准一维电子通道中声电电流的理论计算

表面声波在GaAs/Al _x Ga_1-x As异质结表面上沿由分裂门产生的准一维电子通道方向传 播时，在通道中诱导产生声电电流.采用WKB近似，计算了只有一个电子被量子阱俘获时的声电电流；并在此基础上，详细讨论了表面声波的频率和功率，以及门电压和源漏偏压对声电电流的影响. 关键词： 表面声波 准一维电子通道 量子阱 声电电流     

声诱导电磁场的赫兹矢量表示与多极声电测井模拟

在假设声场不受电磁场影响的前提下，将Pride声电耦合方程组化为具有电流源的麦克斯韦方程组.与空间位置固定的电流源产生的电磁场不同，孔隙地层中声波诱导的电磁场是由空间波动的电流源产生的.通过引入赫兹矢量，将求解麦克斯韦方程组问题转化为求解关于赫兹矢量的非齐次矢量赫姆霍兹方程组.通过求解该方程组，得出电磁场表达式.利用此方法，针对声电效应测井，分别计算了由单极声源、偶极声源、四极声源激发的井内声场及其诱导电磁场的全波波形. 关键词： 孔隙介质 诱导电磁场 测井 多极声源     

时林－声力克低频声波锅炉除灰技术简介

时林－声力克低频声波锅炉除灰技术简介声波锅炉除灰是指利用声波能量的作用，清除锅炉换热器表面积灰和结焦，以达到恢复锅炉的热效率，保证锅炉正常运转并改善其运行状态的目的．＂时林一声力克＂低频声波锅炉除灰技术是由中国科学院声学研究所与北京时林电脑公司五音声...     

水下声辐射激励水表面声波的特征参数测量

采用激光干涉方法对水下声辐射激励水表面声波的特征参数频率和振幅进行了测量研究。从理论上对水表面声波激光相干测量信号的频谱构成进行了分析,在此基础上提出了水表面声波两个重要声学参数频率和振幅的解算方法,并通过数值仿真进行了验证。搭建了一套简单的激光干涉测量实验系统,对不同频率和声压激励的水表面声波进行了测量实验,验证了水表面声波频率和振幅解调方法的准确性。对水表面声波横向传播的振幅衰减现象进行了初步的实验研究,结果表明水表面声波的频率越高,振幅的横向衰减越快。研究表明激光相干检测方法能够准确地实现水表面声波振幅和频率的测量。      

水下低频声信号的激光探测及波的衰减

为了探测几十赫兹的低频水下声信号,建立了水下低频声信号的光学探测系统,得到了稳定、清晰的衍射图样.得到了衍射图样的宽度与声源距离的变化关系,声源距离越小,衍射图样越宽.当水下声波传至水表面后,实验上得到了表面声波的衰减特性,理论上得到了衍射图样的角宽度和液体表面波振幅的解析关系式.发现表面波振幅的衰减随距离是指数型衰减.并研究了衰减系数随频率的变化,频率不同衰减系数也不同,而且频率越大,衰减系数越小.     

水下低频声信号的激光探测及波的衰减

为了探测几十赫兹的低频水下声信号,建立了水下低频声信号的光学探测系统,得到了稳定、清晰的衍射图样.得到了衍射图样的宽度与声源距离的变化关系,声源距离越小,衍射图样越宽.当水下声波传至水表面后,实验上得到了表面声波的衰减特性,理论上得到了衍射图样的角宽度和液体表面波振幅的解析关系式.发现表面波振幅的衰减随距离是指数型衰减.并研究了衰减系数随频率的变化,频率不同衰减系数也不同,而且频率越大,衰减系数越小.     

新型功能材料——声子晶体

声子晶体是20世纪90年代初提出的一种新型声学功能材料，这种周期性弹性结构具有许多重要性质，如声波带隙特性，即处于禁带频率范围内的振动或声波将被禁止在晶体中传播。通过求解声波在晶体中的运动方程可以设计一定的声子禁带和允带，而声子禁带与声波异质结构中声子的安德森局域化问题密切相关。文章重点阐述了声子晶体的主要特征、理论研究方法、潜在应用及前景展望。     

原油中声衰减和声速的温度特性的测量

原油是一种混合物。它的一些性质随温度而变，如原油的声衰减和声速都是温度的函数．本文使用一个换能器发射声波，另一个换能器接收声波，在实验室内测得12t－80℃之间的声波幅度值，利用插值算法，求出该温度范围内原油声衰减的温度特性曲线；利用线性拟合算法，求出原油声速的温度特性曲线。结果表明：随着温度的升高，原油的声衰减和声速都呈下降趋势，而且测量结果与换能器的灵敏度无关．     

托卡马克等离子体环向转动对测地声模的影响

采用回旋动理学方程推导得到了环向转动托卡马克等离子体中测地声模的色散关系,分析了环向转动对测地声模、低频模和声波分支的频率以及无碰撞阻尼率的影响。结果表明,测地声模的频率会随着环向转动马赫数而逐渐增大,而其无碰撞阻尼率则会随着环向转动马赫数而迅速减小。此外,低频模和声波分支的频率以及无碰撞阻尼率都会随着环向转动马赫数而逐渐减小,其中环向转动对声波分支的频率以及无碰撞阻尼率的影响非常小,基本上可以忽略。     

电-声超导电性的对称理论

利用新的库珀对平均汤近似，导出了电－声系统中声子－库珀对有效作用，证明了声子通过交换虚的库珀对能够产生一个有效的吸引力，导致两动量相反的声子配对并构成稳定的声超导态。发现电子超导态与声子超导态的直积能构成稳定的电－声对称的高温超导基态。在声子－库珀对弱耦合极限下，基态对称破缺成为传统的ＢＣＳ基态。     

单极随钻声波测井换能器感知信号类型的研究

在假定钻铤是光滑的提前下，前人理论模拟了随钻测井的声压波形，但未发表关于理论波形与实验波形的比较的文章。为了认识测量信号所对应的力学类型及相应类型的钻铤波在钻铤内的分布，本文将理论模拟的随钻声波测井波形与实验波形进行对比。与前人单独考虑压电效应或井孔传播效应不同，本文模拟单极随钻声波测井响应时，将发射器、接收器、光滑钻铤和井孔结构作为一个整体，采用有限元法计算模拟了电压源激励下接收器纪录的声压信号和位移信号。将模拟的声压波形与电压信号进行比较，发现二者的钻铤波与斯通利波相对幅值相差较大，而模拟的径向位移波形更接近电压信号。进一步比较理论波形与小模型井内实验测量到的电压信号，证实电压信号更接近位移信号而与声压信号差异明显。这表明当钻铤光滑时，单极随钻声波测井换能器感知的主要是径向位移信号。研究还表明声压信号中的钻铤波能量主要集中在钻铤内壁，径向位移信号中的钻铤波能量主要集中在钻铤外壁。     

压电瞬态响应在换能器声功率测量中的应用

探索一种简便的聚焦超声功率测量方法,利用压电陶瓷片直接接收超声信号,通过机电类比得到压电瞬态响应由压电片在声波作用力下引起受迫振动产生的电压响应与固有振动产生的高频衰减响应叠加而成,分析输出压电信号与换能器声功率之间的换算关系。对输出压电信号进行二次包络提取,获得表征声功率变化的电压幅度曲线,分别找出不同换能器驱动电压下包络曲线的最大峰值电压,将其平方值与声功率计所测声功率进行线性拟合,并对理论关系式中的比例系数进行标定。实验结果所得线性拟合度较高,且标定后所得声功率与声功率计所测值相对误差低于8.7%,证明了通过压电瞬态响应测量换能器声功率具有可行性。      

Evaluating the maximum playback sound levels from portable digital audio players

To assess the maximum sound levels that may be experienced by young people in Canada from modern digital audio players, this study measured nine recent models of players and 20 earphones. Measurement methodology followed European standard BS EN 50332. Playback levels ranged from 101 to 107 dBA at maximum volume level. Estimated listener sound levels could vary from 79 to 125 dBA due to the following factors: (i) earphone seal against the ear, (ii) player output voltage, (iii) earphone sensitivity, and (iv) recorded music levels. There was a greater potential for high sound levels if intra-concha "earbud" earphones were used due to the effect of earphone seal. Simpler measurement techniques were explored as field test methods; the best results were obtained by sealing the microphone of a sound level meter to the earphone using a cupped hand and correcting for the free field response of the ear. Measurement of noise levels 0.25 m from the earphone showed that a bystander is unlikely to accurately judge listener sound levels.     

依据扬声器的力学性质拓展其低频响应的电路原理初探

本文阐述了在低频段闭箱上扬声器轴向远场声压频平坦时，分别作用于扬声器阻尼，质量和弹性三元件上的力，以及这三个力与频率的关系以及这三个力间的相位关系，根据这些关系，提出了一种处理声频信号电压的电路原理，该电路将声频信号电压处理为分别上述作用于三元件上的力相对应的三个信号电压，这三信号电压相加后，再馈于扬声器，可拓展其低频响应。     

3-D voltage model for detection of sound radiated from anisotropic materials

The elastic behavior of composite materials has been characterized experimentally by employing a 3-D voltage calculation to model transmission or reflection experiments. With sound propagation along material symmetry directions, integration over the incident-plane angle alone is generally sufficient to model the transducer voltage accurately. In general material directions this integration must be extended to account for asymmetrical variations in the reflection or transmission coefficient out of the incident plane. Theoretical and experimental results illustrate this effect and the relationship between 2-D and 3-D calculations. Experimental measurements are used to in the reconstruction of viscoelastic properties in composite plates. The influence of the phi-dependent integration on the voltage, in the 3-D calculation, is particularly strong when the incident angles are small and the wave paths are large, as typically experienced in air-coupled measurements.     

多应用智能排风扇

设计了一种利用电压比较器对空气传感器检测到的信息进行分析、处理、在发出警报的同时继电器自动控制排风扇净化室内空气的多应用智能排风扇。     

Information contained in the radiating ultrasound during ultrasonic welding

During ultrasonic welding, unnecessary ultrasound together with audible sound is radiated into the air. Audible sound is noisy and uncomfortable, and ultrasound may have bed effects on adjacent equipment. However, it is considered that these sounds potentially contain useful information such as welding state. This article reports the relationship between radiated ultrasound and the change of the welding state during ultrasonic welding. It is known that the welding state can be presumed from the change of the mechanical load impedance, which can be calculated from resonant frequency, motional voltage and the driving current of the vibrating system for the welder when a constant-velocity motional-feedback power oscillator is used. In this study, radiated ultrasound picked up with a microphone and an amplifier is recorded and analyzed with a personal computer. Analyzed results are compared with the change of the mechanical load impedance that is also calculated from the recorded data of the resonant frequency, motional voltage and the driving current of the vibrating system for the welding. Experiments were made on the ultrasonic welding of plastic rods. The relationship between the parameters of radiated ultrasound and the electrical parameters of the vibrating system were compared. The peak amplitude of the radiated ultrasound and the mechanical impedance versus time were very similar. It is shown in this study that radiated ultrasound contains lots of useful information.     

Transport of magnetic vortices by surface acoustic waves

In a thin film of superconducting Y Ba₂Cu₃O₇ the impact of surface acoustic waves (SAWs) traveling on the piezoelectric substrate is investigated. A pronounced interaction between the ultrasonic waves and the vortex system in the type II superconductor is observed. The occurrence of a SAW-induced dc voltage perpendicular to the sound path is interpreted as dragging of vortices by the piezoacoustic SAW, which acts as a conveyor for the flux quanta. The antisymmetry of this voltage with respect to the magnetic field directly evidences the induced, directed flux motion. This dynamic manipulation of vortices can be seen as an important step towards flux-based electronic devices.     

Semicylindrical acoustic transducer from a dielectric elastomer film with compliant electrodes

A semicylindrical acoustic transducer was constructed using a dielectric elastomer film with compliant electrodes that is an electroactive polymer composed of a polyurethane elastomer base and polyethylene dioxythiophene/polystyrene sulfonate electrodes. The use of this dielectric elastomer is advantageous because polyurethane is a common material that keeps its shape without any rigid frame. Because the dielectric elastomer films are essentially incompressible, electric-field-induced thickness changes are usually translated into much larger changes of the film area and side length. Here it is proposed that this change in side length can be utilized for sound generation when the film is bent into a semicylindrical shape. Accordingly, a semicylindrical acoustic transducer was fabricated using a film of thickness of 300 μm and its acoustic characteristics were investigated. The transducer can be operated at low applied voltages by reducing the film thickness, as long as the film is thick enough to generate sufficient force to overcome sound radiation impedance. The second harmonic distortion of the transducer was also investigated as a function of the ratio of the direct current bias voltage to the alternating current audio signal amplitude.     

Time-frequency analysis for pulse driven ultrasonic microscopy for biological tissue characterization

The authors have proposed a new type of ultrasonic microscopy for biological tissue characterization. The system is driven by a nanosecond pulse voltage, the generated acoustic wave being reflected at the front and rear side of the sliced tissue. In this report, a time-frequency analysis was applied to determine the sound speed thorough the tissue. Frequency dependence of sound speed was obtained with a myocardium of a rat sliced into 10 microm. As the reflected waveform had a significant amount of oscillating component, the waveform was once subjected to the deconvolution process. As the result, two reflections were clearly separated in time domain. Then these two reflections were separately analyzed by time-frequency analysis. Each reflection was extracted by using a proper window function. Phase angles of these reflections at the same frequency were compared. A sound speed micrograph at an arbitrary frequency in between 50 and 150 MHz was successfully obtained. A tendency was found that the sound speed slightly increases with frequency.