WO2019182494A1

WO2019182494A1 - Body for improved homogenity during thawing / heating of dielectric materials

Info

Publication number: WO2019182494A1
Application number: PCT/SE2019/000005
Authority: WO
Inventors: Lars Ekemar
Original assignee: Lars Ekemar
Priority date: 2018-03-21
Filing date: 2019-03-21
Publication date: 2019-09-26
Also published as: EP3769587A4; EP3769587A1; SE541885C2; SE1800061A1

Abstract

This invention relates to a device which enables improved homogeneity in heating dielectric materials by oscillating electromagnetic fields. The device is characterized in that in a load, the heating is moved around in the load by moving the potential point by short-circuiting units of electrically conductive material in the sides of the cavity.

Description

Body for improved homogeneity during thawing / heating

of dielectric materials.

The needs for homogeneous heating of materials consisting of organic as well as consisting of both organic and inorganic substances are great.

The materials may consist of solid, liquid as well as a mixture of solid and liquid

ingredients. The needs of heating range from large to small volumes.

Examples include the preparation of food in the food industry, the preparation of food in restaurants and homes, sterilization of slaughterhouse waste, digestion of wood fiber, and degradation, drying and sterilization of sludge.

There are applications where fast heating without the emergence of overheated batches is a must. One such is the warming of cold blood in connection with blood transfusions in the healthcare sector as well as in the thawing of frozen living cells.

In industrial processes such as wood drying, there is a need to measure and utilize dielectric changes.

Established heating techniques such as heating with microwaves and heating with conventional heat radiation and heat convection have in common that heat absorption in a charge/load is characterized by little to negligible penetration depth and that the internal parts of the load are heated by heat transfer from heat absorbing surface areas. In most common dielectric materials, heat transfer is slow. As a consequence, large volumes of organic material require a long time for homogeneous temperature distribution to be obtained.

It is also previously known that dielectric materials can be heated by oscillating high frequency electric fields generated between an electrode pair. The disadvantage of this technique is that it is inflexible for variations in the load geometry and composition.

It is also known in the past that by emitting electromagnetic radiation from an

antenna/applicator in a cavity with electrically conductive walls, dielectric materials placed in the cavity can be heated. (Swedish Patent 9400777-0 and Swedish Patent 9703033-2)

Microwave heating in a resonant cavity has been an established technology for many years. In order for a resonant cavity to be obtained, certain physical conditions are required. The cavity walls must be defined as boundary conditions, the shape of the cavity must meet the requirements of a resonant cavity.

According to Maxwell's equations, the electron concentration on the surface of a conductor is increasing with increasing frequency (Skin effect) At frequencies exceeding 900 MHz (microwave frequencies), the currents in a cavity wall become so superficial that according to Maxwell's equations, the walls have approximately infinite conductivity, thereby the cavity walls can be defined as boundary conditions. With decreasing frequency, the skin depth increases, at frequencies less than 300 MHz, the skin depth is so large that a resonant cavity according to the prior art is not considered possible.

When heating with microwave technology, you can obtain a homogeneous distribution of the microwaves in the cavity. The low penetration depth of the microwaves nevertheless gives an inhomogeneous heat distribution in a variety of applications where the load has a significant thickness.

Apparatus built according to the principles stated in Swedish patent 9400777-0 and Swedish Patent 9703033-2, compared to other devices on the market, gives a

considerably better homogeneity in heating, however homogeneity is insufficient in thawing/heating sensitive loads such as frozen blood plasma.

This invention provides improved homogeneity in thawing / heating of all kinds of dielectric loads.

Swedish Patent 9703033-2 builds on the technique of creating an oscillating

electromagnetic near field in a load placed in a cavity of small dimensions relative to the actual wavelength at applied frequency. By near field is meant the field (s) formed when the distance from the antenna is below one wavelength at applied frequency.

Between one or more antenna(s) in which electromagnetic fields are generated at one or more frequencies which are located in a cavity, it is a phase difference between the antenna (s) and the cavity. The magnitude of the phase difference is at most 180 degrees. The cavity housing with the enclosed antenna / antennas, in conjunction with the antenna / antennas, generates an oscillating electromagnetic field in the load.

Practical results show a good heat distribution in the load, but there are problems with the rapid thawing of sensitive dielectric loads such as frozen blood plasma and frozen living cells. Especially frozen living cells are extra sensitive to overheating while its viability is directly dependent on a rapid thawing process. (The faster thawing the better the viability) To solve the problem of uneven heating of sensitive loads, various solutions have been tried. By equipping the inside of the cavity with units consisting of electrically conductive material which is in electrical contact with the side of the cavity, one can design an oscillating electric field through the load which gives improved homogeneity. However, the improvement has been insufficient for sensitive loads such as frozen living cells. This invention solves the problem of uneven heating when heating sensitive dielectric loads. The basic idea of the invention is to be able to move the oscillating electric field through the load during the thawing/heating process by moving the electric potential while thawing/ heating is in progress. In an apparatus according to the invention the heat generation takes place in load when the emitted electromagnetic field is within the range 50Khz- 1500MHz.

Fig. 1 is an example of a device according to the invention. Between the antenna (2) and the cavity (1 ) there is a phase difference. The magnitude of the phase difference is at most 180 degrees. The sides of the cavity with the enclosed antenna/antennas, in conjunction with the antenna/antennas, generates an oscillating electromagnetic field in the load via a frequency generation (8). On the inside of the cavity is located one or more bodies (3) (4) (5) which consist wholly or partly of electrically conductive material. The bodies are electrically isolated from the cavity wall (cavity side). At each body there is placed a device (s) which establish electrically conductive contact between the cavity wall /cavity side and the body(-ies). The device may, for example, consist of a relay (7). When electrical contact is established between the body (3) and the cavity wall (cavity side), the E-field folds in that direction. If the electrical contact between the body (3) and the cavity side is broken and electrical contact is established between the body (5) and the cavity side, the electric field turns instead in that direction. In this way, the field is moved around in the load and an improved homogeneity of the heat distribution is obtained in the load.

Fig. 2 is an example of a body placed on the inside of the cavity. In this case, the body is a cylinder (A) with integrated bushing (E), both the cylinder and/or the bushing consists wholly or partly of electrically conductive material.

Between the cylinder (A) the bushing (E) and the cavity wall (C) there is one or more electrically insulating material (B).

The electrically insulating material passes through the cavity wall as shown in the figure.

On the cylinder (A), the bushing (E) is mounted which passes through the electrically insulating material and the cavity wall (C). On the outside of the cavity wall there is a relay (D) which, via the bushing, if necessary, ground the cylinder (A) in the cavity wall. This type of body can be designed in a number of different ways, for example they can be, but are not limited to, cylindrical and / or cubic forms)

It appears from the text that there may be several antennas / applicators in the cavity. The oscillating field (s) can thereby be controlled over to the antenna / applicator which is most advantageous for obtaining a homogeneous heating, selection of the applicator may vary during the heating process itself, as well as unit/units selection.

In the cavity and/or through bushings in the cavity there are devices installed for measuring heat radiation. Information from these measured values controls via an algorithm which applicators shall generate oscillating electromagnetic fields and at which different frequencies within the range 50KHz to 1500MHz.

The information from the heat measurement also controls when and which body (-ies) are grounded in the cavity.

Since the invention offers homogeneous heating of dielectric materials without

superheated points and surface zones, it is beneficial for delicate and demanding applications such as thawing frozen cells such as stem cells.

One test has been made. A bag containing 100 ml of T cells was stored at -70 ° C and placed in a field equalizer as described in EP2727030.5.

The critical temperature range for obtaining good viability is in the range -35°C to -5°C and should therefore be passed as quickly as possible.

Following the thawing process, it was found that the viability of the T cells was comparable to thawing 5 ml of T cells in a water bath (30 ° C).

Claims

1. Device for improved homogeneity in thawing/heating of dielectric materials

with oscillating electromagnetic fields generated by antenna/antennas within the frequency range of 50 KHz to 1500 MHz, characterized in that one or more bodies, which bodies consist entirely or partly of electrically conductive material, are located on the inside of the cavity without being in electrical contact with the cavity wall.

2. A device according to the preceding claim, characterized in that electrical contact is established between the cavity wall and one or more bodies in order to control the electric field through the dielectric load.

3. A device according to any one of the preceding claims, characterized in that at one or more units there is a device/devices which, if necessary, can ground one or more bodies in the cavity.

4. A device according to any one of the preceding claims, characterized in that there are units for measuring heat radiation from the dielectric load in order to be able to precision control of the electromagnetic field through the dielectric load and that electrical contact is established between the cavity wall and one or more bodies at different times during heating / heating process and that this contact / contacts are based on information from said units for measuring heat radiation.

5. A device according to any one of the preceding claims, characterized in that said bodies have a passage through the cavity according to detail E in Fig. 2.

6. A device according to any one of the preceding claims, characterized in that body and bushing are electrically insulated according to detail B in Fig. 2

7. A device according to any one of the preceding claims, characterized in that one or more relays according to Fig. 2 exist on the outside of the cavity, which via grounding, if necessary, ground body/bodies in the cavity.

8. A device according to any one of the preceding claims, characterized in that thawing/heating process is optimized by choice of grounding of the body in the cavity and it is done according to an algorithm.

9. A device according to any one of the preceding claims, characterized in that there are several antennas/applicators in the cavity and that the thawing/heating process is optimized by the system choosing the antenna/applicator for generating electromagnetic field/fields according to measured values and an algorithm.