Conductive Fabric Performance

The sampler pack from LessEMF arrived in the mail today, so naturally I was very eager to test the performance of the samples. The pack includes 16 different kinds of material. I don’t think I need to look at all of them in detail, but I will anyway just for the purpose of being thorough, and because I’m curious. For technical details on the different materials or to purchase some, go to LessEMF’s fabric page. It’s not expensive in small quantities.

In order to determine the suitability of using each material for Keyglove sensors, I’ve come up with a list of tests. Not every one of the tests must to be successful, but the more that are, the better the material will be considered. Here is a summary of each different test, in order from most to least critical:

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• Conductivity: it must have very high electrical conductivity so as to create a short when two pieces are lightly touched together. No pressure should be required. This test involves checking for a short between two points on the same fabric, and then again by holding wires against two unique pieces and touching only the fabric together (to simulate the glove action).
• Flexibility: it must bend easily so that any finger position will not feel inhibited due to the material. If it is too stiff, the glove will feel unnatural and be unpleasant to use.
• Solderability: it must be able to have a wire lead attached somehow. Depending on the rest of the tests, if this fails it may be possible to use conductive thread or silver epoxy to get the job done. Solder would be preferable for ease though.
• Sewability: it must be able to attached with some kind of thread to the cotton glove base. Material that is too thick or dense may resist too much. Material that is too weak may pull away or tear from the stitches.
• Phone Tap: it must be able to accurately register a single tap on a capacitive touch screen (such as on an iPhone). This should feel exactly the same as using your finger would and require no more pressure or precision.
• Phone Drag: it must be able to accurately register a tap-hold-drag motion on a capacitive touch screen. Again, it should feel exactly like using a bare finger.
• Elasticity: it must stretch at least a little bit to accommodate certain hand positions more easily. This won’t matter for most sensors, but could be useful for the long ones placed on the palm.

Below is a detailed list of how each of the sampler materials performs under the tests outlined above. One test that I cannot perform well is long-term durability, which is certainly important, but impossible to test quickly. I will have to see how my “best choice” material holds up after I start using it on the glove. My current favorite, the stretch conductive fabric, has a very fine silver coating (which contributes substantially to its cost) which they say will come off after repeated washings in hot water. I wonder if it might come off under other circumstances as well.

Also, note that when I label a particular material as “suitable” or “unsuitable,” I am referring only to the suitability as a Keyglove sensor, and not to the suitability of its intended purpose. I have no doubt that these materials do not behave electromagnetically exactly as they are represented by LessEMF.

Quick verdict: one of Stretch Conductive Fabric, VeilShield™, or Canopy Mesh Fabric depending on budget and wire mounting capabilities. Read on for more detail.

Stretch Conductive Fabric (suitable)

Conductivity	Excellent.
Flexibility	Excellent.
Solderability	None, but a wire can be “melted” into one side.
Sewability	Excellent.
Phone Tap	Excellent.
Phone Drag	Excellent.
Elasticity	Excellent.
Notes	Melting wires into the material is, I’m sure, not what LessEMF intended. However, it does appear to make a solid, reliable electrical connection between the wire and the material. The melted nylon lets of what is probably a small amount of toxic fumes, and it changes the dark gray coloration to be a burnt brown/orange color immediately around the wire tip. It also grips rather tightly to the wire (a consequence of melted nylon). I tested the strength of the hold, and it took quite a lot of pull to remove the wire. I tried re-melting it to another spot and then added a small dot of 5-minute epoxy to test again. It may be possible to achieve the conductivity with epoxy only and skip the melting.

Knit Stainless Steel Mesh (unsuitable)

Conductivity	Excellent.
Flexibility	Excellent.
Solderability	None.
Sewability	Excellent.
Phone Tap	Excellent.
Phone Drag	Excellent.
Elasticity	Slight.
Notes	This is a relatively coarse wire mesh, and if pulled slightly it will return to its shape. However, if pulled with substantial force, it will simply bend the interlocking mesh links, and it will be forever stuck that way. The main problem is that it is 100% stainless steel, and I could not get any solder to meld properly. The canopy fabric below is basically the same but can be soldered.

Canopy Fabric (suitable)

Conductivity	Excellent.
Flexibility	Excellent.
Solderability	Excellent.
Sewability	Excellent.
Phone Tap	Excellent.
Phone Drag	Excellent.
Elasticity	Slight.
Notes	Since this material is nothing more than tin-coated copper wire, it is very conductive and easy to solder. I worry that it might have damaging effects on extremely smooth surfaces like car paint. This stuff exhibits the same elasticity properties as the knit stainless steel mesh above (though less force is required to permanently bend the mesh since the material is thinner). It is actually solderable though, in contrast to the stainless steel mesh.

Ex-Static™ (unsuitable)

Conductivity	None.
Flexibility	Excellent.
Solderability	None.
Sewability	Excellent.
Phone Tap	Excellent.
Phone Drag	Excellent.
Elasticity	Very slight.
Notes	This fabric isn’t conductive at all between two pieces or from point to point on the same surface, so it doesn’t much matter. However, I was surprised to see the phone tests work correctly.

Pure Copper Polyester Taffeta (unsuitable)

Conductivity	Poor.
Flexibility	Excellent.
Solderability	None.
Sewability	Good.
Phone Tap	Excellent.
Phone Drag	Excellent.
Elasticity	None.
Notes	This material is, like others, conductive between two points on the same surface, but not between two different pieces of material. It is also not solderable. It is quite dense, which would make it a little harder to sew, but not impossible.

Nickel/Copper Ripstop (unsuitable)

Conductivity	Poor.
Flexibility	Excellent.
Solderability	None.
Sewability	Good.
Phone Tap	Excellent.
Phone Drag	Excellent.
Elasticity	None.
Notes	This is almost the same as the copper polyester, only it has nickel as well and it a tiny bit less flexible. The effective conductivity is identical.

ShieldIt™ Super (unsuitable)

Conductivity	Poor.
Flexibility	Good.
Solderability	Decent wire attachment possible, but weak.
Sewability	None.
Phone Tap	Excellent.
Phone Drag	Excellent.
Elasticity	None.
Notes	The conductivity is actually excellent on the same surface, but terrible between two pieces. This material has a hot-melting adhesive backing which might have made it very easy to attach to the glove. However, since the conductivity test didn’t pass, it’s kind of pointless to try. Also, the soldered wire lead did stick remarkably well, but due (I assume) to weakening of the fabric by the extreme heat, the small area with solder on it actually broke away from the rest of the fabric after some force was applied. This didn’t happen very easily, but easily enough that I would worry about the reliability of the attachment through daily use.

Bullionet™ Mesh (suitable)

Conductivity	Excellent
Flexibility	Excellent
Solderability	None.
Sewability	Excellent.
Phone Tap	Excellent.
Phone Drag	Excellent.
Elasticity	None.
Notes	This material looks very much like what is used for window screens. The mesh has a square pattern. It’s conductivity is good, but it falls apart under the soldering iron. The side of the mesh makes sewing very easy, and it works well with phones. Given other options though, I’d probably go with the VeilShield™ over this.

ArgenMesh™ (unsuitable)

Conductivity	Poor.
Flexibility	Excellent.
Solderability	Poor.
Sewability	Excellent.
Phone Tap	Excellent.
Phone Drag	Excellent.
Elasticity	None.
Notes	Like some others, this material’s conductivity is excellent on the same surface, but not reliable between two pieces. I believe this material has too much nylon (45%) arranged in such a way that the metal is not always right at the surface. Some of the touch conductivity tests didn’t seem to work well. Soldering made the wire grip the material at the cost of destroying the nylon holding it all together. I’d pass on this stuff, since there are so many other good options.

Soft&Safe™ Shielding (unsuitable)

Conductivity	Poor.
Flexibility	Excellent.
Solderability	None.
Sewability	Excellent.
Phone Tap	Excellent.
Phone Drag	Excellent.
Elasticity	None.
Notes	This stuff is unique because it uses bamboo for the non-conductive part of the material. It was very resistant (by comparison) to heat damage during the solder test. The conductivity is good between two points on the same surface, but not at all between two different pieces.

StatiCot™ Shielding (unsuitable)

Conductivity	Poor.
Flexibility	Excellent.
Solderability	None.
Sewability	Excellent.
Phone Tap	Excellent.
Phone Drag	Excellent.
Elasticity	None.
Notes	This material is made of polyester, cotton, and stainless steel. Soldering is pretty much impossible. The conductivity is not at all good enough for what I would need for a sensor. It is only 25% non-fabric material, and thus looked the most like regular fabric of all of the samples.

RadioScreen™ (suitable)

Conductivity	Excellent.
Flexibility	Excellent.
Solderability	None.
Sewability	Excellent.
Phone Tap	Excellent.
Phone Drag	Excellent.
Elasticity	None.
Notes	This stuff looks and feels great. However, soldering doesn’t work at all. In fact, it seems to destroy the woven mesh wherever the heat is directly applied. It may be possible to “weave” the wire lead into the very fine mesh and then secure it with an epoxy bead. One other note is that this material is nickel-plated and possibly unsuitable for people with extreme nickel allergies (LessEMF’s warning).

VeilShield™ (suitable)

Conductivity	Excellent.
Flexibility	Excellent.
Solderability	None.
Sewability	Excellent.
Phone Tap	Excellent.
Phone Drag	Excellent.
Elasticity	None.
Notes	This is very similar to the RadioShield™ stuff above, except the mesh is even finer and the material is thinner. It is nearly transparent as well, which is kind of neat. Soldering is still not possible.

CobalTex™ (unsuitable)

Conductivity	Poor.
Flexibility	Excellent.
Solderability	None.
Sewability	Good.
Phone Tap	Excellent.
Phone Drag	Excellent.
Elasticity	None.
Notes	This material is almost the same as the the copper polyester and nickel/copper ripstop, except it has a nickel-cobalt alloy coating. The rest of the effective qualities are identical.

ESD Static Fabric (unsuitable)

Conductivity	Good.
Flexibility	Excellent.
Solderability	Possible, not great.
Sewability	Excellent.
Phone Tap	Acceptable.
Phone Drag	Acceptable.
Elasticity	Slight.
Notes	This material has a tendency to “catch” on itself or other nearby fabrics due to the ends of tiny wires in the mesh being exposed after cutting. This could make it slightly annoying to deal with depending on your sewing skills (mine are quite poor at this point). Soldering is possible, but the interwoven fabric inhibits a very clean joint. I would probably rather use one of the non-fabric pure fine meshes instead of this.

AL100 Wall Shielding (unsuitable)

Conductivity	Poor.
Flexibility	Poor.
Solderability	None.
Sewability	Poor.
Phone Tap	Excellent.
Phone Drag	Excellent.
Elasticity	None.
Notes	This material is definitely not suited to be a Keyglove sensor. It’s designed to be EMF wall shielding. I say it has poor flexibility not because it is especially stiff, but rather because it is flexible in somewhat of the same way that a thick piece of aluminum foil is flexible, but not at all like fabric. It is too thick to sew, and there is a plastic-like coating on the back surface that melts easily when attempting to solder. This is just a bad choice for the Keyglove.

So, there we have it: a full run-down of the suitability of each type of sample material. Here are the results in a summary format:

• Only 5 out of the 16 materials could be used for sensors:
  • Stretch Conductive Fabric ($59.95 per linear foot)
  • Canopy Fabric ($15.95 per linear foot)
  • Bullionet™ Mesh ($11.95 per linear foot)
  • RadioScreen™ ($15.99 per linear foot)
  • VeilShield™ ($18.95 per linear foot)
• Almost none of the materials are solderable (of the above, only the canopy fabric)
• Almost all of the materials work on capacitive touch screens
• If capacitive taps work, so do capacitive drags

The “linear foot” prices are from spools of fabric that are typically at least 42 inches wide, so one linear foot is actually at least 500 square inches. Since each glove requires approximately 10 square inches of sensor material (estimated), that means that one foot can do 50 gloves, meaning even the really expensive stretch conductive fabric comes out to be $1.20 of material per glove. Not too bad.

Given all the possibilities, my favorite is the stretch conductive fabric. I only need to find out what the best way of attaching a wire lead to that material is. I’ve sent an email to the people at LessEMF to see if they have any recommendations, and in the mean time, I’m going to try some experiments (involving cheap wire glue and/or epoxy beads). I’d like to avoid using silver epoxy, though I know it would work, because it would greatly add to the cost of any glove—probably as much as $10 per glove, realistically. With 34 sensors, 14 oz. of epoxy goes pretty quick.

On October 15, 2010   /   Development, Hardware, Uncategorized   /   12 Comments