Magnetic induction heating device

Abstract

An induction heating device 1 includes one or more magnetic field generators based on a dielectric ring resonator (DRR) 10 to generate a strong magnetic B-field to stun or dispatch a target, an animal

Description

Description MAGNETIC INDUCTION HEATING DEVICE Technical Field

[0001] The present invention relates to use of a magnetic field (B-field) for pest control in a horticultural environment and uses the same technique / s for the humane euthanasia and / or stun and dispatch of various animals. Background Art

[0002] One of the inventors has already filed a family of patent applications for Magnetic Induction Heating for Pest Control (MIHPC) in the UK, US and Europe (patent publication nos. GB 2562765, US 2020 / 0068866 and EP 3629724 respectively). The Prior Art for these applications is already on record, but most have the problem that they are directed to dielectric heating utilising microwaves (or other electromagnetic wavelengths), which will damage any plant substrate material. Therefore, an important distinction between the invention and the Prior Art is that there is minimal dielectric heating of plant material. Likewise, the use of E-fields (e.g. in parallel plate systems) fail because they cause excessive heating of plant material if used for pest control.

[0003] Since 1979, the stunning of livestock has been mandatory in the EU, although each member state is free to grant its own exemptions for religious reasons. In the UK, the Humane Slaughter Association and the RSPCA have easily accessible information on-line about the humane transportation, stunning and slaughter of animals for human consumption.

[0004] Common stunning methods include electrical stunning, captive-bolt stunning or the use of carbon dioxide gas. Captive-bolt stunning devices where the bolt enters the brain (penetrative bolt) will result in greater stunning efficiency than non-penetrative stunners (‘mushroom-headed’ bolt) that rely on the percussive blow on its own to achieve immediate insensibility. Summary of invention The present invention is aimed at maximising the magnetic B-field and minimising the electric E-field. Magnetic induction heating relies on the electrical conductivity of a material, whereas dielectric heating relies on the permittivity and loss tangent of the material. Bone and plants have low electrical conductivities and high permittivity and loss tangents and are therefore not affected by magnetic induction heating. Another important feature of the invention is that it uses the reactive near electromagnetic field (near-field), which is less than about half a wavelength of the electromagnetic energy from the source. Whereas the Prior Art previously identified uses the radiative far electromagnetic field (far-field), which is a distance greater than about half a wavelength of the electromagnetic energy from the source. Electromagnetic absorption in the near-field is dominated by magnetic effects (i.e. induction heating), whereas in the far-field it is dominated by electric effects (i.e. dielectric heating). Where methods use far-field devices, dielectric heating will dominate, which cause excessive heating of plant material for pest control and bone for HSD. Reactive near-field devices do not tend to radiate energy to the surroundings, whereas with far-field devices all the energy is radiated. A device according to the present invention comprises a ring of dielectric material and an excitation means housed inside a cavity. The inside surface of the cavity must have a high electric conductivity, such as copper or silver for example. The cavity delineates the 'system' and the reason for having a good conductor on the inside surface of the cavity is to prevent a large portion of the 'power budget’ being absorbed by the cavity wall or radiating outside the cavity. For example, if a power of 100 W enters the 'system' via an excitation coil, then the coil itself absorbs very little (2 — 3 W), the dielectric ring absorbs about 60 W and the remainder goes to the cavity wall e.g. 40 W. If a Load (e.g. a pest or an animal brain) is added into the ‘system’, hopefully 70 — 80% of the power goes into the Load and not into the cavity wall or radiates outside the cavity. Therefore, the inside surface of the cavity wall is made from a good electrical conductor to prevent power loss and most of the electric current swirls around in the space between the outside of the dielectric ring and the inside surface of the cavity wall. If the inside of the cavity wall were composed of a very bad conductor e.g. lumpy zinc, there would be very large ohmic losses in the 'system'. However, despite silver and copper being good electrical conductors, they have the disadvantage that they tarnish and the tarnish (an oxide layer) extends to a depth of several um into the metal and gets between grain boundaries, acting to greatly decrease the surface conductivity. Therefore, as an example, the inventors suggest that the inside wall of the cavity could be a 30 pm coating of silver furnished with a 1 um flash of gold. Gold is a poor electrical conductor compared to silver, but gold will not tarnish whereas silver and copper do tamnish. The gold acts to protect the underlying silver and / or copper layer. At high MHz and low GHz frequencies, the electrical conduction skin depth is between 5 ym and around 1.4 ym respectively (hence the suggestion of 30 um). The main structure of the cavity may be made from copper or even plastic. The excitation means drives a resonating frequency in the dielectric material to induce a strong magnetic B-field at the centre of the ring and RF excitation can be induced via a small metal coil, strip line or waveguide for example. To summarise, the present invention provides a device that includes one or more magnetic field generators based on a dielectric ring resonator (DRR) to generate a strong magnetic B-field to stun or dispatch a target, an animal brain or a pest for example, without affecting a remaining part of the animal or surrounding plant material. Thus, the device and may be used in pest control and / or the humane stun and dispatch (HSD) of animals such as rodents, broilers and even larger animals where the pest or the brain of the animal (in the case of HSD) is simply a Load entered into the device. The device has two modes of action: a static mode having a static device where a user inserts a Load into the device and a moving mode where the Load is moved relative to the device. The applications for this technique are very broad, but the inventors are developing the idea specifically for pest control in hardy stock nurseries, pests often found in grain silos or during harvesting and humane stun and / or dispatch of lab rodents, boilers and even extending to larger animals. There is an urgent need for more humane dispatch methods for animals, especially poultry in slaughterhouses. Stunning is commonly used to render the animal unconscious prior to and during exsanguination, preventing unnecessary suffering. Most poultry slaughtered in the UK are stunned using controlled atmospheric stunning (CAS) with CO2, or by the electrical water bath method. Yet, it's recognised that exposure to CO2 can cause pain, anxiety, dyspnoea and nausea, and have high capital and running costs. Electrical water bath stunning is widely recognised as having significant welfare issues. Furthermore, there is a big consumer- driven pull to increase health and welfare of production animals, and the slaughterhouse industry want to respond. The DRR device according to the invention is an alternative, cheaper, contactless humane stun and / or dispatch method based on radio- frequency (RF) magnetic B-field induction heating of the brain for rapid dispatch of slaughter weight broilers. RF magnetic B-field induction may also heat the brain to provoke recoverable unconsciousness (stunning) for the Halal markets. This device can also be used for humane euthanasia of lab rodents. In the UK, 10 million lab rodents per year are killed, which make up the vast majority of research animals. Current techniques for killing them include inhalation methods, such as chambers that fill with carbon dioxide or anaesthetic gases, and injecting barbiturates. Physical methods include cervical dislocation (breaking of the neck), or decapitation with specialist rodent guillotines.

[0019] Therefore, a device including a DRR as described above may produce an electromotive density (frequency x peak B-field) A = 6642 MHz.mT with only 330 W of power, which is sufficient to kill a vine weevil larva (a pest commonly encountered in hardy stock nurseries) in 1 second or heat a rodent or chicken brain by enough to cause a coma or death in under 1 second. Brief description of drawings

[0020] The invention will now be described in more detail, by way of example only, with reference to the accompanying drawings in which:

[0021] Fig. 1a illustrates a general device according to the invention having a ring of dielectric material 10 and an excitation coil 20 housed within a cavity 30 having an internal surface 35. Fig. 1b shows the magnetic flux density 15 around the dielectric ring 10 with the arrow volume providing an indication of the size of the magnetic flux density 15.

[0022] Fig. 2a shows the setup of a conveyor belt (40) as conventionally used in a hardy stock nursery. Fig. 2b illustrates a static example of a pot 42 within a dielectric ring 10 and an excitation means 20 housed within an external cavity (not shown).

[0023] Fig. 3a shows an alternative arrangement where infected grain 47 passes down a plastic pipe 45 during normal grain movement such as during harvest, or into and out of grain silos etc. This could also be a conveyor belt system 40. The strong B-field is generated by a succession of dielectric rings 10 surrounded by a cavity 30. Fig. 3b is provided simply to show the relative size of the grain 62 being harvested relative to the pest B80 (in this case wheat weevil, also known as grain weevil or granary weevil). To break the system down for increased understanding, Fig. 3c shows a portion of the plastic pipe 45 down which the infected grain flows (not shown), surrounded by a dielectric ring 10 and having an excitation means 20 housed within an external cavity 30. The external cavity 30 has an internal wall 35 as previously discussed above. Fig. 3d shows the strong B-field obtained all the way along the treatment section of the pipe (see the magnetic flux density 15).

[0024] The orientation of the grains 62 and pests 50 are very important. Therefore, Figs. 3e & 3f are provided to show a pair of grains 62 and a pair of weevils (pest 50) in a vertical and horizontal orientation to represent the best and worst cases. The heating plot on the right-hand side of Fig. 3f is provided to show the scorched weevils (pests) and the gently warmed grains. (Note that the grain and weevil samples are included in Fig. 3d, in the very centre of the B-field at x = y = z = 0, almost invisible because they are so small with respect to the size of the dielectric ring.)

[0025] Figs. 4a — 4c move to the other application of the invention, namely humane stun and dispatch (HSD). Fig. 4a shows a mouse head 64 in a dielectric ring 10 (cavity not shown), part of a benchtop, pass through DRR device 1. Fig. 4b shows a picture of the mouse skull 66 with the heating plot on the right-hand side indicating the brain 50 temperature distribution caused by the strong B-field generated by the dielectric ring shown in Fig. 4a. operating at a frequency of 915 MHz. Similarly, Fig. 4c shows a picture of a chicken / broiler skull 68 with the heating plot on the right-hand side indicating the brain 50 temperature distribution caused by a strong B-field generated by a similar dielectric ring to that shown in the earlier Fig. 4a operating at a frequency of 168 MHz. Description of embodiments

[0026] Figures 1a and 1b illustrate the basic concept of a pass-through DRR 1. A dielectric ring 10 is resonating at its fundamental frequency and uses the strong magnetic field (B-field) generated in the centre of the ring. The dielectric ring 10 is driven by an excitation means 20 and needs to be housed in a cylindrical cavity 30 having an inner wall surface 35, to prevent power loss due to radiation, although the cavity 30 may be open at one or both ends. Note: The DRR 1 comprises the cavity 30, excitation means 20 and the dielectric ring 10.

[0027] The excitation means 20 takes the form of a small metal coil, strip line or waveguide to induce a RF B-field in the dielectric ring 10. The power electronics can be a loop resonator circuit incorporating a band pass filter to select the correct frequency for the power electronics to drive the DRR 1 or some similar circuit that will be apparent to those skilled in the art. The inside surface 35 of the cavity 30 needs to be a good electrical conductor, as otherwise a large portion of the power budget goes into the cavity wall (up to 50% for a tightly contained dielectric ring 10 in a poor cavity 30). The inside wall 35 of the cavity 30 can be a 30 um coating of silver finished with a 1 um flash of gold. Gold is a poor electrical conductor with respect to silver, but gold will not tarnish whereas silver and copper do tarnish. The tarnish (an oxide layer) extends to a depth of several microns into the metal, and gets between grain boundaries, acting to greatly decrease the surface conductivity, so the gold acts to protect the underlying silver. At high MHz and low GHz frequencies, the electrical conduction skin depth is between 5 um and 1.4 um respectively, and five skin depths should be allowed for 99% of the current to be able to flow (hence 30 um). Referring to Fig. 2a, hardy stock nurseries regularly move their potted plants 44 using a conveyor system 40 at about 1000 pots per hour. A common pest 50 is vine weevil larvae which is a difficult species to treat, following the ban on neonicotinoid soil treatments. A person skilled in the art will appreciate how the arrangement shown in Fig. 2b can be incorporated into this arrangement: A section in the conveyor belt 40 contains a pass-through dielectric ring 10, similar in size to an airport x-ray scanner, whereby the potted plants 44 are passed through the centre of the dielectric ring 10, heating and killing the pest 50 but not heating or damaging the plant or the soil 60. Figures 3a — 3f relate to application of the invention to use in grain silos. In grain silos, the power requirement is much greater because the pests 50 are smaller (see Fig. 3b) and the speeds at which the infected grain 47 is flowing is much faster than that considered previously. The inventors have carried out modelling simulation as follows. The dielectric section is made from alumina and is a 1 m long cylinder with an 884 mm diameter / bore (volume= 6.12 x108 mm3), designed to resonate at 40 MHz. The infected grain 47 flows down the inside of the pipe 45 as shown in Fig. 3c. Figure 3d illustrates the type of B-field obtained that is strong all the way along the treatment 'pipe' with A = 14000 MHz.mT and the bar on the right-hand side showing the magnetic flux density in mT. Referring to Figs. 3e & 3f, the modelling simulation predicted that each pest 50 (weevil) takes 0.44 W to kill in 1's, but in this simulation each grain of wheat 62 also absorbs 0.38 W. There are a lot of grains 62 and pests 50 (weevils) moving at high speed and so the power consumption is very high. Considering a case where there are 107 grains (packing density at 70%) and 108 weevil (10% number of grains) in this volume, the total power consumed = 3.8 MW. This is extremely high, but this solution should not be dismissed, because these sorts of powers are being considered for wireless power transfer at 40 MHz for cold ironing ships. It should also be appreciated that in the simulation the inventors have taken the worst possible scenario. the properties (e.g. loss tangent) the inventors have assumed the highest side of things for the grains 62 and lowest for the pests 50 (weevil), so this simulation is a maximum. For example, the epidermis (part of the grain which will probably get heated) will contain much less moisture than the very generous 50% the inventors have allowed for, which will reduce the power requirement. Figs. 4a — 4c all relate to use of the invention in the humane stun and dispatch (HSD) of animals. Figure 4a provides an example induction method or humane euthanasia of lab rodents using a bench-top, mains- driven pass-through DRR 1. The cavity is sealed at one end but can have an opening at the other end into which a live lab rodent 64 is inserted (for example in a small bag or cardboard box) into the centre of the pass- through dielectric ring before turning the device on. A polystyrene insert can be used to correctly locate the rodent 64 in the centre of the ring. Alternatively, a small conveyor belt can transport the rodent 64 through the device. As shown in Fig. 4b, the mouse brain temperature is 50°C (14°C temperature rise) after 1 s heating at an input power of 188 W at a frequency of 915 MHz (A = 680 MHz.mT). A 14 °C temperature rise of the brain 50 is more than sufficient to euthanise the rodent 64. No part of the rodent 64 is heated to a point which would cause a smell of cooking, or other signs of burning or damage. It is thus a cheap, clean method of euthanasia The same magnetic induction method is also suitable for the HSD of chickens (broilers) in a slaughterhouse. The DRR 1 is fundamentally the same as that shown in Fig. 4a but as apparent to those skilled in the art it will need to be adapted to fit the DRR device according to the invention into a production line. Fig. 4c shows a chicken (broiler) skull 68 with brain 50, whose temperature is 46°C (10°C temperature rise) after 1 s heating at 300 W power at 168 MHz (A = 360 MHz.mT). A 7°C temperature rise of the brain 50 is sufficient to induce a recoverable coma (stun), and 10°C temperature rise sufficient to dispatch the chicken. A recoverable coma is needed for Halal markets. Although several different uses for the pass-through DRR 1 according to the invention have been described above, other means of achieving the same effect as the invention will be apparent to those skilled in the art and this disclosure is not intended to be limiting.

Claims

Claims 1. A magnetic induction heating device comprising a ring of dielectric material (10), an excitation means (20) and a cavity (30) having an inside surface (35), wherein the excitation means (20) drives a resonating frequency in the dielectric material (10) to induce a strong magnetic B-field at the centre of the dielectric ring (10) and the inside surface cavity (35) is a good electrical conductor.

2. A magnetic induction heating device according to claim 1, wherein the excitation means (20) includes a small metal coil, strip line or waveguide.

3. A magnetic induction heating device according to claim 1 or claim 2, wherein the inside surface of the cavity (35) comprises a metal or layers of different metals to provide good electrical conductivity whilst protected from formation of an oxide layer on its innermost surface. 4, A magnetic induction heating device according to any of the preceding claims, wherein the innermost surface of the cavity (35) is furnished with a flash of gold.

5. A magnetic induction heating device according to any of the preceding claims, wherein the device is static.

6. A magnetic induction heating device according to claim 5, wherein a user inserts a target / Load (50) into the device.

7. A magnetic induction heating device according to claim 5, wherein the target / Load (50) is moved through the device.

8. A magnetic induction heating device according to claim 7, wherein the device includes a conveyor belt (40) arranged to pass through the centre of the dielectric ring (10).

9. An arrangement including a plurality of dielectric rings (10) having excitation means (20) surrounded by a continuous or segmented cavity or cavities (30).

10. A humane method of rapid stun and / or dispatch of animals by radio-frequency (RF) magnetic B-field induction heating of the brain (50) of the animals.

11. A humane method of rapid stun of animals according to claim 10, wherein the brain (50) of the animal is heated to provoke recoverable unconsciousness prior to dispatch.

12. A humane method of rapid stun and dispatch according to claim 10, for the humane euthanasia of lab rodents (64). Claims 1. A magnetic induction heating device comprising a ring of dielectric material (10), an excitation means (20) and a cavity (30) having an inside surface (35), where the excitation means (20) drives a resonating frequency in the dielectric material (10) to induce a strong magnetic B-field at the centre of the dielectric ring (10), wherein the cavity (30) has an inner wall surface (35) made from a material having good electrical conductivity.

2. A magnetic induction heating device according to claim 1, wherein the inner wall surface of the cavity (35) is made from a metal or layers of different metals to provide good electrical conductivity.

3. A magnetic induction heating device according to claim 1 or claim 2, wherein the inside surface (35) of the cavity (30) is protected from formation of an oxide layer on its innermost surface to maintain good electrical conductivity.

4. A magnetic induction heating device according to any of the preceding claims, wherein the cavity (30) delineates a 'system' and the excitation means (20) introduces power into the system to provide a 'power budget’.

5. A magnetic induction heating device according to claim 4, wherein the good electrical conductivity on the inside surface of the cavity (35) ensures that the ‘power budget’ is retained in the 'system' and is neither absorbed by the cavity wall nor radiates outside the cavity (30).

6. A magnetic induction heating device according to claim 5, wherein an electric field swirls around in the space between the outside of the dielectric ring (10) and the inside surface of the cavity wall (35).

7. A magnetic induction heating device according to any of claims 3 to claim 6, wherein the innermost surface of the cavity (35) is furnished with a flash of gold.

8. A magnetic induction heating device according to claim 7, wherein the innermost surface of the cavity wall (35) has a 30 um coating of silver finished with a 1 um flash of gold.

9. A magnetic induction heating device according to any of the preceding claims, wherein the device is static.

10. A magnetic induction heating device according to claim 9, wherein a user inserts a target / Load (50) into the device.

11. A magnetic induction heating device according to claim 9, wherein the target / Load (50) is moved relative to the device.

12. A magnetic induction heating device according to claim 11, wherein the device includes a conveyor belt (40) arranged to pass the dielectric ring (10).

13. A magnetic induction heating device according to claim 11, wherein the device includes a plurality of dielectric rings (10) having excitation means (20) surrounded by one or more cavity or cavities (30).

14. A magnetic induction heating device according to claim 13, wherein infected grain (47) passes through the dielectric rings (10) by normal grain movement during harvest or into and out of grain silos.

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