Device and method for projecting light synchronized with a sound wave

Abstract

The present invention relates to a device (1) for projecting light in a fluid environment (40), the device (1) comprising at least one density variation source (10) configured to locally vary the density of the fluid environment so as to produce at least one density front, and at least one light projection source (20) comprising a light source configured to project at least one image (30) onto the at least one density front (11). The density front may be a compression wave having a frequency (F11). The image may be intermittently emitted at a frequency corresponding to the frequency of the wave. The present invention further covers an optical projection method using this device.

Description

Device and method for projecting light synchronized with a sound wave technical field

[0001] The present invention relates to a device for projecting light, particularly two-dimensional images, onto an immaterial surface such as a wavefront or a density front. The optical projection can be emitted intermittently so as to match the frequency of the density front. The invention further covers a method of optical projection onto such an immaterial front. State of the art

[0002] Numerous efforts are being made to study the interaction between sound and light. US Patent 2004021873 A1 describes a method for the optical measurement of sound waves. The method described in US Patent 2010162819 A1 is specifically aimed at locating a sound source. US Patent 2022128883 A1 aims to deflect a beam of light through its interaction with ultrasound. US Patent 2017293259 A1 describes a method for variably focusing a laser point in air. US Patent 2016037146 A1 describes a method for projecting a distorted light wave through a diffusing medium to produce an image within a projection volume.

[0003] However, there is room to further develop current techniques, particularly to improve the quality and / or variety of light projections in the ambient air. SHABE-2-PCT Brief summary of the invention

[0004] One aim of the present invention is to provide a system or device for projecting a variety of images into the ambient air, in this case in the absence of a physical screen.

[0005] Another objective of the invention is to improve the quality and / or diversity of images projected into the ambient air, particularly in the absence of a solid material screen.

[0006] Another object of the present invention is to propose a method of projecting images into a fluid medium, such as ambient air, so that it is visible to an observer.

[0007] These goals are achieved in particular by means of the invention which is the subject of the independent claims and described in more detail in the dependent claims.

[0008] This solution has the advantage over previous methods of producing more diverse and / or higher quality images than projections currently made without a solid screen. Brief description of the figures

[0009] Examples of implementation of the invention are given in the description illustrated by the accompanying figures, in which: • Figure 1: Schematic view of the device according to one embodiment of the present invention, • Figure 2: Schematic view of the device according to one embodiment of the present invention, SHABE-2-PCT Figure 3: Detailed schematic view of the projection of an image onto a density front according to an embodiment of the present invention, • Figure 4: Schematic view of the device according to one embodiment of the present invention, • Figure 5: Schematic view of the device according to one embodiment of the present invention, • Figure 6: Detailed schematic view of a light projection source according to an embodiment of the present invention, • Figure 7: Schematic view of a projection disruption device according to an embodiment of the present invention, • Figure 8: Schematic view of a projection disruption device according to an embodiment of the present invention. Example(s) of an embodiment of the invention

[0010] Device 1 according to the present invention is a device for projecting light onto a surface. Unlike conventional screen projections, where the projection surface is fixed and made of a specific material, the projection surface used in the present invention is defined by a density difference in a gaseous space 40, such as the atmosphere. This density difference produces a variation in the refractive index of light in the gaseous medium, which can make light projections visible. Depending on the angles of incidence of the light projections on a surface defined by a density variation SHABE-2-PCT In a gaseous environment, the reflection and / or refraction of emitted light on such a surface can be observed. This phenomenon is seen in mirages, shimmering effects, or the ripples of distant objects. The present invention, however, aims to control the projected images and their animation, if applicable.

[0011] The device according to the present invention includes a means for varying the density of the ambient gas, in this case air or the atmosphere, so as to produce a refractive and / or reflective surface. The ambient gas 40 has a homogeneous average density D40, or a nearly homogeneous density, in the absence of disturbance. A source of density variation 10 can locally produce a density higher or lower than the average density D40. For example, a heat source, which locally heats the ambient gas, decreases its density relative to its average density D40. The density front, separating the air of average density D40 from the air of lower density, can be more or less distinct, particularly due to thermal diffusion in the atmosphere. Hot air can nevertheless be channeled, for example by being blown from an air source and collected at the end of its path through the atmosphere, so as to minimize thermal diffusion.A source of cold air can alternatively be used for the same purpose. Alternatively, two opposing air currents, one warm and the other colder, can be used to create a density variation front at their interface.

[0012] Alternatively, a heat source, such as a heating element or infrared lamp, can be used directly to heat the air in its vicinity, thereby reducing its density. The locally heated air is preferably exhausted or cooled in a controlled manner to ensure a stable density front.

[0013] The density obtained at the interface can be described as the density front density D11 or simply as the front density. Several hot and / or cold air sources can thus be implemented to maintain the most stable density front possible. SHABE-2-PCT despite the air movement. The density variation front 11 can be more simply referred to as the density front.

[0014] Figures 1 to 6 show examples of implementations where the density variation source 10 is a sound source. The principle remains applicable to other density variation sources, such as the thermal sources mentioned above. The density variation source 10 can produce overpressures by compressing the ambient air, typically through sound emission. In this case, the sound emission produces a compression wave that propagates through the atmosphere at the speed of sound, on the order of 340 ms. 1forming successive compression fronts. Depending on the sound frequency, the compression fronts are more or less spaced apart. These compression fronts thus form several density variation fronts, or density fronts, which can be exploited for their refractive and / or reflective properties. Depending on the sound volume, the density difference, directly related to the difference in ambient gas pressure, can be determined. Louder sound volumes result in the greatest density variations. This is also referred to as high sound pressure levels. The sound volume can then be considered in relation to the sharpness of the image projected onto the density front.

[0015] The sound frequencies used can be audible to humans, typically between 20 Hz and 20 kHz. Alternatively, frequencies below 20 Hz, or even below 15 Hz, 10 Hz, or 5 Hz, in the infrasound range, which are inaudible to humans, can advantageously be used. The sound volume can thus be significantly increased without harm to humans, allowing for large variations in density. Furthermore, the use of inaudible frequencies eliminates potential interference with ambient sounds. However, a frequency that is too low may not be suitable for the needs of the present invention. Indeed, as explained in more detail below, the passage of the density front 11 is too fleeting to constitute a projection surface on its own, so the projection occurs over a series of several successive density fronts. When they are too far apart from each other, the projection can be degraded.Preferably, the frequency. SHABE-2-PCT of the compression wave is greater than 0.5 Hz or 1 Hz. Although infrasound is not audible to humans, it is still referred to, for the purposes of the present invention, as sound or sound waves, its effect being to produce in all cases a density front 11 or a series of density fronts 11.

[0016] The device may include more than one source of density variation 10. In this case, several sound sources can be used. The sound waves emitted by each source can be synchronized to produce a common density front 11. Alternatively, several sound emission sources can be used with a phase shift to produce a three-dimensional effect when projecting light. In this case, the different density fronts 11 produced are shifted in time and space and can be used as a projection surface. Different density fronts 11 can, for example, be shifted by half a phase, a third of a phase, or a quarter of a phase. This arrangement applies when the different sources emit a sound of the same frequency. However, it is still possible to combine sound waves of different frequencies.

[0017] Alternatively, or in addition, several sound sources can be located in different places, producing several distinct sets of density fronts, which may have different propagation directions. These distinct density fronts are located in different places. Such an arrangement can be used for a richer light projection or for three-dimensional or combined visual effects.

[0018] Different types of density variation sources 10 can be combined. For example, a first density front 11 can be obtained thermally, in particular by a hot air source or by a device for locally heating the atmosphere, and a second density front 11 can be produced by one or more sound sources. SHABE-2-PCT

[0019] The surface defined by the density front 11 is preferably flat, or globally flat. One or more sound sources can be designed to emit a density front 11 with a square geometry (Figure 2) rather than a spherical one (Figure 1). The spherical aspect of a density front 11 remains usable, however. Other geometries of density front 11 can alternatively be considered.

[0020] For the purposes of this invention, a sound source means any device capable of emitting sound, in this case sound of controlled intensity and frequency. Typically, a loudspeaker or a set of loudspeakers can be used for this purpose. Various technologies, such as those based on electromagnets or piezoelectric elements, or any other equivalent, can be considered as required.

[0021] The density front 11 can be fixed or globally fixed, that is, localized to a specific location. Such a density front can be described as permanent, in the sense that it persists and can continue as needed. Typically, a thermally produced density front 11, as described above, can be described as fixed or permanent, or pseudo-permanent or semi-permanent. The terms pseudo-permanent and semi-permanent are equivalent here. They reflect, for example, the fact that the density front can weaken over time due to thermal diffusion. The weakening of the density front 11 refers, for example, to a decrease in the density difference on either side of this density front. In this case, a density front 11 can persist for a variable duration, for example, from a few seconds, on the order of 10 to 40 seconds, to a few minutes, such as 1 to 5 or 10 minutes.

[0022] Such a permanent or semi-permanent density front can advance slowly due to thermal diffusion. Indeed, it is possible for cold air to gradually warm up upon contact with warm air, thus leading to the progression of the density front. As detailed below, light projection can be focused over a distance range, allowing images to be projected onto a density front. SHABE-2-PCT progressing through the ambient gas at low speed. Such a density front can then be exploited for a longer period despite the effects of thermal diffusion.

[0023] Alternatively, the density front can be mobile, typically in a propagation direction 12. This is notably the case for a sound wave propagating through a fluid such as air. The density front is then fleeting, being present in a given space for only a brief instant, relative to the speed of sound propagation. In this case, several successive density fronts 11 propagate at a front frequency ΔFl, corresponding to the sound frequency used by the sound source. At a given location, the density varies according to the propagation of the sound wave. The succession of density fronts 11 at a given location can be used as a projection surface. In this case, the projection surface is intermittent. When the frequency of the sound wave is sufficiently high, the projection remains visible. The intermittency of the density front 11 at a given location can alternatively be exploited for optical effects of blinking or scintillation.

[0024] Regardless of the nature of the density variation source 10, the density front 11 comprises one or more projection zones 110 on which the projected images or light effects are printed.

[0025] The propagation direction 12 of the density front 11, if any, can be centrifugal from a sound emission source. This is particularly the case with spherical or semi-spherical waves. The propagation can be more rectilinear if several sound sources are arranged in parallel so as to produce the same density front 11 or the same series of density fronts. Alternatively, sound sources can be designed to emit a non-spherical compression wave, for example, a square wave.

[0026] The terms "density" or "density variation" refer to the fluid mass density at the location considered, for example at the density front or on either side of the density front. Density is SHABE-2-PCT correlated with pressure such that a change in density corresponds to a change in pressure. High densities correspond to high pressures. Low densities correspond to low pressures. A density front is, within the scope of the present invention, equivalent to a pressure front. The density or pressure front is understood here as a surface.

[0027] The present invention can be applied to any fluid, whether liquid or gaseous, provided that local variations in density or pressure can be implemented. Preferably, such density variations are implemented intentionally and in a controlled manner, at least with regard to their location, amplitude, and frequency, if applicable. The density variations lead to variations in the fluid's refractive index, which are exploited for the purposes of the present invention to produce images or optical effects. Preferably, the term "fluid" refers to a gas. More specifically, the term "fluid" refers to ambient air, in this case, the ambient air of a room in a building. It can also refer to outdoor ambient air, for example, air in an urban public space.Ambient air can also refer to a lower layer of the atmosphere, into which large luminous figures can be projected, making them visible to observers on the ground. A light show can thus be offered to a wide audience.

[0028] The device of the present invention comprises at least one light projection source 20. Such a light projection source may be a projector comprising a light source and a lens 24 or a set of lenses for projecting an image 30 at a distance. The light source may be an LED or an array of LEDs or any equivalent device. The light source may be a laser source 202. The emitted light may be polarized or unpolarized. One or more filters may be used in combination with the light source, such as colored, diffractive, and / or polarizing filters. SHABE-2-PCT

[0029] The image 30 can result from a pattern 205 (Figure 6) positioned in front of the lens 24. Such a pattern 205 can take the form of a mask, allowing light to pass through at the points required to produce the image 30. This pattern 205 can be static or animated. In the latter case, several masks can be used. The image 30 is projected along a projection direction 22. The image 30 can thus represent a recognizable pattern such as a commercial logo or slogan. Alternatively, the image 30 can depict abstract patterns such as shades of color of varying intensities, flickers, or other optical effects.

[0030] In one embodiment, the projection direction 22 forms an angle of incidence 60° with the density front 11, as better illustrated in Figure 3. The light projected onto the density front 11 is then capable of producing reflected light 22a and / or refracted light 22b. Either of the reflected light 22a and refracted light 22b can be used to produce optical effects visible to one or more observers 70. The angle of incidence is judiciously chosen so as to produce at least one of the reflected light 22a and refracted light 22b. The angle of incidence 60° can, for example, be less than 40°, or even less than 30° or 20°. It can be between 2° and 45°, or between 5° and 40°, or between 10° and 25°. Alternatively, it can be greater, for example around 45°, 60°, or 80°, or any intermediate value. In this case, it can be between 40° and 89°.According to another embodiment the angle of incidence 60 can be orthogonal to the density front 11, i.e. 90°.

[0031] In one embodiment, the light projection source 20 and the density variation source 10 are arranged opposite each other, forming an angle of 90° or greater. Such an arrangement is illustrated in Figures 1, 2, and 5. When the density variation source 10 is a sound source producing a wave with a propagation direction 12, this arrangement results in the meeting or crossing of the propagation direction 12 and the projection direction 22. This arrangement may be preferred for greater clarity of the light projection. The projection 22 is opposite to the progression of the density front 11. This does not preclude the light projection source 20 and SHABE-2-PCT The two sources of density variation 10 may form an angle of less than 90° with each other. In this case, particularly when the source of density variation 10 is a sound source, the projection 22 joins the density front 11 in the direction of its propagation. Figure 4 gives an example of such a configuration. In this instance, a sound source 10 is coplanar with two light projection sources 20, 20' arranged on either side of the sound source. The projection direction 22 follows the propagation direction 12 and joins the density front 11 at different projection zones 110.

[0032] The light projection source 20 includes at least one lens 24 allowing the projected image 30 to be focused at the level of the projection area 110, coinciding with a density front 11.

[0033] The image 30 can be projected continuously. This arrangement is particularly applicable in the case of a permanent or semi-permanent density front 11. The focusing distance can also be adjusted to align the projected image 30 with the density front 11. This allows the focal length to be adjusted according to the slow movement of the density front 11, for example, during thermal diffusion in air. Continuous projection of an image 30 can also be achieved with a series of moving density fronts 11, such as those emanating from a sound source. The focal length can be precisely targeted at the projection area 110 of a single density front 11, thus avoiding optical effects related to adjacent density fronts. This arrangement is more readily applicable to low-frequency density fronts. In this case, the continuously projected image 30 appears clearly as the density front 11 passes.It can degrade when the density front 30 no longer coincides exactly with the focal length. Depending on the front frequency Fil, the projected image 30 may be perceived as more or less sharp. Depending on the front frequency F1, the projected image may appear intermittent, particularly at low frequencies. SHABE-2-PCT

[0034] Alternatively, the light projection source 20 can be adapted to project an image 30 intermittently onto the projection area 110. Although such an arrangement is applicable to a permanent or semi-permanent density front, it is particularly advantageous for projecting an image 30 onto a series of moving density fronts 11 whose front frequency F11 is known and / or controlled. The projection frequency F30 can then be calibrated to correspond to the front frequency F11 or a fraction thereof. In this way, the image 30 appears on the projection area 110 only when a density front 11 is present. The projection quality is thus controlled. In one embodiment, a front frequency F11 can correspond to an audible sound, and the projection frequency F30 can be a fraction of this frequency so as to project an image 30 onto only certain density fronts 11.This arrangement makes it possible to limit the projection frequency and simplify the equipment. Furthermore, this arrangement allows an audible message to be delivered to observers while simultaneously producing a visual effect on the corresponding sound wave.

[0035] The light projection source 20 may, for this purpose, include a disruption device 21 for periodically interrupting the projection of the image 30 and / or projecting it periodically at a predetermined projection frequency F30. Figure 7 shows an example of a disruption device 21 comprising a disk 220 rotated about an axis of rotation 230 by a motor 210. The disk 220 rotates about the axis of rotation in a direction of rotation R220. It comprises an alternation of opaque sectors 221 and transparent sectors 222. The opaque sectors 221 and transparent sectors 222 pass successively in front of the light source and periodically obscure the projection of the image 30. The width of the opaque sectors 221 and transparent sectors 222 is determined in accordance with the projection and interruption time of the image 30 for a given rotation speed of the disk 220. The widths of the opaque sectors 221 and transparent sectors 222 may be identical or different.Alternatively, the widths of the opaque sectors 221, and / or the transparent sectors 222, can vary according to their angular position on the disk 220. Thus, when the disk rotates at a constant speed in the direction of rotation R222,. SHABE-2-PCT The projection frequencies can change and produce specific lighting effects. For example, the opaque sectors 221 and transparent sectors 222 can have a certain width over one angular portion of the disk 220 and a width divided by 2 or more, or even 2 or more than twice as wide, over another angular sector of the disk 220. The projection frequency F30 is thus increased or decreased by the same factor. The various projection frequencies 30 thus obtained can be multiples of the front frequency F11 of the emitted sound, if any. Alternatively, the various projection frequencies F30 thus obtained can correspond to different front frequencies F11. The sound source can be modulated accordingly so that the front frequencies F11 correspond to the projection frequencies F30.

[0036] Disk 220 is schematically represented with some opaque sectors 221 and transparent sectors 222. It can nevertheless contain a large number of such sectors, such as several dozen or several hundred.

[0037] Alternatively or in addition, several similar discs can be arranged on the rotation axis 230, each comprising a specific arrangement of opaque sectors 221 and transparent sectors 222, and rotated according to the required projection frequencies F30. The unactivated discs are arranged so that a transparent sector 222 is facing the light source.

[0038] Alternatively or in addition, the rotation speed of motor 210 can be modulated or adjusted so as to project an image 30 at the required projection frequency F30.

[0039] The use of occultation discs as described above allows the continuous projection of a 30 image by the light source.

[0040] According to an alternative embodiment, illustrated by Figure 8, the disruption device 21 consists or comprises an electronic system 201 for switching the light source on and off at a frequency SHABE-2-PCT corresponding to the projection frequency F30. The light emission is thus discontinuous, and the image is projected only at the required times. Such an arrangement is advantageous in the case of a laser source that can be electronically controlled.

[0041] It is possible that several disruption devices of different types may be combined. For example, an electronic system 201 allowing intermittent activation of the light source can be combined with one or more occultation discs 220 so as to be able to adapt the projection frequencies F30 over a wide range of values.

[0042] The light projection source 20 preferably includes one or more focusing lenses 24. Such a lens allows the projected image 30 to be focused at a predetermined distance from the light source. In this case, the focusing lens 24 allows the image 30 to be focused onto a density front 11, whether intermittent, as in the case of a sound wave, or continuous, as in the case of a heat source.

[0043] According to certain provisions, a light projection source 20 may include several focusing lenses 24 each allowing the image 30 to be focused on different density fronts 11.

[0044] According to one embodiment, the sound source emits a wave of known frequency and the light projection source 20 is calibrated to synchronize the projection frequency F30 to the front frequency Fil.

[0045] According to another embodiment, the device according to the present invention comprises, or is connected to, a control unit 50. The control unit 50 may be connected to or integrated with the density variation source 11. It may be connected to several density variation sources 11 if necessary. The control unit 50 may be adapted to vary or adjust the position of the density front, or the amplitude of the density difference across the density front, or the frequency of the front F11 if necessary, via control of the variation source(s). SHABE-2-PCT density. In the case where the density front results from a thermal variation, the control unit 50 is adapted for example to activate or deactivate one or more sources of heat or cold and / or to adapt their intensity so that they produce more or less heat or cold.

[0046] In cases where the source of density variation is one or more sound sources, the control unit 50 allows for varying the intensity and / or frequency of the emitted sound. It also allows for activating or deactivating one or more sound sources as needed, either alternatively or in addition to these functions.

[0047] In one embodiment, the control unit 50 is integrated into or connected to at least one light projection source 20. In this case, it can adjust the projection frequency F30 of the image, activate or deactivate a light source, and modify the characteristics of the projected image 30, such as its contours, colors, or other features. The control unit 50 can also, alternatively or in addition, adapt or adjust the projection frequency F30.

[0048] In one embodiment, two separate control units can each be associated with a density variation source and a light projection source. The density fronts 11 and the image projection 30 can in this case each correspond to a pre-established program and be independently controlled by each of the control units 50.

[0049] Alternatively, the device according to the present invention comprises a single control unit 50 connected to at least one density variation source 10 and to at least one light projection source 20. In this way, the control unit 50 is able to actively synchronize the projection of the image 30 onto the density front 11. Such a control unit 50 allows, for example, the synchronous variation of the projection frequencies F30 and the front Fil. It also allows, alternatively or in addition, the activation or deactivation of a device for SHABE-2-PCT light projection 20 and an associated density variation source, so as to produce an optical effect.

[0050] According to one embodiment, the device according to the present invention comprises one or more sensors. Sensors such as optical sensors may be considered, particularly for verifying the quality of the projected image 30. Optical sensors, active in the visible, infrared, or ultraviolet ranges, may be arranged around the projection areas 110. Alternatively or in addition, thermal sensors may be considered, particularly when the density front results from thermal variations. Thermal sensors can be useful for evaluating or characterizing the density front 11.

[0051] According to one embodiment, the data captured by one or more sensors is collected and analyzed by the control unit 50. If the quality of the image 30 does not correspond to that expected, the control unit 50 can adjust one or more parameters such as the projection frequency F30, the front frequency Fil, the intensity of the emitted sound, the temperature of the heat or cold source.

[0052] According to one embodiment, the control unit 50 includes or is connected to a learning program, or artificial intelligence, so as to adapt at least one of the above parameters autonomously.

[0053] The present invention further covers a method for projecting one or more images 30 onto one or more density fronts 11 present in a fluid, preferably a gas such as ambient air. The projection method includes a step of producing one or more density fronts 11 by means of one or more of the density variation sources 10 described above. This step makes it possible, in particular, to control the density difference of the front D11 relative to the density of the medium D40. The local density variation is accompanied by a variation in the refractive index of the ambient medium. The density front can be permanent, semi-permanent, or intermittent. SHABE-2-PCT permanent or mobile. Parameters such as the position, frequency, and / or amplitude of the density fronts are controlled. The step of producing one or more density fronts 11 may include the step of determining and / or controlling the front frequency F11.

[0054] The present method includes the step of projecting an image 30 onto at least one front of density 11. The image may be projected continuously or intermittently. The image may be of any nature; it may represent an optical effect such as a flicker, illumination, a reverberation effect, or color variations. It may have defined contours, either alternatively or in addition to them. It may be fixed, i.e., static, or animated.

[0055] The present method may include a step of focusing the projected image 30 onto at least one density front 11. Focusing may be achieved by one or more suitable optical lenses. In this way, the image is visible to an observer 70 without any projection surface being visible to them.

[0056] The present method may include a step of capturing the projected image 30 using one or more optical sensors. Depending on the quality of the image 30, the focus of the image 30 can be adjusted. The focus adjustment can be done manually. Alternatively, the focus is adjusted automatically, for example, using a control unit 50, with or without the aid of an artificial intelligence program.

[0057] The present method includes a step of activating and deactivating the image projection at a controlled projection frequency F30. The intermittent nature of the projection can be achieved by a disruption device described above, including an electronic control system and / or a perforated disc, or by any other suitable system. SHABE-2-PCT

[0058] The method may include the step of synchronizing the projection frequency F30 to the front frequency F11 if necessary.

[0059] The present method may include the step of adapting the projected image 30 to a sound sequence audible to humans. SHABE-2-PCT Reference numbers used in the figures 1 Projection device 11 Density front 12 Propagation direction 1 Disruption device 22 Projection direction 22a Reflected light 22b Refracted light 24 Projection lens 30 Projected image 0 Gaseous environment 50 Control unit 70 Observer 110 Projection area 201 Electronic system 202 Laser source 210 Motor 230 Rotation axis 220 Disc 221 Opaque sector 222 Transparent sector R220 Direction of rotation D11 Front density D40 Gaseous environment density F11 Front frequency F30 Projection frequency SHABE-2-PCT

Claims

1. Claims 1. Device (1) for projecting light into a fluid environment (40) of environmental density (D40), comprising: - at least one density variation source (10) adapted to locally vary the density of the fluid environment so as to produce at least one density front (11) having a front density (D11), and - at least one light projection source (20), comprising a light source, adapted to project at least one image (30) onto said at least one density front (11).

2. Device according to claim 1, said at least one source of density variation being selected from one or more sound sources, one or more heat or cold sources, or a combination of sound and heat or cold sources.

3. Device according to any one of claims 1 and 2, said at least one light projection source comprising a focusing lens (24) adapted to focus the projected image (30) onto said at least one density front (11).

4. Device according to any one of claims 1 to 3, further comprising a projection disruption device (21) adapted to produce an intermittent projection of the image (30) on said at least one density front (11).

5. Device according to claim 4, said disruption device comprising an electronic system for activating and deactivating the light source and / or a rotating disk (220) provided with opaque (221) and transparent (222) sectors. SHABE-2-PCT 6. Device according to any one of claims 1 to 5, said at least one density variation source comprising at least one sound source and said density front being a compression wave having a front frequency (F11), said at least one light projection source (20) being adapted to project an intermittent image at a projection frequency (F30), the front frequency F11 being identical to or a multiple of the projection frequency (F30).

7. Device according to any one of claims 1 to 6 further comprising a control unit (50) enabling control of said at least one source of density variation, said at least one light projection source or the combination of at least one source of density variation and light projection.

8. Device according to any one of claims 1 to 7, further comprising one or more sensors adapted to determine the position or characteristics of the density front (11) and / or the quality of the projected image (30).

9. Method of projecting at least one image (30) onto one or more density fronts (11) by means of a device according to any one of claims 1 to 8 comprising the steps of: - produce one or more density fronts (11) by means of one or more density variation sources (10), and - project said at least one image (30) onto said one or more density fronts (11).

10. Method according to claim 9, further comprising the step of focusing said at least one image (30) on said one or more density fronts (11) by means of a focusing lens. SHABE-2-PCT 11. Method according to any one of claims 9 and 10, further comprising the step of monitoring said at least one image (30) or said one or more density fronts (11) by means of at least one sensor such as an optical sensor or a thermal sensor and of adjusting the focus and / or the position of the density front in the ambient space.

12. Method according to any one of claims 9 to 11, further comprising activating and deactivating the projection of said at least one image at a controlled projection frequency (F30).

13. Method according to any one of claims 9 to 12, wherein producing one or more density fronts (11) comprises producing a compression wave by means of one or more sound sources, according to which a series of density fronts (11) follow one another at a front frequency (F11).

14. Method according to any one of claims 12 and 13, further comprising the step of synchronizing the projection frequency (F30) with the front frequency (F11) by means of a control unit (50) SHABE-2-PCT

Images