Abstract:
A vortex generator is useable in a model in a fluid-dynamic channel. In order to save time during the development of vehicles, in particular, aircraft, to save wind tunnel time, it is suggested to configure the vortex generator to be switchable. A switchable vortex generator can be used, in particular, on models in fluid-dynamic channels and in fluid-dynamic channel tests.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application is a divisional of prior application Ser. No. 12/436,616, filed on May 6, 2009, which claims priority to German Patent Application No. 10 2008 022 504.5 filed on May 7, 2009. The entire disclosures of U.S. patent application Ser. No. 12/436,616 and German Patent Application No. 10 2008 022 504.5 are hereby incorporated herein by reference. 
    
    
     BACKGROUND OF THE INVENTION 
     Field of the Invention 
     The invention relates to a vortex generator and various uses of the same. 
     Background Information 
     A vortex generator (also referred to as a turbulator or turbulence generator), in the field of aerodynamics, refers to a small artificially applied surface discontinuity, which is supposed to generate a vortex in a fluid medium flowing over a surface. For example, a vortex generator is used to prevent stalling from happening in a controlled manner. Vortex generators can be found, for example, on the top surfaces of the wings of airplanes. An example of an array of vortex generators on a wing profile is explained in more detail in WO 00/15961. 
     Vortex generators are also used, however, in fluid-dynamic channel measuring methods, such as in wind tunnel tests for measuring the acoustics of various vehicle configurations, such as various aircraft configurations. In wind tunnel measurements, vortex generators prevent the generation of individual tones, which would not be generated on the originals, on corresponding vehicle models such as airplane models. 
     If the aerodynamics, rather than the acoustics of the configuration to be tested are to be measured in the wind tunnel, vortex generators are a disturbance. Therefore aerodynamic measurements are carried out without vortex generators. 
     Currently vortex generators are manually applied and also removed. In combined aerodynamic and acoustic measurements, the vortex generators must be repeatedly applied and removed. 
     In conventional wind tunnel tests adhesive vortex generators—also referred to as “tripping tape” or “turbulence tape”—of various structures are common. A main drawback is the re-rigging time needed to repeatedly apply and remove the vortex generators. 
     Various efforts have been made to reduce preparation time for preparing a wind tunnel model for wind tunnel tests. In DE 10 2006 018 133 A1 and WO 2007/11 8628 A1, an apparatus and a method for manufacturing a test adhesive tape roll for making air flows visible is suggested, by means of which test adhesive tape with pieces of string attached to it are provided for quicker application on wind tunnel models. However, again, the test adhesive tape with the pieces of string attached to it must be applied to the model. There is no mention of how vortex generators are handled on the model itself. 
     In the development of aircraft, such as airplanes, in particular, in typical wind tunnel tests, many different aircraft configurations, such as airplane configurations are tested. This can be as many as ten configurations a day. For each configuration, an aerodynamic measurement and an acoustic measurement is carried out. As a consequence the vortex generators must be frequently applied and removed. A lot of time is thus lost which could otherwise be used for measuring. 
     SUMMARY 
     It is an object of the present invention to provide a vortex generator with which the development of new vehicle and airplane configurations can be made substantially quicker and simpler. 
     It is a further object to provide an optimized equipment and method for easy and quick aerodynamic and/or acoustic measurements on all kinds of vehicles. 
     It is a further object to provide an optimized vortex generator that can be easily adapted to special needs without wasting energy. 
     For addressing such objects, the invention provides a switchable vortex generator, in particular, but not exclusively, for a model in a fluid-dynamic channel. 
     According to a first aspect of the invention, there is provided a switchable vortex generator for arrangement on a flow-dynamic surface comprising a vortex generating element reciprocatingly switchable between at least two positions, wherein the vortex generating element is adapted for generating vortices in a flow flowing in the area of said flow-dynamic surface, and a supporting means supporting said vortex generating element, wherein the supporting means is moveable for selectively holding the vortex generating element at least in a first position and in a second position differing from said first position, wherein the supporting means is arranged to hold the vortex generating element in a position extended from the surface and in a position retracted into the surface, the supporting means including a biasing means for biasing the vortex generating element in the first position so that the vortex generating element remains in the first position without energy input. 
     According to a second aspect of the invention, there is provided vortex generator for generating vortices, being switchable between at least two stable switching states, wherein the vortex generator maintains each stable switching state without energy input, the vortex generator comprising a bistable biasing means enabling a switching between the stable switching states just by an energy impulse. 
     Preferably, the vortex generator according to the invention can be switched on and off from outside without interrupting the operation of a wind tunnel. Downtimes are thus avoided. 
     In one embodiment, the vortex generator can be switched by applying a strong permanent magnet, or also by exerting an external force, such as a mechanical force, without however having to remove the vortex generator carrier material from a model. An advantage of this variant is the absence of electric or fluid lines to the model, which would otherwise be used for switching the vortex generator. 
     Generally, switchable vortex generators allow aero-acoustic tests to be carried out more quickly in a wind tunnel or other fluid-dynamic channel. Furthermore, the position of each vortex generator is excellently reproducible, because it can remain in place. 
     The described adaptive or switchable vortex generators can also be used, of course, simply for influencing the flow, i.e. on finished vehicle and aircraft models in operation or in purely aerodynamic tests. For example, the switchable vortex generators could also be used to delay flow separation like well-known vortex generators. The use of the vortex generators can then of course also depend on the respective cruising or flying state. For example, the vortex generators can also be switched off if their contribution to drag becomes too great. 
     An advantageous use of the vortex generator relates to a vortex generating device with an array of a plurality of such switchable vortex generators. For example, a whole array with switchable vortex generators is provided on a surface of an object to be tested or on another body in a flowing fluid medium. Such an array of vortex generators, which can preferably be switched together, has several advantages and possible usages. 
     For simplifying and accelerating aerodynamic and aeroacoustic tests, it is useful to have arrays of vortex generators, in which the vortex generators can be extended and retracted. This enables measurements in wind tunnel tests with and without vortex generators without additional re-rigging time. 
     In contrast, in typical aerodynamic measurements in wind tunnels, no vortex generators are used; these would often be a disturbance in measuring the aerodynamic behavior of the body to be tested. Vortex generators are necessary, however, for a series of acoustic measurements, since they prevent the generation of individual tones on models during measurement in the wind tunnel, which would not occur on the originals. This is why currently the vortex generators are manually applied and removed again in such tests. In combined aerodynamic and acoustic measurement, the vortex generators are repeatedly applied and removed. 
     Vortex generators and vortex generating devices formed by them, can also be used on original vehicles, in particular original airplanes, to influence the flow in a desired manner. A vortex generating apparatus on an original airplane can serve, for example, to avoid flow separation during starting and landing. If original airplanes are equipped with switchable vortex generators, they can be retracted during cruising flight, so as not to generate additional drag. A not inconsiderable amount of fuel can thus be economized. 
     The array of switchable vortex generators can have a wide variety of structures. If only a switch from laminar flow to turbulent flow is needed, the individual vortex generators can be stochastically distributed and also vary in size and shape. This is how unordered turbulences are generated with the classical “transition tape”. 
     In another embodiment, the vortex generators are applied and/or manufactured in an ordered arrangement. For example, the vortex generators can be arranged periodically spaced with respect to each other. Ordered vortex arrays thus occur in the near vicinity of such ordered vortex generator structures. Certain frequency ranges of the spectrum can be highlighted or suppressed, for example, by a suitable arrangement. Desired vortex arrays can be influenced by special shapes and/or by the size ratios of the vortex generating elements of the individual vortex generators. 
     In a preferred embodiment, the switchable vortex generators according to the present invention include a switchable vortex generating element. It can preferably be switched in at least two states:
         1) in an extended state, the vortex generators are active and generate a turbulent boundary layer, and   2) in a retracted state, the flow remains laminar.       

     Preferably, the vortex generating element is arranged on a supporting means, which can move the vortex generating element into a first position and into a second position, and which is switchable between these two positions. 
     The vortex generator preferably has at least one stable switching state. A stable state is characterized in that it is maintained without energy input. For example, the supporting means is formed in such a way that the vortex generating element remains in the first position if no energy is input. For this purpose, in particular, a biasing means can be provided for holding the vortex generating element in the first position. The biasing means, in a concrete implementation, can operate magnetically, electrostatically, electrodynamically or mechanically. For example, a leaf spring element or the like, or a magnet could be present. 
     According to an embodiment with a monostable arrangement, the vortex generator is in a retracted state without energy input and is extended in an energized state. In an alternative monostable arrangement, a stable extended state and an energized retracted state are provided. 
     The vortex generator can have at least one, or two, stable switching states. In a bistable structure, both switching states are maintained without energy input. For example, the vortex generating element is held both in the extended and retracted states without energy input. An energy impulse is only needed for switching states. This can be achieved in a concrete implementation by a corresponding bistable biasing means. For example, holding magnets are associated with each state. In another implementation, a bistable, in particular a mechanical spring element is provided. Mixed forms are also conceivable. 
     Preferably a switching mechanism is provided, with which the vortex generator can be switched between its at least two switching states, preferably under signal control. In an array of switchable vortex generators, they can preferably be jointly switched. 
     A variation with a modified switching mechanism is also possible. In a possible embodiment of the invention, there are thus ferromagnetic and permanent-magnetic areas, which contact each other when deflected and adhere to each other with great force. This force is maintained until an external separating force occurs. For example, this external force can be created by externally passing a permanent magnet over the array of vortex generators. 
     Generally, the switching mechanism for realizing state switching can use various actuator principles. Electromagnetic switches, piezo-electric switches, electrostatic switches, pneumatic switches, hydraulic switches, thermo-mechanical switches and mixed forms can be used. As has just been explained, mobile permanent magnets can also be used as an actuator principle. 
     Irrespective of the actuator principle, basically a general structure of the vortex generator is preferred. Preferably, a covering membrane is provided creating a surface which is as smooth as possible. In an embodiment, this covering membrane can be elastically formed, and can be deformed to the outside or correspondingly moved by actuators situated underneath. In another possible embodiment, through holes of suitable geometry are incorporated in the covering membrane to allow retraction and extension of the vortex generators. 
     In a preferred embodiment, below such a covering membrane, a generator membrane or actuator membrane can be provided switchable between the at least two positions and forming a main component of the supporting means. The vortex generating element can be installed on the actuator membrane. A spacer can be provided between the actuator membrane and the covering membrane to create a space between the covering membrane and the actuator membrane, within which the actuator membrane can move. A further spacer can also be provided below the actuator membrane to create a lower space for additional mobility. A carrier membrane can serve, for example, as a lower closure. A flexible structure formed by a plurality of membranes can be adapted to various bodies and surfaces to be tested. This is why the use of membranes is preferred. A selection of various geometric structures can be used as the actual vortex generators or vortex generating elements. Circular, ellipsoid, rectangular, quadratic, triangular and polygonal structures are possible. Vortex generating elements can also have, for example, the shape of chevrons, i.e. single or double chevrons. The array of switchable vortex generators of the vortex generating apparatus can consist of vortex generating elements of a single geometry or can be mixed. The arrangement in the array can be periodic or statistically distributed. 
     A preferred manner of manufacturing an array of vortex generators comprises making vortex generators of photolithographically structured photoresist. Alternatively, the generators are formed as metallic structures by forming processes. 
     In wind tunnel tests, bodies in flowing fluid media can be used which are provided with such switchable vortex generators. Switching the vortex generators on and off can be done while the wind tunnel is operating. This is how both aerodynamic measurements and acoustic measurements can be carried out under identical flow conditions without having to switch off or slow down the wind tunnel. These measurements can be repeated many times to obtain more precise measuring results. 
     A body in a flowing fluid medium is preferably a model of an airplane for wind tunnel tests, which is provided with a plurality of switchable vortex generators. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       Exemplary embodiments of the invention will be described in the following with reference to the accompanying drawings in more detail, wherein: 
         FIG. 1  is an enlarged sectional view of a surface area of a body in a flowing fluid medium taking an airplane model as an example with a switchable vortex generator in a general structure; 
         FIG. 2  is an enlarged sectional view of a first embodiment of the vortex generator; 
         FIG. 3  is a corresponding view of a second embodiment of a vortex generator; 
         FIG. 4  is a corresponding view of a third embodiment of a vortex generator; 
         FIG. 5  is a perspective view of a fourth embodiment of a vortex generator; 
         FIGS. 6 a  and 6 b    are schematic sectional views of a fifth embodiment of the vortex generator, wherein  FIG. 6 a    shows this embodiment without and  FIG. 6 b    with an additional coating, and wherein a possible stable second state is shown with a broken line; 
         FIGS. 7 a  and 7 b    are views comparable to those of  FIGS. 6 a  and 6 b    for a sixth embodiment of a switchable vortex generator in a passive embodiment without ( FIG. 7 a   ) and with a coating ( FIG. 7 b   ); 
         FIG. 8  is a view comparable to the one of  FIGS. 2 and 3  for a seventh embodiment of the switchable vortex generator; 
         FIG. 9  is a schematic sectional view of an eighth embodiment of a switchable vortex generator in a first position; 
         FIG. 10  is a view of the eighth embodiment in a second position; 
         FIG. 11  is a perspective schematic view of a switching mechanism of a ninth embodiment of a switchable vortex generator; and 
         FIGS. 12-15  are different views of different modifications of the eighth embodiment of the switchable vortex generator. 
     
    
    
     DETAILED DESCRIPTION OF THE EMBODIMENTS 
     First, a general structure of a switchable vortex generator generally indicated by  10  will be described with reference to  FIG. 1 .  FIG. 1  shows the area near the surface of a body in a flowing fluid medium, which in the present example is an airplane model  12  to be tested in a wind tunnel (not shown). Airplane model  12 , on its surface  16 , has an array of vortex generators  10 , of which only one is shown in detail, against which a wind tunnel flow  14  flows. Neighboring identically structured vortex generators  10  are indicated by reference numerals  10  left and right of the structure shown. The array forms a vortex generating apparatus  11  having a plurality of commonly switchable vortex generators  10 . 
     Vortex generator  10  has a vortex generating element  18 , which is movable between a first position—extended state—and a second position—retracted state by means of a supporting means  20 . 
     Vortex generator  10  has a covering membrane  22  for providing a surface  16  which is as smooth as possible. At least one through hole  24  of suitable geometry is incorporated in this covering membrane  22  per vortex generator  10  to enable retraction and extension of a vortex generating element  18 . The supporting means  20  has a moveable actuator membrane  26  for supporting the vortex generating element  18  which fits through hole  24  of covering membrane  22 . By deflecting actuator membrane  26 , vortex generating element  18  is extendable through covering membrane  22 , or it can be retracted into it. Actuators  28  are provided for moving actuator membrane  26 . 
     A first spacer means  30  is provided between actuator membrane  26  and covering membrane  22  for providing a space between covering membrane  22  and actuator membrane  26 . The lower closure of the vortex generator structure with respect to the model body is a carrying membrane  32 . A second spacer means  34  is provided between carrying membrane  32  and actuator membrane  26  for providing a lower movement space—space  82 —for actuator membrane  26 . 
     In the exemplary structure shown, a carrier layer  36  is provided which is adhesively glued on the base body  40  of airplane model  12  by means of an adhesive  38 . 
     Three embodiments of the vortex generator  10  are shown in  FIGS. 2, 3 and 4 , in which electromagnetic drives  42  are provided as actuators  28 . Coil systems  44  can be realized on covering membrane  22 , actuator membrane  26  and/or carrying membrane  32  by means of microstructures. In the exemplary embodiments according to  FIGS. 2 to 4 , the coil systems  44  comprise planar coils  46 . In the first exemplary embodiment according to  FIG. 2  and in the second exemplary embodiment according to  FIG. 3 , they are provided with permanently magnetic cores  48  or ferromagnetic cores  50 . The coil windings are received in a separating layer  52 . 
     If a current flows through these coils  46 , actuator membrane  26  is deflected. Depending on the flow direction of the current, the vortex generating elements  18  are retracted or extended. 
     In manufacture, permanent-magnetic and soft-magnetic structures—shown here as the permanent-magnetic cores  48  and the ferromagnetic cores  50 —can additionally be created, which cause adhesion of actuator membrane  26  in the deflected state even without current flow. The additional separating layer  52  can lead to reduced adhesion between permanent-magnetic and ferromagnetic structures, as the case may be, which facilitates switching. An impulse-like current through the coils causes snapping from one state into the other. 
     The first embodiment according to  FIG. 2  shows a structure possible for a bistable state. The most variable switching ability is provided by an electromagnetic drive with inserted magnetically active layers. The structure of the planar coils  46  and also the vortex generator  10  overall, and in particular of the vortex generating element  18  can advantageously be realized in MEMS technology. 
     However, not all of the elements of the electromagnetic drive shown in  FIG. 2  need to be implemented.  FIG. 3  shows a second embodiment of the vortex generator in a reduced form, wherein the coil systems  44  are only present on one side of actuator membrane  26 . This structure is less cumbersome, but the switching forces achievable are smaller. Without current flow, actuator membrane  26  with vortex generating element  18  is in a resting position. A current through the planar coils  46  in a suitable direction leads to an attraction between the planar coils  46  until the permanent-magnetic core  48  of one coil and the ferromagnetic structure of the other coil come into contact and adhere. This adhesion stays intact after termination of the current flow. Renewed current flow with switched polarity can lead to repulsion between the coils so that the adhesion is overcome and the foil of actuator membrane  26  is deflected back. If the current is switched off, actuator membrane  26  with vortex generating element  18  returns to the rest position. 
       FIG. 4  shows an even simpler version. This results from the embodiment shown in  FIG. 3  if the magnetic structures—cores  48 ,  50 —are omitted. In the structure according to the third embodiment as shown in  FIG. 4 , vortex generating element  18  can be retracted into the coils by means of a current flow. Without current, the vortex generating element springs back to its rest position. 
     An embodiment not shown in any more detail of vortex generator  10  with an electrostatic drive results from a general structure as shown in  FIG. 1  with the use of electrostatic actuators  28 . Capacitor plates with a thin dielectric insulating layer can be realized by microstructures on the covering membrane  22 , the actuator membrane  26  and the carrying membrane  32 . If suitable potentials are applied to these plates, actuator membrane  26  is deflected. Depending on the potential of the plates, the vortex generating elements  18  are retracted or extended. While a bistable arrangement is theoretically possible, it can only be implemented with difficulty due to the losses of the dielectrica in practice. 
     An embodiment not shown in any more detail of vortex generator  10  with a piezo-electric drive results from the use of piezo-electric actuators as actuators  28  in the general structure of  FIG. 1 . For this purpose, piezo-electric layers and metallic electrodes are applied on actuator membrane  26 . An applied voltage leads to warping out of actuator membrane  26  in a suitable direction. 
       FIG. 5  shows a concrete fourth embodiment of vortex generator  10  with a lift-reinforcing piezo-electric drive  54 . This embodiment of the vortex generator  10  has a large piezo membrane  56  at the bottom of a cavity  58  filled with liquid. The boundary surfaces  60  of cavity  58  leave an opening  62  smaller with respect to the surface of piezo membrane  56  at the top, which is closed off by a flexible area of covering membrane  64 . By directly transmitting the volume change initiated by means of piezo membrane  56 , a lift-reinforcement on the flexible area  64  of the covering membrane is achievable by the fluid. Piezo membrane  56  can also have a bistable configuration, wherein two predefined states can be selected: vortex generator ON or OFF. Piezo material is used for switching. 
     Two modifications of an embodiment of the switchable vortex generator  10  with a piezo-electric drive are shown in  FIGS. 6 a  and 6 b   , but without lift reinforcement. For creating this un-reinforced piezo-electric drive  66 , actuator membrane  26  is formed bistable-bistable membrane  76 . Vortex generating element  18  is on actuator membrane  26 . Switching between the two states is with the aid of piezo crystals  68 . Actuator membrane  26  itself can be of any suitable material. The bistability—e.g. “clicker effect”—can be achieved by the geometric form of membrane  26 ,  76 . Each extended position is shown as dashed lines in  FIGS. 6 a  and 6 b   . Such membranes can easily be manufactured e.g. of metals or metal alloys, and thus each membrane  26  and  76  can be configured as a mechanical spring or bistable spring element. Local biasing or local curvature can also be created on plastic material or semiconductors by applying a coating  70  and subsequent structuring of the layers, wherein the structured coatings  70  create local mechanical stresses. A closed elastic layer  78  can be provided for forming the smooth surface  16 .  FIG. 6 a    shows an embodiment without and  FIG. 6 b    an embodiment with this elastic layer  78 . 
     On the basis of the structure according to  FIGS. 6 a  and 6 b   , a passively switchable vortex generator can also be realized as shown in  FIGS. 7 a  and 7 b   . Here, the piezo-electric drive  66  of the embodiment of  FIGS. 6 a  and 6 b    has been replaced by a passive magnetic drive  72 . The passive magnetic drive  72  has a small permanent magnet  74 , which is attached on the bistable membrane  76 . In the example shown, permanent magnet  74  forms the vortex generating element  18 . In other embodiments not shown in any more detail, permanent magnet  74  is part of vortex generating element  18  or is attached at a different place, such as on the back side. 
     In the magnetic drive as shown, for example, in  FIGS. 7 a  and 7 b   , switching between the two states can be achieved by applying an external magnetic field. Switching is carried out, for example, by passing a further (strong) permanent magnet from the outside across the bistable membrane  76  with the small permanent magnets and/or the vortex generating element  18 . Herein, attracting or repelling forces act on the permanent magnet  74 , which can be used for switching the bistable membrane  76 . 
     An advantage of this structure is its simple realization. A drawback is the necessity of manual switching, for example, during tests in the wind tunnel. With signal-controlled actuators  26 , switching can also be carried out from outside. A drawback of this active switching ability is the necessity to have lines for signal and/or energy transmission extend to the individual vortex generator  10 . 
     As shown in  FIGS. 6 b  and 7 b   , the vortex generators of the embodiments can be configured with the bistable membrane  76  in such a way that the entire carrying structure in the retracted state of the bistable membrane  76  is covered with the elastic layer  78  and therefore has a smooth surface in this retracted state. In the extended state, shown as a broken line, this surface is then deformed by the drive, or by the drive and an optionally present vortex generating element  18 . 
       FIG. 8  shows a further embodiment of vortex generator  10  with a pneumatic or generally fluidic drive. This embodiment is distinguished from the general structure according to  FIG. 1  in that a pressure line  80  extends to space  82  between carrying membrane  32  and actuator membrane  26 . A positive pressure or negative pressure can thus be introduced into the cavity between carrying membrane  32  and actuator membrane  26  to cause the actuator membrane  26  to warp out or warp in. Herein, air or any other suitable fluid can be used as the pressurized medium. 
       FIG. 9  shows a further embodiment of vortex generator  10 , which shows a further development of the vortex generator with a pneumatic drive. This vortex generator does not have an extra body as the vortex generating element  18 . Instead of a simple actuator membrane  26 , a folded membrane  84  is provided. The folded membrane  84  has been created, for example, by micro-embossing and can comprise an elastomeric foil  68 , one or more platforms  88  and stiffening structures  29 , which ensure desired deformation of the folded membrane  84  when a positive pressure is introduced into the space  82  between the folded membrane  84  and the carrying membrane  32 .  FIG. 10  shows a deflected state when a corresponding positive pressure is supplied. Accordingly, reference numeral  92  in  FIG. 9  indicates a fluid with a negative pressure, and reference numeral  94  in  FIG. 10  indicates a fluid with a positive pressure.  FIGS. 12-15  show further schematic views of this basic embodiment with a pneumatic drive or a hydraulic drive. 
       FIG. 11  shows a possible thermo-mechanic drive for the vortex generator  10 . For this purpose, heating structures  96  are created on actuator membrane  26  and covered with form structures of bimetal or of a memory alloy. Selective heating of the structures causes warping out or warping in of the actuator membrane  26 .  FIG. 11  shows a possible micro-mechanical double spiral  98  of memory alloy which doubles as a heating filament—heating structure  96 . Heating causes the double spiral  98  to extend. 
     LIST OF REFERENCE NUMERALS 
     
         
           10  vortex generator 
           11  vortex generating apparatus 
           12  aircraft model 
           14  flow 
           16  surface 
           18  vortex generating element 
           20  supporting means 
           22  covering membrane 
           24  through hole 
           26  actuator membrane 
           28  actuator 
           30  first spacer 
           32  carrying membrane 
           34  second spacer 
           36  carrying layer 
           38  adhesive 
           40  base body 
           42  electromagnetic drive 
           44  coil systems 
           46  planar coil 
           48  permanent magnetic core 
           50  ferromagnetic core 
           52  separating layer 
           54  lift-reinforced piezo-electric drive 
           56  piezo membrane 
           58  cavity 
           60  boundary surfaces 
           62  opening 
           64  flexible area of covering membrane 
           66  piezo-electric drive 
           68  piezo crystal 
           70  coating 
           72  passive magnetic drive 
           74  permanent magnet 
           76  bistable membrane 
           78  elastic layer 
           80  pressure line 
           82  space 
           84  folded membrane 
           86  elastomeric foil 
           88  platform 
           90  stiffening structure 
           92  fluid with negative pressure 
           94  fluid with positive pressure 
           96  heating structures 
           98  double spiral