Non-magnetodielectric flux concentrator
The invention also provides a heating apparatus including a holder capable of holding at least one part, an electric current generator and a flux concentrator electrically connected to the electric current generator, the flux concentrator being made of a non-magneto-dielectric material and having a coil with at least one turn forming an inductor to generate an alternating magnetic field that is driven by the alternating electric field, the alternating magnetic field resonating at a frequency of at least 1 MHz in response to the alternating electric current.
1. A heating method comprising:
holding a flux concentrator and at least one part in proximity to one another; and
generating an alternating electric current, the flux concentrator comprising a plate of non-magnetodielectric material, the plate having a slot and a hole at an end of the slot, the hole defining the single turn having a diameter of less than 10 mm forming an inductor to generate an alternating magnetic field that is driven by the alternating electric current, the alternating magnetic field resonating at a high frequency of at least 1 MHz that is selected such that d/δ is at least 4, wherein
δ
=
ρ
π
f
μ
ρ is the resistivity and μ is the permeability of the material,
μ is the permeability of the material;
f is the frequency of the magnetic field, and
d is an outer dimension of the part.
2. The method of claim 1 , wherein d/δ is at least 4, wherein the part is a spherical particle with an axis aligned with a flux field in line of the magnetic field through the spherical particle, wherein:
d/δ is at least 6 at an equator of the spherical particle; and
d/δ is at least 6 at poles of the spherical particle.
3. The method of claim 2 , the coil having a diameter and a thickness, wherein the diameter is less than 10 mm and the alternating magnetic field has a toroidal shape with a cross-section of revolution forming a circle, the circle having a diameter of less than 50 percent of the diameter of the coil.
4. The method of claim 1 , wherein the flux concentrator has a magnetic flux density of at least 1 mT at 0.5 mm.
5. The method of claim 1 , wherein the coil has an inductance of less than 5 nH.
6. The method of claim 1 , wherein the part is between 45 and 55 percent of a diameter of the coil from the coil.
7. The method of claim 1 , further comprising:
collecting and releasing a charge with at least one capacitor in parallel with the inductor to form a tank circuit.
8. The method of claim 7 , further comprising:
a plate, wherein a plurality of capacitors are mounted to the plate in parallel with the inductor.
9. The method of claim 7 , wherein the tank circuit has a resonant frequency f R , wherein
f
R
=
1
2
π
L
C
where:
L is the inductance of the coil; and
C is the capacitor of the at least one capacitor.
10. The method of claim 1 , wherein the coil is a high frequency coil, further comprising:
pre-heating the part with a low frequency coil.
11. The method of claim 1 , further comprising:
monitoring coupling of the alternating magnetic field to the part by monitoring a normalized voltage standing wave (VSWR) ratio θ as:
θ
=
1
-
(
V
S
W
R
K
>
0
V
S
W
R
K
=
0
)
where VSWR K>0 is the VSWR of circuit having the coil when it is coupled to the powder bed, and VSWR K=0 is the VSWR of the circuit when it is completely de-coupled from the powder bed.
12. A heating method comprising:
holding a flux concentrator and at least one part in proximity to one another; and
generating an alternating electric current, the flux concentrator being made of a non-magnetodielectric material and having a coil with at least one turn having a diameter of less than 10 mm forming an inductor to generate an alternating magnetic field that is driven by the alternating electric current, the alternating magnetic field resonating at a high frequency of at least 1 MHz that is selected such that d/δ is at least 4, wherein
δ
=
ρ
π
f
μ
ρ is the resistivity and μ is the permeability of the material,
μ is the permeability of the material;
f is the frequency of the magnetic field, and
d is an outer dimension of the part; and
monitoring coupling of the alternating magnetic field to the part by monitoring a normalized voltage standing wave (VSWR) ratio θ as:
θ
=
1
-
(
V
S
W
R
K
>
0
V
S
W
R
K
=
0
)
where VSWR K>0 is the VSWR of circuit having the coil when it is coupled to the powder bed, and VSWR K=0 is the VSWR of the circuit when it is completely de-coupled from the powder bed.
13. The method of claim 12 , wherein d/δ is at least 4, wherein the part is a spherical particle with an axis aligned with a flux field in line of the magnetic field through the spherical particle, wherein:
d/δ is at least 6 at an equator of the spherical particle; and
d/δ is at least 6 at poles of the spherical particle.
14. The method of claim 13 , the coil having a diameter and a thickness, wherein the diameter is less than 10 mm and the alternating magnetic field has a toroidal shape with a cross-section of revolution forming a circle, the circle having a diameter of less than 50 percent of the diameter of the coil.
15. The method of claim 12 , wherein the flux concentrator has a magnetic flux density of at least 1 mT at 0.5 mm.
16. The method of claim 12 , wherein the coil has an inductance of less than 5 nH.
17. The method of claim 12 , wherein the part is between 45 and 55 percent of a diameter of the coil from the coil.
18. The method of claim 12 , further comprising:
collecting and releasing a charge with at least one capacitor in parallel with the inductor to form a tank circuit.
19. The method of claim 18 , wherein a plurality of capacitors are mounted to the plate in parallel with the inductor.
20. The method of claim 18 , wherein the tank circuit has a resonant frequency f R , wherein
f
R
=
1
2
π
L
C
where:
L is the inductance of the coil; and
C is the capacitor of the at least one capacitor.
21. The method of claim 12 , wherein the coil has only a single turn.
22. The method of claim 21 , wherein the flux concentrator comprises a plate of non-magnetodielectric material, the plate having a slot and a hole at an end of the slot, the hole defining the single turn.
23. The method of claim 12 , wherein the coil is a high frequency coil, further comprising:
pre-heating the part with a low frequency coil.