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How to I properly attach cotton substrate to copper patch in an antenna?

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Shirpo

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I want to build a prototype of a simple microstrip patch antenna with copper patch and cotton substrate, the design work fine and the frequency show correct in HFSS, however, I don't know a proper way to attach the cotton substrate to the patch and ground without effecting thing like dielectric constant. Both of the time I use adhesive tape or super glue doesn't work too well and the frequency showed is wrong.
If anyone know how to properly attach them or create this type of antenna please give me some advice.
 

c_mitra

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Cotton is made of cellulose molecules and is present as fibrils. Cotton cloth or thread is not a good substrate because it is porous and non-uniform. However, a large number of cellulose derived plastics are available that can perhaps serve your purpose (cellulose nitrate, cellulose acetate, cellulose butyrate and cellulose xanthate. They all are available as films and they are thermoplastic. If you insist on using cotton, you may use epoxy resin to bond the two materials.
 

Shirpo

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Cotton is made of cellulose molecules and is present as fibrils. Cotton cloth or thread is not a good substrate because it is porous and non-uniform. However, a large number of cellulose derived plastics are available that can perhaps serve your purpose (cellulose nitrate, cellulose acetate, cellulose butyrate and cellulose xanthate. They all are available as films and they are thermoplastic. If you insist on using cotton, you may use epoxy resin to bond the two materials.
Hi, thanks so much for answering, my project require to use small piece of cotton fabric as substrate so I kinda have to use that. May I ask one more thing? What advantages does epoxy resin has over some other ways to bond those two materials? (using adhesive tape or sewing come to mind).
Is it because those ways will mess up the dielectric constant between two materials?
 

c_mitra

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Hi, thanks so much for answering, my project require to use small piece of cotton fabric as substrate so I kinda have to use that. May I ask one more thing? What advantages does epoxy resin has over some other ways to bond those two materials? (using adhesive tape or sewing come to mind).
Is it because those ways will mess up the dielectric constant between two materials?
Epoxy wets copper surface and penetrates the fabric and the bond will be permanent. The fabric under the copper will appear more like a PCB (common PCBs are fiberglass bonded with epoxy). If you wish to use a two-sided adhesive tape (so called "double scotch tape") use one that is silicone based because they may stick well to the metal.
Depending on the actual frequency, you may have to consider the dielectric constant of the first 0.01cm or 0.1cm of the layer just below the copper surface.
 

Shirpo

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Epoxy wets copper surface and penetrates the fabric and the bond will be permanent. The fabric under the copper will appear more like a PCB (common PCBs are fiberglass bonded with epoxy). If you wish to use a two-sided adhesive tape (so called "double scotch tape") use one that is silicone based because they may stick well to the metal.
Depending on the actual frequency, you may have to consider the dielectric constant of the first 0.01cm or 0.1cm of the layer just below the copper surface.
Oh so I can use adhesive tape, kinda dumb question but do I put the tape above the copper or between the copper and cotton (since most silicon tape is 2mm in thickness) and does it affect the dielectric constant of the network analyzer when using the tape?
Just want you to know you helped me a lot with figuring out the next step of my project, I'm really appreciated it.
 

vfone

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You want to use cotton fabric as substrate or you want to use the old type of laminate named Textolite (Phenolic Cotton Cloth Laminated)?
The dielectric constant of cotton is about 1.4 when the Dk of textolite is 3.4, depending by the reisn used.

Using just cotton fabric as a patch antenna substrate (without reisn) I don't think is the best idea for geting steady measurement results vs mechanical and humidity influence.
Anyway, if you find a glue with Dk of about 1.4 you may not get Dk changes when you use it to glue the cotton material.
 

Shirpo

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You want to use cotton fabric as substrate or you want to use the old type of laminate named Textolite (Phenolic Cotton Cloth Laminated)?
The dielectric constant of cotton is about 1.4 when the Dk of textolite is 3.4, depending by the reisn used.

Using just cotton fabric as a patch antenna substrate (without reisn) I don't think is the best idea for geting steady measurement results vs mechanical and humidity influence.
Anyway, if you find a glue with Dk of about 1.4 you may not get Dk changes when you use it to glue the cotton material.
Sadly I will be using the cotton fabric as substrate, the one that has around 1.3 to 1.6 Dk, my goal is to get close to the frequency of my simulation which is 2.45GHz, last time I tried regular cheap tape but It didn't work out too well (either the tape didn't stick well all the copper to the fabric or something has to do with the permittivity).
But yeah, I think I will give the silicon two-sided tape and epoxy resin a try. Thank you for your advices
 

biff44

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Cotton is made of cellulose molecules and is present as fibrils. Cotton cloth or thread is not a good substrate because it is porous and non-uniform. However, a large number of cellulose derived plastics are available that can perhaps serve your purpose (cellulose nitrate, cellulose acetate, cellulose butyrate and cellulose xanthate. They all are available as films and they are thermoplastic. If you insist on using cotton, you may use epoxy resin to bond the two materials.
i am not sure, but i would think that the glue you use could work with the cotton fabric to make it more well-behaved. I would choose some sort of glue that is in a film form, maybe 0.001 to 0.002 thick, that might be heat activated. i.e. you apply the glue to the cotton, and the copper trace on top, and heat it up with a clothes iron (or other sort of heater/press).

Deliberately using a thicker glue might mitigate the fact that there is a lot of air in the cotton mesh, and the threads might cause anisotropic effects in the dielectric constant.

perhaps something like this:


maybe you can do some research, and find a glue film with a known dielectric constant. that would take some of the empirical work out of it.
 

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