传统声学器件由于硬、脆、易碎的特性无法实现与人体皮肤集成，在医疗方面的应用受到了诸多限制。柔性电子技术改变了传统器件的刚性物理形态，为传统声学器件带来了新的发展方向。本文围绕超声和低频声范围的柔性声学电子器件的设计与生物医疗应用等若干问题，展开了如下研究：首先，针对临床血流连续监测需要，而传统超声探头刚度大、使用光或热等技术的柔性电子器件检测深度低等问题，设计了一种柔性可拉伸超声换能器阵列，发展了相应的多普勒血流速度测量方法。该器件通过微电子加工工艺，使用蛇形导线连接压电复合材料阵列，并由超柔弹性硅胶封装，实现了可弯曲性和可拉伸性；提出不同角度倾斜的超声换能器阵列设计和双声束多普勒方法，解决了多普勒角度未知的问题；通过超弹性本构模型，研究了器件在受拉伸时对测量结果的影响。在人体中心和外周动脉上的测试结果表明，该器件实现了无创、实时、连续、探测深度达25 mm的绝对血流速度值测量，并且能够与人体皮肤良好贴合，在无需耦合剂的情况下实现较高的信噪比和准确度。之后，基于以上研究成果，针对颈动脉血流量和心输出量监测难题，发展了柔性超声血流量监测器件和准实时血流量监测技术。通过在同一器件中集成平置与斜置的超声换能器阵列分别实现血管直径和血流速度的测量；基于动脉波传播模型，提出了两者波形的时滞校正方法，解决了直径波形和速度波形无法同时测量的问题，实现了准实时的血流量监测。通过对比测试人体颈动脉血流量以及计算每搏血量，验证了该器件的有效性。最后，针对低频人体声信号的实时监测需求，通过集成3D打印弹性共鸣腔和柔性电路板，发展了柔性无线生理音监测器件。研究了共鸣腔结构参数对声传播特性的影响，提高了对生理音信号的拾音效果；测试了器件对心音和肠鸣音监测能力，和商用设备取得了很好的一致性，在皮肤表面曲率的变化中器件能够保持信号的稳定；提取了长时间肠鸣音信号的特征，分析肠道活动规律；结合神经网络和后向传播算法，识别两种不同的肠鸣音。该项研究有助于人体生理音长时间监测和分析，拓宽了柔性声音监测器件的临床应用。
Traditional acoustic devices are not conformal to curved human skin because of their hard, brittle and fragile features, so their application in medical field is limited. Flexible electronics technology changes the rigid form of traditional devices and brings new development directions for acoustic devices. In this paper, the design and biomedical application of flexible acoustic electronics in the range of ultrasound and low frequency are studied as follows:Firstly, aiming at the clinical demand for blood flow velocity monitoring, and the problem that the traditional medical ultrasonic probe is bulky and the existing flexible devices using light or heat technologies have a low detection depth, a flexible and stretchable ultrasonic transducer array is designed and a method of measuring blood velocity is developed. Fabricated by microelectronic technology, the device exploits "island-bridge" layout and serpentine wires to connect the piezoelectric composite array, and is encapsulated by thin silicone elastomer, to achieve flexibility and stretchability. The design of ultrasonic transducer array with different angle inclination and dual beam Doppler method are proposed to solve the problem of unknown Doppler angle. Test on central and peripheral arteries show that the device can achieve non-invasive real-time continuous absolute blood flow velocity measurement with a detection depth of 25 mm, and can be conformably attached on the human skin, and achieve high signal-to-noise ratio and accuracy without coupling agent.Then, according to the above research results, a flexible ultrasonic device and a quasi-real-time technology for monitoring blood flow volume are developed, to solve the problems of monitoring carotid blood flow and cardiac output. The flat ultrasonic transducer array and oblique arrays are used to measure the vessel diameter and blood flow velocity respectively. Because the diameter waveform and velocity waveform could not be measured at the same time, a time delay correction method is proposed to calculate quasi-real-time blood flow volume based on the arterial wave propagation model. The effectiveness of the device is verified by the measurement of human carotid blood flow and the calculation of stroke volume.Finally, for monitoring low-frequency human sound signal, a flexible wireless sound monitor is proposed. The structural parameters of the acoustic resonator are studied to optimize sound propagation. The device is tested on collecting heart sound and bowel sound, resulting in good agreement with commercial equipment, and it can maintain the signal stability under the change of abdominal skin surface curvature when being attached to the surface. Through a long time measurement, the changes of bowel sounds in time and frequency domain are analyzed. On this basis, neural network and back propagation algorithm are used to achieve a good recognition accuracy of the two kinds of bowel sounds, which broadens the clinical application of flexible acoustic electronic devices.
