DE10325307B3 - For the mixture of fluids in micro-cavities, in a micro-titration plate, at least one piezo electric sound converter generates an ultrasonic wave to give a wave-induced flow to the fluids - Google Patents

Abstract

To mix two fluids (5,7) together, in at least one micro-cavity (3), a flow is induced by sound using at least one piezo electric sound converter (1). An ultrasonic wave, with a frequency at least 10 MHz, is passed through a solid body layer (15) with a scale in the wave spread direction of more than quarter the ultrasonic wavelength, to generate a wave-induced flow in at least one micro-cavity. To mix two fluids (5,7) together, in at least one micro-cavity (3), a flow is induced by sound using at least one piezo electric sound converter (1). An ultrasonic wave, with a frequency at least 10 MHz, is passed through a solid body layer (15) with a scale in the wave spread direction of more than a quarter the ultrasonic wavelength, to generate a wave-induced flow in at least one micro-cavity. The lateral spread (d) of at least one wave converter is smaller than the lateral scale (D) of the micro-cavity. The micro-cavities are in a micro-titration plate (9).

Description

The invention relates to a method for mixing liquids in micro cavities and a device for performing of the procedure.

Micro cavities, e.g. B. in the arrangement of micro-titer plates, are used in pharmaceutical research and diagnostics are used as reaction vessels. Based on the standard format of micro-titer plates are highly automated Process flows in modern Laboratories possible. So z. B. pipetting robots, devices for optical reading biological assays and also the corresponding transport systems matched to the standard format. Such standard micro-titer plates exist today with 96, 384 or 1536 cavities. Typical volumes are per cavity in the range of 300 μl for 96s Titer plates, about 75 μl for 384s Micro-titer plates and about 12 μl for 1536s Titer plates. Micro-titer plates are generally made of plastic manufactured, e.g. B. made of polypropylene or polystyrene, and often coated or biologically functionalized.

Miniaturization in the form of such Micro-titer plates or micro-cavities in general are found Reason in the often expensive reagents and in the fact that sample material often not in the desired Amount available stands so that reactions at high sample concentrations can only be carried out if the volumes are reduced accordingly.

To speed up the reactions as well as ensuring homogeneous reaction conditions, it is desirable the reactants during to mix the reaction. This is particularly important when a reactant ("probe") is bound, i.e. there is an inhomogeneous assay. Mixing can be a problem here Prevent sample depletion from the bound probes. Generally is the diffusion of the reactants in the absence of thorough mixing the time-determining step. This leads to long reaction times and low sample throughput.

Micro-titer plates or in general microcavities are mixed in known processes by means of so-called shakers. Such shakers include mechanically moving parts and are difficult to handle to integrate highly automated lines. The mixing is about that in addition, especially in small cavities, e.g. B. 384 micro-titer plates or 1536 micro-titer plates very inefficient. With such small ones microcavities become small amounts of liquid apparently very viscous and in small volumes are only laminar Currents possible, i.e. there is no turbulence that causes effective mixing would. To despite the small amounts of liquid apparently high viscosity a sufficient mixing effect To achieve this, high shaker performance is necessary.

This is how WO 00/10011 A1 describes Process with the aid of which a microcavity in the frequency range of 1 shaken up to 300 kHz becomes. Outputs from 0.1 to 10 watts are applied.

There are several in the literature other methods for mixing small amounts of liquid are described.

In US 2002/0009015 A1 the use of cavitation is described for the mixture, i.e. nucleation, expansion and decay or collapse of a local vacuum space in the liquid or a bubble, i.e. a local gas / vapor space in the liquid, due to an acoustic pressure field. The mixing of the liquid is achieved by the dynamics of the local vacuum space or the bubble, i.e. its expansion and decay. Nucleation seeds are required to lower the acoustic power threshold for the formation of the local vacuum spaces or the bubbles. The risk of contamination is great due to these nucleation germs. In addition, the formation of local vacuum spaces or bubbles is often undesirable.

Other known methods (e.g. "Microfluidic motion generation with acoustic waves", X. Zhu et al. Sensors and Actuators, A. Physical, Vol. 66 / 1-3, page 355 to 360 (1998) or "Novel acoustic wave micromixer ", V. Vivek et al., IEEE International Microelectro mechanical systems conference 2002, pages 668 to 673, or US 5,674,742 A describe the use of membrane-like elements which vibrate in so-called "flexural plate wave modes". The movement-mediating medium is in direct contact with the liquid. The production of such thin membranes is very complicated and the risk of contamination through the contact of the liquid with the movement mediating medium is increased.

US 6,357,907 B1 describes the use of magnetic spheres that move in an external, temporally or spatially variable magnetic field. In order to carry out the mixing process, the beads have to be introduced into the liquid, which is often not desirable due to contamination problems.

US 6,244,738 B1 describes a mixing process in an elongated closed channel. Two streams of liquid flow past an ultrasonic transmitter and are mixed in the microchannel. To carry out the method, a complicated structure with a microchannel system is necessary and no separate, individual volumes can be mixed.

US 5,736,100 A describes the use of a turntable with small vessels into which micro cavities, e.g. B. Eppendorf caps can be used. In this potty there is e.g. B. Water that is irradiated from the outside with ultrasound. The The device described thus acts like a conventional ultrasonic bath. The water is set in motion and acts as a movement-mediating element directly on the potty, which is shaken in this way.

DE 101 17 772 A1 describes the mixing of liquids using surface acoustic waves that are generated with the help of interdigital transducers. The liquid is here for. B. directly on the sound-transmitting medium itself. At least with multiple use of the devices, there is a risk of contamination. Use with a micro-titer plate is not possible with the arrangements described.

Object of the present invention is to provide a method and apparatus that is effective Mixing of liquids in micro cavities, especially a micro-titer plate, enable and the risk of Keep contamination low.

This task is done with a procedure with the features of claim 1 and a device with the Features of claim 22 solved. Subclaims are focused on advantageous designs.

According to the invention, at least one is used piezoelectric transducer emits an ultrasonic wave of a frequency bigger or equal to 10 MHz through a solid layer through towards the at least one microcavity and the liquid in it sent to create a sound-induced flow there. The extent of the solid layer in the direction of sound propagation is greater than ¼ of the wavelength of the Ultrasonic wave.

The frequency range larger or equal to 10 MHz ensures that a Shake the entire device as z. B. with shaking mechanisms of the stand the technology is used in the method according to the invention does not occur. A solid layer, which is bigger than ¼ of wavelength the ultrasonic wave, can effectively prevent membrane-like "flexural plate wave modes "or Lamb modes form. In the method according to the invention the ultrasound enters the microcavity directly through the solid layer and generates a sound-induced flow there. The use of the high Frequency also ensures that sound absorption in the liquid is great.

The liquid to be mixed is not in direct contact with the sound generating or transmitting Medium. Contamination with multiple use is therefore excluded.

With the method according to the invention can effectively mix in a few minutes with accomplishments that are typically less than 50 milliwatts per cavity. With good acoustic adjustment, the value can also be less than 5 Milliwatts per cavity be lowered.

A separate substrate can be used as the solid layer. z. B. made of plastic, metal or glass. The fat ones are depending on the ultrasonic wavelength used z. B. in the range from 0.1 mm to a few cm. Typical ultrasonic wavelengths are in the range of 10 μm up to 100 μm. The solid layer can also z. B. directly through the bottom of a microcavity or the bottom of a micro titer plate are formed, which may be set to a desired thickness or is sanded or cover the floor.

The piezoelectric transducer can either be monochromatic by applying a high frequency signal the resonance energy or a harmonic are excited (continuously or pulsed). By changing the frequency or amplitude can be targeted Influence on the resulting mixed pattern can be taken. The feed of the Resonance frequency of the transducer also increases the efficiency of the Converting electrical energy into acoustic energy.

A needle pulse can also be used advantageously that of many other Fourier coefficients as a rule also has those that can resonantly excite the transducer. This lowers the requirements for the required electronics, since none special frequency must be adjustable.

Ultrasound absorption is particularly effective in the liquid to be mixed, if the wavelength the ultrasound wave is chosen in this way is that they are in the liquid is less than or equal to the average fill level in the microcavity.

The transducer can be placed under the Solid layer entire area be trained. However, it is particularly advantageous if the lateral extension of the sound transducer is smaller than the lateral extent of the one used Microcavity. Firstly, with a larger sound transducer the capacitive portion of its impedance increases, which causes electrical matching changed and secondly, the mixing efficiency is lower when the transducer is bigger than the lateral extent of the Microcavity. If the lateral extent of the Transducer, on the other hand, is smaller than the lateral extent of the microcavity Ultrasonic beam has a smaller lateral extent than the lateral one Extent of Microcavity. To the side of the upward directed ultrasound beam liquid flow down again so that optimal mixing of the liquid is achieved. To the For example, the ultrasound wave can be coupled into the microcavity centrally from below be so that the liquid central in the micro cavity moved upwards and can flow back down again at the edge of the microcavity.

The latter effect can be achieved in an alternative procedure by an intermediate layer is introduced between the sound transducer and the microcavity, which comprises a sound-absorbing material in an arrangement which allows the ultrasound to propagate in the direction of the microcavity only in a limited spatial area. Examples of sound absorbing media that can be used advantageously are silicone, rubber, silicone rubber, soft PVC, wax or the like.

Between the micro cavity and the Solid material can be a liquid or solid compensation medium, e.g. B. water, oil, glycerin, silicone, epoxy resin or a gel film can be introduced to compensate for unevenness and to ensure a safe acoustic contact.

As microcavities such. B. Eppendorf caps or Pipette tips or other microreactors can be used. Around parallelize the process to be able can several micro cavities at the same time be used. The use of a is particularly advantageous Micro-titer plate that already has a large number in a given grid dimension of cavities provides.

Likewise, several microcavities, e.g. B. with Help with an adhesive film with holes be defined on a glass slide, preferably in the dimensions of one usual Microtitre plate. For For the purposes of this text, the term "micro-titer plate" is intended to refer to such an arrangement with include. In such an embodiment, e.g. B. the glass slide directly as a solid layer be used, which is irradiated by the ultrasonic wave. In this way, a particularly compact arrangement can be realized. For the Realization of only one microcavity becomes an analog Adhesive film used with only one hole.

The method according to the invention is also possible with a a micro-titer plate analog device can be carried out on a substrate a field of sub-areas is provided, which is preferably of liquid to be mixed be wetted and thus as an anchorage for the liquid to be mixed serve. Are these fields in the grid dimension of a conventional micro-titer plate arranged, results after the application of the liquid a lateral distribution of the fluid like a conventional one Micro-titer plate, with individual drops due to their surface tension be held together. In the present text, the term “micro-titer plate” is intended to include such an embodiment include.

A micro-titer plate can be placed on the Solid layer be put on. Is z. B. only one transducer available, so the micro-titer plate can be moved on the solid layer, around different cavities to sonicate with ultrasound. In this way it can be customized selected what microcavity just to be subjected to mixing.

For mixing liquids in the individual cavities a micro titer plate is in a special embodiment of the method z. B. a Field of piezoelectric transducers below the solid layer used, which have the same arrangement as the cavities of one Microtitre plate. If these sound transducers are controlled individually, can the liquids in the individual cavities independently be mixed. Such a field of piezoelectric transducers let yourself simply in automation solutions integrate.

Another advantageous procedure is with the help of an ultrasonic wave generating device ultrasound such in the solid layer coupled that ultrasonic power at least at two decoupling points from the solid layer into a corresponding one Number of micro cavities can be coupled. This can e.g. B. by an ultrasonic wave generating device can be achieved, which radiates bidirectionally. In one embodiment the invention, the ultrasonic wave is generated with the aid of a surface wave generating device, preferably an interdigital transducer, on a piezoelectric Crystal generated that applied to a piezoelectric crystal is.

The one carrying the interdigital transducer Piezoelectric crystal can be glued, pressed, bonded onto the solid layer or about a coupling medium (e.g. electrostatically or via a gel film) to the solid layer glued, pressed or be bonded.

Such interdigital transducers are comb-shaped metallic electrodes, the double of which Finger distance the wavelength the surface sound wave defined and by optical photolithography z. B. in the range around 10 μm Finger distance can be established. Such interdigital transducers z. B. provided on piezoelectric crystals to surface acoustic waves thereon to stimulate in a manner known per se.

With the help of such an interdigital transducer, volume sound waves can be generated in the solid layer in different ways, which penetrate it obliquely. The interdigital transducer generates a bidirectionally radiating interfacial wave (LSAW) at the interface between the piezoelectric crystal and the solid layer on which it is applied. This interfacial leakage wave emits energy as solid-borne sound waves (BAW) into the solid layer. As a result, the amplitude of the LSAW decreases exponentially, with typical decay lengths being around 100 μm. The radiation angle α of the volume sound waves into the solid layer measured against the normal of the solid layer results from the arc sine of the ratio of the sound velocity V _{S of} the volume sound wave in the solid layer and the sound wave V _{SAW of} the interface sound wave generated with the interdigital transducer (α = arcsine (V _S / V _LSAW ). Radiation into the solid layer is therefore only possible if the speed of sound in the solid layer is lower than the speed of sound of the interface leakage wave. As a rule, transverse waves are therefore excited in the solid-state layer, since the longitudinal sound velocity in the solid-state layer is greater than the speed of the interface leakage wave. A typical value for the interfacial leaky wave speed is e.g. B. 3900 m / s.

The piezoelectrically induced deformations in the piezoelectric crystal below the interdigital transducer fingers which intermesh like a comb radiate volume sound waves (BAW) directly into the solid layer. In this case there is a radiation angle α measured against the normal of the solid layer as the arc sine of the ratio on the one hand of the speed of sound in the solid layer V _S and on the other hand the product of the period of the interdigital transducer I _IDT and the applied high frequency f (α = arcsin (V _S / (I _IDT · f)) For this sound coupling mechanism, the angle of incidence in relation to the normal of the solid layer, the levitation angle, that is to say by the frequency, can be specified. Both effects can occur side by side.

Both mechanisms (LSAW, BAW) enable the slope Radiation through the solid layer. The entire electrical contact of the interdigital transducer can on the microcavity or the liquid opposite side of the solid layer occur.

With an easy to implement embodiment the interdigital transducer is located on the piezoelectric Element on one of the microcavity opposite side of the solid layer. Because of the slant described Coupling of the ultrasound wave into the solid layer are also geometries possible, where the interdigital transducer with the piezoelectric element on an end face the solid layer is arranged.

It is particularly advantageous if the material of the solid layer to be passed through with respect to the acoustic damping at the frequencies used and the reflective properties of the interfaces so selected is that a partial reflection one at an angle coupled ultrasonic wave takes place. For example, a compensating medium be provided between the micro-titer plate and the solid layer, so that an interface between compensating medium and solid layer to be exposed sets in which a reflection coefficient of z. B. 80% up to 90% for sets an ultrasonic wave of the frequency used, so that 10% to 20% of that in the solid layer current ultrasonic wave are coupled out and the rest is reflected becomes. Between solid layer and Air at the other boundary surface of the solid layer there is usually almost 100% reflection. At a another embodiment, in which the bottom of the micro-titer plate itself as a solid-state layer to be passed through is used, is from the soil serving as a solid layer the micro-titer plate into the liquid in the respective microcavity 10% to 20% of the ultrasound output is decoupled and the rest in Bottom of the micro-titer plate is reflected.

Due to the reflection at the interfaces the ultrasonic wave through the solid layer like in a waveguide guided. Where the ultrasonic wave hits the interface between the solid layer and compensating medium or solid layer and liquid in one of the micro cavities, part of the ultrasonic power is extracted. By suitable Choice of geometries, e.g. B. the thickness of the solid layer or the bottom of the micro-titer plate, can be on this Way defined decoupling locations of ultrasound power locally establish. With such a procedure, z. B. several microcavities one Micro-titer plate sonicated at the same time with ultrasonic power be without a size Number of transducers would be necessary. Problems such. B. with wiring of a variety of transducers could occur avoided in this way.

Has been advantageous for. B. due low damping the use of quartz glass as a solid layer at one frequency proven from 10 MHz to 250 MHz. While at the solid / air interface in such a case almost 100% will be reflected on the Solid layer / liquid interface (So e.g. compensation medium or the liquid in the microcavity) a certain Percentage of sound energy in the respective liquid decoupled.

Use of interdigital transducers with non-constant finger spacing ("tapered interdigital transducers"), as they are for another Application z. B. are described in WO 01/20781 A1, enable the selection of the radiation location of the interdigital transducer with Help of the applied frequency. This way it can be set precisely at which point the ultrasonic wave from the solid layer exit. When using a tapered interdigital transducer, the additional has finger electrodes which are not currently formed, in particular z. B. arcuate interlocking finger electrodes, the azimuth angle θ can be varied control the operating frequency. On the other hand, the levitation angle .alpha Frequency through direct BAW generation on the interdigital transducer change.

With the help of the described setting of the radiation direction by selecting the frequency, if necessary by using appropriately shaped interdigital transducers, very precise z. B. individual microcavities of a micro titer plate can be selected for thorough mixing. Through temporal variation a time course of the mixing location can be specified for the operating frequency.

On the piezoelectric element are z. B. one or more interdigital transducers for generation the ultrasonic waves, which are either contacted separately or are contacted together in series or parallel to each other. For example, leave them with different finger electrode spacing this over itself control the choice of frequency separately and thus also offer the possibility the selection of certain areas.

To prevent reflections of unwanted Locating the solid layer can take place in an uncontrolled manner (e.g. on end faces) through suitable selection of a diffusely scattering surface of the Solid layer the ultrasonic wave is diffusely scattered. To do this, the corresponding area z. B. roughened. Such a roughened surface can also be targeted be used to specifically expand the ultrasonic wave, sonicate a larger area to be able to.

Suitable angled side faces of the Solid layer can used for targeted reflection and defines the sound beam to steer.

Especially regarding manufacturing costs and Geometry with well-defined radiation direction in the solid layer another embodiment of the method according to the invention also the use of a piezoelectric volume transducer, e.g. B. a piezoelectric thickness transducer, prove to be advantageous.

A device according to the invention to carry out of the method according to the invention a substrate, on the one main surface of which at least one piezoelectric Sonic migrator is arranged to generate an ultrasonic wave Frequency greater or equal to 10 MHz can be excited electrically, the thickness of the Substrate in the direction of sound propagation is greater than ¼ of the ultrasonic wavelength. The substrate can be formed separately or z. B. by the bottom of a micro-titer plate or a micro-cavity his.

The substrate can e.g. B. also a Glasslide cover, on which an adhesive film with preferably periodically arranged holes is attached in order to obtain an arrangement of microcavities in this way. Such a glass slide with a glued perforated adhesive film can be used like a micro titer plate.

It is particularly advantageous if a variety of piezoelectric transducers in a pitch Micro-titer plates are used to measure the microcavities Sonicate micro-titer plate in parallel with ultrasound.

To individual transducers individually to be able to control a switching device is advantageously provided, the electrical High frequency power applied to individual sound transducers.

Advantages of other embodiments the device according to the invention to carry out the different configurations of the method according to the invention result from the for corresponding process configurations advantages described and properties.

The following are special designs of the method according to the invention or the device according to the invention explained in detail with reference to the accompanying figures. The figures are there only schematic and not necessarily to scale. It shows

1 the detail of a cross section of a device according to the invention while carrying out a method according to the invention,

2 FIG. 2: a section of a cross section of another embodiment of the device according to the invention for carrying out an embodiment of the method according to the invention,

3 the cross section of a further embodiment of the device according to the invention for carrying out an embodiment of the method according to the invention,

4a the top view of a micro-titer plate for use with a device according to the invention for carrying out an embodiment of the method according to the invention,

4b the arrangement of a field of piezoelectric volume oscillators according to an embodiment of the device according to the invention for carrying out an embodiment of the method according to the invention,

5 the mode of operation of a device according to the invention or a method according to the invention using the example of a single microcavity,

6 1: an explanatory sketch of the mode of operation of a piezoelectric thickness transducer, as can be used with the method according to the invention,

7a 1 shows a sectional view through a device for defining a periodic arrangement of microcavities,

7b : a top view of the facility of the 7a .

8a 1 shows a cross-sectional view of a further arrangement for carrying out a method according to the invention,

8b 1 shows a cross-sectional view of an arrangement for carrying out a method according to the invention for explaining a special mode of operation,

9 1 shows a cross-sectional view of an alternative arrangement for carrying out a method according to the invention,

10a : a top view of a cross Section of an arrangement for carrying out an embodiment of the method according to the invention,

10b a plan view of a cross section of a further arrangement for carrying out an embodiment of the method according to the invention,

11 FIG. 2 shows a side cross-sectional view of an apparatus for carrying out a method according to the invention,

12 FIG. 2 shows a lateral cross-sectional view of a further device for carrying out a method according to the invention,

13 1 shows a plan view of a cross section of a further arrangement for carrying out a method according to the invention,

14 FIG. 2 shows a partial side sectional view through an arrangement for carrying out a further embodiment of the method according to the invention,

15 FIG. 2 shows a partial side sectional view through an arrangement for carrying out a further embodiment of the method according to the invention,

16 a plan view of a cross section of an arrangement for carrying out a further embodiment of the method according to the invention,

17a-c : Partial sectional views of different configurations of the electrical contacting of a device for performing a method according to the invention.

1 schematically shows an arrangement according to the invention in cross section. 1 shows a piezoelectric thickness transducer, its operation with reference to 6 will be explained. 9 denotes the schematic cross section through a micro-titer plate in the area of the cavities 3 , Three cavities are shown, but micro-titer plates generally have 96, 384 or 1536 cavities in a rectangular arrangement. The diameter D of a single cavity 3 is larger than the diameter d of the piezoelectric thickness transducer 1 , For example, the diameter D of a 96-well micro-titer plate is 6 mm and the thickness transducer has a diameter of 3 mm. In the micro cavities 3 the micro-titer plate 9 there is liquid 5 , The liquid is shown with the surface curved upwards due to the surface tension. F denotes the average fill level in a single microcavity. Solid material is located between the thickness transducer and the microcavities 15 , e.g. B. made of plastic, metal or glass to protect the thickness transducer or the contacts. 19 denotes a flat electrode below the substrate 15 , This electrode forms an electrical connection for the piezoelectric thickness transducer 1 ,

The other electrode of the thickness transducer is with 21 designated. The electrodes 19 . 21 are about electrical connections 23 . 25 with the high frequency generator 17 connected. On the main surfaces of the substrate 15 there is an optionally available coupling medium 11 . 13 , e.g. B. water, oil, glycerin, silicone, epoxy resin or a gel film to compensate for unevenness in the individual layers and to ensure optimal sound coupling.

A condition is shown in which the thickness transducer 1 emits an ultrasonic wave towards the center cavity shown, causing movement in the liquid 7 is produced.

2 shows another embodiment. The same elements are designated with the same reference numbers. Individual thickness transducers for the individual microcavities of the micro titer plate 9 are provided. With the help of a switching device 26 can the high frequency signal of the high frequency generator 17 to the different thickness transducers 1 be created. 31 schematically denotes an optional sound absorbing medium that prevents crosstalk. This sound-absorbing medium can be a structuring or a correspondingly selected plastic.

3 shows an embodiment in which one or more transducers 33 be used over waveguide 35 are connected to the bottoms of various cavities. These waveguides are preferably made of a material with similar acoustic properties as the thickness transducer itself in order to optimize the coupling. B. metal rods.

4 shows the arrangement in a grid. 4a shows the top view of a micro-titer plate with 96 Cavities. 4b shows the top view of the arrangement of individual piezoelectric thickness transducers 27 on a substrate 29 , The pitch of the micro-titer plate R is also for the distance between the piezoelectric thickness transducers 27 respected. Alternatively, the thickness transducer can cover the entire surface of the substrate 29 be applied and only the electrode arrangement correspond to the pattern of the micro-titer plate.

5 shows in detail the cross section through a single micro-cavity for explanation. It shows 2 the ultrasonic wave emitted by the thickness transducer. 6 denotes the meniscus without ultrasound wave and 4 the meniscus during the irradiation. The thickness of the substrate 15 including the possible coupling media 11 . 13 is greater than ¼ of the wavelength of the ultrasonic wave in the substrate, which is typically in the range of a few 100 microns. As materials for the substrate come z. B. metal, such as aluminum, glass or plastic in question. "Thickness" is the thickness of the substrate 15 meant in the direction of sound propagation. In a substrate made of aluminum, the wavelength of a 20 MHz sound wave is z. B. 315 μm, in glass 275 μm and in plastic 125 μm.

6 explains the principle of the piezoelectric thickness transducer 1 , When creating a high frequency field using the high frequency genera tors 17 to the electrodes 19 . 21 of the thickness transducer, an ultrasonic wave is generated perpendicular to the surface area of the thickness transducer. The direction of vibration is with 37 designated. With a thickness of the thickness transducer of z. B. 200 microns results in a wavelength of 400 microns when the fundamental vibration is excited. Piezoelectric single crystals, e.g. B. quartz, lithium niobate or lithium tantalate in question. Other transducers have piezoelectric layers, e.g. As cadmium sulfide or zinc sulfide or piezoelectric ceramics, for. B. lead zirconate titanate, barium titanate or with admixtures to optimize the speed of sound on the solid. Piezoelectric polymers (e.g. polyvinylidene difluoride) or composite materials are also possible. It when the material of the solid is particularly advantageous 15 or the micro-titer plate 9 is acoustically adapted to the sound transducer, ie has a similar sound velocity and density or a similar product of both sizes.

7 shows a device that can be used like a one-piece micro-titer plate. On a glass slide (e.g. a slide) 109 is a perforated adhesive film 110 applied. 7b shows a plan view in which the cutting direction AA 'of the in 7a shown cut is indicated. The pitch R of the holes corresponds to z. B. the pitch of a conventional micro-titer plate. The periodically arranged holes 3 define microcavities as they are in a micro titer plate. A device of 7 can be used like a micro-titer plate and for the purposes of the present text the term “micro-titer plate” is also intended to encompass a corresponding arrangement.

The inventive method can with the above described inventive devices performed as follows become.

On the substrate 15 becomes the micro-titer plate 9 placed. A compensation medium can be used to optimally compensate for unevenness 11 , e.g. B. water, can be arranged in between. The micro titer plate 9 is placed so that it has a cavity 3 above the piezoelectric thickness transducer 1 is arranged ( 1 ). The liquid 5 is in the micro cavities 3 introduced, taking care that the fill level F is sufficiently high to be greater than the wavelength of the ultrasound that can be generated with the thickness transducer. Applying high frequency to the electrodes 19 . 21 of the thickness transducer 1 with the help of the high frequency generator 17 generates an ultrasonic wave perpendicular to the thickness transducer at a specific frequency, the resonance frequency, which is dependent on the thickness and geometry of the thickness transducer and the solid layer 1 , which is shown in the direction of the middle cavity 3 spreads and a mixture of the liquid therein 7 causes.

The ultrasound beam, the lateral extent of which is the size of the thickness transducer 1 the microcavity from below 3 and creates an impulse and a flow in the liquid upwards, which leads to a deformation of the meniscus 4 (please refer 5 ) can lead. The liquid can flow downward again to the side of the upward directed ultrasound beam, so that thorough mixing of the liquid is achieved.

After mixing the liquid in a micro cavity becomes the micro-titer plate possibly offset to expose another microcavity to the ultrasound.

In one embodiment of the 2 becomes the micro-titer plate 9 also on the substrate 15 set. The microcavity, the liquid of which is to be mixed, can be switched on 26 to be selected. 4b shows the top view of an arrangement of the piezoelectric thickness transducers used for this purpose 27 ,

In one embodiment of the 3 is the ultrasound with the help of the ultrasound generator 33 generated and over waveguide 25 guided under the microcavities, which are then simultaneously sonicated with ultrasound.

The high-frequency excitation can also take the form of an intense needle pulse in all configurations. This contains a wide frequency spectrum, which also includes the resonance frequency of the thickness transducer 1 includes. Alternatively, the high-frequency signal is fed in immediately with the resonance frequency of the thickness transducer or a harmonic. The specimen scatter in the resonance frequency, which may be caused by manufacturing tolerances, can be countered by statistically or periodically varying the excitation frequency by an average frequency value. The size of the frequency modulation can be chosen so that it corresponds to the maximum deviation of the resonance frequency. Typical resonance frequencies are in the range of greater than or equal to 10 MHz, typical variations of the resonance frequencies in the range of a few 10 to a few 100 MHz.

8a shows an embodiment in which an interdigital transducer, as indicated only schematically in all corresponding figures 101 is used to generate the sound wave. 115 denotes the substrate, e.g. B. made of quartz glass. 102 is a piezoelectric crystal element, e.g. B. from lithium niobate. On the piezoelectric crystal element 102 and thus between the piezoelectric crystal element 102 and the substrate 115 there is an interdigital transducer 101 , the z. B. in advance on the piezoelectric crystal 102 was applied. An interdigital transducer is usually formed from comb-like interdigitated metallic electrodes, the double finger spacing of which defines the wavelength of a surface sound wave, which is generated by applying a high-frequency alternating field (in the range of e.g. a few MHz to a few 100 MHz) to the interdigital transducer in the piezoelectric crystal. For the purposes of the present text, the term “surface acoustic wave” is also intended to describe interfacial waves at the interface between the piezoelectric element 102 and substrate 115 be included. As a substrate 115 a material with low acoustic damping is used at the frequencies used. For example, quartz glass is suitable for frequencies in the range from 10 MHz to 250 MHz. Interdigital transducers are in DE-A-101 17 772 described and known from surface wave filter technology. For connecting the electrodes of the interdigital transducer 101 are used for metallic feed lines 8a not shown and with reference to 17 are explained in more detail.

With the help of the bidirectional radiating interdigital transducer 101 can ultrasonic waves 104 are generated in the specified direction, as described above at an angle α to the normal to the substrate 115 the substrate as volume sound waves 115 push through. 111 denotes an optional coupling medium between the substrate 115 and the micro titer plate 109 as described above for another embodiment. 108 denote the areas of the interface between the substrate 115 and coupling medium 111 that are significantly different from the volume sound waves 104 to be hit. 106 denotes the reflection points at the substrate 115 / air interface. With 109 a micro-titer plate is described in its cavities 103 the liquid 105 located.

With the help of the interdigital transducer 101 , on which in a known manner the radio frequency over the in 8a leads, not shown, are applied obliquely into the substrate bulk sound waves 104 generated. These hit at the points 108 on the interface between the substrate 115 and coupling medium 111 , Appropriate selection of substrate material 115 causes part of the ultrasonic wave 104 at the points 108 is reflected and another part is coupled out. The materials are selected so that at the interface between the substrate 115 and coupling medium 111 partial reflection takes place at the interface between the substrate 115 and air, so at the points 106 , almost complete reflection sets in. For example, when using SiO ₂ glass, there is a reflection factor at the interface between the coupling medium and glass of approximately 80% to 90%, that is to say a coupling into the coupling medium of approximately 10% to 20%. Assuming a reflection factor of 80%, the intensity of the beam reflected multiple times in the glass substrate increases 104 after ten reflections about 10 dB. With a substrate thickness of 3 mm, the beam has already covered a lateral distance of 250 mm. By appropriate selection of the geometry, e.g. B. the thickness of the substrate, the points can in this way 108 , on which part of the ultrasonic wave from the substrate 115 is coupled into the coupling medium, to be precisely determined locally and to the grid dimension of the micro-titer plate used 109 be adjusted.

In an alternative, not shown, the bottom of the micro-titer plate is used 109 even as a substrate, on the underside of which is the piezoelectric crystal 102 attached or pressed. The ultrasonic wave 104 is then coupled directly into the bottom of the micro-titer plate and out into the liquid at the interface formed by the bottom of the individual microcavities, as described for the embodiment shown for the coupling into the coupling medium.

8b is used for explanation to show how with an embodiment of the 8a different coupling angles can be set by selecting different frequencies. In the case of direct excitation of volume modes (BAW), the radiation angle .alpha. Can enter the substrate by varying the excitation frequency 115 can be set. With the interdigital transducer 101 it can be a simple normal interdigital transducer, the levitation angle α being set according to the relationship sinα = V _S / (I _IDT · f), where V _{S is} the speed of sound of the ultrasonic wave, f the frequency and I _{IDT is} the periodicity of the interdigital transducer electrodes , By varying the frequency, the radiation angle z. B. change from α to α '. In this way, the decoupling points 108 z. B. the grid dimension of a micro-titer plate 109 be optimally adjusted.

9 shows a variation of B , A sectional side view is shown. From the bidirectional radiating interdigital transducer 101 a beam goes 104L in the 9 to the left and a ray 104R slanted to the right into the substrate 115 , On the edge 112 of the substrate 115 becomes the sound beam 104L reflected and towards the interface between the substrate 115 and coupling medium 111 distracted. By appropriate selection of the geometry, e.g. B. the thickness of the substrate 115 , can also impact points 108 can be adapted to the grid dimension of a micro-titer plate.

In an embodiment not shown, the interdigital transducer is located 101 on the piezoelectric element 102 not on a major surface of the substrate 115 , but on an end face, e.g. B. at the edge 112 as in 9 is visible. In this way, the bidirectional radiating interdigital transducer can also be used 101 two volume sound waves 104 generate that at an angle through the substrate 115 step through and analogous to the procedure that is described in 9 is shown can be used.

Both in the embodiment of the 8th as well as in the embodiment of the 9 can have multiple interdigital transducers on one or more piezoelectric elements 102 be arranged side by side in order to not only a series of Mi krokavitäten 103 to sonicate, but a field of adjacent rows, as it corresponds to a conventional micro-titer plate.

10a shows a plan view of a cross section of an arrangement, approximately at the level of the surface of the substrate 115 , which has a special direction of the sound beam in the substrate 115 allows. From the interdigital transducer 101 go in a way related to them 8th is described, sound rays 104 from that at points 108 on the upper interface of the substrate 115 to meet. The beam cannot be seen in the representation of the figure in the form of a zigzag line analogous to the sectional representation in FIG 8a through the substrate 115 guided. The guided sound beam 104 becomes at interfaces 110 of the substrate 115 distracted. By suitable geometry of the surfaces 110 a desired movement pattern of the sound beam can be generated.

In 10b an arrangement is shown with which it can be achieved that a flat substrate 115 almost completely with the help of only one bidirectional radiating interdigital transducer 101 can be covered in this way, with the help of multiple reflections on the side surfaces 110 of the substrate 115 is achieved. In 10b are the reflection points on the main surface of the substrate 115 Not shown for the sake of clarity, but only the direction of propagation of the ultrasonic waves 104 by reflection on the main surfaces of the substrate 115 , such as B. with reference to 8a described, is effected.

11 shows a side section through another arrangement for performing a method according to the invention. The beam cross section is effectively broadened here by several interdigital transducers 101 for the generation of parallel beams 104 be used. In this way, the upper interface of the substrate can be made in an almost homogeneous manner 115 be sonicated to z. B. several microcavities 105 a micro titer plate 109 sonicate at the same time.

The described reflection effect by selecting a suitable substrate material for the substrate 115 can also be done with the help of a volume transducer 130 generate as it is in 12 is shown. As a piezoelectric volume transducer 130 can e.g. B. a piezoelectric thickness transducer can be used, which is arranged such that an oblique coupling of the sound wave takes place. A so-called wedge transducer is used for this. The angle of incidence α to the surface normal of the surface on which the wedge transducer was applied is determined from the angle β at which it is applied and the ratio of the sound velocities of the wedge transducer v _w and the substrate 115 v _S according to α = arcsin [(v _s / v _w ) · sinβ].

13 shows an embodiment in which an edge 1 18 of the substrate 115 is roughened to diffuse reflection of the impinging sound wave 104 to reach. This can be useful to inactivate an unwanted sound beam reflected at an edge. The sound beam 104 is similar in such an embodiment as with reference to 8th explained by the substrate 115 in the manner of a waveguide due to reflections on the upper and lower main surface of the substrate 115 directed. On the roughened surface 118 finds a diffuse reflection in the individual rays 120 instead of. In this way, the directional sound beam 104 be made ineffective or widened in such a way that a homogeneous sonication of several microcavities is possible, which is on the substrate 115 are located. 13 again shows a plan view of a cross section approximately corresponding to the upper interface of the substrate 115 ,

14 shows an embodiment in which the rear surface 114 of the substrate 115 is roughened. The interdigital transducer is located on this rear surface 101 , With the described coupling of the ultrasonic wave into the substrate 115 becomes the jet due to the roughened surface 104 widened by diffraction. This effect is seen in the further reflections on the surface 114 reinforced. With increasing distance between the coupling points 108 The coupling point is widened accordingly from the substrate into the coupling medium, not shown, on which the micro-titer plate is located. 14 shows a partial cross-sectional view in which the micro-titer plate has not been shown.

A similar effect is with an embodiment of the 15 reachable. Here is the expansion of the sound beam 104 after coupling from the interdigital transducer 101 into the substrate 115 by reflection on a curved reflection edge 116 reached. Just as an expansion is described here, focusing can be achieved with the aid of a correspondingly designed reflection edge. Also 15 shows only a partial cross-sectional view, in which the substrate 115 is shown. On the substrate 115 are in the manner described and not shown here z. B. the coupling medium 111 and the micro titer plate 109 ,

16 shows a further embodiment in a schematic representation. Here, too, is the view of the interface between the substrate 115 and coupling medium 111 shown. As in the other representations, there are only a few interlocking fingers of the interdigital transducer for clarity 201 shown, although an implemented interdigital transducer has a larger number of finger electrodes. The distance between the individual finger electrodes of the interdigital transducer 201 is not constant. The interdigital transducer 201 therefore emits at a high frequency fed in only at a location where the finger distance correlates with the frequency accordingly, as is the case for another application. B. is described in WO 01/20781 A1.

When designing the 16 the finger electrodes are also not straight, but arcuate. Since the interdigital transducer emits essentially perpendicular to the alignment of the fingers, the direction of the emitted surface sound wave can be determined in this way by selecting the high frequency fed in. In 16 are the radiation directions 204 shown for two frequencies f1 and f2, the direction of radiation being indicated by the angle θ1 for the frequency f1 and the angle θ2 for the frequency f2. 16 shows schematically the top view of the interface between the piezoelectric substrate 102 on which the interdigital transducer 201 is applied, and the substrate 115 that with the piezoelectric substrate 102 is in contact.

17a to 17c show different possibilities for electrical contacting of the interdigital transducer electrodes in the embodiments of the 8th . 9 . 10 . 11 . 13 . 14 . 15 or 16 , In the embodiment as in 17a is shown, metallic conductor tracks on the substrate 115 applied on the back. The piezoelectric crystal 102 with the interdigital transducer 101 so on the substrate 115 placed that there is an overlap of the metallic electrode on the substrate 115 with an electrode of the interdigital transducer 101 on the piezoelectric substrate 102 results. When the piezoelectric sound transducer is glued to the substrate, the area of overlap is glued with electrically conductive adhesive, whereas the remaining surface is glued with conventional non-electrically conductive glue. Purely mechanical contact may be sufficient. The electrical contact 122 the metallic conductor tracks on the substrate 115 in the direction of the high-frequency generator electronics, not shown, is done by a soldered connection, an adhesive connection or a spring contact pin.

In the embodiment of the electrical contacting of the 17b becomes the piezoelectric crystal 102 on which the interdigital transducer electrodes with leads 124 are applied in such a way on the substrate 115 applied that there is a protrusion of the first to the second. In this case, contacting continues 122 directly on the on the piezoelectric crystal 102 applied electrical leads 124 on. The contact can be soldered, glued or bonded or made using a spring contact pin.

In the embodiment of the electrical contact, as in 17c is shown, the substrate 115 with a hole 123 per electrical contact and the piezoelectric crystal 102 is directly on the substrate 115 placed the electrical leads attached to the piezoelectric transducer through the holes 123 can be contacted through. In this case, the electrical contact can be directly connected to the electrical leads on the piezoelectric crystal by means of a spring contact pin 102 respectively. Another option is to fill the hole with a conductive glue 123 to fill or glue in a metal bolt. The further contact 122 in the direction of the high-frequency generator electronics then takes place by means of a soldered connection, a further adhesive connection or a spring contact pin.

Another way of feeding the electrical Power at the piezoelectric transducer consists in the inductive Coupling. The electrical leads to the interdigital transducer electrodes trained so that they as an antenna for contactless control of the high-frequency signal serve. In the simplest case, this is an annular electrode on the piezoelectric substrate, which acts as a secondary circuit High-frequency transformer serves, the primary circuit with the high-frequency generator electronics connected is. This is held externally and is directly adjacent attached to the piezoelectric transducer.

Individual configurations of the processes or the features of the described embodiments can be found in suitable form also combine to achieve the effects achieved and being able to achieve effects at the same time.

With the method according to the invention efficient mixing of the smallest amounts of liquid is possible. It the liquid is not necessary comes into contact with the movement-mediating medium itself. It must e.g. B. no mixing element in the liquid be introduced. The method or the device can be simple and inexpensive with today's laboratory machines that are used in biology, diagnostics, pharmaceutical Research or chemistry used to apply. The usage high frequencies effectively prevents the formation of cavitation. Finally let yourself realize a flat design and the device can be simple used in laboratory streets become.

Claims (39)

Process for mixing liquids ( 5 . 7 . 105 ) in at least one micro cavity ( 3 . 103 ) using sound-induced flow, in which at least one piezoelectric sound transducer ( 1 . 101 . 130 . 201 ) at least one ultrasonic wave ( 2 . 104 . 204 ) a frequency greater than or equal to 10 MHz through a solid layer ( 15 . 115 ) a dimension in the direction of sound propagation which is greater than ¼ of the wavelength of the ultrasonic wave, for generating a sound-induced flow into the at least one microcavity ( 3 . 103 ) is sent. The method of claim 1, wherein the wel lenlength of the ultrasonic wave in the liquid is chosen such that it is smaller than the average fill level (F) in the at least one microcavity ( 3 . 103 ) is. Method according to one of Claims 1 or 2, in which the lateral extension (d) of the at least one sound transducer ( 1 . 101 ) is smaller than the lateral dimension (D) of the microcavity ( 3 . 103 ). Method according to one of Claims 1 to 3, in which between the at least one sound transducer ( 1 ) and the micro cavity ( 3 ) an intermediate layer is introduced which comprises an ultrasound-absorbing material in an arrangement such that the ultrasound is only present in a limited spatial area, preferably an area which is smaller than the lateral extent (D) of the microcavity ( 3 ) is towards the micro cavity ( 3 ) can spread. Method according to one of Claims 1 to 4, in which between the microcavity ( 3 . 103 ) and the solid layer ( 15 . 115 ) a compensating medium ( 11 . 111 ) is introduced. Method according to one of Claims 1 to 5, in which a plurality of microcavities ( 3 . 103 ) are used. Method according to Claim 6, in which the microcavities ( 3 . 103 ) a micro-titer plate ( 9 . 109 ) are used. Method according to one of claims 6 or 7, in which a plurality of sound transducers ( 1 ) are used, which are preferably controlled individually. Method according to Claim 7, in which a sound transducer ( 1 ) is used, the lateral dimension (d) of which is smaller than the diameter (D) of a cavity of the micro-titer plate ( 9 ), and the micro-titer plate for the individual mixing of liquid in a selected cavity with this selected cavity above the transducer ( 1 ) on the solid layer ( 15 ) is applied. Method according to one of claims 7 or 8, in which a micro-titer plate ( 9 ) with several sound transducers ( 1 ), the grid dimension (R) of a micro-titer plate ( 9 ) on the solid material ( 15 ) are arranged, are used. Method according to one of Claims 6 or 7, in which, with the aid of the piezoelectric sound transducer ( 101 . 130 . 201 ) Ultrasound ( 104 . 204 ) through the solid layer ( 115 ) that ultrasonic power is sent to at least two decoupling points ( 108 ) from the solid layer into a corresponding number of micro cavities ( 103 ) is coupled. The method of claim 11, wherein the at least one ultrasonic wave ( 104 . 204 ) diagonally through the solid layer ( 115 ) is sent through. Method according to Claim 12, in which a bidirectionally radiating ultrasound generating device, preferably an interdigital transducer ( 101 . 201 ), on a piezoelectric crystal ( 102 ) is used. Method according to one of Claims 11 to 13, in which an ultrasonic wave ( 104 ) into the solid layer ( 115 ) is coupled in that it is reflected at least once within the solid layer, a material being selected for the solid layer in which the reflection ( 106 ) at which the at least one microcavity ( 103 ) facing away from the surface as completely as possible and on the surface facing the microcavity or the liquid ( 108 ) lossy but not equal to 0, and the acoustic damping within the solid layer ( 115 ) is as low as possible. Method according to one of claims 11 to 14, in which the at least two decoupling points by temporal variation of the radiation direction of the at least one piezoelectric sound transducer ( 201 ) be generated. Method according to one of claims 1 to 15, in which the at least one ultrasound wave with the aid of an interdigital transducer ( 201 ) is generated on a piezoelectric element, the interlocking finger electrodes of which are spaced apart from one another in a spatially inconsistent manner, and by changing the values applied to the interdigital transducer ( 201 ) frequency is set the radiation location. The method of claim 16, wherein an interdigital transducer ( 201 ) is used, the interlocking finger electrodes of which are not straight, but in particular arc-shaped, and by selecting the frequency of the high-frequency field applied, the direction of radiation ( 204 ) is selected. Method according to one of Claims 1 to 17, in which the at least one ultrasonic wave ( 104 . 204 ) with the help of an interdigital transducer ( 101 . 201 ) on a piezoelectric element ( 102 ) on one of the at least one microcavity ( 103 ) opposite side of the solid layer ( 115 ) is produced. Method according to one of Claims 1 to 15, in which at least one piezoelectric volume oscillator ( 1 . 130 ) than the at least one piezoelectric sound transducer is used. Method according to one of claims 1 to 19, in which a solid layer ( 115 ) is used that has at least one diffusely scattering surface ( 114 . 118 ) around which at least one ultrasonic wave ( 104 ) widen in the solid layer. Method according to one of Claims 1 to 20, in which the direction of propagation of the at least one ultrasonic wave ( 104 ) in the solid layer ( 115 ) through reflective surfaces ( 110 ) is steered. Device for mixing liquids in at least one microcavity ( 3 . 103 ), especially the microcavities of a micro titer plate ( 9 . 109 ), for carrying out a method according to claim 1 with - a substrate ( 15 . 115 ), and - at least one piezoelectric sound transducer ( 1 . 101 . 130 . 201 ) which is arranged on a main surface of the substrate and for generating an ultrasonic wave ( 4 . 104 . 204 ) a frequency greater than or equal to 10 MHz can be electrically excited, the extent of the substrate ( 15 . 115 ) is greater than ¼ of the ultrasonic wavelength in the direction of sound propagation. Device according to claim 22 with a plurality of piezoelectric sound transducers ( 1 ) in grid dimension (R) of a micro-titer plate ( 9 ). Device according to claim 23 with a switching device ( 26 ) to control individual sound transducers ( 1 ). Device according to one of Claims 22 to 24, in which the at least one sound transducer ( 1 . 101 . 130 . 201 ) is selected such that the ultrasound wave generated by it has a wavelength that is less than the height dimension of the at least one cavity ( 3 ). Device according to one of Claims 22 to 25, in which the lateral extension (d) of the at least one sound transducer ( 1 ) is smaller than the lateral extent (D) of a cavity ( 3 ) a micro-titer plate ( 9 ). Device according to one of claims 22 to 25 with an intermediate layer on a main surface of the substrate ( 15 ), which has an ultrasound absorbing medium in an arrangement which emits the ultrasound radiation in the direction of the microcavity ( 3 ) limited in space, preferably in the arrangement of the microcavities of a micro titer plate ( 9 ). Device according to one of Claims 22 to 27, in which the piezoelectric sound transducer ( 101 . 130 . 201 ) is designed such that at least one ultrasound wave is slanted into the substrate ( 115 ) is coupled. Apparatus according to claim 28, wherein the at least one piezoelectric sound transducer ( 101 . 201 ) is bi-directional. Device according to one of claims 28 or 29, wherein the material of the substrate ( 115 ) is selected such that the reflections ( 106 ) on the microcavity ( 103 ) as far away from the surface as possible and the reflections ( 108 ) lossy on the side facing the microcavity or the liquid, but are not equal to 0, and the acoustic damping within the solid layer ( 115 ) is as low as possible. Device according to one of Claims 22 to 30, in which the at least one piezoelectric sound transducer is an interdigital transducer ( 101 . 201 ) on a piezoelectric element ( 102 ) includes. Apparatus according to claim 31, wherein the electrical connection of the at least one interdigital transducer ( 101 ) by a first lead on the piezoelectric element and a second lead ( 116 ) on the substrate ( 115 ) is formed, which are arranged such that they overlap each other. Apparatus according to claim 31, wherein the piezoelectric element ( 102 ) a supernatant ( 124 ) over the substrate ( 115 ) on which there is a contact point for the electrical supply line ( 122 ) to the at least one interdigital transducer ( 101 ) is located. Apparatus according to claim 31, wherein the at least one interdigital transducer ( 101 ) through a hole ( 123 ) is contacted through the substrate, which is preferably filled with a conductive adhesive. Apparatus according to claim 31, wherein the interdigital transducer via antenna devices features, which can be used for contactless coupling of a high-frequency signal are. Device according to one of Claims 31 to 35, in which the finger electrodes of the interdigital transducer ( 201 ) do not have a spatially constant distance from each other. Apparatus according to claim 36, wherein the finger electrodes of the interdigital transducer ( 201 ) are not straight, but are designed in particular in an arc shape. Device according to one of Claims 22 to 30, in which the at least one piezoelectric sound transducer is a piezoelectric volume oscillator ( 1 ) includes. Device according to one of claims 22 to 38, in which the substrate has at least one diffusely scattering surface ( 114 . 118 ) having.