圆形振动膜ZnO压电微传声器的研制

本文介绍了一种新型圆形振动膜ZnO压电微传声器的制备，并对传声器制备的工艺过程进行了较为详细的描述。圆形振动膜的压电传卢器与以前方形振动膜结构设计相比，较大幅度提高了传声器的灵敏度和成品率，灵敏度达到-70dB（相对于1V／Pa），成品率达到80％。     

几种管道有源降噪器控制系统频率响应函数的确定

管道有源降噪器的控制系统根据传声器检测到的噪声信号,经过加工处理,产生激励次级声源的信号,使其产生的声波在下游与原来的噪声相抵消。控制系统应具备的频率响应函数取决于次级声源及检测传声器的配置,及其本身的频率响应。本文推导了在常用的几种不同次级声源和检测传声器配置下,所需的控制系统的频率响应函数;并介绍了一种测量传声器及扬声器在管道中的频率响应的方法。它们为控制系统的设计提供了依据。     

硅微ZnO压电薄膜传声器的研制

本文介绍了一种利用ZnO压电薄膜为换能器的硅微压电薄膜传声器的制备,并且对微机械加工工艺过程进行了较为详细的描述。本文对传声器的部分结构进行改进,与通常设计相比较大幅提高了传声器的性能,1000Hz基准频率的灵敏度达到-85dB(相对于1V/Pa),500Hz到10000Hz的频率响应的平坦度在±3dB范围内。     

一种基于反馈环的全光纤干涉型传声器

设计了一种基于光纤反馈环的全光纤干涉型传声器，它直接利用声压作用于光纤时产生的光弹效应对光相位进行调制，并通过3×3耦合器构建的反馈环结构形成干涉效应，从而使得输出光信号经光电转换和放大后可以直接驱动扬声器还原出原输入语音信号。我们从理论和实验上对这种全光纤传声器进行了研究，在该传声器的重要参数测量方面均取得了较好的效果。     

测量用驻极体电容传声器

本文介绍了用于精密声学测量的驻极体电容传声器的结构、设计原理及主要性能。该种传声器的主要特点是采用金属振膜后驻极体结构,因而它既具有电容传声器的灵敏度高,频响平直、动态范围大及稳定性好等优异特性,又兼不需要外加极化电压及可在高潮湿环境下工作的特点。因此特别适宜于与微机配套而形成完整声信号提取和处理装置。在当前的声学研究及环境噪声监测等领域具有广泛应用价值。     

发展中的噪声测试仪器

文章介绍了当前国内外噪声测试仪器的现状，对测试传声器和声级计的发展状况进行了说明，并着重介绍了新兴的声强测量技术和声强测量仪的工作原理．     

传声器失配误差对差分传声器圆阵主瓣指向的影响特性

从理论上导出了传声器失配误差对适用于任意阵元数的一阶和二阶差分传声器圆阵的主瓣指向影响规律。揭示了传声器相位误差可造成一阶差分传声器圆阵主瓣指向产生反转现象,是影响其主瓣指向的主要因素。而对于二阶差分传声器圆阵,传声器相位误差和增益误差均可导致其主瓣指向产生反转现象和严重指向误差,进而造成阵列指向性因子严重下降,尤其在低频处失配误差的影响更为显著。然后给出了确保差分传声器圆阵主瓣指向正确时阵列设计参数所需满足的条件,并在此基础上进行了传声器失配误差的容差分析。分析结果表明,随着阵元数增多,失配误差的容差范围增大,差分传声器圆阵对传声器失配误差的敏感性相应降低。      

数字化声学测量技术 Ⅱ.数字式声强及声功率测量系统

本文介绍在数字声学测量分析系统中，通过双传声器信号互谱密度的计算进行声强及声功率测量的基本原理。该数学分析系统由微计算机，数字信号处理卡和Ａ／Ｄ变换卡组成。在一个数字系统中，通过快速傅里叶变换（ＦＥＴ）进行互谱计算是十分有效的。本文着重介绍了，在声强的测量分析中对声强探头两传声器的固有相位差进行补偿的重要性和补偿方法，这是声强测量的重要环节。     

强度解调的F-P干涉型光纤传声器

F-P干涉型光纤传声器具有灵敏度高、结构简单、抗电磁干扰等优势,论文针对基于强度解调的F-P干涉型光纤传声器展开研究。采用多光束干涉理论建立了系统光学模型,采用薄板小挠度弯曲理论建立了传声器振膜的声学模型,在此基础上得到传声器灵敏度的表达式。通过理论分析和仿真,得到了敏感单元结构参数对传声器灵敏度和响应频率的影响关系,并对F-P敏感结构的腔长和端面反射率进行了优化设计。应用厚度为3μm的镍膜,研制出光纤传声器样机,测得其灵敏度为268 mV/Pa、频响特性为±3 dB@50 Hz~4 kHz,可应用于恶劣环境下的声音传感。     

利用Doppler效应设计的可变指向性传声器

在天线工程的领域中,尖锐的指向性是很容易用波干涉的原理获得的。在声学领域中,利用同一原理,曾作过很多努力来实现尖锐指向性的传声器。但是,由于这类传声器必须在声讯号波长相当宽的范围内工作,所以已研制出的任何这类传声器,指向性都不是很满意的。因此,必须引进新的原理来设计指向传声器。     

光纤microphone的理论与实验研究

本文提出了一种新型的反射式光纤ｍｉｃｒｏｐｈｏｎｅ ,它把反射式光纤传感探头应用于传统的麦克风上,来实现对声波的调制．本文从理论和实验两方面给出了反射式光纤ｍｉｃｒｏｐｈｏｎｅ的光强调制函数,并对反射式光纤ｍｉｃｒｏｐｈｏｎｅ系统进行了研究．     

A simulation of condenser microphones in free field by boundary element approach

A boundary element approach to simulate the characteristics of a microphone in free field is presented. To describe the approach, a condenser microphone is considered as a typical model. The usual boundary element technique is applied to the free acoustic field outside the microphone and a new special boundary element is developed to include the effect of a very thin air layer between the diaphragm and the backplate of the microphone. The vibration of the diaphragm is expressed in terms of its normal modes which are combined with the boundary elements to find the frequency response and the directivity. A numerical example is given for the condenser microphone used as the standard microphone in acoustical measurement, in which the diffraction from the preamplifier house and the nose cone is included. The computed results are in good comparison with the measured data in the operating frequency range.     

Effects of Microphone Type on Acoustic Measures of Voice

Acoustic measures provide an objective means to describe pathological voices and are a routine component of the clinical voice examination. Because the voice sample is obtained using a microphone, microphone characteristics have the potential to influence the values of parameters obtained from a voice sample. This project examined how the choice of microphone affects key voice parameters and investigated how one might compensate for such microphone effects through filtering or by including additional parameters in the decision process. A database of 53 normal voice samples and 100 pathological voice samples was used in four experiments conducted in an anechoic chamber using four different microphones. One omnidirectional microphone and three cardioid microphones were used in these experiments. The original voice samples were presented to each microphone through a speaker located in an anechoic chamber, and the output of each microphone sampled to computer disk. Each microphone modified the frequency spectrum of the voice signal; this, in turn, affected the values of the voice parameters obtained. These microphone effects reduced the accuracy with which acoustic measures of voice could be used to discriminate pathological from normal voices. Discrimination performance improved when the microphone output was filtered to compensate for microphone frequency response. Performance also improved when spectral moment coefficient parameters were added to the vocal function parameters already in use.     

Noise in miniature microphones

The internal noise spectrum in miniature electret microphones of the type used in the manufacture of hearing aids is measured. An analogous circuit model of the microphone is empirically fit to the measured data and used to determine the important sources of noise within the microphone. The dominant noise source is found to depend on the frequency. Below 40 Hz and above 9 kHz, the dominant source is electrical noise from the amplifier circuit needed to buffer the electrical signal from the microphone diaphragm. Between approximately 40 Hz and 1 kHz, the dominant source is thermal noise originating in the acoustic flow resistance of the small hole pierced in the diaphragm to equalize barometric pressure. Between approximately 1 kHz and 9 kHz, the noise originates in the acoustic flow resistances of sound entering the microphone and propagating to the diaphragm. To further reduce the microphone internal noise in the audio band requires attacking these sources. A prototype microphone having reduced acoustical noise is measured and discussed.     

Foil electret transducer for blood pressure monitoring

A foil electret microphone for use under the cuff of an automatic blood pressure monitoring system is described. The transducer is designed to operate with relatively flat sensitivity over a static pressure range of 40 to 250 mm Hg (5.33 X 10(4) to 3.33 X 10(5) dyn/cm2). The new electret microphone differs from conventional microphones used for airborne sound reception in two ways: (1) the diaphragm thickness is 50 micron rather than the typical 12.5 or 25 micron, and (2) the backplate contains a set of annular ridges spaced at 4 mm rather than the typical 7-10 mm. This microphone offers three advantages over the piezoelectric microphone now in use: (1) greater tolerance in positioning the microphone over the brachial artery, (2) nearly 20-dB higher sensitivity and signal-to-noise ratio, and (3) the ability to obtain measurements with the microphone placed midway between the elbow and shoulder. Tests of the new foil electret microphone in conjunction with the automatic blood pressure monitoring system indicate that the automatic and conventional measurements of systolic and diastolic blood pressure agree to within 5 mm Hg at least 90% of the time. In addition, the electret microphone is able to obtain automatic measurements on subjects with a wider range of ages and sizes.     

光纤麦克风传感探头设计的理论分析

鉴于光纤传感器具有体积小、结构简单、灵敏度高、抗电磁干扰且光纤本身的低损耗、耐腐蚀和安全可靠等优良特性,将光纤传感器应用到麦克风中可使麦克风的体积显著降低而灵敏度和抗电磁干扰性显著提高。提出一种新型反射式光纤麦克风的设计方法,采用Y形单根多模反射式光纤传感探头结构形式,给出了光纤麦克风的系统框图。由光纤出射光场分布理论出发,给出弹性膜片在声场作用下,中心形变大小h与出射光光强调制函数I(Z″)的关系。根据实际应用中有关参数的取值,用Matlab软件模拟出膜片形变后变形量h与光强调制函数I(Z″)的关系曲线。     

Modelling the pressure field in the vicinity of a microphone membrane using PIV

A new approach for estimating the acoustic pressure in the near field of a microphone based on non-intrusive direct measurement of acoustic particle velocity is proposed.This method enables the estimation of the acoustic pressure inside a domain located in front of the microphone membrane. The acoustic pressure is calculated using the acoustic particle velocity on the frontiers of this domain and a physical model based on the Green function of the system.Results are obtained using the acoustic velocity measured with Particle Image Velocimetry (PIV) in front of a microphone excited with a plane wave inside a rectangular waveguide. They show that the diffraction of the plane wave by the microphone leads to an increase of the acoustic pressure on the microphone edge in the order of magnitude of 0.1 dB.     

Calibration of otoacoustic emission probe microphones

Recently, investigators of otoacoustic emissions (OAEs) have shown interest in measuring OAEs to frequencies higher than 10 kHz. Most commercial instruments used to measure OAEs do not specify the microphone frequency response at higher frequencies, nor does their typically integrated design make it convenient to measure it. OAE probes manufactured by Etymotic Research have reasonably constant microphone sensitivity up to about 10 kHz and allow direct access to both the sound sources and microphone preamplifier output. A detailed procedure for calibrating the Etymotic Research OAE probe microphone to extend its usable frequency range to frequencies up to 20 kHz is described.     

A new microphone system for near whispering

A new microphone system was developed to monitor the human voice near the microphone in a noisy environment. The system is equipped with two special functions in addition to the usual microphone functions: reduction of air-blow effects by the mouth and focused reception to a sound source. A wind filter was developed to reduce the air-blow effects from the mouth during speaking. This filter is a plate perforated by an array of small holes; the method used to design the filter is also presented. To achieve focused reception, four microphones were used in conjunction with a new signal-processing method. The proposed signal-processing method effectively increases the directivity in the desired direction. Additionally, it provides the system with focusing on the source since the source is located adjacent to the system. A prototype of the proposed system was fabricated and subjected to performance tests. The results showed that air-blow effects can be reduced by up to 20 dB and the directional gain is more than 4 dB. The proposed microphone system shows such good performance that it can be used in mobile phones for whispering communication.