基于压电陶瓷的智能超声成像传感器

INTELLIGENT ULTRASONIC IMAGING SENSOR BASED ON PIEZOELECTRIC CERAMICS

梁立成

11930223

硕士

材料工程

洪小平

2021-05-24

2021-06-15

南方科技大学

深圳

压电陶瓷是一种可以转换电能和机械能的陶瓷材料。压电陶瓷具有压电效应，在机械应力作用下，压电陶瓷材料其内部正负电荷中心会发生相对位移从而引起极化，使具有相反符号的电荷出现在电极两端，将机械能转换为电能。逆压电效应则与压电效应相反，在压电陶瓷电极两端施加电场时会使压电陶瓷发生机械变形，使电能转为机械能。因此，利用压电效应和逆压电效应可以让压电陶瓷接收超声波和发射超声波。超声相控阵就是控制阵元产生声波信号的相位，借助不同阵元发出声波的相长和相消干涉以强化超声波束在指定方向上的强度和抑制其他方向的强度，从而控制超声波束的方向，实现电子扫描成像。目前基于压电陶瓷的相控阵超声成像技术已经被广泛运用到了医学成像与无损检测等领域。然而，在这些应用中，超声波的传播介质一般是人体组织和金属固体。而在空气中，传统的空气耦合压电陶瓷换能器口径较小，在空气中无法提供具有成像能力的窄波束，因此更多承担着测距与清洗等任务。为了在空气中能够成像，本文将空气耦合压电陶瓷换能器以阵列的形式排布，以通过较大口径获得高分辨率的窄波束。同时通过相位控制，使波束能够进行扫描成像。本文设计的传感器使用一个10ⅹ10的二维阵列，该阵列具有20cmⅹ20cm大小的口径。但是，如果使用传统的方式均匀地排布这些阵元，将会产生很强的旁瓣，影响成像质量。因此本文通过遗传算法对阵列排布进行了优化，优化后的非均匀阵列产生的波束将具有低至2.15°的角分辨率，而且波束在立体角45度范围内偏转时，所有角度内的峰值旁瓣抑制级都被控制到了0.4以内，极大的降低了旁瓣的影响。同时，为了解决声波在空气中成像速度慢的问题，本文提出了一种基于正交频分复用(Orthogonal Frequency Division Multiplexing，OFDM)原理的超声传感器波形编码技术，并进行了仿真，使传感器理论上可以一次激发出多个不同频率的超声波脉冲来探测多个目标点，极大的提高了传感器的探测速度。为了验证理论的可行性，本文设计了传感器的硬件系统。该传感器可以独立驱动100路换能器阵产生超声波束，同时可以通过FPGA精准地控制这些驱动信号的相位。通过实验证明了其非均匀阵列发出的波束具有接近仿真结果的良好指向性，同时具有波束偏转及目标探测的能力，最后还验证了传感器系统可以进行基本的波束扫描，并可以通过接收阵列的多通道信号降低旁瓣的影响，证明其具备了基本的成像的能力。本文设计的智能超声传感器将声学成像应用到空气中，可以有效弥补光学成像在某些的不足，为空气中的三维成像提供了一种新的传感器选择，将会促进智能驾驶等需要环境感知能力的新兴技术更快更全面地发展。

Piezoelectric ceramics are ceramic materials that can convert electrical and mechanical energy. Piezoelectric ceramics have a piezoelectric effect. Under the action of mechanical stress, the center of positive and negative charges inside the piezoelectric ceramic material will be relatively displaced to cause polarization, causing charges with opposite signs to appear at both ends of the electrodes, converting mechanical energy into electrical energy. The inverse piezoelectric effect is the opposite of the piezoelectric effect. When an electric field is applied to both ends of the piezoelectric ceramic electrode, the piezoelectric ceramic will be mechanically deformed and the electrical energy will be converted into mechanical energy. Therefore, the use of piezoelectric effect and inverse piezoelectric effect can allow piezoelectric ceramics to receive and transmit ultrasonic waves. Ultrasonic phased array is to control the phase of the sound wave signal generated by the array elements, and use the constructive and destructive interference of the sound waves emitted by different elements to strengthen the intensity of the ultrasonic beam in the specified direction and suppress the intensity of other directions, thereby controlling the direction of the ultrasonic beam, Realize electronic scanning imaging. At present, the phased array ultrasound imaging technology based on piezoelectric ceramics has been widely used in the fields of medical imaging and non-destructive testing. However, in these applications, the propagation medium of ultrasonic waves is generally human tissue and metal solids. In the air, the traditional air-coupled piezoelectric ceramic transducer has a small caliber and cannot provide a narrow beam with imaging capabilities in the air, so it is more responsible for tasks such as ranging and cleaning. In order to be able to image in the air, this article arranged the air-coupled piezoelectric ceramic transducers in an array to obtain a high-resolution narrow beam through a larger aperture. At the same time, through phase control, the beam can be scanned and imaged. The sensor designed in this paper uses a 10ⅹ10 two-dimensional array with a diameter of 20cmⅹ20cm. However, if the array elements are arranged uniformly in the traditional way, strong side lobes will be generated, which will affect the imaging quality. Therefore, we have optimized the array arrangement through genetic algorithm. The optimized non-uniform array will produce a beam with an angular resolution as low as 2.15°, and when the beam is deflected within a solid angle of 45 degrees, the peak values in all angles. And the sidelobe suppression level is controlled to within 0.4, which greatly reduces the influence of sidelobes. At the same time, in order to solve the problem of the slow imaging speed of sound waves in the air, this article proposed an ultrasonic sensor waveform encoding technology based on the principle of orthogonal frequency division multiplexing (OFDM), and performed simulations, so that the sensor can theoretically excite at one time Multiple ultrasonic pulses of different frequencies are used to detect multiple target points, which greatly improves the detection speed of the sensor.In order to verify the feasibility of the theory, this article designed the sensor hardware system. The sensor can independently drive 100 transducer arrays to generate ultrasonic beams, and at the same time can precisely control the phase of these drive signals through FPGA. The experiment proves that the beam from the non-uniform array has good directivity close to the simulation results, and has the ability of beam deflection and target detection. Finally, it verifies that the sensor system can carry out basic beam scanning ability, and reduce the influence of side lobe through multi-channel signals of the receiving array, so that the sensor has the basic imaging ability.The intelligent ultrasonic sensor designed in this subject applies acoustic imaging to the air, which can effectively make up for some of the shortcomings of optical imaging, and provides a new sensor choice for three-dimensional imaging in the air, which will promote intelligent driving and other environmental awareness. Capable emerging technologies develop faster and more comprehensively.

压电陶瓷 相控阵超声成像 非均匀阵列 波形编码 硬件系统

piezoelectric ceramics phased array ultrasound imaging non-uniform array waveform coding hardware system

中文

独立培养

南方科技大学

梁立成. 基于压电陶瓷的智能超声成像传感器[D]. 深圳. 南方科技大学,2021.