Figure 6

(a) Experimental data showing the linear chirp from 1–400 kHz produced by the AWR (spectrogram obtained from short-time Fourier Transform of AWR current monitor trace). Although the maximum slew rate of the power amplifier limits chirp amplitude beyond 200 kHz, this amplitude never falls below the SAR safety limits (Fig. 3) even at 400 kHz, thus covering the entire safe parameter space. (b) The AWR is capable of arbitrary waveforms as shown by this composite waveform made up of arbitrary waveform parts: (1) triangular wave (2) linear chirp (3) ramp and (4) composite waveform made up by direct addition of 3 sine waves of equal amplitude but different frequencies (5, 7 and 12 kHz). The drive waveform shape is validated by the internal current monitor of the AE Techron 7224.