WO2010079151A1

WO2010079151A1 - Device for converting mechanical energy into electric energy using at least one piezoelectric transducer

Info

Publication number: WO2010079151A1
Application number: PCT/EP2010/050012
Authority: WO
Inventors: Jean-Pierre Nikolovski
Original assignee: Commissariat A L'energie Atomique Et Aux Energies Alternatives
Priority date: 2009-01-06
Filing date: 2010-01-04
Publication date: 2010-07-15
Also published as: FR2940855B1; EP2374169A1; FR2940855A1

Abstract

The invention relates to a device for converting mechanical energy into electric energy, comprising at least one conversion cell (C) comprising at least one percussion mechanism (6) including one deformable member (7), having at least two opposite anchoring points, rigidly connected in a central area of a percussion member (8), and one or more piezoelectric transducers (10) coupled to an acoustic resonator (9). The deformable member (7) includes at least one stable position in which the percussion member (8) is remote from the acoustic resonator (9), the percussion mechanism (6) and the acoustic resonator (9) being arranged so that when a force exceeding a threshold is applied onto the deformable member (7), the latter leaves the stable position by deformation so that the percussion member (8) hits the acoustic resonator (9) so that it resonates and excites the piezoelectric transducers (10) and so that the energy generated by the force is converted by the piezoelectric transducers.

Description

DEVICE FOR CONVERTING MECHANICAL ENERGY IN ELECTRIC ENERGY USING AT LEAST ONE TRANSDUCER

PIEZOELECTRIC

DESCRIPTION

TECHNICAL AREA

The present invention relates to devices for converting mechanical energy into electrical energy. More specifically, it relates to energy conversion devices using one or more piezoelectric transducers capable of performing this conversion. It is particularly suitable for applications in which the power requirements are short-lived.

STATE OF THE PRIOR ART

Energy conversion devices using one or more piezoelectric transducers are generally formed of conversion cells arranged in a panel or in other configurations. They are formed of a mass that rests on one or more springs. To this mass is attached the piezoelectric transducer so that when a force is applied to the mass, the cell enters into vibration, and the transducer converts this vibration into electrical energy.

Such a device is known in the patent application WO 2006/046938. Figure 1 shows in section such an energy conversion device. This is an energy conversion device vibration device including at least one piezoelectric transducer 2.

It is formed of a test mass 1 resting on a bilayer substrate S formed of a layer of unimorphous piezoelectric material 2, which constitutes the piezoelectric transducer, and a layer of non-piezoelectric material, which constitutes a spring layer 3 The mass 1 is on the side of the layer of piezoelectric material 2. The bilayer substrate S is integral with a support structure 5, by means of elastic legs 4, placed between the spring layer 3 and the support 5.

When a stress is induced on the device, the test mass 1 exerts a force on the piezoelectric layer 2. It deforms as well as the spring layer 3 and the elastic legs 4. The deformation of the piezoelectric layer 2 induces the generation of electrical energy. When the stress is no longer exerted on the device, a restoring force is applied to the spring layer 3 and the elastic legs 4, it deforms the piezoelectric layer 2. This deformation leads to the generation of electrical energy. However, this energy conversion device has drawbacks. First of all, if we look at the very principle that is based on the bending of a unimorphous piezoelectric structure by means of an inertial mass set in displacement by a mechanical vibration, it appears that the frequency and the amplitude of the excitatory vibration have an effect direct on conversion efficiency and available power, but yet these are not known in advance. The piezoelectric transducer 2 is fragile and of low efficiency, much less than 25% for example. At high amplitudes of vibrations, the piezoelectric layer can undergo high stresses, which can weaken it strongly and limit its life.

This energy conversion device is in practice designed to operate with the vibrational mechanical energy available in an amount always sufficient with respect to the task to be performed and corresponding to a limited spectrum of excitation, originating, for example, from the movement of a vehicle or the rotation of a machine, so the question of conversion efficiency is not critical. But these devices can not take advantage of pulsed mechanical energy such as that generated by shocks.

STATEMENT OF THE INVENTION

The object of the present invention is to provide a device for converting mechanical energy into electrical energy which does not have the drawbacks of prior devices, in particular which is capable of taking advantage of pulsed, punctual or repeated events.

Another object of the invention is to propose a device for converting mechanical energy into electrical energy which is robust to shocks. Another object of the invention is to provide a device for converting mechanical energy into electrical energy which has a better conversion efficiency than in the past, especially greater than about 25%.

Yet another object of the invention is to provide an energy conversion device which is very compact and thin.

A further object of the invention is to provide a conversion device in which it is possible to calibrate the electrical output energy.

To achieve these objects, the present invention provides a device for converting mechanical energy into electrical energy formed of at least one conversion cell comprising at least one percussion mechanism including a percussion element and one or more piezoelectric transducers. It further comprises an acoustic resonator to which the piezoelectric transducers are coupled. The percussion mechanism furthermore has a deformable element having at least two opposite anchoring points, the percussion element being integral with the deformable element in a central zone of the latter. The deformable element has at least one stable standby position in which the percussion element is remote from the acoustic resonator, the percussion mechanism and the acoustic resonator being arranged so that when a force greater than a threshold is applied to the deformable element, it leaves its stable standby position by deforming so that the percussion element comes impacting the acoustic resonator in a percussion zone to resonate and excite the piezoelectric transducers so that the force-induced energy is transmitted indirectly to the piezoelectric transducers to convert it into electrical energy.

The deformable element may, instead of being monostable, be bistable, that is to say include another stable position said percussive in which the percussion element is in contact with the acoustic resonator.

For the conversion device to operate with rain, the percussion mechanism will preferably have a mass substantially equal to that of a mean raindrop.

In order for the conversion device to be able to operate efficiently with a flow of fluid, such as wind, the deformable element will be equipped with an obstacle to the circulation of the fluid, placed upstream of its central zone with respect to the circulation of the fluid. .

It is possible to provide a protective membrane that protects the percussion mechanism opposite the acoustic resonator, a shim integral with the deformable element being inserted between the membrane and the deformable element, the force that applies to the element deformable being transmitted to it by the membrane and the wedge.

The protective membrane may be attached to a support frame of the percussion mechanism and the acoustic resonator, the frame cooperating with a bottom to form a box closed sealingly by the protective membrane.

The piezoelectric resonators are located at a distance from the percussion zone of the acoustic resonator, at the periphery of the acoustic resonator.

When there are two percussion mechanisms, they operate alternately, the acoustic resonator having two percussion zones located on two opposite faces of the acoustic resonator.

The acoustic resonator may have a substantially constant thickness or have a lower thickness at the level of the percussion zone than at its periphery.

The acoustic resonator can have a biconical profile and thus have an impedance transformer function.

It is possible to provide an automatic reset mechanism with one or more elastic return tongues, placed between the membrane and the deformable device and having a free end at the central zone of the deformable device and an end anchored to the chassis, this free end being intended to cooperate with a return hook attached to the deformable device.

The elastic tongues have a protrusion on the side of the protective membrane.

The piezoelectric transducers can be connected to a processing circuit with a rectifier at the terminals of which is optionally connected a capacitor tank.

To be bistable, the deformable element may be formed of two superimposed main walls, fixed to one another by a substantially central auxiliary wall extending substantially transversely to the two main walls.

When the energy conversion device comprises several conversion cells, they can be arranged in at least one panel, and when there are several panels they can be superimposed.

The conversion cells can be connected together, in series or in parallel. The present invention also relates to an energy conversion apparatus, formed of a power conversion device thus characterized and a solar panel, the energy conversion device being transparent and overlying the solar panel. The present invention also relates to a measuring device comprising a power conversion device thus characterized and at least one sensor supplied with energy by the energy conversion device. The energy conversion device and the sensor may be embedded in a carpet.

The present invention also relates to a spark producing device comprising a power conversion device thus characterized and a pair of electrodes powered by the energy conversion device. BRIEF DESCRIPTION OF THE DRAWINGS

The present invention will be better understood on reading the description of examples of embodiments given, purely by way of indication and in no way limitative, with reference to the appended drawings, in which: FIG. 1 already described represents a cross-section of a known energy conversion; FIG. 2 represents a device for converting energy according to a first embodiment of the invention, during the transition from a stable standby position to a struck position; Figure 3 shows another embodiment of the invention, in the impacted position; Figures 4A, 4B show yet another embodiment of the invention in the standby position and in the impacted position; FIG. 5 represents a sectional view of an acoustic resonator and of two piezoelectric transducers connected in parallel with a conversion device of the invention; FIG. 6 represents a perspective view of the acoustic resonator and the piezoelectric transducers of FIG. 5; FIG. 7 represents a sectional view of an acoustic resonator and four piezoelectric transducers connected in series with a conversion device of the invention; Figure 8 shows a perspective view of the acoustic resonator and the piezoelectric transducers of Figure 7; Figures 9A-12 show a bistable deformable element in various positions; FIG. 13 is a graph showing the force applied to the bistable deformable element as a function of the displacement of its central portion; FIG. 14 represents a conversion device of the invention with a single acoustic resonator but having two percussion mechanisms; Figure 15 shows a sectional view of a wind panel according to the invention; Figure 16 shows a sectional view of a "cube" wind according to the invention; FIG. 17 is a perspective view of an apparatus for converting mechanical and solar energy into electrical energy. Figure 18 shows in the form of a measuring device mat, using a device for converting energy according to the invention.

Identical, similar or equivalent parts of the different figures described below bear the same numerical references so as to facilitate the passage from one figure to another.

The different parts shown in the figures are not necessarily in a uniform scale, to make the figures more readable.

The different variants described and illustrated should be understood as not being exclusive of each other. DETAILED DESCRIPTION OF PARTICULAR EMBODIMENTS

The energy conversion device according to the invention may comprise one or more conversion cells. The cells can be arranged in a matrix to form a panel, it is even possible to group several panels one above the other so as to produce parallelepipeds.

FIG. 2 represents a conversion cell C of a device for converting mechanical energy into electrical energy, according to a first embodiment of the invention. This cell C is represented during the passage of a first so-called standby or armed position to a second position called activated or impacted. This conversion cell comprises a percussion mechanism 6 formed of a deformable device 7 equipped with a percussion element 8. It is this percussion mechanism 6 that is intended to move from the standby position to the activated position, when a force f applies to him. The percussion mechanism 6 is in a stable position at least in the standby position.

This percussion mechanism 6 is intended to cooperate with an acoustic resonator 9. More specifically, during the transition from the standby position to the activated position, the percussion element 8 comes into contact with a so-called percussion zone 9.1 of the acoustic resonator 9. The acoustic resonator 9 is intended to excite one or more piezoelectric transducers 10. The piezoelectric transducers 10 are coupled to the acoustic resonator 9, they are in contact with the acoustic resonator 9 preferably spaced from the percussion zone 9.1 of the acoustic resonator 9. In the example described, the piezoelectric transducers 10 are annular and sandwich the periphery of the substantially disk-shaped acoustic resonator 9. They are vis-à-vis.

The deformable device 7 takes the form of a deformable membrane which is anchored at its periphery on a support frame of the acoustic resonator 9. The deformable device may be formed of a metal sheet.

The percussion element 8 is shown as a ball integral with the deformable device 7 and placed on the acoustic resonator 9 side. Other configurations are possible such as a projection directed towards the acoustic resonator 9, obtained by deformation of the deformable device 7. protrusion may be a part of the deformable device which has been stamped with the aid of a needle for example. This configuration is inexpensive. The ball could be replaced by a hammer. The mass of the ball or hammer will be chosen so as to optimize the coupling between the mechanical energy supplied and the electrical energy delivered by the piezoelectric transducers.

The piezoelectric transducers 10 may be of the PZT ceramic or lead Titano-Zirconate type, of formula Pb (Zr _x , Tii- _x ) O3. They are intended to convert a bending wave generated by the acoustic resonator 9 into an electrical signal. The piezoelectric transducers 10 are intended to be electrically connected to a user device for electrical energy. We will see later an example.

The energy conversion device may further comprise a housing 11, formed of the frame 15 and a bottom 11.1, so that the acoustic resonator 9 is housed in the box 11 and thus protected. A free space 50 exists between the acoustic resonator 9 and the bottom 11.1 of the box 11. The frame 15 and the bottom 11.1 of the box can be assembled by screwing or clipping via a bar cutting of the frame. In Figure 2, the thread is referenced 16.

A spacer 12 is inserted between the acoustic resonator 9 and the percussion mechanism 6. The percussion mechanism 6, the spacer 12 and the acoustic resonator 9 are held in position relative to one another by means of a return of the frame 15 and the fastening by screwing to the bottom 11.1. Thanks to the screwing, it is possible to adjust the position of the percussion element 8 with respect to the acoustic resonator 9, in particular when the percussion mechanism 6 is in the impacted position.

When a force f is applied to the cell 6 while it is in the first standby position, the deformable device 7 of the percussion mechanism 6 is deformed and the percussion element 8 approaches the acoustic resonator 9 in such a way that let him hit him. The percussion element 8 ensures a substantially punctual impact on the acoustic resonator 9 in a percussion zone 9.1. The percussion element 8 gives up its potential energy of 9. The conversion cell C is then in the percussive position.

The acoustic resonator 9 resonates, the resonance being radial, and oscillates in a radial bending mode, thereby exciting the piezoelectric transducer (s) 10 placed at its periphery, generating a bending wave. The piezoelectric transducers 10 placed at the periphery are able to convert the potential energy yielded by the percussion element 8 to the acoustic resonator 9 into electrical energy. In a variant described below the acoustic resonator 8 can oscillate in an antisymmetric vibration mode relative to its median plane as shown in Figures 5 or 7 described later. The piezoelectric transducers are then located on either side of the median plane.

At low frequencies the antisymmetric modes are bending modes. We generally speak of antisymmetric mode when the geometry of the resonator allows to define a median plane. Even if the resonator 9 does not rigorously have a median plane in the zone of slow decay of the thickness, as is the case in FIG. 2, but the wave arrives at the interface with the piezoelectric transducers 10 located opposite is such that normal components of mechanical displacement are almost antisymmetric with respect to the median plane, so we can also speak of antisymmetric wave. In practice, if there is only one transducer, it is called bending wave and if there are two transducers facing each other, we speak of antisymmetric waves bearing in mind that the phase difference of the normal displacement components between the two transducers is practically nil and is, in practice, less than about 10 ° whatever the chosen form of the resonator.

The acoustic resonator 9 preferably has a mechanical impedance matching function which physically results in a thickness in the percussion zone 9.1 smaller than that of the peripheral zone in which the cooperation with the piezoelectric transducers 10 takes place.

To optimize the energy conversion efficiency, it is advantageous for the acoustic resonator 9 to have a central symmetry, such as a disk, and for the percussion zone 9.1 to be substantially coincidental with the center of symmetry of the acoustic resonator 9. say the focal point of propagation of bending waves. The acoustic resonator 9 may be metal, for example duralumin, brass, copper, steel, stainless steel. Alternatively, it may be made of synthetic material including transparent, such as polycarbonate, or even glass.

The force f can be applied by an operator, using his foot, or at least one finger, preferably substantially in the central zone of the deformable device 7 if it is one-off. But in a general way we will see that the cell of C conversion can take advantage of any kind of mechanical force.

The configuration of FIG. 2 is particularly adapted to take advantage of the flow of a fluid at the surface of the deformable device 7. This fluid may be the wind as will be described more precisely in FIGS. 15 and 16.

In the standby position, the deformable device 7, offers a hold wind, it has a convex shape. The device is monostable and its stable position is its standby position.

From a certain wind speed, the deformable device 7 undergoes a pressure sufficient to cause it to deform and tilt from its stable position to the impacted position. In this impacted position, the deformable device instead of having a convex shape has a concave shape. After tilting and percussion, a depression appears on its surface which favors its return to its initial stable position. Once the deformable device 7 is returned to its initial position, the tilting phenomenon begins again to the extent that it undergoes sufficient pressure. The deformable device 7 oscillates between the stable position and the impacted position.

The deformable device 7 leaves its stable position only if the force applied, in the example by the fluid, exceeds a tipping threshold. That is, the applied force is sufficient to break the stable equilibrium of the deformable device 7. The characteristics of the mechanism of percussion 6, in particular the mass of the percussion element 8, the area of the deformable device 7, its material, its texture, its thickness are chosen according to the desired impact energy and the minimum speed of the fluid allowing oscillating the deformable device 7.

The characteristics of the conversion cell C are preferably chosen so that the duration of the percussion is equal to the half-fundamental radial resonance period of the acoustic resonator 9 according to a bending mode. Such dimensioning makes it possible to ensure that the percussion potential energy is effectively converted into a radial resonance mode of the acoustic resonator 9. Indeed, the desired duration of percussion and therefore the resonance frequency of the acoustic resonator 9 and the The impact energy to be transmitted to the acoustic resonator 9 depends on the dimensioning of the percussion element 8. The duration of percussion is directly a function of the retro-propagation time of the percussion wave inside the percussion element 8 and the deformable device 7.

Indeed, thanks to such a dimensioning, the rebound of the percussion element 8 does not block the resonance of the acoustic resonator 9. This rebound occurs at the latest at the moment of return of the wave propagating in the deformable device 7 from the periphery to the percussion element 8, which corresponds to a half-period of the resonance frequency of the acoustic resonator 9. Thus, in the present invention, the mechanical energy is transmitted indirectly to the piezoelectric transducers 10, unlike prior devices in which they were directly impacted. This makes it possible to use more powerful piezoelectric transducers with a conversion efficiency of the order of 25% or more, for example. This also makes the energy conversion device more robust since the piezoelectric transducer is not directly subjected to mechanical shocks.

FIG. 3 shows a second embodiment of a conversion cell C of a conversion device according to the invention. The conversion cell C is represented in the impacted position. The cell C illustrated in this FIG. 3 is similar to that of FIG. 2, except that now the deformable device 7 is bistable. It therefore has two equilibrium positions, one when the conversion cell C is in the armed standby position and one when the conversion cell C is in the impacted position. In addition, the deformable device 7 equipped with the percussion element 8 is placed between a protective membrane 43 and the acoustic resonator 9. It is on the protective membrane 43 that a pressure is applied. The protective membrane 43 seals the casing 11, being fixed at its periphery to the frame 15 or having its periphery maintained in compression by the return of the frame 15 against the spacer 12. The protection membrane 43 may be astable, monostable or bistable. It is also assumed in this configuration that there is only one piezoelectric transducer 10 placed between the acoustic resonator 9 and the bottom 11.1 of the box 11.

The periphery of the deformable device 7 is maintained in compression between the spacer 12 and the acoustic resonator 9.

The deformable device 7, whether it is monostable or bistable, is a deformable object that is laterally constrained or initially deformed in the first position that is stable by stamping. The percussion element 8 is always integral with the deformable device 7, it projects from the side of the acoustic resonator 9.

A shim 14 is inserted between the protective membrane 43 and the deformable device 7.

The wedge 14 is represented in the form of an inverted "Ω", with open branches on the protective membrane side 43 and a base integral with the deformable device 7, substantially in its central zone. The wedge 14 can be integrated in the deformable device 7. In the central zone, two branches having their opposite free ends can be cut out in the deformable device 7, these branches being straightened towards the protection membrane 43 to obtain the "Ω" shape. reversed.

When the cell C is in a standby position, and a force is applied on the membrane 43, the membrane 43 deforms and pushes on the wedge 14 which presses on the percussion mechanism 6. The deformable device 7 is in the first position. When the force exerted on the deformable device 7 substantially at its center by the wedge 14, is sufficient, it switches to its second equilibrium position, the impacted position. The percussion element 8 then hits the acoustic resonator 9, inducing as previously an electric signal, thanks to the piezoelectric transducers 10.

The shape of the deformable device 7 is chosen so that, in the impacted position, it can match the shape of the acoustic resonator 9, so that the thickness of the deformable device 7 and the acoustic resonator 9 is as small as possible, thus providing a maximum race. The distance between the percussion element 8 and the percussion zone 9.1 on the acoustic resonator 9 is adjusted, so that the percussion occurs with the greatest velocity.

Such an energy conversion device makes it possible to calibrate the impact energy irrespective of the pressure applied on the protective membrane 43 to the extent that this pressure is sufficient to obtain the tilting of the deformable device 7 from the standby position. army in the hitting position. The energy transmitted to the acoustic resonator 9 is always the same, regardless of the force exerted on the protection membrane 43 provided it is greater than a tilting threshold force, denoted Ftop. Referring to FIG. 13 which shows the displacement of the central zone of the deformable device as a function of the force applied to it via the shim 14. Thus, insofar as the energy transmitted to the acoustic resonator 9 is always the same, it is possible to perform a good sizing of the conversion cell C and its elements. In struck mode, since the deformable device 7 best matches the shape of the acoustic resonator 9, this allows the percussion element 8 to travel as far as possible so that the percussion is done with the greatest possible impact. possible speed. The potential mechanical energy stored in the percussion mechanism 6 is optimally transferred to the acoustic resonator 9.

In order for the deformable device 7 to return to its first so-called standby equilibrium position, it is necessary to exert on it a threshold switching force Fbot, of direction opposite to Ftop but not necessarily equal to Ftop. If the Ftop forces, Fbot are not identical in absolute values, the deformable device 7 bistable is said to be asymmetrical. Asymmetry can be obtained with magnetic means, for example by inserting a magnet in the free space 50 vis-à-vis the percussion element 8. The magnet is not shown. Alternatively, it is possible to magnetize the frame 11.1. By then realizing the percussion element 8 made of magnetic material and the acoustic resonator 9 made of non-magnetic material such as duralumin, the tilting threshold of the deformable device 7 can be decreased while increasing the percussion speed of the percussion element 8 . The conversion cell C can return to its standby position automatically, once the pressure has finished exerting on the protective membrane 43. It is then assumed that the conversion cell C is tight, that is to say say that the protective membrane 43 is sealingly attached to the frame 15. When the percussion mechanism 6 is moved into the impacted position, the interior volume of the box 11 closed by the protective membrane 43 has decreased. The vacuum induced in the cell 6, switches the deformable device 7 from its impacted position to the standby position. This is possible only if the force induced by the vacuum is greater than or equal to Fbot. If this is the case, the deformable device 7 returns to its first equilibrium position. As the shim 14 is secured to the deformable device 7 and is in the space between the deformable device 7 and the protective membrane 43, it pushes the membrane 43 in its first position. In this configuration, it is preferable that the membrane 43 and the deformable device 7 are substantially circular to ensure a good seal.

To allow the effective resetting of the percussion mechanism 6, it is preferable that the protective membrane 43 is monostable or bistable and that it generates a restoring force greater than the threshold switching force Fbot of the deformable device 7. FIGS. 4B represent yet another embodiment of the invention. In Figure 4A the conversion cell C is in armed standby mode and in FIG. 4B it is in struck mode.

This embodiment has an automatic reset mechanism 41. This embodiment is equally suitable for configurations in which the protective membrane 43 is waterproof or not.

The reset mechanism 41 comprises one or more resilient return tongues 45 placed between the membrane 43 and the deformable device 7. In FIGS. 4A, 4B, two opposing faces are shown. They may each be formed of a metal strip or a wire arranged in a loop.

They have one end anchored at the level of the frame 15 and more particularly located between the spacer 12 and the membrane 43. They also have a free end located at the central zone of the deformable device 7, this free end is intended to cooperate with a return hook 19. The return tabs 45 comprise at least one projection 46 directed towards the protective membrane 43 between the anchored end and the free end. The projection 46 can be obtained by folding the tongue. The return hook 19 comprises branches 19.1, as well as return tongues, each of the branches has an end attached to the percussion mechanism 6, more particularly to the deformable device 7 substantially at the level of the percussion element 8. The other end of each branch 19.1 is bent so as to hook the free end of a tongue 45. The branches 19.1 can be obtained as previously for the shim 14 by cutting the deformable device 7. The return hook 19 is shown with an inverted Ω profile. In FIG. 4A, the deformable device

7 is in its first stable position. When a force is applied to the membrane 43, it deforms and comes into contact with the projection 46 of the tongues 45, the tongues 45 bend and their free end comes into contact with the deformable device 7. The tongues 45 push the deformable device 7 which passes abruptly into its second position, when the force that is applied to it is greater than or equal to Ftop. The percussion element 8 hits the acoustic resonator 9. The return hook 19 is driven by the deformable device 7 to the acoustic resonator 9. The free end of the branches 19.1 comes in the vicinity of the free end of the tabs 45. return hook 19 with its inverted "Ω" shape does not prevent the percussion mechanism 6 and more particularly its deformable device 7 to follow its course towards its second stable position, it is driven by the return tongues 45. Once that the force has disappeared, the tongues 45 return to their initial position, since they are elastic, the free end of each of them is housed against a free end of a branch of the return hook 14. The hook 14 is removed from the acoustic resonator 9, it carries with it the device deformable 7 until it tilts in its first stable position.

Thus, when no more force is exerted on the cell 6 in the impacted position, the resetting mechanism 41 puts the cell 6 back into its first standby position. The cell 6 is then rearmed and ready for a new use.

The membrane 43 may be in this monostable or bistable configuration and generate a restoring force to rearm the percussion mechanism 6.

Likewise, the return tongues 45 are chosen such that the resultant of the return forces is also greater than Fbot, so that the latter pull on the return hook 19, and allow rearming of the percussion mechanism 6.

These return tongues 45, as well as the percussion element 8, also make it possible to increase the stored potential energy that can be released during the tilting of the deformable device 7. Moreover, the thickness of the percussion element 9 , that is to say its diameter if it is a ball, is chosen to be substantially equal to ten times the thickness of the deformable device 7. The conversion cell C is preferably constructed so that the percussion noise is contained in the chamber 11. In fact this noise, that is to say a sound wave, can propagate in the acoustic resonator 9 and be converted into a compression wave. This compression wave will excite the piezoelectric transducer 10 and induce the generation of electrical energy. Thus the losses related to percussion noise are limited.

We will now explain in more detail the operating mode of a bistable deformable device.

It is assumed that the bistable deformable device is formed of a substantially rectangular plate 29 of which two opposite sides, preferably the sides corresponding to its width, are rigidly fixed to a support 30. FIG. 9A represents the plate 29 in its first stable position at rest, it is flamed at the origin. It comprises a substantially median area 29.1 curved. At the level of the domed central zone 29.1, a force F is applied to deform the deformable device 29 and cause it to assume its other stable position. The force F is substantially normal to the plate at the point of application. Referring to Figure 9B. In Figure 9C, the deformable device 29 has rocked into its second stable position. The force F is directed in the direction of the desired swing to the other stable position. The deformable device can be deformed according to several modes that respond to the laws of elasticity. FIGS. 10A, 10B, 10C illustrate three possible modes of deformation of a thin beam P rigidly fixed at its two ends. Mode 1

(FIG. 10A) and mode 3 (FIG. 10C) are associated with perpendicular displacements of the median region of the beam while mode 2 (FIG. 10B) reveals a rotational movement of its point. middle. Mode 1 is obtained by tangential prestressing.

When the plate 29 switches from the position of Figure 9A to that of Figure 9C, it deforms in geometric modes of lower switching energy, that is to say, following mode 2 and possibly mode 3.

It may be advantageous to force the appearance of mode 3 by blocking the appearance of mode 2. The advantages of blocking mode 2 will be specified later.

One way to prevent the appearance of mode 2 is illustrated in Figures HA, HB, HC.

Now the bistable deformable device is no longer a solid plate, it is formed of two main walls 31, 32 superposed, fixed to one another by a substantially central auxiliary wall 33 extending substantially transversely to the two main walls 31 32. The section of the bistable deformable device is substantially H coated. The bistable deformable device 29 has two ends 29.2 anchored on a support 30, these ends remain fixed when tilting from one stable position to the other stable position. The transverse central wall 33 has the function of blocking all tangential movements and thus blocking the appearance of mode 2 to leave only a deformation according to mode 3. It will be noted that in FIG. 14, the deformable device has been represented with the two main walls 31, 32 interconnected at the level of the attachment of the element of percussion 8 by the transverse auxiliary wall 33centrale.

In Figure HA, the bistable deformable device is in the first stable position before impact. Figure HB shows it being deformed in mode 3, mode 2 being blocked. The impact corresponds to the application of the force F. FIG. HC shows the bistable deformable device after tilting in the second stable position, the tilting being linked to the impact.

It is preferable that the bistable deformable device is asymmetrical so that it passes more easily from the first stable position to the second stable position than the reverse. This means that the force required to cause the first stable position to shift to the second is smaller than the force required to cause the second stable position to shift to the first. In order to describe this particularity in more detail, reference is made to FIG. 12 which illustrates the parameters defining a bistable beam P anchored at its two ends. To be bistable, the beam P is initially curved or flamed in its first stable position. This beam P has a length L, a thickness t. A force F is applied to it at a point of abscissa x = L / 2. On the one hand, the beam P is shown in its first stable position referenced I and being deformed according to mode 2 (referenced II). The point of application of Force F was displaced, during the deformation, a distance d between the two positions I and II.

FIG. 13 shows the curve linking the force F to the displacement d of the point of application of the force F on the beam P of FIG. 12, which deforms according to the mode 3. The fact that the beam P is bistable results in the In fact, after a certain displacement due to a Ftop actuating force, the compressive strength decreases faster than the flexural strength of the beam P increases, which causes on the one hand, a negative dynamic stiffness constant on a part of the curve, on the other hand, the existence of a particular displacement dmid from which it is no longer necessary to apply the force so that the beam P switches to the other stable position in which the displacement is dend. The asymmetry sought is characterized by the fact that the force Fbot necessary to reshape the beam in the first stable position is different from Ftop or that the displacement dmid is different from (dend - dmid) / 2, ie that is, the displacement for which the force is positive is different from the deformation depth for which the force is negative. There are different ways to create asymmetry at the bistable deformable device. This can be done for example by curving a plate by stamping or by molding in a curved mold. It is not necessary to prestress it laterally to obtain the bistability. The curved double-wall bistable deformable device of FIGS. 11 has the advantage of being asymmetrical with different tilting forces depending on whether the tilting is in one direction or the other. The asymmetry comes from the fact that the double wall is curved at the construction and is not subjected to lateral prestressing.

In mode 2, it is the center of the bistable deformable device that is deformed. Or the percussion element 8 is placed substantially in the center of the bistable deformable device. It is therefore preferable to work in mode 2.

We will describe a little more in detail a non-limiting example of an acoustic resonator 9. FIG. 5 shows a sectional view of an acoustic resonator 9 coupled to two piezoelectric transducers 10.1, 10.2 facing each other and which sandwich on its periphery. The acoustic resonator 9 has two main faces 9.0 substantially conical bowl, the cones being opposed by their apex. The two cones have substantially the same angle at the top. It has a central symmetry, it has a circular edge. The tops of the cones are in the center of the circle. The percussion area 9.1 struck by the percussion element (not shown) is the center of the circle. Thus, the percussion zone 9.1 is located at the thinner point of the acoustic resonator 9. In this way, the strong vertical displacements generated in this percussion zone 9.1 of lesser thickness are transmitted radially towards the periphery as far as the piezoelectric transducers. 10.1, 10.2. The pulse wave generated by the impact propagates radially and is then simultaneously detected by the transducers 10.1, 10.2. The property of antisymmetry of the component of normal mechanical displacement with respect to the median plane of the acoustic resonator 9 makes it possible to sum the effects of the wave provided that the electrical connections are orientated and connected in an appropriate manner.

More generally, the acoustic resonator 9 could not have this biconical shape while maintaining a variable thickness, lower at the area of percussion and thicker at the coupling zone with the piezoelectric transducer or 10.1, 10.2. The two cuvettes 9.0 end with a substantially flat edge 9.2, the two 9.2 plane edges being substantially parallel. The annular piezoelectric transducers 10.1, 10.2 are in contact with these substantially plane edges 9.2. The acoustic resonator 9 comprises at the periphery a shoulder 23 of small thickness relative to the thickness of the acoustic resonator at its periphery. The shoulder 23 is intended to ensure the mechanical retention of the acoustic resonator 9 relative to the frame 15. This shoulder 23 may be located at the plane of symmetry of the acoustic resonator 9. The losses are limited because the acoustic resonator is maintained at the level of the acoustic resonator 9. of his plane of symmetry. Each piezoelectric transducer 10.1,

10.2 is provided with a block of piezoelectric material which cooperates with a pair of disjoint electrodes el, e2 across which appears a potential difference. These electrodes el, e2 are in contact with the same face of the block of piezoelectric material. One of the electrodes el occupies almost the entire circumference of the ring, and the other, referenced e2, of semicircular shape is placed at the edge of the ring. It is the potential difference between these two electrodes el, e2 which supplies the electrical energy to be used by a user device (not shown). In the example of Figure 5, the piezoelectric transducers 10.1, 10.2 are connected in parallel, more precisely in antiparallel because they have polarization vectors in the same direction, but in opposite directions. These vectors are illustrated by the arrows in FIG. 5. The piezoelectric transducers 10.1, 10.2 thus recover the energy in phase. The transducers 10.1, 10.2 can convert bending waves from the acoustic resonator 9 into an electrical signal. The electrical signal delivered by the piezoelectric transducer 10.1 is denoted by Al (t), and that by the piezoelectric transducer 10.2 is denoted by A2 (t).

It is of course conceivable that the piezoelectric transducers are connected in series instead of being connected in parallel. A parallel connection makes it possible to obtain a relatively strong current while maintaining a constant voltage, for example to supply an electronic circuit. A series connection makes it possible to obtain a relatively high voltage, for example to produce a spark and to operate in spark gap mode. This makes it possible to produce small space-saving spark gaps with a small stroke depth.

FIG. 6 represents in three dimensions the acoustic resonator and the piezoelectric transducers of FIG. 5.

The angle of each cone is chosen to adjust the resonance frequency. Indeed, the average wave speed of the waves depends on the angle of the cone. In general, the optimal resonance frequency, that is to say that corresponding to the maximum conversion efficiency, varies in the opposite direction to the duration of percussion of the percussion element with the acoustic resonator. For example, during long impacts due to the drop of drops of water or with heavy percussion elements, it is advantageous to use an acoustic resonator 9 of small thickness in the area of percussion or low angle at the top. Indeed, in this case, the average phase velocity is lower, which causes, at constant diameter, a reduction of the radial resonance frequency in an antisymmetric mode.

FIG. 7 represents an acoustic resonator 9 similar to that of FIG. 5. It now cooperates with two piezoelectric transducers per face, each having the form of a half-ring. The piezoelectric transducers of one face are referenced 10.1a, 10.1b and those of the other face are referenced 10.2a, 10.2b. In this example, the piezoelectric transducers are connected in series in pairs, in a pair one of the transducers piezoelectric belongs to one side and the other to the other side. One of the pairs is formed of piezoelectric transducers 10.1a and 10.2a and the other pair of piezoelectric transducers 10.1b and 10.2b. Both pairs are connected in series. The polarization vectors of the four piezoelectric transducers, represented by the arrows in FIG. 7, are oriented symmetrically with respect to the median plane of the acoustic resonator, which has the effect of adding up the voltages produced across the four mounted piezoelectric transducers. in series when an acoustic bending mode is generated in the percussion zone of the biconical acoustic resonator. FIG. 8 shows, in three dimensions, the acoustic resonator-piezoelectric transducer assembly of FIG. 7. In this figure, the electrodes of the piezoelectric transducers 10.1a, 10.1b are visible. They are referenced ela, e2a for the piezoelectric transducer 10.1a and elb, e2b for the piezoelectric transducer 10.1b. The piezoelectric transducers vis-à-vis, each on one side of the acoustic resonator 9 are connected in series, they form a series and the two sets series are also connected in series. A bending mode, generated substantially in the center of the acoustic resonator by a percussion, is thus converted additively by the piezoelectric transducers 10.1a, 10.1b, 10.2a, 10.2b. This is achieved by properly orienting the vectors of polarization of each piezoelectric transducer as shown in FIG.

For example, in FIG. 7, the transducer 10.1b has a polarization vector P1 facing upwards. The transducer 10.1a has its polarization vector P3 facing upwards parallel to P1. The transducer 10.2 has its biasing vector P2 downwards. The transducer

10.2a has its polarization vector P4 facing down parallel to P2.

In this arrangement the transducers are connected in series. If we denote Al (t), A3 (t), A2 (t) and A4 (t) the respective voltages across the electrodes of the piezoelectric transducers 10.1b, 10.1a, 10.2b, 10.2a because of the orientation of the vectors of polarization, we have: A4 (t) = - A3 (t) A2 (t) = - Al (t)

As the transducers are connected in series the output signal A (t) is:

A (t) = Al (t) -A2 (t) + A3 (t) -A4 (t) A (t) = 2xAl (t) + 2xA3 (t)

Due to the symmetry of the assembly we have then: A (t) = 4xAl (t)

In this arrangement the output voltage is thus four times higher than in a conventional mounting to a single piezoelectric transducer. On the other hand, the available current which is proportional to the surface of the piezoelectric transducer is half less for each half-ring than complete ring. Each half-ring behaves like a voltage source, it is in series with other voltage sources. The total voltage source, consisting of the four half-rings in series provides half the current as in the case of a single ring. In total, the power provided by two rings is twice the power provided by a single ring that the assembly is in series or in parallel. This assumes that each ring pumps and converts only a portion of the stored energy into the volume of the acoustic resonator.

It is of course possible to further increase the number of electrode pairs and / or the surface of the piezoelectric transducers, in order to optimize the power available in voltage or current and the piezoelectric conversion efficiency. The choice of this number and / or this surface depends essentially on the intended application. It is the same for the choice of mounting series and / or parallel piezoelectric transducers.

Each conversion cell C may also comprise a circuit 37 for processing the signal delivered by the transducers 10. Referring to FIG. 4B. This processing circuit is generally formed of a conventional diode rectifier bridge 48 which makes it possible to rectify the signal delivered by the piezoelectric transducers 10, this rectifier circuit 48 is generally connected to a reservoir capacitor 49 which makes it possible to store and smooth the electrical energy thus produced. This processing circuit 37 can be housed in the free space 50 arranged between the acoustic resonator 9 and the bottom 11.1 of the box 11, for example. In FIG. 4B, the free space 50 is indicated, but the processing circuit 37 is shown outside this free space 50, otherwise it would not be visible. In order to use the electrical energy converted by the conversion cell C, a user device U is connected to the terminals of the processing circuit 37, in the example at the terminals of the reservoir capacitor 49, possibly by intercalating a voltage regulator and a microcontroller. These are not represented. The regulator is of interest especially when the acoustic resonator is subjected to repeated impacts. Indeed, the reservoir capacitor generally has a much higher capacitance than the static capacitance of the piezoelectric transducer so that the electric charge supplied by the piezoelectric transducer is transferred into the reservoir capacitor and corresponds to a lower output voltage available at the output of the piezoelectric transducer. capacitor tank. In case of repeated impacts at a high rate, the voltage available across the tank capacitor increases during the first impacts until the charging speed is compensated by the discharge rate of the reservoir capacitor.

If we want to have sparks, we will connect as user device U two pointed electrodes across the capacitor tank 49 as shown in Figure 4B. As a variant, it is possible to dispense with the rectifier circuit and to directly connect a user device at the output of the piezoelectric transducers. The capacitance of the reservoir capacitor 49 is chosen as a function of the energy of the percussion on the one hand, and the percussive peak output voltage, desired at the terminals of the outlet capacitor 49, on the other hand. For example, for an output voltage of 2V for at least 50 ms, the capacity of the capacitor can be chosen of the order of 10 μF.

Since the impacts at the percussion mechanism 6 can be repeated, the output voltage across the reservoir capacitor 49 can reach a limiting value. This situation is obtained for high impact frequencies. Given the dimensions of the conversion cell C, the inertia, the races envisaged, and the mode of operation, this frequency of impacts is limited to a hundred impacts per second when, for example, it is is the wind that exerts an exciter force on the conversion cell C, while it is limited to a few impacts per second when it is a human operator who exerts the excitatory force.

In FIG. 14, there is shown a conversion cell C able to operate in antisymmetric mode. It comprises a single acoustic resonator 9 but two percussion mechanisms 6, 6 ', sandwiching the acoustic resonator 9. The acoustic resonator 9 is in this case symmetrical by compared to its median plane. There is shown an even number of piezoelectric transducers 10 which are distributed on either side of the acoustic resonator 9. The acoustic resonator 9 is represented of substantially constant thickness in the percussion zone and in the coupling zone with the piezoelectric transducers 10. One could have represented it of variable thickness, biconical for example. The deformable device 7 of each of the percussion mechanisms 6 is shown bistable with a H-shaped section, that is to say formed of two superimposed main walls and rigidly connected to one another by an auxiliary partition arranged in a central zone of the two superimposed walls. With an acoustic resonator 9 of constant thickness, it is its thickness that sets its resonance frequency. The thickness and / or the diameter of the acoustic resonator 9 is also chosen as a function of the duration of the contact with the percussion element 8 during the percussion. The smaller the thickness and the larger the diameter, the lower the phase velocity and the lower the radial resonance frequency in an antisymmetric mode. A thin acoustic resonator is more suitable for low-frequency shocks, that is to say long-lasting impact, such as those provided by drops of water or large balls.

In this FIG. 14, there is shown a piezoelectric transducer 14 on each main face of the acoustic resonator 9. Piezoelectric transducers may be connected to a processing circuit as shown in Figure 4B.

The deformable devices 7 of the two percussion mechanisms 6, 6 'may have different tilting thresholds or different strokes so that the percussions are done alternately, but with a time interval at least equal to the damping constant of the fundamental resonance of the acoustic resonator 9. Thus a percussion caused by one of the percussion mechanisms 6 does not interfere with the resonance created by a percussion caused shortly before by the other percussion mechanism 6 '.

The time offset between the two percussion mechanisms 6, 6 'will be chosen, preferably, less than the discharge time constant of a reservoir capacitor 49 which would be connected to the piezoelectric resonators as illustrated in Figure 4B. The example of Figure 14 has no protective membrane or reset mechanism but of course we could predict them together or separately. There is also no box with a bottom but two frames 15, 15 'assembled to each other by gripping the shoulder 23 located on the median plane of the acoustic resonator 9.

We will now describe applications of such an electrical energy conversion device. We will see that it can serve as power supply, storage, or even actuator. This list of use is not exhaustive, but is an example of use. Those skilled in the art will obviously find other uses than those mentioned. The energy conversion device can be used for wind energy conversion. Referring to Figures 15 and 16. In this case, it is possible to arrange several conversion cells C similar to that of Figure 2 in a panel 51 oriented substantially parallel to the direction of the wind Ve. The piezoelectric transducers of the C cells are connected in parallel and the C cells of the panel together in parallel to increase the power supplied. If there are several panels 51, they can then be arranged in superimposed layers to form "Aeolian cubes", and possibly introduced together in a nozzle 58, to optimize the windward grip as in Figure 16. Generally speaking when the energy conversion device object of the invention has several conversion cells C, they can be arranged in series or in parallel, or remain independent depending on the needs of the user device with which they will cooperate.

From a certain wind speed, the deformable device 7 which offers a wind catch in the stable standby position, undergoes a pressure sufficient to switch to the other stable position, and for the percussion element 8 to strike. the acoustic resonator 9. After tilting, the wind stops, a depression appears and allows the return of the deformable device 7 in its initial position. Due to the wind resistance the deformable device 7 switches again: the deformable device 7 then enters into oscillation.

To increase the wind resistance of the deformable device 7, as well as the tipping threshold pressure and therefore the energy of the impact, it is possible to provide the deformable device with an obstacle 53 raised facing the wind Ve. This obstacle may be a blade partially cut in the deformable device 7 and then folded to be erected facing the wind Ve. This obstacle 53 is placed upstream of the central zone of the deformable device 7 in the direction of the wind Ve. The blades can have different lengths from one cell to another so that the oscillation frequencies are shifted and the available power is more stable. The different lengths are however quite close to each other.

When these cells C are arranged in a panel as described above, and connected in parallel, the available power is increased. These panels 51 may for example be placed on a building roof.

If the number of percussions is of the order of fifty times per second, with an energy to be transferred at impact of the order of 20 mJ per cell, with a conversion efficiency of 25% of the piezoelectric transducers, the cells of a diameter of the order of 50 mm, and 400 cells per meter square, a panel 51 of 1 m ² , can deliver a peak power of 100 W. Such performance is comparable to that of a polycrystalline silicon solar panel. The invention achieves such power because unlike known devices, it allows the use of high-performance piezoelectric transducers.

A conversion device as described in the first embodiment can also be used to convert the mechanical energy associated with the rainfall. This is the energy of the drop of water, which because of its speed, will allow to tilt the deformable device 7. Advantageously, for such use, the percussion element 8 is a simple deformation of the deformable device 7 in its central zone so as to project towards the acoustic resonator 9. The percussion mechanism 6 is then chosen so that its mass is of the order of that of a drop of water, namely, of the order 0.05 g. Indeed with such a dimensioning, it is easier to transfer energy through a rigid element, namely the percussion element 8, rather than a drop of water that would strike the acoustic resonator 9 Furthermore, it makes it possible to control the duration of impact, and thus to effectively excite the fundamental resonance of the acoustic resonator 9. The kinetic energy of the impact is in short confined in an excitation spectrum optimized for the bandwidth of the acoustic resonator 9. If the conversion device according to the invention is transparent, that is to say, if the membrane 43 if it exists, the percussion mechanism 6 and the acoustic resonator 9 of the C cells are made of a transparent material such as the glass or a plastic material, it is then possible to couple a conversion device arranged in a panel with a solar panel 42. The solar panel 42 is underlying the conversion device. The resulting set is then able to convert both wind energy and photo voltaic energy.

FIG. 17 represents such an assembly 55. The device for converting mechanical energy into electrical energy comprises four cells C arranged in a panel. The solar panel bears the reference 42. It is assumed that in this example, the four C cells are triggered at the same time thanks to a plate 56 which covers the deformable elements (not visible) of the four C cells. This plate 56 is of course, in this example, transparent.

It is possible to use the conversion device object of the invention for the creation of sparks as already mentioned with reference to FIG. 4B. In this case, the output voltage Vs must be as high as possible. It is then advantageous to use a plurality of conversion cells C connected in series. If the conversion cells C have several piezoelectric transducers, the latter are also connected in series as illustrated in FIGS. 7 and 8. One of the advantages of the conversion device of the invention is that it constitutes a autonomous power supply source. Because of its size, it allows to power sensors, and avoids a connection to the mains or the use of batteries. The sensors are thus autonomous. For example, it is possible to place a conversion device of the invention in a shoe, to connect it to a sensor also placed in the shoe to make a pedometer-type measuring device. The mechanical energy used by the conversion device is that induced by walking.

Until now when we wanted to count the passage of people, we housed in the ground sensors for example contactor type, they were permanently powered, even when there was no measure to perform they are kept in a standby mode. We regularly tested all the sensors, for example several times a second. The cost was important

Now we will be able to lodge in the ground or in a carpet 36 of a few millimeters thick, at least one energy conversion device 38 according to the invention and connect a cluster of sensors 35. The conversion device comprises a circuit treatment, not shown, as that described above. A microcontroller 39 can also be provided between the sensors 35 and the conversion device 38, the sensors 35 communicate with the microcontroller 39. Thus, the user device of the energy produced is the sensor cluster. For example, a carpet 36 may comprise 256 clusters of 16 sensors 35 and therefore 256 energy conversion devices 38. The processing circuit may include a reservoir capacitor

(not shown) as already mentioned. Figure 18 shows such a carpet whose surface may be of the order of one or more square meters. This carpet 36 can count a number of people passing through a corridor, in a bus, the subway, on an alley, on a sidewalk, etc.. It also makes it possible to measure their weight, their direction of travel, or their speed, for example if the sensors 35 are appropriate. The sensors 35 may be piezoresistive or piezo-capacitive, for example. Their resistance or capacity respectively varies according to the pressure exerted on them. The conversion device 38 delivers energy to the processing circuit and therefore to the microcontroller 39 and to the sensors 35 when pressure is applied to it, for example when a person walks on the carpet 36. It is this same pressure, which is acquired by one or more sensors 35. The sensors 35 are therefore fed only when a measurement is made. One area of the belt 36 can be fed well while another no. This allows in particular to extend the life of the sensors 35, insofar as only the active sensors are powered. Microcontrollers 39 may communicate with a receiver 37 for measurements made by the sensors (not shown) via a wireless communication device 40. The communication device 40 and the receiving device 37 can use to communicate the ZigBee communication protocol, which is well suited to this kind of wireless measurement.

We realized a self-powered carpet, self-powered, not consuming energy sector and communicating wirelessly.

Thus, only the areas concerned by the measurement are solicited. This modular approach allows, in case of failure, if an area is damaged, it will not disturb other areas that remain operational. The damaged part can be easily repaired or changed. Another advantage of such a modular approach lies in the flexibility on the size of the carpet 36.

In general, it is possible to use the conversion device of the invention to supply any type of user device. It can be a digital thermometer measuring device, a scale, a scale, or even an actuator such as an electric door latch etc. The conversion device can also serve as a force or pressure sensor in that the electrical signal it delivers depends on the force exerted on it.

We will now describe the characteristics and performance of a conversion cell that has been tested. Its acoustic resonator is formed of a biconical section aluminum disc having a thickness of 2 mm at its edge and a thickness of 0.2 mm at its center. Its diameter is 50 mm. The acoustic resonator has a center resonance frequency of 5.5 kHz, which corresponds to a half-period of 92 microseconds. This half-period corresponds substantially to the duration of an impact made by a ball of 0.25 g having a diameter of 3 mm. The acoustic resonator is equipped on its main faces with two annular piezoelectric transducers in PZT. It is assumed that the impact of the ball in the center of the acoustic resonator takes place at a speed of 4.1 m / s or 15 km / h and that the impact energy is 2 mJ. The piezoelectric transducers deliver a voltage of 80 V peak across a 1.2 kΩ load in the absence of a rectifier bridge. The impact keeps the voltage above 2 V for more than 10 ms in the load.

If a rectifier bridge associated with a tank capacitor of 10 micro Farads is used, a voltage of 6 V can be obtained across the tank capacitor. A low-power microcontroller can be connected to the terminals of the reservoir capacitor as a user device. that referenced MSP430 of Texas Instrument. It operates at 1.8 V and consumes 0.3 mA in active mode.

The combined and in-phase use of two annular piezoelectric transducers connected in parallel makes it possible to double the electric power restored. The total energy returned is 0.5 mJ, which represents more than 25% of the first impact efficiency. By counting two successive bounces of the ball, the restitution of energy reaches 31% of the energy of impact. We will now list some advantages of the energy conversion device according to the invention. It is possible to construct a device with one or more cells, these cells being connected in series or in parallel according to the necessary voltage or current requirement. Energy production is almost instantaneous after the impact.

The power and the delivered voltage can be calibrated with the use of the monostable or bistable deformable device. The transfer of the impact energy to the piezoelectric transducer is effective due to the acoustic resonator when it has an impedance transformer function.

The conversion device is very robust because it is the acoustic resonator that receives the impacts and not the piezoelectric transducer.

The resetting of the percussion mechanism can be very fast.

The rate of excitation can be of the order of one hundred percussions per second.

The conversion device can be easily accommodated within a flexible substrate, for example of carpet type. It has a small thickness, it can be waterproof. Although several embodiments of the present invention have been shown and described in detail, it will be understood that various changes and modifications can be made without departing from the scope of the invention.

Claims

A device for converting mechanical energy into electrical energy formed of at least one conversion cell (C) having at least one percussion mechanism (6) including a percussion element (8) and one or more piezoelectric transducers (10). ), characterized in that it further comprises an acoustic resonator (9) to which the piezoelectric transducers (10) are coupled, the percussion mechanism (6) further comprising a deformable element (7) having at least two dots anchoring opposing and substantially integral in a central zone of the percussion element (8), the deformable element (7) having at least one stable standby position in which the percussion element (8) is remote from the acoustic resonator ( 9), the percussion mechanism (6) and the acoustic resonator (9) being arranged so that when a force greater than a threshold is applied to the deformable element (7), it leaves its stable position. e standby by deforming so that the percussion element (8) strike the acoustic resonator (9) in a percussion area (9.1), so that it enters into resonance and excites the piezoelectric transducers (10) so that the force-induced energy is indirectly transmitted to the piezoelectric transducers (10) so that it converts it into electrical energy.

2. Energy conversion device according to claim 1, wherein the deformable element (7) has another stable percussion position in which the percussion element (8) is in contact with the acoustic resonator (9).

3. Energy conversion device according to claim 1, wherein the percussion mechanism (6) has a mass substantially equal to that of a mean raindrop.

4. Energy conversion device according to one of the preceding claims, wherein the deformable element (7) is equipped with an obstacle (53) to the circulation of a fluid (Ve) such as the wind, placed upstream of its central zone with respect to the circulation of the fluid.

5. Energy conversion device according to one of claims 1 or 2, wherein a protective membrane (43), located opposite the acoustic resonator (9) relative to the percussion mechanism (6), protects the percussion mechanism (6), a wedge (14) integral with the deformable element (7) being inserted between the membrane (43) and the deformable element (7), the force applying to the deformable element ( 7) being transmitted to it by the membrane (43) and the shim (14).

The energy conversion device according to claim 5, wherein the membrane (43) is attached to a frame (15) supporting the percussion mechanism (6) and the acoustic resonator (9), the frame (15) cooperating with a bottom (11.1) to form a box (11) sealingly closed by the protective membrane (43).

Energy conversion device according to one of the preceding claims, in which the piezoelectric resonators (10) are located at a distance from the percussion zone (9.1) of the acoustic resonator (9) at the periphery of the acoustic resonator ( 9).

8. Energy conversion device according to one of the preceding claims, wherein when there are two percussion mechanisms (6, 6 '), they operate alternately, the acoustic resonator (9) having two percussion zones (9.1) located on two opposite sides of the acoustic resonator (9).

9. Energy conversion device according to one of the preceding claims wherein the acoustic resonator (9) is of constant thickness or has at the percussion zone (9.1) a smaller thickness than at its periphery.

10. Energy conversion device according to claim 9, wherein the acoustic resonator (9) has a biconical profile.

11. Energy conversion device according to one of claims 6 to 10, comprising in in addition to an automatic reset mechanism (41) with one or more elastic return tongues (45), placed between the membrane (43) and the deformable device (7) and having a free end at the central zone of the deformable device ( 7) and one end anchored to the frame (15), this free end being intended to cooperate with a return hook

(19) attached to the deformable device (7).

An energy conversion device according to claim 11, wherein the resilient tongues (45) have a protrusion (46) on the side of the protective membrane (43).

Energy conversion device according to one of the preceding claims, in which the piezoelectric transducers (10) are connected to a processing circuit (37) with a rectifier (48) at the terminals of which a reservoir capacitor ( 49).

14. Energy conversion device according to one of the preceding claims, wherein the deformable element is formed of two superimposed main walls (31, 32), fixed to one another by an auxiliary wall (33). substantially central extending substantially transversely to the two main walls (31, 32).

15. Energy conversion device according to one of the preceding claims, comprising several cells (C) arranged in at least one panel (51), when there are several panels they are superimposed.

16. Energy conversion device according to one of claims 14 or 15, wherein the cells (C) are connected together, in series or in parallel.

Energy conversion apparatus, formed of a power conversion device according to one of the preceding claims, and a solar panel (42), wherein the energy conversion device is transparent and overlying the solar panel (42).

18. Measuring device comprising a power conversion device (38) according to one of claims 1 to 16, and at least one sensor (35) supplied with energy by the energy conversion device.

19. Measuring device according to claim 18, wherein the energy conversion device (38) and the sensor (35) are embedded in a carpet (36).

20. A spark producing device comprising an energy conversion device according to one of claims 1 to 16 and a pair of electrodes (U) supplied with energy by the energy conversion device.