WO2008003972A1 - An eddy current generation device, apparatus and method - Google Patents

An eddy current generation device, apparatus and method Download PDF

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Publication number
WO2008003972A1
WO2008003972A1 PCT/GB2007/002514 GB2007002514W WO2008003972A1 WO 2008003972 A1 WO2008003972 A1 WO 2008003972A1 GB 2007002514 W GB2007002514 W GB 2007002514W WO 2008003972 A1 WO2008003972 A1 WO 2008003972A1
Authority
WO
WIPO (PCT)
Prior art keywords
coil
electrically conducting
conducting material
nearby
enhancement body
Prior art date
Application number
PCT/GB2007/002514
Other languages
French (fr)
Inventor
Steven Mark Dixon
Xiaoming Jian
Mark David George Potter
Original Assignee
University Of Warwick
Priority date (The priority date is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the date listed.)
Filing date
Publication date
Priority claimed from GB0613427A external-priority patent/GB0613427D0/en
Priority claimed from PCT/GB2007/002169 external-priority patent/WO2007141559A1/en
Application filed by University Of Warwick filed Critical University Of Warwick
Publication of WO2008003972A1 publication Critical patent/WO2008003972A1/en

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Classifications

    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B06—GENERATING OR TRANSMITTING MECHANICAL VIBRATIONS IN GENERAL
    • B06B—METHODS OR APPARATUS FOR GENERATING OR TRANSMITTING MECHANICAL VIBRATIONS OF INFRASONIC, SONIC, OR ULTRASONIC FREQUENCY, e.g. FOR PERFORMING MECHANICAL WORK IN GENERAL
    • B06B1/00—Methods or apparatus for generating mechanical vibrations of infrasonic, sonic, or ultrasonic frequency
    • B06B1/02—Methods or apparatus for generating mechanical vibrations of infrasonic, sonic, or ultrasonic frequency making use of electrical energy
    • B06B1/04—Methods or apparatus for generating mechanical vibrations of infrasonic, sonic, or ultrasonic frequency making use of electrical energy operating with electromagnetism
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01F—MEASURING VOLUME, VOLUME FLOW, MASS FLOW OR LIQUID LEVEL; METERING BY VOLUME
    • G01F23/00—Indicating or measuring liquid level or level of fluent solid material, e.g. indicating in terms of volume or indicating by means of an alarm
    • G01F23/22—Indicating or measuring liquid level or level of fluent solid material, e.g. indicating in terms of volume or indicating by means of an alarm by measuring physical variables, other than linear dimensions, pressure or weight, dependent on the level to be measured, e.g. by difference of heat transfer of steam or water
    • G01F23/28—Indicating or measuring liquid level or level of fluent solid material, e.g. indicating in terms of volume or indicating by means of an alarm by measuring physical variables, other than linear dimensions, pressure or weight, dependent on the level to be measured, e.g. by difference of heat transfer of steam or water by measuring the variations of parameters of electromagnetic or acoustic waves applied directly to the liquid or fluent solid material
    • G01F23/296—Acoustic waves
    • G01F23/2968—Transducers specially adapted for acoustic level indicators

Definitions

  • This invention relates to an eddy current generation device, apparatus and method.
  • EMATs electromagnetic acoustic transducers
  • coils of wire that are designed to generate an eddy current in the surface of an electrically conducting sample.
  • an eddy current generation device comprising an electromagnetic acoustic transducer to produce in use an acoustic wave pulse in a nearby electrically conducting object, the transducer comprising a coil of electrically conductive material and an enhancement body, the coil of electrically conductive material being adjacent to one side of the enhancement body, the enhancement body having a relative magnetic permeability greater than one.
  • the enhancement body behind the coil When current is passed through the coil, the enhancement body behind the coil will become temporarily magnetised. This magnetised layer of the enhancement body behind the coil will produce its own external magnetic field. Where the current is changing, the magnetic field from the enhancement body will act in the same direction as the coil's magnetic field and increase the total magnetic field that is experienced by a nearby electrically conducting object such as a metal object. The increased changing magnetic field results in eddy currents of larger amplitude.
  • the enhancement body has a resistivity greater than 55 x 10 ⁇ 8 ⁇ m.
  • the coil of electrically conductive material is 1.5mm or less, preferably lmm or less, from the surface of the enhancement body, and most preferably the coil of electrically conductive material is on the surface of the enhancement body.
  • the effectiveness of the enhancement body decreases with distance from the coil of electrically conductive material, thus the closer the coil of electrically conductive material is to the enhancement body, the greater the enhancement.
  • the enhancement body lies behind the whole of the coil. Thus, the maximum area of the coil will be affected by the enhancement body.
  • the enhancement body may be at least principally made of ferromagnetic or ferrimagnetic material, preferably ferrite, and preferably is wholly made of ferrite.
  • the surface of the enhancement body is smooth.
  • the surface of the enhancement body may be curved, and may be concave, convex, or curved about one axis, but preferably the surface of the enhancement body is flat. Therefore, a flat coil can lie against the body or can easily be positioned so that no part is more than 1.5mm away.
  • the coil of electrically conductive material is in a substantially flat overall shape.
  • it is simple to create a surface on the enhancement body against which the coil can lie, or which does not lie more than lmm from the surface at any part.
  • the coil may be in a spiral, preferably with at least ten turns.
  • the coil may be a meander coil.
  • the coil may be in an annular overall shape.
  • the coil of electrically conducting material is a metal wire which may have a diameter in the range 0.1mm to 0.5mm, and preferably the wire has a diameter in the range 0.2mm to 0.25mm.
  • the coil of electrically conducting material is no more than about 10mm in maximum extent, and preferably the coil of electrically conducting material is about 4mm in diameter.
  • the sides of the enhancement body, apart from that next to the coil, may be housed in an aluminium block.
  • the device is preferably without a permanent magnet.
  • the device may include an electromagnet.
  • the device may be adapted to produce in use an acoustic wave pulse in a nearby object, which is metal, and may be made wholly or principally of aluminium or steel, and may for example be a metal can.
  • the device is preferably adapted to produce in use an acoustic wave pulse in a nearby object which has an electrical conductivity greater than the electrical conductivity of the enhancement body.
  • the electrical conductivity of the enhancement body in relation to the intended object is suitably such that greater eddy current generation in the object is achieved than if the device is used without the enhancement body.
  • an apparatus including an eddy current generation device according to the preceding aspect of the invention and means to supply an electrical input to the coil of electrically conducting material.
  • the electromagnetic acoustic transducer may be adapted to produce in use an acoustic wave pulse in a nearby electrically conducting object which is of 100 microseconds duration or less, preferably of 20 microseconds duration or less, preferably of 5 microseconds duration or less.
  • the apparatus further includes means to apply a current of at least 10OA, and preferably at least 400A, through the coil of electrically conducting material.
  • the apparatus further includes a capacitor and means to discharge the capacitor through the coil of electrically conducting material.
  • the apparatus further includes means to charge the capacitor to 200 Volts, and preferably 500 Volts or more, for discharge through the coil of electrically conducting material.
  • the apparatus is arranged to pass current through the coil for less than 10 ⁇ s.
  • the apparatus may be arranged to supply the coil of electrically conducting material with a periodically varying voltage.
  • the apparatus may be arranged to supply voltage to the coil of electrically conducting material with a frequency in the range 10kHz to 10MHz.
  • a third aspect of the present invention there is provided a method of generating eddy currents in the surface of a nearby electrically conducting object by passing current through a device according to the first aspect of the invention.
  • the electromagnetic acoustic transducer produces an acoustic wave pulse in a nearby electrically conducting object which is of 100 microsecond duration or less, preferably of 20 microsecond duration or less, preferably of 5 microsecond duration or less.
  • a current of at least 10OA, and preferably at least 400A, is passed through the coil of electrically conducting material.
  • a capacitor is discharged through the coil of electrically conducting material.
  • the capacitor is charged to 200 Volts or more, and preferably to 500 Volts or more, prior to discharging through the coil of electrically conducting material.
  • the current passes through the coil for between 3 ⁇ s and 7 ⁇ s.
  • the coil of electrically conducting material carries a periodically varying voltage of more than one cycle.
  • the coil of electrically conducting material carries a periodically varying voltage with a frequency between 10 kHz and 10 MHz.
  • the electrically conducting object may be a metal object and may be made wholly or principally from aluminium or steel and may, for example, be a metal can.
  • the electrically conducting object preferably has an electrical conductivity greater than the electrical conductivity of the enhancement body.
  • the electrical conductivity of the enhancement body in relation to the electrically conducting object is suitably such that greater eddy current generation in the object is achieved than if the method is carried out without the enhancement body.
  • a fourth aspect of the present invention there is provided a method of generating eddy currents in the surface of a nearby electrically conducting object by operating the apparatus according to the second aspect of the invention to pass current through the device.
  • Fig. 1 illustrates the arrangement of the apparatus of the first embodiment
  • Fig. 2 is a perspective view of the device of the first embodiment, with the spiral coil and the enhancement body of the transducer shown, for clarity, without the housing or epoxy resin;
  • Fig. 3 is an elevation in cross section of the transducer of the first embodiment
  • Fig. 4 is a schematic diagram to explain how the increase in the eddy current amplitude is achieved
  • Fig. 5 is an elevation in cross section of the transducer of the first embodiment in use, creating eddy currents in a sample
  • Fig. 6 is a perspective view of the device of the second embodiment, with the meander line coil and the enhancement body of the transducer shown, for clarity, without the housing or epoxy resin;
  • Fig. 7 is an elevation in cross section of the transducer of the second embodiment in use, creating eddy currents in a sample
  • Fig. 8 is a perspective view of the device of the third embodiment, with the hollow spiral coil and the enhancement body of the transducer shown, for clarity, without the housing or epoxy resin;
  • Fig. *?' is an elevation in cross section of the transducer of the third embodiment in use, creating eddy currents in a sample.
  • the eddy current generation device 10 of the first embodiment comprises an electromagnetic acoustic transducer 12, and means to supply an electrical input 14 to the transducer 12, the means being an electrical device 16 including a capacitor 18.
  • the transducer 12 comprises a coil of electrically conductive material, which is a coil of wire 20, and an enhancement body 22.
  • the wire coil 20 is a flat spiral "pancake" coil consisting of 10 turns of 0.25mm diameter lacquered copper wire.
  • the enhancement body 22 is a ferrite cylinder 24, of diameter approximately 15mm.
  • the coil 20 is wound flat on one surface, which is one of the flat end surfaces 26, of the ferrite cylinder 24.
  • the enhancement body 22 lies behind the whole of the coil 20.
  • the flat surface 26 is smooth, apart from a small groove 28 which allows the inner end 30 of the coil to be run out under the spiral winding 20.
  • the wire coil 20 and the face 26 of the cylinder upon which the coil 20 rests are encapsulated in epoxy resin 32 , with the coil face 34 not more than 0.5mm below the surface 36 of the epoxy resin 32.
  • the ferrite cylinder 24, except for the resin coated end 26, is housed in an aluminium block 38.
  • the epoxy resin layer 32 encapsulating the coil 20 has its outer surface 36 flush with the edges defining the opening into the aluminium block 38.
  • the face 36 of the transducer 12 with the coil 20 is placed 2mm or less from the surface of a nearby electrically conductive object, the target 40, in which ultrasound is to be generated.
  • the target 40 may be an aluminium or steel beverage can.
  • the electrical device 16 is arranged to pass a current pulse (or spike) through the coil 20 which is temporally sharp, being approximately 5 microseconds in duration.
  • the current pulse is obtained from capacitor 18 discharge through the coil 20, where the capacitor 18 has been charged to about 750 Volts. This provides current flow through the coil of about 250 Amps.
  • a lOOOpF capacitor 18 rated to 1000V is used.
  • An eddy current 42 is generated in the electromagnetic skindepth of the target 40, such that the electromagnetic boundary conditions are satisfied and the eddy current 42 travels through the target 40 in the opposite sense to the current in the wire 20.
  • the enhancement body 22 behind the coil 20 will become temporarily magnetised. This magnetised layer of the enhancement body 22 behind the coil will produce its own external magnetic field. Where the current is changing, the magnetic field from the enhancement body 22 will act in the same direction as the magnetic field of the coil 20 and increase the total magnetic field experienced by the target 40.
  • the inductance of the coil 20 does increase slightly but the amplitude of the eddy current 42 of a particular frequency is made significantly larger by the presence of the enhancement body 22, and thus the ultrasonic wave generation efficiency is enhanced.
  • an ultrasonic wave pulse is created in the target, the pulse being of a 20 microseconds duration or less.
  • the device may be used for example in apparatus to monitor fill level in beverage cans. As can be seen in Figs 5, 7 and 9, there is no contact with the target, but an ultrasonic wave can be generated in the can and contents to enable checking that contents are present and to enable monitoring of fill level. This non-contact technique enables rapid processing.
  • the second embodiment is similar to the first and only the differences from the first embodiment will be described.
  • the same reference numerals will be used for equivalent features.
  • the wire coil 50 of the second embodiment is not a spiral but instead is a flat meander coil forming a rectangular shape, as shown in Figs. 6 and 7.
  • the wire meanders five times.
  • the third embodiment is similar to the first and only the differences from the first embodiment will be described.
  • the same reference numerals will be used for equivalent features.
  • the wire coil 60 of the third embodiment is a hollow spiral or annular shape with three turns as shown in Figs 8 and 9.
  • the enhancement body rather than being wholly, for example, ferrite, could be a thin disc of ferrite mounted on a support or a layer of ferrite coated onto a substrate.
  • the coil of electrically conducting material is driven by a toneburst, in particular, a periodically varying voltage of more than one cycle.
  • the coil may be driven by a voltage pulse having a frequency content between 10kHz and 10MHz.
  • sound of an audible frequency may be generated in the target material.

Abstract

The device (10) comprises an electromagnetic acoustic transducer (12) to produce in use an ultrasonic wave pulse in a nearby electrically conducting object (40). The transducer (12) comprises a coil of electrically conducting material (20) and an enhancement body (22). The coil of electrically conducting material (20) is adjacent to one side of the enhancement (body 22), and the enhancement body (22) has a magnetic permeability greater than one, for example being made of ferrite.

Description

An Eddy Current Generation Device, Apparatus and Method
This invention relates to an eddy current generation device, apparatus and method.
Various devices rely on the generation of an electrical eddy current in the electromagnetic skindepth of an electrically conducting sample. Examples of such devices are electromagnetic acoustic transducers (EMATs) or coils of wire that are designed to generate an eddy current in the surface of an electrically conducting sample. When the eddy current interacts with a magnetic field, an impulsive force is generated, which will generate an ultrasonic wave in the sample.
According to a first aspect of the present invention there is provided an eddy current generation device comprising an electromagnetic acoustic transducer to produce in use an acoustic wave pulse in a nearby electrically conducting object, the transducer comprising a coil of electrically conductive material and an enhancement body, the coil of electrically conductive material being adjacent to one side of the enhancement body, the enhancement body having a relative magnetic permeability greater than one.
When current is passed through the coil, the enhancement body behind the coil will become temporarily magnetised. This magnetised layer of the enhancement body behind the coil will produce its own external magnetic field. Where the current is changing, the magnetic field from the enhancement body will act in the same direction as the coil's magnetic field and increase the total magnetic field that is experienced by a nearby electrically conducting object such as a metal object. The increased changing magnetic field results in eddy currents of larger amplitude.
Preferably, the enhancement body has a resistivity greater than 55 x 10~8 Ωm. Preferably the coil of electrically conductive material is 1.5mm or less, preferably lmm or less, from the surface of the enhancement body, and most preferably the coil of electrically conductive material is on the surface of the enhancement body. The effectiveness of the enhancement body decreases with distance from the coil of electrically conductive material, thus the closer the coil of electrically conductive material is to the enhancement body, the greater the enhancement. Preferably, the enhancement body lies behind the whole of the coil. Thus, the maximum area of the coil will be affected by the enhancement body.
The enhancement body may be at least principally made of ferromagnetic or ferrimagnetic material, preferably ferrite, and preferably is wholly made of ferrite.
Preferably the surface of the enhancement body is smooth. The surface of the enhancement body may be curved, and may be concave, convex, or curved about one axis, but preferably the surface of the enhancement body is flat. Therefore, a flat coil can lie against the body or can easily be positioned so that no part is more than 1.5mm away.
Preferably the coil of electrically conductive material is in a substantially flat overall shape. Thus, it is simple to create a surface on the enhancement body against which the coil can lie, or which does not lie more than lmm from the surface at any part.
The coil may be in a spiral, preferably with at least ten turns. Alternatively, the coil may be a meander coil. In either case, the coil may be in an annular overall shape. Preferably the coil of electrically conducting material is a metal wire which may have a diameter in the range 0.1mm to 0.5mm, and preferably the wire has a diameter in the range 0.2mm to 0.25mm.
Preferably the coil of electrically conducting material is no more than about 10mm in maximum extent, and preferably the coil of electrically conducting material is about 4mm in diameter. The sides of the enhancement body, apart from that next to the coil, may be housed in an aluminium block.
The device is preferably without a permanent magnet. The device may include an electromagnet. The device may be adapted to produce in use an acoustic wave pulse in a nearby object, which is metal, and may be made wholly or principally of aluminium or steel, and may for example be a metal can. The device is preferably adapted to produce in use an acoustic wave pulse in a nearby object which has an electrical conductivity greater than the electrical conductivity of the enhancement body. The electrical conductivity of the enhancement body in relation to the intended object is suitably such that greater eddy current generation in the object is achieved than if the device is used without the enhancement body.
According to a second aspect of the present invention there is provided an apparatus including an eddy current generation device according to the preceding aspect of the invention and means to supply an electrical input to the coil of electrically conducting material.
The electromagnetic acoustic transducer may be adapted to produce in use an acoustic wave pulse in a nearby electrically conducting object which is of 100 microseconds duration or less, preferably of 20 microseconds duration or less, preferably of 5 microseconds duration or less.
Preferably the apparatus further includes means to apply a current of at least 10OA, and preferably at least 400A, through the coil of electrically conducting material.
Preferably the apparatus further includes a capacitor and means to discharge the capacitor through the coil of electrically conducting material. Preferably the apparatus further includes means to charge the capacitor to 200 Volts, and preferably 500 Volts or more, for discharge through the coil of electrically conducting material.
Preferably the apparatus is arranged to pass current through the coil for less than 10 μs.
The apparatus may be arranged to supply the coil of electrically conducting material with a periodically varying voltage.
The apparatus may be arranged to supply voltage to the coil of electrically conducting material with a frequency in the range 10kHz to 10MHz.
According to a third aspect of the present invention there is provided a method of generating eddy currents in the surface of a nearby electrically conducting object by passing current through a device according to the first aspect of the invention.
Preferably the electromagnetic acoustic transducer produces an acoustic wave pulse in a nearby electrically conducting object which is of 100 microsecond duration or less, preferably of 20 microsecond duration or less, preferably of 5 microsecond duration or less.
Preferably a current of at least 10OA, and preferably at least 400A, is passed through the coil of electrically conducting material.
Preferably a capacitor is discharged through the coil of electrically conducting material. Preferably the capacitor is charged to 200 Volts or more, and preferably to 500 Volts or more, prior to discharging through the coil of electrically conducting material.
Preferably the current passes through the coil for between 3 μs and 7 μs. Preferably the coil of electrically conducting material carries a periodically varying voltage of more than one cycle.
Preferably the coil of electrically conducting material carries a periodically varying voltage with a frequency between 10 kHz and 10 MHz.
The electrically conducting object may be a metal object and may be made wholly or principally from aluminium or steel and may, for example, be a metal can. The electrically conducting object preferably has an electrical conductivity greater than the electrical conductivity of the enhancement body. The electrical conductivity of the enhancement body in relation to the electrically conducting object is suitably such that greater eddy current generation in the object is achieved than if the method is carried out without the enhancement body.
According to a fourth aspect of the present invention there is provided a method of generating eddy currents in the surface of a nearby electrically conducting object by operating the apparatus according to the second aspect of the invention to pass current through the device.
Three embodiments of the invention will now be described by way of example and with reference to the accompanying drawings, in which:
Fig. 1 illustrates the arrangement of the apparatus of the first embodiment;
Fig. 2 is a perspective view of the device of the first embodiment, with the spiral coil and the enhancement body of the transducer shown, for clarity, without the housing or epoxy resin;
Fig. 3 is an elevation in cross section of the transducer of the first embodiment;
Fig. 4 is a schematic diagram to explain how the increase in the eddy current amplitude is achieved; Fig. 5 is an elevation in cross section of the transducer of the first embodiment in use, creating eddy currents in a sample;
Fig. 6 is a perspective view of the device of the second embodiment, with the meander line coil and the enhancement body of the transducer shown, for clarity, without the housing or epoxy resin;
Fig. 7 is an elevation in cross section of the transducer of the second embodiment in use, creating eddy currents in a sample;
Fig. 8 is a perspective view of the device of the third embodiment, with the hollow spiral coil and the enhancement body of the transducer shown, for clarity, without the housing or epoxy resin; and
Fig. *?' is an elevation in cross section of the transducer of the third embodiment in use, creating eddy currents in a sample.
First Embodiment
The eddy current generation device 10 of the first embodiment comprises an electromagnetic acoustic transducer 12, and means to supply an electrical input 14 to the transducer 12, the means being an electrical device 16 including a capacitor 18.
The transducer 12 comprises a coil of electrically conductive material, which is a coil of wire 20, and an enhancement body 22. The wire coil 20 is a flat spiral "pancake" coil consisting of 10 turns of 0.25mm diameter lacquered copper wire. The enhancement body 22 is a ferrite cylinder 24, of diameter approximately 15mm. The coil 20 is wound flat on one surface, which is one of the flat end surfaces 26, of the ferrite cylinder 24. The enhancement body 22 lies behind the whole of the coil 20. The flat surface 26 is smooth, apart from a small groove 28 which allows the inner end 30 of the coil to be run out under the spiral winding 20. The wire coil 20 and the face 26 of the cylinder upon which the coil 20 rests are encapsulated in epoxy resin 32 , with the coil face 34 not more than 0.5mm below the surface 36 of the epoxy resin 32. The ferrite cylinder 24, except for the resin coated end 26, is housed in an aluminium block 38. The epoxy resin layer 32 encapsulating the coil 20 has its outer surface 36 flush with the edges defining the opening into the aluminium block 38.
In use, the face 36 of the transducer 12 with the coil 20 is placed 2mm or less from the surface of a nearby electrically conductive object, the target 40, in which ultrasound is to be generated. The target 40 may be an aluminium or steel beverage can. The electrical device 16 is arranged to pass a current pulse (or spike) through the coil 20 which is temporally sharp, being approximately 5 microseconds in duration. The current pulse is obtained from capacitor 18 discharge through the coil 20, where the capacitor 18 has been charged to about 750 Volts. This provides current flow through the coil of about 250 Amps. A lOOOpF capacitor 18 rated to 1000V is used.
An eddy current 42 is generated in the electromagnetic skindepth of the target 40, such that the electromagnetic boundary conditions are satisfied and the eddy current 42 travels through the target 40 in the opposite sense to the current in the wire 20. When current is passed through the coil 20, the enhancement body 22 behind the coil 20 will become temporarily magnetised. This magnetised layer of the enhancement body 22 behind the coil will produce its own external magnetic field. Where the current is changing, the magnetic field from the enhancement body 22 will act in the same direction as the magnetic field of the coil 20 and increase the total magnetic field experienced by the target 40. The inductance of the coil 20 does increase slightly but the amplitude of the eddy current 42 of a particular frequency is made significantly larger by the presence of the enhancement body 22, and thus the ultrasonic wave generation efficiency is enhanced. Thus, an ultrasonic wave pulse is created in the target, the pulse being of a 20 microseconds duration or less.
The device may be used for example in apparatus to monitor fill level in beverage cans. As can be seen in Figs 5, 7 and 9, there is no contact with the target, but an ultrasonic wave can be generated in the can and contents to enable checking that contents are present and to enable monitoring of fill level. This non-contact technique enables rapid processing.
Second Embodiment
The second embodiment is similar to the first and only the differences from the first embodiment will be described. The same reference numerals will be used for equivalent features.
The wire coil 50 of the second embodiment is not a spiral but instead is a flat meander coil forming a rectangular shape, as shown in Figs. 6 and 7. The wire meanders five times.
Third Embodiment
The third embodiment is similar to the first and only the differences from the first embodiment will be described. The same reference numerals will be used for equivalent features.
The wire coil 60 of the third embodiment is a hollow spiral or annular shape with three turns as shown in Figs 8 and 9.
Other geometries of coil, for example, square or ellipse, other numbers of coils or meanders, and other enhancement materials to those described here can be used. The enhancement body, rather than being wholly, for example, ferrite, could be a thin disc of ferrite mounted on a support or a layer of ferrite coated onto a substrate.
In one embodiment, the coil of electrically conducting material is driven by a toneburst, in particular, a periodically varying voltage of more than one cycle.
The coil may be driven by a voltage pulse having a frequency content between 10kHz and 10MHz.
Rather than creating an ultrasonic vibration, sound of an audible frequency may be generated in the target material.
The content of the applicant's copending international patent application no. PCT/GB2007/002169 is incorporated herein by reference.

Claims

Claims
1. An eddy current generation device comprising an electromagnetic acoustic transducer to produce in use an acoustic wave pulse in a nearby electrically conducting object, the transducer comprising a coil of electrically conducting material and an enhancement body, the coil of electrically conducting material being adjacent to one side of the enhancement body, the enhancement body having a relative magnetic permeability greater than one.
2. A device as claimed in claim 1, wherein the enhancement body has a resistivity greater than 55 x ICP8 Ωm.
3. A device as claimed in claim 1 or claim 2, wherein the coil of electrically conducting material is 1.5mm or less from one surface of the enhancement body.
4. A device as claimed in claim 3, wherein the coil of electrically conducting material is lmm or less from the surface of the enhancement body.
5. A device as claimed in any preceding claim, wherein the coil of electrically conducting material is on the surface of the enhancement body.
6. A device as claimed in any preceding claim, wherein the enhancement body is at least principally made of ferrite.
7. A device as claimed in claim 6, wherein the enhancement body is wholly made of ferrite.
8. A device as claimed in any preceding claim, wherein the coil of electrically conducting material is in a substantially flat overall shape.
9. A device as claimed in any preceding claim wherein the coil is a meander coil.
10. A device as claimed in any of claims 1 to 8, wherein the coil is in a spiral.
11. A device as claimed in claim 10 wherein the spiral has at least ten turns.
12. A device as claimed in any preceding claim, wherein the coil of electrically conducting material is no more than about 10mm in maximum extent.
13. A device as claimed in any preceding claim, wherein the coil of electrically conducting material is about 4mm in maximum extent.
14. A device as claimed in any preceding claim wherein the coil is in an annular overall shape.
15. A device as claimed in any preceding claim wherein the coil of electrically conductive material is coil of metal wire.
16. A device as claimed in claim 15 wherein the wire has a diameter in the range 0.1mm to 0.5mm.
17. A device as claimed in claim 15 wherein the wire has a diameter in the range 0.2mm to 0.25mm.
18. A device as claimed in any preceding claim wherein the surface of the enhancement body adjacent the coil of electrically conducting material is smooth.
19. A device as claimed in any preceding claim wherein the surface of the enhancement body adjacent to the coil of electrically conducting material is flat.
20. A device as claimed in any preceding claim wherein the enhancement body lies behind the whole of the coil.
21. A device as claimed in any preceding claim, wherein the device includes an electromagnet.
22. A device as claimed in any preceding claim, wherein the device is without a permanent magnet.
23. A device as claimed in any preceding claim, wherein the device is adapted to produce in use an acoustic wave pulse in a nearby metal object.
24. A device as claimed in any preceding claim, wherein the device is adapted to produce in use an acoustic wave pulse in a nearby object made wholly or principally of aluminium or steel.
25. A device as claimed in any preceding claim, wherein the device is adapted to produce in use an acoustic wave pulse in a nearby metal can.
26. A device as claimed in any preceding claim, wherein the device is adapted to produce in use an acoustic wave pulse in a nearby object which has an electrical conductivity greater than the electrical conductivity of the enhancement body.
27. An apparatus including an eddy current generation device as claimed in any preceding claim and means to supply an electrical input to the coil of electrically conducting material.
28. An apparatus as claimed in claim 27, wherein the electromagnetic acoustic transducer is adapted to produce in use an acoustic wave pulse in a nearby electrically conducting object which is of 100 microseconds duration or less.
29. An apparatus as claimed in claim 27, wherein the electromagnetic acoustic transducer is adapted to produce in use an acoustic wave pulse in a nearby electrically conducting object which is of 20 microseconds duration or less.
30. An apparatus as claimed in claim 27, wherein the electromagnetic acoustic transducer is adapted to produce in use an acoustic wave pulse in a nearby electrically conducting object which is of 5 microseconds duration or less.
31. An apparatus as claimed in any of claims 27 to 30, wherein the apparatus includes means to apply a current of at least IOOA through the coil of electrically conducting material.
32. An apparatus as claimed in any of claims 27 to 30, wherein the apparatus includes means to apply a current of at least 400A through the coil of electrically conducting material.
33. An apparatus as claimed in any of claims 27 to 32, wherein the apparatus includes a capacitor and means to discharge the capacitor through the coil of electrically conducting material.
34. An apparatus as claimed in claim 33, wherein the apparatus further includes means to charge the capacitor to 200 Volts or more for discharge through the coil of electrically conducting material.
35. An apparatus as claimed in claim 33, wherein the apparatus further includes means to charge the capacitor to 500 Volts or more for discharge through the coil of electrically conducting material.
36. An apparatus as claimed in any of claims 27 to 35, wherein the apparatus is arranged to pass current through the coil for less than 10 μs.
37. An apparatus as claimed in any of claims 27 to 36, wherein the apparatus is arranged to supply the coil of electrically conducting material with a periodically varying voltage.
38. An apparatus as claimed in any of claims 27 to 37, wherein the apparatus is arranged to supply voltage to the coil of electrically conducting material at a frequency in the range 1OkHz to 10MHz.
39. A method of generating eddy currents in the surface of an electrically conducting object by passing current through a device as claimed in any preceding claim.
40. A method as claimed in claim 39, wherein the electromagnetic acoustic transducer produces an acoustic wave pulse in a nearby electrically conducting object which is of 100 microseconds duration or less.
41. A method as claimed in claim 39, wherein the electromagnetic acoustic transducer produces an acoustic wave pulse in a nearby electrically conducting object which is of 20 microseconds duration or less.
42. A method as claimed in claim 39, wherein the electromagnetic acoustic transducer produces an acoustic wave pulse in a nearby electrically conducting object which is of 5 microseconds duration or less.
43. A method as claimed in any of claims 39 to 42, wherein a current of at least IOOA is passed through the coil of electrically conducting material.
44. A method as claimed in claim 43, wherein a current of at least 400A is passed through the coil of electrically conducting material.
45. A method as claimed in any of claims 39 to 44, wherein a capacitor is discharged through the coil of electrically conducting material.
46. A method as claimed in claim 45, wherein the capacitor is charged to 200 Volts or more prior to discharging through the coil of electrically conducting material.
47. A method as claimed in claim 45, wherein the capacitor is charged to 500 Volts or more prior to discharging through the coil of electrically conducting material.
48. A method as claimed in any of claims 39 to 47, wherein current is passed through the coil for less than 10 μs.
49. A method as claimed in any of claims 39 to 48, wherein the coil of electrically conducting material is supplied with a periodically varying voltage of more than one cycle.
50. A method as claimed in any of claims 39 to 49, wherein the coil of electrically conducting material is supplied with voltage at a frequency between 10 kHz and 10 MHz.
51. A method as claimed in any of claims 39 to 50, wherein the electrically conducting object is a metal object.
52. A method as claimed in any of claims 39 to 50, wherein the electrically conducting object is made wholly of principally of aluminium or steel.
53. A method as claimed in claim 51 or claim 52, wherein the electrically conducting object is a metal can.
54. A method as claimed in any of claims 39 to 53, wherein the electrically conducting object has an electrical conductivity greater than the electrical conductivity of the enhancement body.
55. A method of generating eddy currents in the surface of a nearby electrically conducting object by operating the apparatus as claimed in any of claims 27 to 38 to pass current through the device.
PCT/GB2007/002514 2006-07-05 2007-07-05 An eddy current generation device, apparatus and method WO2008003972A1 (en)

Applications Claiming Priority (4)

Application Number Priority Date Filing Date Title
GB0613427.4 2006-07-05
GB0613427A GB0613427D0 (en) 2006-07-05 2006-07-05 A method and device for enhancing eddy current generation using ferromagnetic or ferromagnetic backing materials
GBPCT/GB2007/002169 2007-06-11
PCT/GB2007/002169 WO2007141559A1 (en) 2006-06-10 2007-06-11 A non-contact apparatus for monitoring the height of contents of a moving container, a monitoring station including the apparatus and a non-contact method of monitoring the height of contents of a container

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WO2008003972A1 true WO2008003972A1 (en) 2008-01-10

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