Various modulation approaches, such as amplitude and frequency modulations, have been applied widely to modify the acoustic field and improve the performance of ultrasound imaging and therapy. However, phase modulation (PM) has not been investigated extensively in the ultrasound applications, especially at a long-pulse duration. In this study, the effects of PM on the acoustic field were investigated. The radiated acoustic pressure waveforms produced using different PM strategies (i.e., sequential phase inversion every cycle, every two cycles, and random phase inversion) were explored, and the distributions of acoustic pressure and average acoustic intensity along and transverse to the transducer axis were compared with those of a sinusoidal wave excitation in both measurement and simulation. It is found that the phase inversion between the modulated signals is not clearly seen in the radiated waveform because of the limited fractional bandwidth of the therapeutic ultrasound transducer. As a result, the radiated waveform has a higher oscillating frequency, and the pressure at the focus and the −6-dB beam size are decreased. Both simulation and measurement show similar trends. Furthermore, produced acoustic fields of the phased array using these PM strategies were also simulated at the varied lateral and axial focus shifting distances. The magnitude and beam size of both the main lobe and grating lobe are found between them, especially at the large focus shifting. In summary, the acoustic field is dependent on the PM, and the appropriate excitation scheme could improve the ultrasound application.

中文翻译：

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调相激励对聚焦声场的影响。

诸如振幅和频率调制之类的各种调制方法已被广泛应用，以修改声场并改善超声成像和治疗的性能。但是，在超声应用中，尤其是在长脉冲持续时间内，相位调制（PM）尚未得到广泛研究。在这项研究中，研究了PM对声场的影响。探索了使用不同PM策略（即每个周期，每两个周期进行顺序相位反转和随机相位反转）产生的辐射声压波形，并比较了沿换能器轴和垂直于换能器轴的声压分布和平均声强分布在测量和仿真中都具有正弦波激励。已经发现，由于治疗超声换能器的有限的分数带宽，在辐射波形中没有清楚地看到调制信号之间的相位反转。结果，辐射波形具有更高的振荡频率，并且焦点处的压力和-6dB的波束尺寸减小。模拟和测量都显示出相似的趋势。此外，还模拟了在不同的横向和轴向焦点移动距离下使用这些PM策略产生的相控阵声场。主波瓣和光栅波瓣的大小和光束大小都在两者之间，特别是在大焦点偏移时。总之，声场取决于PM，适当的激励方案可以改善超声的应用。