Planar inductors with cores on ICs

[Phil Hobbs]

YES! and their dimensions?

Teensy cubed.

Cheers

Phil Hobbs

--
Dr Philip C D Hobbs
Principal Consultant
ElectroOptical Innovations LLC
Optics, Electro-optics, Photonics, Analog Electronics

160 North State Road #203
Briarcliff Manor NY 10510

hobbs at electrooptical dot net
http://electrooptical.net

 

[RobertMacy]

Teensy cubed.

Cheers

Phil Hobbs

The precise technical value not sure of, but EXACTLY! that's why they work
into the 100's MHz

From memory, that ??permalloy stuff has around 10 times the coercivity of
metglas stuff. And I think its permeability has 'direction' too. Which can
be a bit awesome to use.

 

[[email protected]]

Thanks for the food-for-thought, Robert.

From memory a toroid with its distributed air gap did not have as good a
high frequency performance as different type of structure. The skin effect
eats you alive at every turn [pardon the pun] with this material when it's
used as 'gross' material.

In a tape-wound toroid the air gaps are in parallel
with the magnetic path, rather than in series like they
are in the ordinary gapped cores, or in 'distributed-gap'
cores such as iron powder. I have hard time seeing why,
in the first order, a parallel gap would matter.

Calculating from the datasheet numbers, the skin depth
at 10 kHz would be 6um, in the ballpark of half-thickness
of my foil. This sort-of-agrees with what I see in
my crude homemade toroid: Re(Z) begins to rise above
the copper Rdc when f > 20 kHz. Im(Z) begins to drop
above 200 kHz, which OTOH seems to contradict the
skin-depth-eats-away-cross-section hypothesis. A significant
part of the core is air, it's difficult to make the
the wires 'hug' the core with such small dimensions.

In LHe half the initial mu and lower Im(Z) corner
frequency.

I tried to get both vendors to make 2 micron 'beads' by splattering
directly into the liquid nitrogen, passivate the surface of the spheres,
then 'gently' sintering into larger core material to get high perm, no
coercivity, and nonconductivity, but they were too busy making huge cores
for the power industry to be interested. Even little wires would be better.

Any interest for your firm to do it? Or, somebody out there? we'd make a
fortune! maybe as much as $10k, or even $100k. Boy has out-sourcing
changed MY expectations!

Maybe there is, I don't know. You know the composition? I'm wondering
how would one be personally able to cash on it, if there is no
protected IPR to sell, except by starting a company by oneself.

Regards,
Mikko

 

[Tim Williams]

Calculating from the datasheet numbers, the skin depth
at 10 kHz would be 6um, in the ballpark of half-thickness
of my foil. This sort-of-agrees with what I see in
my crude homemade toroid: Re(Z) begins to rise above
the copper Rdc when f > 20 kHz. Im(Z) begins to drop
above 200 kHz, which OTOH seems to contradict the
skin-depth-eats-away-cross-section hypothesis.

Keep in mind skin depth assumes semi-infinite thickness, i.e., current
flow over (and below) the surface of an infinite plane with solid material
on one side, vacuum on the other. The case is more interesting for finite
geometries, such as cylinders, pipes and plates. In the cylindrical case,
Bessel functions arise; unfortunately, I forget what the plate case gives.

Since the current gets phase shifted (due to the bulk L/R time constant)
as it goes deeper, waves from opposite sides interfere to make peaks and
nulls. Under certain conditions, induction heating is capable, not only
of heating a material in bulk, but actually putting more heat (higher
power density) into deeper regions than at the surface. (I don't know if
that's (for the case of cylinders) radial power density, which matters
more than volumetric in matters of heat transfer. It seems remarkable
even to me that the absolute power density could be higher. But I can't
find a reference, unfortunately.)

Tim

 

[RobertMacy]

Thanks for the food-for-thought, Robert.

From memory a toroid with its distributed air gap did not have as good
a
high frequency performance as different type of structure. The skin
effect
eats you alive at every turn [pardon the pun] with this material when
it's
used as 'gross' material.

In a tape-wound toroid the air gaps are in parallel
with the magnetic path, rather than in series like they
are in the ordinary gapped cores, or in 'distributed-gap'
cores such as iron powder. I have hard time seeing why,
in the first order, a parallel gap would matter.

Calculating from the datasheet numbers, the skin depth
at 10 kHz would be 6um, in the ballpark of half-thickness
of my foil. This sort-of-agrees with what I see in
my crude homemade toroid: Re(Z) begins to rise above
the copper Rdc when f > 20 kHz. Im(Z) begins to drop
above 200 kHz, which OTOH seems to contradict the
skin-depth-eats-away-cross-section hypothesis. A significant
part of the core is air, it's difficult to make the
the wires 'hug' the core with such small dimensions.

In LHe half the initial mu and lower Im(Z) corner
frequency.

I tried to get both vendors to make 2 micron 'beads' by splattering
directly into the liquid nitrogen, passivate the surface of the spheres,
then 'gently' sintering into larger core material to get high perm, no
coercivity, and nonconductivity, but they were too busy making huge
cores
for the power industry to be interested. Even little wires would be
better.

Any interest for your firm to do it? Or, somebody out there? we'd make a
fortune! maybe as much as $10k, or even $100k. Boy has out-sourcing
changed MY expectations!

Maybe there is, I don't know. You know the composition? I'm wondering
how would one be personally able to cash on it, if there is no
protected IPR to sell, except by starting a company by oneself.

Regards,
Mikko

the material I used was made as a 'special run', modification of one of
their alloys, but again from memory, one of their standard materials had a
skin depth of 3 microns at 1MHz. Yours must be pretty conductive to
shallow out so fast.

I know I'm preaching to the choir, but skindepth is a nice reference, but
it's related to planar waves and surfaces. When the field has sharp
gradients... or when the material is in a magnetic field; things get a bit
dicey. Surprising effects start happening.

I assume you're using some type of finite elecment analysis program to
explore your possible architectures? Especially take a look at the ribbon
toroid configuration. Surprised me just how much that was NOT a good use
of the material. The resistance started up very early. Had to do with how
the fields must propagate 'along' the ribbon in order to dart across the
air gap, and it was that traveling along the ribbon where eddy currents
thrived. I finally came to the conclusion, supported by Hasegawa's
comments, that the only way to improve the material was not concentrate on
the perm, but lower the conductivity, which he did in ?? material,
saturated at 1T, lowered to somewhere around 0.7 MS/m.

The one thing that kept surprising me was how the optimized structure for
MEMs inductor kept coming back to a single wire 'wrapped' with a core and
NO shared flux, and the optimized structure for a multi-winding
transformer kept coming back to conductors 'wrapped' with a core.
Everything else had less performance.

Sort of 'turns your thinking inside out' Should have remembered, magnetics
are LOW impedance. Look at SQUIDs.