平面扇形域问题的新正交关系和变分原理

通过构造新的对偶向量, 用空间的环向坐标数学上比拟Hamilton体系的时间变量,在平面弹性扇形域问题中导出了一个斜对角Hamilton算子. 该算子具有主对角元为零,斜对角元是非零对称算子的结构特性. 得到两个独立的、对称的子正交关系.恰当选择对偶向量后, 直角坐标系下各向同性平面弹性问题的新正交关系被推广到极坐标情形. 根据控制微分方程的弱(积分)形式及相应的边界条件,建立了对应边值问题的变分原理, 并提出了相应的泛函表达式.      

径向极化压电陶瓷长圆管复合超声换能器的径向振动

提出了一种圆管式径向复合压电陶瓷换能器,并对其径向振动特性进行了分析。该换能器由径向极化的压电陶瓷圆管以及金属外圆管组成。利用解析法得出了金属圆管以及具有任意壁厚的径向极化压电陶瓷圆管径向振动的机电等效电路。基于金属圆管与压电圆管的机械边界条件,得出了换能器的六端机电等效电路。在此基础上得出了换能器共振及反共振频率方程的解析表达式,给出了换能器的共振及反共振频率与其几何尺寸之间的依赖关系。利用数值方法对换能器的径向振动特性进行了模拟及仿真,并与解析结果进行了比较。最后,设计并加工了一些径向复合管式压电陶瓷换能器,利用精密阻抗分析仪对其共振及反共振频率进行了实验测试。研究结果表明,利用解析理论得出的换能器共振及反共振频率与数值模拟结果以及实验测试结果符合很好。      

Piezoelectric transducer parameter selection for exciting a single mode from multiple modes of Lamb waves

Excitation and propagation of Lamb waves by using rectangular and circular piezoelectric transducers surface-bonded to an isotropic plate are investigated in this work. Analytical stain wave solutions are derived for the two transducer shapes, giving the responses of these transducers in Lamb wave fields. The analytical study is supported by a numerical simulation using the finite element method. Symmetric and antisymmetric components in the wave propagation responses are inspected in detail with respect to test parameters such as the transducer geometry, the length and the excitation frequency. By placing only one piezoelectric transducer on the top or the bottom surface of the plate and weakening the strength of one mode while enhancing the strength of the other modes to find the centre frequency, with which the peak wave amplitude ratio between the S0 and A0 modes is maximum, a single mode excitation from the multiple modes of the Lamb waves can be achieved approximately. Experimental data are presented to show the validity of the analyses. The results are used to optimize the Lamb wave detection system.     

应用于微电容超声换能器的信号处理电路设计*

针对微电容超声换能器的输出信号特征及检测要求,文中设计了换能器的微弱信号处理电路,包括基于跨阻的微弱电流信号检测和多重反馈带通滤波电路。通过搭建水下测试平台,对电路性能及功能进行实际测试,并进行水下测距实验。实验结果表明,该电路可对微电容超声换能器输出的400 k Hz信号进行检测放大与滤波;电路的线性度为0.18%,滤波电路中心频率为396 k Hz,带宽为55 k Hz。该电路可用于CMUT的接收信号处理并应用于超声测距及成像的前端信号处理。     

格子玻尔兹曼方法对不同张角聚焦声束的建模

高强度聚焦超声(HIFU)是一种新型的无创治疗肿瘤新技术,其中换能器声场数值计算能够为HIFU治疗提供重要的依据。传统非线性KZK和SBE模型广泛应用于换能器声场数值计算,但依然存在某些不足。我们采用一种介观尺度的新型流体力学方法,即格子Boltzmann方法(LBM),基于2维9离散速度(D2Q9)格子构建了轴对称多弛豫参数LBM模型,并通过调节弛豫参数分析其对模型的影响;利用该模型对两个具有不同张角的球面聚焦换能器的声场进行数值模拟,并与KZK和SBE模型的计算结果进行比较。结果表明LBM模型能够很好地描述超声波的激发和传播机制,从流体力学的角度描述聚焦声场的分布,具有清晰的物理意义,且计算过程不受换能器张角的限制,在换能器声场的理论分析和模拟计算及其在HIFU治疗中的应用有着积极的意义。      

声腔对电动式换能器工作特性的影响

传统的电动式换能器设计理论中,未考虑压力补偿系统等声腔结构对声学性能的影响,声源级理论设计结果与实测结果存在较大差别.研究中将电动式换能器内部的三段气腔视为突变截面声腔结构,给出了声腔的四端网络等效电路,将其作为辐射面的负载添加到电动式换能器的传统等效电路中,获得了电动式换能器改进的等效电路.基于改进的等效电路求解了带...     

An investigation on optical microfiber reflector with low reflectance

The backscattering characteristics of optical microfiber(OM) are experimentally studied by controlling heating temperature and cooling method during the OM fabrication process.OM samples with various reflectances from 0.1% to 1% are achieved.An OM with waist length of 5 mm,waist diameter of 1 μm,and approximately 0.5% reflectance is used as the end reflector of a fiber Fabry-Perol(F-P) interferometer.A piezoelectric ceramic transducer(PZT) fiber phase modulator is used to test the sensing performance of the fiber F-P interferometer.Experimental results verify that the OM with low reflectance can be used as a reflector in the F-P interferometer.     

The application of laser reflective tomography in near-field measurements of ultrasonic transducers

With Laser Reflective Tomography（LRT）,the near fields of ultrasonic transducers were measured and analyzed.The principle of LRT measurement of ultrasonic field distribution was introduced and an experimental system was set up.Acoustic pressure of a multiple element piston transducer was measured by using of a laser vibrometer.Its distribution in amplitude and phase was obtained.The acoustic pressure in the same region was measured with a needle hydrophone to validate the LRT method.Furthermore,through reconstruction of acoustic fields,it indicated that LRT method is suitable for predicting the distribution on transducers＇surface and conditions of active elements.     

《应用声学》2014年总目次 第33卷 第1-6期

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驻波法测量声速实验的讨论

根据声波在2个换能器之间多次反射和声波在空气中的衰减,研究了驻波法测量声速实验中接收器输出信号随接收器到发送器间距离的变化.理论推导结果表明:声波在一般情况下不是严格的驻波,但是当反射比接近-1时则是双曲函数形式的驻波,这与实验测量结果一致.只有接收器到发送器的距离比较远,反射比接近-1时,才能得到几乎理想的驻波.