3D Printed Air Core Inductors for High Frequency Power
Converters
Wei Liang, Luke Raymond, Juan Rivas
Stanford University Power Electronics Research (SUPER) Lab
Design and implementation process
Abstract
Air Core Magnetics
• 3D CAD model is scripted in OpenJSCAD and
3D CAD Model
3D printed plastic mold
cast silver model
3D printed Air Core Inductors
Several examples of air core inductors designed using 3D printing and molding techniques to give
an idea of the geometries that are possible to realize.
A toroid inductor with
square cross section. More
freedom on height selection
can lead to higher quality
factors.
or Curie temperature limitations.
• Toroidal inductors are better than solenoids as
the magnetic field is constrained within the
torus.
a
CAD model
• Lower
stray fields → Lower EMI
• PCB toroidal inductors have better copper
coverage, lower loss but limits in via density
result in fields leaking from the side of the
structure.
• Better air-core passives are possible with modern
fabrication techniques: 3D-printing.
Try it Out! Some of the inductor examples are
available for order at our i.materialise online shop.
inductor photo
VIN
LMR
+
−
CMR
LS
Q1
+
vgs (t)
-
+
vds (t)
-
CS
+
CP
RL
vload (t)
-
200
100
0
-100
0
20
40
60
80
100
120
Time [nS]
• A 70 W 27.12 MHz prototype Φ2 inverter was designed
and implemented with all inductors 3D printed. The
inverter operates at Vin =170 V and Rload =50 Ω. The
efficiency reaches 80 %.
• Three same inductors were 3D printed manufactured
separately and soldered together. It is not designed for
highest efficiency but rather the proof of concept.
not expected to be accurate
FEA magnetic field
L@27.12MHz Q@27.12 Q@54.24 Q@81.36
nH
MHz
MHz
MHz
sim
341
236
313
355
meas
345
140 a
NA
NA
a
A toroid with a round cross
section and four parallel
windings. A structure
impossible for planar
process.
LF
L@27.12MHz Q@27.12 Q@54.24 Q@81.36
nH
MHz
MHz
MHz
sim
84.6
135
187
226
a
meas
81
55
NA
NA
A toroid inductor with
circular section.
A toroid with a round cross
section and two parallel
windings. It cancels the
“one turn” inductance [1].
300
Ongoing Updates
CAD model
• Air-core inductors are not subject to saturation
OpenSCAD.
• A plaster casting mold is 3D printed for lost-wax
casting.
• The parts are cast, or plated
• Here, we got silver cast models from a commercial
3D printing service (Shapeways, i.materialise).
Drain Voltage
400
Voltage [V]
This paper presents the design, modeling and
characterization of 3D printed air core inductors
for high frequency power electronics circuits.
1 3D printing and molding techniques add
flexibility and functionality in the design. They
allow manufacturing of components with
rounded edges and overhanging structures
difficult to realize in planar processes.
2 We present several air core inductors designed
using 3D printing and molding techniques.
3 We describe the software and modeling
toolchain used to design, fabricate and
characterize the electromagnetic performance
of the air core inductors.
4 We implement a 70 W prototype 27.12 MHz
resonant inverter that incorporates some of
the 3D printed components developed for this
work.
We envision a fully 3D-printed power converter
that obviates the need of printed circuits board.
Φ2 Inverter with 3D printed Inductors
inductor photo
not expected to be accurate
• toroids with optimal cross section shape are modeled [2].
• multi-winding structures are possible. 1:1 transformer
may provide good coupling and isolation
Next Steps
FEA magnetic field
• Incorporate thermal and mechanical properties into the
L@27.12MHz Q@27.12 Q@54.24 Q@81.36
nH
MHz
MHz
MHz
sim
22.2
293
411
501
meas
18
65 a
NA
NA
a
CAD model
inductor photo
not expected to be accurate
FEA magnetic field
L@27.12MHz Q@27.12 Q@54.24 Q@81.36
nH
MHz
MHz
MHz
sim
9.3
232
323
392
meas
9
60 a
NA
NA
a
CAD model
inductor photo
FEA magnetic field
The two toroid
inductors are the same
as the one mentioned
above.
“One turn” inductance
cancellation with oppositely
wound series toroids.
CAD model
inductor photo
not expected to be accurate
FEA magnetic field
FEM simulation
• Run FEM of multiple components simultaneously to
evaluate interaction
• Evaluate repeatability and variability of components
• Look into possible mass-production paths
Acknowledgement
The authors would like to thank Mr. Brian Holman and
Prof. Charles Sullivan (Dartmouth College) for their help in
modeling and implementing 3D toroids with optimal cross
section.
References
[1] J. Qiu, A.J. Hanson, and C. R. Sullivan. Design of Toroidal Inductors with Multiple Parallel
Foil Windings. In Proc. IEEE 14th COMPEL, 2013.
[2] C. R. Sullivian, Weidong Li, S. Prabhakaran, and Shanshan Lu. Design and fabrication of
low-loss toroidal air-core inductors. In Proc. IEEE PESC 2007.