . D ρ s Because if these quantities are close, C decreases. However, the emission time T is limited by the attenuation coefficient of the plate τ Beyond an emission time equal to 3. τIncreasing T no longer has any effect. Furthermore, a significant emission time T reduces the detection speed of device 100. On the other hand, the number of usable actuators 106 is limited by the acquisition electronics.

[0116] Given the above, it is preferable to have a plate 102 with high stiffness, and therefore a significant thickness. However, the plate 102 must still be able to transmit plane waves. Furthermore, the stiffer the plate 102, the lower the amplitude of the vibrations, and the device 100 is then affected by ambient noise, which reduces the signal-to-noise ratio. In the configuration where the plate 102 itself receives the echo, the plate 102 is not designed to be so stiff that the echo propagates back into the plate 102. A compromise must therefore be made regarding the stiffness of the plate 102.

[0117] Finally, it is best to avoid a material for plate 102 that is too viscous (as is the case with plastic, for example) to prevent excessive signal attenuation. Attenuation τ It must not be too weak either, otherwise the signals would continue to reverberate long after transmission. Attenuation is controlled by the type of boundary condition (i.e., rigid / free / simply supported) and the material supporting the plate 102. A rigid or free mounting reduces attenuation.

[0118] For example, to meet the constraints outlined above, plate 102 may contain glass, be placed on foam, and have the following parameters: e = 0.7 mm, S = 80 × 160 mm 2< , Y = 60 GPa , v = 0.24, ρ s = 1.62 kg.m -2< , T = 2 ms, B = 80 kHz, Q= 32. With such parameters, it is possible to obtain a focus with the following characteristics: τ = 1 ms, C ideal = 23 YES, C = 22 YES, fc = 18 kHz.

[0119] There figure 5 schematically represents a contactless interaction device 200 comprising a contactless detection device 100. The device 200 is configured to perform one or more actions based on a result of the detection performed by the device 100. For example... figure 5 The device 200 corresponds to a human-machine interface comprising a display surface, for example a screen, to which the detection surface of the device 100 is attached, and which is intended to interact with a hand (a finger 202 is represented on the figure 5) of a user of device 200. For example, depending on the gestures detected by device 100, device 200 can display information whose content depends on the detected gestures. As another example, device 200 can be used to manipulate 3D virtual objects displayed on a screen of device 200, these manipulations corresponding to the gestures detected by device 100.

[0120] According to another embodiment example, device 200 can correspond to a robot in which perceptual functions are implemented via detection device 100.

Claims

1. Contactless detection device (100), including at least: - a detection surface; - several actuators (106) acoustically coupled to the detection surface and configured to emit ultrasonic acoustic waves; - an ultrasonic acoustic wave detector (110); - an electronic and / or \IT computer (108); the device (100) being configured to carry out a detection of one or more element(s) (162) by implementing the following steps several times: - focusing detection ultrasonic acoustic waves emitted by the actuators (106) via the detection surface into a focusing region belonging to a plane located opposite the detection surface, by applying on the actuators (106) control signals (158) calculated by the electronic and / or IT computer (108) from a measurement of an audio impulse response and / or a vibratory impulse response of the detection surface, generated by an emission of ultrasonic calibration acoustic waves by each of the actuators (106), and the application of a first-time reversal method to the audio impulse response and / or to the vibratory impulse response of the detection surface, and characterized by the step of - measuring a duration between the emission of the detection ultrasonic acoustic waves and a reception of an echo of the detection ultrasonic acoustic waves by the ultrasonic acoustic wave detector (110); wherein the electronic and / or IT computer (108) is configured to calculate the control signals (158) such that the detection ultrasonic acoustic waves are focused successively into focusing regions with different shape and / or dimensions.

2. Contactless detection device (100) according to claim 1, wherein the detection surface corresponds to a first face (104) of a material plate (102), and wherein the actuators (106) are secured to a second face, opposite to the first face (104), of the material plate (102).

3. Contactless detection device (100) according to claim 2, wherein the material plate (102) has a thickness comprised between 0.1 mm and 3 mm and / or may include a material whose Young's modulus is comprised between 50 GPa and 300 GPa, and / or may be such that a ratio of its volumetric mass to the Young's modulus of the plate material is comprised between 20x10-8 kg / m.N and 50x10-8 kg / m.N.

4. Contactless detection device (100) according to one of the preceding claims, wherein the ultrasonic acoustic wave detector (110) includes at least one microphone and / or acoustic transducers disposed over the detection surface.

5. Contactless detection device (100) according to one of claims 1 to 3, wherein the ultrasonic acoustic wave detector (110) is formed by the actuators (106) configured to emit the ultrasonic acoustic waves and which are able to further carry out an acoustic transduction.

6. Contactless detection device (100) according to claim 5, wherein the electronic and / or IT computer (108) is configured to apply a second time reversal method to the echo of the detection ultrasonic acoustic waves received by each of the actuators (106).

7. Contactless detection device (100) according to one of the preceding claims, wherein the actuators (106) are configured to emit ultrasonic acoustic waves whose frequencies are comprised between 20 kHz and 100 kHz.

8. Contactless detection device (100) according to one of the preceding claims, wherein the electronic and / or IT computer (108) is configured to measure a frequency shift between the emitted detection ultrasonic acoustic waves and the echo of the detection ultrasonic acoustic waves, and calculating a speed of movement of the detected element(s) (162) from the measured frequency shift.

9. Contactless detection device (100) according to one of the preceding claims, wherein the electronic and / or IT computer (108) is configured to encode the control signals prior to the emission of the ultrasonic acoustic waves.

10. Contactless interaction device (200), comprising at least one contactless detection device (100) according to one of the preceding claims, and configured to carry out one or more action(s) according to a result of the detection carried out by the contactless detection device (100).

11. Contactless interaction device (200) according to claim 10, forming a human-machine interface comprising a display surface to which the detection surface of the contactless detection device (100) is secured.

12. Method for controlling a contactless detection device (100) according to one of claims 1 to 9, including the implementation of the following steps: - calculating, by the electronic and / or IT computer (108), the control signals (158) from a measurement of an audio impulse response and / or a vibratory impulse response of the detection surface, generated by an emission of the calibration ultrasonic acoustic waves emitted by each of the actuators (106), and the application of a first-time reversal method to the audio impulse response and / or to the vibratory impulse response of the detection surface, then - applying the calculated control signals (158) on the piezoelectric actuators (106), focusing the detection ultrasonic acoustic waves emitted by the piezoelectric actuators (106) into a focusing region belonging to a plane opposite the detection surface, and characterised by the step of - measuring a duration between the emission of the detection ultrasonic acoustic waves and a reception of an echo of the detection ultrasonic acoustic waves by the ultrasonic acoustic wave detector (110); and wherein these steps are repeated several times such that the calculated control signals focus the detection ultrasonic acoustic waves successively into focusing regions with different shape and / or dimensions.

13. Method according to claim 12, further including a calibration of the contactless detection device (100) comprising the implementation of the following steps: - emitting calibration ultrasonic acoustic waves by each of the piezoelectric actuators (106); - measuring an audio impulse response and / or a vibratory impulse response of the detection surface generated by the emission of calibration ultrasonic acoustic waves; - applying the first-time reversal method to the audio impulse response and / or to the vibratory impulse response of the detection surface (156); - memorising the signals obtained by applying the first-time reversal method to the audio impulse response and / or to the vibratory impulse response of the detection surface (156).

14. Method according to one of claims 12 or 13, implemented to detect a position or a movement of one or more finger(s) (202) of a user of the contactless detection device (100).