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Producing practical designs for light-weight timber-framed structures that achieve high sound isolation remains a challenging task, in part because of the lack of models that can accurately predict the sound transmission through proposed designs. This work develops detailed modeling of structural vibration in timber floor/ceiling systems, from which sound transmission in the low-frequency regime (10–150 Hz) can be computed, as a design tool for producing practical timber floor/ceiling details that achieve high isolation for low-frequency sound. The mathematical model uses a variational formulation that enables straightforward modeling of complex composite structures, and introduces the notion of coupling layers to model the movement between joined materials that occurs with practical bonding methods, thereby improving on existing models that assume either perfectly bonded or perfectly slipping interfaces. The composite model structure is assembled only at the computational step, giving an efficient computational scheme that also fits well into the design-development cycle. Results from a parallel experimental program are used to validate the model and to determine effective coupling and damping parameters. The influence of coupling parameters is shown for an example floor, demonstrating that finite slippage at joints is required for the model to predict low-frequency vibration in practical constructions.Producing practical designs for light-weight timber-framed structures that achieve high sound isolation remains a challenging task, in part because of the lack of models that can accurately predict the sound transmission through proposed designs. This work develops detailed modeling of structural vibration in timber floor/ceiling systems, from which sound transmission in the low-frequency regime (10–150 Hz) can be computed, as a design tool for producing practical timber floor/ceiling details that achieve high isolation for low-frequency sound. The mathematical model uses a variational formulation that enables straightforward modeling of complex composite structures, and introduces the notion of coupling layers to model the movement between joined materials that occurs with practical bonding methods, thereby improving on existing models that assume either perfectly bonded or perfectly slipping interfaces. The composite model structure is assembled only at the computational step, giving an efficient comput...

Detecting sound from a distance is not a novel concept and laser vibrometers are often used for this purpose. A potentially better method is to measure the reflection of the usually stationary environment in a vibrating window. Experiments were conducted to capture high-speed video of vibrating windows with sound sources located inside a building. Low frequency vibrations produced by a speaker operating between 19 and 37 Hz were clearly visible on high contrast reflections under a very limited set of conditions. To better understand the limitations of the method in terms of variabilities of potential scenarios with sound, window, optical reflection, camera and analysis methods a parallel modeling effort was initiated. The detection of sound using optical methods can vary with sound source parameters (e.g. frequency, spectrum, amplitude, …), the window structure (glass thickness, number of panes, elasticity,…), the character of the reflected environment (contrast ratio, intensity,…), the measuring equipmen...

The present invention discloses an energy harvesting device that converts small magnitude and low frequency vibrations into electrical energy. The device can include a base, a low frequency element, and a piezoelectric element. The low frequency element can be movably attached to the base and the piezoelectric element can also be attached to the base and be spaced apart from the low frequency element with a vacant space therebetween. Upon vibration of the low frequency element resulting from environmental vibrations, the low frequency element can impact the piezoelectric element and cause elastic deformation thereto.

An apparatus for use in low frequency vibration energy harvesting (VEH) and with actuators requiring a low deflection force. The apparatus includes a piezo flexure that is loaded with a compressive pre-load force to place the piezo flexure under compression. The piezo flexure may be supported at an intermediate point or at one end thereof. The compressive pre-load force flexes the piezo flexure into one or the other of two stable positions, these positions being offset on opposite sides of a longitudinal centerline representing the position of the piezo flexure that would be produced without the compressive pre-load force applied thereto. The compressive pre-load effectively provides a negative spring constant which “softens” the piezo flexure and enhances a responsiveness of the piezo flexure to low frequency vibration energy. The piezo flexure also operates over a much wider frequency bandwidth than conventional systems incorporating a tip mass.

Acoustic‐based landmine detection methods have enjoyed success, in part, because of structural resonances in many landmines. The unburied VS 1.6, a member of a family of plastic, cylindrically symmetric anti‐tank landmines, exhibits seven modes below 1.6 kHz and a large frequency shift of the first symmetric mode such that its frequency is greater than that of the first asymmetric mode, a phenomenon observed in timpani of reduced kettle volume [Christian et al., J. Acoust. Soc. Am., 76(5), 1336‐1345 (1984)]. An elastically supported, thin, elastic plate acceptably models the unperturbed modes of the pressure plate. Coupling of the acoustic analog of the first symmetric mode to the cavities beneath the plate shows those cavities to be the cause of the perturbation. Shallow burial in sand effectively removes the frequency shift of the first symmetric mode. Comparisons to burial simulation experiments in water will be made, thus allowing a qualitative explanation of the effect sand has on the first symmetric...

On July 14, 2006, Tungurahua volcano in Ecuador initiated a dramatic eruptive sequence that caused the evacuation of villagers, the destruction of crops, and the reports of ash clouds above 15 km. Acoustic signals have been recorded by the prototype infrasound acoustic‐surveillance system (ASHE) currently operating in Ecuador. The infrasonic signals recorded by the ASHE included explosions, pyroclastic flows, and a sustained low frequency vibration of the ground. We present the features of the different types of eruption signals, and discuss the physics of eruptive processes and volcanic ash injection into the atmosphere. We also compare the July 2006 ash‐rich eruption sequence with the May 2006 eruptive episode, which injected very little ash into the atmosphere. Results are of significance for the future operational use of acoustic monitoring of volcanic activity for aviation safety.

The aim of the research was to investigate how some selected biochemical parameters of living rats depend on exposure of low‐frequency vibrations. Experiments were run on 30 Wistar rats randomly segregated into three groups: (I) 20 days old (before puberty), (II) 70th day after; (III) control group. The exposure was repeated seven times, for 3 h, at the same time of day. Vibrations applied during the first tests of the experiment had acceleration 1.22 m/s2 and frequency 20 Hz. At the 135th day the rats’ bones were a subject of morphometric/biochemical examination. The results of biochemical tests proved decrease in LDL and HDL cholesterol levels for exposed rats as well as the Ca contents in blood plasma. There was evident increasing of Ca in blood plasma in exposed rats for frequency of exposition.

A very low frequency augmentation system consists of a mobile target very w frequency projector (VLFP) adapted for operation as an augmentation device and installed within a torpedo shell housing. The housing is loaded within the torpedo tube of a submarine. A control and power interface is provided between the housing and the submarine to operate and monitor the augmentation device from the submarine. The housing is loaded in one of the submarine's torpedo tubes and the tube is flooded. The VLFP transmits low frequency vibrations into the surrounding seawater, acting as an augmentor.

For the past 10 or so years, various researchers have proposed different ways to measure strain distributions in vivo. The measured strains result from various sources including external palpation, low frequency vibration, or internal motion. By examining the relative strains in adjacent tissues, it is thought that one can infer the relative distributions of tissue stiffness. In this presentation, we discuss the process of creating a quantitative stiffness image from a given measurement of tissue strain. We show that the strain image by itself is insufficient information to infer the elastic stiffness. By examining the well‐posedness of the inverse problem, we determine what information is needed to supplement the strain image in order to quantitatively infer the elastic stiffness distribution. Methods for obtaining the required information in vivo are currently being developed. We show examples of incorrect and misleading stiffness reconstructions in the absence of the required data. [Work supported by B...

A transducer testing system for low frequency vibrations incorporates an electric motor/gearbox assembly (16) with an output shaft (18) and mechanical means for converting low frequency shaft rotation of the output shaft (18) to uniform low frequency sinusoidal excitation of an accelerometer (10). Simultaneously, a data processing unit (14) measures the response of the accelerometer (10) to the uniform low frequency excitation within predetermined frequency ranges. The data processing unit (14) then compares the measured response with predetermined accelerometer response limits to ascertain whether the accelerometer (10) is functional. The transducer testing system overcomes the limitations of electrodynamic testers to provide a means for accurately testing the low frequency response of the accelerometer (10).

Simple and practical formulas are derived for computing the near or far sound‐pressure field radiated by a slender body which vibrates in a low‐frequency whipping mode, or a low‐frequency accordion mode in water. The calculations can be made by simple quadratures, and require a specification of the modal vibration pattern along the length, the cross‐section area along the length, and a mean radiation impedance coefficient which can be estimated from independent data or calculated from an explicit formula derived here. Comparison is made with several other methods used to analyze these sound‐pressure fields. The analyses are specific examples of a general technique for transforming a solution for the incompressive field of a body in low‐frequency vibration to a solution that is valid in the near‐ or farfield of an acoustic compressible medium.Subject Classification: 20.55; 40.20.

The physical responses of the human body to frequencies below approximately 50 cps can be described by analyzing the body as a lumped parameter system. Recent refinements of measurement techniques allow more precise determination of this mechanical model and of many of its parameters, its resonances and mechanical impedances. This model is useful in studying the dynamics of the body exposed to various types of dynamic loads: whole body vibration, transient acceleration, blast exposure, respirator excitation, and rapid decompression. The response of the thorax‐abdomen system is discussed in detail. These studies are valuable as guides in future experimentation, in the interpretation of various types of biological effects, and in developing and understanding protective measures. The limits of linearity of the various components of the system and data on tissue strength are still unknown. The various effects limiting voluntary human tolerance to vibrations and their connection with the body's physical respon...

A fluid-damping vibration-isolating support device comprising a main support body having a rubber base member and a closed enclosure internally thereof; and a partition plate dividing the enclosure into two chambers which intercommunicate through an orifice and are filled with a liquid. The partition plate comprises a separator member and a stopper member. The separator member is formed of an outer peripheral thick wall portion having an orifice and an inner thin flat plate portion having at least one through-hole. The stopper member has two opposed plate sections provided so as to cover the through-hole and is captured to the separator member slightly movably to the degree that the plate sections are in contact with or separate from both faces of the flat plate portion. The stopper member serves to close upon low frequency vibration and open upon high frequency vibration, so that in the high frequency region rise of hydraulic pressure can be suppressed and dynamic spring rate can be lowered.

In response to a Presidential directive, the National Aeronautics and Space Administration (NASA) will launch a space station in the early 1990's. An objective of the Station program is to make customer use of the station cost‐effective. To help meet this objective, the Space Station will be capable of permanent habitation with crew rotations of 90 days. Consequently, means of enhancing and sustaining crew productivity are receiving increased attention. Environmental factors can influence productivity either by direct effects on performance or by indirect effects which ultimately impact performance. Noise and vibration, including low‐frequency vibration, are two factors being studied. This paper will discuss potential low‐frequency vibration sources, impacts on Space Station crew performance, and possible solutions.