Electronic – good and reasonably priced way to make a custom RFID reader and barcode scanner that runs Android

I am be very interested to see how this works out.

I am currently making an RFID controlled lock for a door and I know from my work on that,that RFID have range limitations(depending on what type of reader and chip you use) so the position of both reader and chip may be very important especially because you're planning on using it on an unpredictable living thing. That might be a big challenge and may require more than one RFID reader.

As far as a locking mechanism you can make one really cheap by taking apart an old cd drive and using the slots drive system.

Unfortunately, it is not easy to design a good 13.56 MHz antenna. In general, a good antenna is at least 1/4 of the operating wavelength (of ~22m), so any practical 13.56 MHz antenna would be a bad antenna.

The main problem with electrically small antennas is that radiation resistance is tiny (less than 1 Ohm), making it almost impossible to match it to the 50 Ohm. One technique for matching would be to introduce a small series resistance (e.g. 2 Ohm) and then match to it with capacitors and inductors. However, this approach is difficult without access to a vector network analyzer.

I noticed that the module has a UFL connector. One way to improve the antenna would be to plug in another antenna you buy off the shelf and disable the current one (will probably need to cut traces of the old antenna)

To answer your questions: "How important is material choice (wire/tape/tube)?" - not important at 13.56 (as long as it is metallic)

"Do I need an additional power supply" - not if you are using the same chip

"Can I build a square antenna into the flashing around the card window" - would need more info on this.