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首页> 外文期刊>IEEE Transactions on Ultrasonics, Ferroelectrics, and Frequency Control >A Microwave-Induced Thermoacoustic Imaging System With Non-Contact Ultrasound Detection
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A Microwave-Induced Thermoacoustic Imaging System With Non-Contact Ultrasound Detection

机译：具有非接触超声检测的微波感应热声成像系统

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摘要

Portable and easy-to-use imaging systems are in high demand for medical, security screening, nondestructive testing, and sensing applications. We present a new microwave-induced thermoacoustic imaging system with non-contact, airborne ultrasound (US) detection. In this system, a 2.7 GHz microwave excitation causes differential heating at interfaces with dielectric contrast, and the resulting US signal via the thermoacoustic effect travels out of the sample to the detector in air at a standoff. The 65 dB interface loss due to the impedance mismatch at the air-sample boundary is overcome with high-sensitivity capacitive micromachined ultrasonic transducers with minimum detectable pressures (MDPs) as low as 278 mu Pa-rms and we explore two different designs-one operating at a center frequency of 71 kHz and another at a center frequency of 910 kHz. We further demonstrate that the air-sample interface presents a tradeoff with the advantage of improved resolution, as the change in wave velocity at the interface creates a strong focusing effect alongside the attenuation, resulting in axial resolutions more than 10x smaller than that predicted by the traditional speed/bandwidth limit. A piecewise synthetic aperture radar (SAR) algorithm modified for US imaging and enhanced with signal processing techniques is used for image reconstruction, resulting in mm-scale lateral and axial image resolution. Finally, measurements are conducted to verify simulations and demonstrate successful system performance.
机译：便携式，易于使用的成像系统在医疗，安全检查，无损检测和传感应用方面都有很高的需求。我们提出了一种具有非接触式机载超声（US）检测的新型微波感应热声成像系统。在该系统中，2.7 GHz微波激发在介电强度不同的界面处产生差热，并且通过热声效应产生的US信号以一定的距离从样品中移出，到达空气中的检测器。高灵敏度电容微加工超声换能器可克服由于空气样品边界处的阻抗失配而导致的65 dB接口损耗，其最小可检测压力（MDP）低至278μPa-rms，我们探索两种不同的设计-一种工作模式中心频率为71 kHz，另一中心频率为910 kHz。我们进一步证明，空气采样界面呈现出一种折衷，具有提高分辨率的优势，因为界面处的波速变化会在衰减的同时产生强大的聚焦效果，从而导致轴向分辨率比通过分辨率预测的轴向分辨率小10倍以上。传统速度/带宽限制。分段合成孔径雷达（SAR）算法经过修改，可用于US成像，并通过信号处理技术进行了增强，可用于图像重建，从而获得毫米级的横向和轴向图像分辨率。最后，进行测量以验证仿真并演示成功的系统性能。

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