Janus-Helmholtz换能器的弱辐射耦合机理与带宽特性

针对Janus-Helmholtz (JH)换能器频带内响应起伏较大、模态耦合机制尚不明确的问题,提出了振动模态声辐射独立建模方法。该方法建立换能器各个振动模的独立有限元模型,在仿真计算中将位移载荷直接加载在辐射面上,分析振动模的辐射声场。通过各个结果的对比分析,观察到JH换能器声辐射模态的弱耦合规律,最终给出JH换能器带宽特性的合理物理解释,即JH换能器在同一纵向振子激励下,由于不存在声输出明显干涉加强的模态耦合,因此难以得到通常意义上响应起伏小于3 dB的宽带工作性能。以控制工作频带内响应起伏较小为前提,将拓宽工作频带作为设计目标,优化设计了 JH换能器结构参数。实验中换能器样机的发射电压响应测试结果与仿真计算相吻合,实测谐振频率为1350 Hz与2450 Hz,谐振频率下发射电压响应分别为143 dB,141 dB,在频带1200~3300 Hz范围内响应起伏12 dB,最大声源级204 dB,实现了宽带大功率发射的特性。     

宽带宽波束纵向水声换能器研究

本文通过设计纵向水声换能器辐射头的形状及利用其弯曲振动模,实现宽带宽波束辐射特性,采用后质量块的嵌套结构有效缩小了换能器的长度。利用ANSYS有限元软件模拟了小型宽带宽波束纵向水声换能器的电声特性。研制了换能器样品,实现了与有限元模拟计算结果相一致的电声参数:谐振频率14kHz,最大发射电压响应141．9dB,-3dB带宽为11．3～18．7kHz,-3dB带通Q值为1．9,在14kHz频率下波束宽度为132°,比通常纵向换能器波束宽度宽23％。     

铁镓单晶Janus-Helmholtz换能器

针对深水、低频、宽带换能器的技术需求,结合Janus-Helmholtz换能器的结构特点和铁镓单晶材料低场应变大及机械强度高的特性,提出了铁镓单晶Janus-Helmholtz换能器设计方案。采用永磁偏磁场和环形闭合磁路,建立了一系列铁镓单晶磁致伸缩换能器理论分析模型,包括对磁致伸缩材料参数进行线性化处理,设计了换能器最佳工作点,结合静态磁场和动态磁场分布情况分段细化换能器驱动等效参数,以及利用全阻抗模型通过电感损耗等效计算换能器静态阻抗,然后通过二维有限元分析等效模型,优化分析了换能器的结构参数与电声性能。最后制作了换能器样机,并进行了测试与分析。对比仿真和测试结果表明:全阻抗模型得到的阻抗曲线与样机测试结果相一致,有限元等效模型计算的发送电流响应与样机测试结果良好吻合。换能器样机水中谐振基频为1000Hz,谐振频率下发送电流响应176.4dB;在875~2300Hz频率范围内,发送电流响应起伏不大于6dB;增加驱动电流有效值到16.2A,最大声源级可以达到196.2dB。     

四边型弯张换能器特性研究及宽带设计

四边型弯张换能器通常工作带宽较窄,为了提高带宽性能,对四边型弯张换能器振动及辐射特性进行了研究,重点分析壳体结构参数对换能器发送电压响应的影响。根据分析结果提出了拓宽换能器工作带宽的方法,利用有限元软件进行了仿真计算并制作了四边型弯张换能器样机。测量得到在2.4~5 kHz的频率范围内,换能器的最大发送电压响应值达到140 dB,带内起伏4 dB,有限元仿真结果与实验结果吻合较好。研究结果表明设计的四边型弯张换能器不仅能够低频工作,并且可以在小尺寸下实现大功率发射,同时还具备宽带发射特性。     

采用Helmholtz共鸣器与悬臂梁压电换能器的声能采集器研究

针对环境中广泛存在的声能,提出了一种采用Helmholtz共鸣器和悬臂梁压电换能器的声能采集器。Helmholtz共鸣器对入射声压进行放大,放大后的声压引起共鸣器弹性薄壁振动,薄壁的振动传递到压电换能器产生电能输出。建立了带弹性壁的立方形共鸣器的等效集中参数理论模型,并与压电换能器的机电特性结合,分析了声能采集器的声-机-电转换原理,研究了声压、声波频率和负载阻抗对输出功率的影响,研究结果为此类声能采集器的优化设计及工程应用提供了一种可行的方法。实验中,声源通过声波导管输出声能,当共鸣器管口处的声压级为94 dB时,系统实测最大输出功率达240μW。该采集器不仅可作为声能自供能采集器,还可在较远距离为低能耗电子装置进行有源声供能。     

低频宽带大功率“星型”柱面发射换能器

提出一种具有水平无指向性、低频、宽带、大功率特点的新结构换能器——“星型”柱面发射换能器,换能器由共享后质量块的6个复合棒换能器按“星型”方式组成柱面结构。采用有限元方法对换能器进行了分析设计并制作了换能器样机。在1—10 kHz内,换能器有3个主要工作模态,前两阶工作模态对换能器工作带宽的展宽有贡献,第三阶模态显示出较强的指向性,水池测试换能器具有1倍频程的工作带宽,最大声源级为199.1 dB。有限元模拟结果和实验结果符合较好。研究结果表明,新结构换能器在满足水平无指向性的前提下,利用复合棒的纵振及辐射面的弯曲振动实现了低频、宽带、大功率的要求,提供了一种设计该特性换能器的新思路。     

空气耦合电容式微超声换能器设计

建立了空气耦合电容式微超声换能器(CMUT)的理论方法,分析CMUT各个结构参数对其性能参数的影响。根据理论分析结果结合无损检测应用背景设计了一个由16个阵元构成的CMUT阵列,并采用SOI晶圆键合工艺制作。该阵列每个阵元包含16个圆形CMUT敏感单元,敏感单元的半径400μm,中心频率230 kHz。建立CMUT发射和接收瞬态仿真模型分别得到CMUT发射声压和接收灵敏度与激励电压的关系,并通过实验测试验证该仿真模型的准确性。最后通过实验对CMUT与商用压电空耦超声换能器的性能进行对比,实验结果表明CMUT的发射声压和接收灵敏度与商用换能器达到相同数量级,并且能够成功激发和接收铝合金板中A_0模态Lamb波。     

一种压电超声波物料输送器*

利用压电陶瓷元件具有良好声电转换特性和输出特性,本文提出了一种新型结构的压电超声波物料输送器。设计了超声波物料输送器的结构并分析了其工作原理,采用纵扭复合型压电换能器为驱动源,对压电换能器进行了结构设计和参数计算,并对其进行了性能测试。由此研制出了压电超声波输送器的样机并进行了试验测试,结果表明:当频率为17.9 kHz–18.6 kHz时,输送器具有输送物料能力。驱动负载为1.5 kg时系统的谐振频率为18.3 kHz,输送速度最快,达到64个/min。随着电源输出功率的增大输送物料速度呈线性增加。该输送器的稳定性好,噪声低。与压电片式和电磁式输送器噪声进行对比,超声波输送器的工作噪声仅为31 dB,略小于压电片式,远小于电磁式。     

铌酸钾钠基无铅压电陶瓷纵振换能器*

高性能环境友好型无铅压电陶瓷及其应用是当前压电材料研究的热点之一,为了探究其在水声换能器领域的应用潜力,该文对铌酸钾钠基无铅压电陶瓷和锆钛酸铅压电陶瓷纵振式换能器进行了对比研究。依据仿真结果优化结构尺寸,制作了两种换能器样机并测试了其在空气中和水中的电声性能。测试结果表明,铌酸钾钠基无铅压电陶瓷换能器的谐振频率为35kHz,最大发送电压响应为 151dB,声源级可达 190dB,在 26kHz~67kHz 的频率范围内发送电压响应的起伏不超过±4.5dB,谐振频率处-3dB 的指向性开角约为 76°。该无铅压电陶瓷换能器具有和锆钛酸铅压电陶瓷换能器相当的发射性能,有望推动无铅压电材料在水声换能器领域的应用进程。     

双壳嵌套鱼唇式弯张换能器

研究了一种双壳嵌套鱼唇式弯张换能器,针对特殊结构的空气背衬弯张换能器提出了表征换能器静压形变的系列参数,利用有限元方法研究了这些参数与结构参数的对应关系,并进行了换能器的静态分析。在静态分析基础上,研究了结构参数对换能器声辐射特性的影响,经对比分析得到换能器的优化方案,研制了实验样机,经外场试验验证了双壳嵌套鱼唇式弯张换能器具有小尺寸、频率低、高效率、大功率的工作特性:谐振频率800 Hz、最大声源级199.5 dB、电声效率23.6%、工作深度200 m。     

Cochlear generation of intermodulation distortion revealed by DPOAE frequency functions in normal and impaired ears

Distortion product otoacoustic emission (DPOAE) frequency functions were measured in normal-hearing and hearing-impaired ears. A fixed-f2/swept-f1 paradigm was used with f2 fixed at half-octave intervals from 1 to 8 kHz. L1 was always 10 dB greater than L2, and L2 was varied from 65 to 10 dB SPL in 5-dB steps. The responses were quantified by the frequency and amplitude of the peak response. Peak responses were closer to f2 in higher frequency regions and for lower intensity stimulation. Results from hearing-impaired subjects suggest that audiometric thresholds at the distortion product frequency, fdp, in addition to hearing status at f2, can affect DPOAE results. Results are discussed in terms of several manifestations of a second resonance model, as well as a dual source model for the generation of DPOAEs as measured in the ear canal of humans. It appears that a dual source model accounts for the data better than second filter models.     

Vocal intensity in speakers and singers.

Vocal intensity is studied as a function of fundamental frequency and lung pressure. A combination of analytical and empirical models is used to predict sound pressure levels from glottal waveforms of five professional tenors and twenty five normal control subjects. The glottal waveforms were obtained by inverse filtering the mouth flow. Empirical models describe features of the glottal flow waveform (peak flow, peak flow derivative, open quotient, and speed quotient) in terms of lung pressure and phonation threshold pressure, a key variable that incorporates the Fo dependence of many of the features of the glottal flow. The analytical model describes the contributions to sound pressure levels SPL by the vocal tract. Results show that SPL increases with Fo at a rate of 8-9 dB/octave provided that lung pressure is raised proportional to phonation threshold pressure. The SPL also increases at a rate of 8-9 dB per doubling of excess pressure over threshold, a new quantity that assumes considerable importance in vocal intensity calculations. For the same excess pressure over threshold, the professional tenors produced 10-12 dB greater intensity than the male nonsingers, primarily because their peak airflow was much higher for the same pressure. A simple set of rules is devised for predicting SPL from source waveforms.     

烟火药和压缩氮气声源水下声辐射特征对比研究

为研究烟火药水下燃烧声辐射机理,采用烟火药和压缩氮气喷射声源对比的方法,利用水声测试系统,通过实验研究不同体积流量下两种声源装置的声辐射规律。结果表明,烟火药水下燃烧声源与压缩氮气声源的声辐射特征相似,辐射频率主要集中在0～1000 Hz内,峰值频率均位于100 Hz附近,总声压级、峰值声压级均随着气体流量增加而增强。当气体流量从60 ml/s增加到84 ml/s时,烟火药峰值声压级由155 d B增加到163 d B,0～1000 Hz内总声压级由159 d B增加到165 d B;当喷气流量从70 ml/s增加到141 ml/s时,压缩氮气源峰值声压级由136 d B增加到139 d B,0～1000 Hz内总声压级由144 d B增加到147 d B。当气体流量相近时,烟火药相比压缩氮气声压级相差显著,其声压级均高于同频率下压缩氮气源,两者的峰值声压级分别为157 d B、139 d B,0～1000 Hz内总声压级分别为160 d B、147 d B。     

Distortion product otoacoustic emissions and basilar membrane vibration in the 6-9 kHz region of sensitive chinchilla cochleae

Distortion product otoacoustic emissions (DPOAEs) and basilar membrane (BM) vibration were measured simultaneously in the 6-9 kHz region of chinchilla cochleae. BM-Input-Output functions in a two-tone paradigm behaved similarly to DPOAEs for the 2f1-f2 component, nonmonotonic growth with the intensity of the lower frequency primary and a notch in the functions around 60 dB SPL. Ripples in frequency functions occur in both BM and OAE curves as a function of the distortion frequency. Optimum f2/f1 ratios for DPOAE generation are near 1.2. The slope of phase curves indicates that for low f2f1(<1.1) the emission source is the place location while for f2f1>1.1 the relative constancy of the phase function suggests that the place is the nonlinear region of f2, i.e., the wave location. Magnitudes of the DPOAEs increase rapidly above 60 dB SPL suggesting a different source or mechanism at high levels. This is supported by the observation that the high level DPOAE and BM-DP responses remain for a considerable period postmortem.     

声光调Q CO2激光器的输出特性

采用谐振腔内插入声光调制器（AOM）的方法获得了小型CO2激光器的高重频、窄脉宽、高峰值功率输出。通过分析CO2激光器声光调Q的工作原理,利用基于小信号增益和饱和光强的耦合输出数学模型给出了激光器最佳输出镜透过率的数值解,并运用相关实验装置对该数学模型进行了实验验证。理论分析和实验结果均表明：该声光调Q CO2激光器的最佳输出镜透过率为39%。研究了激光器输出性能随脉冲重复频率的变化规律,当脉冲重复频率〉1 kHz时,激光器输出峰值功率下降,这与CO2分子上能级寿命有关,并受声光调Q开关热效应的影响。实验中获得的激光器脉冲频率在1 Hz～100 kHz可调。在脉冲频率为1 kHz时,获得的激光脉冲宽度为156 ns,脉冲峰值功率为10 kW,且稳定性较好,非常适合于作激光与物质相互作用的光源。     

The influence of systematic primary-tone level variation L2-L1 on the acoustic distortion product emission 2f1-f2 in normal human ears

The purpose of the present study was to determine the effect of primary-tone level variation, L2--L1, on the amplitude of distortion-product otoacoustic emissions (DPOAEs). The DPOAE at the frequency 2f1--f2 (f2 greater than f1) was measured in 20 ears of ten normally hearing subjects. Acoustic distortion products were generated by primaries f1 and f2 with geometric mean frequencies of 1, 2, and 4 kHz. The f2/f1 ratios were 1.25 (1 kHz), 1.23 (2 kHz), and 1.21 (4 kHz). The primary-tone level L1 was kept constant at either 65 or 75 dB SPL while the second primary-tone level L2 was varied between 20 and 90 dB SPL in 5-dB steps. The level differences L2--L1 generating maximal DPOAE amplitudes depended on L1 and on the geometric mean frequency of f1 and f2. There were large interindividual differences. Overall, the L2--L1 evoking maximal mean DPOAE amplitudes was --10 dB for geometric mean frequencies of 1 and 2 kHz with both L1 = 65 dB SPL and L1 = 75 dB SPL. For 4 kHz, L2-L1 was --5 dB with L1 = 65 dB SPL and 0 dB with L1 = 75 dB SPL. The mean slopes of the DPOAE growth functions in the initial linearly increasing portions were steeper at higher stimulus frequencies, increasing from 0.52 at 1 kHz to 0.72 at 4 kHz for L1 = 65 dB SPL and from 0.48 at 1 kHz to 0.72 at 4 kHz for L1 = 75 dB SPL.     

Siamang gibbons exceed the saccular threshold: intensity of the song of Hylobates syndactylus

Measurements are reported of the intensity of the siamang gibbon loud call obtained from the vocal bouts of three family groups at Twycross Zoo, UK. Across 25 samples the maximum intensity ranged from 95 to 113 dB SPL (linear frequency-weighting and fast time-weighting) and exhibited three frequency modes of 250-315 Hz, 630-800 Hz and 1.2-1.6 kHz. The lowest frequency mode, which may correspond to the "boom" sound produced by resonance of the siamang inflated vocal sac, had a mean maximum intensity of 99 dB SPL. These values, which are in excess of the saccular acoustic threshold of about 90 dB at 300 Hz for air conducted sound, suggest that primate loud calls recruit a primitive mode of acoustic sensitivity furnished by the sacculus. Thus reproductive vocal behavior of primates may be influenced by a primitive acoustical reward pathway inherited from a common ancestor with anamniotes. In humans such a pathway could explain the compulsion for exposure to loud music.     

Intensity discrimination as a function of level and frequency and its relation to high-frequency hearing

This paper examines how intensity discrimination depends on the test frequency, the level, and the subjects's high-frequency hearing. Three experiments were performed. In the first experiment, intensity discrimination of pulsed tones was measured as a function of level at 1 and 14 kHz in five listeners. Results show less deviation from Weber's law at 14 kHz than at 1 kHz. In the second experiment, intensity discrimination was measured for a 1-kHz tone at 90-dB SPL as a function of the cutoff frequency of a high-pass masking noise in two listeners. Results show that the audibility of very high frequencies is important for frequency discrimination at 1 kHz. The DL increased by a factor between 1.5 and 2.0 as the cutoff frequency of the noise was lowered from 19 to 6 kHz. In the third experiment, thresholds from 6 to 20 kHz and intensity discrimination for a 1-kHz tone was measured in 12 listeners. Results show that the DLs at 80-dB SPL are correlated with the ability to hear very high frequencies. Results of all three experiments are consistent with the multiband version of the excitation-pattern model for intensity discrimination [Florentine and Buus, J. Acoust. Soc. Am. 70, 1646-1654 (1981)].     

Lateralization and frequency selectivity in normal and impaired hearing

The onset-time difference delta T required to lateralize a 30-ms bifrequency tone burst toward the leading ear was measured as a function of the frequency difference delta F between the tone in the left ear and the tone in the right ear. At center frequencies of 0.5 and 4 kHz, four normal listeners tested at 80 and 100 dB SPL had delta Ts that were relatively constant at subcritical delta Fs, but increased at delta Fs wider than a critical band. At 1 kHz, delta T increased with delta F even at subcritical delta Fs. Ten listeners with cochlear impairments were tested at 100 dB SPL. Seven had normal delta Ts at 4 kHz, despite hearing losses between 50 and 70 dB. At 0.5 and 1 kHz, mildly impaired listeners had nearly normal lateralization functions, whereas more severely imparied listeners had very large delta Ts and no frequency selectivity. These and other findings indicate that listeners even with moderate to severe hearing losses can lateralize normally on the basis of interaural differences in onset envelope, but not on the basis of temporal differences in the fine structure.     

The effect of pure-tone forward masking on overshoot

The overshoot effect can be reduced by temporary hearing loss induced by aspirin or exposure to intense sound. The present study simulated a hearing loss at 4.0 kHz via pure-tone forward masking and examined the effect of the simulation on threshold for a 10-ms, 4.0-kHz signal presented 1 ms after the onset of a 400-ms, broadband noise masker whose spectrum level was 20 dB SPL. Masker frequency was 3.6, 4.0, or 4.2 kHz, and masker level was 80 dB SPL. Subject-dependent delays were determined such that 10 or 20 dB of masking at 4.0 kHz was produced. In general, the pure-tone forward masker did not reduce the simultaneous-masked threshold, suggesting that elevating threshold with a pure-tone forward masker does not sufficiently simulate the effect of a temporary hearing loss on overshoot.