Performance of switched mode arbitrary excitation using Harmonic Reduction Pulse Width Modulation (HRPWM) in array imaging applications

Switched excitation allows the miniaturisation of excitation circuitry for transducer integrated front ends, high channel count and portable ultrasound systems. Harmonic Reduction Pulse Width Modulation (HRPWM) provides a method to design five level switched mode excitation signals with control of instantaneous amplitude, frequency and phase plus minimised third harmonics for advanced ultrasound applications. This paper details the application of HRPWM using commercial transmit front end integrated circuits and linear array transducers. The ability of HRPWM to control the pressure of the ultrasound wave is investigated. A full scale error between desired and measured pressure of 3.5% at 4.1 MHz is demonstrated. The temporal windowing of linear frequency modulated excitation signals using HRPWM is demonstrated. Pulse compression linear imaging of a tissue phantom is demonstrated where an improvement in the -20 dB axial resolution of a nylon mono-filament target from 2.14 mm using bipolar excitation to 1.88 mm using HRPWM is shown.