What is carrier frequency in electrical stimulation equipment?

• A. The frequency of the constant electrical pulse produced by an electrical stimulation device before modulation
• B. The frequency of the modulated waveform after modulation
• C. The rate at which a patient experiences contraction
• D. The total energy delivered per second

Answer: (A)

Carrier frequency is the base, unmodulated frequency of the signal that the stimulator generates before any modulation is applied. It’s the underlying wave that carries the treatment signal, and modulation (whether changing amplitude, pulse width, or timing) shapes how that carrier is delivered to the tissues. This is why the correct choice describes the constant electrical pulse frequency produced by the device before modulation. The frequency after modulation changes in a different way, the contraction rate is a biological response, and total energy per second refers to power, not how often the carrier oscillates. For example, in interferential therapy, two high-frequency carriers (the base frequencies) are used and their interaction produces a lower beat frequency that you perceive clinically, but the carrier frequencies themselves are those unmodulated base rates.