EP3446579A1 - Evaporator unit for an inhaler and method for controlling an evaporator unit - Google Patents

Abstract

An evaporator unit (20) for an inhaler (10) with an electronic control device (21) and at least one heating element (36) is arranged to evaporate liquid supplied from a liquid storage (12). The vaporized liquid is taken up by a stream of air flowing through the evaporator unit (20). The electronic control device (21) is adapted to heat the at least one heating element (36) with a variable control frequency.

Description

The present invention relates to an evaporator unit for an inhaler having an electronic control device and at least one heating element, wherein the evaporator unit is adapted for evaporating liquid supplied from a liquid storage, and the evaporated liquid is taken up by an air flow flowing through the evaporator unit.

The vast majority of currently on the market evaporator units is realized in an electronic cigarette product and is based on the so-called wick-coil principle. A wick, for example of glass fiber, is partially wrapped with a heating coil and is in communication with a liquid storage. Upon heating of the heating coil, the liquid in the wick evaporates in the region of the heating coil. The liquid is typically a mixture of different substances which have different boiling temperatures as well as different physiological effects. In order to control the effect, the droplet size is regulated because different sized droplets are absorbed by the body at different rates. The use of a suitable electronic control device allows the targeted setting of the droplet size of the droplets in the resulting aerosol by means of the adjustment of the heating temperature of the heating element designed as a heating coil. Such an electronic cigarette is exemplary in the US 2016/0021930 A1 (RJ Reynolds Tobacco Company).

As a result of the different boiling temperatures of the substances present in the liquid, for example, a substance having a low boiling temperature can be used up completely after a corresponding period of use without the liquid reservoir being emptied. Thus, in the course of consumption, the physiological or taste effect of the resulting aerosol changes. If, for example, nicotine is used up, the smoking experience can be inhibited.

Furthermore, uncontrollable temperature development can lead to unwanted partial heating and overheating of the liquid, or of one of the substances contained therein, and thus to undesired emissions of pollutants.

The object of the invention is to provide a safe, high-quality and energy-efficient evaporator unit, in which a reliable drug administration is given and a potential risk of overheating and the associated pollutant emissions can be avoided.

The invention solves this problem with the features of the independent claims. It is proposed that the electronic control device is set up to heat the at least one heating element with a variable control frequency.

It has been found that the control frequency with which the at least one heating element is heated, in addition to the geometry and the advantageously established liquid supply has a decisive influence on the size of the droplets located in the aerosol. The amount of steam produced when pulsing or otherwise heating at different frequencies is different and therefore specifically adjustable and also changes the droplet size of the aerosol substantially with the amount of steam, depending on the geometry of the heating element used. A high control frequency favors the generation of smaller droplets, while a low control frequency causes the generation of larger droplets. According to the invention, the uptake and effect of the substances present in the liquid is adjusted by the droplet size with the control frequency. Furthermore, the heating temperature can be set according to the substances in the liquid and overheating can be avoided. Furthermore, it has been found that the energy requirement of the evaporator is improved by adjusting the droplet size over the frequency over the setting of the temperature.

The heating according to the invention with a variable control frequency allows the formation of droplets of variable size and thus a variable effect. The term variable control frequency is to be understood as the temporal and / or local variation of the control frequency. By an example temporally variable control, the administration of physiological agents can be controlled and, for example, the nicotine intake during smoking can be adjusted so that the smoking pleasure is improved.

In a preferred embodiment, the electronic control device is adapted to heat the at least one heating element at a plurality of different control frequencies so as to achieve a multimodal droplet size distribution. The heating of the at least one heating element with the plurality of different control frequencies means that a plurality of control frequencies can be superimposed and thus the at least one heating element simultaneously with a plurality of frequencies can be heated. Several control frequencies may be present globally or at defined locations of the at least one heating element, so that the at least one heating element is divided into different areas with different control frequencies.

Preferably, the evaporator unit has a plurality of heating elements and the electronic control device is adapted to heat different heating elements with different control frequencies. By driving different heating elements with different control frequencies different droplet sizes can be realized simultaneously. For example, each heating element may produce one or more droplet sizes that are collectively received by the airflow passing through the evaporator unit and supplied to the user.

Advantageously, the electronic control device is adapted to control the drive frequency of the plurality of heating elements so that there is a multimodal droplet size distribution of the evaporated liquid. If several heating elements are controlled in parallel with different frequencies, a multimodal, adjustable droplet size distribution can be achieved. For example, if it is desired to produce droplets of large size, for example> 5 .mu.m, and droplets of small size, for example <1 .mu.m, the heating elements can be controlled such that at least one of the heating elements generates large droplets and at least one of the heating elements generates small droplets. Preferably, for this purpose, the at least one heating element for the small droplets is heated at a high control frequency, and the at least one heating element for large droplets is heated at a low control frequency. Likewise, additional heating elements can be added to produce droplets of certain sizes.

The resulting droplet size distribution is multimodal and has maximums at the desired droplet sizes. This, for example, is conducive to a positive sense of smoke, since small droplets penetrate far into the respiratory tract, where nicotine, but also other substances, work effectively, while large droplets can be well perceived in terms of taste. The targeted adjustment of the multimodal distribution corresponds to a specific adjustment of the physiological and taste effects. It would be conceivable to have a 1: 1 ratio of small and large droplets to make the effect fast (small droplets), but also long-lasting (large droplets).

In a preferred embodiment, the electronic control device is adapted to change the drive frequency of the at least one heating element over the discharge duration of the liquid storage. Over the duration of the emptying of the liquid storage, the concentrations of the substances in the liquid may change due to their different boiling temperature and / or volatility. The liquid contained in the liquid storage is separated by the differential distillation taking place during the evaporation. That is, higher-boiling components accumulate, which leads to an inhomogeneous release of active ingredient. For example, significantly less nicotine is present from about half consumed liquid storage. A desired physiological effect of the active substances of the individual substances can preferably be achieved by changing the control frequency over the duration of the emptying of the fluid reservoir.

Preferably, the electronic control device is adapted to increase the drive frequency of the at least one heating element with progressive emptying of the liquid storage. For example, nicotine evaporates at a comparatively low temperature. Therefore, the duration of emptying of the fluid reservoir decreases the dose of nicotine absorbed per puff at the same temperature and droplet size. By adjusting the droplets, e.g. Due to large droplets at the beginning (delayed action in the body) and small droplets at the end (fast action) of the discharge duration of the fluid reservoir, the subjective perception of effect can be homogenized and concentration changes are compensated. In order to promote a positive smoking experience, it is proposed to increase the control frequency over the duration of fluid reservoir drainage and produce more smaller droplets to keep the smoking experience constant.

It is advantageous to change the driving frequency of the at least one heating element over the duration of a train. Over the duration of a turn, the physiological and taste effect can be positively influenced when the control frequency and thus the droplet size is adjusted.

Preferably, the drive frequency of the at least one heating element can be set in a targeted manner such that a desired droplet size of the evaporated liquid of, for example, ≦ 5 μm results. Droplets with a diameter or an aerodynamic diameter (MMD) of less than 5 μm do not remain in the upper respiratory tract, but penetrate into the bronchi which promotes absorption of nicotine or other active ingredients, for example for drug treatment. The aerodynamic diameter is the diameter at which the entirety of those particles with a smaller or larger diameter each contribute half of the total mass of all particles. In particularly preferred embodiments, the droplet size is less than or equal to 0.2μm. These very small droplets with an MMAD or diameter of less than 1 micron penetrate into the alveoli and pass there very quickly the blood-brain barrier. An effect may thus occur early or late according to droplet size. By adjusting the droplet size can thus influence the time of action.

In a preferred embodiment, a drive frequency of the at least one heating element of at least 10 Hz and preferably at most 20 kHz is set. The variable control frequencies according to the invention are in a preferred embodiment in the range of 10 Hz to 20 kHz, more preferably between 500 Hz and 2 kHz. The frequencies can be set individually for each heating element per heater. Thus, a preferred distribution of droplet sizes and energy efficient heating can be favored.

It is advantageous to measure the resistance of the at least one heating element. If the heating element is realized as a thermistor, the temperature can be determined via the resistance measurement. Preferably, a diagnosis of the operating state, the state of the liquid-wetted heating element (with wrong liquid, no liquid, too little liquid, right amount of liquid and / or too much liquid) and / or possible malfunctions can be performed. In a preferred embodiment, the driving and measuring device a data processing unit or is connected to such.

Advantageously, the drive and measuring device has a reference resistor connected in series with the heating element. Preferably, each heating element is connected in series with a separate reference resistor. This allows a precise resistance measurement of the heating element or the heating elements.

Preferably, the drive and measuring device has at least one operational amplifier. An operational amplifier can amplify the current flowing through the heating element and allow easy evaluation by the data processing unit.

In a preferred embodiment, the driving and measuring device has a switching device. The switching device can turn on the driving and measuring device when no heating voltage applied to the heating element (follow-up phase) and turn off when a heating voltage applied to the heating element (heating or evaporation phase). But it can also be measured during a heating pulse in the evaporation phase. The measurement results of the switching device are preferably processed in the preferably common data processing unit.

• Zustandskontrolle, Überwachung und/oder Fehlerdetektion der Verdampfereinheit;
• Steuerung oder Regelung der Verdampfereinheit mit entsprechender Zeitskala;
• Ermittlung der Temperatur des mindestens einen Heizelements.

One or more of the following measures is or are preferably carried out on the basis of the measured values:

• Condition control, monitoring and / or fault detection of the evaporator unit;
• Control or regulation of the evaporator unit with appropriate time scale;
• Determining the temperature of the at least one heating element.

The electronic control unit may be configured to perform the aforementioned measures such as control, regulation, control or further measurement on the basis of the measured values.

Preferably, the at least one heating element is designed as a microsystem unit. A microsystem unit (MEMS) preferably has a very low heat capacity and / or a high thermal conductivity. As a result, the heating element has a low thermal inertia and can rapidly change its temperature and cause a particularly rapid evaporation. A rapid change in temperature is particularly preferred at high control frequencies and allows the production of very small droplets.

Fig. 1

einen schematischen Aufbau eines Inhalators;

Fign. 2,3

einen Schaltplan für eine bevorzugte Ausführungsform eines Inhalators;

Fig. 4

ein Beispiel für den zeitlichen Verlauf der Heizspannung; und

Fig. 5

ein Beispiel für den zeitlichen Verlauf der Ansteuerfrequenz.

The invention will be explained below with reference to preferred embodiments with reference to the accompanying figures. It shows

Fig. 1

a schematic structure of an inhaler;

FIGS. 2.3

a circuit diagram for a preferred embodiment of an inhaler;

Fig. 4

an example of the time course of the heating voltage; and

Fig. 5

an example of the timing of the drive frequency.

FIG. 1 shows the schematic structure of an inhaler 10, for example, an electronic cigarette product. The inhaler comprises a substantially rod-shaped or cylindrical housing 11 with a mouth end 15 and one or more air inlet openings 16. The mouth end 15 designates the end at which the user pulls for the purpose of inhalation. Between the mouth end 15 and the air inlet openings 16, an air channel is provided, which is passable by an air flow 17. When the user pulls on the mouth end 15, the inhaler 10 is subjected to a negative pressure, as a result of which an air flow 17 in the air channel is established between the air inlet openings 16 and the mouth end 15. The air inlet openings 16 may be arranged on the shell side of the housing 11. Additionally or alternatively, at least one air inlet opening 16 may be provided at the end of the inhaler 10, which is opposite to the mouth end 15.

The air stream 17 passes through an evaporator unit 20 arranged in the housing 11. The evaporator unit 20 is provided with liquid from a liquid reservoir 12 and has at least one heating element 36. The inhaler 10 comprises the liquid reservoir 12, which accommodates the liquid to be evaporated. An advantageous volume of the liquid reservoir 12 is in the range of 0.1-5 ml, preferably between 0.5-3 ml, more preferably between 0.7-2 ml or 1.5 ml. The liquid reservoir 12 preferably has a closed surface and is preferably a flexible bag. The liquid supply advantageously results from the evaporated liquid quantity.

The evaporator unit 20 is supplied with liquid from the liquid storage 12 and electrically controlled to evaporate the liquid and add it to the air flow 17 in the form of gas and / or aerosol. The evaporator unit 20 is disposed in the housing 11 in an axial heating section.

The amount of aerosol generated in the evaporator unit 20 can be changed both by changing the applied voltage and by the number of heating elements 36 used in parallel. For example, an electrical voltage may be pulsed, oscillating or applied to the heating elements 36 by pulse width modulation. The characteristic of the voltage, for example the amplitude and / or the frequency spectrum, can be advantageously adjusted over time or by adjustment of the user of the inhaler 10.

The inhaler 10 comprises an electronic unit 14, which is in communication with a power source 27 and can perform measurement, control, regulation, data processing and / or data transfer. For this purpose, the electronic unit 14 advantageously comprises an electronic control device 21, in particular a microprocessor or microcontroller. The electronic unit 14 may preferably include an interface configured to output data to the user of the inhaler 10 and / or to have data entered by the user of the inhaler 10. For example, a smoker can choose their favorite setting via their smartphone and Bluetooth connectivity and share it via social networks, make recommendations, and statistically evaluate their data and user behavior. The data preferably comprise data about the at least one heating element 36, the control frequencies, the level the liquid storage 12, the power source 27 and / or diagnostic and error data. A control of the drive frequencies on a housing 11 arranged on the control element, such as a switch or thumbwheel, is also possible.

The power source 27 may be a disposable electrochemical battery or a rechargeable electrochemical battery, e.g. a Lilon battery or a Li-battery. Using a step-up converter can be, starting from, for example, a lithium battery with 2.7-4.1 V, variable, adapted to the heating elements 36 voltages up to, for example 43 V, preferably 5-15 V, particularly preferably 2.7-15 V. , more preferably 3.6-6V, generate. The current source 27 serves to supply all active electrical components in the inhaler 10 electrically.

The inhaler 10 is preferably modular and divided into at least one consumer unit and at least one reusable unit. The evaporator unit 20 may be a replaceable cartridge, or part of such a cartridge. The main body of the inhaler 10 may be reusable. The electronic unit 14 and / or the current source 27 are preferably connected via an interface with the evaporator unit 20. The power source 27 and / or the liquid storage 12 can be arranged in a consumption unit and intended for one-way use or arranged for reusable consumption in a reusable unit in the housing 11.

The evaporator unit 20 can be used in electronic cigarette products as well as in medical inhalers. In addition to use in rod-shaped electronic cigarette products For example, the evaporator unit 20 can be used in electronic pipes, shishas or other products in which a liquid is to be evaporated from a liquid reservoir 12.

FIG. 2 Fig. 12 shows a circuit diagram for a preferred embodiment of the inhaler 10 with, for example, three heating elements 36. In other embodiments, not shown, the number of heating elements 36 is more or less than three.

The inhaler 10 includes a driving and measuring device 22, which is advantageously supplied by the electronic unit 14 by the power source 27 with electric current. The driving and measuring device 22 is controlled by the electronic control device 21. The drive and measuring device 22 comprises an operational amplifier 23, a switching device 24, at least one reference resistor 25 and at least one transistor 26. Preferably, for each heating element 36 is a reference resistor 25 connected in series (shunt) and a likewise connected in series thereto transistor 26th intended. In a preferred embodiment, the electronic unit 14 comprises the operational amplifier 23, the switching device 24, the reference resistor (s) 25 and / or the transistor (s) 26.

The electronic control device 21 is adapted to detect a pull by the consumer by means of a suitable sensor, for example by means of a pressure sensor, and consequently to control the heating elements 36 in the evaporator unit 20 in order to heat the liquid to a suitable temperature.

The electronic control unit 21 is connected to the transistors 26 and can control them independently of each other to independently control the heating elements 36 corresponding to the transistors 26. The electronic control device 21 is connected to the switching device 24 and the operational amplifier 23 as in FIG FIG. 2 shown connected to realize resistance measurements of the heating elements 36. Further sensors for the measurement of temperatures, pressures, and other variables for describing the operating state can be contained in the drive and measurement device 22 and coupled to the electronic control device 21.

The operational amplifier 23 (current shunt monitor) is connected to the control unit 21, a ground, a positive pole, the reference resistor 25 and the switching device 24 and serves, for example, to measure the voltage drop between one of the reference resistors 25 and the voltage source 27. An amplified measurement result is the operational amplifier 23 to the control unit 21 on where the data processing is done to determine the measured resistance of the corresponding heating element 36.

The switching device 24 is controlled by the control unit 21 and preferably sets one of the reference resistors 25 as the reference resistor 25 to be measured. Preferably, an electrical connection is made with the switching device 24 between the heating element 36 and the associated reference resistor 25. The switching device 24 preferably has a switch for each reference resistor 25 to be measured, in order to enable targeted measurement.

The reference resistors 25 (shunts) are preferably ohmic resistors. Each heating element 36 has a reference resistor 25 for current measurement.

The transistors 26 are preferably designed as field-effect transistors (FET) and serve to control and regulate the heating elements 36. Each heating element 36 can be controlled via an associated transistor 26.

By using a suitable circuit can be integrated in addition to the individual control of the heating elements 36 and control mechanisms. In this way, monitoring and control of the evaporator unit 20 succeeds. Measurements can be made when switching on, off and / or during a train, but with the heating voltage switched off, for example every 10-1000 ms per channel, preferably 20-500 ms, particularly preferably 250 -400 ms. By multiplexing and modulating the signals onto a carrier signal, the amount of data can be reduced.

The obtained current data of the individual heating elements 36 correlate with their resistance. By way of the known NTC or PTC behavior, the resistance clearly correlates with the temperature of the respective heating element 36. In addition to monitoring the structures, resistance and temperature information can be used to control and regulate the heating elements 36. A detailed error detection allows the detection of, for example, incorrect, too little or too much liquid or a defective heating element 36; an accurate state detection taking into account the known during the heating process thermodynamic state and the composition of the liquid is possible.

Additionally, other sensors may be included in the inhaler 10, preferably thermometers, humidity and / or pressure sensors to accurately characterize the operating state of the evaporator 20 and / or the heating elements 36.

The heating elements 36 are preferably implemented as ohmic resistors and as a microsystem unit (e.g., MEMS). The design as a microsystem unit is particularly advantageous because of its very fine structures in the micron range and the associated thermal properties. The microsystem heating elements 36 are preferably made of a semiconductor material, for example doped silicon. This is inert and has no catalytic effect and the heating element 36 can thus be made particularly small, reproducible and stable. Via the doping, a temperature-variable resistance of, for example, 0.1-20 ohms, preferably 0.5-1.5 ohms, can be set. Depending on the doping, a temperature-dependent NTC or PTC behavior of the resistance of the heating elements 36 can be achieved, i. the resistance decreases or increases with increasing temperature.

The heating elements 36 are connected to the liquid storage 12. For example, the liquid is conveyed capillary into a pore structure of the heating elements 36. If the heating elements 36 are heated to a temperature above a boiling temperature of a component of the liquid, evaporation takes place on the surface of the heating elements 36. The structure and surface of the heating elements 36 may, for example, also be based on bionic structures, such as tracheae. Through a networked heater structure of the heating elements 36, a capillary barrier for air from one side and liquid from the other side can be formed. The Heater structures are disposed along the air-to-liquid interface, and upon reaching a boiling temperature, the vaporized liquid may pass through the heater structure and be supplied to the airflow 17.

The heating elements 36 preferably each have a layer structure, wherein in each case a heating element 36 has an area of preferably 0.25-6 mm ² , particularly preferably 0.5-3 mm ² . The total area of all heating elements 36 is preferably 0.2-1 cm ² , more preferably 0.3-0.8 cm ² , and a preferred layer thickness is in the range of 3-400 μm in order to achieve an optimum ratio to the liquid volume to be evaporated, depending on the heating surface , The pores of the heater structure, for example, have a diameter between 10-100 microns, preferably between 15-50 microns.

The design of the heating elements 36 as a microsystem unit offers the possibility of influencing the amount of steam at the same applied average (evaporative) power by changing the drive frequency. This allows a particularly efficient and energy-saving steam generation by the heating elements 36. If the heating element 36 is driven at a certain frequency, ie heated, the proportion of the heating power brought into the evaporation increases with increasing frequency at the same average heating power up to an optimum. Thus, higher vapor levels are to be expected at higher frequencies as the resulting vaporization efficiency increases. The optimization of the energy input leads incidentally to a reduced power consumption.

In addition to the frequency-dependent influencing of the amount of steam, a change in the aerosol quality with the drive frequency of the heating elements 36 can furthermore be observed. As the drive frequency increases, a finer droplet size distribution can be determined, i. the distribution of droplet size shifts in favor of a smaller droplet size. This is due to a, with increasing frequency improved entry of the heat in the liquid to be evaporated. It is suitably pulsed or chosen a sufficient frequency that the heat of the heating element 36 can go into the liquid and without that losses due to too high energy input at too high a frequency (short pulse duration) or too strong cooling at too low a frequency (long Pulse duration). Particularly advantageous is this influence of the steam when the heating elements 36 are designed as a microsystem unit and are able to follow the rapid change of energy input with its Heizflächentemperatur, i. have only a low thermal inertia. In contrast to a spiral or lattice structure, the heating elements 36 have a much higher cutoff frequency.

FIG. 3 shows a circuit diagram for a preferred embodiment of the inhaler 10 with, for example, a heating element 36th

The inhaler 10 comprises a driving and measuring device 22, which is advantageously comprised by the electronic unit 14 and is supplied with electric current by the current source 27. The driving and measuring device 22 is controlled by the electronic control device 21. The driving and measuring device 22 comprises an operational amplifier 23, a switching device 24, a reference resistor 25 and a transistor 26. Preferably, for the heating element 36 in series therewith connected Reference resistor 25 and also connected in series thereto transistor 26 is provided. In one embodiment, not shown, the switching device 24 may be recessed with the use of only one heating element 36 in order to allow a simpler and more cost-effective design.

In this embodiment with only one heating element 36, the heating element 36 can be subjected to different and changeable drive frequencies. Both a superposition of different drive signals as well as a temporal change and / or modulation are conceivable in order to achieve a desired droplet size distribution.

FIG. 4 shows an example of the time course of the heating voltage U _H , which is applied to the heating element 36. The heating element 36 is heated in this embodiment, depending on the time t with pulses 32. A period 33 is subdivided into an evaporation phase 30 and a subsequent phase 31. In the evaporation phases 30, a heating voltage U _{H is applied} to the heating element 36 and allows evaporation of the liquid located on and / or on the heating element 36. During the follow-up phase 31, preferably no heating voltage is applied to the heating element 36. During a period 33, an evaporation phase 30 takes place, the length of which is defined by the duty cycle. For example, 33 different heating elements 36 can be measured sequentially during a period 33 and / or a shorter fraction of a period. With a suitable period duration 33, it is also possible to carry out a plurality of measurements, controls, controls and / or checks on different heating elements 36. In a preferred embodiment, at regular intervals to the controller, Regulation, control and / or data processing simplified.

The heating power in the form of other alternating currents, periodic and aperiodic gradients is conceivable. Of advantage is the superposition of periodic signals with different frequencies or periods 33, which allows the generation of different sized droplets. The period 33 changes in a preferred embodiment over the duration of the operation and / or is preferably adjustable. Each heating element 36 can be heated identically or differently.

FIG. 5 shows an example of the timing of the drive frequency f, which is applied to the heating element 36. The drive frequency f increases over the course of time t over the duration 42. The duration 42 can be given for example by the discharge duration of the liquid reservoir 12. The broken time axis makes it clear that the emptying time in this example should not be limited to the illustrated number of five trains 10. In this example, the drive frequency f is constant over a train 40. The heating power to the heating element 36 follows, for example, during a train to in FIG. 4 illustrated course. The individual trains 40 are interrupted by pauses 41 in which measurement, control, regulation and / or control of the operating state can take place. From train 40 to train 40, the driving frequency f increases over time t and, over time t, allows ever smaller droplets to be generated, for example to homogenize smoking experience and nicotine administration. Depending on the application, other temporal characteristics of the frequency are conceivable.

Claims (16)

An evaporator unit (20) for an inhaler (10) having an electronic control device (21) and at least one heating element (36), wherein the evaporator unit (20) is arranged to evaporate liquid supplied from a liquid reservoir (12) and the evaporated liquid from a stream of air flowing through the evaporator unit (20) is received,
characterized in that
the electronic control device (21) is arranged to heat the at least one heating element (36) with a variable control frequency. Evaporator unit (20) according to claim 1, characterized in that the electronic control device (21) is adapted to heat the at least one heating element (36) with a plurality of different control frequencies. An evaporator unit (20) according to any one of the preceding claims, characterized in that the evaporator unit (20) comprises a plurality of heating elements (36) and the electronic control device (21) is adapted to heat different heating elements (36) at different control frequencies. An evaporator unit (20) according to claim 3, characterized in that the electronic control device (21) is adapted to control the drive frequency of the plurality of heating elements (36) so that a multimodal Droplet size distribution of the evaporated liquid results. Evaporator unit (20) according to one of the preceding claims, characterized in that the electronic control device (21) is adapted to change the driving frequency of the at least one heating element (36) over the discharge duration of the liquid reservoir (12). Evaporator unit (20) according to claim 5, characterized in that the electronic control device (21) is adapted to increase the driving frequency of the at least one heating element (36) with progressive emptying of the liquid reservoir (12). Evaporator unit (20) according to one of the preceding claims, characterized in that the electronic control device (21) is adapted to change the driving frequency of the at least one heating element (36) over the duration of a train. Evaporator unit (20) according to any one of the preceding claims, characterized in that the electronic control device (21) is adapted to set the drive frequency of the at least one heating element (36) so as to give a desired droplet size of the evaporated liquid of, for example ≤ 5 microns , Evaporator unit (20) according to one of the preceding claims, characterized in that the electronic control device (21) is adapted to a driving frequency of the at least one heating element (36) of at least 10 Hz and preferably set the highest 20 kHz. Evaporator unit (20) according to one of the preceding claims, characterized in that a drive and measuring device (22) is provided which is adapted to measure the resistance of the at least one heating element (36). Evaporator unit (20) according to claim 10, characterized in that the drive and measuring device (22) has at least one with the at least one heating element (36) connected in series reference resistor (25). Evaporator unit (20) according to claim 10 or 11, characterized in that the drive and measuring device (22) has at least one operational amplifier (23). Evaporator unit (20) according to one of claims 10 to 12, characterized in that the drive and measuring device (22) has at least one switching device (24). Evaporator unit (20) according to any one of claims 10 to 13, characterized in that on the basis of the measured values of the drive and measuring device (22) one or more of the following measures are performed: - Condition control, monitoring and / or error detection of the evaporator unit (20); - Control or regulation of the evaporator unit (20); - Determining the temperature of the at least one heating element. Evaporator unit (20) according to one of the preceding claims, characterized in that the at least one heating element (36) is designed as a microsystem unit. Method for controlling an evaporator unit (20) for an inhaler (10) having an electronic control device (21) and at least one heating element (36), wherein the evaporator unit (20) is arranged to evaporate liquid supplied from a liquid store (12), and the vaporized liquid is taken up by an air stream flowing through the evaporator unit (20), characterized in that
the electronic control device (21) heats the at least one heating element (36) with a variable control frequency.

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