If you have Onstar and Pikepass

[patric]

That's true, and I thought about doing that.  I was going to use a piece of hard plastic, affix the tag to it, and then use velcro to attach the plastic piece to the car.  (The tags are a bit fragile and do need to be affixed to hard surface or the antenna will eventually break.) That way I could move the tag from car to car, and also take it down if I didn't want to use it.  But now they take a picture of your plate every pass and compare it to your tag, and the tag is supposed to be car-specific so I decided not too.   

I don't think the earliest tags (the big plastic boxes) were car-specific.  When I lived in Dallas years ago, we swapped out toll tags all the time.   And if simply collecting a toll was all that mattered, they wouldn't care now, either.  But as has been noted, they now use these tags to track the car as well,

...which makes the RFID PikePass redundant. 

After DPS made everyone replace their "dirty" tags the Turnpike Authority was kind enough to send a picture they took of my new one, so I had to phone them and make everything Double-Plus Good by updating their records.

[heironymouspasparagus]

That's true, and I thought about doing that.  I was going to use a piece of hard plastic, affix the tag to it, and then use velcro to attach the plastic piece to the car.  (The tags are a bit fragile and do need to be affixed to hard surface or the antenna will eventually break.) That way I could move the tag from car to car, and also take it down if I didn't want to use it.  But now they take a picture of your plate every pass and compare it to your tag, and the tag is supposed to be car-specific so I decided not too.   

I don't think the earliest tags (the big plastic boxes) were car-specific.  When I lived in Dallas years ago, we swapped out toll tags all the time.   And if simply collecting a toll was all that mattered, they wouldn't care now, either.  But as has been noted, they now use these tags to track the car as well, and so have put the kibosh on all of that...

You can set it up on your account as portable - do have to put the 'main' vehicle tag, but moving to another is fine.

[rebound]

You can set it up on your account as portable - do have to put the 'main' vehicle tag, but moving to another is fine.

Did not know that.  Will check it out.

[heironymouspasparagus]

Did not know that.  Will check it out.

I have 5 passes and 1 of them is 'portable' with a main vehicle.  Seems like I remember they charged me a little bit extra for that, but don't hold me to that.   Got those over a year ago and don't remember the details - I just "set it and forget it..."

[WanderingBy]

Hmm, this patent seems to give an overview: "The antenna has a characteristic impedance defined in part by a dielectric constant of the flexible circuit substrate and in combination with a dielectric constant of the glass surface. As a result, proper impedance match is achieved only when the sticker is affixed to the glass surface"

Wow, that's clever, using the windshield glass as part of the circuit! So, I'd like to make my sticker non-permanent (a vintage car where I wouldn't need the sticker hardly ever, maybe never, and don't want to stick the gooey thing onto the original glass). I'd like to keep it in the glovebox to put out temporarily in that rare case I might sometime need it, then put it away.

And thus my question:

Has anyone tried sticking the sticker to a small piece of glass?

Then you could pull it out if needed, rest it on the dash, and put it back away afterwards. I gather the glass would need to be the same thickness as windshield glass, so the dielectric constant is the same as the sticker needs, but I gather the width/height of the glass isn't a factor. Anyone tried anything like this?

[patric]

Has anyone tried sticking the sticker to a small piece of glass?
Then you could pull it out if needed, rest it on the dash, and put it back away afterwards. I gather the glass would need to be the same thickness as windshield glass, so the dielectric constant is the same as the sticker needs, but I gather the width/height of the glass isn't a factor. Anyone tried anything like this?

http://www.tulsanow.org/forum/index.php?topic=16436.msg179796#msg179796

[Red Arrow]

Wow, that's clever, using the windshield glass as part of the circuit! So, I'd like to make my sticker non-permanent (a vintage car where I wouldn't need the sticker hardly ever, maybe never, and don't want to stick the gooey thing onto the original glass). I'd like to keep it in the glovebox to put out temporarily in that rare case I might sometime need it, then put it away.

And thus my question:

Has anyone tried sticking the sticker to a small piece of glass?

Then you could pull it out if needed, rest it on the dash, and put it back away afterwards. I gather the glass would need to be the same thickness as windshield glass, so the dielectric constant is the same as the sticker needs, but I gather the width/height of the glass isn't a factor. Anyone tried anything like this?

I have a pair of "portable" pike passes that suction cup to the windows.  One for 2 axle, one for 3 axle (trailer towing).

[WanderingBy]

http://www.tulsanow.org/forum/index.php?topic=16436.msg179796#msg179796

Right, but in this case it's not only the insulating property of glass that they're using (which I'm guessing is the key to not shorting out the circuitry touching the glass), it's the dielectric property they take advantage of (aka relative permittivity). As noted in the patent referenced earlier in the thread, "The antenna has a characteristic impedance defined in part by a dielectric constant of the flexible circuit substrate in combination with a dielectric constant of the glass surface. As a result, a proper impedance match between the antenna and the transponder circuit is achieved only when the sticker is affixed to the glass surface." The sticker also has a layer with a similar dielectric constant, "The flexible circuit substrate 16 is comprised of an electrically insulating material having a suitable dielectric constant, such as fiberglass or plastic, or other commercially available materials sold under the names of Kapton® or Pyralux®."

Glass has a dielectric constant in the 4-15 range. (Air is about 1.0, paper looks to be in the ~2-4 range.)  Hmm, I googled on this Kapton material that's specifically mentioned, found the DuPont data sheet for it, and it has a dielectric constant of 3.4-3.5 depending on thickness. The Pyralux data sheet says it's 3.4 for that material also. I found a paper about auto glass that gave a dielectric constant of 6.5 for window panels. ( https://interferencetechnology.com/significance-dielectric-materials-vehicle-electromagnetic-field-computation/ ) If I'm reading the spec sheet for tempered glass correctly, the dielectric constant doesn't change much unless it's very thin (around 0.1mm), so I'm guessing any ordinary household thickness will do fine to attach the sticker to. If it's 3.4 inside the sticker, I suppose any material that's 3.4 to that 6.5 number for glass might also work. Porcelain is in the 5-6.5 range. Pyrex glass is 4.3-5, so that might work. Plexiglass is in the 2.6-3.5 range, which sounds dodgy. I see different numbers for Neoprene, one source says 4-6.7, another says 6-9, so that might be an option. (There's a short list I found at http://www.csgnetwork.com/dieconstantstable.html and a long list at http://www.clippercontrols.com/pages/Dielectric-Constant-Values.html ) Plastics look tricky, depends on the exact material.

All of which makes me suspect that if someone were to put the sticker on a small piece of glass of some sort, it might work just fine. (Or porcelain, pyrex, neoprene...)

Still wondering if anyone's tried this yet? Might be worth an experiment for those of us infrequent users who don't want to get the windshield all gunky.

[heironymouspasparagus]

Right, but in this case it's not only the insulating property of glass that they're using (which I'm guessing is the key to not shorting out the circuitry touching the glass), it's the dielectric property they take advantage of (aka relative permittivity). As noted in the patent referenced earlier in the thread, "The antenna has a characteristic impedance defined in part by a dielectric constant of the flexible circuit substrate in combination with a dielectric constant of the glass surface. As a result, a proper impedance match between the antenna and the transponder circuit is achieved only when the sticker is affixed to the glass surface." The sticker also has a layer with a similar dielectric constant, "The flexible circuit substrate 16 is comprised of an electrically insulating material having a suitable dielectric constant, such as fiberglass or plastic, or other commercially available materials sold under the names of Kapton® or Pyralux®."

Glass has a dielectric constant in the 4-15 range. (Air is about 1.0, paper looks to be in the ~2-4 range.)  Hmm, I googled on this Kapton material that's specifically mentioned, found the DuPont data sheet for it, and it has a dielectric constant of 3.4-3.5 depending on thickness. The Pyralux data sheet says it's 3.4 for that material also. I found a paper about auto glass that gave a dielectric constant of 6.5 for window panels. ( https://interferencetechnology.com/significance-dielectric-materials-vehicle-electromagnetic-field-computation/ ) If I'm reading the spec sheet for tempered glass correctly, the dielectric constant doesn't change much unless it's very thin (around 0.1mm), so I'm guessing any ordinary household thickness will do fine to attach the sticker to. If it's 3.4 inside the sticker, I suppose any material that's 3.4 to that 6.5 number for glass might also work. Porcelain is in the 5-6.5 range. Pyrex glass is 4.3-5, so that might work. Plexiglass is in the 2.6-3.5 range, which sounds dodgy. I see different numbers for Neoprene, one source says 4-6.7, another says 6-9, so that might be an option. (There's a short list I found at http://www.csgnetwork.com/dieconstantstable.html and a long list at http://www.clippercontrols.com/pages/Dielectric-Constant-Values.html ) Plastics look tricky, depends on the exact material.

All of which makes me suspect that if someone were to put the sticker on a small piece of glass of some sort, it might work just fine. (Or porcelain, pyrex, neoprene...)

Still wondering if anyone's tried this yet? Might be worth an experiment for those of us infrequent users who don't want to get the windshield all gunky.

The portable ones have suction cups that stick to the window while you use it, then easily come off for storage elsewhere.  When not using, put in glove compartment is what the OTA says.

And they do work outside the context of being next to the glass.  Don't read a patent and make the mistake of thinking that is really how it works.  That may be what's patented, but not what actually went into production.