Acquafresca Alberto, Biagi Elena, Masotti Leonardo, Menichelli David
Department of Electronics and Telecommunications, University of Florence, 50139 Florence, Italy.
IEEE Trans Ultrason Ferroelectr Freq Control. 2003 Oct;50(10):1325-35. doi: 10.1109/tuffc.2003.1244749.
The present generation of devices based on opto-acoustic and acousto-optic conversion lets us foresee the possibility of realizing complete miniaturized transmitting-receiving transducers, able to generate and detect wideband ultrasounds by laser light. In the present paper, a miniaturized ultrasonic transducer entirely based on fiber optic technology is proposed. Such a device springs from the conjunction between our research, which has produced a highly efficient fiber optic opto-acoustic source, with the results obtained by other researchers concerning the realization of an ultrasonic receiver based on optical interferometry. Making use of the thermo-elastic effect for ultrasound generation, a source of ultrasound can be obtained by coupling a fiber optic to pulsed laser, if a film capable of absorbing laser light is placed onto fiber end. Starting from these remarks, we propose an efficient opto-acoustic source, able to generate pressure pulses with amplitude of the order of 10(4) Pa and bandwidth extending up to 40 MHz and beyond by using graphite materials as absorbing film. This solution makes use of a low-power pulsed laser as optical source possible. An ultrasonic receiving element was realized placing a Fabry-Perot cavity over the tip of a fiber optic. The cavity thickness modulation induced by ultrasonic beam is detected by an interferometer optical technique. We have realized a prototype of a receiving device that exhibits a sensitivity comparable with that of piezoelectric devices (10-100 nV/Pa) and an almost flat bandwidth extending up to 20 MHz or more. The extreme miniaturization of the resulting ultrasonic transducer, together with its wide ultrasonic frequency bandwidth, is the first step toward ultrasonic tissue biopsy. In this paper, before discussing the problem of constructing a complete ultrasonic transducer composed by a transmitter and receiver, the results carried out in these fields during the last decade are reviewed.
目前基于光声和声光转换的一代设备让我们预见到实现完全小型化的发射-接收换能器的可能性，这种换能器能够通过激光产生和检测宽带超声波。在本文中，提出了一种完全基于光纤技术的小型化超声换能器。这样一种设备源于我们的研究（已产生了一种高效的光纤光声源）与其他研究人员在基于光学干涉测量实现超声接收器方面所取得的成果的结合。利用热弹性效应来产生超声波，如果在光纤末端放置一层能够吸收激光的薄膜，那么通过将光纤与脉冲激光耦合就可以获得一个超声源。基于这些论述，我们提出一种高效的光声源，通过使用石墨材料作为吸收薄膜，该声源能够产生幅度约为10⁴帕斯卡且带宽扩展至40兆赫兹及以上的压力脉冲。这种解决方案使得使用低功率脉冲激光作为光源成为可能。通过在光纤末端放置一个法布里-珀罗腔实现了一个超声接收元件。由超声束引起的腔厚度调制通过干涉仪光学技术进行检测。我们已经实现了一个接收设备的原型，其灵敏度与压电设备相当（10 - 100纳伏/帕斯卡），并且具有几乎平坦的带宽，扩展至20兆赫兹或更高。所得到的超声换能器的极度小型化及其宽超声频率带宽，是朝着超声组织活检迈出的第一步。在本文中，在讨论由发射器和接收器组成的完整超声换能器的构建问题之前，先回顾了过去十年在这些领域所取得的成果。
