Not only is it highly directed, ultrasonic acoustical frequencies disperse very quickly in air. At 1MHz, the energy absorption in air is ~160dB/meter, so a per

Not only is it highly directed, ultrasonic acoustical frequencies disperse very quickly in air. At 1MHz, the energy absorption in air is ~160dB/meter, so a person sitting at arm's length away from the emitter (even if it weren't highly directed) would receive ~6*10^-17 of the power (if that weren't far below any possible noise floor, which it is).