Method for operating a filter and self-cleaning filter system

Abstract

The invention relates to a method for operating a filter (10), wherein the filter comprises: i) a first polarizing element (12), ii) a second polarizing element (14), iii) a polarizable filter medium (16), and iv) an electrical contacting system (18), wherein the method comprises operating the filter (10) in at least two different operating modes, wherein the filter (10) is operated in a polarization mode for 80% or more of the operating time, wherein in the polarization mode a continuous DC voltage is applied between the first polarizing element (12) and the second polarizing element (14), which varies by 20% or less, relative to the mean value of the DC voltage in the polarization mode, wherein the filter (10) is partially operated in a DC cleaning mode.wherein in DC cleaning mode a pulsed DC voltage is applied between the first polarizing element (12) and the second polarizing element (14) with a plurality of pulses, wherein the mean electric field strength during the pulses is 0.5 kV / cm or more, and / or wherein the filter (10) is partially operated in an AC cleaning mode, wherein in AC cleaning mode a pulsed AC voltage is applied between the first polarizing element (12) and the second polarizing element (14) with a plurality of pulses, wherein the peaks of the magnitude function of the electric field strength during the pulses are at least partially at 0.5 kV / cm or more.

Description

The invention relates to a filter and a filter system for use in a corresponding method. Also disclosed are a filter insert for corresponding filter systems and the use of pulsed electric fields for cleaning polarizable filter media in electrostatic precipitators with filter functionality.Modern filtration technology today discloses numerous powerful alternatives and further developments to the well-known methods for separating undesired components from fluid streams, which are mostly based on a substantially mechanical separation, mostly on a merely partially permeable filter medium, which can consist for example of a porous material.One of these further developments, which is used in particular for gas cleaning, is the so-called electrostatic separation, the devices used also being referred to as electrostatic precipitators. In these electrostatic precipitators, the particles to be removed are ionized by an electrode in a first step and are subsequently deposited on an oppositely charged precipitation electrode. Corresponding electrostatic precipitators are used in particular in industrial plants.However, other requirements are placed on the performance characteristics of interior air filters, in particular for use in vehicles, wherein, for example, reliable separation of pollen and / or particulate matter and / or odors and / or exhaust gases is also desired.In order to meet these requirements for interior air filters, the concept of electrostatic separation, which in many cases is strictly not a filtration, has been combined with mechanical separation methods to obtain efficient filter media. The combination of classic filter materials with an ionization device makes it possible in many cases to increase the separation performance of filters even significantly, the corresponding filter media being referred to within the scope of the present invention as electrostatic separators with filter functionality for the purpose of clear identification. However, in the case of corresponding filter media, it is observed that the separation performance can decrease over the service life of the filter media, which is frequently attributed to an electrostatic charge in the filter material that is reduced over time.To solve this problem, it has been proposed to design electrostatic separators with filter functionality such that a polarization of the filter material can be caused in the filter insert by the application of a voltage to two polarization elements via the build-up of an electric field. In combination with an ionization device, this polarization of the filter material can enable efficient separation, which can advantageously be preserved for the most part over the entire service life of the filter medium. Background information on the basic technology is disclosed, for example, in WO 2007 / 135232 A1 or EP 3 448 540 B1.Despite the basic advantageous nature of corresponding electrostatic precipitators with filter functionality, there are still problems in the systems known from the prior art which have not yet been solved satisfactorily according to the inventors' judgment. One of these problems shared by corresponding electrostatic precipitators with filter functionality with many other filter media is that the filter media used mostly absorb a large number of contaminants over time, which may comprise four or microorganisms, in particular bacteria. In particular in the case of bacteria, the filter media used often offer a large potential colonization surface because of their large surface area, so that a severe contamination of the filter media with bacteria can occur over time. Such contamination is in principle undesirable because there is always the risk that the flow of the fluid to be filtered carries bacteria, for example, out of the filter medium and these can reach the interior of a vehicle, for example.In the prior art, to solve the problem in classical filter media, the use of additional components, for example biocides, is mostly used, which have an antimicrobial, in particular antibacterial, effect. Due to the lack of powerful alternatives to the corresponding procedure, this solution has so far also been used in electrostatic precipitators with filter functionality.However, the use of such additional components with antimicrobial action is considered disadvantageous from numerous points of view. In particular, the equipment required for this purpose of the filter media used with the corresponding antimicrobial substances is complicated in terms of process engineering and perceptibly increases the overall costs associated with the production of corresponding filter media. In addition, some of the components known from the prior art for this purpose as biocides are not unproblematic with regard to their handling from the hazardous point of view. In addition, the substances used are not suitable with regard to their absolute effectiveness and / or with regard to the duration of action after the inventors have been assessed in order to meet all requirements, in particular not over the entire expected service life of a corresponding filter which is intended to be used, for example, in a vehicle.The primary object of the present invention was to eliminate or at least alleviate the disadvantages of the prior art.In particular, it was the object of the present invention to provide a solution for electrostatic precipitators with filter functionality, with which an advantageous removal of microorganisms in the filter, in particular in the filter medium, can be achieved.In this case, it was an object of the present invention that the advantageous antimicrobial effect can be flexibly adapted to the respective application requirements of the occurring contaminants. In addition, it was an object of the present invention that the solution to be specified should have a very long-term cleaning effect in the filter media used, desirably a substantially time-unlimited cleaning effect.It was a further object of the present invention that the solution to be specified for the problem should, if possible, manage without the use of potentially harmful and / or environmentally harmful substances, wherein it was particularly desirable that the use of antibacterial substances or other biocides can ideally be completely dispensed with.It was a further object of the present invention that the solution to be specified for avoiding colonization of the filter media with microorganisms should ideally not have a negative influence on the time and cost efficiency of the production of corresponding filters, wherein it was a desirable requirement that the solution to be specified ideally be easily combined with existing structures of typical filter media.The inventors of the present invention have now found that the above-described objects can be achieved surprisingly if a method for operating a filter, in particular an electrostatic precipitator with filter functionality, is used, in which, in addition to the polarization mode required for the polarization of the filter medium, a cleaning mode is also provided, which can be operated with direct current or alternating current and which is based on the concept of electroporation, which is known in particular from the food industry, by means of the use of pulsed electric fields in order to render microorganisms present in the filter medium harmless, as defined in the claims.The present invention is thus based on the surprising finding that the basic structure of an electrostatic precipitator with filter functionality, in which the polarizable filter medium is arranged in any case between two polarization elements, which are designed for the build-up of an electric field used for polarization, can be advantageously converted with only minor modifications to provide, besides such phases in which the polarization is ensured, relatively short phases of pulsed operation, with which electroporation can be carried out with little additional effort, which can advantageously render the microorganisms present in the filter medium harmless. In addition to the advantageous fact that the basic structure required for carrying out the electroporation is already present in the electrostatic precipitators with filter functionality and can easily be achieved in corresponding filter systems in accordance with the invention by a corresponding programming of the electronic control units, the method according to the invention based on this finding and the filter system suitable for carrying out are also advantageous in particular because the use of biocides can be substantially completely dispensed with. In addition, the desired antimicrobial effect is advantageously based on the use of the electrical or electronic devices which-at least with respect to the service life typically expected for filters-is substantially not subject to relevant aging, which would reduce the effectiveness of the cleaning performance. In addition, it can be seen as a great advantage of the invention that in the method according to the invention and the associated filter systems, the strength of the cleaning performance can be adapted relatively easily to the respective existing application requirements by merely having to adapt the operating parameters during the cleaning phases in order to modify the load experienced by the microorganisms, for example by a change in the field strength and / or a change in the pulse pattern.The above objects are achieved, accordingly, by the subject matter of the invention as defined in the claims. Preferred embodiments according to the invention are evident from the dependent claims and the following explanations.Such embodiments, which are referred to below as preferred, are combined in particularly preferred embodiments with features of other embodiments referred to as preferred. Combinations of two or more of the embodiments referred to below as particularly preferred are thus very particularly preferred. Also preferred are embodiments in which a feature of one embodiment designated as preferred to any extent is combined with one or more further features of other embodiments designated as preferred to any extent. Features of preferred filter systems and uses result from the features of preferred filter systems.The invention relates in particular to methods for operating a filter, wherein the filter comprises:i) a first polarization element,ii) a second polarization element,iii) a polarizable filter medium arranged between the first polarization element and the second polarization element, andiv) an electrical contacting system, wherein the electrical contacting system is configured such that a voltage provided by a voltage source can be applied between the first polarization element and the second polarization element,wherein the method comprises operating the filter in at least two distinct modes of operation, wherein the filter is operated in a polarization mode for 80% or more of the operating time, wherein in the polarization mode a continuous DC voltage is applied between the first polarization element and the second polarization element that varies by 20% or less based on the average of the DC voltage in the polarization mode, wherein the filter is operated partially in a DC cleaning mode, wherein in the DC cleaning mode a pulsed DC voltage is applied between the first polarization element and the second polarization element with a plurality of pulses, wherein the average electric field strength of the electric field during the pulses is 0.5 kV / cm or more, and / or wherein the filter is operated partially in an AC cleaning mode, wherein, in the AC cleaning mode, a pulsed alternating voltage is applied between the first polarization element and the second polarization element with a plurality of pulses, wherein the peaks of the magnitude function of the electric field strength during the pulses are at least partially at 0.5 kV / cm or more.The method according to the invention is a method for operating a filter, which, however, can naturally also be regarded as a method for filtering a fluid to be filtered, in particular air, and which, according to the inventors' judgment, is particularly advantageous in particular for use in the field of vehicle technology. A method according to the invention is accordingly preferred, wherein the filter is an air filter, preferably an interior air filter, particularly preferably an interior air filter for vehicles, in particular for land vehicles.The method according to the invention serves to kill microorganisms present in the filter medium, in particular bacteria, by a suitable procedure. Within the scope of the present invention, this is sometimes referred to as cleaning for the purpose of better understanding. In accordance with the skilled artisan, this cleaning, which may be, for example, at least partial sterilization, does not require the removal of particles or killed microorganisms from the filter medium.In order to be able to be operated with the process according to the invention, the filter used must comprise at least four basic components. In order to both enable the desired polarization of the polarizable filter medium and achieve the cleaning effect desired for the method according to the invention, it is necessary for two elements to be present between which an electric field can be built up. These elements are referred to as first and second polarization elements in the context of the present invention with regard to the main functionality, the voltage being applied via the electrical contact-making system.It can be seen first as an advantage of the method according to the invention that the polarization elements can in principle be designed relatively freely by the skilled person, provided they are designed such that the electric field strengths required in the method according to the invention can be realized. In particularly simple constructions, the polarization elements can be designed, for example, as planar elements between which the filter medium is arranged, which is particularly appropriate for those configurations in which only the filter medium is to be replaced more frequently and in which the polarization elements are provided for recycling, for example because these are designed as a component of a module designed on the vehicle side. In this case, it is a method according to the invention, wherein the first polarization element and / or the second polarization element, preferably the first polarization element and / or the second polarization element, are elements separate from the filter medium. By way of example, additionally or alternatively, a method according to the invention is provided, wherein the first polarization element and / or the second polarization element, preferably the first polarization element and / or the second polarization element, comprise an electrically conductive grid or an electrically conductive plate, wherein the electrically conductive grid and the electrically conductive plate are preferably coated with a metal or consist of a metal. By way of example, additionally or alternatively, a method according to the invention is provided, wherein the first polarization element and the second polarization element have an average distance from one another in the range from 0.03 to 30 cm, preferably in the range from 0.05 to 10 cm, particularly preferably in the range from 0.08 to 0.6 cm.The electrical contacting system to be provided according to the invention can be designed by the person skilled in the art according to the respective application requirements and the design requirements of the filter system, in particular of the vehicle filter module. Regardless of the specific configuration of the electrical contacting system, it will usually comprise a first contacting element and a second contacting element, which are each provided to produce an electrically conductive contacting with the first polarization element or with the second polarization element, respectively. For substantially all embodiments, a method according to the invention is preferred, wherein the electrical contacting system comprises a first contact point and a second contact point for contacting the voltage source. A method according to the invention is preferred, wherein the voltage source is a high-voltage source, preferably a high-voltage source of a vehicle. By way of example, a method according to the invention is thus provided, wherein the maximum applied voltage during operation is 0.3 kV or more, preferably 0.5 kV or more.The polarisable filter medium to be provided according to the invention serves in particular for mechanical filtration, i.e. for the mechanical separation of particles from the fluid to be filtered, which particles are conveyed during operation of the filter during the filtration of a fluid by the filter medium being polarised as a result of the applied electric field. The corresponding polarizability of the filter medium is obtained in accordance with the expert's understanding by the presence of a dielectric layer. In other words, it is a method according to the invention, wherein the filter medium comprises at least one dielectric layer.Particularly advantageous configurations of these electrostatic separators with filter functionality can be obtained if the polarization elements are at least partially, preferably completely, integrated into the filter medium installed in the filter insert. For this purpose, individual layers of a filter medium that is multilayer in this case can be designed as electrically conductive layers. Such an electrically conductive conductor layer of the filter medium can, for example, together with a second polarization element arranged on the vehicle side or together with a second electrically conductive conductor layer, cause the polarization of a dielectric filter material. Due to the at least partial integration of the polarization elements into the filter medium and thus preferably an exchangeable filter insert, efficient filters are obtained which in particular have an advantageous weight and make it possible to reduce or even completely eliminate the requirements imposed on the devices required on the vehicle side if no vehicle-side polarization elements have to be provided in order to realize the polarization of the dielectric layer. In addition, a corresponding configuration as a multilayer filter medium in many cases leads to an advantageous polarization effect on the particle filter layer arranged directly between the conductor layers. In addition, it is hereby possible, without high additional costs and the need for installation space, to integrate all the parts necessary for the polarization effect into a filter insert, which can be designed particularly easily as an exchangeable filter insert. A method according to the invention is particularly preferred accordingly, wherein the elements connected to the filter medium, preferably connected in a materially bonded manner, preferably the first polarization element and / or the second polarization element.In addition or alternatively, a method according to the invention is preferred, wherein the first polarization element and / or the second polarization element, preferably the first polarization element and / or the second polarization element, form a multilayer filter medium with the filter medium. Particularly preferred is a method according to the invention, wherein the filter comprises a multi-layer filter medium, wherein the multi-layer filter medium comprises:I) an electrically conductive first conductor layer as first polarization element, andIII) an intermediate layer connected to the first conductor layer as a filter medium, wherein the intermediate layer comprises at least one dielectric layerParticularly preferred is a method according to the invention, wherein the filter comprises a multi-layer filter medium, wherein the multi-layer filter medium comprises:I) an electrically conductive first conductor layer as first polarization element,II) an electrically conductive second conductor layer as second polarization element, andIII) an intermediate layer as filter medium, arranged between the first conductor layer and the second conductor layer, wherein the intermediate layer comprises at least one dielectric layer.In addition or alternatively, a method according to the invention is preferred, wherein the first conductor layer and the second conductor layer have an average distance from one another in the range from 0.03 to 30 cm, preferably in the range from 0.05 to 10 cm, particularly preferably in the range from 0.08 to 0.6 cm, and / or wherein the multilayer filter medium at 1 kPa has an average thickness in the range from 0.04 to 35 cm, preferably in the range from 0.06 to 12 cm, particularly preferably in the range from 0.09 to 0.7 cm.In particular when using a multilayer filter medium which comprises at least one conductor layer as polarization element, it is preferred, with a view to as simple maintenance and repair as possible of the filters to be used in the method according to the invention, to form parts of the filter in the form of a filter insert as reversibly and non-destructively replaceable units, wherein, according to the inventors's judgment, in addition to the filter medium, in particular also at least one polarization element and the corresponding contacting should be designed to be replaceable. A method according to the invention is preferred accordingly, wherein the filter comprises at least one polarization element, preferably the first polarization element and the second polarization element, the polarizable filter medium and the electrical contacting system as a filter insert arranged in the filter in a reversibly and non-destructively replaceable manner.Preferred embodiments of the multilayer filter medium in which one or two electrically conductive conductor layers are used, and a particularly preferred electrical contacting system for contacting the conductor layers, are further disclosed below. Regardless of whether a multilayer filter medium or only a polarizable filter layer is used, these can be produced in an advantageous manner using customary methods, wherein in particular a pleated arrangement is useful for increasing the available filter surface and a laminated arrangement is useful, in particular if the filter is designed with an exchangeable filter insert. A method according to the invention is accordingly preferred, wherein the filter comprises the filter medium, preferably the multilayer filter medium, as pleated filter medium. A method according to the invention is particularly preferred, wherein at least one of the sides of the pleated filter medium, preferably of the multilayer filter medium, preferably at least two sides, particularly preferably at least the longitudinal sides, very particularly preferably all sides, are laminated with a laminating material, wherein the laminating material is preferably selected from the group consisting of textile planar structures, in particular nonwovens and felts. A method according to the invention is very particularly preferred, wherein the electrical contacting system is connected to the lamination of the pleated filter medium, preferably in a materially bonded manner.According to the inventors' judgment, the method according to the invention is already advantageous for the purpose of achieving an advantageous effect in a filter which comprises only the components described above. Due to the polarization provided according to the invention, the separation performance of the filter medium is improved even in the absence of dedicated ionization devices. In addition, advantageous cleaning of the filter medium is also possible in the absence of an ionization device. However, the skilled person understands that particularly great advantages result synergistically if the filter is an electrostatic separator with filter functionality, for which purpose advantageously an ionization device is provided which can ionize dirt particles present in the fluid to be filtered, so that these can be separated in a particularly efficient manner in the polarized filter medium. In accordance with the expert's understanding, this ionization device interacts with the filter medium polarized between the first and second polarization elements, which can function in particular as a precipitation electrode. A method according to the invention is accordingly preferred, wherein the filter additionally comprises:v) an ionization device for ionizing constituents of the fluid to be filtered.Suitable ionization devices are known to the person skilled in the art and are disclosed, for example, in WO 2023 / 012166 A1. Relevant for essentially all embodiments are electrical ionization devices which are also known from other fields of technology and can bring about ionization in particular by corona discharge. From the standpoint of safety engineering and with regard to their handling and performance, such electric ionization devices are far superior to other methods of ionization, in particular using ionizing radiation. A method according to the invention is therefore preferred, wherein the ionization device is an electric ionization device, wherein the ionization device is preferably configured to cause the ionization of components of the fluid to be filtered at least partially, preferably substantially completely, by means of corona discharge. In addition or alternatively, a method according to the invention is preferred, wherein the ionization device does not comprise a radiation source for ionizing radiation. The skilled person understands that the sought interaction between the ionization device and the filter medium requires that the filter with the filter medium functioning as a precipitation electrode should be placed in a later use, in a meaningful manner, downstream of the ionization device in the flow direction.The method according to the invention is based on the fact that the filter, which is designed as described above with regard to its basic design, is operated in at least two different operating modes, which are referred to as polarization mode on the one hand and as DC or AC cleaning mode on the other hand within the scope of the present invention. These various modes of operation are further disclosed below. In principle, it is conceivable that the filter is moreover operated in further modes which differ from the aforementioned operating modes with regard to the configuration of the electric field, wherein, however, it is preferred in accordance with the expert's understanding if the filter is operated as extensively as possible in the operating modes to be provided according to the invention. a method according to the invention is accordingly conceivable, wherein the filter is partially operated in one or more further operating modes. However, a method according to the invention is additionally or alternatively preferred, wherein the filter is operated for 98% or more, preferably for 99% or more, particularly preferably for 99.5% or more, very particularly preferably for substantially 100%, of the operating time in the polarization mode or in the DC cleaning mode or in the AC cleaning mode, preferably in the polarization mode or in the DC cleaning mode.The first central operating mode is referred to as polarization mode in the context of the present invention. In the polarization mode, a constant as possible DC voltage is applied as the polarization elements to form a rectified electric field, in that the polarizable filter medium can be polarized to promote its separation effect, in particular in an electrostatic separator with filter functionality. In other words, it is a method according to the invention, wherein the filter is configured to cause or to transport the separation of electrically charged particles, in particular of ionized particles, particularly preferably particles ionized by the ionization device, in the polarization mode as a result of a polarization of the multilayer filter medium.Particularly when used in combination with an ionization device, the polarization mode will be the operating mode according to the inventors' judgment in that the filter is operated for the very vast majority of times, while the cleaning modes described further below are used only for short times, which are sufficient to achieve the desired cleaning performance in order to impair the otherwise desired polarization of the filter medium as little as possible. Preference is accordingly given to a process according to the invention, wherein the filter is operated in the polarization mode for 90% or more, preferably 95% or more, particularly preferably 99% or more, very particularly preferably 99.5% or more, of the operating time. Preference is given additionally or alternatively to a process according to the invention, wherein the filter is operated for 10% or less, preferably for 5% or less, particularly preferably for 2% or less, very particularly preferably for 1% or less, particularly preferably for 0.5% or less, of the operating time in the DC cleaning mode or in the AC cleaning mode.As explained above, it is preferred, after the inventors have been evaluated for operation as stable as possible, to vary the DC voltage used for polarization as little as possible. In addition, the inventors have succeeded in identifying electric field strengths with which particularly advantageous polarization effects and, as a result, particularly favorable deposition powers can be realized. Preference is accordingly given to a method according to the invention wherein, in the polarization mode, a DC voltage is applied which varies by 10% or less, preferably 5% or less, particularly preferably 1% or less, particularly preferably substantially not at all, based on the average value of the DC voltage in the polarization mode. In addition or alternatively, a method according to the invention is preferred, wherein the average electric field strength of the electric field in the polarization mode is 0.5 kV / cm or more, preferably 1 kV / cm or more, particularly preferably 2 kV / cm or more, and / or wherein the average electric field strength of the electric field in the polarization mode is in the range from 0.5 kV / cm to 30 kV / cm, preferably in the range from 1 kV / cm to 15 kV / cm, particularly preferably in the range from 2 kV / cm to 10 kV / cm.In addition to the polarization mode, the filter is operated in one of two cleaning modes. These cleaning modes are based on the same concept, but differ in respect of whether a DC voltage or an AC voltage is applied for their conversion. For easier differentiation, the corresponding cleaning modes would be designated as DC and AC cleaning modes, respectively, within the scope of the present invention.In both cleaning modes, a pulsed electric field is generated by pulsed energization of the polarization elements. Microorganisms present in the polarizable filter media are exposed to this pulsed electric field. In the course of this procedure, also referred to as electroporation, the cell membranes of the microorganisms become temporarily permeable, so that molecular transport through the cell membranes becomes possible. By creating the temporary permeability, constituents essential for the microorganisms can migrate out of the interior to the outside as a result of hydrostatic pressure differences and osmotic effects. If the electric field strength is above the critical electric field strength, this process is at least partially irreversible, which leads to death of the microorganisms. Those skilled in the art understand that the pulsed DC voltage generates a pulsed electric field in the DC cleaning mode and the AC cleaning mode. In other words, it is a method according to the invention, wherein the filter is operated in the DC cleaning mode in such a way that microorganisms located in the filter medium, in particular bacteria, are damaged, preferably irreversibly damaged, by the pulsed electric field, in particular in their cell membrane, or a method according to the invention, wherein the filter is operated in the AC cleaning mode in such a way that microorganisms located in the filter medium, in particular bacteria, are damaged, preferably irreversibly damaged, in particular in their cell membrane, by the pulsed electric field.The concept of electroporation and the use of pulsed electric fields for killing microorganisms is known from the food industry and is widely used in the food industry to kill harmful microorganisms during the processing of foods. The electric field strengths required for killing depend on the type of microorganisms and on the applied pulse pattern and can be matched by the person skilled in the art to the type of microorganisms to be killed, wherein it is conceivable to provide different cleaning modes for the operation of the filters in the method according to the invention, which cleaning modes are matched to different microorganisms with regard to the field strength and / or pulse sequence. In an advantageous manner, the skilled person can, in the implementation of the present invention, rely on the comprehensive preliminary work from the field of the food industry, from which a large number of processes and associated process parameters for killing a wide range of different microorganisms is known and established. Further information on the basic technological background of electroporation, the underlying physicochemical relationships and the general use in the food industry is disclosed, for example, in the "handbook of electroporation", Damijan Miklavcic, ISBN 9783319328850, 2017 or the publication "DLG-Expert Science 5 / 2018-Application of Pulsed Electric Fields (PEF) in the food industry".The DC cleaning mode and the AC cleaning mode differ in particular in how the nature of the electric field during the pulse can be described. From the DC voltage used in the DC cleaning mode it follows that the pulses can be described expediently via the mean electric field strength. A method according to the invention is preferred, wherein in the DC cleaning mode the average electric field strength of the electric field during the pulses is 0.75 kV / cm or more, preferably 1 kV / cm or more, most preferably 2.5 kV / cm or more, and / or wherein in the DC cleaning mode the average electric field strength of the electric field during the pulses is in the range of 0.5 kV / cm to 40 kV / cm, preferably in the range of 1 kV / cm to 25 kV / cm, particularly preferably in the range of 2 kV / cm to 10 kV / cm.In contrast to the DC voltage, an alternating field is obtained during the pulses in the AC cleaning mode. To this extent, the inventors believe that it is expedient to characterize the pulses via the electric field strength which is present at the extreme points, wherein the amount can be expediently used. A method according to the invention is preferred, wherein in the AC cleaning mode the peaks of the magnitude function of the electric field strength during the pulses are at least partially, preferably predominantly, particularly preferably all, 0.75 kV / cm or more, preferably 1 kV / cm or more, very particularly preferably 2.5 kV / cm or more, and / or wherein in the AC cleaning mode the peaks of the magnitude function of the electric field strength during the pulses are at least partially, preferably predominantly, particularly preferably all, in the range from 0.5 kV / cm to 40 kV / cm, preferably in the range from 1 kV / cm to 25 kV / cm, particularly preferably in the range from 2 kV / cm to 10 kV / cm.The inventors have identified it advisable if the voltage selected for the cleaning modes is oriented at the value also used for polarization, although higher voltages can also be used for particularly pronounced cleaning effects in the cleaning modes. Preference is given to a method according to the invention, wherein the maximum applied DC voltage in the polarization mode differs from the maximum applied DC voltage in the DC cleaning mode by 50% or less, preferably 25% or less, particularly preferably 10% or less, very particularly preferably 5% or less, in particular preferably 2% or less, very particularly preferably substantially not at all, and / or wherein the maximum applied DC voltage in the polarization mode differs from the maximum amount of the applied AC voltage in the AC cleaning mode by 50% or less, preferably 25% or less, particularly preferably 10% or less, very particularly preferably 5% or less, in particular preferably by 2% or less, very particularly preferably substantially not at all.The inventors have found that, in the implementation of the present invention, the skilled worker can advantageously orient himself to the process guides known from the food industry with respect to the pulse pattern to be used.Preference is given to a method according to the invention, wherein the pulse sequence of the DC cleaning mode or of the AC cleaning mode comprises 5 or more, preferably 10 or more, particularly preferably 20 or more, very particularly preferably 40 or more, pulses. In addition or alternatively, a method according to the invention is preferred, wherein the pulses in the cleaning mode have at least partially, preferably predominantly, particularly preferably essentially all, a length in the range from 40 to 40000 ns, preferably in the range from 100 to 10000 ns, particularly preferably in the range from 300 to 6000, very particularly preferably in the range from 400 to 5000 ns, in particular preferably in the range from 500 to 4000 ns, based on the full width at half maximum of the pulses or the full width at half maximum of the envelope. In addition or alternatively, a method according to the invention is also preferred, wherein the pulses in the DC cleaning mode are at least partially, preferably predominantly, particularly preferably essentially all, rectangular pulses, triangular pulses or sinusoidal pulses, preferably rectangular pulses. In addition or alternatively, a method according to the invention is also preferred, wherein the alternating voltage during the pulses in the AC cleaning mode has a constant frequency, preferably a constant frequency and amplitude.Even if the desired cleaning effect can also be achieved using alternating voltage, it is particularly preferred, according to the inventors' judgment for essentially all embodiments, to set largely to direct voltage in the method according to the invention and to accordingly dispense with the AC cleaning mode as largely as possible, preferably essentially completely. The fact that the desired polarization in each case requires a DC voltage means that the devices used can be made much simpler and more robust, unless the possibilities for generating an alternating field need additionally be provided. A method according to the invention is particularly preferred accordingly, wherein the filter is partly operated in the DC cleaning mode. A method according to the invention is also preferred accordingly, wherein the voltage source is a DC voltage source.Even if it would be conceivable at least theoretically, during alternation between the polarization mode and the DC purification mode, not to set the DC voltage between the pulses entirely to zero, this is less preferred both with regard to the achievable purification effect and the complexity of the control. A method according to the invention is accordingly preferred, wherein the DC voltage in the DC cleaning mode drops between two adjacent pulses at least partially, preferably predominantly, particularly preferably substantially completely, to 10% or less, preferably 5% or less, particularly preferably 1% or less, very particularly preferably to 0.5% or less, of the average DC voltage value of the pulses, wherein the DC voltage in the DC cleaning mode drops at least partially, preferably predominantly, particularly preferably substantially completely, substantially to 0 V, in particular preferably between two adjacent pulses.In accordance with the expert's understanding, the method according to the invention will switch between the operating modes. A particularly simple embodiment for the design of the changeover is to change over between the operating modes at regular intervals, this being matched in preferred embodiments to the operating time of the filter. In this respect, a method according to the invention is preferred, wherein the operation of the filter is changed over at regular time intervals, in particular operating time intervals, for example after 8 h or more, 12 h or more, 24 h or more, 48 h or more or 168 h or more.For particularly advantageous embodiments, however, the inventors propose that the cleaning modes can be used in a need-optimized manner, wherein the need is established on the basis of a predefined criterion, wherein a plurality of criteria are also conceivable, which may be fulfilled alternatively or cumulatively. In addition to a time-based criterion, the cleaning mode can be matched in particular to specific situations, for example the starting or stopping of the filter system, wherein, in particular when used in a vehicle, refueling or charging processes can also be suitable phases for cleaning the filter. In addition, manual request processes are also possible, which can be triggered, for example, via a vehicle computer. A method according to the invention is therefore preferred, wherein the operation of the filter is switched to the DC cleaning mode or AC cleaning mode after a predefined criterion has been reached. A method according to the invention is particularly preferred, wherein the predefined criterion is selected from the group consisting of the expiration of a predefined time period, in particular expiration of a predefined operating time period, the starting of the vehicle engine, the stopping of the vehicle engine, the starting of the filter system, the stopping of the filter system, the registering of a refueling process, the registering of a charging process, the registering of a sensor value with a sensor unit and manual user requests. An example is a method according to the invention, wherein the predefined time period is 60 min or more, preferably 360 min or more, very particularly preferably 480 min or more.The inventors considered particularly preferred if the control of the cleaning modes is carried out with sensor assistance. In this case, a wide range of sensors and the sensor values obtained therewith can be used to identify suitable points in time for carrying out a cleaning step, wherein, in particular, the multiplication conditions for microorganisms can be deduced from the determination of the temperature and the air humidity or the detection of precipitation, in order thereby to control the frequency of the cleaning processes. In addition, it is also possible to use a position sensor, for example a GPS sensor, as a sensor in order to infer the climatic conditions and / or the general load of the fluid to be filtered with microorganisms from the position of the filter or of the vehicle, for example by matching with suitable map material, and to control the cleaning activity in a subsequent manner. A method according to the invention is particularly preferred accordingly, wherein the filter comprises one or more sensor units for detecting the one or more sensor values. A method according to the invention is preferred, wherein the operation of the filter is switched to the AC cleaning mode or DC cleaning mode depending on one or more sensor values, preferably if the one or more sensor values meet a predefined criterion. In addition or alternatively, a method according to the invention is preferred, wherein the proportion of the AC cleaning mode or DC cleaning mode in the operating time of the filter is controlled as a function of one or more sensor values, preferably if the one or more sensor values meet a predefined criterion. In this respect, a method according to the invention is particularly preferred, wherein the pulse sequence and / or the magnitude of the applied voltage in the AC cleaning mode or DC cleaning mode is changed depending on one or more sensor values, preferably if the one or more sensor values meet a predefined criterion. Particularly preferred is additionally or alternatively a method according to the invention, wherein the one or more sensor values are selected from the group consisting of temperature, air humidity, precipitation data and position data, preferably selected from the group consisting of temperature and air humidity.In the embodiments described above, it is preferably a method according to the invention, wherein the filter comprises one or more sensor units for detecting the one or more sensor values. A method according to the invention is preferred, wherein the sensor units are selected from the group consisting of temperature sensors, air humidity sensors, precipitation sensors and GPS sensors, preferably selected from the group consisting of temperature sensors and air humidity sensors.In principle, the inventors propose that, with regard to the main effect of advantageous particle separation that is sought in electrostatic precipitators with filter functionality, it is expedient to provide sufficiently long polarization phases between individual cleaning phases, and conversely, according to the inventors' judgment, it is expedient to configure the cleaning phases sufficiently long in order to achieve a good cleaning effect in the cleaning phases. In this respect, a method according to the invention is preferred, wherein the filter is operated in the polarization mode between two operating times in the AC cleaning mode or DC cleaning mode for 1 min or more, preferably for 30 min or more, particularly preferably for 60 min or more. In addition or alternatively, a method according to the invention is preferred, wherein the filter is operated between two operating times in the polarization mode for a time in the range from 5 μs to 60 s, preferably in the range from 10 μs to 10 s, particularly preferably in the range from 100 μs to 5 s, in the AC cleaning mode or DC cleaning mode.The inventors propose that, in order to avoid adverse effects on the surrounding electronics, in particular when used in the vehicle, it is particularly advantageous to provide electromagnetic shielding of the filter. A method according to the invention is accordingly preferred, wherein the filter comprises one or more shielding elements for electromagnetically shielding the filter.It can be seen as a great advantage of the present invention that it enables reliable killing of microorganisms without relying on the use of biocides for this purpose. To this extent, the inventors propose that it is particularly expedient to utilize this advantage also by omitting the use of such biocides in the filter or filter medium. A method according to the invention is accordingly preferred, wherein the filter does not comprise any antimicrobial additives and / or antimicrobial layers.The inventors have succeeded in identifying preferred configurations for the multilayer filter medium preferably to be used and for the individual layers thereof, in particular the conductor layers, wherein advantageous cleaning performance results when using pulsed electric fields, in particular with the particle filter layers disclosed below.A method according to the invention is preferred first, wherein the first conductor layer comprises a first textile fabric, preferably a first textile fabric coated or impregnated at least in sections with an electrically conductive first material, and / or wherein the second conductor layer comprises a second textile fabric, preferably second textile fabric coated or impregnated at least in sections with an electrically conductive second material.The term "textile fabric" is clear to the skilled person and denotes two-dimensional textile products which can be woven, knitted, needled or knitted, for example. In accordance with the expert's understanding, non-textile fibrous fabrics, for example paper and cardboard, in which the fibers are held together, for example, primarily by binding agents, do not belong to the textile fabrics. Even if a wide range of textile fabrics were in principle possible for the textile fabrics of the conductor layers, the inventors have been able to achieve the best performance characteristics, in particular with so-called "nonwovens" and in this case in particular with spunbonded nonwovens. A corresponding textile fabric made of a non-conductive material can be advantageously achieved by equipping the textile fabric with a conductive material, wherein, according to the inventors' judgment, in principle a multiplicity of possible methods are suitable. A method according to the invention is thus preferred, wherein the first textile fabric and / or the second textile fabric, preferably the first textile fabric and the second textile fabric, are a nonwoven, preferably a spunbonded nonwoven.The distinction between an electrically conductive material as distinct from an electrically insulating material is without any constraint for those skilled in the art and based on their skilled and clear technical understanding of these terms. In this respect, a material in the context of the present invention is particularly considered to be an electrically conductive material when its specific electrical resistance at 20° C. is 10 6 Ω*m or less, preferably 10 5 Ω*m or less, particularly preferably 10 4 Ω*m or less. Conversely, a material in the context of the present invention is particularly applicable as an electrically insulating material when its specific electrical resistance at 20° C. is 10 7 Ω*m or more, preferably 10 9 Ω*m or more, particularly preferably 10 11 Ω*m or more. Accordingly, metals and alloys, however, are also carbon blacks, such as, in particular, conductive carbon black, and plastics made conductive by additives, are electrically conductive materials, whereas typical unmodified plastics such as PET or PE likewise belong to the electrically insulating materials, such as, for example, most glasses and ceramics. The electrical resistivity of materials is a value well known to the skilled person, which can be found in reference tables relevant for most materials. The measurement of the specific electrical resistance in other components takes place in accordance with the usual practice either according to DIN EN ISO 3915 from 1999, which is used in particular for particularly conductive materials, or according to IEC 60093 from 1993, which is used in the case of high specific electrical resistances. The question as to which of the two standards is to be used is directed to the specifications of the two regulations and the properties of the respective material investigated.The skilled person understands that the electrical conductivity of conductor layers, for example of the first conductor layer, can in many cases, for example when using composite materials, result from the presence of conductive material paths which run in an otherwise largely insulating material. Thus, for example, a dielectric fleece whose fibers are provided with a thin layer of conductive carbon black can be an electrically conductive layer, although the macroscopic specific resistance of the composite material is relatively high as a result of the dielectric carrier material.Furthermore, a method according to the invention is additionally or alternatively preferred, wherein the first textile fabric and / or the second textile fabric, preferably the first textile fabric and the second textile fabric, consist of a plastic, based on the mass of the textile fabric, to a mass fraction of 80% or more, preferably 90% or more, particularly preferably 95% or more, very particularly preferably substantially 100%, wherein the plastic is preferably selected from the group consisting of polyacrylonitriles, polyolefins, polyesters and mixtures of these plastics, particularly preferably polyacrylonitriles, polypropylene, polyethylene terephthalate and mixtures of these plastics, particularly preferably polyethylene terephthalate.In addition or alternatively, a method according to the invention is also preferred, wherein the first conductor layer and / or the second conductor layer, preferably the first conductor layer and the second conductor layer, are produced or can be produced by finishing the respective textile planar structure, in particular the nonwoven, with the respective electrically conductive material by a method selected from the group consisting of impregnation, dip coating, in particular with a pad system, spray coating, application coating, in particular by means of a dispersion in the kiss-coat method, and pressure coating.Additionally or alternatively, a method according to the invention is preferred, wherein the electrically conductive first material and / or the electrically conductive second material, preferably the electrically conductive first material and the electrically conductive second material, are selected from the group consisting of metals, conductive plastics and carbon, preferably carbon, in particular carbon black or graphene, wherein the electrically conductive material is particularly preferably identical for the first conductor layer and the second conductor layer.Additionally or alternatively, a method according to the invention is preferred, wherein the first conductor layer and / or the second conductor layer, preferably the first conductor layer and the second conductor layer, are electrically conductive as a result of the coating of the respective textile planar structure at least over 80% or more of the area, preferably over 90% or more, particularly preferably over 95% or more, very particularly preferably over 98% or more, in particular preferably substantially over the full surface.Even if the conductor layers can contribute to the filtration performance of the filter media, in particular if they are designed as textile fabrics, the inventors find it advantageous if the conductor layers are designed with sufficient open pores, so that they primarily restrict the passage of air through the filter medium as little as possible. With regard to the weight of the conductor layers, at least when textile fabrics are used, there is in this respect a conflict of goals between the influence on the total weight of the filter medium and an advantageous stabilizing effect of the conductor layers on the filter medium and thus an improvement in the mechanical properties. In this respect, the inventors have succeeded in identifying suitable weights per unit area for the textile fabrics, with which this conflict of goals can be solved in an advantageous manner. Against this background, a method according to the invention is preferred, wherein the first conductor layer and / or the second conductor layer, preferably the first conductor layer and the second conductor layer, have an air passage at 200 Pa in the range from 500 to 30000 L / (m 2 s), preferably in the range from 2000 to 20000 L / (m 2 s). Additionally or alternatively, a method according to the invention is also preferred, wherein the first textile fabric and / or the second textile fabric, preferably the first textile fabric and the second textile fabric, have a basis weight in the range from 5 to 200 g / m 2, preferably in the range from 10 to 150 g / m 2, particularly preferably in the range from 15 to 50 g / m 2.With regard to the general structure of the multilayer filter medium, a method according to the invention is preferred, wherein the filter layer comprises one or more further layers, preferably further layers arranged between the first conductor layer and the second conductor layer, wherein the filter layer preferably comprises two or more dielectric layers, particularly preferably three or more dielectric layers.In addition or alternatively, a method according to the invention is also preferred, wherein at least one of the dielectric layers, preferably all of the dielectric layers, consists of a dielectric plastic material to a mass fraction of 80% or more, preferably 90% or more, particularly preferably 95% or more, very particularly preferably substantially 100%, based on the mass of the dielectric layer. Particularly preferred is a method according to the invention, wherein the dielectric plastic material is selected from the group consisting of polyolefins, in particular polytetrafluoroethylene, polytetrafluoroethylenepropylene, polypropylene, and polyethylene, polyesters, in particular polyethylene terephthalate, polycarbonates, polyamides, polyvinylidene fluoride, polyacrylonitrile, and polylactides. Particularly preferred is additionally or alternatively a method according to the invention, wherein the dielectric plastic material has a specific electrical resistance at 20° C. of 10 7 Ω*m or more, preferably at 10 9 Ω*m or more, particularly preferably at 10 11 Ω*m or more.A method according to the invention is preferred for the predominant number of embodiments, wherein at least one of the dielectric layers is a particle filter layer which comprises a third textile planar structure. Particularly preferred is a method according to the invention, wherein the third textile fabric is a nonwoven fabric, wherein the third textile fabric is preferably selected from the group consisting of needle-punched nonwovens and meltblown nonwovens. Particularly preferred additionally or alternatively is a method according to the invention, wherein the particle filter layer has a weight per unit area in the range from 10 to 200 g / m 2, preferably in the range from 15 to 150 g / m 2, particularly preferably in the range from 20 to 110 g / m 2.A method according to the invention is preferred for multilayer filter media containing activated carbon in particular, wherein at least one of the dielectric layers is a protective layer which comprises a fourth textile planar structure. a multilayer filter medium according to the invention is particularly preferred here, wherein the fourth textile planar structure is a nonwoven fabric, preferably a spunbonded nonwoven fabric.In addition or alternatively, a method according to the invention is preferred, wherein the protective layer has an air passage at 200 Pa in the range from 500 to 30000 L / (m 2 s), preferably in the range from 2000 to 20000 L / (m 2 s). Additionally or alternatively, a method according to the invention is also preferred, wherein the protective layer has a weight per unit area in the range from 15 to 400 g / m 2, preferably in the range from 50 to 200 g / m 2. Particularly preferred is additionally or alternatively also a method according to the invention, wherein the protective layer has a Cucumbery flexural rigidity, determined according to ASTM D6125-97, in the range from 0.4 to 40 mN, preferably in the range from 0.5 to 20 mN, particularly preferably in the range from 0.6 to 10 mN.For the predominant number of embodiments, according to the inventors' judgment, a method according to the invention is also additionally or alternatively preferred, wherein the filter layer comprises an activated carbon layer, wherein the activated carbon layer comprises activated carbon in a mass fraction of 70% or more, based on the mass of the activated carbon layer.Activated carbon is known as an important material to the skilled person in the field of filtration technology and is commercially available from numerous manufacturers. It is preferred that the activated carbon layer is formed from activated carbon to a high mass fraction, so that, for example, the fraction of fibers or other carrier materials in the activated carbon layer should be kept as low as possible. As a result, starting from the experiments of the inventors, a particularly good separation effect or cleaning performance is achieved with a simultaneous minimization of the thickness or the weight. The inventors have found that particularly efficient filter inserts can be obtained with activated carbon layers which are as pure as possible and which preferably consist essentially exclusively of activated carbon apart from the binder. A method according to the invention is accordingly preferred, wherein the activated carbon layer comprises activated carbon in a mass proportion of 80% or more, preferably 90% or more, particularly preferably 95% or more, based on the mass of the activated carbon layer. In addition or alternatively, a method according to the invention is preferred, wherein the activated carbon is fixed in the activated carbon layer by a binder. The inventors have thus succeeded in identifying, for the selection of activated carbon and for the dimensioning of the activated carbon layer, particularly preferred regions with which excellent filter performance has been obtained in separate experiments. A method according to the invention is namely preferred, wherein the activated carbon is particulate activated carbon, wherein the activated carbon preferably has an average diameter d50in the range from 0.1 to 4 mm, preferably in the range from 0.2 to 2 mm. Additionally or alternatively, a process according to the invention is also preferred, wherein the activated carbon has a specific surface area of 500 m 2 / g or more, preferably of 1000 m 2 / g or more, particularly preferably of 2000 m 2 / g or more. Preference is in turn additionally or alternatively given to a method according to the invention, wherein the activated carbon layer has a weight per unit area in the range from 50 to 1000 g / m 2, preferably in the range from 100 to 600 g / m 2.The inventors have developed a particularly preferred electrical contact system for the preferred use of a multilayer filter medium which has at least one conductor layer integrated. Even though very simple embodiments of the electrical contacting system are theoretically also conceivable for contacting these multilayer filter media which are preferably to be used, which embodiments rely on the use of cables, for example, the inventors have designed a particularly advantageous electrical contacting system with a view to a time- and cost-effective production, which electrical contacting system can be combined particularly efficiently with the conductor layer or layers, in particular by adhesive bonding by means of an electrically conductive plastic material. According to the inventors' judgment, it is especially advantageous if classical electrical wiring is not used or if it is used only to a small extent, but rather the contacting system is designed as largely as possible from components which consist of an electrically conductive plastic. A method according to the invention is accordingly preferred, wherein the electrically conductive components of the electrical contacting system are formed at least partially, preferably predominantly, particularly preferably substantially completely, by an electrically conductive plastic. Particularly preferred is a method according to the invention, wherein the electrically conductive plastic of the electrical contacting system has a specific electrical resistance at 20° C. of 10 6 Ω*m or less, preferably 10 5 Ω*m or less, particularly preferably 10 4 Ω*m or less.According to the inventors' judgment, these electrically conductive components, which preferably consist of an electrically conductive plastic, should be arranged on a preferably thin substrate, which acts as a carrier and advantageously makes it possible to assemble the electrically conductive components of the electrical contacting system before attachment to the filter to be used according to the invention and to apply them during the production process in only a single step, for example to the lateral lamination of the filter. Accordingly, a method according to the invention is preferred, wherein the electrically conductive components of the electrical contacting system are conductive components arranged on a substrate and / or in a substrate. In addition or alternatively, a method according to the invention is preferred, wherein the substrate is selected from the group consisting of electrically insulating films, preferably plastic films, wherein the average thickness of the substrate is preferably in the range from 20 to 500 μm, particularly preferably in the range from 80 to 150 μm.The use of a thin substrate, in particular a film, in combination with conductive components formed from plastic advantageously allows the electrical contacting system not only to be designed in a particularly space-saving and low-weight manner, but results in an electrical contacting system with high flexibility, in which the substrate and the conductive components lying thereon can be adapted particularly easily to the structural requirements of the filter to be used according to the invention.The experiments of the inventors have shown in particular that a corresponding electrical contact-making system can be advantageously printed on the substrate, wherein other additive manufacturing methods could also be considered at least theoretically. A method according to the invention is thus preferred, wherein the electrical contacting system can be produced by printing the substrate with an electrically conductive material, preferably an electrically conductive plastic, wherein the printing is preferably a screen printing method.In particular, additive manufacturing methods advantageously make it possible to obtain an electrical contacting system which is provided with the electrically conductive components on only one side and consequently has an underside, the properties of which are largely influenced by that of the substrate, which can advantageously be embodied as an electrically insulating substrate. With regard to the attachment, a method according to the invention is thus preferred, wherein the electrical contacting system comprises the electrically conductive components of the electrical contacting system at least partially, preferably predominantly, particularly preferably substantially completely, preferably at least the contact points and the contacting elements, on the same side of the substrate.In a particularly preferred embodiment, the substrate is designed as a comparatively thin film, in the central region of which essential elements of the electrical contacting system are arranged, for example the contact points for the external voltage source or also a possible voltage divider. The inventors propose that lateral wing-like or tab-like projections can be formed, on which the contacting elements are applied, which are provided for contacting the conductor layers. When such a contacting system is applied to the lateral lamination of a filter according to the invention, the wing-like tabs can be folded over particularly easily, so that they each contact the conductor layer and can subsequently be glued, for example, with an electrically conductive adhesive, in such a way that a cohesive connection is produced by the plastic material without this connection being made more difficult by excessively strong mechanical stresses. A method according to the invention is preferred accordingly, wherein the first contacting element and / or the second contacting element, preferably the first contacting element and the second contacting element, are arranged on laterally protruding projections of the substrate, wherein the laterally protruding projections preferably have a deformation region and a contact region, wherein the contact region transversely to the longitudinal direction of the filter is preferably wider than the deformation region. A method according to the invention is particularly preferred, wherein the laterally protruding projections are L-shaped. Particularly preferred in this case is additionally or alternatively a method according to the invention, wherein the laterally protruding projections are embodied in the deformation region to be reversibly and non-destructively deformable, in particular bendable.The preferred multilayer filter media with integrated conductor layers are particularly suitable for being combined with an ionization device in the electrostatic precipitator with filter functionality. The voltage required for ionization will generally be significantly higher than the polarization voltage necessary for polarization or that can be applied to the maximum extent, which is limited by the voltage at which undesired breakdown occurs, in particular when the two polarization elements are integrated into the multilayer filter medium. One conceivable solution would be to provide different voltage sources for the ionization device and the filter insert. However, the inventors have recognized that such a provision of separate high-voltage sources is in many cases not possible or is associated with a high outlay on apparatus, and therefore a corresponding configuration is less preferred. For this purpose, it is proposed to design the electrical contacting system as a voltage divider, with which a voltage taken over by the ionization device can be matched to the requirements of the multilayer filter medium. A method according to the invention is thus preferred, wherein the electrical contacting system is a voltage divider. For this purpose, the electrical contacting system can have contact points which are provided for being contacted directly or indirectly via the ionization device with an electrical potential difference which is designed for the ionization device. Between these contact points, a resistance path is provided, which preferably has a meandering contour. The voltage that is dropped across the first contacting element or, if applicable, the second contacting element can be advantageously adjusted by positioning the contacting element along this resistance path, so that, for example, only a reduced voltage is present between the two contacted conductor layers compared to the ionization device. Against this background, a method according to the invention is preferred, wherein in the electrical contacting system the first contact point is electrically conductively connected to the second contact point via a resistance path, wherein the first contacting element is electrically conductively connected to the resistance path between the first contact point and the second contact point, and wherein the second contacting element is electrically conductively connected to the second contact point. In addition or alternatively, a method according to the invention is also preferred, wherein the resistance path is formed in a meandering fashion. In addition or alternatively, a method according to the invention is also preferred, wherein the first contacting element and / or the second contacting element, preferably the first contacting element and the second contacting element, are connected to the resistor path in such a way that the contact area between the resistor path and the contacting element is larger than the cross section of the resistor path orthogonal to the longitudinal direction of the resistor path. In addition or alternatively, a method according to the invention is preferred, wherein the second contact element is not electrically conductively connected to the resistance path between the first contact point and the second contact point.In particularly preferred embodiments, in addition to the electrically conductive components of the contacting system, machine-readable information, for example in the form of a QR code, can also be provided on the substrate. In particular, if the electrical contacting system is applied to the lateral lamination of the multi-layer filter medium, it is particularly easy to read from the outside. This makes it possible to provide the customer or the workshop operation with important information about the handling and / or the installation of corresponding filters.The invention also relates to a filter system for use in a method according to the invention, comprising: a) a filter, comprising: i) a first polarization element, ii) a second polarization element, iii) a polarizable filter medium arranged between the first polarization element and the second polarization element, and iv) an electrical contacting system, wherein the electrical contacting system is configured such that a voltage can be applied between the first polarization element and the second polarization element, b) a voltage source, and c) an electronic control device for controlling the filter system, wherein the electronic control device is configured to operate the filter in at least two operating modes different from one another, wherein the electronic control device is configured to operate the filter in a polarization mode for 80% or more of the operating time, wherein, in the polarization mode, a continuous DC voltage varying by 20% or less is applied between the first polarization element and the second polarization element with respect to the average value of the DC voltage in the polarization mode, wherein the electronic control device is configured to operate the filter partially in a DC cleaning mode, wherein in the DC cleaning mode, a pulsed DC voltage is applied between the first polarization element and the second polarization element with a plurality of pulses, wherein the average electric field strength of the electric field during the pulses is 0.5 kV / cm or more, or wherein the electronic control device is configured to operate the filter partially in an AC cleaning mode, wherein in the AC cleaning mode, a pulsed AC voltage is applied between the first polarization element and the second polarization element with a plurality of pulses, wherein the peaks of the magnitude function of the electric field strength during the pulses are at least partially at 0.5 kV / cm or more.A filter system according to the invention is preferred, wherein the filter system is installed in a vehicle, preferably in a land vehicle.Disclosed within the scope of the invention is also a filter insert for use as a reversibly and non-destructively replaceable component in a filter system according to the invention, comprising at least one of the polarization elements, preferably the first polarization element and the second polarization element, the polarizable filter medium and the electrical contacting system.Also disclosed is the use of pulsed electric fields for cleaning polarizable filter media in electrostatic precipitators with filter functionality.The invention and preferred embodiments of the invention are explained and described in more detail below with reference to the attached figures. In the figures, the following are shown: FIG. 1 shows a schematic illustration of a filter system according to the invention in a preferred embodiment; FIG. 2 shows an exemplary visualization of an exemplary voltage curve of a filter over the operating time in the method according to the invention; and FIG. 3 shows a perspective illustration of a filter to be used according to the invention in a preferred embodiment.FIG. 1 shows a schematic illustration of a filter system 28 according to the invention in a preferred embodiment during the performance of the method according to the invention, which is used in the course of fluid filtration. In FIG. 1, the large arrows indicate the direction of flow of the fluid to be filtered through the filter 10 or the filter system 28. The fluid to be filtered initially passes through an ionization device 32, where dirt particles contained in the fluid are ionized by a corona discharge. After the ionization device 32, the fluid to be filtered impinges on a multilayer filter medium 22, The multilayer filter medium 22 comprises a first conductor layer 24 as the first polarization element 12 and a second conductor layer 26 as the second polarization element 14, wherein the first conductor layer 24 and the second conductor layer 26 are connected to one another by an electrical contact system 18 in such a way that an electrical voltage can be applied between the conductor layers.In the example shown in FIG. 1, the electrical contacting system 18 is supplied from the same voltage source 20 as the ionization device 32, which is a direct voltage source arranged in the vehicle. A polarizable filter medium 16 is arranged between the first conductor layer 24 and the second conductor layer 26, which filter medium, in addition to a dielectric particle filter layer, also comprises an activated carbon layer for absorbing pollutants. Via the electronic control unit 30, the filter system 28 according to the invention is configured to operate the method according to the invention.For this purpose, the filter 10 is operated for the most part in the polarization mode, in which the direct voltage applied via the electrical contact-making system 18, which is substantially constant, forms an electric field between the first polarization element 12 and the second polarization element 14, which polarizes the polarizable filter medium 16 and thus promotes the separation of the previously ionized dirt particles. The filter system 28 according to the invention of FIG. 1 is configured, via a corresponding software-side programming of the electronic control device 30, to switch from the polarization mode to the DC cleaning mode at regular intervals with respect to the operating time of the filter, wherein the DC voltage provided by the voltage source 20 is now no longer continuously transmitted to the conductor layers, but rather is transmitted to the conductor layers in a multiplicity of short pulses in order to generate a corresponding pulsed electric field. In addition, the filter 10 is provided with sensor units (not shown) by means of which the temperature and the air humidity can be maintained. After phases of a very high air humidity in combination with a high temperature, the filter system according to the invention is designed to additionally switch into the DC cleaning mode, in addition to the series, preferably during stationary phases of the vehicle, in particular in the context of tank or charging processes.In the example shown in FIG. 1, the electronic control device 30 is an on-board vehicle computer which can take over the necessary control of the filter system 28. In order to prevent the onboard electronics from being impaired in view of the pulsed operation of the filter 10 in the DC cleaning mode, the filter 10 is equipped with a suitable electromagnetic shield.FIG. 2 shows a schematic illustration of an exemplary profile of the DC voltage over time, in which a first and a second operation in the polarization mode M 1 is interrupted from an operation in the DC cleaning mode M 2.FIG. 3 shows a perspective illustration of a filter insert 34 which can be used according to the invention and which has a pleated multilayer filter medium 22 with integrated conductor layers, which filter medium is fixed by a lamination 36 on both sides with a felt material. On the side wall formed by the lateral lamination 36, a preferred electrical contacting system 18 is arranged, which is designed as a voltage divider made of an electrically conductive plastic on an insulating substrate and comprises two contact points, via which the voltage provided by the voltage source 20 can be taken indirectly via the ionization device 32, wherein the voltage dropped on the multi-layer filter medium 22 can be adjusted via the voltage divider.Reference numerals denote reference numerals10 Filter 12 First polarization element 14 Second polarization element 16 Polarizable filter medium 18 Electrical contacting system 20 Voltage source 22 Multilayer filter medium 24 First conductor layer 26 Second conductor layer 28 Filter system 30 Electronic control device 32 Ionization device 34 Filter insert 36 LaminationReferences included in the specificationThis list of documents cited by the applicant has been produced in an automated manner and is only included for the better information of the reader. The list is not part of the German patent application or utility model application. The DPMA does not take any adhesion for any faults or omissions.Patent Literature citedWO 2007 / 135232 A1

[0006] EP 3 448 540 B1

[0006] WO 2023 / 012166 A1

[0033] Cited Non-Patent LiteratureDIN EN ISO 3915

[0058] ASTM D6125-97

[0069]

Claims

A method of operating a filter (10), the filter comprising: i) a first polarization element (12), ii) a second polarization element (14), iii) a polarizable filter medium (16) arranged between the first polarization element (12) and the second polarization element (14), and iv) an electrical contacting system (18), the electrical contacting system (18) being configured to apply a voltage provided by a voltage source (20) between the first polarization element (12) and the second polarization element (14), the method comprising operating the filter (10) in at least two different operating modes, wherein the filter (10) is operated in a polarization mode for 80% or more of the operating time, wherein in the polarization mode a continuous DC voltage varying by 20% or less is applied between the first polarization element (12) and the second polarization element (14), Related to the mean value of the direct voltage in the polarization mode, wherein the filter (10) is partially operated in a DC cleaning mode, wherein in the DC cleaning mode a pulsed direct voltage is applied between the first polarization element (12) and the second polarization element (14) with a plurality of pulses, wherein the mean electric field strength of the electric field during the pulses is 0.5 kV / cm or more, and / or wherein the filter (10) is partially operated in an AC cleaning mode, wherein in the AC cleaning mode a pulsed alternating voltage is applied between the first polarization element (12) and the second polarization element (14) with a plurality of pulses, wherein the peaks of the magnitude function of the electric field strength during the pulses are at least partially at 0.5 kV / cm or more.The method of claim 1, wherein the filter (10) is partially operated in the DC cleaning mode.The method according to any one of claims 1 or 2, wherein the average electric field strength of the electric field in the polarization mode is 0.5 kV / cm or more.The method according to any one of claims 1 to 3, wherein in the DC cleaning mode the average electric field strength of the electric field during the pulses is 0.75 kV / cm or more, and / or wherein in the AC cleaning mode the peaks of the magnitude function of the electric field strength during the pulses are at least partially 0.75 kV / cm or more.Method according to one of claims 1 to 4, wherein the elements connected to the filter medium are the first polarization element (12) and / or the second polarization element (14).The method of claim 5, wherein the filter (10) comprises a multilayer filter medium (22), wherein the multilayer filter medium (22) comprises: I) an electrically conductive first conductor layer (24) as the first polarizing element (12); II) an electrically conductive second conductor layer (26) as the second polarizing element (14); and III) an intermediate layer as the filter medium, disposed between the first conductor layer (24) and the second conductor layer (26), wherein the intermediate layer comprises at least one dielectric layer.Method according to one of Claims 1 to 6, wherein the operation of the filter (10) is switched to the DC cleaning mode or AC cleaning mode after a predefined criterion has been reached.The method of claim 7, wherein the predetermined criterion is selected from the group consisting of expiration of a predetermined time period, starting of the vehicle engine, stopping of the vehicle engine, starting of the filter system, stopping of the filter system, registering a refueling operation, registering a charging operation, registering a sensor value with a sensor unit, and a manual user request.Method according to either of Claims 7 and 8, wherein the filter comprises at least one polarization element, the polarizable filter medium and the electrical contact-making system as a filter insert (34) arranged in the filter such that it can be exchanged reversibly and non-destructively.Filter system (28) for use in a method according to one of Claims 1 to 9, comprising: a) a filter (10) comprising: i) a first polarization element (12), ii) a second polarization element (14), iii) a polarizable filter medium (16) arranged between the first polarization element (12) and the second polarization element (14), and iv) an electrical contacting system (18), wherein the electrical contacting system (18) is configured such that a voltage can be applied between the first polarization element (12) and the second polarization element (14), b) a voltage source (20), and c) an electronic control device (30) for controlling the filter system, wherein the electronic control device (30) is configured to operate the filter (10) in at least two mutually different operating modes, wherein the electronic control device (30) is configured to operate the filter (10) in a polarization mode for 80% or more of the operating time, wherein in the polarization mode a continuous DC voltage is applied between the first polarization element (12) and the second polarization element (14), which varies by 20% or less, based on the average value of the DC voltage in the polarization mode, wherein the electronic control device (30) is configured to operate the filter (10) partially in a DC cleaning mode, wherein in the DC cleaning mode a pulsed DC voltage is applied between the first polarization element (12) and the second polarization element (14) with a plurality of pulses, wherein the average electric field strength of the electric field during the pulses is 0.5 kV / cm or more, or wherein the electronic control device (30) is configured to partially operate the filter (10) in an AC cleaning mode, wherein in the AC cleaning mode a pulsed alternating voltage is applied between the first polarization element (12) and the second polarization element (14) with a plurality of pulses, wherein the peaks of the magnitude function of the electric field strength during the pulses are at least partially at 0.5 kV / cm or more.

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