首页 | 本学科首页   官方微博 | 高级检索  
相似文献
 共查询到10条相似文献,搜索用时 171 毫秒
1.
本文对充砂振动柱在基础激励下的动态特性进行了理论和实验研究。把砂作为一种具有均匀密度的连续体,假设砂的弹性模量是砂柱高度的幂函数和砂柱中只存在纵向波,建立了波动方程,导出了原点导纳和传递导纳的理论公式。这个公式亦适用于非常短的砂柱。同时采用阻抗方法推导了充砂振动柱的结构损耗因子表达式。实验值和预估值基本相符。  相似文献   

2.
A flextensional transducer, in which the electrostrictive poly(vinylidene fluoride-trifluoroethylene) [P(VDF-TrFE)] copolymer was used as the active driving element, was fabricated and characterized. The results show that transducers of several millimeters thick can produce an axial displacement of more than 1 mm in air along the thickness direction, and a transmitting voltage response of 123 dB re 1 /spl mu/Pa/V at 1 m in water at frequencies of several kilohertz. A finite element code (ANSYS, Inc., Canonsburg, PA) was used to model the in-air and underwater responses of the flextensional transducer over a broad frequency range. The calculated resonance frequencies and transmitting voltage response spectra show good agreement with the experimental data. In addition, the performance of both the in-air actuator and underwater transducer was analyzed for different design parameters of the flextensional structure. These results show that the performance of the flextensional transducer could be tailored readily by adjusting the parameters of the flextensional metal shell.  相似文献   

3.
The design and the static and dynamic response of a thin film magnetoresistive transducer with superconducting control lines cooled at 4.2 K are described. The transducer facilitates a linear transfer of electrical signals by transformation of the impedance level and by perfect electrical insulation between the input and output circuit. In addition, voltage and power amplifications at low frequencies are achieved.The device can be used to sense supercurrents or currents generated by sources of very low impedance, such as superconducting quantum interferometers (SQUID's).  相似文献   

4.
Transducer performance is considered separately for transmission and reception operations. The transmission operation is traditionally characterized by its traditional transfer function. Using a Thevenin source, the transfer function may be scaled to become the absolute radiation efficiency. Transmission lines are accurately modeled, and a matched impedance design is recommended. The reception operation also is characterized by its traditional transfer function. However, reception sensitivity is defined as the signal-to-noise ratio achieved by the combined transducer, transmission line, and preamplifier. The thermal noise arises from the media and other noise sources contributed by the transducer, transmission line, and preamplifier. An absolute sensitivity measure is defined as the acoustic noise figure, which is the sum of individual transducer and preamplifier noise figures. The transducer noise figure is independent of the receiver load impedance and depends critically on dissipative loss. Preamplifier noise figure performance requires noise matching to the transducer. High performance design methods are presented that incorporate transmission lines, which include loss. Modeled examples are used to demonstrate performance.  相似文献   

5.
We investigated the magnetic-field behavior of the off-diagonal impedance in Co-based amorphous wires under sinusoidal (50 MHz) and pulsed (5 ns rise time) current excitations. For comparison, we measured the field characteristics of the diagonal impedance as well. In general, when an alternating current is applied to a magnetic wire, the voltage signal is generated not only across the wire but also in a pickup coil wound on it. These voltages are related to the diagonal and off-diagonal impedances, respectively. We demonstrate that these impedances have a different behavior as functions of axial magnetic field: the diagonal impedance is symmetrical, whereas the off-diagonal one is antisymmetrical with a near-linear portion within a certain field interval. For the off-diagonal response, the dc bias current is necessary to eliminate circular domains. In the case of the sinusoidal excitation without a dc bias current, the off-diagonal response is very small and irregular. In contrast, the pulsed excitation, combining both high- and low-frequency harmonics, produces the off-diagonal voltage response without additional biasing. This behavior is ideal for a practical sensor circuit design. We discuss the principles of operation of a linear magnetic sensor based on a complementary metal-oxide-semiconductor transistor circuit.  相似文献   

6.
7.
Numerical analysis of the radiated fields of ultrasonic transducers   总被引:8,自引:0,他引:8  
A finite element model is implemented for simulating the radiated fields of both planar and curved transducers in acoustic media. The approach is based on general finite element analysis developed for solving the governing equations of elastic wave propagation. The distributions of the wave fields are presented for both the nearfield and farfield regions of the transducer. Three excitation pulses with the same center frequency but different bandwidths are examined and the accuracy is indicated by a comparison of the simulation results for the axial and transverse fields with the analytical results for continuous wave excitation.  相似文献   

8.
A pulse-echo single-frequency method for B/A measurement is reported. The technique is based on excitation of the medium at a progressively increasing amplitude level and the computing of B/A from the deviation in linearity of the transducer input-output relationship. Starting from the nonlinear wave equation, a three-dimensional analytical formulation that predicts the approximate field distribution for finite-amplitude waves is derived. This provides the computation for the transducer output voltage for progressively increasing signal levels. It is shown that, by a suitable normalization, the effects of the diffraction can be excluded. From a nonlinear least-squares fit of the experimental data to the analytical equation, the B/A is computed. A number of simulations for the model together with preliminary experiments that were carried out at 3.5 GHz are presented  相似文献   

9.
The design of a wideband acoustic source made of the piezoelectric polymer polyvinylidine fluoride (PVDF) is described. The source was developed for the characterization and absolute calibration of ultrasonic hydrophone probes. Construction details are described and performance characteristics of the wideband PVDF transmitter, including its transmitting voltage response and directivity patterns, are compared with theoretical predictions in the frequency range up to 40 MHz. The Krimholtz-Leedom-Mattaei (KLM) model was used to examine the influence of the PVDF polymer film thickness, the backing acoustic impedance, the cable length, and the electrical source resistance on overall transmit transfer characteristics. A comparison is made with traditional piezoelectric ceramic acoustic sources, and it is shown that piezopolymer transmitters exhibit some improved properties and are well suited for certain ultrasound dosimetry applications. In particular, the polymer sources have been found useful in measurements based on swept-frequency excitation. Those measurements allow characterization of transmitters and receivers to be performed as a virtually continuous function of frequency.  相似文献   

10.
高琦  周红生  王彤宇 《声学技术》2016,35(6):579-583
设计了一种超声手术刀用的新型推挽激励换能器。它是在夹心式单晶堆压电超声换能器的经典构造基础上,把原先激励一组压电陶瓷晶片堆的方式,改为同时施加反相激励的前后两组晶堆。利用有限元方法,对该推挽激励换能器进行模态分析和频率响应分析。在相同大小的电压激励下,相对单晶堆换能器,推挽激励换能器可以获得更高的工作带宽和机电耦合系数,提高了换能器的电声转换效率。按照仿真结果加工推挽激励换能器,实现良好的动力学和电学特性,满足设计要求。  相似文献   

设为首页 | 免责声明 | 关于勤云 | 加入收藏

Copyright©北京勤云科技发展有限公司  京ICP备09084417号