变波长水平剪切波电磁超声换能器设计

针对大型常压储罐底板厚度在线测量需要,设计并制作了一种可变波长的低阶水平剪切波电磁超声换能器,该换能器主要由永磁铁阵列、可变间距机械夹具、PCB板、阻抗匹配模块、接口、保护层及外壳等组成.对研制的换能器进行了性能测试,结果表明:研制的电磁超声换能器可在一定波长变化范围内激励出单一的低阶水平剪切波,且信噪比较好.设计的可变波长电磁超声换能器为压力容器在线检测提供了可能的传感器手段.     

厚圆片超声换能器电路系统设计

针对水果超声检测时存在声波穿透性能差,致使无法实现水果特征参数有效检测的问题,设计了一种用于水果超声检测的电路系统,用于解决这一技术瓶颈。该系统中,换能器采用厚径比为R/H=259的厚圆片压电陶瓷作为敏感元件,通过AT89S52控制的MOS管半桥对DC/DC升压转换电路产生的幅值为450 V的直流高压进行调制,将得到的高压方波信号（可调脉宽范围3～12 μs）对换能器进行激励,以产生高能低频的超声波。通过将该电路系统应用于苹果中声速的测定,验证了该电路系统的有效性。该检测系统可为水果特征参数、水果品质以及损伤的超声检测提供技术参考。     

导波激励/接收压电换能器参数检测电路的设计与实现

提出了一种基于π网络零相位法的测量压电换能器谐振频率、反谐振频率和静电容的新方法,并据此设计研制了试验测量装置,对压电换能器的谐振频率、反谐振频率及自由电容等参数进行测量。经过试验测试,该装置可以实现压电换能器基本参数的测量。     

基于工业机器人的超声换能器回波自动测量系统设计

针对医用超声换能器回波测量中存在的自动化水平低、测试人员主观判断对结果产生很大影响等问题,基于工业机器人设计了一套超声换能器回波自动测量系统。详细阐述了回波自动测量系统设计思路,对系统构建的关键——自动对位功能的实现方案进行了对比分析,在Matlab环境中开发了完整的参数设置、自动对位和回波采集与处理程序,对自动对位算法进行了详细描述。试验结果表明该系统达到了设计指标,灵敏度测量的偏移系数小于0.5%,能够满足日常工作中的测试需要。本工作为医用超声换能器研发、生产全流程的智能制造打下了良好的基础。     

超声谐振器在传感器测距中应用分析

设计一种超声谐振器,旨在解决超声传感器远程测距中因超声波能量分散和衰减过快导致的回波信号难以识别问题。首先,根据声学理论分析了超声谐振器可以通过改善阻抗匹配提高其辐射效率;再利用Bessel函数分析了超声谐振器影响声源指向性的重要设计参数,通过改变声源频率、谐振器开口面积等设计参数可以使指向性尖锐,能量更集中。Matlab仿真计算与相应的实验均证明了理论分析的正确性和优化谐振器设计参数对提高超声探测距离的有效性与可控性。     

基于PIC12C508单片机的超声测距系统

介绍一种基于PIC12C508单片机的超声波测距系统，给出了系统的设计和分析，进行了测距实验和数据分析。该系统可以用在汽车倒车雷达，机器人控制等自动控制领域。     

超声回波信号包络相关时延估计优化算法

相关函数的时延估计方法是脉冲回波测距常用的算法。常规的算法直接以回波采样数据为样本处理,运算处理的数据量过于庞大,在嵌入式系统中实现困难且实时性差。提出将采样数据预处理,并以面向该应用采取的递归算法,快速获取相关系数的优化算法。可满足回波时间测量的精度,并显著降低数据存储器的需要量和数据的处理量。实现方法简便可靠,具有较高实用性。     

超声回波信号解调及其包络相关时延估计算法

互相关函数法是脉冲法超声测距中最常用的时延估计算法,但窄带超声回波信号的振荡特性导致它们的相关函数在峰值位置近似作等幅振荡,从而为精确搜索相关函数的峰值带来困难,所以有必要对相关函数包络的峰值进行搜索.首先分析了超声回波信号解调的常规算法,然后提出了基于FFT的直接提取相关函数包络的快速算法.仿真与实验研究表明,该方法能精确提取相关函数的包络,在不增加计算量的情况下精确搜索到相关函数的峰值位置.     

超声换能器发射激励能量利用率的研究

在全数字化B超或者是彩色B超当中前级收发电路和回波的质量直接影响到整个产品的性能;而超声换能器发射激励的不同更大程度上决定了超声图像的质量.在试验中发现利用双极性发射,3.5 M探头回波信号的峰峰值达到了1 V,而单极性的回波信号只有500 mV左右;这说明了不同发射激励对图像质量有很大的影响,而双极性发射方式的能量利用率最高,可以有效地控制发射频率,从而使变频等效果明显的显现出来,能够提高回波信号的质量.     

基于双阀值法的超声油品密度检测系统的研究

介绍一个超声油品密度检测系统的测量原理和基本结构,提出了采用了多次反射法和恒温油浴的方法来提高精度,使精度能达到国家标准要求,具有一定的实用价值。     

The microfabrication of capacitive ultrasonic transducers

Surface-micromachined capacitive ultrasonic transducers, which are suitable for operation in both air and water, have been fabricated and tested. Amorphous silicon is used as a sacrificial layer because of its good etching selectivity versus a nitride membrane, and improved cell-size control is obtained by lithographic definition of cavity walls. In addition, appropriate feature designs based on two-dimensional (2-D) process simulations make it possible to achieve device cavity sealing with g-line optical lithography. Transmission experiments in both water and air are presented. A dynamic range in excess of 110 dB is observed in air at 2.3 MHz. In water, a single pair of transducers is able to operate from 2 to 15 MHz. When tuned, a 3.5-MHz tone burst results in a received signal with better than 60-dB signal-to-noise ratio (SNR). The transducer behaviour agrees with a theoretical understanding of transducer dynamics. The dynamic ranges achieved in this paper are the best reported to date for surface-micromachined capacitive ultrasonic transducers     

Characterization of capacitive micromachined ultrasonic transducers

This paper describes numerical and experimental characterization of capacitive micromachined ultrasonic transducers (CMUTs) for ultrasound transmission. Simulations based on a finite elements method to model the electromechanical behaviour of CMUTs and to determine the dimensions of elementary cells are presented. In particular, we analyse how the collapse voltage and the capacitance are affected by different parameters of a circular cell and by different bias voltages. The fill factor is defined as the ratio of the top electrode radius to the membrane radius and we study the influence of the fill factor in the performances of CMUTs. The fabrication process of a CMUT uses anodic bonding of a SOI wafer on a borosilicate glass substrate and we compare experimental results with numerical results in terms of eigenfrequencies, bandwidth, quality factor and capacitance for non-metallized and metallized membranes.     

基于超声波换能器的来人探测装置

许多场合需要照明设备能够根据来人情况自动开关,该装置使用了一对收发独立的超声波换能器,能够在一定空间内有效地探测是否有人通过,并控制照明设备的开关.当它正常工作时,会持续发射一定频率的超声信号.如果有人通过,由运动人体返回的超声信号会因为多普勒效应而产生频率偏移.根据此频率偏移,该装置便可以准确地探测到有人来到,继而打开照明设备,并控制照明设备延时关闭,其延迟时间为15 s～30 min可调.该装置可以方便地安装在多种场合,其正面有效探测距离为1.0～5.5 m可调.     

Fabricating capacitive micromachined ultrasonic transducers with wafer-bonding technology

Introduces a new method for fabricating capacitive micromachined ultrasonic transducers (CMUTs) that uses a wafer bonding technique. The transducer membrane and cavity are defined on an SOI (silicon-on-insulator) wafer and on a prime wafer, respectively. Then, using silicon direct bonding in a vacuum environment, the two wafers are bonded together to form a transducer. This new technique, capable of fabricating large CMUTs, offers advantages over the traditionally micromachined CMUTs. First, forming a vacuum-sealed cavity is relatively easy since the wafer bonding is performed in a vacuum chamber. Second, this process enables better control over the gap height, making it possible to fabricate very small gaps (less than 0.1 /spl mu/m). Third, since the membrane is made of single crystal silicon, it is possible to predict and control the mechanical properties of the membrane to within 5%. Finally, the number of process steps involved in making a CMUT has been reduced from 22 to 15, shortening the device turn-around time. All of these advantages provide repeatable fabrication of CMUTs featuring predictable center frequency, bandwidth, and collapse voltage.     

换能器双匹配层参数的计算

研究了纵振超声换能器前端粘接胶层和匹配层参数(厚度、特性阻抗)的变化对换能器声能量辐射的影响。通过计算得到了多组最佳匹配厚度的组合,扩大了匹配层材料的可使用范围。计算结果表明:粘接胶层的厚度、匹配层的材料和厚度都对换能器的辐射功率有着较大影响。最后比较了换能器对水辐射时,粘接胶层和匹配层参数的设计方案,为实际匹配层的设计提供帮助。     

超声波风速风向仪的研制

超声波风速风向的设计仪国内少有报道.本系统采用时差法原理实现对风速风向的测量,利用单片机PIC18F4580为控制核心,构成高速计时模块,利用多重阈值比较电路,结合软件设计实现发射时间范围控制和可靠性检验.实验结果表明系统在风速30m/s以下与参照曲线拟合程度较高,实现了用时差法超声波测量风速风向的目的,具有一定实用价值.     

压电换能器瞬态接收特性的有限元模拟研究

接收信号在压电换能器压电层中的多次反射及波形转换对超声检测的灵敏度和分辨率有重要影响,如何优化阻尼结构与材料参数是提高压电换能器接收性能的关键之一。本文用ANSYS有限元软件中的力-电耦合瞬态模拟方法,研究了压电直探头中阻尼结构的几何尺寸及声阻抗对其瞬态响应的影响,得到了压电换能器中不同时刻的弹性波场、电场分布以及输出电压响应曲线,揭示了换能器瞬态响应产生的多次反射波对其检测灵敏度和分辨率的影响。研究结果表明：通过改进的阻尼结构与材料参数对消减接收信号的多次反射,缩短余振时间具有明显的作用,也可以大大降低换能器的研发周期和成本。     

Reduction of blind zone in ultrasonic transmitter/receiver transducers

Most ultrasonic sensorial systems are based on transducers that work as emitters and receivers in the same scanning process. This fact implies that, during the emission process, the reception stage stays disabled, in order to avoid the emission coupled. This disabling interval provides that the nearest area to the transducers, the blind zone, cannot be scanned, since echoes coming from reflectors placed inside it are overlapped with the coupled emission. On the other hand, the encoding of the ultrasonic emission by binary sequences allows the process gain to be increased, so better precision is achieved and higher levels of noise are supported by the system. The length of the used binary sequence determines not only the process gain, but also the duration of the emission interval. The usage of long sequences to improve the performance also implies the existence of a larger blind zone, where reflectors are not detected. This work presents a novel encoding technique, based on Golay complementary pairs, where the dimension of the blind zone is reduced to negligible distances thanks to some features from the binary sequences.