WO2011004124A2

WO2011004124A2 - Microsystem for generating a synthetic jet, corresponding manufacturing method and device for flow control

Info

Publication number: WO2011004124A2
Application number: PCT/FR2010/051438
Authority: WO
Inventors: Leticia Gimeno Monge; Abdelkrim Talbi; Philippe Pernod; Alain Marcel Emile Merlen; Vladimir Preobrazhensky; Romain Viard
Original assignee: Centre National De La Recherche Scientifique (C.N.R.S); Université De Lille 1 - Ustl; Ecole Centrale De Lille
Priority date: 2009-07-07
Filing date: 2010-07-07
Publication date: 2011-01-13
Also published as: FR2947813B1; WO2011004124A3; FR2947813A1

Abstract

Microsystem for generating a synthetic jet, corresponding manufacturing method and device for flow control. This microsystem (10) for generating a synthetic jet of fluid, comprising a chamber defining a cavity (12) and provided with an outlet orifice (14) for the jet and with at least one deformable diaphragm (16) associated with actuating means for causing the diaphragm (16) to start vibrating at least once and thus fluid to be sucked into and discharged from the cavity (12) through the orifice in order to generate the synthetic jet, is characterized in that the actuating means comprise electromagnetic means (18, 20).

Description

Microsystem for generating a synthetic jet, method of manufacture and corresponding flow control device

The present invention relates to a microsystem for generating a synthetic fluid jet comprising an enclosure defining a cavity for receiving the fluid and provided with an outlet orifice of the jet and at least one deformable membrane associated with actuating means. to cause at least one vibration of the membrane and thus suction and discharge of fluid into and out of the cavity through the orifice to generate the synthetic jet.

It also relates to a method of manufacturing such a microsystem and a corresponding flow control device.

More particularly, the invention relates to the field of devices generating synthetic jets.

Synthetic jets are jets of fluids, generally gaseous, expelled through an orifice and produced by the alternative emptying and filling of a cavity consisting of one or more vibrating walls.

In the state of the art, various means for generating volume variations of the cavity have been used.

A first example is the use of a piston actuated by a motor. The synthetic jets, generated with such an actuation are powerful but at the cost of a low frequency of operation and a significant consumption. In addition, they are bulky systems.

A second example of actuation commonly applied is the use of one or more piezoelectric elements. These piezoelectric devices are less efficient in terms of speed than the devices using a piston, but the frequency ranges are more versatile.

Nevertheless, the performances of the synthetic jets are dependent on the resonances of the piezoelectric elements, the best results being obtained at the resonant frequencies. The size, although reduced compared to devices using a piston as a means of actuation, is still important (of the order of several cubic centimeters).

Currently, devices for generating synthetic jets are of interest to researchers and industrialists, particularly in the fields of flow control, jetting vectorization, improvement of fluid mixture at small scales of turbulence (typically <1 mm), for example air-fuel mixture in combustion systems and in cooling of electronic components.

Flow control is a technique that manipulates a flow (free or near a wall) using devices (passive or active) to produce favorable changes. These changes are, for example at the boundary layer, the retardation or advancement of a laminar / turbulent transition and the prevention of detachment. These changes in flow have positive consequences for the user, such as drag reduction, increased lift, noise reduction, or improved boundary layer mixing.

The main problem at present is the congestion of the flow control devices.

Indeed, the two most interesting control solutions, namely the boundary layer control and the detachment control, act on scales where the orders of magnitude of the structures on which we want to produce an effect are of the order of a millimeter. see submillimetric. This means that the means of action used must be of the same order of magnitude.

Microsystems called MEMS (Micro Electro Mechanical Systems) provide answers to the stated problems, namely a small footprint and suitable scaling for the problems of control delamination and boundary layer. These systems are of small size which allows a very localized operation but also information taking using microsensors with improved spatial resolution compared to conventional sensor elements. In addition, their collective machining techniques and low consumption help improve their performance in flow control applications. This benefit is indicated at the end of the description on page 8.

In the state of the art, there are today very few examples of synthetic generating devices made using microtechnologies.

In addition, none of the current devices has performance satisfying the specifications of flow control applications for air vehicles (aircraft, missiles, rockets, ...) or terrestrial (cars, trains, ...). Moreover, the existing devices are not integrable on realistic macroscopic configurations of vehicle elements.

In addition, none of the MEMS type devices includes integrated microsensors for real-time measurement of the speed of the synthetic jet at the orifice outlet. The speed of the jet is typically between zero and a few tens of m / s (for example 100 m / s). These sensors also make it possible to envisage a closed-loop control by using the measurement of a local speed to trigger the control of the actuation in order to optimize an overall quantity, for example the lift.

The object of the invention is to solve these problems.

For this purpose, the subject of the invention is a microsystem of the aforementioned type, characterized in that the actuating means comprise electromagnetic means.

According to particular embodiments, the microsystem comprises one or more of the following characteristics, taken in isolation or according to all the technically possible characteristics:

the electromagnetic means comprise a coil connected to a source of electric current and a permanent magnet;

- The magnet is fixed on the membrane by means of a rigid pad fixed thereto opposite the orifice and the coil is placed above the magnet;

the outlet orifice and / or the rigid pad have a circular shape;

the coil is a solenoid of inner radius greater than the radius of the rigid pad;

the cavity and the orifice are machined from two silicon substrates;

the membrane is made of elastomeric material;

the elastomeric material is polydimethylsiloxane (PDMS);

the magnet is made of NdFeB;

the magnet is made of SmCo;

the rigid pad is made of silicon;

it comprises a hot wire sensor disposed inside the cavity, on an outer wall of the microsystem or at the outlet of the orifice; - The ratio of surfaces between the rigid pad and the membrane is substantially equal to three quarters;

the material forming the membrane has a Young's modulus substantially less than 2 MPa.

The subject of the invention is also a method for manufacturing a synthetic jet generation microsystem as defined above, characterized in that it comprises:

a) a thermocompression bonding step of a first and a second silicon substrate;

b) a step of deep reactive ion etching (DRIE) of the first and second silicon substrates to respectively form the cavity and the outlet; and

g) a step of fixing the electromagnetic actuation means of the membrane.

According to particular embodiments, the manufacturing method comprises one or more of the following characteristics, taken in isolation or according to all the technically possible characteristics:

the step of deep reactive ion etching uses the Bosch method;

the process comprises:

c) a step of deep reactive ion etching (DRIE) of a third silicon substrate;

d) a step of depositing polydimethylsiloxane (PDMS) on the third substrate to form the membrane;

e) a step of wet etching the third substrate to form the rigid pad; and

f) a step of bonding the third substrate provided with the membrane on the first substrate containing the cavity;

the process comprises:

k) a step of bonding the third substrate provided with the membrane on the first substrate containing the cavity.

I) a one-shot molding step of a fourth membrane-forming substrate, a membrane port and the stiffening pad; m) a step of insertion of the magnet into the stiffening pad; and n) a step of bonding the fourth substrate provided with the membrane on the first substrate containing the cavity.

The invention further relates to an aerodynamic flow control device, characterized in that it comprises a synthetic jet generation microsystem as defined above.

Thus, the invention makes it possible to overcome the disadvantages of existing synthetic jet generation microsystems by providing an operational integrated actuation device meeting the needs, in terms of flow control, of aeronautical or automobile manufacturers.

In addition, the device for generating synthetic jets proposed by the invention provides an effective means for inducing, in a flow, an amount of movement greater than that obtained by the devices of the state of the art.

This device having a small footprint and ease of integration is very useful in cooling applications of electronic power components.

Embodiments of the invention will now be described more specifically, but not limitatively, with reference to the accompanying drawings, in which:

FIG. 1 is a diagram illustrating the structure of a synthetic jet generator of the state of the art,

FIGS. 2a and 2b are diagrams illustrating the operation of the synthetic jet generator of FIG. 1,

FIG. 3 is a diagram illustrating the structure of a synthetic jet generator according to the invention,

FIG. 4 is a diagram illustrating the steps of the manufacturing method of the synthetic jet generator of FIG. 3,

FIG. 5 is a diagram of another embodiment of a synthetic jet generation microsystem according to the invention, and

FIGS. 6 and 7 are diagrams illustrating a microsystem for generating synthetic jets comprising a hot-wire micro-sensor respectively in section and seen from above. FIG. 1 illustrates the structure of a generator 2 of synthetic jets of the state of the art. This structure comprises three basic elements, namely a cavity 4, an outlet orifice 6 of the synthetic jet and a wall or membrane 8 mobile. The movable membrane 8 is associated with actuating means (not shown) to cause this membrane 8 to vibrate.

The outlet orifice 6 of the synthetic jet also serves as a fluid inlet for generating the synthetic jet. The reception of the fluid and the ejection of the synthetic jet are thus performed by the same orifice 6.

Figures 2a and 2b illustrate the operation of the generator 2 of synthetic jets.

The moving of the movable membrane 8 by the actuating means causes a variation of volume in the cavity 4. On an oscillatory movement, the progression can be divided into two half-periods. When the change in volume is positive, the fluid is sucked into the cavity 4 and when it is negative, the fluid is expelled from the cavity 4 by creating a swirling structure.

The alternation of ejections and aspirations of fluid through the orifice 6 creates interactions of a series of vortices which thus generate a synthetic jet.

The "synthetic" name of such a jet is due to the fact that the mass flow rate resulting over a period (suction / ejection) is zero. This implies that such a jet is formed without external fluid supply and can therefore inject momentum into the system without net mass input.

The jet is thus "synthesized" from the succession of vortex structures emitted, so that it constitutes an unsteady fluidic actuator, that is to say non-stationary over time, certainly but generating a persistent fluidic structure in the flow well beyond the simple alternation of aspirations and blows.

Evidently this synthesis of vortex structures is not independent of the characteristics of the flows inside and outside the device, the internal flow being the flow generated following a suction phase of the fluid. For example, it is known that a low ejection speed does not allow the coalescence of vortex structures. The realization of an operational synthetic jet device therefore imposes particular constraints in terms of frequency and variation of cavity volume.

In particular, it is known that for the synthetic jet to be formed, the jet expelled by the emptying of the cavity must not be reabsorbed during the suction phase. It is therefore necessary that its penetration distance L in the flow is sufficient to leave the immediate vicinity of the orifice. This penetration distance L is estimated as the product of the debiting speed of expulsion U by the duration of this expulsion phase T: L = U x T. The expelling debiting speed U is the ratio of the average flow expelled by the orifice section and the duration of this expulsion phase T is the half-period for a sinusoidal cycle.

Comparing this length L with the diameter d of the orifice we obtain a

U x T

topological criterion of elongation of the structure:.

d

If this elongation is sufficient, the vortex structures furthest from the hole are no longer sucked by the device. In the literature, this criterion is often expressed with the frequency or the pulsation Ω of the synthetic jet:> K where K is a number determined by the experiment which

Ω x d

depends on the geometry of the orifice (cylindrical hole or slot for example). For example, K is substantially equal to 2 for the present invention described later.

In the state of the art, two types of synthetic jets are known according to the shape of the outlet orifice. If the orifice is circular, swirl rings are generated. The jet thus obtained is called an axisymmetric jet. If the orifice is a rectangular slot, the jet obtained is a two-dimensional jet generating pairs of swirling layers. However, different experiments show that the performances of axisymmetric jets in terms of speed are greater than those of two-dimensional jets.

FIG. 3 illustrates the structure of a generator 10 of synthetic jets according to the invention.

The generator 10 of synthetic jets comprises an enclosure defining a cavity 12 for receiving a fluid, generally a gas, in particular air in the targeted applications. The chamber is also provided with an outlet orifice 14 and a deformable membrane 16.

The membrane 16 is associated with electromagnetic actuation means comprising a coil 18 connected to a source of electrical current, not shown, and a permanent magnet 20. The actuation of the membrane 16 thus rests on the interaction of the magnetic field created by the coil 18 on the magnet 20.

The magnet 20 is fixed on the membrane 16 by means of a rigid pad 22 fixed thereto opposite the orifice 14, the coil 18 being placed above the magnet 20.

The experiments conducted by the inventors have indeed shown that the inclusion of the rigid pad 22 on the membrane 16 substantially improves the performance of the jet while offering more technological latitude to integrate the electromagnetic actuation means on the generator 10 synthetic jets .

Such a microsystem thus generates synthetic jets at a frequency in the range of a few tens of Hz to more than 1 kHz. The speed of ejection jets is a few tens of m / s to more than 50 m / s, unlike the devices of the state of the art where the speed is less than 10 m / s.

The membrane is ultra-thin, that is to say having a Young's modulus of less than 2 MPa, unlike conventional membranes, generally made of silicon, having a Young's modulus of the order of 500 GPa.

In addition, the surface of the rigid pad is at least substantially equal to three quarters of the surface of the membrane 16.

The membrane can thus move several hundred microns, for example 300 microns, homogeneously and thus generate twice the volume displacements that those conventional cavities to exceed the criterion of synthetic jet formation.

The actuating forces can thus exceed 0.2 N.

In addition, the total size of the microsystem including in particular the coil and the actuating magnet is less than 1 cm ³ .

According to one embodiment of the invention, the cavity 12, the orifice 14 and the rigid pad 22 have a circular shape. Furthermore, the coil 18 is a finned solenoid of inner radius greater than the radius of the rigid pad 22, so as not to hinder the displacement of the membrane 16.

The magnet 20 is a cylindrical permanent magnet with high coercivity and substantial remanent magnetization. The material chosen for this magnet 20 is, for example, NdFeB or SmCo.

The different manufacturing steps of the synthetic jet generator 10 in MEMS technologies are described in the following description with reference to FIG. 4.

The method of manufacturing micro-system 10 for generating an axisymmetric synthetic jet uses micro-machining techniques derived from microelectronics which make it possible to obtain a high definition and precision of the machined patterns and a collective machining capability of several structures on the same substrate, which allows a reduction in the unit manufacturing cost during production.

The first step 30 of the manufacturing method according to the invention consists in bonding a first 32 and a second 34 silicon substrates.

The first substrate 32 is intended to contain the cavity 12 and the second substrate 34 is intended to contain the orifice 14.

The preferred method of bonding is thermo-compression bonding. The use of this method of assembly allows precise control of the thickness of the cavity 12 and the orifice 14 and a very regular surface state in the etching background, since the metal bonding layer, designated 36 in FIG. 4, acts as a barrier layer.

Then, two double-sided metal layers 38, 40 are deposited by sputtering respectively on the first substrate 32 and the second substrate 34, to form a physical mask for the subsequent etching of the silicon.

In 42, the physical mask formed by the metal layers is open.

At 44, the first 32 and the second 34 substrates are etched by Bosch's deep reactive ion etching (DRIE) method to respectively form the cavity 12 and the orifice 14. The Bosch process DRIE is a physicochemical etching of the family of plasma etchings also called dry etchings. This etching is carried out in a chamber impregnated with a molecular gas in low pressure flow (approximately 1 and 1000 mTorr). Plasma is created from an inert gas (usually argon) that is ionized by electromagnetic excitation. The plasma electrons decompose the molecular gas into several chemically active species that will render the medium corrosive. This combines a neutral ion beam (physical etching) and a reactive species flow (chemical etching). The particularity of the DRIE is the alternation of very short steps (a few seconds) of anisotropic etchings and wall passivations. For anisotropic etching, the gases used are SF ₆ and I ¹ O ₂ and for wall passivations, C ₄ F _{8 is used} .

The main advantages of this mode of engraving are its speed (between 6 and 8 μm / min) and the possibility to control the engraving profile that is realized. It is thus possible to make an anisotropic profile with straight flanks on large depths.

At 46, the intermediate metal bonding layer 36 is opened and then at 48, a deposit of a layer 50 of SiO ₂ oxide PECVD is produced on the first substrate 32 containing the cavity 12.

Thus, the steps 30 to 48 allowed the formation of the cavity 12 and the outlet orifice 14.

The following description of the manufacturing process concerns the formation of the membrane 16.

The material chosen to form the membrane 16 is a silicone-type two-component flexible elastomer, for example polymethilsiloxane (PDMS). This material makes it possible to obtain a large deformability, an important elastic domain (deformation domain without rupture or plasticity) and compatibility with micromachining techniques.

At 52, two double-sided SI _x Ny rupture layers 54, 56 are deposited on both sides of a third silicon substrate 58 to form a physical mask for subsequent silicon etching.

At 60, the physical mask formed by the SlχN _γ 54 layer is open. At 62, the third substrate 58 is etched by an etching method

DRIE.

Then, at 64, a PDMS deposit is made on the third substrate 58 to form the membrane 16.

At 66, wet etching using potassium hydroxide (KOH) is performed on the third substrate 58 to release the rigid pad 22.

According to one variant, an entirely DRIE etching is used for this step if the temperature of the sample holder in the etching unit is well chosen, for example a temperature substantially between -10 ^° C. and 0 ^° C.

Finally, at 68, the third substrate 58 provided with the membrane 16 is bonded to the first substrate 32 containing the cavity 12. The bonding method used at 68 is a so-called PDMS bonding, since it brings into contact a PDMS surface (the membrane 16) and an SiO 2 surface (layer 50). This method makes it possible to obtain hydrogen bonds or covalent Si-O bonds by bringing the two surfaces 16 and 32 into contact, the surface 32 being activated beforehand by a surface oxidation (layer 50).

The electromagnetic actuation means of the membrane 16 are then placed by fixing the magnet 20 above the rigid pad 22 and then positioning the coil 18 above the magnet 20.

Another method of manufacturing a microsystem for generating synthetic jets is shown in FIG.

Steps 30 to 48 described above for the formation of the cavity 12 and the outlet 14 are identical in this method of manufacture.

The following description of the manufacturing process concerning the formation of the membrane 16 will now be detailed.

This method comprises a single-stage molding step of a fourth elastomer substrate forming the membrane 16, a support 80 of the membrane and the stiffening pad 22. The molding step also makes it possible to define two housings 84, 86 .

It then comprises a step of inserting and fixing the moving actuator magnet 20 in a housing 84 of the molded stiffening pad and on the membrane 16. Fixing is carried out by a second permanent magnet 82 placed opposite the actuating moving magnet 20, on the membrane in the second housing 86. The magnets 20, 82 are located on either side of the membrane 16.

The two magnets are located in the housings 84, 86 molded for this purpose allowing precise lateral positioning of the magnets.

The magnets then simultaneously serve as a stiffening pad for the flexible membrane 16, thus making it possible to form the rigid part of the membrane by the magnet-magnet interaction.

Then the fourth substrate provided with the membrane 16 is bonded to the first substrate 32 containing the cavity 12.

Finally, the coil 18 of the electromagnetic actuation means of the membrane 16 is placed above the magnet 20.

This method has the advantage of simplifying the manufacturing process allowing reproducible production of a large number of elements. It also allows an original fixation without bonding of the movable actuator magnet on the membrane.

In addition, the robustness of the device is improved at the magnet-membrane junction and the risks of tearing are thus minimized.

The synthetic jet generation microsystem thus obtained can in particular be integrated into an aerodynamic flow control device for overhead or ground vehicles.

Thanks to the electromagnetic actuation means, the forces obtained, proportional to the gradient of the magnetic field, are important.

In addition, the geometrical choice made (axisymmetric jet) and the choice of PDMS elastomer material for the membrane has the consequence of associating the large forces obtained with large displacements.

The microgenerative micro-generation system of the invention thus provides an effective means enabling it to induce in the flows a greater amount of movement than any other known micro-mechanical device.

Thus, the combination of magnetic actuation, geometrical options and materials as well as the development of microfabrication processes allow the device according to the invention to be the only one today. to be directly integrable into realistic macroscopic configurations of aircraft or automobile components.

In addition, the rigid pad 22 combines the flexibility of the membrane 16, essential for a large displacement, and its rigidity, essential for obtaining high frequencies.

Thus, the combination of the two effects: large variation of the volume of the cavity and high frequencies allows a large instantaneous flow, essential to the creation of the train of vortex structures constituting the synthetic jet.

In this respect, the invention is distinctly different from any pinching system of a channel used, for example, for peristaltic pumps or any microfluidic device which operate with a low Reynolds number in a quasi-static mode for which mechanical or pneumatic actuations can be used. considered.

Indeed, the combination of the magnetic actuation and fixed coil / mobile magnet interactions of the microsystem allows it to be the only one to allow:

- large displacements and thus exploit the flexibility of the rigidified membrane,

- large forces to inject a large amount of movement, required by the specifications of the flow control, and

- operate with fixed electrical connections.

The microsystem according to the invention, however, requires a large optimization work of the geometry of the coil / magnet system for it to work in the maximum intensity zone of the magnetic field gradient.

Indeed, the piezoelectric actuation by the small displacements that it induces would require at equal frequency to increase the size of the membrane to produce the same variation of volume. This excludes piezoelectric MEMS microsystems or results in performance that is incompatible with the generation of exploitable synthetic jets. While it is possible to try to compensate for the insufficient flow obtained by the multiplication of the jets on a matrix, but this is not enough to fulfill the condition of ejection of the vortex structure. Such approaches do not meet the requirements of flow control. The microsystem according to the invention allows the individualization of a MEMS type device, other than piezoelectric and fulfilling such specifications and thus allows the manufacture of synthetic jet matrix, or each jet is individually adjustable.

According to another embodiment of a microsystem for generating a synthetic fluid jet shown in FIGS. 6 and 7, it comprises a hot-wire micro-sensor 100, also called a hot-wire anemometric microprobe, for measuring the speed of the synthetic jet generated. The hot-wire micro-sensor 100 is disposed at the outlet of the orifice.

The hot wire micro-sensor 100 comprises two gold metal tracks

102, 104 and a hot wire or active portion 101 having a diamond layer 106 and at least one metal layer 108. The two gold metal tracks 102, 104 are connected to the active part for making electrical contacts.

The thickness e _f , ι of the active part 101 is for example between

500 nm and 2.5 μm, its length L _fl ι between 200 microns and 1000 microns, and its width l _fl ι between 1 micron and 5 microns. Nevertheless these limits are not absolute.

The micro-sensor 100 further comprises a support in contact with the second silicon substrate 34 of the microsystem located between the two gold metal tracks and the second silicon substrate 34. The support is preferably at least one thermally insulating layer, preferably S102 located between the diamond layer and the second silicon substrate 34 at the contact.

The choice of the elements that constitute the micro-sensor 100 strongly depends on the quality of the measurement to be made and the mechanical strength of the structure to the conditions of measurement.

For example, to ensure compatibility with collective machining methods, the second substrate 34 is made of silicon.

For a hot wire micro-sensor, the metal layer or layers can be used to define the sensitivity of the micro-sensor. Knowing the evolution of the ohmic resistance R (T) of the wire with the temperature makes it possible to make the optimal choice among the metals to be used. For example, the metal layer of the part active sensor 101 of the micro-sensor consists of at least one of the following metallic materials: Ag, Ti, Cr, Al, Cu, Au, Ni, W or Pt.

The wire 101 is formed of a combination of two metal layers 108 having residual stresses of opposite signs providing stress self-compensation in a known manner, for example a nickel-tungsten bilayer structure.

According to a variant, the wire 101 is a multilayer structure composed of four bilayers Ni (250nm) -W (65nm) having a total residual stress of 170 MPa and a temperature resistance coefficient of 2000ppm / ° C.

The support layer has the lowest thermal mass possible, ie the highest possible thermal conductivity, for example greater than about 10 W / K.m (for example 100 W / K.m).

For example, it is nanochstallin diamond and its thickness is less than 5 microns to limit the intrusive effect of the beam on the measurement (for example between 100 nm and 3 microns).

The diamond support layer 106 provides mechanical support, electrical insulation, and thermal mass reduction. Indeed, the nanochtalline diamond has excellent mechanical and thermal properties namely a Young's modulus of about 1000 GPa and a thermal conductivity of 500W / K.m. Optimization of the thermal mass can also be obtained by introducing a thermal insulator (for example 100 nm to 1 μm SIO2) between the nano-diamond layer and the silicon at the embedding of the part. active.

According to one variant, a local implantation of boron B atoms in the nano-diamond thus makes it possible to reduce its thermal conductivity at the level of the embedding.

According to other variants, the micro-sensor is located elsewhere in the microsystem, for example inside the cavity, or on the outer wall of the microsystem.

The integration of this micron sized hot wire micro-sensor makes it possible to ensure a real-time characterization of the flows, and a control of the proper functioning of the actuating means 18, 20. This also allows a closed-loop control by measuring the characteristics of the external flow.

This hot-wire micro-sensor can also be used individually or in a network independently of the means for actuating the synthetic jet generation micro-system for the multi-component speed measurement and the speed gradient component.

The hot wire micro-sensor is compatible with commercial hot wire measurement electronics, to have a sensitivity of the same order of magnitude as that of conventional hot wires, and to withstand the same mechanical stresses as the latter.

The main advantage of this hot wire micro-sensor over conventional hot wires is its small size which allows for both better spatial resolution, minimal disturbance of the characteristic flow and micro-channel insertion for micro metrology. -aerulic or flow control.

This device also has the advantage of being able to be used for other applications, for example for gaseous micro-discharges, or even liquid or the small-scale cooling of electronic components. Other applications of this device are also possible in microturbines, micromotors as well as in the micromanipulation of small amounts of materials.

In a number of these applications, the industrial interest of these synthetic microjets is based on the mass production typical of low-cost microelectronics technology streams, allowing these devices to be used in the form of giant digital collections. Distributed actuators (upholstering of a rear body of the vehicle, jet air intakes or aircraft wings, ...).

Of course, other embodiments and other applications may be contemplated.

Claims

1. Microsystem (10) for generating a synthetic fluid jet comprising an enclosure defining a cavity (12) for receiving the fluid and provided with an orifice (14) for discharging the jet and at least one membrane ( 16) associated with actuating means for causing at least one vibration of the membrane (16) and thus suction and discharge of fluid into and out of the cavity (12) through the orifice to generate the synthetic jet, characterized in that the actuating means comprise electromagnetic means (18, 20).

2. Microsystem (10) according to claim 1, characterized in that the electromagnetic means comprises a coil (18) connected to a source of electric current and a magnet (20) permanent.

3. Microsystem (10) according to claim 2, characterized in that the magnet (20) is fixed on the membrane (16) by means of a rigid pad (22) fixed thereto. of the orifice (14) and that the coil (18) is placed above the magnet (20).

4. Microsystem (10) according to claim 3, characterized in that the orifice (14) outlet and / or the rigid pad (22) have a circular shape.

5. Microsystem (10) according to claim 4, characterized in that the coil (18) is a solenoid of inner radius greater than the radius of the rigid pad (22).

6. Microsystem according to claim 1, wherein the cavity and the orifice are machined from two silicon substrates.

7. Microsystem (10) according to any one of claims 1 to 6, characterized in that the membrane (16) is made of elastomeric material.

8. Microsystem (10) according to claim 7, characterized in that the elastomeric material is polydiméthilsiloxane (PDMS).

9. Microsystem (10) according to any one of claims 2 to 8, characterized in that the magnet (20) is made of NdFeB.

10. Microsystem (10) according to any one of claims 2 to 8, characterized in that the magnet (20) is made of SmCo.

11. Microsystem (10) according to any one of claims 3 to 10, characterized in that the rigid pad (22) is made of silicon.

12. Microsystem according to claim 1, characterized in that it comprises a hot-wire sensor disposed inside the cavity outlet of the orifice (14).

13. Microsystem (10) according to any one of claims 3 to 12, characterized in that the surface ratio between the rigid pad (22) and the membrane (16) is substantially equal to three quarters.

14. Microsystem (10) according to any one of claims 1 to 11, characterized in that the material forming the membrane (16) has a Young's modulus substantially less than 2 MPa.

15.- A method of manufacturing a microsystem (10) for generating synthetic jets according to any one of claims 3 to 14, characterized in that it comprises:

a) a thermocompression bonding step (30) of a first (32) and a second (34) silicon substrate;

b) a step (44) of deep reactive ion etching (DRIE) of the first (32) and second (34) silicon substrates to respectively form the cavity (12) and the exit orifice (14); and

g) a step of fixing the electromagnetic actuating means of the membrane (16).

16. A manufacturing method according to claim 15, characterized in that the step (44, 62) of deep reactive ion etching (DRIE) uses the method

Bosch.

17. A manufacturing method according to claim 15 or 16, characterized in that it comprises:

c) a step (62) of deep reactive ion etching (DRIE) of a third substrate (58) of silicon;

d) a step (64) of depositing polydimethylsiloxane (PDMS) on the third substrate (58) to form the membrane (16);

e) a wet etching step (66) of the third substrate (58) to form the rigid pad (22); f) a step (68) of bonding the third substrate (58) provided with the membrane (16) on the first substrate (32) containing the cavity (12).

18. A manufacturing method according to claim 15 or 16, characterized in that it comprises:

h) a step of integrally molding a fourth substrate forming the membrane, a support of the membrane and the stiffening pad;

i) a step of insertion of the magnet into the stiffening pad; and j) a step of bonding the fourth substrate provided with the membrane (16) on the first substrate (32) containing the cavity (12).

19. A device for controlling aerodynamic flow, characterized in that it comprises a microsystem (10) for generating synthetic jets according to any one of claims 1 to 14.