Non-contact element detection device

Abstract

The present invention relates to a non-contact detection device (100) comprising a detection surface, a plurality of actuators (106) acoustically coupled to the detection surface, an ultrasonic detector (110), and an electronic and / or IT computer (108), the device (100) being configured to detect one or more elements (162) by repeating the following steps: obtaining waves emitted by the actuators and applying a time reversal method to focus the ultrasonic waves emitted by the actuators in a focusing region; and measuring the time between the emission of the waves and the reception of echoes of these waves by the detector, the computer being configured to calculate control signals such that the detection waves are successively focused in focusing regions of different shapes and / or dimensions.

Description

[Technical Field]

[0001] The present invention relates to a field of non-contact detection and remote interaction with one or more elements. More specifically, the present invention relates to a device that enables one or more elements to interact with the device without the need for contact between the device and the elements, and to a method for controlling such a device. [Background technology]

[0002] Non-contact element detection devices can determine or characterize the presence, location, 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. The detection then enables interaction between the detected element and the device.

[0003] There are several techniques for fabricating such devices.

[0004] For example, non-contact element detection devices can be fabricated using the principle of optical capture, employing one or more cameras, lasers, or infrared sensors. However, such devices are highly sensitive to the optical conditions of the environment in which they are used. Furthermore, if such devices are used to allow users to interact with virtual objects, the computational power required for their operation becomes very high, as they must perform analysis of the captured images. Moreover, using lasers for optical capture is an expensive solution. Finally, using infrared sensors for optical capture also has several drawbacks: they are large, have a narrow perceptual area, and require numerous sensors to adequately represent the observation area. In addition, privacy concerns can arise with such devices, because optical capture captures everything visible around the element being detected, such as the user's face.

[0005] Furthermore, non-contact element detection devices can be fabricated using miniature radar. However, the performance obtained is not satisfactory, especially when the object being detected is not metal (for example, a hand or finger).

[0006] Non-contact element detection devices using Wi-Fi waves or shorter electromagnetic waves have also been proposed. However, these solutions require complex external elements that risk saturating the communication network through which the device communicates.

[0007] Furthermore, the fabrication of non-contact element detection devices using capacitive matrices has also been proposed. However, such matrices become inefficient when the distance between the matrix and the element to be detected exceeds several centimeters, and disturbances can occur due to the surrounding electric field.

[0008] Non-contact detection and interaction technologies implemented using the microphones and speakers of mobile phones or smartphones have also been suggested. Some of these technologies perform gesture detection using the measurement of frequency deviations and phase disturbances induced by motion relative to sound waves emitted by the phone's microphone. Pre-training makes it possible to associate various gestures with disturbances induced by user gestures relative to the emitted sound waves. However, these technologies cannot accurately locate the elements being detected if they are stationary. Therefore, for example, they cannot perform the manipulation of virtual objects or the detection of the movement of virtual cursors. Furthermore, the gestures to be detected must be predefined by the device manufacturer. Other technologies allow for tracking the motion of elements being detected, locating these elements in space using triangulation, and monitoring of time of flight, phase deviation, or impulse response. However, measurements made in this way are not highly accurate, and generally, trajectory reconstruction needs to be corrected by Doppler effect or phase change tracking, which allows for the determination of direction, velocity, and distance traveled. These techniques do not facilitate the detection of quasi-static interactions (i.e., low-amplitude motion), making it difficult to measure these motions and preventing the distinction between several elements detected simultaneously, such as several fingers of a user.

[0009] Compared to the systems listed above, ultrasonic teledetection technology has many advantages. Specifically, the elements used are smaller, it is not hypersensitive to optical conditions during use, it can be operated through translucent surfaces, the required computing power is finite, privacy concerns are eliminated, it can detect many materials (there are very few materials that do not reflect sound waves), and it is not hypersensitive to electromagnetic disturbances.

[0010] The paper "Strata: Fine-grained acoustic-based device-free tracking" by Yun, S. et al., 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 in real time without physical contact with the latter. By using the smartphone's two microphones, this algorithm can track the finger's trajectory in a two-dimensional plane from a certain distance away from the smartphone. However, this solution has several drawbacks: it requires pre-defining the possible range of interaction distance between the finger to be detected and the smartphone; it requires obtaining finger motion data; it cannot detect and distinguish between multiple fingers; it is not a highly stable solution because finger positioning is achieved by performing optimization including phase shift; it relies on the selection of reflection paths based on the absolute position of the finger; and the finger tracking trajectory is only possible within a selected two-dimensional plane.

[0011] The paper "Acoustic imaging device with one transducer" by Etaix, N. et al., The Journal of the Acoustical Society of America 131, 2012, pp. 395-399, describes a detection technique using time reversal to perform stereoscopic image formation. Several piezoelectric actuators are arranged on a so-called "chaotic" metal plate containing randomly punched holes. Known signals are generated by each actuator, and the corresponding step response at each point on the plate surface is measured by a vibrometer. The time reversal method is applied to the signals, which are later modified by mathematical functions. By applying these new signals to the actuators, sound waves are focused on a selected point in space. Subsequently, the plane is scanned at a selected height, and the echo is observed by a microphone. A time window corresponding to the theoretical time required for the echo potential is selected so that it reflects from the plate at a distance D and then returns to the microphone. By measuring the maximum amplitude of the sound within this time window, the presence or absence of an object at a distance D, positioned at the selected focal coordinates, is identified. In this paper, a plane positioned at a distance D from the plate is scanned by focusing sound waves point by point and analyzing each time window. Furthermore, some planes need to be scanned point by point to obtain a complete stereoscopic image of the environment. This results in an extremely long acquisition time. [Prior art documents] [Non-patent literature]

[0012] [Non-Patent Document 1] 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. [Non-Patent Document 2] Etaix, N. et al., "Acoustic imaging device with one transducer", The Journal of the Acoustical Society of America 131, 2012, pp. 395-399. [Overview of the project] [Means for solving the problem]

[0013] The present invention aims to provide a non-contact detection device that uses ultrasound and is free from all of the aforementioned drawbacks. That is, it is interactive through the simultaneous detection of the position and / or motion of one or more elements, which may or may not be located in a plane at various distances from the device, and this can be done in a short acquisition time.

[0014] For this purpose, the present invention provides a non-contact detection device, which comprises at least: - Detection surface and, - Several actuators, such as piezoelectric ones, configured to be acoustically coupled to a detection surface and emit ultrasonic waves, - Ultrasonic detector and, - Electronic and / or IT computers and A non-contact detection device comprising the following, the device is configured to perform the detection of one or more elements by performing the following steps several times, these steps include: - Measuring the acoustic impulse response and / or the vibration impulse response of the inspection surface generated by the calibration ultrasonic waves emitted by each actuator, and applying the first time reversal method to the acoustic impulse response and / or the vibration impulse response of the inspection surface, thereby applying the control signal calculated by the electronic and / or IT computer to the actuator, so that the detection ultrasonic waves emitted by the actuator are focused through the inspection surface into the focal region on the plane located on the opposite side of the inspection surface; - Measuring the duration between the emission of the detection ultrasonic waves and the reception of the echoes of the detection ultrasonic waves by the ultrasonic detector; The electronic and / or IT computer is configured to calculate the control signal so that the detection ultrasonic waves are continuously focused within the focal regions of various shapes and / or dimensions.

[0015] This device suggests performing the detection of one or more elements based on the use of acoustic focusing obtained by the time reversal principle applied to ultrasonic waves (with wavelengths from 16 kHz to 10 MHz) emitted from a planar or other inspection surface, for example, to identify the position of an element that is at least one finger or one hand of the user within the space in front of this inspection surface.

[0016] The identification of the position of the element is based on the measurement of the time required until the focused sound wave is emitted and returns in the form of an echo. The estimation of the position of the element is performed three-dimensionally by the echo of the focused wave that enables the definition of the presence of one of the elements or a plurality of elements detected in the focal region in a two-dimensional plane, and by measuring the delay between the emission of the wave and the reception of the echo that enables the identification of the distance between the detected element and the ultrasonic detector, which is preferably on the same plane as the plane where the inspection surface is located.

[0017] By performing the focusing of ultrasonic waves in various focal regions, several fingers can be detected independently.

[0018] Thereafter, this positioning can enrich the mode of interaction with the device without contacting the device.

[0019] By appropriately selecting the characteristics (dimensions and / or shape) of the continuous focusing regions of the ultrasonic waves, for example, by changing the size of the focusing region and the reach distance of the focused ultrasonic waves, and by performing dynamic target tracking, it is possible to significantly reduce the acquisition time by appropriately traversing various regions in the space where the detection target element is located.

[0020] It should be understood that the "focusing point" is the point where the ultrasonic waves are focused and converged.

[0021] The detection performed by the device may be static because it does not involve the comparison of signals between two separate time points. It may also be quasi-static (small movement of the detection target element) or dynamic.

[0022] This device can be used to improve the capabilities of an interactive system by enabling gestures and non-contact interactions beyond tactile interactions.

[0023] The device may be used to detect several fingers of the user.

[0024] This device can enable real-time interaction with the user.

[0025] This device is not sensitive to the optical state during use and is stable against electrical disturbances.

[0026] This device can perform detection at a long distance, for example, up to about 1 meter from the detection surface.

[0027] Furthermore, because this device does not use image processing methods to identify the elements to be detected, it has the advantage of being able to operate with low electronic or IT computing power. The device directly reconstructs the position of the nearest object that returned an ultrasonic echo.

[0028] Furthermore, this device has the advantage of protecting privacy because it does not capture images, operates at ultrasonic frequencies, and processes acquired data locally.

[0029] This device is suitable for use when multiple fingers do not interact dynamically. In fact, the device generates virtual sound sources by performing ultrasonic focusing. The number of generated virtual ultrasonic sources can be large, improving the accuracy of positioning the detected element. Furthermore, by performing focusing, the energy of all actuators is concentrated in the focused region. This concentration increases the amplitude of the reflected signal (echo), making detection easier. By focusing the wave in the focused region, it becomes possible to isolate the observation area from all parasitic reflections with even lower amplitudes. This ensures that detection performed by the device within the focused region is not disturbed by elements outside this region.

[0030] For example, each finger can be detected independently. Furthermore, even if these fingers are stationary, the device recognizes their position within the area where focusing is performed. Upon receiving a response, it associates the precise position of the detected finger. The distance from the finger can be measured even more accurately by measuring the time between the detection ultrasound and emission and the reception of the echoes of these waves.

[0031] By focusing ultrasonic waves from multiple piezoelectric actuators, the amplitude of the received echo increases. Consequently, this echo becomes easier to detect and distinguish from all other possible parasitic echoes.

[0032] This results in an inexpensive solution that is easily integrated and allows for interaction with a large workspace.

[0033] Possible applications of such devices would be related to human-machine interfaces, or HMIs. For example, contactless interactive screens, vehicle dashboards, switches in the construction sector, or interactive tables. The device could also be used for contactless interaction with IT devices, tablets, or smartphones. Possible functions that this device could implement include, for example, manipulating virtual objects, using contactless interactive screens (advantageous from a health / hygiene perspective), or interacting with dashboards in small spaces.

[0034] Furthermore, this device can be used in other types of applications. For example, it can be used in industrial fields such as system applications for three-dimensional positioning of objects for robot control or part shape control, or for inverse conversion of vehicle radar or adjustment of vehicle orientation relative to a target.

[0035] For example, this device can simply, compactly, and inexpensively integrate control buttons within a vehicle's dashboard or a musical instrument. The proposed device allows for the integration of numerous buttons and virtual lighting switches within a small, reconfigurable space that creates volume for interaction in front of the dashboard.

[0036] The device may also be capable of providing perceptual capabilities to robots in challenging environments (for example, when light intensity is difficult or almost impossible to control, when observing objects with poor texture or that are transparent, or when there are many obstacles).

[0037] The elements detected by the device can be of any shape or made of any material, as long as they do not absorb ultrasound.

[0038] In the fields of mobile phones and IT, contactless detection devices can be used to add dimensions to interactions, facilitate three-dimensional manipulation, and enable user gesture-based interaction. Examples of device applications include: - Interacting with applications and background processes (e.g., music, camera) or activating small functions (e.g., flashlight, volume), - Interacts with the normal user interface but does not involve physical contact (for example, when hands are wet or dirty, or when the device is out of the user's reach). - Enhance the functionality that allows interaction with the application (e.g., zoom, rotate, tilt, and translate images; drag or drop files; copy or paste text, etc.). - This includes enhancing the interactivity of video games.

[0039] Furthermore, a smartphone or IT device equipped with such a device may be used directly as a stereometric system to scan three-dimensional objects during virtual or augmented reality activities, or for any other stereoscopic image formation applications.

[0040] In the automotive sector, devices can be used to replace buttons or touchscreens, or to enable gesture-based interaction. Interaction devices may also be directly integrated into the vehicle's dashboard.

[0041] In the field of industrial robotics, this device may be used to enable an industrial robot arm to perform a 3D scan of its immediate vicinity, getting as close as possible to obstacles (sensors mounted on the effector) while avoiding interference even when sensors are concentrated.

[0042] In the construction / agricultural machinery sector, this device, with its inverse transformer / proximity radar, can improve the machine's ability to consider the surrounding environment (shape for better positioning of nearby objects).

[0043] The calibration performed involves calculating the actuator's control signal, enabling the emission of detection ultrasound, and can be carried out in several ways. These methods include: - Measure the acoustic impulse response generated by the emission of calibrated ultrasound near the detection surface or at some distance from the detection surface, and apply the first time reversal method to this measured acoustic impulse response, and / or - The method involves measuring the vibration impulse response of the detection surface generated by the emission of calibrated ultrasound, and applying the first time reversal method to this measured vibration impulse response.

[0044] The closer the acoustic impulse response is to the detection surface being measured, the more accurately the radiating portion of the calibration ultrasound is measured (resulting in less information loss), and the more accurately the subsequent detection ultrasound is focused.

[0045] The vibration impulse response of the detection surface may be measured by a vibration meter, such as a laser vibrometer.

[0046] The actuator may be a piezoelectric actuator. Furthermore, the actuator may be of a type other than piezoelectric, provided it has a broadband frequency response; for example, it may be electrostatic.

[0047] The detection surface may correspond to the first surface of the material plate, and the actuator may be fixed to the second surface of the material plate opposite the first surface. This configuration facilitates the integration of the detection device, and the actuator is fixed behind the surface to be measured.

[0048] The plate forming the detection surface may include glass and / or plastic and / or metal. The material of the plate may be transparent or not. The plate may be flat or not, and may be curved, for example.

[0049] The material plate may have a thickness between 0.1 mm and 3 mm, and / or may contain a material with a Young's modulus from 50 GPa to 300 GPa, and / or the ratio of its volume mass to the Young's modulus of the plate material is 20.10 -8 kg / mN and 50.10 -8 It may be between kg / mN. In particular, this characteristic ensures good transmission of ultrasound through the air by the plate.

[0050] The ultrasonic detector may include at least one microphone and / or acoustic transducer arranged across the detection surface. The acoustic transducer may correspond to a piezoelectric actuator distinct from the actuator configured to emit the detection ultrasound.

[0051] In addition, the ultrasonic detector may be formed by an actuator, such as a piezoelectric actuator, and configured to emit ultrasonic waves and perform acoustic conversion. This modification is advantageous because it allows for very good integration of the device.

[0052] Furthermore, in this modification, the electronic and / or IT computer may be configured to apply the second time-reversal method to the echo of the detected ultrasonic waves received by each actuator. In this case, the element to be detected, to which the focused wave reflects, can be likened to a sound source. Therefore, the computer, recognizing the signal emitted by this virtual sound source along with the impulse response that associates the vibrations on the plate with every point in the observable volume, may determine the location of the virtual sound source by measuring the vibrations on the plate and applying the time-reversal principle. By applying this second time-reversal method, the localization information can be added to the data regarding the presence or absence of reflectors within the focused region. This modification can often be used during pre-detection when the size of the acoustic focal spot, i.e., the area where the sound waves intersect, is large, thereby allowing for the selection of a future detection area in which the sound waves are focused in a more relevant manner. This makes it possible to improve localization accuracy and the detection speed of the device.

[0053] The actuator may be configured to emit ultrasound with frequencies ranging from 20 kHz to 100 kHz. This range is sufficiently far from the human audible frequency range to avoid inconvenience for the device user.

[0054] An electronic and / or IT computer may be configured to measure the frequency shift between the emitted detection ultrasound and the echo of the detection ultrasound, and to calculate the velocity of the detected element from the measured frequency shift. This velocity is obtained according to the direction between the detected element and the ultrasonic detector, using the principle of the Doppler effect.

[0055] An electronic and / or IT computer may be configured to encode a control signal prior to the emission of ultrasound. This encoding may be performed such that, for the focused wave, the frequency content is known, the phase is discrete, the frequency is variable, or the frequency is modulated. In this case, for decoding of the echo-derived wave, the detection device can be made more stable, and it can be ensured that this signal correlates well with the emitted signal and is not derived from ambient noise.

[0056] Furthermore, the present invention relates to a non-contact interaction device comprising at least one non-contact detection device as described above, and configured to perform one or more actions according to the results of detection performed by the non-contact detection device.

[0057] The non-contact interaction device may form a human-machine interface in which the detection surface of the non-contact detection device has a fixed display surface.

[0058] Furthermore, the present invention relates to a method for controlling a non-contact detection device as described above, and this method includes performing the following steps, these steps are: - The steps include: measuring the acoustic impulse response and / or the vibration impulse response of the detection surface generated by the emission of calibration ultrasound emitted by each actuator, and applying a first time reversal method to the acoustic impulse response and / or the vibration impulse response of the detection surface to calculate a control signal using an electronic and / or IT computer; - The calculated control signal is applied to the piezoelectric actuator, and the detection ultrasonic waves emitted by the piezoelectric actuator are focused within a focusing region on a plane located opposite the detection surface. - The step of measuring the duration between the emission of the detected ultrasound and the reception of the echo of the detected ultrasound by the ultrasound detector. These steps are repeated several times so that the calculated control signal continuously focuses the detected ultrasonic waves within a focusing area of ​​various shapes and / or dimensions.

[0059] This method may further include calibration of a contactless detection device, which includes performing the following steps, - A step in which calibration ultrasonic waves are emitted by each piezoelectric actuator, - A step of measuring the acoustic impulse response and / or the vibration impulse response of the detection surface generated by the emission of calibration ultrasound, - A step of applying the first time reversal method to the acoustic impulse response and / or the vibration impulse response of the detection surface, - The step of storing the signals obtained by applying the first time reversal method to the acoustic impulse response and / or the vibration impulse response of the detection surface.

[0060] This method may be implemented to detect the position or movement of one or more fingers of a user of a detection device.

[0061] The present invention will be better understood by reading the description of the exemplary embodiments, which are purely for illustrative purposes and not for limitation, with reference to the accompanying drawings. [Brief explanation of the drawing]

[0062] [Figure 1] A schematic diagram of a non-contact detection device according to a specific embodiment is shown. [Figure 2] The operating principle of a non-contact detection device according to a specific embodiment is schematically shown. [Figure 3] This shows the spatial distribution of focus obtained at various distances from the detection surface of a non-contact detection device for the same emission of sound waves focused at the same focal point. [Figure 4] This shows several echoes of ultrasound obtained by reflecting the same wave emission from objects at various distances. [Figure 5] This document illustrates a non-contact interaction device according to a specific embodiment. [Modes for carrying out the invention]

[0063] Identical, similar, or equivalent parts in the various drawings described below will be given the same reference number to facilitate transitions from one drawing to another.

[0064] The various parts shown in the drawings are not necessarily depicted at a uniform scale in order to make the drawings easier to read.

[0065] Various possibilities (modifications and embodiments) should be understood as non-exclusive and may be combined.

[0066] The following description of a non-contact detection device 100 according to a specific embodiment will be given with reference to Figure 1.

[0067] The device 100 comprises a material plate 102 and a first surface 104 that forms the detection surface of the device 100. For example, the plate 102 includes glass, plastic, or metal. For example, the plate 102 has a thickness between 0.1 mm and 3 mm and / or includes a material with a Young's modulus from 50 GPa to 300 GPa and / or the ratio of its volume mass to the Young's modulus of the material of the plate 102 is 20.10 -8 kg / mN and 50.10 -8 It falls between kg / mN and [another value].

[0068] Here, the plate 102 is fixed to the frame 103. If the device 100 is mounted on the front of the screen, the plate 102 may include a transparent material so that the screen is visible when the piezoelectric actuator 106, described later, is positioned around the plate 102.

[0069] In a specific embodiment, the dimensions of the plate 102 are, for example, equal to 156 mm × 76 mm, and the thickness is equal to 0.5 mm.

[0070] The plate 102 may or may not be flat; for example, it may be curved.

[0071] The device 100 may also include several actuators 106 configured to acoustically couple with a detection surface and emit ultrasonic waves. The actuators 106 may be piezoelectric actuators. Alternatively, the actuators 106 may be electrostatic.

[0072] In the specific embodiment described herein, the actuator 106 is fixed, for example, to a second surface of the plate 102 opposite to the first surface 104. Furthermore, in the specific embodiment described herein, the actuator 106 is fixed to the plate 102 in close proximity to its edge. Alternatively, the actuator 106 may be positioned at any point on the second surface of the plate 102. In another modification, the actuator 106 may be positioned on the first surface 104 side of the plate 102, i.e., the detection surface side.

[0073] In one embodiment, each piezoelectric actuator 106 includes a piezoelectric material, such as a PZT, positioned between at least two control electrodes capable of applying a potential difference to the piezoelectric material. For example, each piezoelectric actuator 106 may include a PZT portion formed as a thin film with dimensions equal to 70 mm × 10 mm × 0.2 mm, to which 16 electrodes are connected to activate this PZT thin film.

[0074] Generally, the number of first actuators 106 acoustically coupled to the sensing surface of device 100 is, for example, between 1 and 32, and may be greater depending on the operating electronics of device 100. As the number and size of actuators 106 increase, the power of the signal radiated by device 100 increases, and the resulting focusing resolution improves.

[0075] The piezoelectric actuator 106 is configured to emit ultrasonic waves with a frequency between 20 kHz and 100 kHz.

[0076] Furthermore, device 100 includes an electronic and / or IT computer 108, which is schematically represented in Figure 1 by a rectangle labeled reference numeral 108. One of the functions of this computer 108 is to calculate the control signals to be applied to the piezoelectric actuator 106.

[0077] The device 100 also includes an ultrasonic detector 110. This detector 110 is configured to capture ultrasonic echoes emitted through the plate 102 by the piezoelectric actuator 106. In the specific embodiment described herein, the detector 110 includes at least one microphone positioned in close proximity to the plate 102.

[0078] In addition, the detector 110 may correspond to an additional piezoelectric actuator positioned across the detection surface of the device 100, either on the first surface 104 of the plate 102, or on the second surface opposite to the first surface 104, separate from the actuator 106. In other modifications, the detector 110 may be formed by the piezoelectric actuator 106, which ensures both the emission of ultrasonic waves and the reception of ultrasonic echoes.

[0079] The operating principle of device 100 will be explained below with reference to Figure 2.

[0080] Prior to the detection of one or more elements by device 100, device 100 is calibrated.

[0081] For this calibration, in the first embodiment, the ultrasonic measuring device 150 is positioned at a non-zero distance from the detection surface of device 100. For example, the plane on which device 150 is positioned during calibration is located at a distance between 0 cm and 50 cm from the detection surface.

[0082] Subsequently, calibration ultrasound is emitted by each actuator 106. For example, such calibration ultrasound corresponds to a periodic or pseudo-periodic signal whose instantaneous frequency varies in at least part of the frequency range used for the operation of device 100. These signals are commonly referred to as "chirps." Reference numeral 152 shows an example of a pseudo-periodic control signal applied to one of the control electrodes of piezoelectric actuator 106.

[0083] The calibration ultrasound emitted by each piezoelectric actuator 106 propagates, is reflected by the plate 102, and is measured by the device 150. In Figure 2, reference numeral 154 schematically shows one of the calibration ultrasounds measured by the device 150. Each sound wave, measured at a certain point and extracted from the radiation of each piezoelectric actuator 106, is recorded as calibration data at that point.

[0084] Subsequently, the time reversal method is applied to each calibration ultrasound measured by device 150. The signals obtained after applying this method correspond to the waves that each piezoelectric actuator 106 attempted to emit in order to focus these waves at a focal point corresponding to the position of device 150. In Figure 2, reference number 156 schematically shows the signal obtained after applying the time reversal method. For details on the implementation of the time reversal method, see, for example, Fink M., "Time Reversal of Ultrasonic Fields - Part I: Basic Principles," IEEE Transactions on Ultrasonics, Ferroelectrics, and Frequency Control, Vol. 39, No. 5, pp. 555-566, September 1992.

[0085] Subsequently, this time-reversal calibration method is repeated for a number of positions on the device 150 on the opposite side of plate 102. For example, in the modified example shown in Figure 2, this calibration is repeated so that the positions on device 150 form a mesh that completely covers the surface of the first surface 104 and the distance between two adjacent positions on device 150 is 10 mm.

[0086] Subsequently, the signals obtained after applying the time reversal method to each calibration ultrasound measured by device 150 are recorded, for example, in the memory or database of device 100, which forms part of computer 108.

[0087] In a second embodiment, the calibration may be performed by measuring the vibrational impulse response on a detection surface generated by the emission of calibration ultrasound, rather than by measuring the acoustic impulse response generated by the emission of calibration ultrasound. In this case, device 150 is replaced, for example, by a laser-type vibrometer positioned opposite plate 102 and capable of measuring this vibrational impulse response.

[0088] Once this calibration stage is complete, device 100 is used, for example, to detect one or more elements that attempt to interact with device 100.

[0089] For this purpose, actuator 106 is controlled to simultaneously emit detection ultrasound that focuses within a region of space where an element intending to interact with device 100 exists. A control signal capable of focusing the ultrasound within a desired focal region is calculated by computer 108 by applying transformations and filters to the signal previously recorded at the end of the calibration stage. In Figure 2, reference numeral 158 schematically shows the calculated control signal capable of focusing the ultrasound to the desired focal point indicated by reference numeral 160.

[0090] The signal emitted and focused by actuator 106 is selected to excite only ultrasonic frequencies, for example, filter frequencies below 20 kHz. Filtering of the emitted waves is possible.

[0091] Several functions are realized by filtering the signal before emission. First, during calibration, the recorded vibration signal is adapted to the surface of plate 102 so that it is focused at a selected distance from the surface of plate 102. The completed calculation is derived, for example, by solving a simplified Kirchhoff-Helmholtz integral. For example, this integral determines the sound pressure at a certain point in the volume, given that the sound pressure and velocity are known at all points on plate 102. It is also assumed that the environment in which device 100 operates does not contain any sound sources other than plate 102, in which case the system performance is expected to be reduced. Furthermore, an assumption made for solving the integral is that the boundary conditions of plate 102 are known. The edges of plate 102 are embedded rigidly or flexibly. In these two cases, computer 108 can solve a simple integral that includes all signals recorded during the calibration of the emitter. Thus, the computer 108 can determine the theoretical impulse response between this radiator and a point in the observation volume. By inverting this theoretical signal in time and performing this procedure for all radiators, the signal emitted to focus the sound wave at this point becomes known. All these calculations may be performed in real time before emission, or they may be pre-recorded following the calibration stage. Details of this procedure can be found in the paper "Imagerie acoustique a faible nombre de transducteurs au moyen d'une cavite acoustique" by Nicolas Etaix, Acoustics [physics.class-ph], Paris-Diderot University - Paris VII, 2012, Chapter 2: Plate acoustic radiation and focusing.

[0092] The second role of filtering is to limit the frequencies emitted by device 100 within a selected frequency band, and since the frequencies should remain in the ultrasonic range, high-pass filtering may be performed for this purpose. Furthermore, the selected frequency band should allow for adjustment of the size of the acoustic focus formed by the emitted waves. Thus, low-pass filtering may also be performed so that high frequencies are excluded to broaden the acoustic focus.

[0093] A third role of filtering may include adding frequency or phase coding so that the measured echoes can correlate well with the emitted signal.

[0094] By performing this focusing, the energy of the waves radiated by the actuator 106 is concentrated within the focused region, thereby enabling the acquisition of a stronger signal within this region.

[0095] Figure 3 shows the spatial distribution of focus at various distances from the detection surface for the same emission of sound waves focused on a focal point located at a distance equal to 183 mm from the detection surface. In the three figures of Figure 3, the power of the focused wave obtained in a plane parallel to the detection surface is expressed as a function of the position in this plane. In figure a), the surface under consideration is at a distance of 168 mm; in figure b), the surface under consideration is at a distance of 183 mm (equal to the distance between the detection surface and the focal point); and in figure c), the surface under consideration is at a distance of 198 mm.

[0096] When the emitted ultrasound strikes the element indicated by reference numeral 162 in Figure 2, it is reflected in the form of an echo. This echo is detected by the detection means 110 of device 100. Device 100 can then determine the distance between device 100 and the detected element by measuring the duration from the emission of the ultrasound to the reception of these ultrasound echoes by the detector 110.

[0097] Figure 4 shows several echoes of ultrasound obtained from reflections by objects at various distances from the same wave emission. Curve 164 corresponds to the echo measured for a wave that was emitted, focused at a focal point 200 mm away from the detection surface, and reflected by an object located 185 mm from the detection surface. Curve 166 corresponds to the echo measured for a wave that was emitted, focused at a focal point 200 mm away from the detection surface, and reflected by an object located 200 mm from the detection surface. Curve 168 corresponds to the echo measured for a wave that was emitted, focused at a focal point 200 mm away from the detection surface, and reflected by an object located 215 mm from the detection surface.

[0098] To reduce the time required to measure the position of the element to be detected, the computer 108 is configured to calculate a control signal so that the ultrasonic waves emitted by the piezoelectric actuator 106 continuously focus on areas of various shapes and / or sizes. In this way, the dimensions and / or shape of the areas to which the ultrasonic waves continuously focus are appropriately adjusted to reduce the time required to detect the element to be detected.

[0099] For example, detection of the target element can be initiated with a coarse view of the environment. That is, a relatively wide first focus region can be defined, and then focusing can be performed on one or more regions of the emitted acoustic wave, for example, a smaller region, to improve the spatial resolution of the measurement made by device 100, thereby precisely determining the location of the target element. This does not require additional calibration, but requires additional filtering of the emitted signal to calculate a different control signal. Subsequently, device 100 may perform wave emission that focuses on a smaller region around the measurement point. If the distance between the detection surface and the detected element has been predetermined by measuring the reception time of the wave echo, the next focus region can be selected at a distance from the detection surface equal to the distance between the detected object and the detection surface. This can limit the reception of parasitic echoes.

[0100] To improve the element detection speed, device 100 may be able to select the relevant observation area and adjust the observation area according to the selected area. Technically, the modification of the observation area may be done by slightly widening the size of the acoustic focus, that is, by slightly widening the area where sound waves converge. This is done by filtering the high frequencies of the signal emitted by each actuator 106. In fact, the fewer high frequencies the emitted signal contains, the wider the resulting acoustic focus. Thus, when an element is located away from the center of the focus, it returns an echo, indicating to device 100 that the search area needs to be deepened. In this case, this point becomes an ellipsoid with a changing horizontal diameter. By changing the size of the ellipsoid according to the bisection method, device 100 can pinpoint the precise location of the detected element.

[0101] To obtain a first image of an element in the observation scene, device 100 may emit detection waves to form several large-diameter ellipsoids at several heights. Since the distance of the element to the detection surface can be determined fairly accurately by time of flight, this determination is faster even if the focus is broadened, as in a beam. It turns out that this technique does not allow control over the expansion of these ellipsoids. However, it is possible to control the distance of the bottom of this shape to the radiating surface, thereby maximizing the acoustic energy focused above this point.

[0102] The selected focal size depends on the size of the space being scanned, the desired spatial accuracy, and the desired response time of device 100. A focal diameter at which the intensity is halved will acoustically align to half the wavelength. This means that the frequency used by the radiated signal directly affects the size of the focal. For example, in air, this corresponds to a frequency of 40 kHz at a 4 mm diameter focal. However, this size also increases as the focal point moves away from the detection surface, and this effect is compensated for by an equivalent radiating hole in device 100. This hole corresponds to the dimensions of plate 102, and modifications are made in relation to the quality of reflection in plate 102 and the number of actuators 106. Thus, 150 × 150 mm 2 For the plate 102, the detection resolution at 50 cm is theoretically 14 mm, and this resolution can be improved by the embedding conditions of the device 100 and the number of actuators 106.

[0103] On the other hand, the frequency at which detection is performed over a wide focus area is selected according to the application. If the interaction requires only one finger, the device 100 may be configured to track only the detected finger without continuing detection over a wide focus area.

[0104] Algorithmic work may be implemented to select the optimal area for scanning.

[0105] If device 100 is configured to perform detection of one or more moving elements, device 100 may be configured to measure at least one frequency shift between the emitted detection sound wave and its echo, and to calculate the velocity of the detection element from the measured frequency shift. In this way, the velocity of the detection element can be determined by measuring the Doppler effect (corresponding to the measured frequency shift). Subsequently, other information about the motion of the detection element can be determined, such as predicting its future position relative to the detection surface after a given duration, or predicting the focal position where the ultrasound will be focused during the next detection. In parallel with such motion tracking, device 100 can focus the ultrasound over a wide focus area, for example, to detect the appearance of a new element attempting to interact with device 100.

[0106] On the other hand, the shape of the focus region may also be modified. For example, it is possible to generate a type of ray that can detect an object over a wide height range without having to scan each individual height.

[0107] To improve the stability of echo observation and measurement, the focused ultrasound may be encoded. This encoding may be achieved by repeatedly changing the phase of the signal and / or the frequency components of the control signal applied to the first piezoelectric actuator 106. In practice, even if the wave focusing performed by device 100 prevents the completed detection from being disturbed by obstacles located further away from, i.e., outside, the focused region under consideration, some of the emitted ultrasound may be detected by the detector 110 with some delay after the wave has moved out of focus and been reflected. By encoding the emitted ultrasound, it is possible to ensure that the echo captured by the detection means actually corresponds to the initially emitted wave by comparing whether the received echo contains the same encoding as that performed on the emission.

[0108] In a modified version of device 100, the piezoelectric actuator 106 may be used to eliminate or dampen residual vibrations of plate 102 in order to facilitate the detection method or improve the signal-to-noise ratio of the measurement. In fact, vibrations of plate 102 continue even after the emission of the focus signal as a result of many reflections that occur before the natural damping of the wave is complete. Also, the unintended extension of the emitted signal results in an extension of the received echo signal, requiring either waiting for the entire system to stabilize or accepting a decrease in signal quality before generating a new pulse. Thus, damping the vibrations of plate 102 avoids new receptions that are interfering with previous ones.

[0109] To shorten and control the radiation, residual vibrations can also be actively damped. In fact, the response of plate 102 following the radiation of the focusing signal is known through calibration. Since actuator 106 corresponds to a large surface exposed to these waves, the waves can be controlled with a signal of the opposite amplitude to the residual vibration signal, which is known at each position. Such an actively damped signal may be applied in direct response to the focusing signal by time reversal.

[0110] In other modifications, such residual vibrations may be digitally removed because they are known to be due to the calculated emission of ultrasonic waves. Their effect at the focal point is digitally calculated. In fact, since the residual vibrations of plate 102 are known after calibration, the sound field generated within the volume can be calculated. Knowing this signal, if an object is detected within the focus region, this signal can be directly suppressed in the acoustic measurement following the next focus. In this way, detection can be performed at a new point without such disturbance to the measurement before the echo from the previous measurement has completely attenuated.

[0111] These modifications allow for the reconstruction of ultrasonic echoes that are free from, or have very little of, disturbance from such residual vibrations.

[0112] In one modification, if the detection means 110 used corresponds to a piezoelectric actuator 106, a second time-reversal method, which can improve the accuracy of positioning the detected element, can be applied to the received wave. In fact, the element to be detected, to which the focused wave reflects, can be likened to a sound source. A computer 108, which recognizes the signal radiated by this virtual sound source and the impulse response that associates the vibrations on the plate 102 with every point in the observable volume, may determine the position of the virtual sound source by measuring the vibrations on the plate 102 and applying the time-reversal principle. By applying this second time-reversal method, positioning information can be added to the data on the presence or absence of reflectors within the focused region. This can be advantageous when the size of the focal point is large during prior detection, thereby enabling a more appropriate selection of the future focal region. This can improve the positioning accuracy and detection speed of the device 100.

[0113] In other modifications, to complement all these acoustic localization techniques, the electrodes of the piezoelectric actuator 106 may be used as mutual capacitance sensors. In this case, disturbances in the electric field near the detection surface may be measured and associated with the presence of the element to be detected. This would improve the near-field interaction accuracy of device 100.

[0114] In another variation, the upper electrode of the piezoelectric actuator 106 bonded to the detection surface may be connected to an electronic capacitive measuring system, for example, formed by a computer 108. The latter can measure the capacitance formed by the upper electrodes of two adjacent actuators 106. If there is an object with a dielectric constant different from air, the latter deforms the electric field lines, thereby changing the mutual capacitance between these electrodes. For example, if there is a finger with a higher dielectric constant than air, this mutual capacitance increases. The increase in mutual capacitance depends on the size of the finger and its distance from the detection surface, but by using several sets of electrodes, this information can be detected, thereby accurately determining the position of the finger in terms of both its distance from the detection surface and the surface on which it is positioned. This technique can improve the accuracy of interactions in the vicinity of a surface, but if the object is in contact with the surface, time reversal is no longer applicable because the object attenuates the focused wave and there is no echo. However, the accuracy decreases very rapidly with increasing distance (a few centimeters), although this is not the case for acoustic properties (up to a few decimeters). This modification has the advantage of using a single system that leverages several complementary physical principles to perform interaction detection.

[0115] In all the modifications and embodiments described above, the physical principle of ultrasonic acoustic detection used by device 100 does not require any specific characteristics to form the detection surface. However, detection performance can be improved by several parameters, and trade-offs with these parameters can maximize the resulting focus contrast, focus resolution, and echo signal amplitude. These parameters in the plate 102 forming the detection surface are related to the mass ρ per unit area. s The parameters are the Young's modulus Y, which is related to the Poisson's ratio ν of the material of plate 102, the thickness e of plate 102 and detection surface S, the number Q of actuator 106, the operating frequency bandwidth B, the minimum frequency of signal f, and the signal emission time T.

[0116] The first element to be considered is the coincidence frequency f c This corresponds to the acoustic wavelength in the plate 102 being equal to that in air. At this frequency and slightly above it, the coupling between the plate and air is maximized, enabling maximum radiation from the plate 102, thereby increasing the amplitude and richness of the radiation signal to obtain ideal focusing. This frequency is selected at 20 kHz, and good coupling is obtained up to 100 kHz. This coincidence frequency is represented by the following equation.

[0117] [Number]

[0118] where c0 is the speed of sound in air, Y, ν, ρ s relate to the material of the plate 102, and mainly by adjusting the thickness e of the plate 102, the rigidity of the plate

[0119] [Number]

[0120] is

[0121] [Number]

[0122] is defined such that as e, and thus D, increases, the low-frequency coupling of the plate 102 improves. However, it is necessary to avoid f c from becoming too low to avoid radiation in the audible range.

[0123] For good focusing contrast C ideal it is preferable that there are many vibration modes within the operating frequency band with respect to the rigidity, frequency, and surface of the plate 102. This focusing contrast is given by the relational expression

[0124] [Number]

[0125] This is represented by [the given formula]. In this way, by improving rigidity and widening the surface and radiated signal bandwidth of plate 102, an ideal contrast can be obtained.

[0126] However, that is because the product QT is

[0127]

number

[0128] It is assumed that it is larger than . This is because if these quantities are close, C decreases. Furthermore, the radiation time T is limited by the plate's attenuation coefficient τ. 3. If the radiation time exceeds τ, extending T becomes meaningless. Furthermore, a longer radiation time T reduces the detection speed of device 100. On the other hand, the number of usable actuators 106 is limited by the acquiring electronic equipment.

[0129] Considering the above, it is preferable to have a plate 102 with high rigidity and therefore considerable thickness. However, the plate 102 must be able to continuously transmit plane waves. Furthermore, if the rigidity of the plate 102 is too high, the amplitude of vibration decreases, and the device 100 itself will be exposed to the effects of ambient noise that reduces the signal-to-noise ratio. In a configuration where the plate 102 itself receives the echo, the plate 102 should not be made so stiff that the echo cannot repropagate through it. Thus, a trade-off must be found regarding the rigidity of the plate 102.

[0130] Finally, it is preferable to avoid excessive signal attenuation by preventing the material of plate 102 from becoming too viscous (for example, as in the case of plastic). The attenuation τ should also not be too low, in which case the signal would continue to reverberate for a long time after emission. Attenuation is controlled by the type of boundary conditions (i.e., rigid / free / simply supported) and the material holding plate 102. Attenuation is reduced by rigid or free embedded mounting.

[0131] For example, to accommodate the limitations disclosed above, the plate 102 may include glass, be placed on a foam, and have the following parameters: e = 0.7 mm, S = 80 x 160 mm 2 Y=60GPa, v=0.24, ρ s = 1.62 kg.m -2 The parameters are T=2ms, B=80kHz, and Q=32. With these parameters, it is possible to achieve focus with the following characteristics: τ=1ms, C ideal =23SI, C=22SI, f c = 18kHz.

[0132] Figure 5 schematically shows a non-contact interaction device 200 equipped with a non-contact detection device 100. Device 200 is configured to perform one or more actions in accordance with the results of detection performed by device 100. In the example in Figure 5, device 200 corresponds to a human-machine interface, including, for example, a display surface such as a screen on which the detection surface of device 100 is fixed and which interacts with the user's hand (fingers 202 are shown in Figure 5) of device 200. For example, in accordance with a gesture detected by device 100, device 200 may display information whose content depends on the detected gesture. In another example, device 200 may be used to perform operations on a virtual object displayed on the screen of device 200. Such operations correspond to gestures detected by device 100.

[0133] In other embodiments, device 200 may correspond to a robot in which perceptual functions are implemented via device 100. [Explanation of Symbols]

[0134] 100 contactless detection devices 102 Material board 103 frames 104 Page 1 106 Piezoelectric Actuator 108 Electronic and / or IT computers 110 Ultrasonic detector 150 devices 154 Calibrated Ultrasound 156 Signal 158 Control signals 162 elements 164 Curve 166 Curve 168 Curve 200 Non-contact Interaction Devices 202 fingers

Claims

1. at least, - Detection surface and, - Several actuators (106) configured to be acoustically coupled to the detection surface and emit ultrasonic waves, - Ultrasonic detector (110), - Electronic and / or IT computers (108) A non-contact detection device (100) comprising, wherein the device (100) is configured to perform the detection of one or more elements (162) by performing the following steps several times, these steps include - The steps include: measuring the acoustic impulse response and / or the vibration impulse response of the detection surface generated by the emission of calibration ultrasonic waves from each actuator (106), applying the first time reversal method to the acoustic impulse response and / or the vibration impulse response of the detection surface, and applying the control signal (158) calculated by the electronic and / or IT computer (108) to the actuator (106) to focus the detection ultrasonic waves emitted by the actuator (106) into a focus region on a plane located on the opposite side of the detection surface, via the detection surface; - The step of measuring the duration between the emission of the detected ultrasonic wave and the reception of the echo of the detected ultrasonic wave by the ultrasonic detector (110), The electronic and / or IT computer (108) is configured to calculate the control signal (158) such that the detection ultrasonic wave continuously focuses within focusing regions of various shapes and / or dimensions, and is a non-contact detection device (100).

2. The non-contact detection device (100) according to claim 1, wherein the detection surface corresponds to a first surface (104) of the material plate (102), and the actuator (106) is fixed to a second surface of the material plate (102) opposite to the first surface (104).

3. The material plate (102) has a thickness between 0.1 mm and 3 mm and / or contains a material with a Young's modulus between 50 GPa and 300 GPa, and / or the ratio of its volume mass to the Young's modulus of the material of the plate is 20.10 －８ kg / m. N and 50.10 －８ A non-contact detection device (100) according to claim 2, wherein the value is between kg / m.N.

4. The non-contact detection device (100) according to any one of claims 1 to 3, wherein the ultrasonic detector (110) comprises at least one microphone and / or acoustic transducer arranged across the detection surface.

5. The non-contact detection device (100) according to any one of claims 1 to 3, wherein the ultrasonic detector (110) is formed by the actuator (106) which is configured to emit ultrasonic waves and is capable of further acoustic conversion.

6. The non-contact 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 received by each of the actuators (106).

7. The actuator (106) is configured to emit ultrasonic waves having a frequency between 20 kHz and 100 kHz, the non-contact detection device (100) according to any one of claims 1 to 6.

8. The non-contact detection device (100) according to any one of claims 1 to 7, wherein the electronic and / or IT computer (108) is configured to measure the frequency deviation between the emitted detection ultrasound and the echo of the detection ultrasound, and to calculate the motion velocity of the detected element (162) from the measured frequency deviation.

9. The non-contact detection device (100) according to any one of claims 1 to 8, wherein the electronic and / or IT computer (108) is configured to encode the control signal prior to the emission of the ultrasonic waves.

10. A non-contact interaction device (200) comprising at least one non-contact detection device (100) according to any one of claims 1 to 9, and configured to perform one or more actions according to the result of the detection performed by the non-contact detection device (100).

11. The non-contact interaction device (200) according to claim 10, wherein the detection surface of the non-contact detection device (100) is equipped with a fixed display surface, forming a man-machine interface.

12. A method for controlling a non-contact detection device (100) according to any one of claims 1 to 9, comprising the following steps, these steps: - The steps include: measuring the acoustic impulse response and / or the vibration impulse response of the detection surface generated by the emission of the calibration ultrasonic waves emitted by each actuator (106), and applying the first time reversal method to the acoustic impulse response and / or the vibration impulse response of the detection surface, thereby calculating the control signal (158) by the electronic and / or IT computer (108); - The calculated control signal (158) is applied to the actuator (106), and the detection ultrasonic waves emitted by the actuator (106) are focused within a focusing region on a plane located on the opposite side of the detection surface. - The step of measuring the duration between the emission of the detected ultrasonic wave and the reception of the echo of the detected ultrasonic wave by the ultrasonic detector (110), A method in which these steps are repeated several times so that the calculated control signal continuously focuses the detected ultrasonic wave into a focusing region of various shapes and / or dimensions.

13. Calibration of the non-contact detection device (100) further includes performing the following steps, these steps include: - A step of emitting calibration ultrasound from each actuator (106), - A step of measuring the acoustic impulse response and / or the vibration impulse response of the detection surface generated by the emission of the calibration ultrasound, - The step of applying the first time reversal method to the acoustic impulse response and / or the vibration impulse response of the detection surface (156), The method according to claim 12, comprising the step of storing the signal obtained by applying the first time reversal method to the acoustic impulse response and / or the vibration impulse response of the detection surface (156).

14. The method according to claim 12 or 13, wherein the non-contact detection device (100) detects the position or movement of one or more fingers (202) of the user.

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