EP3997961B1 - Household microwave oven with mode variation device - Google Patents

Description

The invention relates to a household microwave appliance, having a cooking chamber that can be charged with microwaves, at least one mode variation device that is set up to change a field distribution of the microwaves in the cooking chamber, and at least one microwave leakage sensor for detecting microwave leakage radiation escaping from the cooking chamber , wherein the domestic microwave appliance is set up to vary setting values of the at least one mode variation device. The invention also relates to a method for operating a domestic microwave appliance in which microwaves are applied to a cooking chamber and setting values of at least one mode variation device that is set up to change a field distribution of the microwaves in the cooking chamber are varied. The invention can be applied particularly advantageously to stand-alone microwave devices and to combination devices such as ovens with an additional microwave function.

It is known for microwave household appliances to measure microwave leakage radiation emerging from a cooking chamber in order to protect a user. The field strengths of the microwave radiation are measured inside the device housing or on a door closing the cooking chamber and checked for compliance with a limit value. If this limit value is exceeded, an appliance malfunction can be assumed and the operation of the microwave household appliance is stopped for safety reasons.

For example disclosed EP 2 148 553 A1 a method for detecting the microwave leakage radiation by means of a microwave sensor device arranged between a cooking chamber wall and a housing. A time profile of the detected microwave leakage radiation is stored for a time interval by a memory device that is connected to the microwave sensor device and is checked for threshold value violations. It is also described how one or more microwave sensors are placed in areas of openings in the cooking chamber wall.

EP 2 152 047 A1 discloses a safety device for detecting leakage radiation in a cooking appliance with a microwave function and a cooking appliance with such a function safety device. The safety device comprises at least one microwave sensor, which comprises a probe in which an alternating current can be induced by leakage radiation, or which is suitable for tapping off alternating currents that are induced in other objects by leakage radiation. The sensor also includes a fuse through which the alternating current is passed. Finally, the safety device includes a device that is suitable for switching off a microwave source of the cooking appliance as soon as the safety device trips.

DE 2 029 559 A1 discloses a safety device against the escape of radiation from microwave devices, using at least one microwave-responsive gas tube, which is arranged in the vicinity of the zone of a possible emission of radiation and is electrically connected in the control circuit of a controlled semiconductor diode, which in turn is in the supply circuit of a relay, the excitation of which causes the electrical supply circuit of a microwave generator to open.

DE 195 37 755 A1 discloses a microwave oven, in particular for a laboratory, with a heating chamber surrounded by a housing into which microwaves can be coupled and which is accessible through a closable access opening, with a microwave sensor being arranged in the area of a gap in the housing emanating from the heating chamber in such a way that when microwave radiation exceeding a certain value enters and/or passes through the gap, the sensor activates the emission of a warning signal or switches off the microwave exposure of the heating chamber.

Furthermore, it is known that a cooking space can be considered approximately as a cavity resonator. Therefore, there is a finite number of microwave field distributions (also referred to as "modes" or "mode images") that are determined by the cooking chamber geometry. Typical microwave field distributions are spatially inhomogeneous and have one or more sub-areas with increased microwave power or energy (so-called "hotspots"). The transition from one mode image to the other typically does not occur continuously, but is largely discrete.

To measure the field distribution of microwaves in a cooking chamber of a microwave household appliance, intrusive methods have been used to date, in which microwave fields are measured directly in the cooking chamber. This can either be on direct electrical Way through receiving antennas or through evaluation of a change (e.g. warming) of introduced indicator objects. For example disclosed U.S. 2008/0302958 A1 an indicator object in the form of a so-called "lightboard" with several distributed light sources that can be excited to glow by microwaves. In any case, however, an object (sensor, indicator object) is brought into the interior of the cooking chamber.

In today's microwave household appliances, a rotary antenna, via which microwaves are radiated into the cooking chamber, or a mode stirrer is rotated at a fixed, predetermined angular velocity in order to equalize the microwave field distribution over time in an item to be heated and thus to avoid static hotspots in the item. This leads to an angle-dependent change in the microwave field distribution in the cooking chamber. In the case of microwave generation by a magnetron, the rotation of a rotating antenna can also change the operating frequency of the magnetron due to what is known as "load pulling", which can generally also lead to a drastic change in the mode image. Additionally or alternatively, a turntable on which the item to be heated is placed can be rotated at a fixed, predetermined angular speed.

Fig.7 shows a schematic of a dependence of a microwave field distribution or a mode image on an angular position or an angle of rotation φ of a rotating antenna in degrees for a correspondingly equipped microwave household appliance. In this example, the rotary antenna is used in the rotary range from ϕ = [0°; 150°] produce a mode image #1 in the cooking chamber. This is equivalent to the fact that the distribution of the microwave radiation and thus the heat distribution in many goods remains practically unchanged in the period of time required to travel through this angular range. Another mode image #2 occurs in the angular range φ=[150°; 190°] up. A mode image #3 exists for a comparatively short portion of a rotation of the rotating antenna, which only exists in the range φ=[190°; 205°] is present, etc. This makes it clear that several different mode images - and the associated heating patterns in the food - are present during one rotation of the antenna. These do not necessarily occur equidistantly in relation to the angle of rotation of the rotary antenna, which significantly increases the risk of hotspots forming in the food to be cooked, since the heat distribution then generated acts on the food for a disproportionately long time for certain angular ranges.

EP 0 839 435 A1 discloses a domestic microwave oven according to the preamble of claim 1.

It is the object of the present invention to at least partially overcome the disadvantages of the prior art and in particular to provide an improved possibility of heating food by means of microwaves.

This object is solved according to the features of the independent claims. Advantageous embodiments are the subject matter of the dependent claims, the description and the drawings.

The object is achieved by a household microwave appliance, having a cooking chamber that can be acted upon by microwaves, at least one mode variation device that is set up or provided to change a field distribution of the microwaves in the cooking chamber, and at least one microwave leakage sensor for detecting leaks from the cooking chamber escaping microwave leakage radiation, wherein the household microwave appliance is set up to vary setting values of the at least one mode variation device and to define at least one operating point of the at least one mode variation device based on the quantity of measurement data of the detected microwave leakage radiation resulting from the variation.

This domestic microwave appliance advantageously makes it possible, by means of a cost-effective design and within a very short time, to determine which setting values of the at least one mode variation device have identical or practically identical microwave field distributions or mode images. Analogously, it is made possible to systematically determine the setting parameters belonging to all possible mode images. This in turn can advantageously reduce the total available basic set of setting values of the at least one mode variation device to a subset of operating points that is significantly smaller than their actual control, with the operating points being able to be selected in particular in such a way that each operating point leads to or belongs to a different mode image. As a result, temporal inequalities in the generation of different mode images can be avoided in a particularly simple manner. There is also the advantage that mode images can be assigned to setting values for an empty cooking chamber as well as for basically any load located in the cooking chamber. The assignment of mode images to setting values is therefore adapted to the actual loading of the cooking chamber. There is no need to wait for a reaction (eg a temperature increase that can be measured by means of a thermal camera) of the item to which the microwaves are to be applied, which enables a particularly rapid assignment. In addition, advantageously, no microwave sensors or indicator objects need to be arranged in the cooking space, which allows for a particularly inexpensive and simple construction. The underlying idea can also be seen in such a way that by measuring a microwave leakage radiation as a function of settings that change the field image in the cooking chamber, a conclusion can be drawn about the corresponding mode image in the cooking chamber. This in turn allows operating parameters to be adjusted in order to operate the microwave device in an improved manner. In other words, operating parameters, in particular operating points, of an operating sequence of a domestic microwave appliance can be adjusted depending on a measurement of a change in the leakage radiation.

The domestic microwave appliance has a cooking chamber with a loading opening, typically on the front, which can be closed by means of a microwave-tight door. The household microwave appliance also has a microwave generator such as a magnetron or a semiconductor-based microwave generator. The microwave generator is advantageously inverter controlled. The microwaves generated by the microwave generator can be coupled into the cooking chamber, e.g. directly or via a wave guide. In a further development, the domestic microwave appliance has a rotary antenna for coupling the microwaves into the cooking chamber.

The household microwave device can be an independent microwave device, the energy for the treatment of items located in the cooking space is provided only by the microwaves. However, the domestic microwave appliance can also be a combination appliance which, in addition to the microwave generator, has at least one other energy source for treating the food in the cooking chamber, e.g. a heat source such as at least one resistance heating element. The combination appliance can be, for example, an oven with additional microwave functionality or a microwave appliance with an additional oven function.

The cooking space is delimited by a cooking space wall, which may have leakage openings such as lead-through openings, for example for cables, rotary antennas, etc., through which the microwave radiation leaks through the cooking space wall and into the appliance can. “Microwave leakage radiation” is understood to mean microwave radiation escaping from the cooking chamber, in particular when the cooking chamber door is closed.

A mode variation device can be understood in particular as a device that can be set on the appliance side and is suitable or provided for bringing about noticeably different field distributions of the microwaves in the cooking chamber as a function of its setting values. Two or more setting values thus lead to two or more different microwave field distributions. The microwave field distribution in the cooking chamber can therefore be changed by changing the setting values. It cannot be ruled out that two or more different setting values lead to the same or practically the same microwave field distributions or mode images. In individual cases that depend, for example, on the type of loading of the cooking chamber, it is also possible that all setting values of at least one mode variation device lead to the same or practically the same microwave field distributions.

The type of at least one microwave leakage sensor is not limited in principle. Consequently, there can also be several leakage sensors that are of different or the same type (e.g. detection method). If there are several leakage sensors, a spatially resolved detection of the microwave leakage radiation is made possible. However, in order to determine the switchover points, it is also possible to determine only the strength of the microwave leakage radiation that is emitted overall.

If several mode variation devices are present and/or the setting values of several setting parameters can be varied in a mode variation device, the setting values of the at least one mode variation device can be varied, for example, by setting all possible combinations of the setting values of all setting parameters. Measurement data can then correspond to multidimensional tuples of setting values of different setting parameters.

An “operating point” can in particular be understood as a specific value or, in the multidimensional case, a specific value tuple of the at least one mode variation device to which the at least one mode variation device can be set or is set in a targeted manner in order to operate the household microwave appliance.

• einen Einstellbereich mindestens einer Modenvariationsvorrichtung zu durchfahren;
• für die jeweiligen eingestellten Werte ("Einstellwerte") des durchfahrenen Einstellbereichs eine Stärke der Mikrowellen-Leckagestrahlung zu messen; und
• aus dem sich ergebenen Kurvenverlauf mindestens eine charakteristische Eigenschaft zu bestimmen, aus denen sich der mindestens eine Arbeitspunkt festlegen lässt.

In one configuration, the household microwave appliance is set up to determine the switchover points

• to run through an adjustment range of at least one mode variation device;
• to measure a strength of the microwave leakage radiation for the respective adjusted values ("adjustment values") of the adjustment range traversed; and
• to determine at least one characteristic property from the resulting curve, from which the at least one operating point can be determined.

In this way, the operating points can advantageously be determined in a particularly robust and rapid manner. Passing through an adjustment range includes, in particular, setting several adjustment values, in particular all adjustment values, of a possible or predetermined value range of at least one adjustment parameter, which is referred to as the “adjustment range”, in chronological succession. Characteristic properties are to be understood in particular as points or areas of the measured curve from which the operating points can be determined particularly clearly or reliably.

In a further development, a change in a mode image can be determined or ascertained using at least one characteristic property, ie such a point correlates with a change in a mode image.

In a further development, the retention of a mode image can be determined or ascertained based on at least one characteristic property, ie such a point correlates with a stable mode image.

Characteristic properties can occur at points or areas of the curve where there is a particularly strong change in the measured microwave strength. However, this is not mandatory, and characteristic properties that are indicative of a change in the model image can, for example, also be derived from a wide range of curves (eg, an angular range of 100° or greater). It is thus possible for a continuous transition between different mode images while passing through an adjustment range of at least one mode variation device occurs. This is then characterized, for example, by a long flank with an almost constant slope in the course of the curve.

In one configuration, the at least one characteristic property includes the presence of switchover points at which a significant change in the field distribution occurs, and that the household microwave appliance is set up to define operating points of the at least one mode variation device such that they lie outside the switchover points . This ensures that different mode images are reliably generated.

The fact that a significant or strong change in the field distribution occurs can include, in particular, that a change between different mode images takes place at or in the area of a switching point. However, a mode image remains at least largely the same between two adjacent switching points, e.g. with regard to the number and spatial position of hotspots. Fluctuations in a mode image between adjacent switching points can then include, for example, changes in the relative field strength and/or extent of the hotspots. The switching values are therefore setting values of the at least one mode variation device, in which there is a noticeable change in the field distribution, in particular a rapid change between two mode images.

The fact that an operating point is outside of the switchover points includes, in particular, that there is a sufficient value difference between the operating point on the one hand and the closest or neighboring switchover points (e.g. a next smaller switchover point and a next larger switchover point).

This advantage is achieved in a particularly reliable manner by the design in which the operating points lie in the middle between adjacent switchover points.

In one configuration, the switchover points are determined from turning points of the curve. This can in particular be implemented in such a way that the turning points associated with switching points are determined from extreme points of a first derivation of the curve of the measured values.

In an alternative or additional configuration, the characteristic properties include extreme points and/or terrace points of the curve and the domestic microwave appliance is set up to define the extreme points and/or terrace points as operating points of the at least one mode variation device. This has the advantage that the operating points can be determined directly from points on the curve or derivatives thereof and not indirectly from a relationship to switchover points.

In general, characteristic properties of the curve, such as switching points, can be determined with the help of standard curve evaluations or curve discussions. In this way, characteristic points can be determined as zeros, zeros of a slope, maxima/minima, maxima/minima of a slope, turning points, terrace points, etc. of the measurement curve or any derivatives.

In one configuration, the domestic microwave appliance is set up to redetermine the operating points at the beginning of each microwave operating sequence, e.g. a microwave cooking sequence. This determination can also be referred to as an "initial scan". A particularly accurate and reliable determination of the operating points is achieved in this way. Typically, only a few seconds are required for an initial scan.

Alternatively, the operating points can be carried out once for the respective operating sequences and/or cooking parameters such as a type of food to be cooked (e.g. pizza) etc. and then stored and subsequently retrieved from a data memory for the same or similar operating sequences and/or cooking parameters. This has the advantage that an initial determination of the operating points can be dispensed with in many cases. In a further development, the operating points are only determined every nth time for the same or similar operating sequences and/or cooking parameters. This has the advantage that changes in the assignment of mode images to setting values can be taken into account.

In a further development, exactly one operating point is defined for a specific mode image, ie several operating points are not defined for each mode image. A further development is that no operating point is defined for at least one mode image, for example because the adjacent switchover points are too close together.

In a further development, the domestic microwave appliance is set up to adjust the operating points with equal time shares during a microwave operating sequence. A particularly uniform microwave field distribution is thus achieved over the duration of the microwave operating sequence. This development can be implemented, for example, by setting the desired operating points cyclically one after the other and holding them for the same period of time.

In one configuration, the at least one mode variation device has or is at least one device from the group consisting of rotary antenna, mode stirrer (also referred to as “stirrer”), turntable and/or microwave generator. These devices have the advantage that their adjustment can result in a particularly noticeable change in the field distribution. At least the turntable, the rotary antenna and the (rotatable) mode stirrer are even specifically intended to change the field distribution, typically by changing their rotary or angular position.

The rotary antenna, the mode stirrer and the rotary plate have, as mode-influencing setting parameters, in particular at least one rotary angle φ that can be adjusted within a rotary angle range. The angle of rotation ϕ can be adjusted continuously or in steps (e.g. in increments of Δϕ = 1°, 5° or 10°) within the angle of rotation range. The usable angle of rotation range can e.g. [0°; 180°] or [0°; 360°]. In particular, the rotary antenna can be rotated. However, depending on the design, the rotary antenna and/or the mode stirrer can also include other mode-influencing setting parameters such as their height position along their axis of rotation and/or a relative angular position of two wings or blades to one another about an axis of rotation of the rotary antenna.

The microwave generator, in particular if it is in the form of a semiconductor-based microwave generator, has the microwave frequency of the microwaves generated thereby as a mode-influencing setting parameter. The microwave frequency can be in a range f=[2.4 GHz; 2.5 GHz] can be adjusted continuously or in steps (eg in increments of Δf=0.01 GHz or 10 MHz, 5 MHz or 1 MHz). If more than one feed point for microwaves is used in the cooking chamber, the phase shift between the feed paths can also be used as a setting parameter.

In principle, leakage radiation can be measured at any point with the door closed. In one configuration, the at least one microwave leakage sensor is set up to measure microwave leakage radiation passing through a cooking chamber wall. In an additional or alternative configuration, the at least one microwave leakage sensor is set up to measure microwave leakage radiation passing through a door gap between a housing flange and a door closing the cooking chamber.

In one configuration, the at least one microwave leakage sensor includes or has at least one sniffer line laid or present outside the cooking chamber. A "sniffer line" is understood to mean an electrically conductive, in particular metallic, line (e.g. a strip conductor, wire, cable, etc.) in which electrical currents can be induced by microwaves. At least one sniffer line is connected to an evaluation circuit of the microwave leakage sensor, the evaluation circuit being designed for the quantitative measurement of a variable of alternating currents induced in the at least one sniffer line connected to it. The sniffer line can advantageously have a great length and be routed in many ways in the household microwave appliance. This in turn has the advantage that a sniffer line can be used to monitor large areas of the household microwave appliance outside the cooking chamber for microwave leaks, which means that the number of microwave leak sensors can be reduced compared to microwave sensors that measure only selectively. In particular, electric currents from different leakage points can be induced in a sniffer line at the same time, so that the sniffer line has a site-integrating effect. It has been shown that the switchover points can advantageously also be determined with high accuracy in this case.

In a development, a sniffer line can be used, which leads past all selected leakage points. This achieves the advantage that the switching points can be determined using only a single sniffer line.

A further advantage of the sniffer line is that the evaluation circuit can be arranged remotely from sources of radiation leakage in areas of the household microwave appliance that are subject to little thermal, chemical and/or electromagnetic stress. The sniffer lines On the other hand, they are noticeably more resistant and can easily pass through thermally and chemically stressed (e.g. hot and/or humid) areas.

The evaluation circuit is set up in particular to determine the strength of a microwave-induced current induced in the at least one sniffer line, which is a measure of the strength of the leakage or leakage rate. The evaluation circuit can have one or more electrical and/or electronic components and/or functional units such as capacitors, resistors, processors (e.g. microcontrollers, ASICs, FPGAs), rectifiers, A/D converters, etc.

In one development, an evaluation circuit can be connected to precisely one sniffer line and therefore only evaluate this sniffer line or determine the strength of a microwave-induced current in this sniffer line. In an alternative development, an evaluation circuit is connected to a number of sniffer lines. In this case, several sniffer lines can be evaluated together by the evaluation circuit. The joint evaluation makes it possible to provide a particularly simple and inexpensive detection device. The covered or detectable detection area can also be additionally enlarged as a result, so that the evaluation unit can respond even earlier in the event of a mode switchover. In a further development, several sniffer lines can be brought together electrically and connected to the evaluation circuit at a common node. Alternatively, several sniffer lines can be evaluated individually using the same evaluation circuit, e.g. at different times or in parallel. The individual evaluation enables an improved localization of one of the mode changes. Alternatively, the household microwave device can have several evaluation circuits, each connected to a sniffer line, for example. These can be distributed over the household microwave oven.

In one development, at least one sniffer line has or performs at least one additional function, at least in sections. In particular, an electrical line that is already present for another purpose can also be used as a sniffer line. A line having the at least one further function would therefore also be present in the device if it were not used to detect the microwave leakage. So the advantage is achieved that for this sniffer line no separate electrical line is needed to detect leakage of microwaves. This in turn advantageously enables a particularly cost-effective construction.

In a further development, the at least one further function comprises a power supply function for supplying electrical energy to at least one electrical consumer of the household microwave appliance and/or a data transmission function. In other words, at least one sniffer line is also a power supply line for at least one electrical consumer and/or a data transmission line. The current used to operate the load ("load") can be direct current or alternating current. Such sniffer lines have the advantage that they are typically of the same design over their length and/or have a defined, particularly low electrical resistance. As a result, a particularly precise and reliable detection or evaluation of the alternating currents induced therein by the microwave can be achieved. A further advantage consists in the fact that such sniffer lines typically connect functional units to one another which are located in areas of the household microwave appliance which are subject to little thermal and/or chemical and/or electromagnetic stress. Consequently, the evaluation circuit can also be arranged on the end sections of the sniffer lines in these areas with little or no adaptation effort.

In principle, however, it is also possible to use other electrically conductive components of the household microwave device that, for example, fulfill a mechanical function as sniffer lines, in particular elongated components such as struts, fastening wires, etc. In this case, it may be necessary to separate the components with additional line sections in E.g. to lengthen the form of wires to the evaluation circuit, so that the evaluation circuit can be accommodated in a room area with little thermal and/or chemical stress and/or to enable an electrical connection to the evaluation circuit. The additional line sections can be soldered etc. to the electrically conductive components.

In a further development, the at least one electrical load includes a heating element, a light generating device, a motor, a power supply device and/or electronics (eg a control board), etc. The heating element can For example, be a resistance heating element for heating the cooking chamber or an evaporator. The light-generating device can, for example, be or have a lamp or other lighting device, for example for lighting the cooking chamber, operating elements or decorative elements. The motor can be a motor for moving a rotary antenna, a skewer, a fan, a flap (eg a vapor flap), a turntable, a cooking chamber door, a pump, etc., for example. In principle, however, the at least one electrical consumer is not limited to this and can be any other consumer such as a control panel or component thereof, a camera, a communication module (eg a WLAN or Ethernet module), etc.

In one embodiment, at least one sniffer line has at least one data transmission function and is connected to at least one functional unit of the device that is not an electrical consumer, e.g. to a sensor, a reed contact or other magnetic switch, etc. This may be the case, for example, if the power-consuming functional unit is a sensor, e.g. a temperature sensor, specifically a temperature sensor. However, there are also sensors that represent electrical loads, for example oxygen sensors in the form of lambda probes that have a heating element. If the functional unit that is not an electrical consumer is a reed contact, in one variant this could only switch signal levels (e.g. a microcontroller evaluating the switching state), in another variant e.g. an excitation current of a relay coil. The wiring of both reed contacts would be suitable sniffer lines.

An electrical line can also be set up or used as a sniffer line, which is used both for power supply and for data transmission, e.g. by modulating a power supply signal with a data signal. In principle, an electrical load can be connected both to a dedicated power supply line and to a dedicated data line, one or more of which can serve as a sniffer line.

In one development, at least one sniffer line has at least one section whose shape and/or position is (only) determined by the function of the sniffer line for detecting the microwave leakage radiation. So this section does not contribute to the implementation of the further function of the sniffer line or can even (if typically only slightly) have a negative effect on it. The advantage of such a section is that it is shaped and/or routed for improved detection of microwave leakage radiation and thus enables its particularly reliable detection. The section can be placed, for example, through or around areas of openings in a cooking chamber wall. The increased length increases its ohmic resistance, but this may have negligible or virtually no effect on its power-carrying and/or data-transmission function. The section can also have an intricate (eg meandering) shape.

In one development, at least one sniffer line has a length of at least 800 mm, in particular at least 1000 mm, in particular at least 1500 mm, in particular at least 2000 mm. Such a long length has the advantage that as many/large areas as possible inside the housing of the household microwave device can be covered with a sniffer line and locally distributed sources of radiation leakage can be sensed or detected with a small number of sniffer lines.

However, it is also possible for the microwave detection device to have at least one sniffer line which has no other signal-conducting (i.e. no current and/or data-conducting) function, in particular no other function. Such a sniffer line is therefore only installed for the purpose of detecting a microwave-based induction. The provision of a sniffer line has the advantage that it can be routed in a particularly variable manner in the device, e.g. because it is functionally connected to the evaluation circuit at one end, but the other end is a freely positionable end. Such a sniffer line can be, for example, a wire, a cable, a conductor track applied to a substrate, etc. The household microwave appliance can consequently be designed in such a way that the evaluation circuit is connected to at least one sniffer line which also fulfills at least one further function and/or to at least one sniffer line without a dedicated further function.

In a further development, at least one evaluation circuit is an independent component of the domestic microwave appliance, is arranged separately from a control device and is connected to the control device via at least one signal line is. This achieves the advantage that at least one evaluation circuit can be positioned particularly flexibly in the household microwave appliance. The evaluation circuit can provide information about the strength of the microwave-induced alternating current as an output signal or output information. The output signal or information can be in analog or digital form. The output signal or output information can be used by the control device to assess whether at least one action related to the strength of the leak rate should be triggered, as will be described in more detail below.

In one configuration, the evaluation circuit is integrated into a control device of the household microwave appliance. This achieves the advantage that the evaluation circuit is accommodated in a spatial area which is particularly well suited or provided for accommodating electrical and/or electronic components. This is particularly advantageous if the control device is accommodated in a specially protected compartment, division or compartment that is, for example, thermally insulated and/or ventilated to cool the evaluation unit. A further advantage is that the signal paths between the evaluation circuit and the control device are particularly short and therefore not susceptible to interference. In particular, the output signals or output information can be routed directly to a processor (e.g. a microcontroller, FPGA, ASIC, etc.) of the control device. Another advantage is that typically several electrical lines (power supply lines and/or data lines) lead from the control device to loads, so that the positioning of the evaluation circuit on the control device enables particularly short distances from the at least one sniffer line to the evaluation circuit.

It is a further development that the evaluation circuit is integrated into the control device of the household microwave oven in such a way that it is an independent structural unit (e.g. has its own circuit board or circuit board) which is attached to the circuit board or circuit board of the control device, e.g. by a soldered connection (s), a slot, etc.

In a further development, the evaluation circuit is integrated into the control device of the domestic microwave appliance in such a way that a printed circuit board of the control device is equipped with the components of the evaluation circuit.

In one development, the evaluation circuit is functionally integrated into the control device to the extent that a processor of the control device also evaluates the sniffer line(s). A separate or separately manufactured evaluation circuit is then advantageously no longer required.

In one configuration, the evaluation circuit is connected to the at least one sniffer line via at least one conductor track on a printed circuit board of the control device. A particularly simple, space-saving and robust connection of the evaluation circuit to the at least one conductor track is thus made possible. In particular, a sniffer line is routed to the circuit board and connected there to the conductor track, e.g. by soldering points, clamps, plugs, etc.

In one configuration, the evaluation circuit is connected to the at least one sniffer line via a coupling capacitor. This achieves the advantage that the sniffer line is galvanically isolated from the evaluation circuit, but AC signals can be transmitted through the coupling capacitor. The coupling capacitor thus achieves DC voltage isolation between the sniffer line and the evaluation circuit. In particular, one connection of the coupling capacitor is electrically connected to at least one sniffer line and the other connection is electrically connected to the evaluation circuit. The coupling capacitor can also represent part of the evaluation circuit.

In one configuration, the coupling capacitor is a component of a high-pass filter. In this way, the advantage is achieved that the comparatively high-frequency, microwave-induced alternating currents (which, for example, can have a frequency in the microwave frequency range) are let through to the evaluation circuit, while low-frequency alternating currents, such as those typically used for powering a consumer with alternating current (e.g. with a mains frequency of 50 Hz), cannot be let through. This prevents the measuring signal of the microwave leakage radiation from being disturbed by electrical currents in the sniffer lines with lower frequencies, which in turn increases the evaluation accuracy.

In one development, the coupling capacitor forms the high-pass filter together with an ohmic resistor that is, in particular, grounded. The resistance can be a component of the evaluation circuit, e.g. its input resistance.

aufweist, wobei R dem Widerstandswert des ohmschen Widerstands und f_u einer unteren Grenzfrequenz des Hochpassfilters entspricht.In one configuration, the high-pass filter additionally has a resistor connected to the coupling capacitor, in particular an input resistor, and the coupling capacitor has a capacitance of size C (Eq. 1): $$C=\frac{1}{2\cdot \pi \cdot R\cdot f_{\mathrm{and}}}$$

has, where R corresponds to the resistance value of the ohmic resistor and f _u corresponds to a lower limit frequency of the high-pass filter.

This formula results from a complex transfer function T, which reflects the ratio of a voltage U ₂ passed on by the high-pass filter to the voltage U ₁ present on the monitored or tapped sniffer line (Eq. 2): $$\underset{\_}{T}=\frac{\underset{\_}{{\mathrm{<figure-callout\; id="2"\; label="u"\; filenames="imgf0005.png"\; state="\{\{state\}\}">u</figure-callout>}}_2}}{\underset{\_}{{\mathrm{<figure-callout\; id="1"\; label="u"\; filenames="imgf0001.png,imgf0004.png"\; state="\{\{state\}\}">u</figure-callout>}}_1}}=\frac{1}{1-\frac{i}{2\pi \cdot f\cdot R\cdot C}}$$

Since only the absolute value of the transfer function (and not its phase position) is of interest here, it follows (Eq.3): $$\left|\underset{\_}{T}\right|=\frac{\left|\underset{\_}{{\mathrm{<figure-callout\; id="2"\; label="u"\; filenames="imgf0005.png"\; state="\{\{state\}\}">u</figure-callout>}}_2}\right|}{\left|\underset{\_}{{\mathrm{<figure-callout\; id="1"\; label="u"\; filenames="imgf0001.png,imgf0004.png"\; state="\{\{state\}\}">u</figure-callout>}}_1}\right|}=\frac{1}{\sqrt{1+\frac{1}{{\left(2\pi \cdot f\cdot \mathrm{<figure-callout\; id="2"\; label="R\; \cdot \; C"\; filenames="imgf0005.png"\; state="\{\{state\}\}">R</figure-callout>}\cdot C\right)}^2}}}$$

bzw. ca. 70,7% der Amplitude des Originalsignals U ₁ beträgt bzw. das Originalsignal U ₁ um diesen Faktor abgeschwächt vorliegt. Es folgt daraus für den Betrag der Übertragungsfunktion $$\left|\underset{\_}{T}\right|=\frac{1}{\sqrt{2}}=\frac{1}{\sqrt{1+\frac{1}{{\left(2\pi \cdot f\cdot R\cdot C\right)}^2}}}$$

For the selection and dimensioning of the coupling capacitor C, it was assumed that a lower limit frequency f _u of the resulting high-pass filter is as high as the signal to be measured requires (the measurement signal has a typical microwave frequency of 915 MHz or 2.45 GHz). The lower limit frequency f _u is set so that the transmitted voltage U ₂ only $1/\surd 2$

or about 70.7% of the Amplitude of the original signal U ₁ is or the original signal U ₁ is present weakened by this factor. It follows from this for the absolute value of the transfer function $$\left|\underset{\_}{T}\right|=\frac{1}{\sqrt{2}}=\frac{1}{\sqrt{1+\frac{1}{{\left(2\pi \cdot f\cdot \mathrm{<figure-callout\; id="2"\; label="R\; \cdot \; C"\; filenames="imgf0005.png"\; state="\{\{state\}\}">R</figure-callout>}\cdot C\right)}^2}}}$$

This results in the advantageous size of the capacitance value C of the coupling capacitor according to Eq.

The output or calculation values determined by the evaluation circuit, which represent a measure of the strength of the microwave leakage, can be used, for example, by the control device or another data processing device to determine the switchover and operating points.

In general, the microwave leakage radiation can also be measured indirectly, for example by quantifying secondary effects in frequency ranges that differ from the microwave frequency, e.g. at typical frequencies of 20 kHz to 100 GHz relevant for EMC (electromagnetic compatibility), which can also be discharged on the power line .

• ein Garraum mit Mikrowellen beaufschlagt wird,
• Einstellwerte mindestens einer Modenvariationsvorrichtung, die dazu eingerichtet ist, eine Feldverteilung der Mikrowellen in dem Garraum zu ändern, variiert werden,
• für die verschiedenen Einstellwerte der mindestens einen Modenvariationsvorrichtung die aus dem Garraum austretende Mikrowellen-Leckagestrahlung gemessen wird und
• anhand der dabei detektierten Mikrowellen-Leckagestrahlung Arbeitspunkte der mindestens einen Modenvariationsvorrichtung festgelegt werden.

The object is also achieved by a method for operating a household microwave oven in which

• a cooking chamber is charged with microwaves,
• Setting values of at least one mode variation device that is set up to change a field distribution of the microwaves in the cooking chamber are varied,
• the microwave leakage radiation emerging from the cooking chamber is measured for the various setting values of the at least one mode variation device and
• Working points of the at least one mode variation device can be defined on the basis of the microwave leakage radiation detected in the process.

The method can be designed analogously to the household microwave device and has the same advantages.

In one embodiment, switching points are determined on the basis of the detected microwave leakage radiation, at which there is a noticeable change in the field distribution of the microwaves inside the cooking chamber. Operating points of the at least one mode variation device are set so that they lie outside the switching points.

In order to carry out the method, the domestic microwave appliance can have a correspondingly set up, e.g. programmed, data processing device. The data processing device can be functionally integrated into a control device of the household microwave appliance, i.e. the control device can be set up to run the method described above.

Fig.1

zeigt als Schnittdarstellung in Seitenansicht ein Haushalts-Mikrowellengerät;

Fig.2

zeigt in Draufsicht eine Steuereinrichtung des Haushalts-Mikrowellengeräts aus Fig.1 mit einer Auswerteschaltung;

Fig.3

zeigt eine alternative Auswerteschaltung für das Haushalts-Mikrowellengerät aus Fig.1;

Fig.4

zeigt eine Auftragung eines durch den Mikrowellen-Leckagesensor des Haushalts-Mikrowellengeräts aus Fig.1 gemessenen Messwerts, der eine Stärke der Mikrowellen-Leckagestrahlung repräsentiert, gegen einen Drehwinkel der Drehantenne des Haushalts-Mikrowellengeräts aus Fig.1;

Fig.5

zeigt eine Auftragung eines Betrags einer Ableitung der aus Fig.4 bestimmten und zusätzlich geglätteten Kurve gegen den Drehwinkel der Drehantenne;

Fig.6

zeigt eine Auftragung von aus der Kurve aus Fig.5 bestimmten Umschaltpunkten gegen den Drehwinkel der Drehantenne; und

Fig.7

zeigt schematisch eine Abhängigkeit einer Mikrowellen-Feldverteilung von dem Drehwinkel ϕ der Drehantenne für das Mikrowellen-Haushaltsgerät aus Fig.1.

Fig.8

zeigt ein sog. Lightboard als Messaufbau das die Feldverteilung im Garraum in Abhängigkeit von dem Drehwinkel ϕ der Drehantenne für ein Mikrowellen-Haushaltsgerät nach Fig.1 anzeigt.

The characteristics, features and advantages of this invention described above, and the manner in which they are achieved, will become clearer and more clearly understood in connection with the following schematic description of an exemplary embodiment, which will be explained in more detail in connection with the drawings.

Fig.1

shows a sectional side view of a household microwave oven;

Fig.2

FIG. 12 shows a control device of the household microwave appliance in a plan view Fig.1 with an evaluation circuit;

Fig.3

shows an alternative evaluation circuit for the household microwave oven Fig.1 ;

Fig.4

FIG. 12 shows a plot of a leak through the microwave leak sensor of the household microwave oven Fig.1 measured measurement value representing a strength of the microwave leakage radiation against a rotating angle of the rotary antenna of the household microwave oven Fig.1 ;

Fig.5

shows a plot of an amount of a derivative of the from Fig.4 determined and additionally smoothed curve against the rotation angle of the rotating antenna;

Fig.6

shows a plot from off the curve Fig.5 certain switching points against the rotation angle of the rotating antenna; and

Fig.7

shows a schematic of a microwave field distribution as a function of the rotation angle φ of the rotating antenna for the microwave household appliance Fig.1 .

Fig.8

shows a so-called lightboard as a measurement setup that shows the field distribution in the cooking chamber as a function of the rotation angle ϕ of the rotating antenna for a microwave household appliance Fig.1 indicates.

Fig.1 shows a sectional side view of a sketch of a household microwave appliance 1 with a cooking chamber 2. The cooking chamber 2 is surrounded by a cooking chamber wall or muffle 3, which has a front loading opening that can be closed with a door 4. The domestic microwave appliance 1 has at least one microwave generator 5 for treating the material in the cooking chamber 2 (not shown), possibly also further heating elements such as one or more resistance heating elements (not shown).

The microwaves generated by the microwave generator 5 are routed via a microwave guide 6 to the cooking chamber 2 and there coupled into the cooking chamber 2 via a rotary antenna 7 serving as a mode variation device. The rotary antenna 7 has an antenna wing 8 here, for example, and can be rotated by 360° about an axis of rotation D, e.g. by means of a stepping motor (not shown). The rotary antenna 7 can therefore have angular positions or angles of rotation in a range φ=[0°; 360°], e.g. in steps of Δϕ = 1° or 5°.

The household microwave appliance 1 or its controllable components including the microwave generator 5 and the rotating antenna 7 can be controlled or actuated by means of a central control device 9 (also referred to as “appliance control”).

An evaluation circuit 10 is integrated into the control device 9 and is connected to a sniffer line 11 . The sniffer line 11 is set up so that alternating currents can be induced in it by microwaves. It is designed, for example, as a simple wire or cable. The evaluation circuit 10 is designed to determine the strength of alternating currents induced in the sniffer line 11 . The evaluation circuit 10 and the sniffer line 11 form a detection device 10, 11 for detecting microwave leakage radiation outside the cooking chamber 2, in particular in a space between the cooking chamber 2 and an outer housing 12 of the household microwave appliance 1 and/or in the area of the door 4 The sniffer line 11 can be a Have a length of at least 800 mm, in particular at least 1000 mm, in particular at least 1500 mm, in particular at least 2000 mm.

Fig.2 shows a plan view of a sketch of the control device 9 with some of the components present on it. A plurality of electrical lines 15 are routed to a printed circuit board 14 of the control device 9, which are connected at their other ends to functional units of the domestic microwave appliance 1, such as electrical consumers and/or sensors, and/or are sniffer lines. Here one of the electrical lines 15 corresponds to the sniffer line 11.

The electrical lines 15 are connected to the printed circuit board 14 at connection points 16 such as terminals or the like and merge there into corresponding conductor tracks 17 on the printed circuit board 14 . In the exemplary embodiment shown, purely by way of example, only one sniffer line 11 is connected to an evaluation circuit 10 arranged on the circuit board 14, which in turn is connected to a processor 18, e.g. a microcontroller, ASIC or FPGA, of the control device 9. The evaluation circuit 10 is therefore integrated into the control device 9 .

In particular, the evaluation circuit 10 is connected here by the conductor track 17 connected to the sniffer line 11 via a coupling capacitor 19 which separates the evaluation circuit 10 and the sniffer line 11 from the DC voltage.

As shown in the enlarged section A, the evaluation circuit 10 has at least one ohmic resistor 20 which is connected on the one hand to the terminal connected to the processor 18 and on the other hand to a predetermined reference potential or ground. The coupling capacitor 19 and the resistor 20 form a high-pass filter 19, 20 for the signal arriving from the sniffer line 11.

mit R dem Widerstandswert des Widerstands 20 und f_u einer gewünschten unteren Grenzfrequenz des Hochpassfilters 19, 20 auf. Die untere Grenzfrequenz f_u ist so gewählt, dass praktisch nur die mikrowelleninduzierten Spannungsanteile durchgelassen werden.In this case, the coupling capacitor 19 advantageously has a capacitance value C of the size $$C=\frac{1}{2\cdot \pi \cdot R\cdot f_{\mathrm{and}}}$$

with R the resistance value of the resistor 20 and f _u a desired lower limit frequency of the high-pass filter 19, 20. The lower limit frequency f _u is selected in such a way that practically only the microwave-induced voltage components are allowed to pass.

The - e.g. analog - output signal of the evaluation circuit 10 is routed to the processor 18 for evaluation (e.g. to an analog input of a microcontroller). However, the evaluation circuit 10 can also have other components or parts (not shown), for example an A/D converter, operational amplifier, etc.

The control device 9 is set up, based on a strength of the microwave-induced alternating current in the sniffer line 11, represented by the output signal of the evaluation circuit 10, to determine switching points at which there is a noticeable change in the field distribution in the cooking chamber 2, and to determine corresponding operating points.

Fig.3 12 shows an evaluation circuit 21 that is an alternative to the evaluation circuit 10. The alternative evaluation circuit 10 also has a filter function, but now with the provision of an LC filter.

Instead of the in Fig.2 ohmic resistance 20 shown, a first coil 22 with an inductance value L1 and an anode side of a diode 23 are now connected to the coupling capacitor 19 via a common node. The other terminal of the first coil 22 is connected to ground, while the cathode terminal of the diode 23 is connected via a further node to a second capacitor 24 having a capacitance value C2 and to a second coil 25 having an inductance value L2. The other terminal of the second capacitor 24 is connected to ground while the other terminal of the second inductor 25 is connected to the processor 18 .

Fig.4 shows a plot of a measured value (detector voltage) LMW in millivolts measured by the microwave leakage sensor 10, 11 of the household microwave appliance 1, which represents a strength of the microwave leakage radiation, against the rotation angle ϕ of the rotating antenna 7 for slightly more than one full rotation of the rotary antenna 7.

The measured value LMW can be tapped, for example, at the output of the evaluation circuit 10 leading to the processor 18.

Due to the cyclic nature of the antenna rotation, the measured values LMW are approximately repeated after one rotation (Δϕ = 360°). The course of the measured values LMW is logarithmically proportional to the measured field strength of the microwaves. Angular areas with a practically constant stress profile and cracks are evident. A surprising finding is that this voltage curve allows direct conclusions to be drawn about changes in the field distribution of the microwaves in the cooking chamber 2 . In particular, experiments have shown that the jump points correspond with a change in the mode pattern in the cooking chamber 2 with a very high degree of reliability. The change in the mode image can, for example, be carried out experimentally using a method as in U.S. 2008/0302958 A1 "Lightboards" described can be determined. Angle ranges with almost constant measured values LMW also show a constant brightness image of the lightboard, while a switching of the mode image can be seen directly in the voltage curve. This is more detailed in the below Fig.8 described.

Only a slight change in the mode image takes place within the angle ranges I to VII shown. This becomes particularly clear, for example, for the angular range V and there between approx. ϕ = 130° and ϕ = 160°, the angular range VI and there between approx. ϕ = 190° and ϕ = 250° and the angular range VII and there between approx. φ = 290° and φ = 335°.

• Kurvenglättung der in Fig.4 dargestellten Kurve,
• Bestimmen der Kurvensteigung der geglätteten Kurve,
• Bilden des Betrags der Kurvensteigung,
• Datenreduktion, und daraus
• Bestimmen der Arbeitspunkte der Drehantenne 7.

A possible variant for the device-side, automated determination of the operating points of rotary antenna 7 can include the following subsequent steps:

• Curve smoothing of the in Fig.4 shown curve,
• determining the curve slope of the smoothed curve,
• forming the magnitude of the slope of the curve,
• data reduction, and from it
• Determining the working points of the rotary antenna 7.

The optional curve smoothing advantageously reduces the influence of measurement errors.

The slope of the curve, e.g. expressed as ΔLMW / Δϕ or ∂LMW / ∂ϕ, provides information about rising and falling edges of the (smoothed) measured value curve.

Since only the absolute change in the course of the measured value or the absolute slope of the curve is of interest in the present case, an amount is also formed as an option.

Fig.5 shows a first derivation of the in Fig.4 shown and smoothed curve as a plot of an amount of measured value change |ΔLMW / Δϕ| against the angle of rotation ϕ of the rotary antenna 7.

In the following step, the data is reduced to switching points, e.g. by selecting the values with the locally maximum gradient. At these e.g. interpolated switching points, the change from one mode image to another takes place.

Fig.6 shows a plot from off the curve Fig.5 corresponding to certain switching points U1 to U7 ("0" not present, "1" present) against the angle of rotation φ of the rotary antenna 7, ie the angle of rotation φ or angular positions of the switching points U1 to U7. From this, operating points of the cooking appliance can be determined in a manner that is easy to implement: the particularly advantageous operating points are in each case in the middle between two adjacent switchover points U1, U2; U2, U3 etc., ie at a rotation angle ϕ = (ϕ (U2) - ϕ (U1))/2; etc. In the present exemplary embodiment, these are at least approximately the angles of rotation φ=10°, 50°, 75°, 110°, 145°, 225° and 315°. Possible field distributions or mode images are detailed below Fig.8 shown.

This process for determining the operating points can be carried out at the beginning of a microwave operating process and can be referred to as an initial scan.

The control device 9 can be set up, following the initial scan, to control the rotary antenna 7 or the associated stepping motor in such a way that the different mode images associated with the different operating points are maintained for the same length of time and the food to be cooked is thus treated in equally large time intervals (and no more proportional to the proportion of angles that the mode images assume during one revolution). Thus, the risk of disadvantageous formation of hotspots be significantly reduced in the same places in the food for longer periods of time without changing.

For advanced cooking controls, it is also advantageous that it can be determined practically without a time delay when a change in the setting parameters leads to a change in the resulting mode pattern and thus, equivalently, to a change in the heat distribution in the food to be cooked.

Of course, other evaluation methods can also be used to determine the operating points. For example, zeros of the derivation of the curve progression can also be made Fig.4 to get voted. This means that extreme points as well as turning and terrace points are recorded.

In addition, the method is generally not limited to household appliances whose mode variation device only has a single setting parameter or degree of freedom (such as the angle of rotation ϕ of the rotary antenna 7), but can also be used with several degrees of freedom (e.g. the angles of rotation of at least two rotary antennas or other field-changing elements such as a Mode stirrer) are used.

In general, not only the leakage rate within the housing needs to be examined, but any microwave leakage radiation emerging from the cooking chamber can be used to determine the operating points. This also includes microwave radiation that escapes in the area of the closed door (i.e., the "classic" leakage radiation in the front area). The measurement of the microwave leakage radiation is therefore not limited to the inside of the housing.

Fig.8 shows several camera images of a "lightboard" that correspond to the measured curve progression of the application 4 fit. The associated angular range and the angle of rotation φ of the rotating antenna 7 are drawn in for each image. The light sources, which can be excited to glow by microwaves and which can be attached to a styrofoam plate, for example, in the manner of a matrix, serve as indicators for the field distribution in the cooking chamber 2 . The higher the local microwave power, the brighter a light source shines.

The light patterns produced for the angles of rotation φ=0°, 50°, 75°, 106°, 130°, 160°, 190°, 240°, 290° and 335° are shown here. Each of the associated angular ranges I - VII has an individual light pattern. However, within one of the angular ranges I-VII, the field distribution of the microwaves in the cooking chamber 2 remains practically unchanged. This is exemplified for angles of 130° and 160° in angle range V, for angles of 190° and 240° in angle range VI and for angles of 290° and 335° in angle range VII.

Of course, the present invention is not limited to the embodiment shown.

In general, "a", "an" etc. can be understood as a singular or a plural number, in particular in the sense of "at least one" or "one or more" etc., as long as this is not explicitly excluded, e.g. by the expression "exactly a" etc.

A numerical specification can also include exactly the specified number as well as a usual tolerance range, as long as this is not explicitly excluded.

Reference List

1

household microwave oven

2

cooking chamber

3

cooking chamber wall

4

door

5

microwave generator

6

microwave guide

7

rotary antenna

8th

antenna wings

9

control device

10

evaluation circuit

11

sniffer line

12

Housing

14

circuit board

15

Electrical line

16

connection points

17

trace

18

processor

19

coupling capacitor

20

ohmic resistance

21

evaluation circuit

22

First coil

23

diode

24

Second condenser

25

Second coil

C

capacitance value

C2

capacitance value

D

axis of rotation

LMW

reading

L1

inductance value

L2

inductance value

R

resistance value

U1-U7

switching points

ϕ

angle of rotation

I - VII

angular ranges

Claims (12)

1. Household microwave appliance (1), having

   - a cooking chamber (2) to which microwaves can be applied,

   - at least one mode variation apparatus (7), which is designed to modify a field distribution of the microwaves in the cooking chamber (2), and

   - at least one microwave leakage sensor (10, 11) for detecting microwave leakage radiation exiting from the cooking chamber (2),
   wherein the household microwave appliance (1) is designed

   - to vary setting values (ϕ) of the at least one mode variation apparatus (7),
   characterised in that the household microwave appliance is also designed

   - to set at least one operating point of the at least one mode variation apparatus (7) based on the quantity of measurement data of the detected microwave leakage radiation resulting from the variation.
2. Household microwave appliance (1) according to claim 1, wherein the household microwave appliance (1) is designed

   - to pass through a setting range of at least one mode variation apparatus (7);

   - to measure a strength of the microwave leakage radiation for the respective set values (ϕ) of the setting range passed through; and

   - to determine at least one characteristic property from the resulting curve profile, from which the at least one operating point can be set.
3. Household microwave appliance (1) according to one of the preceding claims, wherein the characteristic properties include switching points (U1-U7) at which a significant modification of the field distribution occurs, and the household microwave appliance (1) is designed to set operating points of the at least one mode variation apparatus (7) so that they lie outside the switching points (U1-U7).
4. Household microwave appliance (1) according to claim 3, wherein the household microwave appliance (1) is designed to set the operating points centrally between adjacent switching points (U1-U7).
5. Household microwave appliance (1) according to claim 2 in combination with one of claims 3 to 4, wherein the switching points (U1-U7) are determined from turning points of the curve.
6. Household microwave device (1) according to claim 2, wherein the characteristic properties include extreme and/or terrace points of the curve and the household microwave device (1) is designed to set the extreme and/or terrace points as operating points of the at least one mode variation apparatus (7).
7. Household microwave appliance (1) according to one of the preceding claims, wherein the at least one mode variation apparatus (7) comprises at least one apparatus from the group

   - rotary antenna (7);

   - turntable;

   - mode stirrer;

   - microwave generator.
8. Household microwave appliance (1) according to one of the preceding claims, wherein the at least one microwave leakage sensor (10, 11) is designed to measure a microwave leakage radiation passing through a cooking chamber wall (3).
9. Household microwave appliance (1) according to one of the preceding claims, wherein the at least one microwave leakage sensor (10, 11) is designed to measure microwave leakage radiation passing through a door gap between a housing flange and a door (4) that closes the cooking chamber (2).
10. Household microwave appliance (1) according to one of the preceding claims, wherein the at least one microwave leakage sensor (10, 11) comprises at least one sniffer line (11).
11. Method for operating a household microwave appliance (1), wherein

    - microwaves are applied to a cooking chamber (2),

    - setting values (ϕ) of at least one mode variation apparatus (7), which is designed to modify a field distribution of the microwaves in the cooking chamber (2), are varied,

    - the microwave leakage radiation exiting from the cooking chamber (2) is measured for the different setting values (ϕ) of the at least one mode variation apparatus (7), characterised in that

    - operating points of the at least one mode variation apparatus (7) are set based on the detected microwave leakage radiation.
12. Method according to claim 11, wherein the detected microwave leakage radiation is used to determine switching points (U1-U7), at which a marked modification of the field distribution of the microwaves occurs within the cooking chamber (2) and operating points of the at least one mode variation apparatus (7) are set so that they lie outside the switching points (U1-U7).

Images