PVDF压电薄膜测量脉动压力可行性研究

PVDF压电薄膜是一种新型的高分子聚合物型传感器材料,具有高的压电常数,质量轻、柔性好、加工性能好、频率响应宽、对高频激励实用性强等优点,该文利用PVDF薄膜的压电特性设计了一种传感器,通过对传感器测试发现,在测量压力范围内,PVDF压电薄膜传感器具有良好的线性度、较高的灵敏度、较宽的频域响应、较低的迟滞性误差和重复性误差,并且温度对传感器的灵敏度影响较大,实际测试时需考虑温度的影响,激励测试表明PVDF压电薄膜传感器满足测量脉动压力的需求。     

基于多普勒激光测振仪的Ⅲ型弯张换能器振动模态分析

为了测量和验证Ⅲ型弯张换能器在工作状态时辐射面的振动情况,采用多普勒激光测振仪对Ⅲ型弯张换能器的振动模态进行了测量,并与有限元软件仿真结果进行了对比。测量得到换能器壳体的一阶振动模态的谐振频率为1729 Hz,换能器一阶振动模态的谐振频率为2 065 Hz,与有限元模态仿真结果吻合较好。研究结果表明,多普勒激光测振仪能较好地对换能器的振动模态进行测量,可用于换能器的辅助设计。     

Ⅱ型弯张换能器壳体的振动特性分析

弯张换能器是一种新型大功率换能器,具有低频、高效、结构紧凑、功率容量比大等优点。本文分析了Ⅱ型弯张换能器壳体的振动特性。讨论了壳体振动问题的数学建模及非伸长型振动条件下固有模态和准静态解,得出了对称式最低阶振型。     

利用PVDF阵列测量结构曲率模态的实验

提出利用PVDF阵列直接测量结构曲率模态。在振动梁表面均匀布置一组PVDF压电薄膜,测量结构在外加点激励作用下的动态响应,得到频率响应函数,进而通过模态软件对数据进行分析,得到其曲率模态。数值分析和实验结果表明：利用PVDF阵列可以有效地测量得到结构的曲率模态,且方法与激励力位置无关。由于方法操作简便,PVDF压电薄膜附加质量可忽略不计,与常规通过模态振型计算曲率模态的方法相比具有明显优越性。     

IV型弯张换能器的数学建模

ＩＶ型弯张换能器的振动机理比较复杂,它包涵着驱动振子的振动、壳体的振动、 水介质振动及它们之间相互耦合而构成的复合振动。本文对其进行了较详细的理论分析,给 出了换能器壳体的振动位移分布和谐振频率。并根据干模态讨论了换能器在水中的声辐射特 性;再者,结合压电方程及换能器的振速、应力分布给出了换能器在水中的电机声等效电路。 理论分析结果与有限元法及实验测量进行了比较,符合较好。     

聚偏氟乙烯压电薄膜的实验研究

一、聚偏氟乙烯薄膜性能特点 聚偏氟乙烯(以下称为PVDF)薄膜为一种新型压电材料,在水声、超声、电声等领域中可与现有的PZT压电陶瓷取长补短,是压电材料领域新添的一员。 自从五十年代PZT压电陶瓷问世以来,三十多年中它始终在换能器材料中占主导地位,尽管PZT作为压电材料有着无可比拟的优点,但也存在着由陶瓷固有性能所带来的缺点和在换能器设计上的不便之处,如陶瓷的高密度和易碎性使大于10cm的水听器太厚、太重,而薄的器件     

用于声化学的复合换能器的研究

设计了一种夹心式纵弯复合振动模式超声换能器,该换能器由纵向夹心式压电超声换能器与弯曲正六边形薄板组成。采用有限元方法,对一定几何尺寸边界自由的正六边形薄板进行模态分析,得到中心位移最大的某一模态,设计以该模态的频率作为共振频率的纵弯复合模式换能器。当复合振动系统振动模式的共振频率与纵向换能器的共振频率以及正六边形薄板弯曲振动的共振频率一致时,复合振动系统具有较高的有效机电耦和系数,系统声辐射能力较强;频率的理论与测量值的误差可能是设计纵向换能器时未考虑预应力螺栓、前后盖板的形状以及横向振动的影响,材料参数的取值与实际值有误差。弯曲振动的正六边形薄板的几何尺寸大,将会增大复合振动系统声波的辐射面积,因此可以改善局部空化腐蚀问题,并且可以提高槽内声场的均匀性,从而可以提高声化学产率;实验结果表明,换能器的共振频率测试值与设计值基本吻合。     

基于PVDF压电薄膜的能量收集系统研究

压电能量收集系统作为一种自发电系统，可以将施加在系统上的压力转换为可供负载使用的电能。以100μm厚的PVDF薄膜作为压电能量收集系统的能量来源，以电学与力学为基础，设计了一种基于PVDF薄膜的压电能量收集系统；用ANSYS软件建立模型仿真，用origin软件处理PVDF薄膜输出信号参数，确定了箱式结构下的压电薄膜双并联结构；设计了采用三倍压电路的基于LTC3588芯片的能量收集电路，使得能量采集效率提升了3倍。     

基于反射探针的聚焦超声测量传感器设计和方法研究

基于钨钢探针和PVDF压电薄膜材料,设计研制了一种用于聚焦超声测量的新型传感器。同时,通过理论分析和有限元分析软件建立了传感器物理模型,并对传感器的内部声场及反射状况进行了模拟仿真,获得传感器输出信号的波形和幅值。最后,利用研制的传感器对聚焦换能器焦域声压和声强进行检测,并将检测结果与理论仿真结果对比,在10W的声功率范围内,证明了新型传感器及其测量理论和方法在聚焦超声测量中的可行性与可靠性。该新型反射探针传感器将为高强度聚焦超声声场的测量提供一种新的方法。     

纵—弯复合模式超声换能器的研究

研究了一种新型的纵-弯复合振动模式超声换能器,该换能器由均匀截面细棒及两组不同结构的压电陶瓷元件组成.导出了此类换能器的频率设计方程.实验表明,纵向共振频率与弯曲振动共振频率基本一致,且实测值与设计值比较符合.     

新型智能隔振复合结构的动态特性研究

针对精密机械的微位移隔振问题,设计了一种以PVDF压电薄膜为作动器和传感器的新型智能隔振复合结构。根据压电方程推导出了层叠式PVDF压电薄膜作动器厚度变形量表达式,建立了该智能复合结构的隔振理论模型,采用LMS自适应控制算法,以Matlab和有限元混合建模分析方式对本智能隔振复合结构的动态特性进行研究。有限元模型的分析结果与Matlab计算数据一致,验证了本新型智能隔振复合结构对微位移隔振的有效性,其结论将为精密仪器、微纳米设备的微位移智能主动隔振奠定理论基础。     

基于拓扑优化的压电分流阻尼抑振实验研究

将结构拓扑优化引入压电分流振动抑制中,以压电元件的分布面积为设计变量,压电元件产生的电荷最大化为优化目标,对压电元件的拓扑进行了优化以获得最佳抑振效果。针对悬臂梁结构,得到了对不同的结构模态进行抑制时的压电元件最优拓扑构型。建立了带有压电分流阻尼系统的悬臂梁振动控制实验模型,将压电元件拓扑优化后的压电分流阻尼系统应用于悬臂梁多阶弯曲模态的振动响应抑制实验,并对比分析了带最优拓扑和非优拓扑压电元件的悬臂梁压电分流阻尼抑振效果。结果表明,对压电元件进行拓扑优化可以明显提高压电分流阻尼系统的抑振效果。     

Curved PVDF airborne transducer

In the application of airborne ultrasonic ranging measurement, a partially cylindrical (curved) PVDF transducer can effectively couple ultrasound into the air and generate strong sound pressure. Because of its geometrical features, the ultrasound beam angles of a curved PVDF transducer can be unsymmetrical (i.e., broad horizontally and narrow vertically). This feature is desired in some applications. In this work, a curved PVDF air transducer is investigated both theoretically and experimentally. Two resonances were observed in this transducer. They are length extensional mode and flexural bending mode. Surface vibration profiles of these two modes were measured by a laser vibrometer. It was found from the experiment that the surface vibration was not uniform along the curvature direction for both vibration modes. Theoretical calculations based on a model developed in this work confirmed the experimental results. Two displacement peaks were found in the piezoelectric active direction of PVDF film for the length extensional mode; three peaks were found for the flexural bending mode. The observed peak positions were in good agreement with the calculation results. Transient surface displacement measurements revealed that vibration peaks were in phase for the length extensional mode and out of phase for the flexural bending mode. Therefore, the length extensional mode can generate a stronger ultrasound wave than the flexural bending mode. The resonance frequencies and vibration amplitudes of the two modes strongly depend on the structure parameters as well as the material properties. For the transducer design, the theoretical model developed in this work can be used to optimize the ultrasound performance.     

Contact-Type Vibration Sensors Using Curved Clamped PVDF Film

This paper describes a new type of contact vibration sensor made by bonding a piezoelectric polyvinylidene fluoride (PVDF) film to a curved frame structure. The concave surface of the film is bonded to a rubber piece having a front contact face. Vibration is transmitted from this face through the rubber to the surface of the PVDF film. Pressure normal to the surface of the film is converted to circumferential strain, and an electric field is induced by the piezoelectric effect. The frequency response of the device was measured using an accelerometer mounted between the rubber face and a rigid vibration exciter plate. Sensitivity (voltage per unit displacement) was deduced from the device output and measured acceleration. The sensitivity was flat from 16 Hz to 3 kHz, peaking at 6 kHz due to a structural resonance. A contact vibration sensor theory has been developed, which accounts for the effect of the radiation medium. It has been found that the imaginary part of the radiation impedance has an effect equivalent to the addition of mass to the curved PVDF film structure, which reduces the resonance frequency by about one order. Calculations predicting performance against human tissue (stethoscope or contact microphone) show results similar to data measured against the metal vibrator. This implies that an accelerometer can be used for calibrating a stethoscope or contact microphone. The observed arterial pulse waveform from the new PVDF sensor showed more low-frequency content than a conventional electronic stethoscope.     

Piezoelectrically actuated flextensional micromachined ultrasound droplet ejectors

This paper reports a variation on the design of the flextensional transducer for use in ejecting liquids. The transducer is constructed by depositing a piezoelectric thin film to a thin, edge-clamped, circular annular plate. By placing a fluid behind one face of a vibrating compound plate that has an orifice at its center, we achieve continuous or drop-on-demand ejection of the fluid. We present results of ejection of water and isopropanol. The ejector is harmless to sensitive fluids and can be used to eject fuels as well as chemical and biological samples. Micromachined two-dimensional array piezoelectrically actuated flextensional droplet ejectors were realized using planar silicon micromachining techniques. Typical resonant frequency of the micromachined device ranges from 400 kHz to 4.5 MHz. The ejection of water through a 5-μm diameter orifice at 3.5 MHz was demonstrated by using the developed micromachined two-dimensional array ejectors     

Phase-matched air ultrasonic transducers using corrugated PVDF filmwith half wavelength depth

A new type of large area PVDF film air transducer is proposed. The transducer features a high power output and a sharp beam angle. Conventionally known curved length mode resonators with two clamps at both ends have a resonance frequency determined by the curvature. In the present work, PVDF was formed into alternating concave and convex multiple curved sections, eliminating clamps, i.e., a periodic corrugation structure using a single PVDF film. Each convex and concave section has a common resonance frequency. A common excitation voltage induces vibration for each section, and the vibration direction is normal to the film surface. The vibration phase of convex section is shifted 180 degrees from the concave section. These waves add constructively to form a strong acoustic beam when corrugation height is approximately one-half of the wavelength. The corrugation height controls propagation path difference, canceling excitation phase difference. The design principle based on a uniform vibration mode is presented. Experimental investigations using 8.8×2.5-, 10×5-, and 20×20-cm² transducers are presented. Side lobes unique to this corrugation structure have been observed. A theoretical analysis of the side lobes is also presented. According to the theory, choosing the corrugation height appropriately will reduce side lobes to -15 dB with regard to the main lobe, and the observed side lobe height agreed with the theoretical result     

嵌入式外部驱动IV型弯张换能器设计

为了减小外部驱动IV型弯张换能器长度,提高此类换能器的实用性,提出在弯张壳长轴方向设计一U型凹槽、驱动单元置于凹槽内驱动的方案。利用有限元软件重点分析U型凹槽尺寸对换能器谐振频率和体积位移的作用规律,同时结合水中模型的发射电压响应,设计了一款谐振频率为2.2 k Hz、-3 d B带宽为330 Hz的嵌入式外部驱动IV型弯张换能器。这种结构的换能器不仅吸收了已有外部驱动IV型弯张换能器的优点,还弥补了其长度尺寸过大的缺陷。     

稀土IV型弯张换能器研究

IV型弯张换能器低频发射时具有尺寸小、重量轻的特点,是一种常用的水下低频大功率声源。稀土超磁致伸缩材料相较于压电陶瓷拥有更大的应变量和能量密度,并且杨氏模量较小,可以有效降低换能器谐振频率。利用稀土超磁致伸缩材料作为激励材料,设计了一种低频IV型弯张换能器,对其静态磁场和动态磁场进行了分析,构建出双棒式磁路,并使用有限元分析软件进行了换能器的结构建模与计算。根据计算结果制作了稀土IV型弯张换能器样机,测试结果表明所设计的换能器与仿真结果吻合较好,水中谐振频率为370 Hz,最大声源级为196 d B,能够实现低频、大功率发射。     

一种测量一维结构振动功率流的新方法

通过设计正弦和余弦形状PVDF传感器，提出了一种测量一维结构振动功率流和位移的新方法，并与用压电加速度传感器的测量结果进行了比较，结果表明：这种新的测量方法测量方便、数据精确，完全可以取代传统测量方法。并且PVDF传感器还可以同时测量角位移、弯矩、剪力等其它振动量，因此这种传感器功能齐全、应用广泛，具有重大的研究价值和现实意义。     

Miniature multimode monolithic flextensional transducers

Traditional flextensional transducers classified in seven groups based on their designs have been used extensively in 1-100 kHz range for mine hunting, fish finding, oil explorations, and biomedical applications. In this study, a new family of small, low cost underwater, and biomedical transducers has been developed. After the fabrication of transducers, finite-elements analysis (FEA) was used extensively in order to optimize these miniature versions of high-power, low-frequency flextensional transducer designs to achieve broad bandwidth for both transmitting and receiving, engineered vibration modes, and optimized acoustic directivity patterns. Transducer topologies with various shapes, cross sections, and symmetries can be fabricated through high-volume, low-cost ceramic and metal extrusion processes. Miniaturized transducers posses resonance frequencies in the range of above 1 MHz to below 10 kHz. Symmetry and design of the transducer, polling patterns, driving and receiving electrode geometries, and driving conditions have a strong effect on the vibration modes, resonance frequencies, and radiation patterns. This paper is devoted to small, multimode flextensional transducers with active shells, which combine the advantages of small size and low-cost manufacturing with control of the shape of the acoustic radiation/receive pattern. The performance of the transducers is emphasized.