WO2023212779A1

WO2023212779A1 - Cooking oven

Info

Publication number: WO2023212779A1
Application number: PCT/AU2023/050373
Authority: WO
Inventors: Ottavio Cimino
Original assignee: ORA Australia Pty Ltd
Priority date: 2022-05-04
Filing date: 2023-05-04
Publication date: 2023-11-09

Abstract

The present invention relates to a cooking oven. The oven includes a heating body defining a cooking chamber. An induction coil surrounds the heating body and is suitable for exciting to heat the heating body. Advantageously, the induction coil surrounds the heating body and the heating body may be evenly heated for even cooking of food.

Description

COOKING OVEN

TECHNICAL FIELD

[0001] The present invention generally relates to a cooking oven for cooking food. The present invention has particular, although not exclusive application to domestic ovens.

BACKGROUND

[0002] The reference to any prior art in this specification is not, and should not be taken as an acknowledgement or any form of suggestion that the prior art forms part of the common general knowledge.

[0003] Ever since “fire” was used by prehistoric humans, it has been a challenge to manage a way of cooking food, that required moderate heat, in an intense heat open fire place. The fundamental problem has always been how to manage intense heat emanating from a naked flame, which can reach in excess of 650 °C temperature, while food that needs to be cooked, requires a temperature ranging from 150 - 200 °C. To cope with this basic heat distribution problem, over the last millennia’s, humans around the world, have invented different types of ovens, fueled with, wood, gas and in the last century, with electricity. In recent years, the heat distribution problem in ovens was improved with the invention of the combination of an electric element and Fan forced ventilation.

[0004] Fan forced ovens have somewhat improved the foregoing heat distribution problem, but still suffer from heat distribution problem, requiring frequent user’s supervision to evenly cook food. As illustrated in Figure 1 , it is not uncommon for different heating levels within a cooking chamber of an oven 100 whereby the rear 102 of the oven 100 is hotter than the front 104 of the oven 100 resulting in uneven cooking of the food 104.

[0005] The main heat distribution problem is related to two factors:

• Electrical heating elements generally produce high temperature from 400 -

• All food, generally speaking, has different shapes and/or sizes and as cited above, require cooking temperatures ranging from 130-230°C

[0006] The graphs in Figure 2 show the temperature of the fan forced airflow, that will eventually impact on the food surfaces, ranging from 210°C to 300°C for a 200°C oven temperature setting (Fig. 2a) and from 184°C to 264°C for the 180°C oven temperature setting (Fig. 2b).

[0007] Another cooking limitation with existing electric conventional ovens is related to dehydrating effect on food. The cooked food with these type of ovens causes the following well documented problems:

• Reduction in mass

• Toughen fibre (especially with meats)

• T aste

• Nutrient losses

[0008] A conventional heated oven utilizes typical electric resistive heating elements that reach 650°C, while the cooking temperature requirements ranges from 100 to 250°C. As shown in Figure 3, food needs to be distanced from the resistive heating elements 300 to avoid burning by the 650°C temperature.

[0009] Special pizza cooking temperature is required to be around 350°C and Pyrolytic cleaning process requires a temperature of 480°C.

[00010] The preferred embodiment provides for more even heating of food.

[00011] Precision heating is a desirable functionality for many oven applications. It has the capability to control the temperature across a heated object (workpiece) and thus can achieve a uniform temperature distribution.

[00012] Reference [1] proposed an induction heating system with physically adjustable heating coils. Reference [2] used bidirectional switching network to control each heating coil individually. Reference [3] suggested that a single inverter with varied operation frequency can selectively control the heat distribution of multiple heating coils of which resonant frequencies are with tuned distinctively. Among the existing solutions, a zone control induction heating (ZCIH) system was invented to perform high quality precision heating using multiple coils wound around a single workpiece, operated by multiple inverters [4], The ZCIH system detects and controls all coil currents at the same time at the same frequency to overcome the mutual magnetic coupling between the coils. This approach was proven to be effective, however the cost is significant and thus it is only really suitable for high power applications.

[00013] The preferred embodiment provides cost reduction of precision heating at lower power for a household oven.

[00014] With regard to the induction coils, pure copper wire has melting point of 1085°C and it starts to loose mechanical strength or begins to soften above 150°C.

[00015] The preferred embodiment provides for a suitable induction coil for a household oven.

SUMMARY OF THE INVENTION

[00016] According to a first aspect of the present invention, there is provided a cooking oven including: a heating body defining a cooking chamber; and an induction coil surrounding the heating body and for exciting to heat the heating body.

[00017] Advantageously, the induction coil surrounds the heating body and the heating body may be evenly heated for even cooking of food. The heating body may not be heated more than oven thermostatic temperature setting during cooking.

[00018] The oven may include an insulator located between the heating body and the induction coil. The insulator cay be a ceramic insulator. The insulator may be an electrical and/or heat insulator.

[00019] The body may be endless. The body preferably includes heating panels. The panels may be heated in the range of 50°C to 480°C. Each panel may include carbon steel with vitreous enamel coating. Alternatively, each panel may be layered. Each layered panel may include an outer ferric stainless steel layer, and an inner aluminum layer. [00020] The oven may further include a power supply for supplying power to the induction coil. The power supply may be an alternating current (AC) power supply. The AC power supply may provide AC power with a frequency of at least 20kHz. The oven may further include a thermostat for deactivating the power supply to regulate the temperature in the cooking chamber.

[00021] The oven may further include one or more other induction coils surrounding the heating enclosure and for exciting to heat the heating body. The induction coils may be separately excited to heat separate zones of the body. The induction coils may be sequentially or sporadically excited.

[00022] The oven may further include an electromagnetic radiation shield for shielding electromagnetic radiation. The shield may surround the coil to shield outwardly emanating radiation. The shield may be located withing the coil to shield inwardly emanating radiation. The shield may include aluminium.

[00023] According to a second aspect of the present invention, there is provided a power supply including: a DC to AC inverter for supplying AC power to one or more induction coils surrounding a heating body.

[00024] Advantageously, the coils may form heating zones to deliver precision heating at lower power for a household oven. Each heating zone may include a respective temperature sensor. Preferably, there is no need to detect coil currents, thus lowering the cost and control complexity for the power supply.

[00025] The DC to AC inverter may be configured to supply AC power at varying frequencies or at a synchronized frequency. The DC to AC inverter may be configured to switch between exciting respective coils. The DC to AC inverter may be configured to vary the time in exciting respective coils to accommodate for varying temperature in corresponding zones in the oven. The DC to AC inverter may be configured to excite respective coils concurrently.

[00026] The DC to AC inverter may include one or more half bridge inverters driving respective induction coils. Alternatively, the DC to AC inverter may include a full bridge inverter. [00027] The power supply may further include an AC to DC converter for supplying DC power to the DC to AC inverter. The AC to DC converter may be supplied by mains power (e.g. 230V, 50Hz).

[00028] According to a third aspect of the present invention, there is provided an induction coil including: a conductor having a number of turns; and an insulator located between the turns.

Preferably, the coil further includes an insulator between filaments.

[00029] Advantageously, the insulator may be a thermal insulator and thermally protect the conductor from a heated oven. Preferably, the insulator is an electrical insulator.

[00030] The insulator may include filament passing between the turns. The filament may be woven between the turns. The filament may alternately pass between the turns. The filament may pass between the turns in rows. Adjacent rows may be staggered. The filament may include silica. The filament may include glass. The coil may further include a coating for coating the insulator. The filaments may include Sol-Gel insulating coatings.

[00031] The conductor may include copper wire. The conductor may include a Litz (i.e. multicore) wire. The Litz wire may be coated or saturated with moisture resistant substance.

[00032] The insulator may include a coating for coating the conductor. The coating may be a ceramic coating.

[00033] The turns may form an array. The induction coil may include another insulator for insulating the array. The other insulator may include a coating for coating the array.

[00034] According to a fourth aspect of the present invention, there is provided an electromagnetic radiation shield for shielding electromagnetic radiation, the shield including at least one layered panel, and preferably four in interconnected layered panels. [00035] Advantageously, one of the layers of the panel may be excited whereas another layer of the panel may not be excited by an induction coil of an oven.

[00036] Each layered panel may include an outer heating layer, and an inner shielding layer. The outer heating layer may include ferric material, preferably including steel or ferric stainless steel. The inner shielding layer may include aluminum.

[00037] The outer heating layer may be perforated. Each layered panel may include locking joints.

[00038] Any of the features described herein can be combined in any combination with any one or more of the other features described herein within the scope of the invention.

BRIEF DESCRIPTION OF THE DRAWINGS

[00039] Preferred features, embodiments and variations of the invention may be discerned from the following Detailed Description which provides sufficient information for those skilled in the art to perform the invention. The Detailed Description is not to be regarded as limiting the scope of the preceding Summary of the Invention in any way. The Detailed Description will make reference to a number of drawings as follows:

[00040] Figure 1 shows uneven cooking of food in a known oven owing to poor heat distribution;

[00041] Figure 2a is a graph of temperature over time in a known fan forced oven with thermostat temperature set to 200°C;

[00042] Figure 2b is a graph of temperature over time in a known fan forced oven with thermostat temperature set to 180°C;

[00043] Figure 3 is a schematic front view of a known fan forced convection oven;

[00044] Figure 4 is a schematic front view of an induction oven in accordance with an embodiment of the present invention;

[00045] Figure 5 is a close-up sectional view of the induction oven of Figure 4; [00046] Figure 6a is an upper perspective view of an induction coil of the induction oven of Figure 4 and 5;

[00047] Figure 6b is an upper perspective view of a dual induction coil arrangement in accordance with another embodiment;

[00048] Figure 6c is an upper perspective view of a triple induction coil arrangement in accordance with another embodiment;

[00049] Figure 7 is a schematic of a power supply for driving the triple induction coil arrangement of Figure 6c;

[00050] Figure 8 is a schematic showing the switching operating principle of the power supply of Figure 7;

[00051] Figure 9 is a schematic showing a half bridge inverter of the power supply of Figure 7; and

[00052] Figure 10 a schematic showing a full bridge inverter of the power supply of Figure 7;

[00053] Figure 11 is an upper perspective view showing an induction coil in accordance with an embodiment;

[00054] Figure 12 is a sectional view of the induction coil of Figure 11 ;

[00055] Figure 13 is a sectional view of a conductor of an induction coil;

[00056] Figure 14 is a sectional view of an induction coil in accordance with another embodiment including the conductor of Figure 13;

[00057] Figure 15 is a sectional view of another conductor of an induction coil;

[00058] Figure 16 is a sectional view of an induction coil in accordance with another embodiment including the conductor of Figure 15;

[00059] Figure 17 is a schematic front view of the oven of Figure 4 showing electromagnetic radiation; [00060] Figure 18 is a perspective front view of a radiation shield in accordance with an embodiment;

[00061] Figure 19 is a sectional close up of the radiation shield of Figure 19;

[00062] Figure 20 shows a plan view of a stainless steel layer of the radiation shield;

[00063] Figure 21 shows a side sectional view of the stainless steel layer of Figure 20;

[00064] Figure 22 shows a side sectional view of a layered radiation shield including the stainless steel layer of Figure 21 ;

[00065] Figure 23 shows a front perspective view of a radiation shield of Figure 22;

[00066] Figure 24 shows the strength characteristic of aluminum; and

[00067] Figure 25 shows an outer radiation shield casing for the oven of Figure 4.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

[00068] According to one aspect of the present invention, there is provided a domestic induction cooking oven 400 as shown in Figure 4. The oven 400 includes a rectangular heating body 402 defining an internal cooking chamber 404. The endless body 402 includes four planar heating panels 406.

[00069] The panels 406 can be heated in the range of 50°C to 480°C. Each panel 406 can include carbon steel with vitreous enamel coating. Alternatively, each panel 406 can be layered. Each laminated panel 406 can include an outer ferric stainless steel layer, and an inner aluminum layer which will be described in greater detail below.

[00070] Turning to Figure 5, an induction coil 500 surrounds the outside of the heating body 402 and is excited to heat the interconnected panels 406 of the heating body 402. Advantageously, the induction coil 500 surrounds the heating body 402 and the heating body 402 is evenly heated for even cooking of food in the internal cooking chamber 404. The heating body 402 cannot be heated more than oven thermostatic temperature setting during cooking, to prevent burning of the food. [00071] The excited induction coil 500 generates electromagnetic flux incident onto the cooking chamber panels 406 which thus become the heat source of the oven 400, utilizing an Eddy current effect. The resulting internal temperature generated by the cooking chamber oven 400 can be controlled and maintained at the same selected cooking temperature of food.

[00072] The kitchen oven 400 also includes an endless ceramic insulator 502 located between the heating body 402 and the induction coil 500. The blanket-like insulator 502 is a 20mm thick electrical and thermal insulator.

[00073] As can best be seen in Figure 6a, the oven 400 includes a single induction coil 500 spanning the depth of the heating body 402. However, as shown in Figure 6b, the oven 400 can instead include a pair of adjacent induction coils 600a, 600b surrounding and spanning the depth of the heating body 402.

[00074] As shown in Figure 6c, the oven 400 can also instead include three serially arranged induction coils 602a, 602b, 602c surrounding and spanning the depth of the heating body 402. The induction coils 602a, 602b, 602c can be separately excited to heat separate zones of the body 402. The induction coils 602a, 602b, 602c can be sequentially or sporadically excited using a zone controller. The coils include high temperature electric insulation surrounding the copper conductor.

[00075] In this regard, the oven 400 can further include a power supply for supplying power to the induction coils 500, 600a, 600b, 602a, 602b, 602c. The power supply is an alternating current (AC) power supply providing AC power with a frequency of at least 20kHz. The oven 400 further includes a thermostat for deactivating the power supply to regulate the temperature in the cooking chamber 404.

[00076] In contrast to known resistive heating elements, the induction heating oven 400, by using the cooking chamber panels 406, provides a uniform heating distribution and consequently avoiding localized hot spots or burning. The pyrolytic self-cleaning induction heating panels 406 are the source of the heating and, owing to the localized electromagnetic field generated by the induction coils 500, 600a, 600b, 602a, 602b, 602c, will reach the required temperature of 480°C more rapidly than a remotely located resistive element heating system, resulting in faster cleaning cycles and large energy savings. [00077] The cooking chamber body 402 has its specific and individual technical characteristics:

• Material Permeability

• Material Conductivity

• Skin Depth

• Distance of the coil to the cooking chamber panels

[00078] The geometry of the cooking chamber 404 affects the design of the electronics operating systems, as exemplified in the table below.

[00079] The coil 500 needs to be variable in length to accommodate the various turns around the above listed cooking chambers perimeter. The area sizes that need to be heated, while maintaining the system operating electrical current ranges between 2000W and 3500W at 240V, requires manufacture of a single or multi-zones induction heating oven 400 with induction coils 500, 600a, 600b, 602a, 602b, 602c specifically designed for the cooking chamber 404 as described above.

[00080] Turing to Figure 7, a power supply 700 is provided for supplying power to the induction coils 602a, 602b, 602c. The power supply 700 includes a DC to AC inverter 702 for supplying AC power to the induction coils 602a, 602b, 602c surrounding the heating body 402.

[00081] Advantageously, the adjacent coils 602a, 602b, 602c form respective heating zones to deliver precision heating at lower power for the household oven 400. Each coil 602a, 602b, 602c controls the temperature of its proximate heating area i.e., heating “zone.” The oven temperature is measured by three temperature sensors in respective zones and sent to a feedback controller of the power supply 700 to achieve a uniform temperature distribution across the oven 400. There is no need to detect coil currents, thus lowering the cost and control complexity for the power supply 700 when compared with other known systems. [00082] The power supply 700 further includes an AC to DC converter 704 for supplying DC power to the DC to AC inverter 702. The AC to DC converter 704 is supplied by residential mains power 706 (e.g. 230V, 50Hz). The oven thereby operates from the household electrical grid, e.g., 230V, 50Hz with the oven 400 having from 2.3kW to 3.5kW heating power capability.

[00083] The DC to AC inverter 702 can be configured to supply AC power at varying frequencies when the coils 602a, 602b, 602c are operating alone, or at a synchronized frequency when the coils 602a, 602b, 602c are operating together.

[00084] Turing to Figure 8, the DC to AC inverter 702 can be configured to switch between exciting respective coils 602a, 602b, 602c. The 3-coil heating oven 400 operates in intermittently sequential cycles. In a normal setting, each coil 602a, 602b, 602c operates from approx. 2.3 kW to 3.5kW for a limited time interval before switching to another coil 602a, 602b, 602c. This sequence will repeat to keep a consistent heat generation across the oven 400. Due to the sporadic operation, each coil 602a, 602b, 602c only handles a part of the full power on average.

[00085] In Figure 8, from time tO to t3, coils 1 , 2, 3 operate in a sequence with equal time intervals, assuming a uniform temperature distribution across the oven 400.

However, when uneven temperature is detected, such as when the temperature in zone 1 is lower than the others, the operating interval (t3 to t4) of coil 1 is extended to provide extra heat to zone 1 before switching back to the normal sequence (t4 to t6). In this manner, the DC to AC inverter 702 can be configured to vary the time in exciting respective coils 602a, 602b, 602c to accommodate for varying temperature in corresponding zones in the oven 400.

[00086] At a different operating mode or “turbo mode”, two or more of the heating coils 602a, 602b, 602c can be operated simultaneously to increase the total heating power. Accordingly, the DC to AC inverter 702 can be configured to excite coils 602a, 602b, 602c concurrently.

[00087] Figure 9 shows the detailed structure of the DC-to-AC inverter 702 where a distributed half-bridge system is used with 3 separated half-bridge inverters 900a, 900b, 900c connected to the 3 heating coils 602a, 602b, 602c. Here, a single half-bridge inverter 900 can deliver 2.3kW to a single coil 602 in a sequence interval, and then turns to open/short circuit to let the other half-bridge operate. As a result, each halfbridge inverter 900 only delivers approximately a third of the full power (767W) in average.

[00088] Alternatively, for higher power applications, the DC to AC inverter 702 can include a distributed full bridge inverter as shown in Figure 10.

[00089] Figure 11 shows an induction coil 500 (or 600, 602) of the oven 400. The coil 500 includes a looped copper conductor 1100 having a number of turns 1102. An electrical insulator 1104 is located between the turns 1102. Advantageously, the insulator 1104 is also a thermal insulator and thermally protects the conductor 1100 from the heated oven 400.

[00090] As can best be seen in Figure 12, the insulator 1 104 includes woven filament 1200 passing between the turns 1102. The filament 1200 alternately passes, over and under, between the turns 1 102. The filament 1200 forms rows, with adjacent rows being staggered.

[00091] The coil 500 manufacture involves weaving sixteen turns 1 102 of uncoated copper conductor 1100 with Silica (yarn) filament 1200. Silica material characteristics are as per the following data:

• Temperature Range: 1000C

• Cost per kg 2.8 USD

• Fibre diameter: 0.01 mm

[00092] An acceptable alternative, cheaper glass fibre yarn filament 1200 that features temperature limits:

• Temperature Range: 600C

• Cost per kg 1 .4 USD

• Fibre diameter: 0.01 mm

[00093] The E-CR-Glass, which is an alumino- lime silicate composite version, has even better electric insulation characteristics.

[00094] Figure 12 illustrates the physical separation of each turn 1102 of wire by weaving 0.1 mm silica or glass-fibre yarn filament 1200 between them. A ribbon can be subsequently wrapped in glass fibre braid to completely cover and encapsulate the copper wire turns 1102. Alternatively, the coil 500 may further include a ceramic glass coating 1202 for coating the insulator 1104.

[00095] The conductor 1100 can include a Litz (i.e. multicore) wire. The Litz wire may be coated or saturated with moisture resistant substance. Humidity contamination of the Litz wire coil 500 can occur during the operation of the final product. The consequential risk could result in an electrical insulation failure between the Litz wire, compromising the electromagnetic flux efficiency or electrical insulation integrity and safety of the coil 500. A solution is to spray the litz/glass-fibre coil 500 with a thin coat of moisture resistant ceramic or saturate it with silicone such as Aremco Silicone P4010.

[00096] Alternative system, the silica and or Glass Fiber woven copper filament conductor assembly, as final stage, can be coated with Alumina-Glass coating 1202 as shown in Figure 12. Also, can be coated with Sol-Gel

[00097] Figures 13 and 14 shows a glass coating ribbon, and high temperature resistant and water-proof induction Litz wire coil 1300.

[00098] An insulator 1302 coats the conductor 1100, being greater than 0.2mm in diameter, and is located between the turns 1 102. The electrical insulator 1302 is a ceramic coating.

[00099] The diameter of the copper conductor 1100 can vary and it is conditioned by the design, whether single core or multicore (Litz wire), to achieve an electromagnetic flux magnitude and power rating and energy efficiency objectives.

[000100] In the case of a fragile and thin (0.2 mm diameter) cooper conductor 1100, the following process ensures copper turns 1102 are electrically insulated from each other. The first stage is to coat the electric metal conductor 1 100 with the ceramic coating insulator 1302 as shown in Figure 13. The second stage is to loop and position the coated conductor 1100 as required, whereby the ceramic coating insulator 1302 will ensure correct spacing between the copper turns 1102. As shown in Figure 14, the turns 1102 form a grid array. The third stage is to coat and encase the electrical ceramic insulated conductors 1100, arranged in an array, with > 0.01 mm thick ceramic glass encapsulating coating 1400 (i.e. another insulator) as illustrated in Figure 14. [000101] Figures 13 and 14 illustrate a variable arrangement of copper filaments per row and superimposed number of rows. The final design of the induction of the coil 1300 will depend on the application purpose of the induction heating in terms of power rating, electromagnetic flux and skin depth objectives.

[000102] Figure 15 illustrates a single core coil arrangement, this variation it will a more economical induction heating solution, however its resulting electromagnetic flux is limited by the copper conductor surface area.

[000103] Figure 16 illustrates illustrates a multicore arrangement, with 0.65mm diameter copper turns 1102, to increase the resulting coil electromagnetic flux and the heating efficiency.

[000104] The encapsulating coating 1400 can include Borosilicate Glass or Aluminosilicate Glass. Borosilicate Glass has a melting point temperature of 1 ,648°C, with a transition temperature of Approx. 820°C. Alumino-silicate Glass transition temperature is >820°C.

[000105] The apply glass coating 1400 is applied, at transition temperature, into stages as follows:

• In stage one: A ribbon >10 micron thick molten glass, is placed onto special designed precision ceramic conveyor chain belt. A heating duct station will keep the glass at a transition temperature.

• In stage two, copper wires with gap between individual strands of > 0.1 mm or a singular core system, are positioned on top of the glass base. A special designed ceramic conveyor, will position the copper wire filament on top of the very thin glass. A heating duct module keeps the glass and the copper at a suitable temperature.

• In stage three, a layer of >10 micron thick transition temperature glass, is position on top of the copper filament with special design precision conveyor chain belt. A heating duct module follows the final stage to cool down the ribbon and or the single core copper wire.

[000106] The induction heating oven 400 needs to be safe for the consumers who will be exposed to radiation that will be emitted and propagate into the ambient from the heating coils 500 (or 600, 602). [000107] The range of frequencies the induction oven 400 operates is typically limited to 30-100 kHz, which corresponds to a wavelength from 9,993 to 2,898 meters. Therefore, the induction-heating oven 400 operates at low frequency (LF) of 25 to 100 KHz, and it is classified as a Non-Ionizing Radiation.

[000108] Turning to Figure 17, the potential electromagnetic (EM) astray radiation in the induction heating oven 400 can emanate from the panels 406 of the heating body 402, and from external surfaces as well as the internal surface. The external EM stray radiation is actually emanated by the induction coils 500 (or 600, 602) themselves, being located on the external face of the heating body 402 defining the cooking chamber 404. While, the internal EM stray radiation emanates from the exited cooking chamber panels 406, which then propagates to the ambient through the glass door of the oven 400.

[000109] One solution to the external EM shield solution is to provide a simple thick aluminum foil wrapped outside the insulation 502 or the induction coils 500 (or 600, 602).

[000110] A solution is also provided to impede the EM radiation into the cooking chamber 404. Ferric stainless steel can be effectively inducted or excited at a frequency 30KHz, while Aluminum can only be inducted or excited at around 100KHz. In this application, aluminum can be an effective EM radiation shield at around the 30KHz frequency range.

[000111] Accordingly, as shown in Figure 18, an electromagnetic radiation shield 1800 is provided including four interconnected layered panels 406. Each layered panel may include an outer ferric stainless steel heating layer 1802, and an inner aluminum shielding layer 1804. The induction coils 500 (or 600, 602) excite the Ferric Stainless steel layer 1802, but not the aluminum layer 1804.

[000112] Turning to Figure 19, the Ferric Stainless steel layer 1802, located on the external face of the body 402 defining the cooking chamber 404, will heat up by the induction process and transfer the heat to the Aluminum layer 108, Aluminum being a good thermal conductor by thermodynamic convection. EM stray will be shielded by the aluminum layer 108 which is positioned on the internal face of the cooking chamber 404. [000113] A Thermo-Mechanical Bonding Lamination manufacturing process is used in forming the radiation shield 1800 with the following technical parameters:

• Induction coil-inducted ferric stainless steel

• Thermal conduction between the stainless steel and the aluminium

• Effective EM shield

• Thermal-distortion stability (no buckling expansion noises)

[000114] To improve mechanical bonding between the two layers 1802, 1804, perforated stainless steel 1802 is used as shown in Figures 20 and 21 (with dimensions in mm), to allow heated aluminum 1804 to be pressed and to protrude through these perforations 2200 and create a mechanical key bond as shown in Figure 22.

[000115] The flat sheet of stainless steel 1802 measures from > 0.5mm thick, 400mm wide and with variable lengths as required according to the cooking chamber 404 being selected. The stainless steel 1802 is perforated with holes measuring 3.5mm diameter arranged in a matrix, and not necessarily limited to this configuration.

[000116] A protruding design of the orifices 2200 maximize surface contact area between the stainless steel 1802 and the aluminum sheet 1804 and also will create a mechanical locking and frictional bonding.

[000117] The laminating manufacturing process involves the following steps:

• Pre-heat the aluminium 1804 to a temperature in which the aluminium becomes more malleable;

• Place and align the stainless steel 1802 on top of the pre-heated aluminium 1804

• Apply uniform pressure to the laminated stainless steel 1802 and aluminium 1804 to a point when the aluminium 1804 creeps through the stainless steel orifices 2200 creating a locking key between the two sheets 1802, 1804

• Allow the laminated assembly 1800 to cool before proceeding to the forming stages

[000118] The only common size in oven cooking chambers 404 is its depth, which measures 438mm. Logically, the perimeter of the cooking chamber 404 varies according to its final width and height as detailed in the following table (dimensions in mm):

[000119] The strength of Stainless steel decreases as the temperature increases. As shown in Figure 24, the compressive strength of aluminium also decreases as the temperature increases. The aluminium sheet is heated and pressed, similar to aluminium extrusion manufacturing process, where pre-heated aluminium 1804, is pressed to creep through the perforated stainless steel 1802.

[000120] Figure 25 shows that the oven 400 can further include an outer electromagnetic radiation shield 2500, surrounding the coil 500, for shielding outward electromagnetic radiation. The shield 2500 is for a 60 cm built in oven 400, featuring an aluminum outer casing to mitigate induction EM propagating into the ambient.

[000121] A person skilled in the art will appreciate that many embodiments and variations can be made without departing from the ambit of the present invention.

[000122] In compliance with the statute, the invention has been described in language more or less specific to structural or methodical features. It is to be understood that the invention is not limited to specific features shown or described since the means herein described comprises preferred forms of putting the invention into effect.

[000123] Reference throughout this specification to ‘one embodiment’ or ‘an embodiment’ means that a particular feature, structure, or characteristic described in connection with the embodiment is included in at least one embodiment of the present invention. Thus, the appearance of the phrases ‘in one embodiment’ or ‘in an embodiment’ in various places throughout this specification are not necessarily all referring to the same embodiment. Furthermore, the particular features, structures, or characteristics may be combined in any suitable manner in one or more combinations.

[000124] REFERENCES [1 ] J. C. Lewis, “Control device for parallel induction heating coils,” US patent, no. 4 307 278, Dec. 22, 1981.

[2] T. J. Bowers, C. F. Der, J. D. Parker, “Multi-zone induction heating system with bidirectional switching network,” US patent, no. 6 078 033, Jun. 20, 2000.

[3] D. S. Schatz and J. M. Dorrenbacher, “Frequency selected, variable output inductor heater system,” U.S. Patent, 6 316 754 B1 , Nov. 13, 2001.

[4] Uchida, O. Yoshihiro, K. Ozaki, H. Fujita, Ha Pham N., "Induction heating device, method for controlling the same and program," Patent JP 2010-245002, publication date: 28 October 2010.

Claims

The claims defining the invention are as follows:

1 . A cooking oven including: a heating body defining a cooking chamber; and an induction coil surrounding the heating body and for exciting to heat the heating body.

2. A cooking oven as claimed in claim 1 , wherein the induction coil surrounds the heating body and the heating body is evenly heated for even cooking of food.

3. A cooking oven as claimed in claim 1 , wherein the heating body is not heated more than an oven thermostatic temperature setting during cooking.

4. A cooking oven as claimed in claim 1 , including an insulator located between the heating body and the induction coil.

5. A cooking oven as claimed in claim 4, wherein the insulator is a ceramic insulator.

6. A cooking oven as claimed in claim 4, wherein insulator is an electrical and/or heat insulator.

7. A cooking oven as claimed in claim 1 , wherein the body is endless.

8. A cooking oven as claimed in claim 1 , wherein the body includes heating panels, preferably heated in the range of 50°C to 480°C.

9. A cooking oven as claimed in claim 8, wherein each panel includes carbon steel with vitreous enamel coating.

10. A cooking oven as claimed in claim 8, wherein each panel is layered, preferably including an outer ferric stainless steel layer, and an inner aluminum layer.

11. A cooking oven as claimed in claim 1 , further including a power supply for supplying power to the induction coil.

12. A cooking oven as claimed in claim 11 , wherein the power supply is an alternating current (AC) power supply providing AC power with a frequency of at least 20kHz.

13. A cooking oven as claimed in claim 1 , further including a thermostat for deactivating the power supply to regulate the temperature in the cooking chamber.

14. A cooking oven as claimed in claim 1 , wherein the oven further includes one or more other induction coils surrounding the heating enclosure and for exciting to heat the heating body.

15. A cooking oven as claimed in claim 14, wherein the induction coils are separately excited to heat separate zones of the body.

16. A cooking oven as claimed in claim 14, wherein the induction coils are sequentially or sporadically excited.

17. A cooking oven as claimed in claim 1 , wherein further including an electromagnetic radiation shield for shielding electromagnetic radiation.

18. A cooking oven as claimed in claim 17, wherein the shield surrounds the coil to shield outwardly emanating radiation.

19. A cooking oven as claimed in claim 17, wherein the shield is located within the coil to shield inwardly emanating radiation.

20. A cooking oven as claimed in claim 17, wherein the shield includes aluminium.

21. A power supply including: a DC to AC inverter for supplying AC power to one or more induction coils surrounding a heating body.

22. An induction coil including: a conductor having a number of turns; and an insulator located between the turns.

23. An electromagnetic radiation shield for shielding electromagnetic radiation, the shield including at least one layered panel, and preferably four in interconnected layered panels.