Beard P C, Hurrell A M, Mills T N
Department of Medical Physics and Bioengineering, University College London, London WClE 6JA, UK.
IEEE Trans Ultrason Ferroelectr Freq Control. 2000;47(1):256-64. doi: 10.1109/58.818769.
A small aperture wideband ultrasonic optical fiber hydrophone is described. The transduction mechanism is based on the detection of acoustically induced changes in the optical thickness of a 25-microm thick parylene polymer film acting as a low finesse Fabry Perot (FP) interferometer that is deposited directly onto the end of a single mode optical fiber. The acoustic performance compares favorably with that of PVDF needle and membrane hydrophones with a peak noise-equivalent-pressure (without signal averaging) of 10 kPa over a 25-MHz measurement bandwidth, a wideband response to 20 MHz, and a near omnidirectional performance at 10 MHz. The dynamic range was 60 dB with an upper limit of linear detection of 11 MPa and a temporal stability of <5% over a period of 20 h. The hydrophone can also measure temperature changes with a resolution of 0.065 degrees C, offering the prospect of making simultaneous acoustic pressure and temperature measurements. The transduction parameters of the FP sensing element were measured, yielding an ultrasonic acoustic phase sensitivity of 0.075 rad/MPa and a temperature phase sensitivity of 0.077 rad/ degrees C. The ability to achieve high acoustic sensitivity with small element sizes and to repeatably fabricate rugged sensor downleads using polymer deposition techniques suggests that this type of hydrophone can provide a practical alternative to piezoelectric hydrophone technology.
本文描述了一种小孔径宽带超声光纤水听器。其传感机制基于检测厚度为25微米的聚对二甲苯聚合物薄膜光学厚度的声学诱导变化，该薄膜作为低精细度法布里 - 珀罗（FP）干涉仪直接沉积在单模光纤末端。与聚偏二氟乙烯针状和薄膜水听器相比，该水听器的声学性能良好，在25兆赫测量带宽内的峰值噪声等效压力（无信号平均）为10千帕，对20兆赫有宽带响应，在10兆赫时具有近乎全向的性能。动态范围为60分贝，线性检测上限为11兆帕，在20小时内时间稳定性小于5%。该水听器还能以0.065摄氏度的分辨率测量温度变化，有望实现声压和温度的同步测量。测量了FP传感元件的传感参数，得到超声声相位灵敏度为0.075弧度/兆帕，温度相位灵敏度为0.077弧度/摄氏度。能够以小尺寸元件实现高声学灵敏度，并使用聚合物沉积技术可重复制造坚固耐用且带有传感器的引出线，这表明这种类型的水听器可为压电水听器技术提供一种实用的替代方案。
