Resistive sheet

[Don A. Gilmore]

Hi guys:

I'm looking for a relatively thin electrically-resistive sheet material.
The resistivity I need depends on the thickness I can get. Basically I need
for the resistivity to be somwhere near

rho = .24 / t

where rho is the resistivity in ohm-m and t is the thickness of the sheet in
meters. I would like for it to be thin enough to be flexible in large
sheets (say, measured in square meters). Here are the corresponding
resistivities for some nominal inch thicknesses:

..031 in ---> 300 ohm-m
..062 in ---> 150 ohm-m
..125 in ---> 75 ohm-m
..188 in ---> 50 ohm-m

Are any of you aware of a material that meets these specs (or is close) that
is not extremely expensive? I have seen graphite-impregnated plastics that
could work well, but only in McMaster-Carr, which has a limited selection.
The material must be uniformly resistive throughout its cross section (not
just surface conductive).

Thanks for any replies.

Don
Kansas City

 

[cwsachs.dejazzd.com]

Teflon??

Carl Sachs

Don A. Gilmore wrote:

Hi guys:

I'm looking for a relatively thin electrically-resistive sheet material.
The resistivity I need depends on the thickness I can get. Basically I need
for the resistivity to be somwhere near

rho = .24 / t

where rho is the resistivity in ohm-m and t is the thickness of the sheet in
meters. I would like for it to be thin enough to be flexible in large
sheets (say, measured in square meters). Here are the corresponding
resistivities for some nominal inch thicknesses:

.031 in ---> 300 ohm-m
.062 in ---> 150 ohm-m
.125 in ---> 75 ohm-m
.188 in ---> 50 ohm-m

Are any of you aware of a material that meets these specs (or is close) that
is not extremely expensive? I have seen graphite-impregnated plastics that
could work well, but only in McMaster-Carr, which has a limited selection.
The material must be uniformly resistive throughout its cross section (not
just surface conductive).

Thanks for any replies.

Don
Kansas City

 

Don, We need to know a little more about what you are trying to do.

Sheet restivity has dimensions of ohms, not ohm-meters. so it is not
clear what conduction path you are thinking of.

Also will you be using DC or could you work at high frequencies? At
high frequencies the thickness of sheet involved in point-to-point
conduction depends on the frequency.

 

See: http://www.esdjournal.com/techpapr/ohms.htm for an example of
sheet resistivity.

Dave

 

[Don A. Gilmore]

<dmartin@newarts.com> wrote in message
news:1104532332.506815.181170@c13g2000cwb.googlegroups.com...

Don, We need to know a little more about what you are trying to do.

Sheet restivity has dimensions of ohms, not ohm-meters. so it is not
clear what conduction path you are thinking of.

Also will you be using DC or could you work at high frequencies? At
high frequencies the thickness of sheet involved in point-to-point
conduction depends on the frequency.

For my application the bulk resistivity in ohm-m is more useful. But you're
right, it would be more likely to be given by the manufacturer in "ohms per
square" for a thin sheet. To convert we would divide by the thickness of
the sheet, so the new values would be

..031 in ---> 9840 ohms/square
..062 in ---> 2450 ohms/square
..125 in ---> 610 ohms/square
..188 in ---> 270 ohms/square

Hopefully this will be of more use to all of you. Thanks for pointing out
the discrepancy.

Don

 

Don,

For a good short paper that gives the relationship between
point-to-point resistance and plate thickness see:
http://microlab.berkeley.edu/ee143/Four-Point_Probe/

It has info that may be needed to answer your question.
Contact me directly if you like.

Dave

 

[Uncle Al]

"Don A. Gilmore" wrote:

Hi guys:

I'm looking for a relatively thin electrically-resistive sheet material.
The resistivity I need depends on the thickness I can get. Basically I need
for the resistivity to be somwhere near

rho = .24 / t

where rho is the resistivity in ohm-m and t is the thickness of the sheet in
meters. I would like for it to be thin enough to be flexible in large
sheets (say, measured in square meters). Here are the corresponding
resistivities for some nominal inch thicknesses:

.031 in ---> 300 ohm-m
.062 in ---> 150 ohm-m
.125 in ---> 75 ohm-m
.188 in ---> 50 ohm-m

Are any of you aware of a material that meets these specs (or is close) that
is not extremely expensive? I have seen graphite-impregnated plastics that
could work well, but only in McMaster-Carr, which has a limited selection.
The material must be uniformly resistive throughout its cross section (not
just surface conductive).

What does carbon fiber composite look like?

--
Uncle Al
http://www.mazepath.com/uncleal/
(Toxic URL! Unsafe for children and most mammals)
http://www.mazepath.com/uncleal/qz.pdf

 

[Uncle Al]

"Don A. Gilmore" wrote:

dmartin@newarts.com> wrote in message
news:1104532332.506815.181170@c13g2000cwb.googlegroups.com...
Don, We need to know a little more about what you are trying to do.

Sheet restivity has dimensions of ohms, not ohm-meters. so it is not
clear what conduction path you are thinking of.

Also will you be using DC or could you work at high frequencies? At
high frequencies the thickness of sheet involved in point-to-point
conduction depends on the frequency.

Oops. I didn't convert to meters before I divided. Here are (hopefully)
the correct values.

t = .031 in ---> 387 x 10^3 ohm/square
t = .062 in ---> 96.5 x 10^3
t = .125 in ---> 24.2 x 10^3
t = .188 in ---> 10.8 x 10^3

Sorry about that.

Metal-filled epoxies?

<http://www.devcon.com/devconcatsolution.cfm?catid=34>
http://www.plasticworld.ca/Devcon.htm
<http://www.loctite.com/int_henkel/loctite_us/binarydata/pdf/LT3355v4_MROepoxies.pdf>
<http://www.tra-con.com/pdf/tpb/2122.pdf>

Dilute to adjust resistance. Maintain viscosity (~1 wt-% fumed silica
will render organics thixotropic) to keep it homogeneous during cure.
You can cast thin slabs between silanized glass plates using nylon
fishing line as the spacer and those black squeeze clips for stacks of
paper as compression along the edges. Position the gasket with a thin
metal ruler.

--
Uncle Al
http://www.mazepath.com/uncleal/
(Toxic URL! Unsafe for children and most mammals)
http://www.mazepath.com/uncleal/qz.pdf

 

[artie]

In article <r3lBd.73703$NO5.63637@twister.rdc-kc.rr.com>, Don A.
Gilmore <eromlignod@kc.rr.com> wrote:

dmartin@newarts.com> wrote in message
news:1104532332.506815.181170@c13g2000cwb.googlegroups.com...
Don, We need to know a little more about what you are trying to do.

Sheet restivity has dimensions of ohms, not ohm-meters. so it is not
clear what conduction path you are thinking of.

Also will you be using DC or could you work at high frequencies? At
high frequencies the thickness of sheet involved in point-to-point
conduction depends on the frequency.

Oops. I didn't convert to meters before I divided. Here are (hopefully)
the correct values.

t = .031 in ---> 387 x 10^3 ohm/square
t = .062 in ---> 96.5 x 10^3
t = .125 in ---> 24.2 x 10^3
t = .188 in ---> 10.8 x 10^3

Sorry about that.

Don

Have you looked at indium tin oxide (ITO) coatings? Thin coatings,
high resistivity, commonly used in stylus or touch-operated displays
(think Palm Pilot). Thicker coatings, lower resistivity, may be used
to heat (microsocope) slides and other materials.

Google is your friend.

--
Namaste--

 

Don A. Gilmore wrote:

Oops. I didn't convert to meters before I divided. Here are
(hopefully)
the correct values.

t = .031 in ---> 387 x 10^3 ohm/square
t = .062 in ---> 96.5 x 10^3
t = .125 in ---> 24.2 x 10^3
t = .188 in ---> 10.8 x 10^3

Sorry about that.

A paper at:
http://www.site.uottawa.ca/~sloyka/papers/1999/EMC_ground_resistance.pdf
Has a reasonable formula showing that the apparent resistance between
two electrodes on a plate of thickness t depends on the electrode
diameters, the distance between the electrodes, and the plate
thickness.

In particular the apparent resistance depends most strongly the
electrode diameter times conductivity and on the ratios of: (1)
electrode diameter to thickness and (2) electrode separation to
distance.

Dave

 

[Robert Baer]

Uncle Al wrote:

"Don A. Gilmore" wrote:

dmartin@newarts.com> wrote in message
news:1104532332.506815.181170@c13g2000cwb.googlegroups.com...
Don, We need to know a little more about what you are trying to do.

Sheet restivity has dimensions of ohms, not ohm-meters. so it is not
clear what conduction path you are thinking of.

Also will you be using DC or could you work at high frequencies? At
high frequencies the thickness of sheet involved in point-to-point
conduction depends on the frequency.

Oops. I didn't convert to meters before I divided. Here are (hopefully)
the correct values.

t = .031 in ---> 387 x 10^3 ohm/square
t = .062 in ---> 96.5 x 10^3
t = .125 in ---> 24.2 x 10^3
t = .188 in ---> 10.8 x 10^3

Sorry about that.

Metal-filled epoxies?

http://www.devcon.com/devconcatsolution.cfm?catid=34
http://www.plasticworld.ca/Devcon.htm
http://www.loctite.com/int_henkel/loctite_us/binarydata/pdf/LT3355v4_MROepoxies.pdf
http://www.tra-con.com/pdf/tpb/2122.pdf

Dilute to adjust resistance. Maintain viscosity (~1 wt-% fumed silica
will render organics thixotropic) to keep it homogeneous during cure.
You can cast thin slabs between silanized glass plates using nylon
fishing line as the spacer and those black squeeze clips for stacks of
paper as compression along the edges. Position the gasket with a thin
metal ruler.

--
Uncle Al
http://www.mazepath.com/uncleal/
(Toxic URL! Unsafe for children and most mammals)
http://www.mazepath.com/uncleal/qz.pdf

Metal filled epoxies would fail all his criteria: 1) not flexible, 2)
resistivity too low, 3) not uniform unless carefully formulated.
Case in point: silver filled epoxy.

 

[Robert Baer]

artie wrote:

In article <r3lBd.73703$NO5.63637@twister.rdc-kc.rr.com>, Don A.
Gilmore <eromlignod@kc.rr.com> wrote:

dmartin@newarts.com> wrote in message
news:1104532332.506815.181170@c13g2000cwb.googlegroups.com...
Don, We need to know a little more about what you are trying to do.

Sheet restivity has dimensions of ohms, not ohm-meters. so it is not
clear what conduction path you are thinking of.

Also will you be using DC or could you work at high frequencies? At
high frequencies the thickness of sheet involved in point-to-point
conduction depends on the frequency.

Oops. I didn't convert to meters before I divided. Here are (hopefully)
the correct values.

t = .031 in ---> 387 x 10^3 ohm/square
t = .062 in ---> 96.5 x 10^3
t = .125 in ---> 24.2 x 10^3
t = .188 in ---> 10.8 x 10^3

Sorry about that.

Don

Have you looked at indium tin oxide (ITO) coatings? Thin coatings,
high resistivity, commonly used in stylus or touch-operated displays
(think Palm Pilot). Thicker coatings, lower resistivity, may be used
to heat (microsocope) slides and other materials.

Google is your friend.

--
Namaste--

Fails in the "not surface effect" criteria.
Prolly would also fail (crack) if flexed.

 

[Terry]

"Uncle Al" <UncleAl0@hate.spam.net> wrote in message
news:41D5DCF2.A0FCCE84@hate.spam.net...

"Don A. Gilmore" wrote:

Hi guys:

I'm looking for a relatively thin electrically-resistive sheet material.
The resistivity I need depends on the thickness I can get. Basically I
need
for the resistivity to be somwhere near

rho = .24 / t

where rho is the resistivity in ohm-m and t is the thickness of the
sheet in
meters. I would like for it to be thin enough to be flexible in large
sheets (say, measured in square meters). Here are the corresponding
resistivities for some nominal inch thicknesses:

.031 in ---> 300 ohm-m
.062 in ---> 150 ohm-m
.125 in ---> 75 ohm-m
.188 in ---> 50 ohm-m

Are any of you aware of a material that meets these specs (or is close)
that
is not extremely expensive? I have seen graphite-impregnated plastics
that
could work well, but only in McMaster-Carr, which has a limited
selection.
The material must be uniformly resistive throughout its cross section
(not
just surface conductive).

What does carbon fiber composite look like?

--
Uncle Al

TO: Don Gilmore:

This is a comment about your question concerning an electrically conductive
carbon fibre material;
More than 50 years ago, shortly post W.W. II, some miles outside London,
England, my uncle had a small manufacturing company that made such a
material.
It was definitely not wires embedded in an insulating material.
AFIK it was a carbon loaded conductive material. I have no idea what the
filler was; although it looked, come to think of it, rather like the colour
of whole wheat flour! I seem to remember it was sort of 'mixed up' in
various consistencies looking rather like a (carbon) speckled cake mix, with
the then new resins, and was spread/rolled into sheets. IIRC It was made in
various thicknesses, widths and lengths to obtain various resistances and
wattage ratings. Before drying (Or maybe it was 'baked' to cure the resins?
and it became rigid and/or maybe it could be manufactured that way) it could
be curved, or even bent. One interesting heater was a circular collar, about
four inches in diameter, that heated the shaft of a radio direction finding
antenna that projected through the surface of a pressurized jet aircraft. I
also recall that a typical heater was dark grey in colour, typically a few
millimetres thick and had a sort of stiff/crisp feel.
Electrical connections to each heater were made by a commercially available
vaporized metal spray process (zinc or copper I think!) to the edges of the
conductive material. The material heated evenly and homogeneously throughout
with the flow of electric current.
They produced heaters to work on various voltages; AC mains 230 volt 50
cycle, 28 volt DC aircraft heaters, 12 volt car seat heaters etc. I recall
that as trial my grand parents had two 12 volt personal car warmers that
they tucked behind their backs (or under their "Ahem", 'derrieres') in their
otherwise unheated Lanchester car (The 1934 car did have a semi-automatic
manually preselected gear box though!).
All the heaters that I can recall were two connection single phase or DC.
But I can think of no reason why such a material could not have been used to
make say, a three phase heater etc. And therefore, if eventually cheap
enough, homogeneous electric heaters that could become part of a building
structure!
In the meantime I'll re-read the postings in this thread to understand the
mathematics of resistance of a homogeneously conductive (or sheet?)
material.
I do recall my uncle and his staff talking about 'Square Ohms and even
'Square Watts' (Which was rapidly abbreviated to 'Sqwatts') as they devised
heaters to meet various specifications.
Never thought I'd get a chance to talk about that product again!
I'll follow up with my surviving cousins and try to find out what happened
to that company and or the product.
Will post back if I can get some more info.

Terry.

 

[Uncle Al]

Robert Baer wrote:

Uncle Al wrote:

"Don A. Gilmore" wrote:

dmartin@newarts.com> wrote in message
news:1104532332.506815.181170@c13g2000cwb.googlegroups.com...
Don, We need to know a little more about what you are trying to do.

Sheet restivity has dimensions of ohms, not ohm-meters. so it is not
clear what conduction path you are thinking of.

Also will you be using DC or could you work at high frequencies? At
high frequencies the thickness of sheet involved in point-to-point
conduction depends on the frequency.

Oops. I didn't convert to meters before I divided. Here are (hopefully)
the correct values.

t = .031 in ---> 387 x 10^3 ohm/square
t = .062 in ---> 96.5 x 10^3
t = .125 in ---> 24.2 x 10^3
t = .188 in ---> 10.8 x 10^3

Sorry about that.

Metal-filled epoxies?

http://www.devcon.com/devconcatsolution.cfm?catid=34
http://www.plasticworld.ca/Devcon.htm
http://www.loctite.com/int_henkel/loctite_us/binarydata/pdf/LT3355v4_MROepoxies.pdf
http://www.tra-con.com/pdf/tpb/2122.pdf

Dilute to adjust resistance. Maintain viscosity (~1 wt-% fumed silica
will render organics thixotropic) to keep it homogeneous during cure.
You can cast thin slabs between silanized glass plates using nylon
fishing line as the spacer and those black squeeze clips for stacks of
paper as compression along the edges. Position the gasket with a thin
metal ruler.

Metal filled epoxies would fail all his criteria: 1) not flexible, 2)
resistivity too low, 3) not uniform unless carefully formulated.
Case in point: silver filled epoxy.

Take a two-part silicone rubber (probably peroxide cure for its
resistance to poisoning) or reactive oligomer or vulcanizing rubber,
load with graphite or metal powder, degas (big containier when you
reduce pressure - it will foam. Make and break the vacuum to burst
bubbles), cure. Flexible. Local resistivity may vary with strain
allowing static or dynamic mapping with an adressable electrode array
combed one way on top and perpendicularly on bottom.

Don't siliconize your mold when casting silicone rubber.

I suppose one could extrude, injection mold, or calendar a loaded
Kraton rubber. Choose any durometer you like. It will require some
equipment. The shape and mix of shape of the particles - ball, flake
aluminum, chopped filaments and fibers - determiness the loading at
which percolation conduction kicks in. Adding a little short fiber
will substantially decrease resistivity at sparse loadings. Waste
Kraton goes back into the hopper for another run.

How much does he need, of what quality and other physical properties,
to survive what... how much will he spend?

--
Uncle Al
http://www.mazepath.com/uncleal/
(Toxic URL! Unsafe for children and most mammals)
http://www.mazepath.com/uncleal/qz.pdf

 

[Boris Mohar]

On Fri, 31 Dec 2004 14:17:56 -0600, "Don A. Gilmore" <eromlignod@kc.rr.com>
wrote:

Hi guys:

I'm looking for a relatively thin electrically-resistive sheet material.
The resistivity I need depends on the thickness I can get. Basically I need
for the resistivity to be somwhere near

From
http://www.elecdesign.com/Articles/Print.cfm?ArticleID=2323

"..Many people have inquired about where to buy Teledeltos paper. The
original source in England will still sell you a big roll for $95, including
shipping; www.searchkingslynn.com/senco3.html will get you to the right
address for Sensitised Coatings, or call +44 1553764836. Plus, a new source
for resistive paper is online:
www2.pasco.com/products/scripts/products.taf?PN=PK-9023. The KIT PK9023 costs
$114, but PK9025 paper with centimeter grid runs $34 for 100 23- by 30-cm
sheets. Buy your own pen with conductive silver ink. This is about 32
kO/square. "




Regards,

Boris Mohar

Got Knock? - see:
Viatrack Printed Circuit Designs (among other things) http://www.viatrack.ca

 

[Don A. Gilmore]

"Boris Mohar" <borism_-void-_@sympatico.ca> wrote in message
news:js8et0hq20p72vbb9iu43apvn8al9m1p19@4ax.com...

On Fri, 31 Dec 2004 14:17:56 -0600, "Don A. Gilmore"
eromlignod@kc.rr.com
wrote:

Hi guys:

I'm looking for a relatively thin electrically-resistive sheet material.
The resistivity I need depends on the thickness I can get. Basically I
need
for the resistivity to be somwhere near

From
http://www.elecdesign.com/Articles/Print.cfm?ArticleID=2323

"..Many people have inquired about where to buy Teledeltos paper. The
original source in England will still sell you a big roll for $95,
including
shipping; www.searchkingslynn.com/senco3.html will get you to the right
address for Sensitised Coatings, or call +44 1553764836. Plus, a new
source
for resistive paper is online:
www2.pasco.com/products/scripts/products.taf?PN=PK-9023. The KIT PK9023
costs
$114, but PK9025 paper with centimeter grid runs $34 for 100 23- by 30-cm
sheets. Buy your own pen with conductive silver ink. This is about 32
kO/square. "

Thanks Boris:

This is intriguing; but is the paper only conductive on one side? The
reason I ask is that for my application, electrical current will be
conducted through the sheet from face to face, not along its length/width.

If it is resistive throughout it might work well indeed. Is it?

Don
Kansas City

 

Don,
Your previous comment (Jan 3, 8:32 am) implies you are interested in
current flow that is due to electrical boundary conditions on opposite
sides of the sheet. Is that correct?

Your original post said.."Here are the corresponding
resistivities for some nominal inch thicknesses:

..031 in ---> 300 ohm-m
..062 in ---> 150 ohm-m
..125 in ---> 75 ohm-m
..188 in ---> 50 ohm-m"

I may have mis-interpreted this as meaning you are interested in
current flow between electrode areas separated in the plane of the
sheet. The resistance one would measure perpendicular to such a sheet
will depend on the size and lateral displacement of the electrodes
relative to the thickness of the sheet.

Perhaps your question was much simpler: if I had a material with a
bulk resistivity of 75 ohm-m and gave you a piece in the shape of a
..125" thick sheet is that all you want?
If so, how large a sheet? Flexible or rigid? Durable?

Dave

 

cured, wet concrete and typical soils & clays have resistivities in the
100 ohm-m range.

Dave

 

[Robert Baer]

legg wrote:

On Fri, 31 Dec 2004 14:17:56 -0600, "Don A. Gilmore"
eromlignod@kc.rr.com> wrote:

Hi guys:

I'm looking for a relatively thin electrically-resistive sheet material.
The resistivity I need depends on the thickness I can get. Basically I need
for the resistivity to be somwhere near

rho = .24 / t

where rho is the resistivity in ohm-m and t is the thickness of the sheet in
meters. I would like for it to be thin enough to be flexible in large
sheets (say, measured in square meters). Here are the corresponding
resistivities for some nominal inch thicknesses:

.031 in ---> 300 ohm-m
.062 in ---> 150 ohm-m
.125 in ---> 75 ohm-m
.188 in ---> 50 ohm-m

Are any of you aware of a material that meets these specs (or is close) that
is not extremely expensive? I have seen graphite-impregnated plastics that
could work well, but only in McMaster-Carr, which has a limited selection.
The material must be uniformly resistive throughout its cross section (not
just surface conductive).

Thanks for any replies.

You might try looking at some ferrite polymer material sheet stock,
though most mfrs are only interested in surface finish resistivity of
the treated material.

They are not designed for use as strictly resistive materials, so who
knows what they would do over a range of temperature or pressure.

Where defined, published resistivity shows a range between 500 and 21
ohm-meter, below 10KHz.

Siemens-Matsushita FPC C302, C350, C351.

http://www.epcos.com/inf/80/db/fer_01/05590563.pdf

http://www.epcos.com/inf/80/db/fer_01/05610563.pdf

http://www.epcos.com/inf/80/ap/e0001000.htm

Other mfrs MMG, Tokin, TDK, Hitachi, TSC and NEC.

RL

Not flexible; brittle.
Also not usually available in sheets.

 

[John Fields]

On Tue, 04 Jan 2005 02:25:38 GMT, "Don A. Gilmore"
<eromlignod@kc.rr.com> wrote:

dmartin@newarts.com> wrote in message
news:1104778786.321726.203130@z14g2000cwz.googlegroups.com...
Don,
Your previous comment (Jan 3, 8:32 am) implies you are interested in
current flow that is due to electrical boundary conditions on opposite
sides of the sheet. Is that correct?

Your original post said.."Here are the corresponding
resistivities for some nominal inch thicknesses:

.031 in ---> 300 ohm-m
.062 in ---> 150 ohm-m
.125 in ---> 75 ohm-m
.188 in ---> 50 ohm-m"

I may have mis-interpreted this as meaning you are interested in
current flow between electrode areas separated in the plane of the
sheet. The resistance one would measure perpendicular to such a sheet
will depend on the size and lateral displacement of the electrodes
relative to the thickness of the sheet.

Perhaps your question was much simpler: if I had a material with a
bulk resistivity of 75 ohm-m and gave you a piece in the shape of a
.125" thick sheet is that all you want?
If so, how large a sheet? Flexible or rigid? Durable?


Yes, that's all I want. I would prefer sheets as large as possible...in
roll form would be great. It doesn't have to be super-flexible, but I don't
want it brittle like glass either. It will be applied to a slightly
irregular surface, but generally planar...maybe sort of like a large
airplane wing. It will not be subjected to much abuse, but it might be
exposed to normal outdoor temperatures.

So far I'm leaning toward some conductive plastic sheet material that
McMaster-Carr carries. But only because it's all I've found yet (and it
only comes in 12" x 12" sample sheets". That's why I was wondering if one
of you clever guys might have heard of something else that I missed.

---
You might want to try:

http://www.advsys.com.au/downloads/cuming%20catalogue.pdf

In particular, Technical Bulletin 320-8 on page 67.


Also, Series Number 26200 at:

http://www.right-tape.com/html/prod_silicone_rubber.html#photo6


Also there are a lot of hits you might want to check out at:

http://www.google.com/search?q=electrically+conductive+rubber+sheet&hl=en&lr=&start=20&sa=N


--
John Fields