Tube Terminals Research Articles

Modified two-microphone method: Determination of acoustic properties in upper audible and lower ultrasonic range using impedance tube based on two MEMS microphones

The standardized two-microphone method is widely established for determining normal-incidence acoustic properties. Instead of numerous low-frequency usages, only a few high-frequency applications are reported. This paper provides insights into implementing the two-microphone method in an impedance tube based on two MEMS microphones for a frequency range of 5 kHz to 50 kHz. In doing so, we encountered technical issues associated with the MEMS microphone utilization and the high-frequency application. These issues can be addressed by implementing a modified method, in which an adaptive stepped sine excitation and a curve-fitting technique were applied. The modified method was validated by using three classical tube terminations, e.g., closed, open, and horn. The measured data of these terminations are in line with their analytic solutions. In conclusion, when proper concerns are taken, the acoustic properties up to the lower ultrasonic range can be determined using the modified two-microphone method in an impedance tube based on two MEMS microphones.

Transmission loss measurement of recycled granular material using wave decomposition by impulse response extraction based on deconvolution

A simplified method for measuring transmission loss with a single fixed microphone inside an impedance tube is proposed. The separation of the incident wave from the reflected wave is achieved by deconvolving the loudspeaker driver voltage signal with the microphone signal to extract the impulse response. Random noise and a sinusoidal sweep signal were used as excitation signals for extraction of the impulse response, and two deconvolution methods were employed: linear deconvolution based on the adaptive LMS algorithm and simple spectral division. To avoid the overlap of incident and reflected pulses, a long impedance tube was used. Using a long impedance tube eliminates the need for an anechoic tube termination and the need to calibrate microphones. It is found that a reflective tube termination provides more accurate results compared to an approximately anechoic termination. The approximately anechoic termination shortens the available time window of the reflected pulse because it reflects some of the low-frequency sound. The standard deviation of the results and the dynamic range of the proposed method were determined experimentally. The applicability of the new method was tested on samples of unconsolidated granular material recycled from construction sites. The measured transmission losses of the different granular fractions were compared with a theoretical model for transmission losses at low frequencies. Samples consisting of smaller granule fractions were found to have surprisingly high transmission loss values. The design of the extended vertical impedance tube in combination with the proposed method is cost effective, speeds up the measurement procedure and provides reliable results.

EPAC2 acts as a negative regulator in Matrigel-driven tubulogenesis of human microvascular endothelial cells

Angiogenesis is physiologically essential for embryogenesis and development and reinitiated in adult animals during tissue growth and repair. Forming new vessels from the walls of existing vessels occurs as a multistep process coordinated by sprouting, branching, and a new lumenized network formation. However, little is known regarding the molecular mechanisms that form new tubular structures, especially molecules regulating the proper network density of newly formed capillaries. This study conducted microarray analyses in human primary microvascular endothelial cells (HMVECs) plated on Matrigel. The RAPGEF4 gene that encodes exchange proteins directly activated by cAMP 2 (EPAC2) proteins was increased in Matrigel-driven tubulogenesis. Tube formation was suppressed by the overexpression of EPAC2 and enhanced by EPAC2 knockdown in endothelial cells. Endothelial cell morphology was changed to round cell morphology by EPAC2 overexpression, while EPAC2 knockdown showed an elongated cell shape with filopodia-like protrusions. Furthermore, increased EPAC2 inhibited endothelial cell migration, and ablation of EPAC2 inversely enhanced cell mobility. These results suggest that EPAC2 affects the morphology and migration of microvascular endothelial cells and is involved in the termination and proper network formation of vascular tubes.

A New System for the Measurement on Small Samples of the Normal-Incidence Insertion Loss of Acoustic Multilayers

<div class="section abstract"><div class="htmlview paragraph">This article presents a new system for the measurement on small samples of the normal-incidence Insertion Loss (IL) of multilayers used for the manufacturing of automotive sound package parts. The system consists of a rigid piston connected to an electrodynamic shaker and facing a tube positioned just above it. The measurement principle is based on the evaluation of the Transfer Matrix (TM) of the piston-and-sample assembly, from which the desired IL can be calculated. The TM can, in turn, be evaluated from the measurement of the piston velocity and of the acoustic pressure inside the tube, with two different tube termination conditions.</div><div class="htmlview paragraph">The proposed measurement system is first of all aimed at simplifying the assessment of the acoustic insulation of multilayers used for the manufacturing of sound package parts. In the automotive field, this assessment is customarily done by measuring the diffuse-field Insertion Loss (IL) of flat samples having an area of around 1m<sup>2</sup> in two-chambers facilities. A kind of test that, while being well-established, may be quite demanding and resource-consuming, in particular when many different multilayers (different materials, different constructions, different layers’ thickness, etc.) have to be compared. With the proposed system, the amount of material and the time needed for a test is strongly reduced compared to this standard practice. Furthermore, the system intends to overcome the limitations of the 4-microphones test procedure based on the ASTM E2611 standard that cannot provide the actual IL of a package (but only its TL, without any support) and that suffers from the influence that samples’ edge conditions may have on the results.</div><div class="htmlview paragraph">In a first part, the article first discusses the principles on which the measurement system is based. In a second part it focuses on some aspects of the measurement hardware that are particularly delicate (e.g. sample’s edge conditions). Eventually, the article describes how a prototype of the measurement system was built and validated.</div></div>

Measurement of Sound Absorption Using a Single Fixed Microphone in a Circular Pulse-Tube

This study presents a method for measuring the normal incidence sound absorption coefficient of acoustical materials by separating the incident and first reflected waves in the time domain using a pulse-tube with only a single microphone whose position is fixed. Based on the pulse generation technique, the effect of the characteristics of tube termination can be eliminated, and the drive signal used for the measurement is obtained. A moveable piston is used to move the sample to a certain position in the tube, which renders the recorded incident and first reflected waves separated. As a validation of the proposed method, two different materials are investigated. Good agreement is found between the proposed method and both the well-established two-microphone transfer function (TMF) method and the verified pulse separation method.

Shape optimization of micro-acoustic devices including viscous and thermal losses

Since the late 1980s, numerical shape optimization has been applied successfully to improve the design and development of novel acoustic devices. Most often, viscous and thermal dissipation effects are neglected in the optimization process, as this is an acceptable assumption in e.g. room acoustics, etc. However, in many acoustic devices, ranging from hearing aids to metamaterials, dissipation can significantly influence the acoustic wave behaviour. In this paper, we propose a numerical acoustic shape optimization technique and we demonstrate it using two-dimensional quarter-wave and Helmholtz resonators including accurate modelling of viscous and thermal dissipation. By combining a dissipative boundary element method with shape optimization, the sound absorption capability of the resonators located at an impedance tube termination is maximized. Numerical experiments demonstrate the importance of viscothermal dissipation and its impact on the optimization outcome. The resulting resonator shapes, optimized using a lossy assumption, yield significantly better performance compared to their lossless counterpart, with near-perfect absorption at the desired optimization frequencies.

Plant Reproduction: Autocrine Machinery for the Long Journey of the Pollen Tube

Many receptor-like kinases localized at the pollen tube tip precisely control tube functions in flowering plants. Two recent reports have identified autocrine peptide ligands and receptor systems, providing insight into the molecular machinery that controls pollen tube growth and termination.

The interaction between Boron-carbon-nitride heteronanotubes and lithium atoms: Role of composition proportion

A series of Li@BCN models were systematically investigated to explore the physical origin of the interaction between lithium atoms and BCNs. Theoretical results show that the crucial electron population in the BCNs of Li@B-BCN and Li@N-BCN series is dramatically different. As results, the first hyperpolarizability of Li@B-BCN series increases with the increase of carbon proportion whereas that of Li@N-BCN series significantly decreases with the increase of carbon proportion. The results indicate that the physical properties of Li@BCN models are significantly dependent on the different chemical environment of the tube termination.

Theoretical Insight into the Hydrogen Evolution Activity of Open-Ended Carbon Nanotubes.

Carbon nanotubes (CNTs), while inactive by themselves, are often used as a platform in the search of new catalysts for the hydrogen evolution reaction (HER) by introducing metal nanoparticles or other dopants. Here, we examine the HER activity of pristine open-ended CNTs considering both the effects of chirality and hydrogen coverage using electronic structure calculations. The results indicate that the formation of different 5-ring structures at the end of the CNT introduces surface sites that are highly active toward HER, whereas the activity of traditional 6-ring sites is not greatly altered by tube termination. At fixed hydrogen coverage, the enhanced activity of these sites was attributed to valence orbitals residing close to the highest occupied molecular level facilitating electron transfer to protons.

Prediction of sound absorption by a circular orifice termination in a turbulent pipe flow using the Lattice-Boltzmann method

The Lattice Boltzmann method was used to perform numerical simulations of the sound and turbulent flow inside a standing wave tube terminated by a circular orifice in presence of a forced mean flow. The computational domain comprised a standard virtual impedance tube apparatus in which sound waves were produced by periodic pressure oscillations imposed at one end. An orifice plate was located between the driver and the tube termination. All waves transmitted through the orifice were effectively dissipated by a passively non-reflecting (i.e. anechoic) boundary at the tube termination. A turbulent jet was formed at the discharge of the orifice by the forced mean flow inside the tube. The acoustic impedance and sound absorption coefficient of the orifice plate were calculated from a wave decomposition of the sound field upstream of the orifice. Simulations were carried out for different excitation frequencies, and orifice Mach numbers. Results and trends were in good quantitative agreement with available analytical solutions and experimental data. The Lattice Boltzmann method was found to be an efficient numerical scheme for prediction of sound absorption by realistic three dimensional orifice configurations.

Measurement of sound absorption by underwater acoustic material using pulse-separation method

An alternative pulse-separation method is presented for measuring the sound absorption at normal incidence of an underwater acoustic material in a water-filled impedance tube. A damped sine pulse was generated in the water-filled impedance tube with a regular waveform and a short duration time of approximately 1ms. During the generation of the pulse, the inverse filter principle was used to compensate for the transducer response. In addition, the effects of the characteristics of the tube termination can be eliminated during the generation of the pulse to obtain a single plane pulse wave in the impedance tube, which is a necessary condition for this technique. Measurements of the sound absorption coefficient of the rubber material and the reflection coefficient from a water/air interface were used to verify the pulse-separation method.

Experimental Evaluation of Transmission Loss of a Glass Cylinder Tube Containing a Fluid

Transmission Loss (TL) of a glass cylinder tube containing a fluid is studied experimentally. This test specimen represents a typical double layer panel including a fluid. The tests are carried out by using a modified four-microphone standing-wave (impedance) tube for specimens with different lengths, 15 and 30 mm. Each cylinder tube is tested filled with one of the fluids at a time. The fluids are air, water, motor oil and a nanoparticle fluid (in absence of magnetic field). The effects of the cylinder length (thickness), impedance tube terminations, and the containing fluid are discussed. The increasing of the thickness led to an increase of the TL values and a decrease in resonance frequencies. Also, the addition of liquid middle layer led to considerable increase of the TL.

Evaluation of moving-coil loudspeaker and passive radiator parameters using normal-incidence sound transmission measurements: Theoretical developments

The parameters of moving-coil loudspeaker drivers are typically determined using direct electrical excitation and measurement. However, as electro-mechano-acoustical devices, their parameters should also follow from suitable mechanical or acoustical evaluations. This paper presents the theory of an acoustical method of excitation and measurement using normal-incidence sound transmission through a baffled driver as a plane-wave tube partition. Analogous circuits enable key parameters to be extracted from measurement results in terms of open and closed-circuit driver conditions. Associated tools are presented that facilitate adjacent field decompositions and derivations of sound transmission coefficients (in terms of driver parameters) directly from the circuits. The paper also clarifies the impact of nonanechoic receiving tube terminations and the specific benefits of downstream field decompositions.

An improved water-filled pulse tube method using time domain pulse separation method

Based on existing low-frequency water-filled impedance tube testing facilities, which is a part of the Low Frequency Facility of the Naval Undersea Warfare Center in Beijing, an improved water-filled pulse tube method is presented in this short paper. This proposed study is significantly different from the conventional pulse tube method because of the capability for a single plane damped sine pulse wave to generate in the water-filled pulse tube with a regular waveform and short duration time of about 1ms. During the generation process of the pulse, an inverse filter principle was adopted to compensate the transducer response. The effect of the characteristics of tube termination can be eliminated through the generation process of the pulse. Reflection coefficient from a water/air interface was measured to verify the proposed method. When compared with the expected theoretical values, a relatively good agreement can be obtained in the low frequency range of 500–2 000 Hz.

Laser triangulation sensor and six axes anthropomorphic robot manipulator modelling for the measurement of complex geometry products

A laser triangulation sensor and six-axis manipulator mathematical modeling for the measurement of complex geometry parts will be outlined in the article. The integrated system model is showed covering the laser triangulation sensor, the geometry of the manipulator and the relative positions of the components during the measurement process. The method to calibrate the sensor and relate the positions of the sensor and the robot is explained in this work. The measurement process is carried out with the parameters calculated with this method and the nominal parameters of the robot. Finally, plane surfaces with holes and termination of tubes placed in different orientations will be measured; the accuracy of the integrated system (sensor and robot) will be presented as well.

Transmission loss measurement of acoustic material using time-domain pulse-separation method (L)

An alternative method for measuring the normal incidence sound transmission loss (nSTL) is presented in this paper based on the time-domain separation of so-called Butterworth pulse with a short-duration time about 1 ms in a standing wave tube. During the generation process of the pulse, inverse filter principle was adopted to compensate the loudspeaker response, besides this, the effect of the characteristics of tube termination can be eliminated through the generation process of the pulse so as to obtain a single plane pulse wave in the standing wave tube which makes the nSTL measurement very simple. A polyurethane foam material with low transmission loss and a kind of rubber material with relatively high transmission loss are used to verify the proposed method. When compared with the traditional two-load method, a relatively good agreement between these two methods can be observed. The main error of this method results from the measuring accuracy of the amplitude of transmission coefficient.

The screening effect on field enhancement factor of the finite-length small radius single-walled carbon nanotubes

The screening effects on the field enhancement factors of (3,3) and (5,0) finite length single-walled carbon nanotubes (SWCNTs) with respect to different kinds of tube terminations, either capped or H-terminated, are examined using first-principles calculations. Results show that for capped SWCNTs, the field enhancement factors of the (3,3) tube are slightly greater than those of (5,0) ones, while for H-terminated tubes exhibit the opposite effect. The effects of different endings on the SWCNT work functions are also investigated. Calculations show that for the capped SWCNTs, the work functions of (3,3) tubes are larger than those of (5,0) tubes, whereas for the H-terminated cases, the work functions of (3,3) tubes are smaller than those of the (5,0) tubes. Moreover, a saturated behavior of enhancement factors β versus the length of tubes is observed. Finally, the field enhancement factors of fixed length tubes can be enhanced to eventually achieve a convergent tendency as their tube-tube distance increases.

An experimental study of Sound Transmission Loss (STL) measurement techniques using an impedance tube

A comparison between the two sound transmission loss (STL) measurement techniques using an impedance tube (i.e. two‐load method and anechoic termination method) is presented. A modified B&K type 4206 impedance tube has been designed and built. STL tests have been carried out for three homogeneous and isotropic materials with disk‐type test samples of identical diameters and different thicknesses. In addition, the results have been compared with those of the classical and more reliable method of two‐room. For both methods, the effect of downstream (tube termination) boundary conditions have been completely studied. The two‐load method yields results which matches with two‐room measurements, especially when the two boundary conditions are considerably different. The anechoic termination method, on the other hand, is significantly dependant on the termination boundary conditions.

Transmission loss measurement of consolidated granular media (L)

The normal incidence transmission loss of a new class of sustainable acoustic materials, i.e. consolidated granular media, has been measured to determine their sound insulating performance. Tests performed on different samples in a standing wave tube suggest that the traditional method employing an anechoic termination assumption can yield serious errors because its accuracy depends significantly on the properties of both the termination and the tested sample. Since it is not possible to implement a perfect anechoic termination over a wide frequency range, a well-developed alternative approach has been adopted. A simple theoretical analysis has been carried out to compare these two methods. It has been shown that the two-load method, based on two sets of measurements with different boundary conditions at the tube termination, can give more reliable and predictable results. Greater discrepancies have been observed in the case of the anechoic termination method applied to samples with higher values of flow resistivity. Results of the two-load method match well with predictions based on a simple model for acoustic transmission through a porous plate.

Broadband sound generation by confined turbulent jets.

Sound generation by confined stationary jets is of interest to the study of voice and speech production, among other applications. The generation of sound by low Mach number, confined, stationary circular jets was investigated. Experiments were performed using a quiet flow supply, muffler-terminated rigid uniform tubes, and acrylic orifice plates. A spectral decomposition method based on a linear source-filter model was used to decompose radiated nondimensional sound pressure spectra measured for various gas mixtures and mean flow velocities into the product of (1) a source spectral distribution function; (2) a function accounting for near field effects and radiation efficiency; and (3) an acoustic frequency response function. The acoustic frequency response function agreed, as expected, with the transfer function between the radiated acoustic pressure at one fixed location and the strength of an equivalent velocity source located at the orifice. The radiation efficiency function indicated a radiation efficiency of the order (kD)2 over the planar wave frequency range and (kD)4 at higher frequencies, where k is the wavenumber and D is the tube cross sectional dimension. This is consistent with theoretical predictions for the planar wave radiation efficiency of quadrupole sources in uniform rigid anechoic tubes. The effects of the Reynolds number, Re, on the source spectral distribution function were found to be insignificant over the range 2000<Re<20000. The source spectral distribution function approximately obeyed a St(-3) power law for Strouhal number values St<0.9, and a St-5 power law for St>2.5. The influence of a reflective open tube termination on the source function spectral distribution was found to be insignificant, confirming the absence of a feedback mechanism.