Intensity Probe Research Articles

Low-frequency calibration of a multidimensional acoustic intensity probe for application to rocket noise

Measurements of acoustic vector quantities in the near field of a solid-fuel rocket motor are useful for enhancing prediction models related to rocket noise. However, the probes used to measure these quantities traditionally have low-frequency bandwidth limitations (e.g., below 45 Hz) thereby excluding the lowest, and in some cases, the loudest frequencies generated by large rocket motors. At these low frequencies, the phase and magnitude mismatch between microphones become greater and the acoustic phase separation between any two microphones becomes smaller, resulting in more error in estimating the pressure gradient between microphones. To investigate the low-frequency response of an acoustic intensity probe, a turntable is used to rotate a four-microphone probe with variable microphone spacing in a low-frequency noise field and an experimental assessment of the bandwidth is given for both magnitude and directional response. Also discussed is the effectiveness of a microphone interchange calibration technique to remove amplitude and phase mismatch and increase the usable bandwidth of the probe.

Identification of the Vehicle Noise Source by Sound Intensity Method

In this paper, we analysed the level of radiation noise and distribution of noise sources of car’s engine and front panels by using sound intensity method. To get the nephogram of sound intensity and sound power spectrum, we used the sound intensity probe and Multi-channel Data Acquisition Regulation System B&K 3560-D and Pulse Data Processing Analysis Software. By analysing experimental results, we can conclude the location of noise sources of these parts. The measurement results will serve as a reference for the car noise reduction.

Monitoring attosecond dynamics of coherent electron-nuclear wave packets by molecular high-order-harmonic generation

A pump-probe scheme for preparing and monitoring electron-nuclear motion in a dissociative coherent electron-nuclear wave packet is explored from numerical solutions of a non-Born-Oppenheimer time-dependent Schr\odinger equation. A mid-ir intense few-cycle probe pulse is used to generate molecular high-order-harmonic generation (MHOHG) from a coherent superposition of two or more dissociative coherent electronic-nuclear wave packets, prepared by a femtosecond uv pump pulse. Varying the time delay between the intense ir probe pulse and the uv pump pulse by a few hundreds of attoseconds, the MHOHG signal intensity is shown to vary by orders of magnitude, thus showing the high sensitivity to electron-nuclear dynamics in coherent electron-nuclear wave packets. We relate this high sensitivity of MHOHG spectra to opposing electron velocities (fluxes) in the electron wave packets of the recombining (recolliding) ionized electron and of the bound electron in the initial coherent superposition of two electronic states.

Calibration of pressure-velocity probes using a progressive plane wave reference field and comparison with nominal calibration filters

A procedure for calibrating pressure-velocity (p-v) sound intensity probes using a progressive plane wave as reference field is presented here. The procedure has been checked for a microelectromechanical system technology-based Microflown(®) match-size probe by comparing the calibration results with the nominal correction curves available from the manufacturer. The reference field was generated along a wave guide by means of a dual cone loudspeaker supplying acoustic energy in the range 20 Hz-20 kHz through an impedance adaptor. Different from the current in-field procedures, the one proposed here allows the calibration of probes under test to be executed at once up to 10 kHz without any change in the experimental setup. After a detailed review of the general principles of calibration, the procedure has been finalized with three main stages: (a) determination of the full coherence calibration bandwidth of the probe, (b) comparison calibration of the probe built-in pressure microphone over the full coherence frequency range, and (c) relative calibration of the velocity sensor over the calibrated pressure one. Calibration results for the probe under test have been best fitted against the calibration filters modeled by the manufacturer and the direct comparison of the obtained data with the factory ones has been reported.

Electronic enhancement of the directional response of a micromachined biomimetic optical microphone.

A silicon micromachined biomimetic optical microphone has been recently demonstrated to have directional response and low noise [J. Acoust. Soc. Am. 125(4), 2013–2026 (2009)]. In this microphone, the motion of one end of the pivoting rectangular diaphragm is detected using an integrated optical interferometer and each end can be actuated using separate electrostatic actuators. This configuration enables one to selectively enhance either the directional, anti-symmetric rocking mode or the omni-directional symmetrical second vibrational mode of the diaphragm in two separate active feedback loops. A circuit model with two electrical ports to actuate each side of the diaphragm, and two acoustic ports to drive each mode has been developed to illustrate the electronic method. The model includes the effect of the air medium and the backside cavity through mechanical impedances which are verified through measurements. With the two-sided active feedback scheme, the model predicts significant improvements in the directional response resulting in more than 10-dB improvement in the residual intensity index when the microphone is used for gradient measurement in an intensity probe.

Redistribution of vibrational population in a molecular ion with nonresonant strong-field laser pulses

We present an experimental demonstration of nonresonant manipulation of vibrational states in a molecule by an intense ultrashort laser pulse. A vibrational wave packet is generated in ${\mathrm{D}}_{2}{}^{+}$ through tunnel ionization of ${\mathrm{D}}_{2}$ by a few-cycle pump pulse. A similar control pulse is applied as the wave packet begins to dephase so that the dynamic Stark effect distorts the electronic environment of the nuclei, transferring vibrational population. The time evolution of the modified wave packet is probed via the ${\mathrm{D}}_{2}{}^{+}$ photodissociation yield that results from the application of an intense probe pulse. Comparing the measured yield with a quasiclassical trajectory model allows us to determine the redistribution of vibrational population caused by the control pulse.

Time-Resolved Photoelectron Angular Distributions from Strong-Field Ionization of Rotating Naphthalene Molecules

A nanosecond laser pulse confines the spatial orientation of naphthalene in 1D or 3D while a femtosecond kick pulse initiates rotation of the molecular plane around the fixed long axis. Time-dependent photoelectron angular distributions (PADs), resulting from ionization by an intense femtosecond probe pulse, exhibit pronounced changes as the molecular plane rotates. Enhanced 3D alignment, occurring shortly after the kick pulse, provides strongly improved contrast in molecular-frame PADs. Calculations in the strong-field approximation show that the striking structures observed in the PADs originate from nodal planes in occupied valence orbitals.

A Study of Wideband Absorbers in a Non-Environment Control Room: Characterisation of the Sound Field by Means of p-p Probe Measurements

Wideband absorbers are a fundamental part of non-environment control rooms, providing high absorption in all the frequency range. They consist of huge angled panels hanging in front of the rear wall, the side walls, and the ceiling. As a first step to understand their absorption mechanisms, the sound field in the vicinity of the wideband absorbers of the rear wall has been measured with a p-p intensity probe in the control room at the 'Universidade de Vigo'. The characteristics of the sound field in the proximity of the rear wall will be discussed on the basis of the analysis of the pressure, particle velocity and intensity measurements.

649 音響インテンシティベクトルを計測空間で表示する一体型プローブの開発

Sound intensity method is one of the acoustic measurement techniques. Sound intensity means the propagation of sound energy and helps us to figure out sound field. Sound Intensity mapping is general measurement method that measures sound intensity vectors on each measurement points and combines the photograph of measurement field and measured sound intensity vectors. This measurement method has the problem that takes a long time to figure out sound field because of large amount of measurement points. If sound intensity vector is shown on measurement field directly aiming to find out the Noise Source, we figure out sound field quickly and simply. In this paper, all-in-one probe displaying sound intensity vector on measurement field was developed. The sound intensity probe consists of four microphones and the displaying device for sound intensity vector. The displaying device consists of LED array. In this report, the effects of the LED array structure to the measured sound field is investigated experimentally. This report demonstrates sound intensity mapping and noise source identification used the proposed probe.

Coherent control of the ultrafast dissociative ionization dynamics of bromochloroalkanes

We report on the coherent control of the ultrafast ionization and fragmentation dynamics of the bromochloroalkanes C(2)H(4)BrCl and C(3)H(6)BrCl using shaped femtosecond laser pulses. In closed-loop control experiments on bromochloropropane (C(3)H(6)BrCl) the fragment ion yields of CH(2)Cl(+), CH(2)Br(+), and C(3)H(3)(+) are optimized with respect to that of the parent cation C(3)H(6)BrCl(+). The fragment ion yields are recorded in additional experiments in order to reveal the energetics of cation fragmentation, where laser-produced plasma radiation is used as a tunable pulsed nanosecond vacuum ultraviolet radiation source along with photoionization mass spectrometry. The time structure of the optimized femtosecond laser pulses leads to a depletion of the parent ion and an enhancement of the fragment ions, where a characteristic sequence of pulses is required. Specifically, an intense pump pulse is followed by a less intense probe pulse where the delay is 0.5 ps. Similarly optimized pulse shapes are obtained from closed-loop control experiments on bromochloroethane (C(2)H(4)BrCl), where the fragment ion yield of CH(2)Br(+) is optimized with respect to that of C(2)H(4)BrCl(+) as well as the fragment ion ratios C(2)H(2)(+)/CH(2)Br(+) and C(2)H(3)(+)/C(2)H(4)Cl(+). The assignment of the underlying control mechanism is derived from one-color 804 nm pump-probe experiments, where the yields of the parent cation and several fragments show broad dynamic resonances with a maximum at Δt = 0.5 ps. The experimental findings are rationalized in terms of dynamic ionic resonances leading to an enhanced dissociation of the parent cation and some primary fragment ions.

Dynamics of two-photon picosecond absorption in ZnWO4 and PbWO4 crystals

A method has been proposed to analyze the dynamics of interband two-photon absorption in a nonlinear medium excited by a sequence of picosecond laser pulses of variable intensity and continuous probe radiation. Induced absorption leading both to hysteresis in the dependence of the absorption on the intensity of laser pump radiation and to the opacity of crystals at the pump wavelength has been revealed in initially transparent ZnWO4 and PbWO4 crystals irradiated by a train of 523.5-nm pulses with a duration of 20 ps at pump intensities of 5 to 140 GW/cm2. The kinetics of an increase in absorption and its subsequent relaxation at a 523.5-nm picosecond excitation of the crystals have been measured with continuous 633-nm probe radiation. An exponential component of the increase in absorption with the time constant τ = 2−3.5 and 8–9.5 μs depending on the direction of the linear polarization of pump radiation has been revealed at 300 K in ZnWO4 and PbWO4 crystals, respectively. The absorption relaxation kinetics in the crystals are complicated and approach an exponential at a late stage with the constant τ = 40−130 and 12–80 ms for the ZnWO4 and PbWO4 crystals, respectively.

Characterization of scattered acoustic intensity fields in the resonance region of a motionless rigid sphere

In this study, the properties of the scattered acoustic vector fields generated by simple rigid motionless spheres are investigated. Analytical solutions are derived from general acoustic pressure scattering models, and analyzed for wave numbers in the resonance region. The separable active and reactive components of the acoustic intensity are used to investigate the structural features of the scattered field components. Numerical results are presented. The ability to extract scattered field features is illustrated with measurements obtained from a recent in-air experiment using an anechoic chamber and acoustic intensity probes to measure the scattered acoustic vector field from motionless rigid spheres.

Ultrasound-assisted solid liquid extraction (USLE) of olive fruit ( Olea europaea) phenolic compounds

A new method of ultrasound-assisted solid liquid extraction (USLE) of olive fruit phenols is described. Phenolics were extracted using high intensity probe ultrasonication and analysed by HPLC-DAD-FLD-MS/MS. Four USLE parameters – sonication time (4, 15, 20, 30 min), temperature (25, 45 °C), solvent composition (80%, 100% methanol) and extraction steps (1–5) were studied and optimised on the basis of nine major olive fruit phenols. A three-step extraction of 20 min with pure methanol (25 mL) at 45 °C was needed for sufficient phenol recoveries (94.1–98.7%) from 1.5 g of freeze-dried olive fruits. The proposed USLE method was more efficient in comparison to US bath and agitation, with up to 33% and 80% enhancement in the case of oleuropein, respectively. In addition, the overall method provided high selectivity, precision and sensitivity with LODs/LOQs ranging from 0.66–4.92 μg g −1 and 2.00–14.77 μg g −1 of olives DW, respectively.

Noise generation in contraction joints in Portland cement concrete.

Contraction joints between slabs of Portland cement concrete have a major impact on measured tire‐pavement noise levels. It has been proposed that during the interval when the contact patch of the tire is over the joint, the system acts as a Helmholtz resonator, and that this mechanism is responsible for the majority of the increased noise due to contraction joints. In this paper, this mechanism is investigated through theoretical calculations and experimentation. Intensity probes were used to measure noise near joints of varying widths using Purdue University’s Tire‐Pavement Test Apparatus (TPTA). The TPTA was used to discover relationships between vehicle speed, joint width, and measured sound pressure and sound intensity spectra near the joint and the tire.

Laboratory measurements of sound transmission at low frequencies.

The ability of acoustic materials to attenuate sound is usually determined in accordance with ASTM E-90 or ISO 140-3, both based on the diffuse field theory. However, the reality is that the size of typical reverberant chambers does not provide a sufficiently diffuse field at low frequencies. As a result, there is significant variation in sound transmission data of tested materials below 150 Hz. Several attempts were undertaken to improve the accuracy of measuring TL such as increasing field diffuseness by using reflecting surfaces, installing near-field array of loudspeakers, and using sound intensity probes on the receiving sides. None of these proved totally satisfactory. This work presents studies on using various approaches to more accurately determine acoustic mitigation of low-frequency transmitted noise. A metal box consisting of a very rigid frame supporting elastic panels on all sides was acoustically excited by a loudspeaker suspended inside of the box. The panels and box interior were designed to have very low-fundamental frequencies. The box was suspended by its frame in an anechoic room. An intensity probe was used to measure the transmitted sound from the box panels. The acoustic performance of various acoustic materials was compared for frequencies below 500 Hz.

Generation of intense frequency-tunable few-cycle femtosecond pulses in hollow fiber

We theoretically show an approach to generate intense frequency-tunable few-cycle femtosecond pulses by molecular phase modulation combined with self-phase modulation. An intense pump pulse propagates through a gas-filled hollow fiber to excite alignment of the gas molecule, which induces temporal modulation of the refractive index. Then the spectrum of a time-delayed intense probe pulse is continuously tuned by the alignment and broadened simultaneously by self-phase modulation. The modification to the pump-induced alignment by the intense probe pulse is considered. Frequency-tunable intense few-cycle pulses in the visible and near-infrared spectrum range are obtained using initial 20 fs, 800 nm pulses.

High-pressure phase diagram of the drug mitotane in compressed and/or supercritical CO 2

This work provides experimental phase diagram of mitotane, a drug used in the chemotherapy treatment of adrenocortical carcinoma, in compressed and/or supercritical CO 2. The synthetic-static method in a high-pressure variable-volume view cell coupled with a transmitted-light intensity probe was used to measure the solid-fluid (SF) equilibrium data. The phase equilibrium experiments were determined in temperature ranging from (298.2 to 333.1) K and pressure up to 22 MPa. Peng–Robinson equation of state (PR-EoS) with classical mixing rule was used to correlate the experimental data. Excellent agreement was found between experimental and calculated values.

Patch near field acoustic holography based on particle velocity measurements

Patch near field acoustic holography (PNAH) based on sound pressure measurements makes it possible to reconstruct the source field near a source by measuring the sound pressure at positions on a surface that is comparable in size to the source region of concern. Particle velocity is an alternative input quantity for NAH, and the advantage of using the normal component of the particle velocity rather than the sound pressure as the input of conventional spatial Fourier transform based NAH and as the input of the statistically optimized variant of NAH has recently been demonstrated. This paper examines the use of particle velocity as the input of PNAH. Because the particle velocity decays faster toward the edges of the measurement aperture than the pressure does and because the wave number ratio that enters into the inverse propagator from pressure to velocity amplifies high spatial frequencies, PNAH based on particle velocity measurements can give better results than the pressure-based PNAH with a reduced number of iterations. A simulation study, as well as an experiment carried out with a pressure-velocity sound intensity probe, demonstrates these findings.

Development of Standard Testing Procedure for Experimentally Determining Inherent Source Pulsation Power Generated by Hydraulic Pump

This paper reports on the experimental determination of the level of inherent pulsation power generated by a hydraulic pump, using both a test method newly developed for the measurement of fluid pulsation power in a pipeline and a theoretically derived conversion equation for eliminating the influence of a hydraulic circuit on the measurement. The suitability of the test procedure as a standard method for assessment of the inherent source pulsation power of a hydraulic pump is confirmed. First, it was determined that the pulsation power in a pipeline can be measured using a pressure sensor unit called the “pulsation intensity probe”, which utilizes the same measurement principle as a conventional “sound intensity probe”, with good repeatability and with sufficient accuracy for practical usage. Next, a standard test procedure for determining the inherent source pulsation power of a hydraulic pump, which is independent of the hydraulic circuit, from the measurements of a pulsation power in a reference pipe was proposed. Finally, it was verified from the experimental measurements and simulations that this proposed standard test method is very useful for both absolute and relative assessments of the level of source pulsation power of a hydraulic pump.

Diffraction based optical microelectromechanical systems microphone and its application to the measurement of sound intensity.

Diffraction based optical MEMS microphones and force feedback capabilities of these microphones are presented earlier [Bicen et al., J. Acoust. Soc. Am. 123, 3230 (2008)]. Further investigation is done in order to see the capabilities of these optical microphones in measuring the sound intensity. The biomimetic diaphragms of these microphones are designed for responding to pressure gradient which can be used for extracting the particle velocity required to measure the sound intensity. In order to show the velocity measuring capability of these microphones, an impedance tube method is used because the velocity and pressure at each point in the impedance tube can be found accurately. The comparison of the measured velocities and sound intensities with the optical microphone and commercially available sound intensity probes is presented. Model results are discussed in order to show the effect of the different mode shapes on the accuracy of the pressure gradient measurements. Optimization of these biomimetic diaphragms will result in the measurement of the sound intensity in a larger bandwidth without using any spacers and additional microphone adapters like in commercial sound intensity probes. [Work supported by National Institutes of Health (NIH) and the Catalyst Foundation.]