Can program up to 1 trillion code numbers. Their injectable transponder is the TX1400L, 11mm x 2.1mm, glass encapsulated. The very best Christian community authority on this subject matter today is Terry L. Cook. I will give you the generic principle behind them, the implementations may vary but the principle will be the same. First, the capsule does not contain a battery.
All radio is transmitted electrical energy.
All receivers are rated as to their sensitivity in receiving that energy. One can improve the reception by adjusting the antenna length, also known as tuning the antenna and adding elements to receive more energy. The improvement means the receiver receives more electrical energy. The higher the frequency the shorter the antenna. At microwave frequencies a very efficient antenna can be shorter than an eighth of an inch.