Self-made NFC in the phone - failed experiment

For more than a year and a half, I am the happy owner of the Android phone HTC Desire. And now 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 shove a ticket directly into the phone,” I thought. Metro is the main mode of transport that I use. But very often there were cases when I forgot to shift a ticket from one garment to another, and had to re-stand in queues to buy a ticket. At the same time, I always had a mobile phone with me and I never forgot it.



I must say that the experiment failed ... but first things first.
Who is interested in trying to create a NFC travel card in the phone? I ask for a habracut.

')
At first, I tried to take and simply shove a travel ticket under the back cover of the phone, but the ticket turned out to be very thick and slightly 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 had washed her backpack along with a subway ticket. The ticket is completely wiped out. The cardboard was peeled off from it and only a thin film with an antenna inside remained. 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 the stream of warm water, I began to slowly and gently scrape the cardboard layer on the ticket. The cardboard was 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 on the phone. The ticket fit perfectly under the back cover of the phone.



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

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

Then I removed the cover from the phone and attached the remnants of the ticket to the reader - HE WORKED! After that, I repeatedly passed through this ticket through the turnstile until it ended the trip.

Those. the ticket was absolutely working (even after being under the tap). But I didn’t want to read the ticket through the back cover. I even tried to apply the ticket to the reader through the back cover of the phone without the phone itself, thinking that the phone was causing some kind of interference. But he did not read.

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

The opinion of the habr-community on this matter is interesting, does the back panel of the phone have a special coating or composition that does not give a signal?
Are there any other ideas on how to shove a ticket into the phone? Answers like - just sticking a ticket with scotch tape outside the phone is not accepted.

UPD: Thank you all for your help. The comments are very good ideas and tips.
I will continue to experiment. I will definitely write about the results.