Decrease In Transmission Loss Research Articles

Analysis of seamount propagation through the first convergence zone

During the recent Office of Naval Research (ONR) New England Seamounts Acoustics (NESMA) Pilot experiment, continuous measurements were made of underwater acoustic propagation and scattering from close range through the first deep-water acoustic convergence zone (CZ) using a stationary mid-frequency source and the ONR Three Octave Research Array (THORA) at Penn State. The source was positioned at a shallow depth over the plateau of one of the Atlantis II seamounts; the THORA was towed from 1 km range to a maximum of 85 km from the source. High-level goals of this work are to: 1) assess the influence of seamount scattering on mid-frequency transmission loss (TL) within the shadow zone, and 2) characterize how seamount interaction and the CZ is influenced by the shallow sound speed profile (SSP) in this region. The data was beamformed and analyzed using narrowband and broadband techniques, while ray-based and parabolic equation (PE) based models were used to develop an understanding of the influence of the seamount bathymetry, roughness, and the SSP. This talk will discuss a frequency dependent decrease in TL (acoustic enhancement) within the shadow zone due to seamount interaction and the limited influence of the seamount within the first CZ.

Theoretical study on lowering loss of skin effect suppressed multi-layer transmission line with positive/negative (Cu/NiFe) permeability materials for high data-rate and low delay-time I/O interface board

This paper proposes a new application of skin effect suppression technology for long wiring on high-speed & low-delay I/O board. This proposal will overcome the difficulty of further reducing the transmission losses on the I/O board with vert >vert 50 Gb/s data rate. In previous research, it was demonstrated that suppression of the skin effect by electroplated conductor/magnetic multi-layer, and estimated that the degree of transmission loss decrease at 16 GHz would be 5 %. A major challenge in this paper is to propose an electromagnetic field calculation theory for rectangular multi-layer transmission line, verify it under the same conditions, clarify a lower loss structure by changing thickness of each layer. Also it is expanded to low loss design technology. Cu and NiFe were selected as metal conductor material and negative permeability magnetic material, respectively. The Cu and NiFe films are alternately stacked to form the multi-layer. The top and bottom surface layers are Cu layers. The loss suppression was compared under the following conditions. 1) Total number of layers was 33 and total thickness was 12.67 μm by a constant ratio, Cu: tN = 0.51μm and NiFe: tF = 0.25μm. 2) Optimal stacking determined by changing the thickness of each layer. Compared to conventional thickness by a constant ratio 1), in our proposal 2), we estimated that the loss would dropped to 92% in optimal thickness. By offsetting the phase change of current density, a lower loss structure could be determined. Compared with Cu conductor, the top and bottom surface current densities become low, and depth center current density becomes slightly high for the multi-layer, showing the skin effect is suppressed.

Fiber Bragg grating inscription in multi-core photonic crystal fiber by femtosecond laser

The inscription of fiber Bragg grating (FBG) in a pure-silica multi-core photonic crystal fiber (PCF) using femtosecond laser and phase mask is reported. Three resonant dips are observed in the transmission spectrum due to the multiple supermodes transmitted in the PCF. The induced refractive index modulation of 2.2 × 10−4 is achieved for a peak power density of 4.8 × 1013 W/cm2 without any fiber sensitization. The experimental results show that type II grating is inscribed and it has high thermal stability. The temperature corresponding to 50% decrease in transmission loss of the FBG is about 970 °C. The central wavelengths of the three dips linearly shift with pressure sensitivity of −4.8 pm/MPa and strain sensitivity of 1.2 pm/με. This FBG will find applications in optical fiber sensing under high temperature.

Absorption and transmission of boundary layer noise through flexible multi-layer micro-perforated structures

This paper describes analytical and experimental studies conducted to understand both the absorption and transmission performance of non-fibrous micro-perforated partitions excited by a turbulent boundary layer (TBL). This is of relevance in surface and air transport systems for the airframe design of external liners. A fully-coupled modal formulation is established that predicts the absorption coefficient and the transmission loss (TL) of finite-sized and infinite-sized partitions made up of a micro-perforated panel (MPP) backed by an air cavity and a thin plate. The front MPP undergoes random wall-pressure fluctuations with prescribed auto- and cross- correlation properties such as a TBL and/or an acoustic diffuse field (ADF). An experimental methodology is proposed to evaluate in a closed wind tunnel both the absorption and insulation performance of a TBL-excited MPP partition. This leads to an approximation of the frequency-averaged power flow injected by the TBL into the MPP partition. Both the predictions and the measurements show significant differences in the absorption and TL curves when considering either a low speed TBL or an ADF excitation. These properties are examined considering a weighted contribution of the acoustic and turbulent components, as it is the case for an aeroacoustic excitation. A hole-based transitional Strouhal number is found below which low-back scattering of the wall-pressures occurs and above which the MPP apertures efficiently convert turbulence into back-scattered sound whatever the magnitude of the acoustic component. As for the TL, a minute increase of the acoustic component generates most of the TL decrease. Finally, the effects of adding a second MPP within the cavity are assessed for both the absorption and the TL.

Transmission loss of a silencer using resonator arrays at high sound pressure level

Helmholtz resonator is generally used to reduce the low frequency noise. However, it has only high transmission loss in a narrow band at the resonance frequency. In order to obtain broad band transmission loss, studies of a silencer using various resonator arrays have been carried out. These previous studies have been limited to low incident sound pressure level conditions with no change of impedance with respect to pressure. In the case of high sound pressure, the resistance increases due to nonlinear behavior at the neck of a resonator. As a result, the desired noise reduction performance cannot be achieved due to the transmission loss decrease. To predict the transmission loss of a silencer using resonator arrays at high sound pressure level, impedance variation depending on the incident sound pressure level should be considered. Furthermore, resonator’s numbers and order of arrangement are significant design parameters for design of transmission loss shape.

Highly birefringent phase-shifted fiber Bragg gratings inscribed with femtosecond laser

We demonstrate a highly birefringent phase-shifted fiber Bragg grating (PS-FBG) inscribed in H2-free fiber with a near-infrared femtosecond Gaussian laser beam and uniform phase mask. The PS-FBG was fabricated from an ordinary fiber Bragg grating (FBG) in a case in which overexposure was applied. The spectral evolution from FBG to FS-FBG was observed experimentally with a decrease in transmission loss at dip wavelength, blueshift of the dip wavelength, decrease in the cladding mode loss, and an increase in the insertion loss. A high birefringence was demonstrated experimentally with the existence of PS-FBG only in TM polarization. The formation of the PS-FBG may be due to a negative index change induced by the higher intensity in the center of the Gaussian laser beam.

Using Life-cycle Analysis to Assess Energy Savings Delivered by Building Insulation

The present paper contains calculations of energy savings delivered through the use of mineral wool insulation throughout the life cycle. The calculation of energy savings in the production of the insulation material is based on ISO 14025 Principles and Procedure of Environmental Labels and Declarations. The calculation of energy savings in the process of building operation is based on comparing the heat energy losses through the external walls of a model Moscow apartment building before and after façade insulation. The insulation material used is 100-mm ISOVER's staple glass wool with synthetic binding agents. The insulation system type is hinged ventilated facade. The calculations yield a decrease in heat leakage through II-18/12 buildings’ external walls over heating period, achieved through façade insulation. Based on the calculated decrease in transmission loss, we were able to evaluate the energy savings potentially achieved over the life cycle of the insulation. The energy used to produce a unit of insulation material was compared to the amount of energy saved throughout the life cycle.

국부 공진을 고려한 주름강판의 차음 설계

In a railway vehicle, corrugated steel panel is widely used for the floor structure because of its high bending stiffness and light weight. However, this panel shows lower sound insulation performance than that of the flat plate with the same weight. Especially, in a particular frequency region, transmission loss(TL) rapidly decreases and it results in the deterioration of sound insulation performance of the overall floor structure. This study identifies that the severe decrease in TL is caused from the local resonance of the periodic corrugated structure. TL decrease by local resonance is investigated by experiment and finite element analysis. Finally, design modification of the corrugation is proposed to improve TL and the effect is verified by experiment.

A comparison of sound transmission loss on metal stud partitions as the stud configuration changes.

The draft “Interim sound and vibration design guidelines for hospital and healthcare facilities” drafted by the Joint Subcommittee on Speech Privacy of the ASA recommends STC 50 partitions between exam rooms with no masking sound provided. These partitions are typically constructed of multiple layers of gypsum board on single steel studs, which are widely believed to achieve the required ratings based on published test reports. However, virtually all laboratory testing is with 25 gauge studs 24 in. on center, whereas with a 15 ft floor to floor height typical of hospitals, 16 in. gauge studs installed 16 in. on center are often required for structural reasons. There is little published data on the changes in sound transmission loss changes with stud gauge and spacing. A testing program was established, and transmission loss (STC) tests were performed on drywall partitions with various configurations of stud gauges, spacing, and layers of drywall. Measureable decrease in transmission loss as the studs become heavier and as the spacing between studs decreases was measured. The results of the testing program are presented.

Sound transmission in elliptical ducts

Transverse pressure distributions and cut‐on frequencies for higher order duct modes were computed using series expansions of the relevant Mathieu functions. Of particular interest is the shift of the cut‐on frequencies relative to those of a circular duct. Propagation of the first few higher order modes were observed by transmission loss measurements of expansion chambers of elliptical cross section with inlet and outlet tubes preferentially located to excite these modes. Propagation of these modes can be observed by a decrease in transmission loss after the cut‐on frequency for a particular mode. Observed cut‐on frequencies are compared to computed cut‐on frequencies. [This work was begun under NSF Grant No. SPI‐8160217 and continued with support from Nelson Industries, Inc.]

Effect of air flow, panel curvature, and internal pressurization on field-incidence transmission loss

In the context of sound transmission through aircraft fuselage panels, equations for the field-incidence transmission loss (TL) of a single-walled panel are derived that include the effects of external air flow, panel curvature, and internal fuselage pressurization. These effects are incorporated into the classical equations for the TL of single panels, and the resulting double integral for field-incidence TL is numerically evaluated for a specific set of parameters. Flow is shown to provide a modest increase in TL that is uniform with frequency up to the critical frequency. The increase is about 2 dB at Mach number M = 0.5, and about 3.5 dB at M = l. Above the critical frequency where TL is damping controlled, the increase can be slightly larger at certain frequencies. Curvature is found to stiffen the panel, thereby increasing the TL at low frequencies, but also to introduce a dip (analogous to the coincidence dip at the critical frequency) at the ’’ring frequency’’ of a full cylinder having the same radius as the panel. This effect, up to now qualitatively understood, can now be quantitatively estimated. Pressurization appears to produce a slight decrease in TL throughout the frequency range, and also slightly shifts the dips at the critical frequency and at the ring frequency. Subject Classification: [43]50.50, [43]50.45; [43]55.80, [43]55.75.

Optimization of the Mass Distribution and the Air Spaces in Multiple-Element Soundproofing Structures

A method is evolved for predicting the transmission loss of soundproofing multiple-element configurations containing any number of elements. The optimum distribution of mass between the impervious elements (fuselage skin panel, blanket septa, trim panel) is determined for a general theoretical configuration and for a typical aircraft structure. The theoretical improvement obtained by mass distribution optimization (approximately uniform distribution between the impervious elements) is about 3 to 6 dB in the low frequencies (below 500 cps) and 8 to 14 dB in the speech interference range (600 to 4800 cps). It is shown that a large increase in air spaces between elements is required to obtain only about 8- to 10-dB improvement (in theory), neglecting contact flanking paths between the elements. Also, replacing air spaces with acoustical blankets produces small improvements (2 to 8 dB) at the cost of possible structural flanking transmission between the elements. It is also shown that covering a hard terminating trim panel with an acoustical blanket increases the overall transmission loss by about 2 to 6 dB in the 300- to 4800-cps frequency region. Finally, it is shown that reducing the ambient pressure in a fuselage reduces the sound attenuation properties of soundproofing, viz., the decrease in transmission loss due to pressurizing an aircraft to an equivalent altitude of 8000 ft is about 3 to 6 dB.