WO2015084240A1 - Heating arrangement, method for heating, and arrangement and method for controlling an electric current - Google Patents

Heating arrangement, method for heating, and arrangement and method for controlling an electric current Download PDF

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Publication number
WO2015084240A1
WO2015084240A1 PCT/SE2014/051433 SE2014051433W WO2015084240A1 WO 2015084240 A1 WO2015084240 A1 WO 2015084240A1 SE 2014051433 W SE2014051433 W SE 2014051433W WO 2015084240 A1 WO2015084240 A1 WO 2015084240A1
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WIPO (PCT)
Prior art keywords
main body
radiation
electrical resistivity
radiation source
whichever
Prior art date
Application number
PCT/SE2014/051433
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French (fr)
Inventor
Tom Francke
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Conflux Ab
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Publication date
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Publication of WO2015084240A1 publication Critical patent/WO2015084240A1/en

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Classifications

    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01B—CABLES; CONDUCTORS; INSULATORS; SELECTION OF MATERIALS FOR THEIR CONDUCTIVE, INSULATING OR DIELECTRIC PROPERTIES
    • H01B1/00—Conductors or conductive bodies characterised by the conductive materials; Selection of materials as conductors
    • H01B1/20—Conductive material dispersed in non-conductive organic material
    • H01B1/24—Conductive material dispersed in non-conductive organic material the conductive material comprising carbon-silicon compounds, carbon or silicon
    • H—ELECTRICITY
    • H05—ELECTRIC TECHNIQUES NOT OTHERWISE PROVIDED FOR
    • H05B—ELECTRIC HEATING; ELECTRIC LIGHT SOURCES NOT OTHERWISE PROVIDED FOR; CIRCUIT ARRANGEMENTS FOR ELECTRIC LIGHT SOURCES, IN GENERAL
    • H05B6/00—Heating by electric, magnetic or electromagnetic fields
    • H05B6/64—Heating using microwaves
    • H05B6/6408—Supports or covers specially adapted for use in microwave heating apparatus
    • H—ELECTRICITY
    • H05—ELECTRIC TECHNIQUES NOT OTHERWISE PROVIDED FOR
    • H05B—ELECTRIC HEATING; ELECTRIC LIGHT SOURCES NOT OTHERWISE PROVIDED FOR; CIRCUIT ARRANGEMENTS FOR ELECTRIC LIGHT SOURCES, IN GENERAL
    • H05B6/00—Heating by electric, magnetic or electromagnetic fields
    • H05B6/64—Heating using microwaves
    • H05B6/647—Aspects related to microwave heating combined with other heating techniques
    • H05B6/6491—Aspects related to microwave heating combined with other heating techniques combined with the use of susceptors
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01C—RESISTORS
    • H01C7/00—Non-adjustable resistors formed as one or more layers or coatings; Non-adjustable resistors made from powdered conducting material or powdered semi-conducting material with or without insulating material
    • H01C7/02—Non-adjustable resistors formed as one or more layers or coatings; Non-adjustable resistors made from powdered conducting material or powdered semi-conducting material with or without insulating material having positive temperature coefficient
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01C—RESISTORS
    • H01C7/00—Non-adjustable resistors formed as one or more layers or coatings; Non-adjustable resistors made from powdered conducting material or powdered semi-conducting material with or without insulating material
    • H01C7/04—Non-adjustable resistors formed as one or more layers or coatings; Non-adjustable resistors made from powdered conducting material or powdered semi-conducting material with or without insulating material having negative temperature coefficient

Definitions

  • the technical field is generally directed to arrangements and methods for heating and controlling electric currents by using radiation.
  • Electric heating is any process in which electrical energy is converted to heat.
  • An electric heater is an electrical appliance that converts electrical energy into heat.
  • the heating element inside every electric heater is simply an electrical resistor, and works on the principle of Joule heating: an electric current through a resistor converts electrical energy into heat energy.
  • Microwaves are a form of electromagnetic radiation with wavelengths ranging from as long as one meter to as short as one millimeter, or equivalently, with frequencies between 300 MHz (0.3 GHz) and 300 GHz. Microwave technologies are extensively used for point-to-point or long range telecommunications and communications. Microwaves are also employed in radar technology and in microwave ovens.
  • Microwave ovens heat foods quickly and efficiently because excitation is fairly uniform in the outer 25-38 mm of a dense (high water content) food item; food is more evenly heated throughout (except in thick, dense objects) than generally occurs in other cooking techniques.
  • a first aspect refers to a heating arrangement comprising a main body including a polymer based material, a plurality of particles of a material capable of absorbing microwave radiation arranged in the main body, and a radiation source, e.g. a magnetron, configured to irradiate the main body with microwave radiation to thereby heat the main body.
  • the main body is, during use, arranged in thermal contact with an object to be heated.
  • an arrangement that utilizes microwaves for heating, but which does not heat directly an object to be heated.
  • the microwaves are utilized for heating a main body of a polymer based material, which in turn can be arranged in thermal contact with, e.g. placed on top of, the main body to thereby be heated.
  • object which does not absorb microwave radiation, can still be heated by this arrangement.
  • the main body may mainly comprise a cross-linked polymer or elastomer, such as for example a silicone, e.g. polydimethyl siloxane, and optionally a filler, e.g. based on silica, whereas the particles maybe carbon-containing particles, such as for example carbon blacks.
  • the main body may be provided as a sheet or film.
  • the may be flexible and bendable and cut to suitable sizes to suit a variety of objects having planar and non planar surfaces.
  • the main body e.g. provided a thin flexible film may be arranged, temporarily or permanently, on the rotating blades of a wind power plant or on the wings of an aircraft, wherein the microwave radiation source maybe arranged on the ground or on a vehicle and be configured to irradiate the thin flexible film during some periods of times, e.g. at periods of low temperatures and/or before take off (for the aircraft).
  • the main body with the plurality of particles arranged therein has strong, e.g. exponential, temperature dependent electrical resistivity, or is thermally connected to an additional body having strong, e.g. exponential,
  • the main body, or the additional body, whichever having strong temperature dependent electrical resistivity maybe made of a PTC (Positive Temperature Coefficient) material. It has advantageously an electrical resistivity which is increasing with increasing temperature.
  • the radiation source may be fed by a feeding current, which is at least partly flowing through the main body or the additional body, whichever having strong temperature dependent electrical resistivity.
  • the temperature of the main or additional body will be used to regulate the current to the radiation source, and thus the power of the radiation source and the heating power.
  • the main or additional body will be cold and have low resistance, which increases the current fed to the radiation source and the heating power will be high.
  • the main or additional body will not be cooled by the object, and the resistance of the main or additional body will become higher limiting or cutting off the current fed to the radiation source, and as a result the heating power will be reduced or cut off.
  • This self regulating mechanism is very important to not overheat an object to be heated.
  • the main or additional body will soon be heated and the resistance of the main or additional body will become high limiting or cutting off the current fed to the radiation source, and as a result the heating power will be reduced or cut off. This prevents overheating the main or additional body, which could cause damages of the same.
  • the main body, or the additional body, whichever having strong temperature dependent electrical resistivity may have an electrical resistivity, which is increasing with temperature faster than linearly, at least within a desired temperature interval.
  • the temperature derivative of the electrical resistivity may be strictly increasing with temperature, at least within a desired temperature interval, or in other words, the temperature derivative of the electrical conductivity may be strictly decreasing with temperature, at least within the desired temperature interval.
  • the above alternative formulations are intended to better define the term "strong” in the expression "strong temperature dependent electrical resistivity".
  • a material having "strong temperature dependent electrical resistivity" maybe a PTC material or a material having a trip temperature, at which temperature the temperature coefficient changes abruptly or sharply.
  • the material may also be any NTC (Negative Temperature Coefficient) material, e.g. an NTC material having an electrical resistivity, which is decreasing with temperature faster than linearly, at least within a desired
  • a second aspect refers to a method for heating comprising the steps of providing a main body comprising a polymer based material, and a plurality of particles of a material capable of absorbing microwave radiation arranged in the main body, and irradiating the main body with microwave radiation from a radiation source, preferably a magnetron, thereby heating the main body.
  • An object to be heated is arranged in thermal contact with, preferably placed on top of, the main body.
  • the main body may, as above, be provided as a sheet or film.
  • the main body with the plurality of particles arranged therein may have strong, e.g. exponential, negative temperature dependent electrical resistivity, or maybe thermally connected to an additional body having strong, e.g. exponential, negative temperature dependent electrical resistivity, and wherein the radiation source is fed by a feeding current, which is at least partly flowing through the main body or the additional body, whichever having strong temperature dependent electrical resistivity.
  • a third aspect refers to an arrangement for controlling an electric current comprising a main body, electrical terminals, a radiation source, and a control device, wherein the main body has strong temperature dependent electrical resistivity, the electrical terminals are electrically connected to the main body, the main body is capable of absorbing radiation from the radiation source or the arrangement comprises a supplementary body, which is capable of absorbing radiation from the radiation source and which is thermally connected to the main body, e.g. firmly attached to the main body.
  • the radiation source is capable of irradiating the main body or the supplementary body, whichever being capable of absorbing the radiation, in response to which the main body gets heated and alters its electrical resistivity
  • the control device is configured to control an electric current flown through the main body via the electrical terminals by means of controlling the power of the radiation irradiating the main body or the supplementary body, whichever being capable of absorbing the radiation.
  • the main body has exponential temperature dependent electrical resistivity and/or negative temperature dependent electrical resistivity, i.e. the electrical resistivity is decreasing with increasing temperature.
  • the radiation capable of being absorbed by the main body or the supplementary body may be microwaves, and the radiation source, e.g. a magnetron, may be capable of irradiating the main body or the supplementary body, whichever being capable of absorbing the radiation, with microwaves.
  • the radiation source e.g. a magnetron
  • control arrangement can be used for electric circuitry arranged in hazardous environments, in cramped spaces with no or low access to the circuitry.
  • the control arrangement (control device and radiation source) can also be moved with respect to the electric circuitry including the main body and the optional supplementary body.
  • one control arrangement (control device and radiation source) can be used for controlling electric current in multiple positions or in multiple circuitry, wherein each of these positions or circuitry houses a main body and optionally a supplementary body as defined above.
  • a fourth aspect refers to a switch for switching an electric current, which comprises the arrangement of the third aspect, wherein the main body is electrically conducting at a first temperature and electrically insulating at a second temperature, higher than the first temperature, the radiation source is capable of irradiating the main body or the supplementary body, whichever being capable of absorbing the radiation, such that main body can alternately reach the first and second temperatures, and the control device is configured to control an electric current flown through the main body via the electrical terminals by means of controlling the power of the radiation irradiating the main body or the supplementary body, whichever being capable of absorbing the radiation, to alternately reach the first and second temperatures, thereby switching the electric current.
  • an electric switch which can be operated in a contactless manner from a remote position.
  • a fifth aspect refers to an amplifier for amplifying an input current signal, which comprises the arrangement of the third aspect and a current source for inputting an electric input current to the radiation source, in response to which the radiation source irradiates the main body or the supplementary body, whichever being capable of absorbing radiation, with radiation, wherein the power of the radiation irradiating the main body depends on the electric input current to the radiation source.
  • the control device is configured to vary the electric input current to the radiation source to form an input current signal, in response to which the temperature of the main body is varied, and the main body is arranged to modulate an electric current flown there through by means of its varying temperature to output an amplified current signal.
  • the main body ought to have strong temperature dependent electrical resistivity. Given a negative temperature dependent electrical resistivity, the amplified current signal will be phase shifted 180 degrees with respect to the input current signal.
  • the above amplifier can be used in a microwave transmitter.
  • the output power is sensed and the amplifier can be used to regulate the output power since a high output power will heat the main body and increase its resistance, and as a result thereof the current to the radiation source is decreased and the output power is decreased, and correspondingly a low output power will heat the main body less and decrease its resistance, and as a result thereof the current to the radiation source is increased and the output power is increased.
  • Another application of the above amplifier is a galvanically separated amplifier. It can be used for regulating a high voltage alternating current by means of microwaves, wherein common problems obtained with electronic circuits are entirely avoided.
  • the galvanically separated amplifier is also rather insensitive for EMC disturbances, electric grid transients, lightning, etc.
  • a sixth aspect refers to a method for controlling an electric current with an arrangement comprising a main body, electrical terminals, a radiation source, and a control device, wherein the main body has strong temperature dependent electrical resistivity, the electrical terminals are electrically connected to the main body, and the main body is capable of absorbing radiation from the radiation source or the arrangement comprises a supplementary body, which is capable of absorbing radiation from the radiation source and which is thermally connected to the main body.
  • the method comprises the steps of irradiating the main body or the supplementary body, whichever being capable of absorbing the radiation, with radiation from the radiation source to thereby heat the main body and alter its electrical resistivity, and controlling an electric current flown through the main body via the electrical terminals by means of controlling the power of the radiation irradiating the main body or the supplementary body, whichever being capable of absorbing the radiation.
  • the body having strong temperature dependent electrical resistivity is of a compound comprising an electrically insulating bulk material, electrically conductive particles of a first kind, and electrically conductive particles of a second kind.
  • the bulk material holds the particles of the first and second kinds in place, the particles of the second kind are smaller than the particles of the first kind, the particles of the second kind are more in number than the particles of the first kind, the particles of the second kind have higher surface roughness than the particles of the first kind, wherein the particles of the second kind comprise tips and the particles of the first kind comprise even surface portions, the particles of the first and second kinds are arranged to form a plurality of current paths through the compound.
  • Each of the current paths may comprise galvanically connected particles of the first and second kinds and a gap between a tip of one of the particles of the second kind and an even surface portion of one of the particles of the first kind, wherein the gap is narrow enough to allow electrons to tunnel through the gap via the quantum tunneling effect.
  • the tips of the particles of the second kind maybe so sharp that the very ends of the tips comprise a single atom or a few atoms only.
  • the bulk material has a thermal expansion capability such that it expands with temperature, thereby increasing the gap widths of the current paths, which in turn increases the electrical resistivity.
  • the bulk material may comprise a cross-linked polymer or elastomer, such as for example a silicone, e.g. polydimethyl siloxane, and optionally a filler, thickener, or stabilizer, such as for example silica, distributed in the compound, and the particles of the first and second kinds may be carbon-containing particles, such as for example carbon blacks.
  • a cross-linked polymer or elastomer such as for example a silicone, e.g. polydimethyl siloxane, and optionally a filler, thickener, or stabilizer, such as for example silica, distributed in the compound, and the particles of the first and second kinds may be carbon-containing particles, such as for example carbon blacks.
  • the number of the current paths through the compound and the widths of the gaps therein at any given temperature may be selected depending on the thermal expansion capability of the electrically insulating bulk material to obtain strong temperature dependent electrical resistivity of the compound in a selected temperature interval.
  • Fig. 1 illustrates, schematically, a heating arrangement according to an embodiment.
  • Figs.2 and 3 illustrate each, schematically, an arrangement for controlling an electric current according to an embodiment.
  • Fig. 4 illustrates, schematically, a circuitry including a switch for switching an electric current according to an embodiment.
  • Fig. 5 illustrates, schematically, a portion of a compound having strong temperature dependent electrical resistivity according to an embodiment.
  • Fig. 6 illustrates, schematically, a detail of the structure of the compound in Fig. ⁇ in more detail.
  • Fig. 7 illustrates, schematically, a portion of the compound in Fig. l, wherein a plurality of current paths through the compound is shown.
  • Fig. l illustrates, schematically, a heating arrangement according to an embodiment.
  • the heating arrangement comprises a main body n and a radiation source 13, e.g. a magnetron.
  • the main body 11 comprises a polymer based material and a plurality of particles 12 of a material capable of absorbing microwave radiation arranged in the main body 11.
  • the particles may be carbon-containing particles, such as for example carbon blacks.
  • the radiation source 13 is configured to irradiate the main body 11 with microwave radiation to thereby heat the main body 11 and any object in thermal contact with the main body 11.
  • the main body 11 may comprise mainly a cross-linked polymer or elastomer, such as for example a silicone, e.g. polydimethyl siloxane, and optionally a filler, e.g. based on silica, and maybe provided as a sheet.
  • a cross-linked polymer or elastomer such as for example a silicone, e.g. polydimethyl siloxane, and optionally a filler, e.g. based on silica, and maybe provided as a sheet.
  • the main body 11 maybe flexible and bendable and cut to suitable sizes to suit a variety of planar and non planar surfaces.
  • an object to be heated is arranged in thermal contact with, e.g. placed on top of, the sheet-shaped main body 11.
  • the main body 11 with the plurality of particles 12 arranged therein has strong, e.g. exponential, negative temperature dependent electrical resistivity, i.e. an electrical resistivity which is increasing with increasing temperature.
  • the main body 11 with the plurality of particles 12 arranged therein is thermally connected to an additional body (e.g. body 21 of Fig. 2) having strong, e.g. exponential, negative temperature dependent electrical resistivity.
  • the radiation source 13 may be fed by a feeding current from a power source 14, wherein the feeding current is at least partly flowing through the main body 11 or the additional body, whichever having strong temperature dependent electrical resistivity.
  • a radiation/microwave based self-regulating heating arrangement is provided, which can be tuned such that when the main body 11, the optional additional body, or an object to be heated and placed in thermal contact with the main body 11, or the optional additional body, has reached a selected temperature, the further heating is switched off, or at least strongly decreased, due to the limitation of the feeding current as caused by increased resistance through the main body 11 or the additional body, whichever having strong negative temperature dependent electrical resistivity.
  • Fig.2 illustrates, schematically, an arrangement for controlling an electric current according to an embodiment.
  • the arrangement comprises a main body 21, a supplementary body 25, electrical terminals 22a-b electrically connected to the main body 21, a radiation source 13, and a control device 24 operatively connected to the radiation source i3for controlling the operation thereof.
  • the main body 21 has strong temperature dependent electrical resistivity, preferably a negative temperature dependent electrical resistivity, and a negative exponential dependent electrical resistivity.
  • the supplementary body 25 is capable of absorbing radiation such as microwaves from the radiation source 13 and is thermally connected, e.g. firmly attached, to the main body 21.
  • the supplementary body 25 may be of the same material as the main body of the embodiment of Fig. 1 and the main body maybe of any of the compounds disclosed in this document with reference to Figs. 5-7.
  • the radiation source 13 such as a magnetron is capable of irradiating the supplementary body 25 with radiation such as microwaves, in response to which the main body 21 gets heated (via the thermal connection between the main body 21 and the supplementary body 25) and alters its electrical resistivity.
  • the control device 24 is configured to control an electric current flown through the main body 21 via the electrical terminals 22a-b by means of controlling the power of the radiation irradiating the supplementary body 25. That is, an electric current is controlled by means of microwave radiation and the arrangement is a transducer for converting radiation into current, or a radiation signal into a current signal provided that the signal speed is low enough to allow the temperature to increase and decrease in response to an increased or decreased power of the radiation irradiating the supplementary body 25. To remove heat fast enough when the radiation is decreased or switched off, the main body 21 and/or supplementary body 25 may be provided with coolers or heat sink structures (not illustrated).
  • Fig. 3 illustrates, schematically, an arrangement for controlling an electric current according to an embodiment, which differs from the arrangement of Fig. 2 in that the supplementary body 25 is dispensed with. Instead the main body, denoted here with reference numeral 31, is capable of absorbing radiation such as microwaves from the radiation source 13.
  • Fig. 4 illustrates, schematically, a circuitry 41 including a power source 42, a load 43, and a switch 44 serially connected to one another.
  • the switch 44 may be the main body 21 and the supplementary body 25 of the embodiment of Fig. 2, or the main body 31 of the embodiment of Fig. 3, wherein the electrical terminals 22a-b are connected to the load 43 and the power source 42, respectively.
  • the main body 11, 21 has such a strong negative temperature dependent resistivity (or strong positive temperature dependent resistivity) that is electrically conducting at a first temperature and essentially electrically insulating at a second temperature, higher than the first temperature.
  • the switch 44 is operated by a radiation source 13 and a control device 24 opera tively connected to the radiation source 13, wherein the radiation source 13 is capable of irradiating the supplementary body 25 of the embodiment of Fig. 2 or the main body 31 of the embodiment of Fig. 3, such that main body 21, 31 can alternately reach the first and second temperatures.
  • the control device 24 is configured to control an electric current flown in the circuitry of Fig. 4 and through the main body 21, 31 via by means of controlling the power of the radiation irradiating the supplementary body 25 or the main body 31 to alternately reach the first and second temperatures.
  • the electric current in the circuitry can be alternately switched on and off, wherein the load 43 is alternately connected to, and disconnected from, the power source 42.
  • the arrangement of Fig. 2 or Fig. 3 is used in an amplifier for amplifying an input current signal.
  • the current source 13 is provided with a power source, such as the power source 14 of Fig. 1, for inputting an electric input current to the radiation source 13, in response to which the radiation source 13 irradiates the supplementary body 25 Fig. 2) or the main body 31 (Fig. 3) with radiation, wherein the power of the radiation irradiating the supplementary body 25/main body 31 depends on the electric input current to the radiation source 13.
  • the control device 24 (Figs. 2 and 3) is operatively connected to the power source and is configured to vary the electric input current to the radiation source 13 to form an input current signal. In response thereto, the temperature of the main body 21, 31 is varied or modulated.
  • a current is flown through the main body 21, 31 from e.g. electrical terminal 22a to electrical terminal 22b, and this current is modulated by the varied or modulated temperature of the main body 32, 21 such that a modulated current signal can be output.
  • the output modulated current signal can be an amplification of the input current signal, and as a result the arrangement of Fig. 2 or Fig. 3 embodies an amplifier which amplifies an input current signal (current to the radiation source) and outputs an amplified current signal at electrical terminal 22b.
  • the amplified current signal will be phase shifted 180 degrees with respect to the input current signal. If the main body 21, 31 has a linear temperature dependent resistivity within a temperature interval used, the amplifier may have a good linearity. However, the heating, and thereby increased resistivity, of the main body 21, 31 due to the current input at electrical terminal 22a may have to be considered.
  • This document also encompasses methods for heating, controlling an electric current, switching an electric current, and amplifying an input current signal comprising method steps for performing the functions disclosed above with reference to Figs. 1-4.
  • Fig. 5 illustrates, schematically, a portion of a compound having strong temperature dependent electrical resistivity according to an embodiment.
  • the compound comprises an electrically insulating bulk material 51, electrically conductive particles 52 of a first kind, and electrically conductive particles 53 of a second kind arranged in the bulk material 51.
  • the bulk material 51 may comprise an amorphous cross-linked polymer or elastomer, such as for example a siloxane elastomer (often called silicone elastomer) such as polyfluorosiloxane or polydimethyl siloxane and possibly also a filler, thickener, or stabilizer, such as silica.
  • a siloxane elastomer often called silicone elastomer
  • the bulk material holds the particles of the first and second kinds firmly in place in the bulk material after cross-linking.
  • the filler, thickener, or stabilizer maybe mixed with the bulk material to obtain a compound having a desired consistence, flexibility, and/ or elasticity.
  • the electrically conducting particles 52, 53 of the first and second kinds maybe carbon-containing particles, such as for example carbon blacks.
  • the particles 53 of the second kind may (i) be smaller, (ii) be more in number, (iii) have higher surface roughness, and (iv) have more irregular shape than the particles 52 of the first kind as being schematically illustrated in Fig. 5.
  • Fig. 6 illustrates schematically a detail of the structure of the compound in Fig. 5 in more detail including one particle 53 of the second kind and a portion of one particle 52 of the first kind firmly secured in the bulk material 51.
  • the highly irregularly shaped particles 53 of the second kind comprise tips 53a and the more regularly shaped particles 52 of the first kind comprise even surface portions 52a.
  • the tips 53a of the particles 53 of the second kind maybe so sharp that the very ends of the tips 53a comprise a single atom or a few atoms only.
  • the particles 53 of the second kind may be covered by a lubricant 61, such as for example a homo-oligomer, e.g. vinylmethoxysiloxane homo-oligomer, as being illustrated for one of the particles 53 of the second kind in Fig. 6.
  • the lubricant 61 may assist in a suitable positioning of the particles 53 of the second kind in the bulk material 51.
  • Fig. 7 illustrates schematically a portion of the compound in Fig. 1, wherein a plurality of current paths 54 through the compound is shown.
  • the particles 52, 53 of the first and second kinds are arranged to form the current paths 54 through the compound, wherein each of the current paths 54 comprises galvanically connected particles 52, 53 of the first and second kinds and a gap 54a between a tip 53a of one of the particles 53 of the second kind and an even surface portion 52a of one of the particles 52 of the first kind, wherein the gap 54a has a width which is small enough to allow electrons to tunnel through the gap via the quantum tunneling effect.
  • Fig. 7 illustrates three current paths through the compound, it shall be appreciated that there may be thousands of current paths per square millimeter through a film of the compound. At a certain gap width w of the current paths 54, the quantum tunneling effect disappears and the compound does not conduct any longer.
  • the bulk material 51 has a thermal expansion capability such that it expands with temperature, thereby increasing the gap widths w of the current paths 54, which in turn increases the electrical resistivity of the compound exponentially.
  • the number of the current paths 54 through the compound and the widths w of the gaps 54a therein at any given temperature are provided depending on the thermal expansion capability of the compound to obtain a strong, e.g. exponential, temperature dependent electrical resistivity of the compound in a selected temperature interval.
  • the number of the current paths 54 through the compound, the widths w of the gaps 54a therein, and the thermal expansion capability of the compound can be controlled by adjusting the various ingredients of the compound, varying the amounts of the various ingredients of the compound, varying the order and manner in which they are mixed, and/ or varying the cross-linking of the polymer or elastomer comprised in the bulk material.
  • the particles of the second kind may be covered by a lubricant before the particles of the first and second kinds are arranged in the bulk material.
  • the particles of the second kind and the lubricant are mixed together in a solvent, after which the solvent is removed.
  • the mixture of the particles of the second kind and the lubricant may be mixed with the filler, thickener, or stabilizer in a solvent, after which the solvent is removed.
  • the mixture of the particles of the second kind, the lubricant, and the filler, thickener, or stabilizer may be mixed with the mixture of the particles of the first kind and the polymer or elastomer to obtain the compound.
  • the filler, thickener, or stabilizer may be mixed with the particles of the first kind and/ or the polymer or elastomer, to which the mixture of the particles of the second kind and the lubricant is added.
  • the compound is made up the following ingredients and amounts thereof (as given in weight percentages based on the weight of the compound), wherein the carbon blacks of the first kind have an average size of 500 nm and the carbon blacks of the second kind have an average size of 50 nm : polydimethyl siloxane 44
  • the individual sizes of the particles of each kind may vary quite much, such as e.g. by a factor 10. Therefore it is advantageous that the sizes are given as some kind of statistical sizes, such as e.g. average sizes.
  • the above compound can be tailored to obtain the desired strong negative temperature dependent resistivity in any desired temperature interval in the temperature range of minus 80 to plus 80 degrees Celsius, and may have very low resistance, e.g. 1-10 ohms, in a lower portion of such temperature interval.
  • Alternative materials which can be used in the main body or additional body of the embodiment of Fig. 1, and in the main body 21, 31 of the embodiments of Figs. 2-4 comprise PTC materials such as PTC ceramics or functional ceramics such as e.g. barium titanates, which have strong negative temperature dependent resistivity in a relatively high temperature interval, e.g. above 140 degrees Celsius, while the resistances at lower temperatures are still often above 100 ohms.
  • PTC materials such as PTC ceramics or functional ceramics such as e.g. barium titanates, which have strong negative temperature dependent resistivity in a relatively high temperature interval, e.g. above 140 degrees Celsius, while the resistances at lower temperatures are still often above 100 ohms.

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  • Chemical & Material Sciences (AREA)
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  • Spectroscopy & Molecular Physics (AREA)
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Abstract

A heating arrangement comprises a main body (11; 25; 31) comprising a polymer based material, in which a plurality of particles (12) of a material capable of absorbing microwave radiation is arranged, and a radiation source (13) configured to irradiate the main body with microwave radiation to thereby heat the main body. An object to be heated is arranged in thermal contact with the main body. The main body (31) may have strong, e.g. exponential, temperature dependent electrical resistivity, or may be thermally connected to an additional body (21) having such electrical resistivity, wherein the radiation source (13) may be fed by a feeding current, which is at least partly flowing through the main body (11) or the additional body (21), whichever having strong temperature dependent electrical resistivity. The arrangement may comprise electrical terminals (22a-b) and a control device (24), wherein the electrical terminals may be connected to the main body (31) or the additional body (21), whichever having strong temperature dependent electrical resistivity, and the control device may be configured to control an electric current flown through the main body (31)/additional body (21) via the electrical terminals by means of controlling the power of the radiation irradiating the main body.

Description

HEATING ARRANGEMENT, METHOD FOR HEATING, AND
ARRANGEMENT AND METHOD FOR CONTROLLING AN ELECTRIC CURRENT
TECHNICAL FIELD
The technical field is generally directed to arrangements and methods for heating and controlling electric currents by using radiation.
DESCRIPTION OF RELATED ART AND BACKGROUND
Electric heating is any process in which electrical energy is converted to heat.
Common applications include space heating, cooking, water heating, and industrial processes. An electric heater is an electrical appliance that converts electrical energy into heat. The heating element inside every electric heater is simply an electrical resistor, and works on the principle of Joule heating: an electric current through a resistor converts electrical energy into heat energy.
Microwaves are a form of electromagnetic radiation with wavelengths ranging from as long as one meter to as short as one millimeter, or equivalently, with frequencies between 300 MHz (0.3 GHz) and 300 GHz. Microwave technologies are extensively used for point-to-point or long range telecommunications and communications. Microwaves are also employed in radar technology and in microwave ovens.
Microwave ovens heat foods quickly and efficiently because excitation is fairly uniform in the outer 25-38 mm of a dense (high water content) food item; food is more evenly heated throughout (except in thick, dense objects) than generally occurs in other cooking techniques.
SUMMARY
There are a number of applications, in which electric heating or microwave oven heating is impracticable or unsuitable or even unmanageable.
There are thus demands for novel heaters using alternative manners of transferring energy into heat for heating objects in various applications. There are also a number of areas, in which microwaves have seen little or no attention this far. For instance, the application of microwaves for controlling electric circuits, for switching electric currents, and for amplifying electric signals, seem not to be recognized.
There is an aim of this document to reveal novel applications for microwaves that are useful in heating and electrical systems.
A first aspect refers to a heating arrangement comprising a main body including a polymer based material, a plurality of particles of a material capable of absorbing microwave radiation arranged in the main body, and a radiation source, e.g. a magnetron, configured to irradiate the main body with microwave radiation to thereby heat the main body. The main body is, during use, arranged in thermal contact with an object to be heated.
Hereby, an arrangement is provided that utilizes microwaves for heating, but which does not heat directly an object to be heated. Instead, the microwaves are utilized for heating a main body of a polymer based material, which in turn can be arranged in thermal contact with, e.g. placed on top of, the main body to thereby be heated. Thus, object, which does not absorb microwave radiation, can still be heated by this arrangement.
The main body may mainly comprise a cross-linked polymer or elastomer, such as for example a silicone, e.g. polydimethyl siloxane, and optionally a filler, e.g. based on silica, whereas the particles maybe carbon-containing particles, such as for example carbon blacks. The main body may be provided as a sheet or film.
Hereby, the may be flexible and bendable and cut to suitable sizes to suit a variety of objects having planar and non planar surfaces.
An object, which cannot be heated by sending an electric current through it, or, which is difficult to connect to an electric current, e.g. due to a cramped or remote access, can be heated by an arrangement as disclosed herein. The main body e.g. provided a thin flexible film may be arranged, temporarily or permanently, on the rotating blades of a wind power plant or on the wings of an aircraft, wherein the microwave radiation source maybe arranged on the ground or on a vehicle and be configured to irradiate the thin flexible film during some periods of times, e.g. at periods of low temperatures and/or before take off (for the aircraft).
In one embodiment, the main body with the plurality of particles arranged therein has strong, e.g. exponential, temperature dependent electrical resistivity, or is thermally connected to an additional body having strong, e.g. exponential,
temperature dependent electrical resistivity. The main body, or the additional body, whichever having strong temperature dependent electrical resistivity, maybe made of a PTC (Positive Temperature Coefficient) material. It has advantageously an electrical resistivity which is increasing with increasing temperature. The radiation source may be fed by a feeding current, which is at least partly flowing through the main body or the additional body, whichever having strong temperature dependent electrical resistivity.
Hereby, the temperature of the main or additional body will be used to regulate the current to the radiation source, and thus the power of the radiation source and the heating power. This means that if a cold object is placed in thermal contact with, or on top of, the main or additional body, the main or additional body will be cold and have low resistance, which increases the current fed to the radiation source and the heating power will be high. When the object is heated, the main or additional body will not be cooled by the object, and the resistance of the main or additional body will become higher limiting or cutting off the current fed to the radiation source, and as a result the heating power will be reduced or cut off. This self regulating mechanism is very important to not overheat an object to be heated.
Besides, if no object is placed in thermal contact with the main or additional body, the main or additional body will soon be heated and the resistance of the main or additional body will become high limiting or cutting off the current fed to the radiation source, and as a result the heating power will be reduced or cut off. This prevents overheating the main or additional body, which could cause damages of the same.
The main body, or the additional body, whichever having strong temperature dependent electrical resistivity, may have an electrical resistivity, which is increasing with temperature faster than linearly, at least within a desired temperature interval. The temperature derivative of the electrical resistivity may be strictly increasing with temperature, at least within a desired temperature interval, or in other words, the temperature derivative of the electrical conductivity may be strictly decreasing with temperature, at least within the desired temperature interval. The above alternative formulations are intended to better define the term "strong" in the expression "strong temperature dependent electrical resistivity". Further, a material having "strong temperature dependent electrical resistivity" maybe a PTC material or a material having a trip temperature, at which temperature the temperature coefficient changes abruptly or sharply. The material may also be any NTC (Negative Temperature Coefficient) material, e.g. an NTC material having an electrical resistivity, which is decreasing with temperature faster than linearly, at least within a desired
temperature interval. A second aspect refers to a method for heating comprising the steps of providing a main body comprising a polymer based material, and a plurality of particles of a material capable of absorbing microwave radiation arranged in the main body, and irradiating the main body with microwave radiation from a radiation source, preferably a magnetron, thereby heating the main body. An object to be heated is arranged in thermal contact with, preferably placed on top of, the main body. The main body may, as above, be provided as a sheet or film.
In one embodiment, the main body with the plurality of particles arranged therein may have strong, e.g. exponential, negative temperature dependent electrical resistivity, or maybe thermally connected to an additional body having strong, e.g. exponential, negative temperature dependent electrical resistivity, and wherein the radiation source is fed by a feeding current, which is at least partly flowing through the main body or the additional body, whichever having strong temperature dependent electrical resistivity.
The advantages of this embodiment are those disclosed above.
A third aspect refers to an arrangement for controlling an electric current comprising a main body, electrical terminals, a radiation source, and a control device, wherein the main body has strong temperature dependent electrical resistivity, the electrical terminals are electrically connected to the main body, the main body is capable of absorbing radiation from the radiation source or the arrangement comprises a supplementary body, which is capable of absorbing radiation from the radiation source and which is thermally connected to the main body, e.g. firmly attached to the main body.
The radiation source is capable of irradiating the main body or the supplementary body, whichever being capable of absorbing the radiation, in response to which the main body gets heated and alters its electrical resistivity, and the control device is configured to control an electric current flown through the main body via the electrical terminals by means of controlling the power of the radiation irradiating the main body or the supplementary body, whichever being capable of absorbing the radiation.
Advantageously, the main body has exponential temperature dependent electrical resistivity and/or negative temperature dependent electrical resistivity, i.e. the electrical resistivity is decreasing with increasing temperature.
The radiation capable of being absorbed by the main body or the supplementary body may be microwaves, and the radiation source, e.g. a magnetron, may be capable of irradiating the main body or the supplementary body, whichever being capable of absorbing the radiation, with microwaves.
This aspect can be used in a variety of applications, wherein an electric current should be controlled in one manner or the other. Advantages include that the current control is contactless and that the control can be made from a remote position by means of the radiation. As a result, the control arrangement can be used for electric circuitry arranged in hazardous environments, in cramped spaces with no or low access to the circuitry. The control arrangement (control device and radiation source) can also be moved with respect to the electric circuitry including the main body and the optional supplementary body. In fact, in some applications one control arrangement (control device and radiation source) can be used for controlling electric current in multiple positions or in multiple circuitry, wherein each of these positions or circuitry houses a main body and optionally a supplementary body as defined above.
A fourth aspect refers to a switch for switching an electric current, which comprises the arrangement of the third aspect, wherein the main body is electrically conducting at a first temperature and electrically insulating at a second temperature, higher than the first temperature, the radiation source is capable of irradiating the main body or the supplementary body, whichever being capable of absorbing the radiation, such that main body can alternately reach the first and second temperatures, and the control device is configured to control an electric current flown through the main body via the electrical terminals by means of controlling the power of the radiation irradiating the main body or the supplementary body, whichever being capable of absorbing the radiation, to alternately reach the first and second temperatures, thereby switching the electric current.
That is an electric switch is provided which can be operated in a contactless manner from a remote position.
A fifth aspect refers to an amplifier for amplifying an input current signal, which comprises the arrangement of the third aspect and a current source for inputting an electric input current to the radiation source, in response to which the radiation source irradiates the main body or the supplementary body, whichever being capable of absorbing radiation, with radiation, wherein the power of the radiation irradiating the main body depends on the electric input current to the radiation source. The control device is configured to vary the electric input current to the radiation source to form an input current signal, in response to which the temperature of the main body is varied, and the main body is arranged to modulate an electric current flown there through by means of its varying temperature to output an amplified current signal. To get an amplified current signal, the main body ought to have strong temperature dependent electrical resistivity. Given a negative temperature dependent electrical resistivity, the amplified current signal will be phase shifted 180 degrees with respect to the input current signal.
The above amplifier can be used in a microwave transmitter. By arranging the main body or the supplementary body, whichever being capable of absorbing radiation, in the radiation path of the microwave transmitter, the output power is sensed and the amplifier can be used to regulate the output power since a high output power will heat the main body and increase its resistance, and as a result thereof the current to the radiation source is decreased and the output power is decreased, and correspondingly a low output power will heat the main body less and decrease its resistance, and as a result thereof the current to the radiation source is increased and the output power is increased.
Another application of the above amplifier is a galvanically separated amplifier. It can be used for regulating a high voltage alternating current by means of microwaves, wherein common problems obtained with electronic circuits are entirely avoided. The galvanically separated amplifier is also rather insensitive for EMC disturbances, electric grid transients, lightning, etc.
A sixth aspect refers to a method for controlling an electric current with an arrangement comprising a main body, electrical terminals, a radiation source, and a control device, wherein the main body has strong temperature dependent electrical resistivity, the electrical terminals are electrically connected to the main body, and the main body is capable of absorbing radiation from the radiation source or the arrangement comprises a supplementary body, which is capable of absorbing radiation from the radiation source and which is thermally connected to the main body. The method comprises the steps of irradiating the main body or the supplementary body, whichever being capable of absorbing the radiation, with radiation from the radiation source to thereby heat the main body and alter its electrical resistivity, and controlling an electric current flown through the main body via the electrical terminals by means of controlling the power of the radiation irradiating the main body or the supplementary body, whichever being capable of absorbing the radiation.
Further method steps may be added to the sixth aspect in order to perform the switching function disclosed with reference to the fourth aspect and/or the amplifying function disclosed with reference to the fifth aspect.
In one embodiment, the body having strong temperature dependent electrical resistivity is of a compound comprising an electrically insulating bulk material, electrically conductive particles of a first kind, and electrically conductive particles of a second kind. The bulk material holds the particles of the first and second kinds in place, the particles of the second kind are smaller than the particles of the first kind, the particles of the second kind are more in number than the particles of the first kind, the particles of the second kind have higher surface roughness than the particles of the first kind, wherein the particles of the second kind comprise tips and the particles of the first kind comprise even surface portions, the particles of the first and second kinds are arranged to form a plurality of current paths through the compound. Each of the current paths may comprise galvanically connected particles of the first and second kinds and a gap between a tip of one of the particles of the second kind and an even surface portion of one of the particles of the first kind, wherein the gap is narrow enough to allow electrons to tunnel through the gap via the quantum tunneling effect. The tips of the particles of the second kind maybe so sharp that the very ends of the tips comprise a single atom or a few atoms only.
The bulk material has a thermal expansion capability such that it expands with temperature, thereby increasing the gap widths of the current paths, which in turn increases the electrical resistivity.
The bulk material may comprise a cross-linked polymer or elastomer, such as for example a silicone, e.g. polydimethyl siloxane, and optionally a filler, thickener, or stabilizer, such as for example silica, distributed in the compound, and the particles of the first and second kinds may be carbon-containing particles, such as for example carbon blacks.
The number of the current paths through the compound and the widths of the gaps therein at any given temperature may be selected depending on the thermal expansion capability of the electrically insulating bulk material to obtain strong temperature dependent electrical resistivity of the compound in a selected temperature interval.
Further characteristics and advantages will be evident from the detailed description of embodiments given hereinafter, and the accompanying Figs. 1-7, which are given by way of illustration only.
BRIEF DESCRIPTION OF THE DRAWINGS
Fig. 1 illustrates, schematically, a heating arrangement according to an embodiment.
Figs.2 and 3 illustrate each, schematically, an arrangement for controlling an electric current according to an embodiment. Fig. 4 illustrates, schematically, a circuitry including a switch for switching an electric current according to an embodiment.
Fig. 5 illustrates, schematically, a portion of a compound having strong temperature dependent electrical resistivity according to an embodiment.
Fig. 6 illustrates, schematically, a detail of the structure of the compound in Fig. ι in more detail.
Fig. 7 illustrates, schematically, a portion of the compound in Fig. l, wherein a plurality of current paths through the compound is shown.
DETAILED DESCRIPTION OF EMBODIMENTS
Fig. l illustrates, schematically, a heating arrangement according to an embodiment. The heating arrangement comprises a main body n and a radiation source 13, e.g. a magnetron. The main body 11 comprises a polymer based material and a plurality of particles 12 of a material capable of absorbing microwave radiation arranged in the main body 11. To this end, the particles may be carbon-containing particles, such as for example carbon blacks. The radiation source 13 is configured to irradiate the main body 11 with microwave radiation to thereby heat the main body 11 and any object in thermal contact with the main body 11.
The main body 11 may comprise mainly a cross-linked polymer or elastomer, such as for example a silicone, e.g. polydimethyl siloxane, and optionally a filler, e.g. based on silica, and maybe provided as a sheet. The main body 11 maybe flexible and bendable and cut to suitable sizes to suit a variety of planar and non planar surfaces.
In one embodiment, an object to be heated is arranged in thermal contact with, e.g. placed on top of, the sheet-shaped main body 11.
In one embodiment, the main body 11 with the plurality of particles 12 arranged therein has strong, e.g. exponential, negative temperature dependent electrical resistivity, i.e. an electrical resistivity which is increasing with increasing temperature. Alternatively, the main body 11 with the plurality of particles 12 arranged therein is thermally connected to an additional body (e.g. body 21 of Fig. 2) having strong, e.g. exponential, negative temperature dependent electrical resistivity.
Examples of compounds having strong, e.g. exponential, negative temperature dependent electrical resistivity are disclosed in this document with reference to Figs. 5-7·
The radiation source 13 may be fed by a feeding current from a power source 14, wherein the feeding current is at least partly flowing through the main body 11 or the additional body, whichever having strong temperature dependent electrical resistivity. Hereby, a radiation/microwave based self-regulating heating arrangement is provided, which can be tuned such that when the main body 11, the optional additional body, or an object to be heated and placed in thermal contact with the main body 11, or the optional additional body, has reached a selected temperature, the further heating is switched off, or at least strongly decreased, due to the limitation of the feeding current as caused by increased resistance through the main body 11 or the additional body, whichever having strong negative temperature dependent electrical resistivity.
Fig.2 illustrates, schematically, an arrangement for controlling an electric current according to an embodiment. The arrangement comprises a main body 21, a supplementary body 25, electrical terminals 22a-b electrically connected to the main body 21, a radiation source 13, and a control device 24 operatively connected to the radiation source i3for controlling the operation thereof.
The main body 21 has strong temperature dependent electrical resistivity, preferably a negative temperature dependent electrical resistivity, and a negative exponential dependent electrical resistivity. The supplementary body 25 is capable of absorbing radiation such as microwaves from the radiation source 13 and is thermally connected, e.g. firmly attached, to the main body 21.
The supplementary body 25 may be of the same material as the main body of the embodiment of Fig. 1 and the main body maybe of any of the compounds disclosed in this document with reference to Figs. 5-7. The radiation source 13 such as a magnetron is capable of irradiating the supplementary body 25 with radiation such as microwaves, in response to which the main body 21 gets heated (via the thermal connection between the main body 21 and the supplementary body 25) and alters its electrical resistivity.
The control device 24 is configured to control an electric current flown through the main body 21 via the electrical terminals 22a-b by means of controlling the power of the radiation irradiating the supplementary body 25. That is, an electric current is controlled by means of microwave radiation and the arrangement is a transducer for converting radiation into current, or a radiation signal into a current signal provided that the signal speed is low enough to allow the temperature to increase and decrease in response to an increased or decreased power of the radiation irradiating the supplementary body 25. To remove heat fast enough when the radiation is decreased or switched off, the main body 21 and/or supplementary body 25 may be provided with coolers or heat sink structures (not illustrated).
Fig. 3 illustrates, schematically, an arrangement for controlling an electric current according to an embodiment, which differs from the arrangement of Fig. 2 in that the supplementary body 25 is dispensed with. Instead the main body, denoted here with reference numeral 31, is capable of absorbing radiation such as microwaves from the radiation source 13.
Fig. 4 illustrates, schematically, a circuitry 41 including a power source 42, a load 43, and a switch 44 serially connected to one another. The switch 44 may be the main body 21 and the supplementary body 25 of the embodiment of Fig. 2, or the main body 31 of the embodiment of Fig. 3, wherein the electrical terminals 22a-b are connected to the load 43 and the power source 42, respectively.
The main body 11, 21 has such a strong negative temperature dependent resistivity (or strong positive temperature dependent resistivity) that is electrically conducting at a first temperature and essentially electrically insulating at a second temperature, higher than the first temperature.
The switch 44 is operated by a radiation source 13 and a control device 24 opera tively connected to the radiation source 13, wherein the radiation source 13 is capable of irradiating the supplementary body 25 of the embodiment of Fig. 2 or the main body 31 of the embodiment of Fig. 3, such that main body 21, 31 can alternately reach the first and second temperatures. The control device 24 is configured to control an electric current flown in the circuitry of Fig. 4 and through the main body 21, 31 via by means of controlling the power of the radiation irradiating the supplementary body 25 or the main body 31 to alternately reach the first and second temperatures. Hereby, the electric current in the circuitry can be alternately switched on and off, wherein the load 43 is alternately connected to, and disconnected from, the power source 42.
In a further embodiment, the arrangement of Fig. 2 or Fig. 3 is used in an amplifier for amplifying an input current signal. The current source 13 is provided with a power source, such as the power source 14 of Fig. 1, for inputting an electric input current to the radiation source 13, in response to which the radiation source 13 irradiates the supplementary body 25 Fig. 2) or the main body 31 (Fig. 3) with radiation, wherein the power of the radiation irradiating the supplementary body 25/main body 31 depends on the electric input current to the radiation source 13.
The control device 24 (Figs. 2 and 3) is operatively connected to the power source and is configured to vary the electric input current to the radiation source 13 to form an input current signal. In response thereto, the temperature of the main body 21, 31 is varied or modulated.
A current is flown through the main body 21, 31 from e.g. electrical terminal 22a to electrical terminal 22b, and this current is modulated by the varied or modulated temperature of the main body 32, 21 such that a modulated current signal can be output.
If the main body 21, 31 has a strong temperature dependent conductivity, the output modulated current signal can be an amplification of the input current signal, and as a result the arrangement of Fig. 2 or Fig. 3 embodies an amplifier which amplifies an input current signal (current to the radiation source) and outputs an amplified current signal at electrical terminal 22b.
If the main body 21, 31 has a negative temperature dependent resistivity, the amplified current signal will be phase shifted 180 degrees with respect to the input current signal. If the main body 21, 31 has a linear temperature dependent resistivity within a temperature interval used, the amplifier may have a good linearity. However, the heating, and thereby increased resistivity, of the main body 21, 31 due to the current input at electrical terminal 22a may have to be considered.
This document also encompasses methods for heating, controlling an electric current, switching an electric current, and amplifying an input current signal comprising method steps for performing the functions disclosed above with reference to Figs. 1-4.
Next, with reference to Figs. 5-7, a compound which can be used in the main body or additional body of the embodiment of Fig. 1, and in the main body 21, 31 of the embodiments of Figs. 2-4 will be described.
Fig. 5 illustrates, schematically, a portion of a compound having strong temperature dependent electrical resistivity according to an embodiment. The compound comprises an electrically insulating bulk material 51, electrically conductive particles 52 of a first kind, and electrically conductive particles 53 of a second kind arranged in the bulk material 51.
The bulk material 51 may comprise an amorphous cross-linked polymer or elastomer, such as for example a siloxane elastomer (often called silicone elastomer) such as polyfluorosiloxane or polydimethyl siloxane and possibly also a filler, thickener, or stabilizer, such as silica. The bulk material holds the particles of the first and second kinds firmly in place in the bulk material after cross-linking. The filler, thickener, or stabilizer maybe mixed with the bulk material to obtain a compound having a desired consistence, flexibility, and/ or elasticity.
The electrically conducting particles 52, 53 of the first and second kinds maybe carbon-containing particles, such as for example carbon blacks. The particles 53 of the second kind may (i) be smaller, (ii) be more in number, (iii) have higher surface roughness, and (iv) have more irregular shape than the particles 52 of the first kind as being schematically illustrated in Fig. 5.
Fig. 6 illustrates schematically a detail of the structure of the compound in Fig. 5 in more detail including one particle 53 of the second kind and a portion of one particle 52 of the first kind firmly secured in the bulk material 51. It can be seen that the highly irregularly shaped particles 53 of the second kind comprise tips 53a and the more regularly shaped particles 52 of the first kind comprise even surface portions 52a. The tips 53a of the particles 53 of the second kind maybe so sharp that the very ends of the tips 53a comprise a single atom or a few atoms only.
If the width w of a gap 14a between a tip 53a of one of the particles 53 of the second kind and an even surface portion 52a of one of particles 52 of the first kind is narrow enough, electrons are enabled to tunnel through the gap via the quantum tunneling effect.
In one embodiment, the particles 53 of the second kind may be covered by a lubricant 61, such as for example a homo-oligomer, e.g. vinylmethoxysiloxane homo-oligomer, as being illustrated for one of the particles 53 of the second kind in Fig. 6. The lubricant 61 may assist in a suitable positioning of the particles 53 of the second kind in the bulk material 51.
Fig. 7 illustrates schematically a portion of the compound in Fig. 1, wherein a plurality of current paths 54 through the compound is shown. The particles 52, 53 of the first and second kinds are arranged to form the current paths 54 through the compound, wherein each of the current paths 54 comprises galvanically connected particles 52, 53 of the first and second kinds and a gap 54a between a tip 53a of one of the particles 53 of the second kind and an even surface portion 52a of one of the particles 52 of the first kind, wherein the gap 54a has a width which is small enough to allow electrons to tunnel through the gap via the quantum tunneling effect. While, Fig. 7 illustrates three current paths through the compound, it shall be appreciated that there may be thousands of current paths per square millimeter through a film of the compound. At a certain gap width w of the current paths 54, the quantum tunneling effect disappears and the compound does not conduct any longer.
The bulk material 51 has a thermal expansion capability such that it expands with temperature, thereby increasing the gap widths w of the current paths 54, which in turn increases the electrical resistivity of the compound exponentially.
The number of the current paths 54 through the compound and the widths w of the gaps 54a therein at any given temperature are provided depending on the thermal expansion capability of the compound to obtain a strong, e.g. exponential, temperature dependent electrical resistivity of the compound in a selected temperature interval.
The number of the current paths 54 through the compound, the widths w of the gaps 54a therein, and the thermal expansion capability of the compound can be controlled by adjusting the various ingredients of the compound, varying the amounts of the various ingredients of the compound, varying the order and manner in which they are mixed, and/ or varying the cross-linking of the polymer or elastomer comprised in the bulk material.
The particles of the second kind may be covered by a lubricant before the particles of the first and second kinds are arranged in the bulk material. To this end, the particles of the second kind and the lubricant are mixed together in a solvent, after which the solvent is removed. The mixture of the particles of the second kind and the lubricant may be mixed with the filler, thickener, or stabilizer in a solvent, after which the solvent is removed. The mixture of the particles of the second kind, the lubricant, and the filler, thickener, or stabilizer may be mixed with the mixture of the particles of the first kind and the polymer or elastomer to obtain the compound.
Alternatively, the filler, thickener, or stabilizer may be mixed with the particles of the first kind and/ or the polymer or elastomer, to which the mixture of the particles of the second kind and the lubricant is added.
In one example the compound is made up the following ingredients and amounts thereof (as given in weight percentages based on the weight of the compound), wherein the carbon blacks of the first kind have an average size of 500 nm and the carbon blacks of the second kind have an average size of 50 nm : polydimethyl siloxane 44
silica 3
carbon blacks of the first kind 48
carbon blacks of the second kind 4.95
vinylmethoxysiloxane homo-oligomer 0.05
It shall be appreciated that the individual sizes of the particles of each kind may vary quite much, such as e.g. by a factor 10. Therefore it is advantageous that the sizes are given as some kind of statistical sizes, such as e.g. average sizes. The above compound can be tailored to obtain the desired strong negative temperature dependent resistivity in any desired temperature interval in the temperature range of minus 80 to plus 80 degrees Celsius, and may have very low resistance, e.g. 1-10 ohms, in a lower portion of such temperature interval.
Further reference is given to our co-pending patent application entitled Compound having exponential temperature dependent electrical conductivity, use of such compound in a self-regulating heating element, self-regulating heating element comprising such compound, and method of forming such compound and filed with the Swedish Patent Office on December 2, 2013. The contents of the co-pending patent application are hereby incorporated by reference.
Alternative materials, which can be used in the main body or additional body of the embodiment of Fig. 1, and in the main body 21, 31 of the embodiments of Figs. 2-4 comprise PTC materials such as PTC ceramics or functional ceramics such as e.g. barium titanates, which have strong negative temperature dependent resistivity in a relatively high temperature interval, e.g. above 140 degrees Celsius, while the resistances at lower temperatures are still often above 100 ohms.
It shall be appreciated by a person skilled in the art that the above disclosed embodiments may be combined to form further embodiment falling within the terms of the claims, and that any measures are purely given as example measures.

Claims

1. A heating arrangement comprising
- a main body (n; 25; 31) comprising a polymer based material;
- a plurality of particles (12) of a material capable of absorbing microwave radiation arranged in said main body; and
- a radiation source (13) configured to irradiate the main body with microwave radiation to thereby heat the main body, wherein
- the main body is, during use, arranged in thermal contact with an object to be heated.
- the particles are carbon-containing particles, such as for example carbon blacks and the main body comprises mainly a cross-linked polymer or elastomer, such as for example a silicone, e.g. polydimethyl siloxane, and optionally a filler, e.g. based on silica.
2. The heating arrangement of claim 1 wherein the main body is provided as a sheet (11; 31)·
3. The heating arrangement of claim 1 or 2 wherein the main body (31) with the plurality of particles arranged therein has strong, e.g. exponential, temperature dependent electrical resistivity, or is thermally connected to an additional body (21) having strong, e.g. exponential, temperature dependent electrical resistivity.
4. The heating arrangement of claim 3 wherein the radiation source (13) is fed by a feeding current, which is at least partly flowing through the main body (11) or the additional body (21), whichever having strong temperature dependent electrical resistivity.
5. The heating arrangement of claim 3 or 4 wherein
- the main body (11) or the additional body (21), whichever having strong
temperature dependent electrical resistivity, is of a compound comprising an electrically insulating bulk material (51), electrically conductive particles (52) of a first kind, and electrically conductive particles (53) of a second kind, wherein - the electrically insulating bulk material holds the electrically conducting particles of the first and second kinds in place;
- the electrically conducting particles of the second kind are smaller than the electrically conducting particles of the first kind;
- the electrically conducting particles of the second kind are more in number than the electrically conducting particles of the first kind;
- the electrically conducting particles of the second kind have higher surface roughness than the electrically conducting particles of the first kind, wherein the electrically conducting particles of the second kind comprise tips (53a) and the electrically conducting particles of the first kind comprise even surface portions (52a);
- the electrically conducting particles of the first and second kinds are arranged to form a plurality of current paths (54) through the compound, wherein each of said current paths comprises galvanically connected electrically conducting particles of the first and second kinds and a gap (54a) between a tip (53a) of one of the
electrically conducting particles of the second kind and an even surface portion (52a) of one of the electrically conducting particles of the first kind, which gap is narrow enough to allow electrons to tunnel through the gap via the quantum tunneling effect, and
- the electrically insulating bulk material has a thermal expansion capability such that it expands with temperature, thereby increasing the gap widths (w) of the current paths, which in turn increases the electrical resistivity of the compound.
6. The heating arrangement of claim 5 wherein the tips of the electrically conducting particles of the second kind are so sharp that the very ends of the tips comprise a single atom or a few atoms only.
7. The heating arrangement of any of claims 3-6 comprising electrical terminals (22a- b) and a control device (24), wherein - the electrical terminals are electrically connected to the main body (31) or the additional body (21), whichever having strong temperature dependent electrical resistivity; and
- the control device is configured to control an electric current flown through the main body (31) or the additional body (21), whichever having strong temperature dependent electrical resistivity, via the electrical terminals by means of controlling the power of the radiation irradiating the main body.
8. The heating arrangement of claim 7 wherein
- the main body (31) or the additional body (21), whichever having strong
temperature dependent electrical resistivity, is electrically conducting at a first temperature and electrically insulating at a second temperature, higher than the first temperature;
- the radiation source (13) is capable of irradiating the main body, such that main body or the additional body, whichever having strong temperature dependent electrical resistivity, can alternately reach said first and second temperatures; and
- the control device (24) is configured to control an electric current flown through the main body or the additional body, whichever having strong temperature dependent electrical resistivity, via the electrical terminals by means of controlling the power of the radiation irradiating the main body to alternately reach said first and second temperatures, thereby switching the electric current.
9. The heating arrangement of claim 7 comprising
- means (14) for inputting an electric input current to the radiation source (13), in response to which the radiation source irradiates the main body (25; 31) with radiation, wherein the power of the radiation irradiating the main body depends on the electric input current to the radiation source, wherein
- the control device (24) is configured to vary the electric input current to the radiation source to form an input current signal, in response to which the
temperature of the main body (31), or the additional body (21), whichever having strong temperature dependent electrical resistivity, is varied; and - the main body, or the additional body, whichever having strong temperature dependent electrical resistivity, is configured to modulate an electric current flown there through by means of its varying temperature to output an amplified current signal.
10. The heating arrangement of any of claims 1-9 wherein the main body, or the additional body, whichever having strong temperature dependent electrical resistivity, has an electrical resistivity which is increasing with increasing
temperature.
11. A method for heating an object comprising the steps of:
- providing a main body (11; 25; 31) comprising a polymer based material, and a plurality of particles (12) of a material capable of absorbing microwave radiation arranged in the main body;
- irradiating the main body with microwave radiation from a radiation source (13), preferably a magnetron, thereby heating the main body; and
- arranging the main body in thermal contact with an object to be heated, wherein
- the particles are carbon-containing particles, such as for example carbon blacks and the main body comprises mainly a cross-linked polymer or elastomer, such as for example a silicone, e.g. polydimethyl siloxane, and optionally a filler, e.g. based on silica.
12. The method of claim 11 wherein the main body is provided as a sheet (11).
13. The method of claim 11 or 12 wherein the main body (31) with the plurality of particles arranged therein has strong, e.g. exponential, temperature dependent electrical resistivity, or is thermally connected to an additional body (21) having strong, e.g. exponential, temperature dependent electrical resistivity.
14. The method of claim 13 wherein the radiation source (13) is fed by a feeding current, which is at least partly flowing through the main body (11) or the additional body (21), whichever having strong temperature dependent electrical resistivity.
15. The method of claim 13 or 14 wherein the main body, or the additional body, whichever having strong temperature dependent electrical resistivity, has an electrical resistivity which is increasing with increasing temperature.
16. An arrangement for controlling an electric current comprising a main body (21; 31), electrical terminals (22a-b), a radiation source (13), and a control device (24), wherein
- the main body has a temperature dependent electrical resistivity, preferably a strong temperature dependent electrical resistivity;
- the electrical terminals are electrically connected to the main body;
- the main body (31) is capable of absorbing radiation from the radiation source or the arrangement comprises a supplementary body (25), which is capable of absorbing radiation from the radiation source and which is thermally connected to the main body;
- the radiation source is capable of irradiating the main body or the supplementary body, whichever being capable of absorbing the radiation, in response to which the main body gets heated and alters its electrical resistivity; and
- the control device is configured to control an electric current flown through the main body via the electrical terminals by means of controlling the power of the radiation irradiating the main body or the supplementary body, whichever being capable of absorbing the radiation.
17. The arrangement of claim 16 wherein
- the radiation capable of being absorbed by the main body or the supplementary body is microwaves; and
- the radiation source, e.g. a magnetron, is capable of irradiating the main body or the supplementary body, whichever being capable of absorbing the radiation, with microwaves.
18. The arrangement of claim 16 or 17 wherein the arrangement comprises the supplementary body (25), which is firmly attached to the main body (21).
19. The arrangement of any of claims 16-18 wherein the main body is of a compound comprising an electrically insulating bulk material (11), electrically conductive particles (12) of a first kind, and electrically conductive particles (13) of a second kind, wherein
- the electrically insulating bulk material holds the electrically conducting particles of the first and second kinds in place;
- the electrically conducting particles of the second kind are smaller than the electrically conducting particles of the first kind;
- the electrically conducting particles of the second kind are more in number than the electrically conducting particles of the first kind;
- the electrically conducting particles of the second kind have higher surface roughness than the electrically conducting particles of the first kind, wherein the electrically conducting particles of the second kind comprise tips (13a) and the electrically conducting particles of the first kind comprise even surface portions (12a);
- the electrically conducting particles of the first and second kinds are arranged to form a plurality of current paths (14) through the compound, wherein each of said current paths comprises galvanically connected electrically conducting particles of the first and second kinds and a gap (14a) between a tip (13a) of one of the electrically conducting particles of the second kind and an even surface portion (12a) of one of the electrically conducting particles of the first kind, which gap is narrow enough to allow electrons to tunnel through the gap via the quantum tunneling effect, and
- the electrically insulating bulk material has a thermal expansion capability such that it expands with temperature, thereby increasing the gap widths (w) of the current paths, which in turn increases the electrical resistivity.
20. The arrangement of claim 19 wherein the insulating bulk material comprises a cross-linked polymer or elastomer, such as for example a silicone, e.g. polydimethyl siloxane, and optionally a filler, thickener, or stabilizer, such as for example silica, distributed in said compound; and the electrically conducting particles of the first and second kinds are carbon-containing particles, such as for example carbon blacks.
21. The arrangement of claim 19 or 20 wherein the tips of the electrically conducting particles of the second kind are so sharp that the very ends of the tips comprise a single atom or a few atoms only.
22. The arrangement of any of claims 19-21 wherein the number of the current paths through the compound and the widths of the gaps therein at any given temperature are provided depending on the thermal expansion capability of the electrically insulating bulk material to obtain strong temperature dependent electrical resistivity of the compound in a selected temperature interval.
23. A switch (44) for switching an electric current comprising the arrangement of any of claims 16-22, wherein
- the main body (21; 31) is electrically conducting at a first temperature and electrically insulating at a second temperature, higher than the first temperature;
- the radiation source (13) is capable of irradiating the main body (31) or the supplementary body (25), whichever being capable of absorbing the radiation, such that main body can alternately reach said first and second temperatures; and
- the control device (24) is configured to control an electric current flown through the main body via the electrical terminals by means of controlling the power of the radiation irradiating the main body or the supplementary body, whichever being capable of absorbing the radiation, to alternately reach said first and second temperatures, thereby switching the electric current.
24. An amplifier for amplifying an input current signal comprising
- the arrangement of any of claims 16-22; and
- means (14) for inputting an electric input current to the radiation source, in response to which the radiation source irradiates the main body (31) or the
supplementary body (25), whichever being capable of absorbing radiation, with radiation, wherein the power of the radiation irradiating the main body or the supplementary body, whichever being capable of absorbing radiation, depends on the electric input current to the radiation source, wherein - the control device (24) is configured to vary the electric input current to the radiation source to form an input current signal, in response to which the
temperature of the main body (21; 31) is varied; and
- the main body is configured to modulate an electric current flown there through by means of its varying temperature to output an amplified current signal.
25. The arrangement of any of claims 16-22, the switch of claim 23, or the amplifier of claim 24 wherein the main body has exponential temperature dependent electrical resistivity.
26. The arrangement of any of claims 16-22 or 25, the switch of claim 23, or the amplifier of claim 24 wherein the main body has an electrical resistivity which is increasing with increasing temperature.
27. A method for controlling an electric current with an arrangement comprising a main body (21; 31), electrical terminals (22a-b), a radiation source (23), and a control device (24), wherein the main body has a temperature dependent electrical resistivity, preferably a strong temperature dependent electrical resistivity; the electrical terminals are electrically connected to the main body; and the main body (31) is capable of absorbing radiation from the radiation source or the arrangement comprises a supplementary body (25), which is capable of absorbing radiation from the radiation source and which is thermally connected to the main body, the method comprising:
- irradiating the main body or the supplementary body, whichever being capable of absorbing the radiation, with radiation from the radiation source to thereby heat the main body and alter its electrical resistivity; and
- controlling an electric current flown through the main body via the electrical terminals by means of controlling the power of the radiation irradiating the main body or the supplementary body, whichever being capable of absorbing the radiation.
28. A method for switching an electric current comprising the method of claim 27, wherein the main body is electrically conducting at a first temperature and
electrically insulating at a second temperature, higher than the first temperature, the method comprising the steps of: - alternately irradiating the main body or the supplementary body, whichever being capable of absorbing the radiation, with radiation from the radiation source to alternately heat the main body, such that it alternately reach said first and second temperatures; and
- controlling an electric current flown through the main body via the electrical terminals by means of controlling the power of the radiation irradiating the main body or the supplementary body, whichever being capable of absorbing the radiation, to alternately reach said first and second temperatures.
29. A method for amplifying an input current signal comprising the method of claim 27, and comprising the steps of:
- inputting an electric input current to the radiation source, in response to which the radiation source irradiates the main body or the supplementary body, whichever being capable of absorbing radiation, with radiation, wherein the power of the radiation irradiating the main body or the supplementary body, whichever being capable of absorbing radiation, depends on the electric input current to the radiation source;
- varying the electric input current to the radiation source to form an input current signal, to thereby obtain a temperature of the main body that is varied; and
- modulating the electric current flown through the main body by means of the varying temperature of the main body to thereby output an amplified current signal.
30. The method of any of claims 27-29 wherein the main body has exponential temperature dependent electrical resistivity.
31. The method of any of claims 27-30 wherein the main body has an electrical resistivity which is increasing with increasing temperature.
PCT/SE2014/051433 2013-12-03 2014-12-02 Heating arrangement, method for heating, and arrangement and method for controlling an electric current WO2015084240A1 (en)

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SE1351435 2013-12-03

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Citations (6)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
WO1994027887A1 (en) * 1993-05-21 1994-12-08 James River Paper Company, Inc. Self limiting microwave susceptor
CN1124869A (en) * 1994-12-15 1996-06-19 殷芳卿 High molecular polymer thermistor with positive temp. coefficient
US6114672A (en) * 1997-10-07 2000-09-05 Sony Corporation PTC-element, protective device and electric circuit board
US20030218530A1 (en) * 2002-05-24 2003-11-27 Tdk Corporation Organic PTC thermistor
JP2005217387A (en) * 1998-11-02 2005-08-11 Tdk Corp Organic positive temperature coefficient (ptc) thermistor
WO2008048176A1 (en) * 2006-10-17 2008-04-24 Conflux Ab Heating element

Patent Citations (6)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
WO1994027887A1 (en) * 1993-05-21 1994-12-08 James River Paper Company, Inc. Self limiting microwave susceptor
CN1124869A (en) * 1994-12-15 1996-06-19 殷芳卿 High molecular polymer thermistor with positive temp. coefficient
US6114672A (en) * 1997-10-07 2000-09-05 Sony Corporation PTC-element, protective device and electric circuit board
JP2005217387A (en) * 1998-11-02 2005-08-11 Tdk Corp Organic positive temperature coefficient (ptc) thermistor
US20030218530A1 (en) * 2002-05-24 2003-11-27 Tdk Corporation Organic PTC thermistor
WO2008048176A1 (en) * 2006-10-17 2008-04-24 Conflux Ab Heating element

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