Homemade NFC on the Phone - A Failed Experiment

For more than a year and a half, I have been the proud owner of the HTC Desire Android phone. And so I wanted to upgrade the phone. In addition to installing custom firmware, I wanted to do something unusual. And then I remembered about NFC and contactless payment methods. “It would be great to put a ticket right on the phone,” I thought. Metro is the main form of transport that I use. But very often there were times when I forgot to transfer a ticket from one clothes to another, and had to stand in line again to buy a ticket. At the same time, I always had a mobile phone with me and I never forgot it.



I must say right away that the experiment failed ... but first things first.
Who is interested in trying to create an NFC ticket on the phone - I ask for a hubcut.


At first, I tried to take and just put a ticket under the back cover of the phone, but the ticket turned out to be very thick and a little wider than the phone itself by 2-3 millimeters, respectively, the cover of the mobile phone simply did not close.

Then I remembered that somehow my wife washed her backpack along with a subway ticket. The ticket was completely wiped out. The cardboard exfoliated from it and only a thin film remained with the antenna inside. We thought that the ticket would not work, but it was well read and worked.

Then I took a ticket and went with him to the bathroom. Under a stream of warm water, I began to slowly and accurately scrape the cardboard layer on the ticket. Cardboard soaked and easily lagged behind the ticket.



After a couple of minutes, I had a clean and very thin ticket in my hands.



I dried it and tried it on the phone. The ticket fit perfectly under the back cover of the phone.



Satisfied, I picked up the phone and headed for the subway. He went to the turnstile, took out the phone, put it on the reader and ... Nothing happened. As an idiot, I began to drive the phone over the reader - but nothing happened.

“Probably the ticket has deteriorated,” I thought, and walked away from the turnstile and went to the checker, which gives information about the number of trips on the ticket and its validity. I attached the phone to the reader, but it also did not read anything.

Then I removed the cover from the phone and attached the rest of the ticket to the reader - IT WORKED! After that, I repeatedly passed through the turnstile for this ticket until the trip was over.

Those. the ticket was absolutely working (even after being under a stream of water). But through the back cover the phone did not want to read the ticket. I even tried to attach a ticket to the reader through the back cover of the phone without the phone itself, thinking that the phone was causing any interference. But he was not read.

Why??? After all, we all know that a ticket is perfectly readable at a distance of 2-3 cm from the reader (therefore, it can be used without removing it from a bag or purse), but why didn’t it want to be read through the back cover of the phone?

The opinion of the Habr community on this subject is interesting, is it possible that the back panel of the phone has a special coating or composition that does not allow signal transmission?
Are there any other ideas how to put a ticket in your phone? Answers like - just stick a ticket with adhesive tape on the outside of the phone - are not accepted.

UPD: Thank you all for your help. Very good ideas and tips are given in the comments.
I will continue to experiment. I’ll write about the results.