Transmission Loss Measurements Research Articles

Correlations between transmission loss measurements and sediment type

We report the results of a study correlating mid-frequency transmission loss (TL) measurements with properties of nearby sediment core samples. A large number of measurements were made in shallow water areas with water depths ranging from 50 to 160 m. The statistical distributions of the derived bottom-loss values are found to be nearly invariant to various sediment properties derived from the corresponding core samples. These properties include seafloor sound speed, density, and porosity as well as a number of others. It is shown from Parabolic Equation model calculations that use Hamilton’s values for the different sediment types [J. Acoust. Soc. Am. 68, 1313 (1980)] that the TL can vary by 15 dB or more at a range of 20 km. Therefore the absence of substantial bias in the data with respect to sediment types is somewhat surprising and worth investigation. The possible explanations, such as high spatial variability of seafloor processes including presence of ripples, gas, and other causes are being investigated and will be discussed. [Approved for public release].

Fabrication of low-loss hollow waveguide with multiple dielectric layers for infrared cavity ring-down spectroscopy

Low-loss hollow waveguides with a multiple dielectric layer are designed and fabricated for use in cavity ring-down spectroscopy (CRDS). Calculations of the waveguide design revealed that hollow waveguides for infrared CRDS system need to have transmission loss of 0.1 dB/m or less. We fabricated rectangular hollow waveguides with multiple dielectric layers to obtain low-loss properties. The waveguides are composed of four glass strips each with a dielectric multilayer deposited on the surface in advance. Experimental results show that the waveguides with double dielectric layers have lower losses at a target wavelength in the infrared than those with a single dielectric layer. The measured transmission loss of a 10-cm long waveguide deposited with a multilayer of Si/Al 2 O 3 /Ag for the transverse magnetic wave and Al 2 O 3 /Ag for the transverse electric wave was 0.24 dB at a target wavelength of 5.2 μm. The loss of the waveguide will be reduced when only the lowest-order mode is excited in the waveguide.

High frequency acoustic transmission loss of perforated plates at normal incidence

A study has been conducted on the transmission loss of perforated plates at normal incidence. The investigation includes a theoretical analysis of the problem with validation through experimentation. The experiments comprised microphone measurements of transmission loss for 11 perforated plates with variable thickness, hole size, and porosity. The theoretical model is based on planar wave propagation through a single contraction/expansion chamber with modifications to account for hole interaction effects. The resulting formula for transmission loss yields superior predictions over past theories for the range of properties investigated. Deviations between experimental measurements and theoretical predictions of transmission loss are less than about 1.5 dB for dimensionless hole diameter d/λ < 0.5. The accuracy of the model does not show a strong dependence on plate thickness-to-diameter ratio or porosity.

The measurement of transmission loss and absorption coefficient of the rat and porcine skin: Synthesizing artificial material for an implantable microphone test

With the advent of totally implantable hearing aids, the implementation and measurement of the microphone becomes an important issue. Engineers have to consider effects of the skin on the implantable microphone that did not exist in conventional hearing aid tests. In this paper, the transmission loss (TL) and absorption coefficient of rat and porcine skins were measured, and the synthesized skin was then implemented by using a gelatin gel that is widely used as an ultrasound phantom. From the measurement, the TL for rat and porcine skin was found to be 23.5±2.7dB and 30.4±2.8dB (mean±std) at 1kHz, respectively. Further, the absorption coefficients or the rat and porcine skin were measured as 0.029±0.011 and 0.031±0.012 at 1kHz, respectively. From the measurements, the TL values were found to be significantly increased at the high frequency and the absorption coefficients did not changed significantly in the 1–6kHz range. In additionally, the synthesized tissues also showed similar properties when compared with the animal experiments and they could be used to replace animal experiments for implantable microphones.

Enhancement of low-frequency sound insulation using piezoelectric resonators

In this paper, piezoelectric patches and electrical circuits are associated to attenuate vibration of a flat panel. The resulting electrical network is equivalent to a resistor–inductor–capacitor circuit performing as a tuned vibration absorber, denoted by piezoelectric resonator. The choice of design parameters, such as the correct placement for piezoelectric patches and the optimal electrical circuit elements, is assisted by finite element simulation and theoretical analysis. Measurements of sound transmission loss and modal analysis are conducted to demonstrate the structural vibration control and its resulting sound insulation performance. It is shown that, despite its reduced mass, the piezoelectric resonator can be more effective than conventional damping in low frequencies, which enables the overall sound insulation system to perform, with lower mass, in a wider frequency range.

Experimental investigation of the sound transmission of vegetated roofs

The purpose of this research was to determine the phenomenological parameters that impact the sound transmission of vegetated roofs. A reverse indoor-to-outdoor testing method involving propagating sound from an interior diffuse field to an exterior free field was first implemented at an existing field site. The findings from the field work supported the development of a purpose-built field laboratory specifically designed and commissioned as part of this research. Transmission loss measurements were completed on 2 non-vegetated reference panels, on gradients of substrate depth (25-mm increments), and on 2 plant communities established in 150mm of substrate depth. Increased transmission loss, resulting from the installation of vegetated roof material layers on the reference roof, at the field site (wood frame construction) and at the field laboratory (light-weight metal) generally aligned in the low and mid frequency ranges. The increased transmission loss of the wood frame roof was 5–13dB in the 50–2000Hz frequency range, and up to 8dB above 2000Hz. For the light-weight metal deck, the increased transmission loss was up to 10dB, 20dB, and >20dB in the low, mid, and high frequency ranges, respectively. Field mass law, using an effective mass to describe the composite roof deck, predicted the transmission loss of non-vegetated reference roofs. A gradient increase in substrate depth (equated in terms of mass) incrementally increased transmission loss, but not as predicted by mass law. A variation in the moisture content of the substrate did not translate to a measurable change in transmission loss. The deep roots of the coastal meadow community contributed to an increase in transmission loss relative to the shallow-rooted sedums community. The results of this research confirm that vegetated roofs increase transmission loss over non-vegetated roofs and have a beneficial application towards architectural situations requiring high transmission loss and specifically mitigation of low frequency noise.

Lowered threshold energy for femtosecond laser induced optical breakdown in a water based eye model by aberration correction with adaptive optics.

In femtosecond laser ophthalmic surgery tissue dissection is achieved by photodisruption based on laser induced optical breakdown. In order to minimize collateral damage to the eye laser surgery systems should be optimized towards the lowest possible energy threshold for photodisruption. However, optical aberrations of the eye and the laser system distort the irradiance distribution from an ideal profile which causes a rise in breakdown threshold energy even if great care is taken to minimize the aberrations of the system during design and alignment. In this study we used a water chamber with an achromatic focusing lens and a scattering sample as eye model and determined breakdown threshold in single pulse plasma transmission loss measurements. Due to aberrations, the precise lower limit for breakdown threshold irradiance in water is still unknown. Here we show that the threshold energy can be substantially reduced when using adaptive optics to improve the irradiance distribution by spatial beam shaping. We found that for initial aberrations with a root-mean-square wave front error of only one third of the wavelength the threshold energy can still be reduced by a factor of three if the aberrations are corrected to the diffraction limit by adaptive optics. The transmitted pulse energy is reduced by 17% at twice the threshold. Furthermore, the gas bubble motions after breakdown for pulse trains at 5 kilohertz repetition rate show a more transverse direction in the corrected case compared to the more spherical distribution without correction. Our results demonstrate how both applied and transmitted pulse energy could be reduced during ophthalmic surgery when correcting for aberrations. As a consequence, the risk of retinal damage by transmitted energy and the extent of collateral damage to the focal volume could be minimized accordingly when using adaptive optics in fs-laser surgery.

Measurement of thin conductive dielectric coating material parameters in a high noise environment

The tolerances of very thin, possibly conductive dielectric coating material parameters measured using the wideband free space transmission loss measurement technique in a high noise environment was investigated. The advanced postprocessing algorithm that improves those tolerances has been developed. This algorithm allows extracting thin coating material parameters with practically acceptable accuracy even when the level of systematic and random measurement noise is much greater than the level of transmission loss and insertion phase delay characteristics of the tested material sample. © 2013 Wiley Periodicals, Inc. Int J RF and Microwave CAE, 2013.

Development of a hybrid wave based–transfer matrix model for sound transmission analysis

In this paper, a hybrid wave based-transfer matrix model is presented that allows for the investigation of the sound transmission through finite multilayered structures placed between two reverberant rooms. The multilayered structure may consist of an arbitrary configuration of fluid, elastic, or poro-elastic layers. The field variables (structural displacements and sound pressures) are expanded in terms of structural and acoustic wave functions. The boundary and continuity conditions in the rooms determine the participation factors in the pressure expansions. The displacement of the multilayered structure is determined by the mechanical impedance matrix, which gives a relation between the pressures and transverse displacements at both sides of the structure. The elements of this matrix are calculated with the transfer matrix method. First, the hybrid model is numerically validated. Next a comparison is made with sound transmission loss measurements of a hollow brick wall and a sandwich panel. Finally, numerical simulations show the influence of structural damping, room dimensions and plate dimensions on the sound transmission loss of multilayered structures.

Integrated 40-$\lambda$1$\,\times\,$2 Wavelength Selective Switch Without Waveguide Crossings

A compact integrated 1×2 wavelength-selective switch (WSS) is demonstrated for which the structure is designed such that the WSS has no waveguide crossings. By employing a loopback configuration, only one arrayed-waveguide grating is needed in the WSS. The channel spacing is 100 GHz and the number of channels is 40. The measured transmission loss of the selected wavelength was <; 8.1dB, and the average crosstalk from two output ports were 23.0 and 40.7 dB.

Theoretical Analysis and Measurement of Sound Transmission Loss in Louver Elements with a Sound Attenuating Function Using a Narrow Tube Array

Theoretical Analysis and Measurement of Sound Transmission Loss in Louver Elements with a Sound Attenuating Function Using a Narrow Tube Array

Attenuation Characteristics of Double Orifice Silencer Jointed by Permeable Membrane (Measurement and Theoretical Analysis of Sound Transmission Loss)

Attenuation Characteristics of Double Orifice Silencer Jointed by Permeable Membrane (Measurement and Theoretical Analysis of Sound Transmission Loss)

Theoretical Analysis and Measurement of Sound Transmission Loss in Louver Elements with a Sound Attenuating Function Using a Narrow Tube Array

Theoretical Analysis and Measurement of Sound Transmission Loss in Louver Elements with a Sound Attenuating Function Using a Narrow Tube Array

A rapid inversion scheme for seabed single parameter using time-domain impulse response

Compared with multi-dimension inversion, the single parameter inversion has the main advantages that inversion complexity decreases with the number of parameters increasing. Firstly, the slop of bottom loss versus grazing angle FdB is proposed to serve as a single parameter. Secondly, in terms of mode and ray paths, the relation between impulse response and seabed reflection loss property FdB is discussed. Finally, a time-domain inversion method using least-squares fitting to intensity decay rate is designed accordingly. Experimental data in North Yellow Sea are inverted. The inverted results are evaluated by the core samples. Good agreement is also obtained between measurement and predictions of transmission losses with using the inverted result. As this method only requires single hydrophone and comparatively few measurements, it is believed to provide a rapid but robust estimation of FdB which can meet the need for many applications.

The prediction of silencer acoustical performances by 1D, 1D–3D and quasi-3D non-linear approaches

The design of silencers for internal combustion (I.C.) engines is a key issue to attenuate or emphasize certain spectral components of tailpipe noise. The optimization of complex shape silencing systems is generally a time-consuming operation, which must be carried out by means of concurrent experimental measurements and numerical simulations. This paper describes the development and application of different non-linear models: a coupled 1D–multiD model and a coupled 1D-quasi-3D model, to predict the silencer behavior in the time and frequency domains. Second order time and space discretization were adopted in the 3D and quasi-3D approaches, whereas specific coupling strategies were developed to realize the interface between them and the 1D model. In particular, since the 3D relies on a collocated grid discretization, a Riemann solver based method was developed to realize the coupling with the 1D code, while a cell overlapping procedure was exploited to interface the 1D code with the quasi-3D method, in order to fit with the pseudo-staggered grid arrangement. Both a white noise and a single impulse boundary condition have been imposed upstream of the pipe system to excite the wave motion. The integrated 1D–multiD and the quasi-3D approaches were applied to predict the transmission loss of reactive and dissipative mufflers in which the pressure waves can be significantly non-planar, to point out the influence of higher order modes on the acoustical performance. Reverse chambers with extended inlet and outlet and perforates have been investigated, showing the potential of both the hybrid 1D–3D code and the quasi-3D code with respect to a simple, fully 1D model. A comparison between predicted results of transmission loss and experimental measurements has pointed out the importance of correctly capturing multi-dimensional wave effects at mid and high frequencies as well as the effects of high amplitude perturbations and mean flow.

Clutter reduction using Doppler sonar in a harbor environment

A high frequency experiment was conducted in the Woods Hole Harbor in Massachusetts to evaluate the effectiveness of Doppler sonar for discriminating targets from reverberation. Using a pulsed linear frequency modulated signal, one finds that the matched filtered outputs are filled with high-level discrete backscattered returns, referred to as clutter, which are often confused with the target echo. The high level non-target returns have an amplitude distribution that is heavy-tailed. Using a Doppler-sensitive binary-phase-shift-keying signal coded with an m-sequence, the target echo and clutter can be separated by Doppler and delay, and tracked using the Doppler spectrogram (Dopplergram). The Doppler filtered time series show a background reverberation with a Rayleigh-like amplitude distribution, with an improved signal-to-(peak) reverberation ratio compared with that without Doppler filtering. The reduced reverberation level with Doppler processing decreases the probability of false alarm (Pfa) for a given threshold level. Conversely, for a given Pfa, the higher signal-to-(peak) reverberation ratio implies a higher probability of detection. Transmission loss measurement was conducted to estimate some of the system parameters, e.g., the source level and target strength relative to the noise level.

ACOUSTICAL PROPERTIES OF PARTICLEBOARDS MADE FROM BETUNG BAMBOO (Dendrocalamus asper) AS BUILDING CONSTRUCTION MATERIAL

Acoustic panels are used to overcome noise problems; the purpose of this study was to determine the acoustical properties of particleboard made from Betung bamboo (Dendrocalamus asper). The acoustic parameters measured were the transmission loss (TL) value and sound absorption coefficient. Particleboards of two different densities (0.5 g/cm3 and 0.8 g/cm3) that were made with three particle sizes (fine, medium, and wool or excelsior) were used in this study. The sound TL value was measured in a reverberation room, while the sound absorption coefficient was determined using the impedance tube method. A single-number rating of sound transmission class (STC) was determined based on TL measurements. The results showed that sound TL and STC values of medium-density particleboard (0.8 g/cm3) were better than low-density (0.5 g/cm3) board. However, low-density particleboard performed well as sound absorber panels. Generally, the boards absorbed sound at low ( 1000 Hz) and reflected sound at middle frequencies. The sound absorption coefficient was better with the fine- and medium-sized particles than with the wool size; meanwhile, boards made from wool- or excelsior-sized particles possessed higher TL and STC values.

Measurements of acoustic transmission loss over a rough water surface

Recent interest in understanding acoustic propagation over rough water surfaces has been driven largely by the increasing presence of offshore wind turbines and concerns about the potential for community noise disturbance. In addition, there has been interest in evaluating directional acoustic hailing devices for use at sea, in determining potential environmental impact of naval gunfire exercises, and in understanding the in-air acoustic footprint of maritime-based military assets. Measurements of acoustic transmission loss over a rough water surface were made during the period of 3 Oct and 7 Dec 2011 near Halifax, Nova Scotia, Canada. The acoustic source was a propane cannon, firing four consecutive shots once per hour during daylight hours. A receiver was positioned at ranges of 2 km to 7.5 km from the source, with a clear line-of-sight across the water, for periods ranging from 5-21 days at each location. Temperature, wind velocity, relative humidity, and ocean surface wave height were acquired from a ...

High dynamic range terahertz-wave transmission loss measurement at 330–500 GHz

Terahertz-wave transmission loss measurement systems at 330–500 GHz using single- and dual-channel superheterodyne receivers are described. It is shown that the phase noise effect in a single-channel system causes significant signal level fluctuation in the lock-in amplifier. The dual-channel system can eliminate the phase noise effect in synchronous detection and achieve a room-temperature noise floor of −170 dBm. The dynamic range of the dual-channel system is estimated to be 140–152 dB. The measurement uncertainty of the system is analyzed. A 0–100 dB WR-2.2 waveguide attenuator can be measured with expanded uncertainties of 0.078–0.24 dB at 480 GHz. The dual-channel system can serve as a national measurement standard for waveguide transmission measurement at 330–500 GHz and provide traceability for measurements made using commercial instruments.

Characteristics of Electromagnetic Waves Propagation in Corridor for High-Rise Buildings

With the popularity of wireless communication systems, the question of radio signal coverage is getting more and more attentions in corridor for high-rise buildings. Using loss rectangular dielectric waveguide theory, the attenuation of electromagnetic wave transmission rate is calculated in theory. Because of the complexity of electromagnetic waves propagation conditions, site measurement of transmission loss is done in band 210MHz, 460MHz, 1.2GHz and 2.0GHz. Measurement results show that the wireless signal transmission loss rate is similar with the calculation of loss rectangular dielectric waveguide theory on the trend