神经调控技术在神经科学的基础研究和神经疾病的临床诊断与治疗中发挥着重要作用。经颅磁声耦合刺激 (Transcranial magneto–acoustical stimulation, TMAS) 是一种新型的基于多物理场耦合的无创神经调控方法，可在深部脑区非侵入的产生高空间分辨率聚焦电刺激，在脑科学研究中具有重要的研究意义和应用前景。

TMAS基于组织的磁声耦合效应，组织中的带电粒子被超声波激发产生同频振动，在静磁场中受洛伦兹力的作用产生耦合电场，即可实现神经电刺激。目前，国内外对TMAS的研究主要关注于原理性验证，神经电模型仿真，以及刺激效果评价，TMAS技术有待深入研究。

基于磁声耦合理论，TMAS中的超声声场特性决定了耦合电刺激的刺激深度、空间分辨率、刺激强度及刺激功率等关键指标，磁声耦合中声场的重要性不言而喻。本文针对TMAS脑深部刺激的应用要求和技术特点，对其声场特性进行了分析和改进，提出标准正弦超声激励源设计方案和相控阵设计方案，并进行了研制与测试。

本文首先设计研制了基于单阵元超声换能器的适用于TMAS刺激的标准正弦脉冲超声激励源。实验结果显示：该超声激励源单通道即可提供V_pp=120V的激励电压，使超声换能器在焦点处产生约0.35MPa的声压。相较门控RF功率放大器、以及广泛用于超声激励的基于DE类功率放大的方波激励源和以Verasonic平台为代表的修正弦波激励源，本文设计的标准正弦超声激励源输出脉冲的能量转换效率更高，是门控RF放大器的1.93倍，是方波激励源的1.8倍；并且激励波形的保真度更好、频率失真更低，频谱分析结果显示输出信号的高次谐波分量占比低于10%。还可以将该单通道激励源灵活扩展为多通道激励源，更适用于TMAS的精准脑刺激需求。

本文又设计了适用于TMAS脑深部刺激的相控阵超声换能器，对相控阵换能器进行仿真建模，探究换能器阵元数量、阵元排布方式、阵元宽度、阵元间距等参数对聚焦性能的影响，获得最优参数并定制换能器。为了验证所设计定制的换能器的声场性能，本文搭建了超声换能器三维声场分布测试平台并对其进行了系统集成，对定制换能器的聚焦性能及声场分布进行了测试验证。仿真结果表明，定制主频500kHz，阵元宽度5mm，阵元间距0.1mm的64阵元面阵相控阵超声换能器，可在刺激深度5cm处获得最优的聚焦性能。测试结果表明，本文建立的超声换能器声场分布测试平台可进行精度为0.3mm的三维声场分布测试，定制换能器在5cm焦距处的焦斑尺寸为3.4mm，与仿真计算中的3.1mm相近，可以实现TMAS在深部脑区更高的刺激分辨率。

综上，本文对基于TMAS脑深部刺激的磁声耦合声场特性进行了分析及改进研究，为TMAS在无创精确脑深部刺激领域的应用奠定了技术基础。

Neural regulation technology plays an important role in the basic research of neuroscience and the clinical diagnosis and treatment of neurological diseases. Transcranial magneto acoustic stimulation (TMAS) is a new noninvasive neural regulation method based on multi physical field coupling. It can produce high spatial resolution focused electrical stimulation in deep brain non-invasively. It has important research significance and application prospect in brain science research.

TMAS is based on the magneto acoustic coupling effect of tissue. The charged particles in the tissue are excited by ultrasound to produce the same frequency vibration, and the coupled electric field is generated by Lorentz force in the static magnetic field to realize the electrical stimulation of nerve. At present, the research on TMAS at home and abroad mainly focuses on principle verification, neuroelectric model simulation and stimulation effect evaluation. TMAS technology needs to be further studied.

Based on the magneto acoustic coupling theory, the characteristics of ultrasonic sound field in TMAS determine the key indexes of coupled electrical stimulation, such as stimulation depth, spatial resolution, stimulation intensity and stimulation power. The importance of sound field in magneto acoustic coupling is self-evident. According to the application requirements and technical characteristics of TMAS deep brain stimulation, this paper analyzes and improves its sound field characteristics, puts forward the design scheme of standard sinusoidal ultrasonic excitation source and phased array, and develops and tests it.

Firstly, a standard sinusoidal pulse ultrasonic excitation source suitable for TMAS stimulation based on single array ultrasonic transducer is designed and developed in this paper. The experimental results show that the single channel of the ultrasonic excitation source can provide an excitation voltage of Vpp = 120V, making the ultrasonic transducer produce a sound pressure of about 0.35Mpa at the focus. Compared with the gated RF power amplifier, the square wave excitation source based on de power amplification widely used for ultrasonic excitation and the modified chord wave excitation source represented by Verasonic platform, the energy conversion efficiency of the output pulse of the standard sinusoidal ultrasonic excitation source designed in this paper is higher, which is 1.93 times that of the gated RF amplifier and 1.8 times that of the square wave excitation source; Moreover, the fidelity of the excitation waveform is better and the frequency distortion is lower. The spectrum analysis results show that the high-order harmonic component of the output signal accounts for less than 10%. The single channel excitation source can also be flexibly expanded into a multi-channel excitation source, which is more suitable for the precise brain stimulation needs of TMAS.

This paper also designs a phased array ultrasonic transducer suitable for TMAS deep brain stimulation, simulates and models the phased array transducer, explores the influence of the number of transducer elements, array element arrangement mode, array element width, array element spacing and other parameters on the focusing performance, obtains the optimal parameters and customizes the transducer. In order to verify the sound field performance of the designed customized transducer, a three-dimensional sound field distribution test platform of ultrasonic transducer is built and integrated, and the focusing performance and sound field distribution of the customized transducer are tested and verified. The simulation results show that the 64-array phased array ultrasonic transducer with customized main frequency of 500KHz, array width of 5mm and array spacing of 0.1mm can obtain the best focusing performance at the stimulation depth of 5cm. The test results show that the ultrasonic transducer sound field distribution test platform established in this paper can test the three-dimensional sound field distribution with an accuracy of 0.3mm. The focal spot size of the customized transducer at the focal length of 5cm is 3.4mm, which is close to 3.1mm in the simulation calculation, and can achieve higher stimulation resolution of TMAS in the deep brain region.

In conclusion, this paper analyzes and improves the characteristics of Magnetoacoustic coupling sound field based on TMAS deep brain stimulation, which lays a technical foundation for the application of TMAS in the field of noninvasive and accurate deep brain stimulation.