Transmission Loss Measurements Research Articles

Flexible PTFE hollow dielectric waveguides for terahertz applications: analysis and experimental study

In recent years, terahertz technology has developed rapidly, and one of the important topics is low-loss, flexible, and low-cost terahertz waveguides. In this paper, PTFE tubes are used as hollow terahertz dielectric waveguides with an operating frequency of up to 500 GHz. Using numerical analysis and simulation, transmission properties such as transmission loss and bending loss are discussed. In particular, special attention is given to the impact of deformation caused by compression during use on transmission performance. To validate our analysis, we fabricated PTFE tubes with an inner diameter of 0.3 mm and an outer diameter of 0.6 mm as well as the corresponding mode converters, which were measured in the 325–500 GHz frequency range. The measured transmission loss was less than 16.6 dB/m, and the bending loss was less than 2 dB/Turn.

Transmission loss of surface-reflected ray arrivals underneath seasonally varying sea ice in the Canada Basin during 2016-2017.

During the 2016-2017 Canada Basin Acoustic Propagation Experiment, an ocean acoustic tomography array with a radius of 150 km measured the impulse responses of the ocean every 4 hr at a variety of ranges and bearings using broadband signals with center frequencies from 172.5 to 275 Hz. Ice-profiling sonar data showed a gradual increase in ice draft over the winter with daily median ice drafts reaching maxima of about 1.5 m and daily standard deviations reaching maxima of about 1.2 m. The travel-time variability of early, resolved arrivals from refracted-surface-reflected rays with lower turning depths below 500 m was reported in a previous paper [Worcester et al. (2023). J. Acoust. Soc. Am. 153, 2621-2636]. Here, the transmission loss of these same ray arrivals is analyzed. The transmission loss was lowest when open water was present and increased as the ice draft increased. The excess transmission loss per surface reflection, defined as the increase in transmission loss relative to open water conditions, increased with center frequency and surface grazing angle. The combination of transmission loss measurements for resolved ray arrivals and ice drafts from the ice-profiling sonars provides an excellent dataset for testing ice-scattering models.

Attenuation of bulk waves using locally resonant soil-coupled metabarriers

Abstract Low frequency ground-borne vibrations generated by transport infrastructure are one of the most serious causes of disturbance to the general population. One possibility to reduce this problem is to use the wave filtering properties of elastic metamaterials. However, their integration in the soil complicates the prediction of their response, and the influence of soil-structure interaction needs to be correctly evaluated for an efficient design. The aim of this work is to experimentally evaluate the efficiency of metamaterial trench barriers set in soil in attenuating vibrations, using low-frequency local resonance mechanisms. A lab scale model is proposed comprising different resonating structures and a cylindrical encasement is adopted to couple the structure to the soil. The influence of various parameters is evaluated, such as metamaterial structure, geometrical characteristics of the resonator, and constituent materials. Finite Element simulations are used to develop a suitable design, analysing mode shapes and resonance frequencies of structures with and without the surrounding encasement. Experimental modal analysis is then performed on the corresponding fabricated samples, providing both model validation and out-of-soil mechanical characterization. Finally, vibration transmission loss measurements are performed in a setup in which different resonant metamaterial barriers are embedded into the soil sample, allowing the evaluation of barrier performance. Results indicate that the metamaterial structures provide good attenuation of vibrations in selected intervals in the low to high frequency range (1–5 kHz), demonstrating the feasibility of the approach in a scaled sample. Preliminary data regarding the structures providing preferable design characteristics is also obtained. These results can be useful for the design of trench barriers scaled to large dimensions in more realistic applicative settings.

Vibroacoustic characterization of small woven fabrics

This study is aimed to analyze the vibroacoustic behaviour of woven fabrics utilized in small acoustic devices for ingress protection. We first concentrate on predicting and describing the vibration behaviour of the woven fabric structure through flip around, since lumped modelling comes first. A vibration experiment is also conducted to measure the motion of the woven fabric structure under external excitation to validate the modelling. The numerical model is then employed to simulate the vibroacoustic behaviour of the woven fabric via transmission loss calculation; the simulation is then compared with transmission loss measurement based on the four-microphone method. This research demonstrates that despite some limitations, both the numerical and lumped models show a good degree of accuracy in predicting the vibration of the woven structure; the numerical model also performs well in vibroacoustic modelling.

Estimation of random incidence sound transmission loss of panels based on normal incidence sound transmission loss measurements

The performance of building sound insulation is an important parameter for evaluating the quality of construction projects. So far, the sound insulation performance testing of building walls requires the installation of large-dimensioned wall samples in specialized sound insulation laboratories, which is time-consuming and costly. If small-dimensioned components of the wall panels can be applied and quickly tested at the project site, it could significantly improve efficiency and reduce costs. To address this issue, this paper investigates a method for estimating the random incidence sound transmission loss of wall panels based on the measurement of the normal incidence sound transmission loss of corresponding small samples. Initially, the sound transmission loss of single-layer and composite structures is theoretically analyzed based on the theories of Equivalent Single Layer method and Layer-Wise method. Subsequently, the random incidence sound transmission loss is estimated by the normal incidence sound transmission loss. The methodology for estimating the random incidence sound transmission loss of wall panels proposed in this study offers both a practical approach and theoretical support for the rapid assessment of the sound insulation performance of building walls. This study is of great significance for improving the quality of construction projects and inspection efficiency.

Development of vibration isolation system for halls and report on sound insulation and vibration experiment

Rubber and polyurethane have been widely used as vibration isolation materials in halls and studios. In this project, we have developed a floor-mounted coil spring vibration isolator with improved vibration isolation and sound insulation characteristics, while keeping the installation height equivalent or lower than rubber and polyurethane. In this paper, we evaluate the vibration isolation performance of the developed device by measuring vibration transmission loss, and confirm that the device can suppress surging, which is a weak point of metal springs, while achieving a low natural frequency. The sound transmission loss measurement also confirmed that the floating slab incorporating the device has sufficient sound insulation performance, and these results indicate that the device can be applied to acoustic spaces such as concert halls, where quietness is required.

Optimization of a metal additively manufactured hydraulic silencer with array resonators

As mobile machines shift to electrification, hydraulic circuit noise, previously masked by combustion engine noise, has emerged as a significant concern. To address acoustic comfort issues, this paper investigates an innovative solution for high-performance noise reduction in hydraulic circuits. The proposed silencer design incorporates an optimized array of Helmholtz resonators, strategically arranged to broaden the narrow band characteristics of single resonators. The chosen configuration effectively reduces pressure pulsations across a broad mid-frequency spectrum. While this design is well-established in air medium, its application in a hydraulic oil medium is pioneering. Fabricated through metal additive manufacturing, the silencer undergoes testing on a dedicated bench. Transmission Loss measurements validate both the concept and the optimization methodology.

Investigation of light earth sound transmission loss at the wall scale

A fine understanding of the acoustic dissipation in walls made from biobased concrete is needed to predict and design properly their performances and to create comfortable spaces. This understanding is one of the objective of LOB+HIE (LOW BETON / HIGH EARTH) project, funded by Ademe, and focusing on the use of light earth (a biobased concrete resulting from the mix between clay and hemp shiv) to meet acoustic requirements in a public worksite. Acoustic data are already available in the literature at the material scale for this kind of solution. The aim of the present work is to provide experimental reference data at the wall scale for sound transmission on full-scale vertical walls, and then to extend it to other configurations by numerical simulations. The work is organised in three parts, including the transmission loss measurements on two different walls, the modelling of the walls with numerical simulations using a transfer matrix method approach, and finally the extension by simulation to other wall configurations, with a view to producing design aids for use by building professionals.

Basic examinations of the sound transmission loss measurement using two cardioid microphones

This paper reports results of an experiment on sound transmission loss measurement using the C-C method. This method is an inexpensive and stable method for measuring the sound pressure, the particle velocity, and the sound intensity. The measurements are carried out in accordance with JIS A 1441-1:2007 based on ISO 15186-1:2000, and the C-C method is applied for measuring the sound intensity. Comparing the measured results with those of the sound pressure level difference method, comparable results are obtained above 250 Hz. Naturally, the precision of the measurements depends on the microphone calibration used in the C-C method. In this report, we employ two calibration methods using an acoustic tube and an anechoic chamber, and also exhibit comparison of the results obtained by these methods.

Empirical observations of significant wave height and atmospheric acoustic transmission loss in a near-shore environment

Sound is influenced by meteorological conditions as it travels, which can have profound effect on transmission loss over long ranges. Conditions, such as wind speed, wind direction, and temperature, are primary atmospheric variables affecting transmission loss. At longer ranges, the surface roughness of the water is also an important factor to consider. Significant wave height is a typical metric to characterize the water surface roughness. A June 2024 field measurement campaign was completed in the Pamlico Sound adjacent to the East Carolina University Outer Banks campus. Measurement of meteorological conditions and concurrent acoustic transmission losses were performed over water only at ranges from 250 m to 2 km. A buoy that records three-dimensional wave motion was incorporated into the measurement process and deployed between the acoustic source and receiver array. The record of wave dynamics allows for the calculation of significant wave height. The approach to synchronizing wave height measurements to the acoustic measurements is discussed. Results are presented to show how water surface roughness relates to measured transmission loss.

PTFE-Based Circular Terahertz Dielectric Waveguides

This paper presents the transmission characteristics of flexible solid circular dielectric waveguides in the terahertz frequency band. In this paper, we measured the electrical properties of certain polymers within 325–500 GHz. Through simulation and measurement, the transmission loss, bending loss, and electric field distribution of solid-core polymer dielectric waveguides were analyzed and discussed. Additionally, we considered the surrounding cladding of the dielectric waveguide, the signal-feeding mode transmitter, and the interconnection of the dielectric waveguide. Ultimately, in the operating frequency range of 325–500 GHz, we selected PTFE rods with diameters of 0.5 mm and 1 mm as the dielectric waveguides, with measured transmission loss of less than 30 dB/m and 33 dB/m, respectively, and bending loss of less than 1 dB/m. The described dielectric waveguide has engineering significance for short-distance connections in complex geometric environments and provides a reference for subsequent research.

Experimental characterization of littoral atmospheric acoustics: Concurrent meteorological and acoustic observations.

The aim of this work is to describe a rich set of acoustic transmission loss observations that were completed in a coastal environment. The data library, enumerated in detail and publicly posted, is comprised of pitch-catch acoustic transmission loss measurements along with concurrent high spatial resolution meteorological observations. The meteorological parameters include near-surface temperature profiles, vertical wind speed profiles in the acoustic propagation direction, and significant wave height estimates. The acoustic source is positioned on an anchored vessel such that the first several hundred meters of the acoustic range is over open water with one microphone array positioned at the shore. A second microphone array is placed several hundred meters inland along the same source-to-receiver heading. The path between the two acoustic arrays is uniform salt marsh vegetation. Observations were made during seven sessions, which represent a variety of atmospheric conditions. That variety of conditions allows for some experimental generalizations about transmission loss as a function of meteorological observations. These include (1) the relationship between vertical effective sound speed profile and transmission loss, and (2) the variability of acoustic pressure with turbulence over time and elevation.

Experimental Investigation on Transmission of Sound in To Metallic Enclosures During Static Firing Tests Of Solid Rocket Motor

Satellite launch vehicle during lift-off generates intense dynamic environment mainly the acoustic noise, which in turn acts on the nearby launch pad systems. Reliable operation of these launch pad ground systems needs to be ensured by safeguarding against these dynamic loads with adequate protection measures. For future launch vehicle programs where the launch turnaround time is a crucial aspect, sensitive systems like ground check-out electronic packages are planned to be placed adjacent to the launch vehicle mounting pedestal on the launch pad to ensure minimal time for preparation. The enclosures housing these electronic packages needs to be configured to minimize the transmission of acoustic levels being imposed from the lift-off induced noise. In the present work, an experimental investigation is carried out on acoustic transmission characteristics of metallic enclosures of different material and thickness during the static firing tests of solid rocket motors. Acoustics generated from the supersonic jet noise has a wide frequency band from 100 to 10,000 Hz with sound power peaking near 1,000 Hz. The electronic components and packages, which are generally vulnerable to the high frequency noise, need to be protected from this lift-off induced acoustics. The enclosures are placed in the far field of this jet noise and the transmission loss measurements are obtained. Variation of transmission loss with material and thickness of the enclosures are studied with specific attention to the internal acoustic modes and the coincidence phenomena. Subsequently, the enclosures treated with acoustic blankets of different thickness are investigated to verify its influence on internal acoustic modes and also the additional reduction in transmission of sound in the dominant frequency band of supersonic jet noise.

Advancement of the exterior façade measurement method by Jerry Christoff

Acoustical design of façade elements is a key element in architectural acoustics. The assessment is required for multi-family housing projects and environmental projects. In the 1980s, when labs around the US were measuring the transmission loss (TL) of exterior façade elements, it was assumed that measurement of TL with a diffuse sound field method is valid for TL of real facades where a diffuse sound field does not exist. Jerry evaluated how the TL of exterior façade elements change based on the incident angle. In this talk, we will shed some light on the history of the work done by Jerry in the advancement of the exterior façade assessment methods.

Predicting excess attenuation: An investigation of turbulence in a littoral environment

This work presents an effort to effectively represent turbulence in a numerical model of atmospheric sound propagation in a near-shore environment. Model results are compared with a set of atmospheric transmission loss measurements made in a pitch-catch configuration with a stationary source 500 m from shore. High resolution temperature profiling and scanning Doppler LIDAR wind profiling measurements in the source-to-receiver direction are concurrent with the acoustic transmission loss measurements at the shoreline. These meteorological measurements inform the input parameters used in the parabolic equation. The numerical predictions are compared to the measured transmission loss values to evaluate model performance with a variety of different approaches to implement turbulence parameters.

A hybrid test method for measurement of airborne sound transmission loss of building partitions and elements

Single-number ratings, such as sound transmission class (STC), outdoor to indoor transmission class (OITC), and weighted sound reduction index (Rw), have been widely used to indicate the sound transmission properties of the building elements. The required transmission loss values over the frequency spectrum can be obtained from the two reverberation rooms test method (ASTM E90, ISO 10140), field measurement method (ASTM E966), or intensity method (ISO 15186). The limitations of the number of testing facilities that can provide the diffused field, minimum cut-off frequency, and other standard laboratory requirements, made the sound transmission loss measurement a costly and time-consuming procedure. In this study, alternative methods to measure the sound pressure and intensity have been investigated. The main objective of this research was to eliminate the complicated requirements of the diffused field and the room absorption measurement by averaging the direct sound amplitude at several angle of incidents and using the intensity probe to measure the sound intensity. In conclusion, the sound transmission loss, STC, and OITC values of double-glazed windows obtained from the hybrid method have been compared with predictions from the existing theory and the ASTM E90 standard test results.

Measurements of the frequency dependence of geo-alpha in clayey silt at low frequencies

Transmission loss (TL) measurements in the Santa Barbara Channel, together with co-located chirp measurements, show that geo-alpha (dB/l) in clayey silt increases approximately linearly with frequency (f) at f < 3 kHz. TL was measured between a fixed source and fixed vertical array at 3.7 km at 0.3 < f < 5 kHz. Geo-alpha was inverted from the TL data at 0.3, 1.1 and 1.9 kHz. Inversion calculations at 1.1 and 1.9 kHz considered both geo-alpha and bio-alpha due to layer of anchovies at 12 m. Inversion calculations at 0.3 kHz considered only the effect of geo-alpha; the effect bio-alpha on TL was small. Geo-alpha was also inferred from chirp sonar measurements at 3.2 and 6.2 kHz at the ends and middle of the TL track. Chirp sonar showed that the bottom consisted of a layer of unconsolidated sediments overlying a layer of sand. Co-located cores revealed that the unconsolidated layer consisted of clayey silt. Bio-alpha data were compared to Biot and VGS theories and the theory of attenuation in suspended sediments (Pierce et al., 2017). The measured frequency dependence is consistent with Pierce et al.’s theory. This research was supported by The Office of Naval Research Ocean Acoustics Program.

Introducing the sound transmission loss suite at the British Columbia Institute of Technology

A sound transmission loss suite is a facility for measuring the airborne sound insulation by building elements such as wall assemblies and partitions. It consists of two neighboring reverberation chambers (called the source and receiving rooms), where the only significant sound transmission path is presented by the test specimen, enclosed in the common wall separating the two chambers. In this talk, an overview of the sound transmission loss suite that was newly built and commissioned at the British Columbia Institute of Technology in late 2023 is given. The suite is comprised of two reverberation chambers with interior volumes of 200 m3 (source room) and 125 m3 (receiving room) and can test for frequencies from 63 to 20000 Hz, making it one of a kind in Western Canada. The talk touches upon the acoustical characteristics of the suite and the relevant test method for measuring transmission loss according to the ASTM E90 standard. [Work supported by Canada Foundation for Innovation—Project No. 36346.]

Development of Acoustic Metamaterial Sheets with Two-Dimensional Array of Hollow Local Resonators

Novel practical acoustic metamaterial sheets with hollow local resonators that can be processed with simple integral molding have been developed. This acoustic metamaterial is a variant of the acoustic metamaterial sheet reported by our group in 2021, which consists of two-dimensionally connected non-hollow-shaped stubs embedded with metal weights. Each hollow-shaped stub can work as a local resonator using the vibration mode of a circular membrane. This acoustic metamaterial can handle lower frequencies even with smaller and lighter stubs compared to those with the non-hollow-shaped stubs we previously reported. It has a particular advantage when used for objects with limited space and weight. It is also possible to control the resonant frequency by altering the material properties or adjusting the shape and size of the stub. It has been experimentally shown that significant sound insulation performance exceeding the mass law can be obtained around the resonant frequencies of the hollow stubs. We show the results of finite element method simulations, modal vibration testing, and transmission loss measurements.

FMBEM simulation of the laboratory measurement of sound transmission loss in rectangular test rooms

In order to predict sound transmission loss of building elements, the fast multipole boundary element method is applied to simulate the laboratory measurement method in rectangular test rooms specified by ISO 10140-2 (JIS A 1416) for all the frequency bands from 100 to 4 kHz. Firstly, fine and simplified models are validated in comparison with theoretical and measured results for reference samples of membrane materials. Secondly, in addition to the sound pressure method, the sound intensity method is numerically simulated. As a result, it was shown that both models are applicable at mid and high frequency bands, but a simplified model overestimates the transmission loss more than a fine model at low frequency bands. Regarding the sound intensity method, the simulated values are lower than those with the sound pressure method, however approaching the theoretical values.