Field of the invention

This invention concerns a compact microwave oven for selectively heating of meals. More particularly, it concerns a microwave oven provided with a cavity, enclosed by walls wherein a dish with food, such as for catering services, can be inserted and wherein the space between the dish and the walls is substantially limited. Furthermore, the device enables selectively heating a part of the dish. The microwave oven comprises a warm and cold compartment and means to manage efficiently the microwaves in the hot compartment in respect with the food compounds.

Background of the invention

Heating food by microwave technology in a microwave oven is well-known. An important problem with microwave ovens is an inefficient use of energy. First, the energy in the cavity of the oven is not sufficiently used and secondly, the composition and the characteristics of the food are not taken in account. A few solutions have been proposed in order to solve this problem. First, it concerns a static device, like described in US4354083, comprising a microwave oven with apertures in the upper and bottom walls and microwave reflecting means to distribute the microwave energy homogeneously. Another solution proposes dynamic means, like in US5828042, concerning a device for heating food homogenously by using a rotating plate with apertures and provided with a weight and microwave sensor, to adapt the amount of energy. Both devices use a cavity with a volume that is a multitude of the volume of the food. When vertically stacking multiple of these microwave ovens, a lot of space will be lost.

Furthermore, according to the precedent references, the apertures for distributing the microwave energy have a regular fixed pattern. So, both devices are targeted to heat the food homogenously, but not to heat some of the food compounds selectively. However, it is known to heat meals selectively with a warm and cold compartment, like described in EP2037784. It describes U-shaped profiles that separate a warm and cold compartment. This invention is a further improvement of the device for selectively heating foodstuff with an efficient energy usage.

Summary of the invention

This invention offers a solution for the previously mentioned problems by providing a microwave oven with a closed cavity and wherein the space, between the 6 wall panels of said cavity and the food dish, is substantially limited. The device, according to the invention, is further provided with a stirrer with a horizontal

rotating axle and a distribution space with irregular adapted openings. Consequently, the cavity that houses the rotating stirrer can be limited consequently in height. The stirrer scatters the microwaves homogenously in the cavity. The combination of the limited space in the cavity for the dish, the horizontal rotating stirrer and irregular adapted openings enable the adaptable heating of foodstuffs. Moreover, this combination

provides a selective heating, based on the composition and the characteristics of the food or food composition. According to another embodiment of this invention, warm and cold compartments are provided- in the cavity, resulting in a partly heating of the meal and another part that will not be heated. Both compartments are separated by an electromagnetic filter for only passage of microwaves in the warm compartment.

Still another embodiment according to this invention provides a coupling between at least two microwave ovens and whereby the power between both microwave ovens is managed by an electronic device. Stacking a multitude of microwave ovens just takes a limited space.

Brief description of the drawings

The invention will be explained in more detail by the following drawings.

Figure 1: sectional view of a microwave oven with a warm and cold compartment

Figure 2 : side view of an electromagnetic filter for mounting in a cavity of a microwave oven Figure 3 : side view of an electromagnetic filter for mounting in a cavity of a microwave oven

Figure 4: front view of a door in a microwave oven with electromagnetic filter

Figure 5: irregular openings in a wall panel of the cavity of the microwave oven

Figure { 6a) : side view rotating stirrer Figure ( 6b) : side view of wing with irregular pattern

Figure (6c) : side view of wing with irregular pattern Figure <6d) : side view of wing with irregular pattern

Figure (6e) : side view of wing with irregular pattern

Description of the preferred embodiments of the invention

A microwave oven comprises a cavity for inserting a meal, an instrument panel with a timer, a magnetron and a power source. The instrument panel and the power source are not illustrated in the drawings.

According to Figure 1, the compact microwave oven(l) comprises a cavity (2), enclosed by a bottom panel (3), a ceiling panel (4), two side panels (5a, 5b) , a back panel (6) and a front door (7) . Along the X, Y and Z axis, the size of the cavity (2) is respectively, 55cm, 44.2cm and 9cm, according to a preferred embodiment of this invention. A distribution space (8) (along the X, Y and Z axis, the size of the distribution cavity (8) is respectively,

36.9cm, 51.5cm and 4cm) with a magnetron antennae (9) is situated above the cavity (2). A horizontal rotating stirrer (10) is located on the inner rear side of the warm compartment. The ceiling panel (4) between the

distribution space (8) and the cavity (2) is provided with irregular adapted openings (11) for selectively

distributing microwaves in the cavity (2).

According to another embodiment, the cavity (2) is divided in a warm (2a) compartment (dimensions along the X, Y and Z axis are 34.5cm, 44,2cm and 9cm) and cold (2b)

compartment (dimensions along the X, Y and Z axis are 15,7cm, 44,2cm and 9cm). Both compartments (2a, 2b} are separated by an electromagnetic filter (12), enabling only microwaves in the warm compartment (2a) over the food.

Figures 2 and 3 illustrate two different electromagnetic filters (12). According to an embodiment, illustrated in Figure 2, the filter (12) is made of a metal sheet with a vertical upstanding plate (12a), provided on its bottom with a beam-shaped body(12b). The upstanding plate (12a) is attached to the ceiling panel (4). Another upstanding plate (12c), adjacent to the door (7) is located

perpendicular on the front end of the upstanding

plate (12a) . The rear end of the upstanding plate (12a) is joining the back panel(6) of cavity (2). The beam-shaped body (12b) is provided with recesses ( 12d) .

Figure 3 shows an another embodiment of a filter (12), with an upstanding plate (12a), another upstanding

plate (12c), perpendicular to the upstanding plate (12a), and with on its bottom, perpendicularly a horizontal plate (12e) with beam-shaped protuberances (12f) . The upstanding plate (12a) joins the ceiling panel (4) and on its front end, the upstanding plate (12c), adjacent to the door (7) and on its rear end the back panel (6) of

cavity (2) .

Figure 4 illustrated a door (7), provided with a

filter (13). A first filter (13a) encloses the periphery of the door, located on the cold compartment. A second filter (13b) is located around the periphery of the door at the warm compartment. Both filters (13a, 13b) are separated by a filter (13c) on the door(7). The upstanding plate (12a) of the filter (12), that separates the warm and cold compartments, joins the filter (12c) of the door(7). A service tray will be inserted under the filter (12) on the bottom panel (3) . The part of the serving tray with food that needs to be heated will be situated in the warm compartment (2a) under the irregular openings (11) in the ceiling panel(4). These irregular openings ( 11 ) , according to Fi ure 5 , (illustrated in a matrix structure according the X and Y axis of the warm compartment: Xa: 34.5cm Ya: 44.2cm) are formed in accordance with a number of

parameters. These parameters comprise the size of the cavit (2) and the distribution cavity (8) with the

magnetron antennae (9) above said cavity (2), the position of the magnetron antennae (9) (the center of the magnetron antennae is located 32.8mm from the backwall in the center of the distribution cavity) , the composition of the meal and the dielectric properties of the different food compounds, the pattern of the filter (12) in the cavity(2) and the filter(13) of the door(7), the position and the configuration of the stirrer (10).

An experimental extrapolated simulation with 3 different microwaves ovens (800 ) with a cavity size like mentioned above and a nominal frequency of 2.46GHz for heating simultaneously a food composition of soup (V=345.6cm ³ ) , beef (V=208. cm ³ ) , potatoes (V=45.5cm ³ per piece), carrots (V=36.7cm ³ per piece) and peas (V=68.2cm ³ all pieces) has been executed. The first microwave oven (a) has a

stirrer (10) and irregular openings (11) , the second (b) , only irregular openings (11) and no stirrer and the third (c) has no stirrer nor irregular openings. The results in the following Table 1, show that in the third case (c) , no stirrer and without irregular openings, the absorbed energy in all the food compounds is the highest. This is illustrated by the highest main value 97.4 (case (c) ) > 40.7 (case (a}) . Although this high absorbance of the food compounds, the energy distribution over the food compounds and regarding their dielectric properties (8 _r ) (these dielectric properties are for soup 78-jll.67, for beef 40-jl2, for potato 53.7-jl5.7, for carrots 72-j23, for peas 4.3-j0.8) is best in case (a). This is

illustrated by a lower standard deviation, 25.6 (case a) < 49.4 (case c) .

Table 1 : Experimental extrapolated simulation (-18 dB) - similar power levels (Technical

University of Cartagena - Spain)

Food compound Case (a) Case (b) Case (c)

(Vnf ¹ ) {Vnf ¹ ) (Vm ^"1 )

Soup 66.46 157.18 156.06

Beef 26.41 54.63 97.03

Potato 1 18.90 56.79 65.97

Potato 2 16.67 57.34 42.06

Potato 3 21.35 48.87 43.91

Carrot 1 33.44 82.96 77.94

Carrot 2 33.62 78.35 105.28

Peas 108.60 249.28 190.80

Standard 29.60 66.67 49.39

deviation

Mean value 40.68 96.90 97.38

Next, the operating of the compact microwave oven will be explained. Microwaves are generated by the magnetron antennae (9) in the distribution space (8) above the cavity (2). A horizontal rotating stirrer (10) is provided in the warm compartment (2a) . Such a stirrer (10) is illustrated in figure 6a. The horizontal rotating stirrer (10) comprises a number of wings (lOal, 10a2, 10a3 and 10a4), longitudinally provided on the axle (10b).

According to this embodiment and shown in figure 6a, the wings (lOal, 10a2, 10a3, 10a4) are situated in two perpendicular planes around the axle (10b). In this example, 4 wings (lOal, 10a2, 10a3 and 10a4) with an adapted pattern are provided around said axle (10b) .

The wings are composed of a wide and narrow part, extending along the axle (10b). The stirrer is powered by a motor, which is not shown on the drawings. The pattern of said stirrer (10) will be adapted regarding the

irregular openings (11) and the size of the warm cavity. Such a stirrer (10) with a horizontal rotating axle (10b) enables to limit the height of the warm cavity size.

Figures (6b), (6c), (6d) and (6e) show the specific dimensions for each wing.

The dimensions for the wings are:

(6b) : Xa is 112.14mm, Xb is 226.28mm, Xc is 340. 2mm,

Ya is 13.42mm, Yb is 15.70mm, Yc is 18 .84mm

(6c) : Xa is 112.14mm, Xb is 226.28mm, Xc is 340.42mm,

Ya is 11.06mm, Yb is 11.19mm, Yc is 18 .33mm

(6d) : Xa is 112.14mm, Xb is 226.28mm, Xc is 340.42mm,

Ya is 19.11mm, Yb is 25.15mm, Yc is 13 .68mm

(6e) : Xa is 112.14mm, Xb is 226.28mm, Xc is 340.42mm,

Ya is 15.30mm, Yb is 13.48mm, Yc.is 18 .78mm

This invention, in particular, concerns a combination of a microwave oven with a compact cavity (2) and wherein the generated microwaves are distributed on the food in the cavity (2) to heat selectively.

Another embodiment concerns the coupling of at least 2 compact microwave ovens. The coupling comprises a

horizontal or vertical attaching. A microprocessor manages the microwave energy in the different microwave ovens in relation to the requested energy level and usage. The power is determined, based on a number of criteria, such as the food contents and the preferred heating time. An electronic control device checks the uniform distribution of the microwave energy over the different microwave ovens. This embodiment limits the maximal power generation. The coupling of multiple microwave ovens enables the heating of different

foodstuffs or multiple meals simultaneously. This is in particular advantageous on places where different

foodstuffs or meals need to be heated rapidly at the same time .