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 higher the frequency the shorter the antenna. At microwave frequencies a very efficient antenna can be shorter than an eighth of an inch. This antenna may be a multi element antenna like a TV yaggi antenna to supply more energy.