Field of the invention

The invention relates to a plasma applicator for application of a non- thermal plasma, particularly for disinfection purposes.

Background of the invention

The use of a non-thermal, low-temperature plasma for the treatment of wounds and for disinfection purposes is disclosed, for example, in WO 2010/094304 A1 , WO 2010/034451 A1 , WO 2010/022871 A1 , WO 2008/138504 A1 , WO 2007/031250 A1 and WO 2010/094307 A1. These publications disclose plasma applicators comprising an electrically powered plasma source, wherein the electric energy needed for the operation of the plasma source is supplied either by mains or by an integrated battery. However, mains-operated plasma applicators do not allow a mobile use of the plasma applicator and battery-powered plasma applicators have the disadvantage of a limited battery capacity and the need to accommodate a quite heavy and large battery.

Moreover, a number of known plasma applicators typically comprise plasma sources based on sparks or on the principle of corona discharge. However, these sources suffer from the fact that plasma generation is local in a surface area less than 1 mm ² . Thus, for obtaining in a reasonable time - by concentration gradient driven diffusion - a concentration of reactive species at the surface to be treated which is high enough to have a considerable sterilizing, disinfecting and/or healing effect on the treated area during the lifetime of the plasma, either a very high particle density of reactive species must be generated during a single discharge event, or several such dis- charges have to be activated. This means that the power consumption of such a source is high, and that a single discharge develops considerable temperature detrimental to or even burning human tissue which is to be treated.

Such a plasma source is not suitable with small, mobile power sup- plies which in general deliver much less power than needed to drive the source effectively.

Moreover, corona discharge plasma sources mainly generate ozone, such that the chemistry of the plasma is in particular not adequate for the treatment of human skin, e. g. for wound healing, reducing itchi- ness, infections, skin irritations or other inconveniences, in particular caused by insect bites.

Summary of the invention

Therefore, it is a general object of the invention to provide an improved plasma applicator for applying a non-thermal, low- temperature plasma without a need for a battery or a connection to mains.

In particular, it is an object of the invention to provide a plasma applicator with a plasma source having a power consumption which is low enough that it can be driven by a small portable power source, in par- ticular an energy harvesting device. Further, it is an object of the invention to provide a plasma applicator having a plasma source generating a plasma chemistry which is adapted to be used in a treatment of human tissue, e. g. skin, or human teeth, while at the same time being able to be integrated in a hand held, mobile device which in particular can be used independent from the mains or any batteries or accumulators.

This object is achieved by a novel plasma applicator according to the main claim.

The invention is based on the general idea to combine energy har- vesting techniques with a suitable plasma source. This is advantageous since it eliminates the need for a battery or a connection to mains while at the same time an adequate plasma chemistry is provided in particular for sensitive surfaces, such as human skin.

The plasma source comprises a first and a second electrode, the electrodes being spaced apart by at least one dielectric layer. Preferably, the first electrode is embedded in the at least one dielectric layer. In another embodiment, the first electrode may be arranged directly on one side of the dielectric layer. The second electrode then is arranged directly on an opposing side of the dielectric layer or of a further dielectric layer which is in contact with the first dielectric layer. In another embodiment, the second electrode may be embedded in the at least one dielectric layer. In particular, there is no air gap between the dielectric layer and the first and second electrode.

In one embodiment, the plasma source may preferably be a surface micro discharge (SMD) plasma source as disclosed, for example, in WO 2010/094304 A1 which is therefore incorporated by reference herein. In this case, the first electrode may be embedded in the di- electric layer or arranged directly at a surface thereof. The second electrode is arranged directly on an opposing surface of this or a further dielectric layer. If more than one dielectric layer is present, the layers are arranged in contact with each other. No air gap is present between the electrodes and the dielectric layer(s). In particular, the first electrode is arranged on a side of the dielectric layer facing away from the treated region. The second electrode is preferably arranged in front of the treated region or surface. In this case, most preferably, the second electrode is grounded while a potential is applied to the first electrode.

In another embodiment, the plasma source may preferably be constructed according to the principle of a self sterilizing surface (SSS) as disclosed, for example, in the patent applications EP 10005236.4 and PCT/EP2011/002506, as well as in WO 2011/110343 A1 , which are therefore incorporated by reference herein. In this case, preferably both electrodes, but at least the second electrode is/are embedded in the dielectric layer, such that a plasma is generated on a surface of the dielectric layer confronting the treated region, while no electrode is exposed at least on this side. Thus, a contact of, e. g., human skin to the second electrode is definitely avoided. Nevertheless, also in this embodiment, it is preferred that the second electrode may be grounded.

Independent of whether the plasma source is embodied as a SMD source or as a self sterilizing surface, there is no current running through the treated area, e. g. human skin. Moreover, the plasma source only emits a small amount of UV radiation which is not dangerous to human skin. In order to achieve a reduction of pathogen load, in particular bacterial load, on a treated surface by 3 orders of magnitude (log 3 reduction), a concentration of approximately 1 to 10 ppm of reactive species is needed. Such a concentration is sufficient to support mild wound healing and/or help to suppress itchiness, infections, skin irritations and other inconveniences, e. g. caused by insect bites.

At standard conditions of temperature and pressure, a volume of 1 cm ³ comprises approximately 10 ¹⁹ gas particles, as is evident from the fact that the molar volume of an ideal gas at standard conditions is approximately 22,4 L.

Thus, if the volume above the treated surface amounts to 1 cm ³ and a concentration of 1 to 10 ppm of reactive species is desired, a total number of approximately 10 ¹³ to 10 ¹⁴ reactive particles has to be created, which should be homogeneously distributed throughout the volume. Thus, assuming that approximately 10 eV are needed to create a single reactive particle, e. g. an ion, or an atom or molecule in an excited state, only an energy of approximately 0,02 to 0,2 mJ per discharge event - relating to approximately 0 ¹⁴ to 10 ¹⁵ eV - is necessary to generate a sufficient number density of reactive spe- cies. This energy may, e. g., easily be generated by the movement of a finger acting on a piezoelectric generator.

Typically, a micro discharge has an extent of approximately 10 mm ² .

In contrast, a conventional single spark or single corona discharge, due to the much smaller area of plasma generation, must generate a much higher concentration of reactive species in order to guarantee that a homogeneous concentration in a comparable volume will reach the desired value driven by diffusion in a comparable time. In total, a plasma applicator comprising the plasma source described here has a sufficiently low power consumption and covers a sufficiently large area, thus opening the door for the use of a small, low power mobile power source such as an energy harvesting device. In particular, due to the fact that the discharge is spread over a sufficiently large surface area, diffusion lengths and time to a treated surface can be significantly reduced compared to a source which mainly generates a highly localized discharge.

In principle, it is possible to drive the plasma source described above in a corona regime or in a micro discharge regime. It depends mainly on the voltage and frequency applied to the electrodes which regime is adopted. According to the invention, the plasma source is driven in the micro discharge regime - rather than in the corona regime - in order to generate cold atmospheric plasma with the right chemistry, which is particularly adapted to the treatment of sensitive surfaces such as human skin, and at the same time, the power consumption of the source is adapted for the use with a small, low power mobile power source, in particular an energy harvesting device.

Reactive particles comprised by a cold atmospheric plasma gener- ated in air in the micro discharge regime include O, N, NO, NO2, O3, OH, H2O2. These species are to a large part identical with the products of the human innate immune system and therefore support a natural defense against pathogens. The respective plasma chemistry is ideal for the purpose of wound healing and/or suppressing itchi- ness, skin irritations or infections, e. g. caused by insect bites, and/or treating fungal, viral and bacterial skin diseases and/or acne. Further, the plasma has a disinfecting and/or sterilizing effect. It is generally applicable to organic and inorganic surfaces for sterilization and/or disinfection. Moreover, it is able to be used against bacteria, viruses, fungi, spores, and is able to effectively destroy proteins, in particular proteins causing allergies or other inconveniences, and other - in particular large - unwanted or disturbing molecules, like odorous substances, allergens, and others. A load of a surface with such substances can be reduced by treating the surface with the plasma. Molecules are preferably destroyed by electron dissociation due to hot electrons in the micro discharge of the plasma.

The plasma can also be applied for the treatment of body orifices, in particular to suppress irritations and/or infections of body orifices, e. g. inflammation of the ears. Further, in particular noses or other body parts contaminated with MRSA (multi-resistant staphylococcus au- reus) or other resistant germs can be treated with the plasma in order to reduce bacterial load.

The invention is in no way restricted to air as a medium for generating the plasma. Other gases, like noble gases or gas mixtures, may also be used. Therefore, the applicator may comprise a gas source. By choosing an appropriate medium, the plasma chemistry can carefully be adapted to a predetermined use.

In total, there are a number of reasons why - according to the invention - micro discharge plasma is favored over plasma generated by other types of sources like corona discharges, in particular for a mo- bile, hand held device powered by a low power portable energy source like an energy harvesting device. Further, the plasma applicator according to the convention comprises an electric power source providing electric energy, wherein the power source is connected to the plasma source and powers the plasma source. In contrast to the conventional plasma applicators, the power source is not a battery or a mains-connection. Instead, the power source comprises an energy harvesting device converting ambient energy into the electric energy needed for the operation of the electrically driven plasma source. The term energy harvesting is known as a process in which electric energy is derived from external sources, e.g. solar power, thermal energy, wind energy, salinity genetic energy. These types of energy harvesting devices are generally known in the state of the art.

For example, US 2006/0021261 A1 discloses an energy harvesting device in the form of a piezoelectric generator which is integrated in the heel of a piece of footwear so that the piezoelectric generator is actuated by footsteps thereby generating electric energy.

A piezoelectric generator is most preferred because it is able to generate a voltage, in particular amounting to approximately 16 kV, di- rectly applicable to the plasma source in order to drive a micro discharge. Thus, no converter circuit is needed in this case. The power delivered by a single activation of the piezoelectric generator suffices for generating a number of reactive species the number being large enough to at least reduce the bacterial load on a surface enclosing a volume of 1 cm ³ by approximately 3 orders of magnitude as described above. Thus, it is possible to directly convert the energy harvested by the piezoelectric generator into a non-thermal, cold atmospheric plasma by combining the piezoelectric generator with a plasma source as described above. Further, in a preferred mode to carry out the invention, the relatively short discharge event triggered by the energy harvesting device, in particular a piezoelectric generator, may be followed by a considerable long afterglow effect of the plasma lasting for, e. g., a time of the order of 10 to 30 seconds. Thus, the plasma chemistry not only sur- vives the actual discharge event by a considerable time, but also develops during this time in a way which is ideal for the treatment purposes the invention is focused on. This means, that a short discharge event followed by a long afterglow time has even a better effect than a longer discharge time followed only by a short or even no time for afterglow. For example, an afterglow lasting for 15 seconds can provide a factor 10 higher bactericidal effect.

Thus, the invention also includes a method for using a portable plasma applicator, wherein the plasma applicator is initially brought in a treating position for plasma treating a surface, at least one dis- charge event is triggered to generate plasma when the applicator is in its treating position, and wherein the applicator is left in its treating position at a treated area for 5 to 30 seconds, preferably 10 to 20 seconds, most preferably 15 seconds, following the last discharge event. Thus, the afterglow effect of the plasma can be used in order to obtain better results for the treatment. Moreover, due to the additional time more reactive particles reach the treated surface by diffusion. In total, an energy harvesting device, in particular a piezoelectric generator, combining an efficient discharge with the effect of afterglow, develops a hitherto unforeseen synergy effect with the plasma source according to the invention. If a larger volume or surface area is to be treated, more than one piezoelectric generator may be employed and/or a conversion circuit may be used in order to convert the voltage pulses generated into a waveform which allows storage of the electric energy in some electric storage device like a capacitor or an accumulator. Alternatively, the piezoelectric generator may be triggered more than once.

For example, while testing the invention, it was proven that a SMD source consisting of two intertwined wires having a length of 2 meters powered by 1000 piezo discharges during 20 seconds produces a desired amount of plasma. Linear scaling is possible, such that a single piezo discharge is able to power such a source having a length of 3 mm. The micro discharges itself have an extension of 2 mm in both directions perpendicular to the wires, such that in this case the generated plasma covers an area of 12 mm ² .

Another example of an energy harvesting device is a thermo-electric generator which uses temperature gradients and generates a corresponding thermo-voltage according to the well-known Seebeck effect.

However, the invention is not restricted to the afore-mentioned types of energy harvesting devices for powering the electrically driven plasma source. For example, it is conceivable to generate the electric energy needed for the operation of the plasma source by biome- chanical harvesting, ambient-radiation sources, pyroelectric energy harvesting, electrostatic (capacitic) energy harvesting or blood sugar energy harvesting. Further, magnets movable in coils, hydrogen cells, electrochemical harvesters, or tidal energy harvesters can be used. However, the preferred embodiment of the invention uses a piezoelectric generator to power the plasma source.

In this connection, it should be noted that the energy harvesting device generally provides the electric energy in a format (e.g. voltage, pulse duration, frequency etc.) which is not in all embodiments directly suitable for powering the plasma source, as already indicated above. Then, the power source preferably comprises a converter circuit which converts the electric power provided by the energy harvesting device in the power needed for operating the plasma source. For example, the converter circuit can be adapted to transform the voltage of the electrical energy. Further, the converter circuit can be adapted to accumulate the electrical energy provided by the energy harvesting device. Moreover, the converter circuit might comprise a rectifier. Suitable converter circuits are disclosed, for example, in US 2006/0021261 A1 which is therefore incorporated herein by reference. In a preferred embodiment of the invention, the power source and/or the plasma source is at least partially arranged in a piece of clothing, particularly in a glove, in a coat, shirt or undershirt, wherein the power source is preferably activated by movements of a person wearing the piece of clothing. For example, the afore-mentioned pie- zoelectric generator can be arranged in an armpit of the piece of clothing so that movements of the arms of the person wearing the piece of clothing actuate the piezoelectric generator thereby generating the electric energy needed for the operation of the plasma source. Further, the plasma source itself is preferably also arranged within the armpit of the piece of clothing so that the plasma generated by the plasma source disinfects the armpit of the piece of clothing thereby avoiding maloudor. Moreover, odorous substances are destroyed by the plasma.

In another embodiment of the invention, the piezoelectric generator is at least partially arranged in a piece of footwear, particularly in a heel of a shoe. Such an arrangement is per se known in the state of the art, e.g. from US 2006/0021261 A1 so that this publication is incorpo- rated by reference herein. The piezoelectric generator is preferably driven by footsteps of a person carrying the piece of footwear so that the biomechanical energy provided by the person wearing the piece of footwear is used for actuating the piezoelectric generator. In this embodiment, the plasma source is at least partially arranged in the piece of footwear, particularly in a sole of the piece of footwear that the plasma source disinfects the interior of the piece of footwear thereby avoiding maloudor and fungal infections. Also, odorous substances are destroyed by the plasma.

In yet another embodiment of the invention, the piezoelectric genera- tor and/or the plasma source is at least partially arranged in a manual operating element, particularly in a door knob, in a door handle or in a bathroom device, in particular with a movable component, like e. g. a toilet seat or part thereof. In this embodiment, a manual actuation of the manual operating element causes the piezoelectric generator to generate the electric energy needed for the operation of the plasma source. Further, the plasma source disinfects the surface of the manual operating element. Such an improved door handle could be used, for example, in hospitals to avoid infections caused by patients touching the door handles.

In yet another embodiment, the novel plasma applicator is substantially pin-shaped like a ball pen, wherein the plasma applicator com- prises a piezoelectric generator. In this embodiment, the piezoelectric generator is preferably mechanically coupled by a mechanism to a manual operating element, wherein any movement of the operating element is mechanically transmitted to the piezoelectric generator, so that a manual actuation of the manual operating element causes the piezoelectric generator to generate the electric energy needed for the operation of the plasma source. The mechanism preferably allows an axial movement of the operating element along the pin-shaped plasma applicator like in a conventional ball pen.

Moreover, the novel plasma applicator according to the invention can be used for treatment of insect bites (suppression of itching), inclusion in shoes (prevention of malodor, protection against fungal infections), inclusion in sanitary clothing such as gloves and bandages to reduce transmission of diseases (in principle all textiles that require some amount of local disinfection), inclusion in door knobs and han- dies to disinfect these after each use (in principle all mechanically activated devices that require some amount of local disinfection) and for use in temporary dental pain relief by reducing bacterial load in cavities.

Further, it should be noted that the plasma applicator according to the invention is preferably mains-independent, mobile and/or handheld. Finally, it should be noted that the invention is not restricted to the afore-mentioned plasma applicator as a separate device but also encompasses the afore-mentioned articles (e.g. a piece of clothing, a piece of footwear, a manual operating element) comprising an inte- grated plasma applicator.

The invention and its particular features and advantages will become apparent from the following detailed description considered with reference to the accompanying drawings.

Brief description of the drawings Figure 1 shows a simplified drawing illustrating the general design of an embodiment of a plasma applicator according to the invention.

Figure 2 shows a cross-section of a shoe comprising an integrated plasma source for generating a low-temperature plasma and an integrated piezoelectric generator for powering the plasma source. Figure 3A shows a cross-section of a pen-shaped plasma applicator comprising an integrated piezoelectric generator for powering the plasma source.

Figure 3B shows an enlarged and simplified cross section of the plasma source of the plasma applicator according to Figure 3A. Figure 4 shows a coat comprising a integrated plasma applicators in the armpits of the coat.

Figure 5 shows a simplified schematic drawing illustrating a door handle comprising an integrated piezoelectric generator and an integrated plasma source. Figure 6 shows a simplified schematic drawing illustrating a toilet seat comprising an integrated plasma applicator for disinfecting the toilet seat.

Figure 7 shows a simplified schematic drawing illustrating another embodiment of a small, hand held, mobile plasma applicator comprising an integrated piezoelectric generator for powering the plasma source.

Detailed description of the drawings

Figure 1 shows a schematic diagram illustrating the general design of a plasma applicator 1 according to the invention.

Firstly, the plasma applicator 1 comprises an electrically driven plasma source 2 as described above which generates a non-thermal, low-temperature plasma which is suitable for disinfection of wounds and other purposes as mentioned above. Further, the plasma applicator 1 according to the invention comprises a power source 3 providing the electric energy needed for the operation of the plasma source 2.

The power source 3 comprises an energy harvesting device 4 instead of a battery or a mains connection as in conventional plasma applicators. The energy harvesting device 4 can be, for example, a piezoelectric generator or a thermo-electric generator.

Further, the power source 3 may comprise a converter circuit 5 which converts the electric energy provided by the energy harvesting device 4 into the electric energy needed for the operation of the plasma source. The converter circuit 5 may be necessary for some applica- tions, since the energy harvesting device 4 typically does not provide the electric energy in a form suitable for powering a larger plasma source 3. For example, a rectifier and a buffer can be included in the converter circuit 5. The novel plasma applicator 1 can be used for disinfecting surfaces as disclosed in, for example, WO 2010/094304 A1 , WO 2010/034451 A1 , WO 2010/022871 A1 , WO 2008/138504 A1 , WO 2007/031250 A1 and WO 2010/094307 A1.

Figure 2 shows a cross section of a preferred embodiment of the in- vention, wherein the energy harvesting device 4 is realized by a piezoelectric generator which is integrated in a heel 6 of shoe 7. Therefore, each footstep of the shoe 7 causes the piezoelectric generator in the energy harvesting device 4 to generate electric energy which may be temporally stored by a converter circuit 5, wherein the con- verier circuit 5 may also be integrated in the heel 6 of the shoe 7.

Further, the plasma source 2 is preferably realized by an electrode arrangement according to the principle of a self sterilizing surface - as indicated above - being integrated in the sole 8 of the shoe 7, so that the plasma source 2 generates the low-temperature plasma within the shoe 7 thereby avoiding any maloudor. It is also possible that the plasma source 2 is embodied as a SMD source, as also indicated above.

Figures 3A and 3B illustrate another embodiment of a plasma applicator 1 according to the invention, wherein the plasma applicator 1 is substantially pin-shaped and comprises in axially movable operating element 9 which acts on the energy harvesting device 4 in the form of a piezoelectric generator. Therefore, each movement of the oper- ating element 9 by an operator causes the piezoelectric generator to generate electric energy.

At the tip of the pen-shaped plasma applicator 1 , a plasma source 2 is integrated, wherein the plasma source 2 substantially consists of two electrodes 10, 11 which are embedded in a dielectric 12 as shown in Figure 3B. In this embodiment, typically the converter circuit 5 is not needed. However, it is possible to provide one.

The type of plasma applicator 1 as shown in Figures 3A and 3B can be used, for example, in temporary dental pain relief by reducing bacterial load in cavities.

The embodiment according to Figures 3A and 3B does not provide a closed volume for the plasma to be generated. Thus, the afterglow effect of the plasma is typically not used in conjunction with this embodiment, because the advantages of the afterglow effect are most prominent when the plasma is generated in a closed volume. However, even without using the afterglow, an efficient treatment, in particular with the plasma applicator 1 as shown in Figures 3A and 3B is possible.

Figure 4 shows another embodiment of a plasma applicator 1 which is arranged in the armpits of a coat 13, a shirt or an undershirt, wherein the plasma applicators 1 each comprise a piezoelectric generator which is actuated by any movements of arms 14 of the coat 13. In other words, any arm movements of the person wearing the coat 13 activate the piezoelectric generators of the plasma applica- tors 1 , so that the piezoelectric generators provide the electric energy needed for the operation of the plasma sources which are also arranged in the armpits of the coat 13 thereby avoiding any maloudor caused by sweat. If the plasma applicator 1 is arranged in the armpits of a shirt or undershirt, it is possible to directly treat the skin of the armpit in order to reduce a number of bacteria causing malodour and/or destroy odorous substances present on a surface of the skin. Figure 5 illustrates another embodiment of a plasma applicator 1 according to the invention, wherein the energy harvesting device 4 in the form of a piezoelectric generator is mechanically actuated by a door handle 15, so that each movement of the door handle 15 causes the piezoelectric generator to provide electric energy to the plasma source 2, preferably via the converter circuit 5, when needed.

Further, the plasma source 2 is arranged in such way that the low- temperature plasma is provided to the surface of the door handle 15 thereby disinfecting the surface of the door handle 15.

Figure 6 shows a schematic view of another embodiment of the in- vention, wherein a plasma applicator (not shown) according to the invention is embedded into a cover 16 of a toilet seat 17, so that a non-thermal plasma 18 is triggered between the cover 16 and the toilet seat 17 thereby disinfecting the surface of the toilet seat 16.

The plasma applicator comprises a piezoelectric generator which is mechanically coupled to the cover 16, so that a closing movement of the cover 16 actuates the piezoelectric generator thereby generating the plasma.

When the cover 16 is closed, the charge is released in the form of cold atmospheric plasma using an encapsulated electrode arrange- ment also located in the cover 16. The cover 6 is shaped to trap the plasma thus ensuring maximum bactericidal efficiency by using the afterglow as well.

Alternatively, the piezoelectric generator could also be coupled to the movable toilet seat 17. In this case, the area of the toilet seat 17 is so large, that typically a converter circuit is needed to provide sufficient energy for producing an appropriate concentration of reactive particles. However, it is also possible that the energy harvesting device may be actuated more than once for generating a larger amount of plasma. It is also possi- ble that the energy produced by multiply actuating the energy harvesting device - e.g. in a sequence of 100 discharges in 5 seconds - is stored and/or accumulated in an energy storage device like a capacitor, battery or accumulator, before transferring it to the plasma source 2 in order to ignite a plasma producing discharge. Finally, Figure 7 shows a schematic cross-sectional view of another embodiment of a plasma applicator 1 .

The plasma applicator 1 is embodied as a mobile, hand held device 19 which is adapted for treating a surface 21 , preferably human skin. For example, there is an insect bite 23 located on the surface 21 which causes itchiness.

The device 19 comprises a plasma source 2 comprising a first electrode 25 and a second electrode 27 which are spaced apart from each other by a dielectric layer 29. It is possible to provide more than one dielectric layer between electrodes 25, 27, in particular layers comprising different dielectric materials. In the present embodiment, the first electrode 25 is arranged directly on a first surface 31 of the dielectric layer 29. In another embodiment, the electrode 25 could be embedded in the dielectric layer 29. The second electrode 27 is - in the present embodiment - embed- ded in the dielectric layer 29 near a second surface 33 opposing the first surface 31. In another embodiment, the second electrode 27 could be arranged directly on the surface 33.

Since the second surface 33 faces the surface 21 which is to be treated, the second electrode 27 is preferably grounded. First and second electrodes 25, 27 may comprise wires which are preferably arranged in a crossing configuration. However, the first electrode 25 may as well be a plate or have a mesh structure, while the second electrode 27 most preferably has a mesh structure.

An energy harvesting device 4, preferably a piezoelectric generator, is connected to the plasma source 2. It can be triggered by an actuating means not shown here like a switch, which is preferably arranged on a circumferential surface 35 or on a back surface 37 of the device 19.

Preferably, a plasma is generated within a closed volume over or enclosed at least partially by the surface 21 which is to be treated. The embodiment of the device 19 according to figure 7 therefore comprises at least one wall 39 having a distal edge 41. Thus, a closed volume 43 can be formed when the distal edge 41 contacts the surface 21. The device 19 preferably has a cylindrical shape, such that the wall 39 circumferentially encloses a volume 43. In order to suppress itchiness, the insect bite 23 should be arranged inside the volume 43.

It is desirable in particular for using the afterglow effect but also for guaranteeing a sufficient flux of reactive particles to the surface 21 , that the volume 43 may be sealingly closed. For this purpose, the distal edge 41 preferably comprises a soft and/or elastic material which can act as a sealing lip. Moreover, an application of device 19 to human skin is much more comfortable for the user when the distal edge 41 is soft.

Preferably, the wall 39 is constructed and/or arranged in such a way that the closed volume 43 is substantially flat, which means that it has an extension in a plane defined by the surface 21 which is much greater than its extension in a direction perpendicular thereto - here in a length direction of the device 19. Thus, a diffusion pathway from the second surface 33 where plasma is generated to the surface 21 is short, while plasma is generated all over the relatively large area of the second surface 33.

If the volume 43 is of the order of 1 cm ³ , a single discharge event of the energy harvesting device 4, preferably embodied as a piezoelectric generator, suffices to generate a particle density of reactive species which effectively reduces itchiness caused by insect bite 23, or provides another treatment to surface 21. In this case, no converter circuit is needed, but the energy generated by the energy harvesting device 4 can directly be transformed into cold atmospheric plasma for treating the surface 21. Since the embodiment according to Figure 7 provides a closed volume for the plasma, the afterglow effect is preferably used in conjunction with this embodiment. In order to use this effect, it is necessary that the applicator 1 is left in its treating position at the treated area for 5 to 30 seconds, preferably 10 to 20 seconds, most preferably 15 seconds, following a single discharge event or the last discharge event of a sequence. Thus, it is possible to use the afterglow effect in order to improve the results for the treatment. However, it is also possible to apply the embodiment of Figure 7 without using the afterglow effect. Also in this case, an efficient treatment is possible.

In particular, the invention includes a portable, hand-held plasma applicator 1 which is preferably designed for carrying it, e. g., in a purse, thus being always readily available. The applicator 1 is mains- independent and does not need to be charged or have any batteries changed, because it is comfortably powered by an energy harvesting device 4. This is possible due to the plasma source 2 being operated in a micro discharge regime. Most preferably, the device and/or a treated volume is/are small enough such that no converter circuit 5 is needed, and a single activation of the energy harvesting device 4, preferably a piezoelectric generator, is sufficient for effective treatment. The cold atmospheric plasma generated by the plasma source 2 driven in the micro discharge regime comprises particles which are ideal for mild wound healing and/or help to suppress itchiness, infections, skin irritations and other inconveniences, e. g. caused by insect bites, or for reducing tooth ache.

The mobile device may in particular be embodied as shown in figures 3A, 3B or in figure 7. Although the invention has been described with reference to the particular arrangement of parts, features and the like, these are not intended to exhaust all possible arrangements of features, and indeed many other modifications and variations will be ascertainable to those of skill in the art.