A system comprises a flexible pad, an antenna wire disposed within the flexible pad, and an electronics unit connected to or capable of being connected to the antenna wire. The electronics unit can include circuitry configured to access a stored playlist representing a sequence of tones at different frequencies, and to generate signals representing the tones such that two or more of the tones are generated in the sequence according to the stored playlist. The electronics unit further can include an oscillator to generate a carrier signal and coupled so that the signals representing the tones modulate the carrier signal according to the sequence when applied to an input of the oscillator, where the oscillator has an output connected to transmit the modulated carrier signal onto an antenna when the electronics unit is in operation.
