Human motion analyses using footstep ultrasound and Doppler ultrasound

Human footsteps generate periodic broadband frequency envelopes of sound due to dynamic friction forces. Also, human body motion when walking is a cyclic temporal process. The individual body parts have different acoustic cross sections and velocities that form unique human Doppler signatures. The paper introduces an approach to analyze this motion using passive and active ultrasound. The passive method employs a narrowband microphone that is sensitive to the sound from footsteps. The active method utilizes continuous-wave ultrasound to measure the Doppler shifted signal from the body appendages. These two methods show time synchronization between Doppler and ultrasonic human footstep signatures.     

Ultrasonic wave generation due to human footsteps on the ground

Human footsteps generate broadband frequency vibrations in the ground/floor and sound in the air from a few Hertz up to ultrasonic frequencies due to striking and sliding contacts between a foot and the ground/floor. The high-frequency (above 1 kHz) vibrations from footsteps were detected on a building floor, but were not detected on the outdoor ground, even at 1 m from a walker. This paper presents results of ultrasound registration from footsteps on the ground at greater distances. Results are based on sound measurements in air, since the sound absorption in air is less than vibration absorption in the ground.     

Rhythm analysis of orthogonal signals from human walking

In physical terms, periodic movements of a human body resulting from walking produce a pulse sequence with repetition time T(1) (instant cadence frequency, 1/T(1)) and duration time T(2). Footstep forces generate periodic T(1) broadband seismic and sound signals due to the dynamic forces between the foot and the ground/floor with duration time T(2), which is equal to the time interval for a single footstep from heel strike to toe slap and weight transfer. In a human gait study (for normal speeds of walking), T(1) was detected as 0.5-0.69 s and double limb support takes up about 12% of the gait cycle (2T(1)), so T(2) is greater than 0.12-0.17 s. Short range (of about 50 m) signatures for 30 humans were recorded simultaneously by four orthogonal sensor types at two locations. The sensor types were active Doppler sonar/radar and passive seismic/acoustics. Analysis of signals from these four sensors collected for walking humans showed temporal synchronization and stability of the cadence frequencies, and the cadence frequency from each sensor was equivalent. The time delay between signals from these sensors due to the differences in speeds of propagation for seismic, sound, and electromagnetic waves allows calculation of the distance from a walker to the sensor suite.     

基于低频吸声超构材料的复合消声器研究*

针对管道内低频噪声难以抑制的问题，本文基于亥姆霍兹共振腔（HR）阵列吸声板和穿孔管消声器组合，设计了一种复合式宽带消声器。首先利用有限元法仿真分析传统穿孔管消声器，发现中低频消声能力较差，通过嵌入HR阵列吸声板吸收中低频噪声。采用仿真与实验的方式研究吸声板的声学性能：在400-1000 Hz频段内的平均吸声系数达到了0.88。然后对复合式消声器进行数值模拟及3D打印阻抗管实验测试对比：复合式消声器在400-1718Hz频率范围内的平均传递损失为18.15 dB ，最终实现了管道内全频带噪声有效控制。     

局域共振复合单元声子晶体结构的低频带隙特性研究

本文提出了一种新型局域共振复合单元声子晶体结构, 并结合有限元方法对结构的带隙机理及低频共振带隙特性进行了分析和研究. 共振带隙产生的频率位置由所对应的局域共振模态的固有频率决定, 并且带隙宽度与局域共振模态的品质因子及其与基体之间的耦合作用强度有关. 采用局域共振复合单元结构可以实现声子晶体的多重共振, 在低频范围能打开多条共振带隙, 但受到共振单元排列方式的的影响. 由于纵向和横向局域共振模态的简并, 复合单元结构能在200 Hz以下的低频范围打开超过60%宽度的共振带隙, 最低带隙频率低至18 Hz. 这为声子晶体结构获得低频、超低频带隙提供了一种有效的方法. 关键词： 局域共振 低频带隙 复合单元 声子晶体     

Effect of woodwool shuttering in party floors on the flanking transmission of sound between maisonettes

The sound insulation of party walls in a four storey block of maisonettes was found to be considerably lower at first floor level than at other floor levels in the frequency range of approximately 600 to 3000 Hz. The rooms at first floor level lie immediately below the party floor which is built of dense concrete cast on woodwool shuttering, plastered beneath; the other floors are timber joist floors and this seems to be the only major difference in construction at different floor levels. Vibration measurements indicated that appreciable flanking transmission of sound was occurring through the ceiling in the frequency range 600 to 3000 Hz and it seems probable that the use of woodwool shuttering has led to a resonance effect producing these high vibration levels.     

Optimal design of PZT actuators in active structural acoustic control of a cylindrical shell with a floor partition

Genetic algorithms (GAs) are employed to optimize locations of PZT actuators in an active structural acoustic control (ASAC) system comprising a cylindrical shell with an internal floor partition. The effect of PZT actuators is simulated using a bending model and an in-plane force model, respectively. The characteristics of the optimal placements of both models are discussed and compared. Numerical simulations demonstrate that for the investigated structure, the in-plane force model has a better control performance than the bending model in the low-frequency range. The underlying physics of the control results are analyzed. Considering the practical applicability of optimally designed ASAC systems, the control performance of the optimal configuration obtained at a single frequency is assessed in the low-frequency range between 100 and 500 Hz, with results showing a significant sound attenuation in the whole range of interest.     

Effect of source spectrum on sound localization in an everyday reverberant room

Two experiments explored how frequency content impacts sound localization for sounds containing reverberant energy. Virtual sound sources from thirteen lateral angles and four distances were simulated in the frontal horizontal plane using binaural room impulse responses measured in an everyday office. Experiment 1 compared localization judgments for one-octave-wide noise centered at either 750 Hz (low) or 6000 Hz (high). For both band-limited noises, perceived lateral angle varied monotonically with source angle. For frontal sources, perceived locations were similar for low- and high-frequency noise; however, for lateral sources, localization was less accurate for low-frequency noise than for high-frequency noise. With increasing source distance, judgments of both noises became more biased toward the median plane, an effect that was greater for low-frequency noise than for high-frequency noise. In Experiment 2, simultaneous presentation of low- and high-frequency noises yielded performance that was less accurate than that for high-frequency noise, but equal to or better than for low-frequency noise. Results suggest that listeners perceptually weight low-frequency information heavily, even in reverberant conditions where high-frequency stimuli are localized more accurately. These findings show that listeners do not always optimally adjust how localization cues are integrated over frequency in reverberant settings.     

充液管路系统流体声与结构声的复合有源控制

采用基于谐频自适应控制算法的有源消声与消振系统对充液管路系统突出的低频线谱噪声进行有源控制实验研究.建立了泵水循环管路实验系统,在管路中安装有源消声器对流体声进行控制,在管路出口障板上采用8×8通道有源消振系统控制结构声辐射。开展的低频线谱噪声与振动有源控制实验结果表明,在50~200 Hz频带内,通过结合有源噪声与振动控制可在多数频点取得10 dB以上的降噪效果。针对该实验系统,通过分别控制流体声和结构声分析了两者的贡献.实验结果验证了有源消声与消振系统具有较好的降噪性能,各频点处流体声与结构声占比情况不同,需要综合控制流体声与结构声才可以取得显著的降噪效果。      

薄膜型声学超材料对低频振动的隔声特性分析*

高效共振混合机工作频率为60 Hz,且系统处于共振,产生较大低频噪声。针对振动机械产生的有害噪声,分析了高效共振混合机低频高加速度共振混合过程的特点,得到了60 Hz低频声波穿透力强特点,相比传统的以吸声材料构建的50~100 mm厚度、隔声效果小于10 dB的隔声罩,分析了薄膜型声学超材料在低频减振降噪中的隔声特性。通过多物理场仿真分析,60 Hz时隔声量为31.4 dB,确定了硅橡胶弹性薄膜的预应力和质量块的面密度;采用3D打印机快速成型技术,构建了隔声实验装置,分析了独立隔声单元、面密度、薄膜尺寸等隔声特性规律。基于人耳在实际环境中感受到的噪声强度,提出了噪声衰减量和插入损失的分析方法,在距离声源380 mm和1000 mm的位置,60 Hz时隔声量分别为27 dB和38 dB。研究成果丰富了低频隔声特性理论,为薄膜型声学超材料的工程设计和优化提供了技术支撑。     

基于深度学习的低频宽带隔声器件设计*

在实际应用中，通常需要将多个声人工结构单元进行组合来实现低频宽带的隔声降噪。这种组合结构往往参数较多，传统的设计方法很难对其进行高效的自动化设计。本文在集总参数模型的基础上，提出了一种基于深度学习的低频宽带隔声器件设计方法，并基于该方法完成了由9个二阶亥姆霍兹共鸣器单元组合而成的低频宽带隔声装置的设计。仿真结果表明，该隔声装置在158 Hz~522 Hz范围内均具有良好的隔声效果，从而验证了所提出方法的有效性。与传统方法相比，本文所提出的设计方法不仅减少了对设计者专业知识和设计经验的依赖，而且具有更高的设计效率，更强的通用性，未来有望进一步推广至其他声人工结构的设计领域。     

小波尺度相关滤波及其改进算法在电火花声源信号处理中的应用

分析提取宽带电火花声源信号,受到船舶辐射噪声的严重干扰,在5 kHz以下的能量集中区信噪比低,且二者Lipschitz指数特性相近,传统基于相邻尺度相关的滤波算法抗干扰能力有限。根据宽带电火花声源信号不同频带所受干扰的不同,信噪比较高的小尺度高频小波系数,采用相邻尺度相关的滤波算法;信噪比较低的大尺度中低频小波系数,采用跨尺度相关的滤波算法,并对算法中阈值系数的选取方法进行修正。结果表明,该算法滤波效果良好,有效的提取了电火花声源信号,适合窄带强干扰背景噪声下的宽带水声信号处理。      

Real-time monitoring of structural vibration using spectral-domain optical coherence tomography

We report in this paper the development of a spectral-domain optical coherence vibration tomography (OCVT) using a broadband CCD-based spectrometer and a short-coherence white light source. We demonstrate that both the vibration amplitude and frequency can be quantified, in the frequency range 0-250 Hz, with an axial resolution of 1 μm. Furthermore, the inner structure (layer thickness) of a vibrating sample can also be quantified simultaneously. The developed OCVT is non-contact and noninvasive in nature, thus is ideal for real time and in situ monitoring of low-frequency micro-vibrations that have critical impacts on many high-precision manufacturing and engineering processes.     

LOCAL-MODE RESONANCE AND ITS STRUCTURAL EFFECTS UNDER HORIZONTAL GROUND SHOCK EXCITATIONS

The dynamic response of building structures has been studied extensively for relatively low-frequency seismic actions, and it is established that the seismic response generally is governed by the global-mode vibration, i.e., the vibration in terms of the floor movement. Much less fundamental study has been done regarding the structural response to ground shock excitations with principal frequencies many times of the fundamental frequency of the structural system. Most of the existing code provisions on ground shock control have U001remained empirical. In this paper, it is demonstrated through numerical study and laboratory model testing that the structural response to high-frequency ground shocks have distinctive characteristics as compared to the seismic response, and most significant is the participation of the vibration at the local elemental level. Local-mode resonance could occur when the shock frequency is sufficiently high, and to a large extent it can be uncoupled from the global floor vibration. As a result, large force effects can develop at relatively small floor displacement, rendering the conventional displacement-based criteria inapplicable, while more focus on the stress-strain response is deemed necessary. The results pave a way for further development of more rational criteria for this category of the structural vibration problems.     

Optimization of locally resonant acoustic metamaterials on underwater sound absorption characteristics

The study of acoustic metamaterials, also known as locally resonant sonic materials, has recently focused on the topic of underwater sound absorption. The high absorption occurs only within a narrow frequency band around the locally resonant frequency. Nevertheless, this problem can be addressed through a combination of several acoustic metamaterial layers that have different resonant frequencies. In this paper, an optimization scheme, a genetic and a general nonlinear constrained algorithm, is utilized to enhance the low-frequency underwater sound absorption of an acoustic metamaterial slab with several layers. Both the physical and structural parameters of the acoustic metamaterial slab are optimized to enlarge the absorption band. In addition, the sound absorption mechanism of the acoustic metamaterial slab is also analyzed. The result shows that each layer is found to oscillate as a nearly independent unit at its corresponding resonant frequency. The theoretical and experimental results both demonstrate that the optimized metamaterial slab can achieve a broadband (800–2500 Hz) absorption of underwater sound, which is a helpful guidance on the design of anechoic coatings.     

Optimal synthesis of 2D phononic crystals for broadband frequency isolation

The spatial distribution of material phases within a periodic composite can be engineered to produce band gaps in its frequency spectrum. Applications for such composite materials include vibration and sound isolation. Previous research focused on utilizing topology optimization techniques to design two-dimensional (2D) periodic materials with a maximized band gap around a particular frequency or between two particular dispersion branches. While sizable band gaps can be realized, the possibility remains that the frequency bandwidth of the load that is to be isolated might exceed the size of the band gap. In this paper, genetic algorithms are used to design squared bi-material unit cells with a maximized sum of band-gap widths, with or without normalization relative to the central frequency of each band gap, over a prescribed total frequency range of interest. The optimized unit cells therefore exhibit broadband frequency isolation characteristics. The effects of the ratios of contrasting material properties are also studied. The designed cells are subsequently used, with varying levels of material damping, to form a finite vibration isolation structure, which is subjected to broadband loading conditions. Excellent isolation properties of the synthesized material are demonstrated for this structure.     

Optimal synthesis of 2D phononic crystals for broadband frequency isolation

The spatial distribution of material phases within a periodic composite can be engineered to produce band gaps in its frequency spectrum. Applications for such composite materials include vibration and sound isolation. Previous research focused on utilizing topology optimization techniques to design two-dimensional (2D) periodic materials with a maximized band gap around a particular frequency or between two particular dispersion branches. While sizable band gaps can be realized, the possibility remains that the frequency bandwidth of the load that is to be isolated might exceed the size of the band gap. In this paper, genetic algorithms are used to design squared bi-material unit cells with a maximized sum of band-gap widths, with or without normalization relative to the central frequency of each band gap, over a prescribed total frequency range of interest. The optimized unit cells therefore exhibit broadband frequency isolation characteristics. The effects of the ratios of contrasting material properties are also studied. The designed cells are subsequently used, with varying levels of material damping, to form a finite vibration isolation structure, which is subjected to broadband loading conditions. Excellent isolation properties of the synthesized material are demonstrated for this structure.     

Broadband low-frequency acoustic absorber based on metaporous composite

Broadband absorption of low-frequency sound waves via a deep subwavelength structure is of great and ongoing interest in research and engineering. Here, we numerically and experimentally present a design of a broadband low-frequency absorber based on an acoustic metaporous composite (AMC). The AMC absorber is constructed by embedding a single metamaterial resonator into a porous layer. The finite element simulations show that a high absorption (absorptance A>0.8) can be achieved within a broad frequency range (from 290 Hz to 1074 Hz), while the thickness of AMC is 1/13 of the corresponding wavelength at 290 Hz. The broadband and high-efficiency performances of the absorber are attributed to the coupling between the two resonant absorptions and the trapped mode. The numerical simulations and experimental results are obtained to be in good agreement with each other. Moreover, the high broadband absorption can be maintained under random incident acoustic waves. The proposed absorber provides potential applications in low-frequency noise reduction especially when limited space is demanded.     

Responses of pigeon vestibular nerve fibers to sound and vibration with audiofrequencies

Single unit recordings were made from the nerve branch innervating the crista in the horizontal semicircular canal of a pigeon. The vestibular organ was either stimulated with sound through the ear canal or with a vibrator in contact with the membraneous ampulla roof. Units responding to sound or vibration showed tuning with a best frequency of approximately 0.7 kHz. The average low-frequency slope of the tuning curves is--16 dB/oct; the average high-frequency slope 20 dB/oct. The threshold amplitude for vibrator stimulation is 30 nm. This value comes close to the calculated threshold value for cupula deflection in the human semicircular canal.     

薄膜型声学超材料的结构设计与隔声特性*

为探讨薄膜型声学超材料用于汽车前围声学包、提高其中低频隔声能力的可行性,设计一种米字摆臂多质量块薄膜型声学超材料,构建其隔声分析有限元模型 ,分析其隔声特性及影响因素,开展结构优化及其在汽车前围声学包上的应用探索。研究表明,所设计的薄膜型声学超材料单胞在中低频区域具有较宽的隔声频带;增加薄膜上质量块半径或厚度会使传声损失曲线整体向低频区域移动,且质量块半径的增加还会拓宽高频区域的隔声频带;增加薄膜厚度或预应力会使传声损失曲线整体向高频区域移动;优化后的薄膜型声学超材料与钢板组合应用于汽车前围板,可明显提高其中低频隔声能力。