RU2393650C2 - Microwave oven - Google Patents

Abstract

FIELD: electricity.

SUBSTANCE: microwave oven for thermal processing of food is implemented in the form of double-unit structure including heating chamber with flap door and electronics unit. Heating chamber and electronics unit are rigidly connected by mechanical and electrical plug joints in horizontal plane. Bottom wall of the chamber is top cover of electronics unit case, and radiation of magnetron and waveguide units mounted in electronics unit case is screened by throttle filter installed in case aperture along the whole perimetre. Double-element stripline antenna with in-phase supply is used as electromagnetic field exciter in the chamber. Antenna structure includes emitter in the form of compressed eight, and screen attached rigidly by an orifice in the centre in external conductor of coaxial output of coaxial/waveguide adapter. Electromagnetic field exciter is connected to the chamber by diagonal (in ridge diagonal pattern).

EFFECT: uniform distribution of heating sources ~92% without loading platform rotation, efficiency ~58%, significant reduction of metal consumption of microwave oven and production cost.

3 cl, 2 dwg

Description

Technical field

The invention relates to microwave equipment, in particular, to electric heaters using microwave zero energy, and is intended for heat treatment of food products.

State of the art

A microwave oven is known, which is a device for heat treatment of food products, containing a parallelepiped-shaped heating chamber, in one of the side walls of which there is a rectangular hole for connecting an electromagnetic field exciter (EMF) in the chamber cavity, which is a shortened pyramidal horn antenna, microwave a generator, the output of which is connected to the input of the pathogen, as well as a rotating platform for accommodating the processed product, made of dielectric whom material. The heating chamber is equipped with a door fixed with hinges [1].

The main disadvantage of the known device is its low efficiency. The reason for this is the use of the orthogonal method of connecting the pyramidal horn to the heating chamber, which does not allow for uniform distribution of the heating sources in the chamber cavity, and therefore, to achieve high quality product processing. The distribution uniformity coefficient of heat sources is α = 38% in the absence of rotation and α≈62% when the processed product is rotated on the platform. (The measurements were performed according to [4]).

The rotation of the platform due to the anisotropy of the dielectric material leads to a noticeable change in the impedance of the camera and its resonant frequency, and as a result, a decrease in the microwave power entering the camera, i.e. decrease in profit center efficiency. In addition, the hinge of the furnace door hinges is unreliable: over time, there is a skew of the door plane with an integrated throttle filter relative to the “flanges” at the inlet of the heating chamber, leading to a noticeable increase (by two to five times) in the microwave energy emitted into free space.

The closest technical solution to the invention is the MEP [2], which is a device for heating with microwave energy, comprising a heating chamber equipped with a door, a microwave generator located in a removable housing of the electronic unit having a common wall with a heating chamber, and an excitation module installed in made in the common rear wall of the heating chamber of the communication hole for inputting microwave energy; the excitation module contains a segment of the coaxial line, the output of which is connected to a single-element strip antenna, exciting in the cavity of the EMF working chamber with circular polarization, while the longitudinal axis of symmetry of the strip antenna, which coincides with the direction of radiation, is perpendicular to the door of the front wall of the camera; the heating chamber and the body of the electronic unit are mechanically and electrically detachably connected using locks, microwave radiation from the slots at the junction is shielded by a throttle filter installed around the entire perimeter of the common wall of the working chamber [2].

The main disadvantage of this device is its low efficiency. A single-element strip causative agent, when connected orthogonally to a heating chamber, forms an EMF in its cavity with a uniform distribution (40 ÷ 45)% without a rotating platform. This leads to uneven heating of products and poor quality cooking. The efficiency of the furnace is also not high.

Disclosure of invention

The main objective of the invention is to increase the efficiency of the device by improving the characteristics of the electromagnetic field excitation system in the cavity of the heating chamber, reducing production costs and designing new models by using the block layout of the MVP design and eliminating the rotating platform from the structure, improving the quality heat treatment of food and reduced operating costs.

, совпадает с «диагональю ребра» - прямой, соединяющей точку, делящую пополам линию изгиба 17, 19 задней стенки камеры, фиг.16, совпадающую с поперечной осью симметрии антенны, с точкой 21, делящей пополам ребро «двугранного угла», образованного криволинейной поверхностью дверки 1, фиг.1а и поверхностью нижней стенки камеры; 2-х элементная полосковая антенна, состоящая из излучателя 5, имеющего форму двух пересекающихся краями дисков ("сжатая восьмерка"), изготовленного как единое целое из листового металла с высокой электропроводностью, и экрана 7 эллипсообразной формы, также изготовленного из листового металла с высокой электропроводностью и закрепленного через отверстие в центре жестко механически с хорошим гальваническим контактом на внешнем проводнике коаксиального отрезка коаксиально-волноводного перехода (КВП) 6, фиг.1а, при этом каждая из ветвей излучателя-«восьмерки» для обеспечения синфазного питания соединена механически и гальванически в характерных точках с помощью втулок из металла с высокой электропроводностью с экраном 7, а центр симметрии «восьмерки» 0 соединен с центральным проводником коаксиального отрезка КВП 6, по прямоугольному волноводу 8, фиг.1б, которого с размерами сечения 90х20 мм микроволновая энергия передается от источника микроволновой мощности; дверка 1 камеры 3, кривизна поверхности которой описывается уравнением параболы с горизонтальной осью, изготовлена из тонкой, толщиной 0,3 мм, листовой нержавеющей стали, ~1/2 поверхности дверки перфорирована отверстиями с Ф 2 мм, краями (шириной ~15 мм) по всему периметру дверка плотно, с зазором ~0,1 мм, прилегает к дроссельному фильтру (на фиг.1 не показано), установленному внутри раскрыва камеры с целью экранирования ЭМП работающей МВП, при открытии-закрытии камеры 3 дверка 1 поворачивается вокруг оси 2; камера 3, имеющая в сечении 11, 12, 13, 14, 15 криволинейный профиль, изготовлена из листовой низкосортной стали толщиной 0,5 мм, на ее задней стенке 13, 14, 15 точечной сваркой закреплен П-образный металлический профиль с внутренними размерами 90×20 мм, образующий прямоугольный волновод 8 с этими же размерами, к выходному фланцу которого подключается источник микроволновой мощности, установленный вместе с системой управления, блокировки и охлаждения в корпусе 4 электронного блока (на фиг.1 не показано), на передней панели которого 10 закреплен пульт управления. Защитная крышка 9 обеспечивает экранирование излучения КВП.This is achieved due to the fact that the MVP, which is a device for heating food products with microwave energy, comprising a heating chamber equipped with a door, a microwave generator located in the housing of the electronic unit having a common wall with the heating chamber, and an excitation module installed in the common rear wall of the chamber of the communication hole for introducing microwave energy, which is a segment of a coaxial line, to the output of which a single-element strip antenna is connected, I excite in the cavity of the EMF chamber with circular polarization; the heating chamber and the body of the electronic unit are mechanically and electrically detachably connected using locks, microwave radiation from the slots at the junction of the camera and the body of the electronic unit is shielded by a throttle filter installed around the entire perimeter of the common wall, according to the invention, in a device for heat treatment by microwave energy in As the EMF causative agent in the heating chamber, a 2-element strip antenna is used, which excites circularly polarized EMF in the cavity of the chamber, connected without a hole in the rear wall 13, 14, 15 of the chamber 3, figa, and is oriented in the cavity of the chamber so that the longitudinal axis of symmetry of the antenna, in the direction of which it emits electromagnetic energy

, coincides with the "diagonal of the rib" - a straight line connecting the point bisecting the bend line 17, 19 of the rear wall of the camera, Fig. 16, coinciding with the transverse axis of symmetry of the antenna, with the point 21 bisecting the edge of the "dihedral angle" formed by a curved surface door 1, figa and the surface of the lower wall of the chamber; 2-element strip antenna, consisting of a radiator 5, having the form of two disks intersecting at the edges ("squeezed eight"), made as a single unit of sheet metal with high electrical conductivity, and an elliptical screen 7, also made of sheet metal with high electrical conductivity and fixed through a hole in the center rigidly mechanically with good galvanic contact on the outer conductor of the coaxial segment of the coaxial waveguide transition (CVC) 6, figa, with each of the branches radiating The G-8 atelier for providing common-mode power supply is connected mechanically and galvanically at characteristic points using high-conductivity metal bushings with a shield 7, and the G8 symmetry center 0 is connected to the central conductor of the coaxial segment KVP 6, along a rectangular waveguide 8, FIG. .1b of which, with a cross-sectional size of 90x20 mm, microwave energy is transmitted from a microwave power source; door 1 of chamber 3, the surface curvature described by the equation of parabola with a horizontal axis, is made of thin, 0.3 mm thick stainless steel sheet, ~ 1/2 of the door surface is perforated with holes with Ф 2 mm, edges (~ 15 mm wide) along the entire perimeter of the door is tight, with a gap of ~ 0.1 mm, adjacent to a throttle filter (not shown in Fig. 1) installed inside the chamber opening to shield the EMF of the working MEP; when opening and closing the chamber 3, door 1 rotates around axis 2; a chamber 3 having a curved profile in sections 11, 12, 13, 14, 15 is made of low-grade steel sheet with a thickness of 0.5 mm, a U-shaped metal profile with internal dimensions of 90 is fixed by spot welding on its rear wall 13, 14, 15 × 20 mm, forming a rectangular waveguide 8 with the same dimensions, to the output flange of which is connected a microwave power source installed together with a control, blocking and cooling system in the housing 4 of the electronic unit (not shown in Fig. 1), on the front panel of which 10 fixed remote control eniya. The protective cover 9 provides shielding of the radiation of the CVP.

Due to the use of a diagonal (“rib diagonal” type) method of connecting the EMF pathogen to the heating chamber — a two-element strip antenna with a “squeezed eight” emitter, a parabolic shape of the door upon excitation in the cavity of the EMF chamber with circular polarization, the distribution coefficient of distribution of heating sources without rotation is exemplary load amounted to ~ 92%, which corresponds to the almost ideal mode of heat treatment of food in the profit center.

Due to the uniform distribution of microwave energy in the chamber cavity, good matching of the generator-exciter-chamber line with the load, and the stability of the characteristics of the two-element type of “compressed eight” strip antenna in the frequency drift band of the generator, a significant increase in the efficiency of the furnace was achieved.

The use of the block layout of the design of the profit centers, the exclusion of an additional casing made of metal covering the working chamber, hinges of the suspension of the door and the rotating platform significantly reduces the costs of manufacturing and designing new models of the profit center.

Brief Description of the Drawings

On figa shows a General view of the profit center in the context of a vertical plane parallel to the side wall, and Fig.1b is a General view in section of a vertical plane parallel to the rear wall of the camera.

The best embodiment of the invention

A microwave oven, which is a device for heat treatment of food products with microwave energy, contains a hinged door 1, a heating chamber 3 and an electronic unit 4.

The door 1 is fixed on the axis 2, around which it rotates when opening and closing the chamber 3. Shielding of the electromagnetic field in the chamber with the working MEP is achieved by a quarter-wave filter (not shown) installed around the entire perimeter in the chamber opening to which the metal surface of the door is adjacent . Inside the chamber 3, a two-element strip antenna is installed, which excites the EMF with circular polarization and consists of an emitter 5 and a screen 7. The left and right elements of the emitter at characteristic points using racks of metal with high electrical conductivity are connected to the screen 7, mounted through an opening in the center on the external KVP 6 coaxial output conductor is rigidly with good galvanic contact. The center of symmetry 0 of the two-element strip antenna is mechanically and electrically connected to the central conductor of the coaxial output of the KVP 6. With this connection, the left and right parts of the strip antenna are fed in phase.

On the outside of the curved rear wall 13, 14, 15, a U-shaped metal profile is fixed (by soldering or welding), forming a rectangular waveguide with a cross-sectional size of 90 × 20 mm, through which the microwave field energy is transmitted through the HFC to a two-element strip antenna and then to the camera heating up. All nodes of the microwave path are carefully worked out, and the path itself is matched up to VSWR ≈ 1.3 (VSWR is the standing wave voltage coefficient).

The heating chamber 3 is installed on the housing 4 of the electronic unit. They are interconnected by detachable locks, the design of the profit center in the assembly is stable. To shield the radiation field KVP 6 applied protective metal cover 9.

Experimental studies of the current sample of the profit center made according to the invention gave the following results:

o the coefficient of uniformity of distribution of heat sources in the chamber with a reference load in the form of a dielectric cassette of 25 cells with water with a volume of 0.04 l each α% = 92

- the efficiency of the profit center η% = 58

- the density of the radiation power flux into the free space μW / cm ² = 15

Testing of the profit centers is performed according to [4].

Industrial applicability

Tests of the current sample of the microwave oven made according to the invention, yielded results indicating a significant increase in the efficiency of the MEP. The main ones are the uniformity distribution coefficient of heat sources α≈92% without platform rotation and efficiency η = 58%. In these parameters, the created microwave oven significantly exceeds the known models.

An office profit center with a drawing-based design can be spectacular. The unconventional shape of the chamber and door significantly expand the possibilities of artistic design in comparison with the traditional parallelepiped.

Information sources

1. Microwave Oven M245 / M945. Samsung Electronics. 2001 year

2. Microwave. RF patent №2149520 from 05.20.2000. Author Zhilkov B.C.

3. A.F. Harvey. The technique of superhigh frequencies. Translation from English, ed. V.I.Sushkevich. Publishing house "Sovradio", M., 1965, 783 pp.

4. Norma International CEI IEC. International Standard 60705, Edition 3.2.2006-03.

Claims (3)

1. A microwave oven, which is a device for heat treatment of food products with microwave energy, comprising a heating chamber equipped with a door, a microwave generator located in a housing of the electronic unit having a common wall with a heating chamber, and an excitation module installed in an opening made in the rear wall communications for inputting microwave energy; a segment of a coaxial line, to the output of which a single-element strip antenna is connected, which excites an electromagnetic field (EMF) with circular polarization in the chamber cavity; the heating chamber and the body of the electronic unit are mechanically and electrically detachably connected using locks, microwave radiation from the slots at the junction of the chamber and the body of the electronic unit is shielded by a throttle filter installed around the entire perimeter of the common wall, characterized in that in the device for heat treatment using microwave energy field as an EMF causative agent in the heating chamber, a 2-element strip antenna is used, exciting in the cavity of the circularly polarized EMF chamber, connected through without a hole in the rear wall of the camera and oriented in the cavity of the camera so that the longitudinal axis of symmetry of the antenna, in the direction of which it emits electromagnetic energy, coincides with the "diagonal of the rib" - a straight line connecting the point that bisects the bending line of the rear wall of the camera, which coincides with the transverse axis of symmetry of the antenna, with a point bisecting the edge of the "dihedral angle" formed by the curved surface of the door and the surface of the lower wall of the chamber. 2. The device according to claim 1, characterized in that the 2-element strip antenna is made in the form of a radiator having the form of intersecting disk edges ("compressed figure eight"), made as a unit of sheet metal with high electrical conductivity, and a screen also made of sheet metal with high electrical conductivity and fixed through a hole in the center rigidly mechanically with good galvanic contact on the outer conductor of the coaxial segment of the coaxial waveguide transition (CVP), each of which branches a G8 radiator for providing common-mode power supply is connected mechanically and galvanically at characteristic points using high-conductivity metal bushings with a shield, and the G8 center of symmetry is connected to the central conductor of the coaxial section of the CVP, along a rectangular waveguide with 90 × 20 mm microwave energy is transferred from the microwave power source to the HVAC. 3. The device according to claim 1, characterized in that the chamber door, the surface curvature of which is described by the equation of a parabola with a horizontal axis, is made of thin, 0.3 mm thick stainless steel sheet, ~ 1/2 of the door surface is perforated with holes with D = 2 mm, edges (~ 15 mm wide), around the entire perimeter, the door is tight, with a gap of ~ 0.1 mm, adjacent to the throttle filter installed inside the chamber opening to shield the electromagnetic field of a working microwave oven, when opening and closing the camera, the door rotates around axis.