Vibration and sound signatures of human footsteps in buildings

The acoustic signature of a footstep is one of several signatures that can be exploited for human recognition. Early research showed the maximum value for the force of multiple footsteps to be in the frequency band of 1-4 Hz. This paper reports on the broadband frequency-dependent vibrations and sound pressure responses of human footsteps in buildings. Past studies have shown that the low-frequency band (below 500 Hz) is well known in the literature, and generated by the force normal to the ground/floor. The seismic particle velocity response to footsteps was shown to be site specific and the characteristic frequency band was 20-90 Hz. In this paper, the high-frequency band (above 500 Hz) is investigated. The high-frequency band of the vibration and sound of a human footstep is shown to be generated by the tangential force to the floor and the floor reaction, or friction force. The vibration signals, as a function of floor coverings and walking style, were studied in a broadband frequency range. Different walking styles result in different vibration signatures in the low-frequency range. However, for the walking styles tested, the magnitudes in the high-frequency range are comparable and independent of walking style.     

The influence of turbulence on noise propagation from a point source above a flat ground surface

The presence of turbulence in the atmosphere affects the interaction between an acoustic wave and the ground surface. The noise attenuation by the ground in the presence of atmospheric turbulence is smaller than in non-turbulent atmosphere.A simple engineering model of noise propagation above a flat ground surface, for stationary and moving point sources, has been proposed. The model takes into account the air absorption and ground effect in the presence of turbulence.As well as parameters for type of ground and air absorption, the model introduces two adjustable parameters which must be deduced from in situ measurements at two ranges or two heights. The model’s free parameters have been obtained as a function of the resultant sound speed gradient on the basis of the field measurements performed for a stationary noise source. Also, using field data for a vehicle moving at steady speeds up to 100 km/h, the model has been verified for a moving point source.     

A mathematical model for a single screen barrier in open-plan offices

In open-plan offices, single screen barriers are widely used to separate individual workplaces as a means of improving acoustical privacy. In this paper, a general model for calculating the insertion loss of a single screen barrier in the presence of a floor and a ceiling is developed using the image source technique. In addition to the acoustical properties of the floor and ceiling, this model also takes the sound absorption of the screen, the sound transmission through the screen and the interference between the sound waves into account. This model is able to separate the contribution of reflected sound and diffracted sound from the total sound pressure level at the receiving point, which can help indicate how best to improve the acoustical design of an open office. The mean differences between the predicted 1/3 octave band insertion loss values behind the screen and the corresponding measured results are within 2 dB.     

NUMERICAL MODELLING OF THE SOUND FIELDS IN URBAN STREETS WITH DIFFUSELY REFLECTING BOUNDARIES

A radiosity-based theoretical/computer model has been developed to study the fundamental characteristics of the sound fields in urban streets resulting from diffusely reflecting boundaries, and to investigate the effectiveness of architectural changes and urban design options on noise reduction. Comparison between the theoretical prediction and the measurement in a scale model of an urban street shows very good agreement. Computations using the model in hypothetical rectangular streets demonstrate that though the boundaries are diffusely reflective, the sound attenuation along the length is significant, typically at 20-30 dB/100 m. The sound distribution in a cross-section is generally even unless the cross-section is very close to the source. In terms of the effectiveness of architectural changes and urban design options, it has been shown that over 2-4 dB extra attenuation can be obtained either by increasing boundary absorption evenly or by adding absorbent patches on the façades or the ground. Reducing building height has a similar effect. A gap between buildings can provide about 2-3 dB extra sound attenuation, especially in the vicinity of the gap. The effectiveness of air absorption on increasing sound attenuation along the length could be 3-9 dB at high frequencies. If a treatment is effective with a single source, it is also effective with multiple sources. In addition, it has been demonstrated that if the façades in a street are diffusely reflective, the sound field of the street does not change significantly whether the ground is diffusely or geometrically reflective.     

Resonance absorption of ultrasound due to rotational lattice vibrations

The nuclear spin-phonon interaction Hamiltonian for Van Vleck paramagnets is derived in general form with allowance for rotational vibrations of the crystal lattice. The specific form of the Hamiltonian is given for tetragonal crystal symmetry in the cases S=1/2 and S > 1/2. The coefficient of sound absorption at the electron-nuclear levels as well as the electron spin system is calculated. It is verified that the contribution of rotational lattice vibrations can in a number of cases turn out to be an order of magnitude greater than the contribution depending on the shear and compressive strain.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 3, pp. 80–85, March, 1980.     

On operating deflection shapes of the violin body including in-plane motions

Earlier investigations have assumed only "out-of-plane" vibrations of the plates of the violin. The violin body can, however, be described as a thin-walled, double-arched shell structure and as such it may very well elongate in one direction as it contracts in another. Therefore, at least two orthogonal vibration components have to be included to describe the vibrations. The operating deflection shapes (ODSs) of a good, professionally made and carefully selected violin were therefore measured in several directions by TV holography to determine both "in-plane" and out-of-plane vibration components of the ODSs. The observations were limited to the frequency range 400-600 Hz, as this interval includes two most-prominent resonance peaks of bridge mobility and sound radiation as well as a third poorly radiating resonance. These three peaks clearly showed orthogonal vibration components in the ODSs. The vibration behavior of the violin body, sectioned in the bridge plane, was interpreted as the vibrations of an "elliptical tube" with nodal diameters. The number of nodal diameters increases from two to three in the selected frequency range. The TV holography measurements were supported by electrodynamical point measurements of bridge mobility, of air volume resonances, and by reciprocity, of radiation properties. Furthermore, a fourth mode, the air mode, A1, is involved indirectly in the sound radiation via influence on the body vibrations.     

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.     

Determination of the Absorbing and Scattering Properties of the Sea Floor in a Shallow Water Environment by the Spectra of Wide-Band Signals

Sound propagation in a shallow sea is considered within the framework of the two-component model of the sea floor. The porosity and the coefficients of absorption and volume scattering are treated as the parameters characterizing the sea floor. These parameters are determined on the basis of the comparison between the experimental and theoretical frequency spectra of a signal received from a wide-band source. A conclusion is made about the relative contributions of different mechanisms of losses (absorption or scattering) in the sea floor at different sound frequencies.     

Numerical investigation of active porous composites with enhanced acoustic absorption

The paper presents numerical analysis - involving an advanced multiphysics modeling - of the concept of active porous composite sound absorbers. Such absorbers should be made up of a layer or layers of poroelastic material (porous foams) with embedded elastic inclusions having active (piezoelectric) elements. The purpose of such active composite material is to significantly absorb the energy of acoustic waves in a wide frequency range, particularly, at lower frequencies. At the same time the total thickness of composite should be very moderate. The active parts of composites are used to adapt the absorbing properties of porous layers to different noise conditions by affecting the so-called solid-borne wave - originating mainly from the vibrations of elastic skeleton of porous medium - to counteract the fluid-borne wave - resulting mainly from the vibrations of air in the pores; both waves are strongly coupled, especially, at lower frequencies. In fact, since the traction between the air and the solid frame of porous medium is the main absorption mechanism, the elastic skeleton is actively vibrated in order to adapt and improve the dissipative interaction of the skeleton and air in the pores. Passive and active performance of such absorbers is analyzed to test the feasibility of this approach.     

An experimental and theoretical study of the modelling of road traffic noise and its transmission in the urban environment

This paper describes experiments conducted on the modelling of traffic noise using a $\text{1}\text{80th}$ scale model of a subdivision of a city. The emphasis in this study was on the correct evaluation of ground absorption effects. There were essentially four phases to the study. First, the applicability of various scaling law regimes was examined. It was shown that $\text{1}\text{80th}$ scaling using air as a transmission medium was at least a practical choice. The second phase concerned itself with the choice of materials for the model, particularly that which was to simulate the ground. An impedance measuring apparatus was developed and used to test materials. The third part of the work concerned itself with the development of an anechoic enclosure and a sound source to simulate traffic noise; modulated Hartmann whistles were used for this purpose. Finally, a model of part of a residential area of Calgary was built and sound transmission measurements obtained. These results were compared with field measurements. It was shown that good agreement existed between the field and model measurements.     

Seven-hole hollow polyester fibers as reinforcement in sound absorption chlorinated polyethylene composites

A series of thin, lightweight and low-cost sound absorption composites consisting of chlorinated polyethylene (CPE) and seven-hole hollow polyester fibers (SHPF) were fabricated. The sound absorption property of the fiber composites was tested in an impedance tube, the morphology was characterized by a scanning electron micrographs (SEM) and the mechanical property of fiber composites was measured by strength tester. The effect of fiber content, composite thickness, and cavity depth on the sound absorption property, and the effect of fiber content on mechanical property and micro-structure were investigated. The results demonstrated that acoustical characteristics of porous materials were exhibited by mixing with SHPF. Acoustical absorption of materials increased significantly with increasing SHPF content. Furthermore, the acoustic property of composite with 20% SHPF concentration and 3 mm thickness was noted in the low frequency range, giving a sound absorption coefficient peak, 0.695 at 2500 Hz. Composite with air back cavity had resonance characteristics of a lamella with an absorption peak only occurring at a specific frequency. Compared with pure CPE of similar thickness, mechanically CPE/SHPF composite at the 1 mm thickness and 20% SHPF exhibited 228% higher tensile stress and 96% lower breaking strain. It appears from these results that CPE/SHPF composites have potential for engineering applications especially as sound absorbers.     

Low frequency impact sound transmission in dwellings through homogeneous concrete floors and floating floors

An experimentally validated analytical model has been developed in order to investigate the effect on impact sound transmission at low frequencies of location of the impact, type of floor, edge conditions, floor and room dimensions, position of the receiver and room absorption. The model was developed in order to allow rapid repeated calculations necessary for a parametric survey, described in a companion paper. The analytical model uses natural mode analysis to predict the sound field generated in rectangular rooms by point sound sources and the point excitation of homogeneous rectangular plates with different edge conditions. A floor-room model of the sound field generated in a room by a vibrating floor also has been derived. Laboratory and in situ measurements confirm that the models can be used to estimate impact sound transmission at low frequencies. The approach applies to homogeneous simply supported base plates of uniform thickness with homogenous floating floors, which again were experimentally validated in the laboratory and in situ.     

微穿孔板吸声结构水下应用研究

马大猷教授提出的微穿孔板吸声结构在空气噪声降低和隔离方面得到了广泛的应用,但未见水下应用的相关研究和报道。本文将空气中微穿孔板理论应用到水中,得到了水下微穿孔板吸声结构的吸声公式。通过理论分析,得出了微穿孔板结构直接应用于水中无法获得宽频吸收的结论。提出了通过匹配液将微穿孔板间接应用到水下的设想。设计了单层板和双层板吸声结构,并对它们的吸声特性进行了理论分析与仿真。结果表明,本文设计的微穿孔板吸声结构在水中能够获得优于空气中的宽频带吸声效果。实验测量了自制的微穿孔板吸声结构,吸声系数的测量值与理论曲线基本吻合,从而验证了理论分析的正确性。     

The effect of construction material, contents and room geometry on the sound field in dwellings at low frequencies

An experimentally validated finite element method is used to model the sound level in rooms at low frequencies. It is demonstrated that the dimensions of rectangular rooms strongly influence the sound pressure level difference. Additional factors were investigated which are not normally considered in the frequency range where diffuse sound field conditions can be assumed. Three effects were investigated: room damping due to wall vibrations, furniture, the effect of small deviations from simple rectangular shapes. It is confirmed by field measurements that the vibrations of masonry walls and floors introduce less damping than surfaces of lightweight construction. Assigning to the FE model a damping equivalent to a surface absorption of 0.02 reproduces the effect of walls of heavyweight construction. Damping equivalent to a surface absorption of 0.15 reproduces the effects of plastered timber-frame walls, floors and ceilings. The work was briefly extended to a room pair built with heavyweight and lightweight material of construction. The modification of the shape of the room frequency response highlights well the effect of material of construction. In-situ and laboratory measurements show that furniture has little effect on steady-state room response below 100 Hz. Modelling a wall recess smaller than 0.5 m improved the agreement between prediction and measurements but the assumption of a simple rectangular room remains appropriate.     

Young’s modulus and internal friction of the SiC/Si biomorphic composite based on the sapele wood precursor

The effect of the vibrational strain amplitude on the Young’s modulus and ultrasound absorption (internal friction) of a SiC/Si biomorphic composite prepared by pyrolysis of sapele wood followed by infiltration of silicon were investigated. The studies were conducted in air and in vacuum by the acoustic resonance method with the use of a composite vibrator in longitudinal vibrations at frequencies of about 100 kHz. Measurements performed on sapele wood-based bio-SiC/Si samples revealed a substantial effect of adsorption-desorption of molecules contained in air on the effective elasticity modulus and elastic vibration decrement. Microplastic characteristics of the SiC/Si composites prepared from wood of different tree species were compared.     

Influence of ultrasonic vibrations on the growth of semiconductor single crystals

The influence of ultrasonic vibrations on striations in InSb, GaAs and Bi-Sb alloy single crystals grown by a modified Czochralski method was investigated. Ultrasonic vibrations at frequencies of 0.15, 0.25, 0.6, 1.2, 2.5, 5 or 10 MHz were introduced into the melt parallel to the pulling axis. The introduction of ultrasonic vibrations at a frequency up to 5 MHz eliminates the striations in GaAs and Bi-Sb alloy single crystals growing with constant diameter. It was found that for Bi-Sb alloy single crystals of constant diameter growth, after ‘processing’ of the melt with ultrasonic vibrations, the striations do not reappear until after 2 h. The effectiveness of the influence of the ultrasonic vibrations on the decrease of growth striations in InSb, GaAs and Bi-Sb alloy growing crystals was estimated with the help of the calculation of the sound absorption coefficient.     

L-阿拉伯糖指纹区太赫兹光谱和拉曼光谱的研究

为了解生物体内L-阿拉伯糖在代谢过程中的合成与降解机制,采用太赫兹和拉曼光谱系统,对其指纹区的振动进行检测。结果表明,L-阿拉伯糖太赫兹图谱在频率49.5和72.2 cm-1分别检测出了振动吸收,其中72.2 cm-1的振动为首次检出。该振动频率与其折射率图谱反常色散的频率基本一致,故这两个振动吸收可以作为L-阿拉伯糖的特征吸收。最为重要的是,在该频域内,检测得到图谱的波型与三种异构体理论值简单叠加后波型极为相似,故可以初步判定样品含有三种构象异构体(α-型、β-型和l-型结构),非单一组分,而是混合组分;对于拉曼图谱而言,其特点简洁而明晰,一般将指纹区的振动,从高到低分为四个区域：吡喃环结构的伸缩振动、亚甲基的摇摆振动、环上羟基的扭曲振动及环骨架扭曲和畸变振动。同时也根据密度泛函理论B3LYP/6-311G**基组,分别对L-阿拉伯糖的三种构象异构体的振动进行模拟计算,利用势能分布对这些振动进行归属和指认。与理论值相比,振动频率检测值有不同程度的红移,即振动频率向低频发生了偏移,其原因是样品内不同分子间相互影响所致。     

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.     

Parameters influencing low frequency impact sound transmission in dwellings

As sound and vibration fields in dwellings exhibit modal behaviour at frequencies below 200 Hz, a systematic investigation of measurement and prediction uncertainty associated with impact sound transmission at low frequencies must include the effects of: location of the impact, type of floor, edge conditions, floor and room dimensions, room absorption and position of the receiver. Experimentally validated analytical models, described in a companion paper, have been used in an extensive investigation of impact sound transmission through rectangular homogeneous concrete floors and floating floors. The models were used to describe the effect of modal coupling and then to perform parametric and statistical studies aimed to identify the main factors affecting low frequency impact sound transmission.