Cowell David M J, Smith Peter R, Freear Steven
IEEE Trans Ultrason Ferroelectr Freq Control. 2013 Jun;60(6):1084-97. doi: 10.1109/TUFFC.2013.2672.
Switched-mode operation allows the miniaturization of excitation circuitry but suffers from high harmonic distortion. This paper presents a method of phase-inversion-based selective harmonic elimination (PI-SHE) and the use of multiple switching levels. PI-SHE is shown to enable multiples of any selected harmonic to be eliminated through controlled timing of the transition between different excitation voltage levels. Multiples of the third harmonic are shown to be eliminated in three-level tone waveforms. In addition, multiples of the fifth harmonic are shown to be eliminated using five-level tone waveforms. A method of calculating the expected amplitude of each harmonic is presented. The application of PI-SHE in linear frequency-modulated (LFM) excitation is proposed. A heuristic derivation of the spectral properties of multilevel switched LFM waveforms is presented. The performance of the proposed PI-SHE method is confirmed through experimental measurement of the harmonics present in an ultrasound wave using two, three, and five levels for both tone and LFM excitation. The proposed method of controlling harmonics through the use of multilevel switched excitation is especially suitable for applications in which portability, high channel counts, and precise harmonic control are required.
开关模式操作允许激励电路小型化，但存在高谐波失真问题。本文提出了一种基于反相的选择性谐波消除（PI-SHE）方法以及多开关电平的使用。PI-SHE方法能够通过控制不同激励电压电平之间转换的定时来消除任何选定谐波的倍数。在三电平单音波形中可消除三次谐波的倍数。此外，在五电平单音波形中可消除五次谐波的倍数。本文还提出了一种计算各谐波预期幅度的方法。提出了PI-SHE方法在线性调频（LFM）激励中的应用。给出了多电平开关LFM波形频谱特性的启发式推导。通过使用两电平、三电平以及五电平的单音和LFM激励对超声波中存在的谐波进行实验测量，证实了所提出的PI-SHE方法的性能。所提出的通过使用多电平开关激励来控制谐波的方法特别适用于需要便携性、高通道数和精确谐波控制的应用。
