Acoustic Resonance Frequency Research Articles

Noise investigation of a cavitating orifice: use of cfd simulation and ffowcs williams–hawkings (fw-h) formulation to gain insight into acoustics condition

In piping systems, hydrodynamic cavitation is well known for its destructive capabilities such as generation of intense noise. The investigation of the effect of the cavitation on acoustic pressure fluctuations and resonance frequencies provides much information about the geometry of the cavitation area, the propagation and the damping characteristics of the cavitation medium. The acoustical effects of cavitation caused by a water flow through a single-hole orifice have been investigated by using Computational Fluid Dynamics (CFD) and Ffowcs Williams–Hawkings (FW-H) formulation. The fluid zone downstream of the orifice where the cavitation happens considered as acoustic source. Time-accurate solutions of the flow-field variables are obtained from large eddy simulation (LES). Two cavitation regimes are investigated and for each regime, the sound pressure signals far downstream of the orifices are computed by applying the Ffowcs Williams–Hawkings (FW-H) formulation. From the results, it can be concluded that the spectral characteristics of the sound pressure fluctuations are influences by the cavitation condition. The super cavitation condition generates significantly more noise than the developed cavitation condition. Moreover, the results demonstrate that a combination of LES and FW-H formulation is a promising tool for acoustical study of cavitating orifices.

Damage monitoring of three-point bending concrete specimens by acoustic emission and resonant frequency analysis

The crack propagation process in pre-notched concrete beam specimens, tested in the lab under three-point bending, was monitored by the Acoustic Emission (AE) technique and the extraction of resonant frequencies. The loading process was carried out in displacement-controlled conditions up to the final failure of the specimen. Average frequency vs. RA value analysis was used to characterize the crack propagation mode, whereas the cumulative AE energy and the variation in the resonant bending frequencies were selected as the main parameters to monitor the damage progress due to crack advancement. Moreover, finite element models were implemented to reproduce the load–deflection curve and to evaluate the resonant frequencies for different notch depths. An inverse procedure was therefore applied to estimate the crack advancement based on the measured and calculated frequencies.

Acoustic effects in halide lasers

Oscillations in the output power of halide lasers were recorded by varying the excitation frequency from 11.7 to 30 kHz. An effect arises in the laser tube, which performs both as an optical and an acoustic resonator at the acoustic resonant frequencies, just like other metal vapor lasers. It is shown that a similar effect occurs when amplifying the parameters of lasers. In other words, the oscillatory behavior of laser output power comes from the competition between the microscopic laser parameters and the excitation frequency as an operational and macroscopic parameter.

Experimental observation of spontaneous depolarized guided acoustic-wave Brillouin scattering in side cores of a multicore fiber

Spontaneous depolarized guided acoustic-wave Brillouin scattering (GAWBS) was experimentally observed in one of the side cores of an uncoated multicore fiber (MCF). The frequency bandwidth in the side core was up to ∼400 MHz, which is 0.5 times that in the central core. The GAWBS spectrum of the side core of the MCF included intrinsic peaks, which had different acoustic resonance frequencies from those of the central core. In addition, the spontaneous depolarized GAWBS in the central/side core was unaffected by that in the other core. These results will lead to the development of polarization/phase modulators using an MCF.

Helix structure for low frequency acoustic energy harvesting.

In this study, a novel helix acoustic resonator is proposed to realize acoustic energy harvesting (AEH). Compared with the traditional acoustic resonators, the proposed structure occupies a small volume and is suitable for the low frequency range. At a specific incident frequency, the mechanical component of the AEH device can be intensely excited and the bonded piezoelectric patch is utilized to convert the strain energy into electrical energy. Analytical studies are carried out to disclose the acoustic resonant system properties. Meanwhile, the pure acoustic and coupled vibro-acoustic properties of the proposed device are analyzed via the finite element method. The major part of the AEH device is fabricated via 3D printing for experimental study, which is favored for rapid prototyping. At acoustic resonance frequency 175 Hz, 100 dB sound pressure level excitation working condition, the measured experimental data show that the harvested power can be up to 7.3 μW.

Design and demonstration of acoustically optimized, fully-printed, BST MIM varactors for high power matching circuits

AbstractThis work addresses the piezoelectric induced reduction of quality factor in fully-printed metal-insulator-metal (MIM) barium strontium titanate (BST) thick film varactors designed for high power operation. An acoustically optimized varactor design is presented and compared to a non-optimized high-power varactor. The design is utilized to present a narrowband acoustic suppression technique based on defined weights. The acoustically optimized varactor consists of 162 varactor cells in a capacitive matrix. The cells in the matrix are interconnectable allowing for a variable unbiased capacitance and power rating. Due to this setup, surface acoustic waves are interrupted, and the reduced size of the cells allows for a reduced BST layer thickness, shifting the acoustic resonance away from the operational frequency. Therefore, an inverted behavior in comparison to the high-power varactor is observed with an increasing quality factor with biasing voltage. Compared to the high-power varactor, the acoustically optimized varactor design shows a 40% increased quality factor in biased state. By applying the narrowband acoustic suppression technique, an increase in quality factor of 145% is achieved compared to the unsuppressed design. In comparison to the high-power varactor, the acoustical suppressed design shows an increase in quality factor of 480% at the first acoustic resonance frequency.

Determining the mass of gas in large collection volumes with acoustic and microwave resonances

We characterized a 1.8 m3, quasi-spherical resonator, a pressure vessel informally known as the “big blue ball” or “BBB.” The BBB will be the collection volume of a NIST-designed gas-flow standard that will operate at pressures up to 7 MPa. Using microwave resonance frequencies, we determined the volume of the BBB filled with argon as a function of pressure (up to 7 MPa) and temperature (near ambient). The measured pressure- and temperature-dependences of the BBB’s volume are consistent with the published properties of carbon steels. We filled the BBB with 220 kg of argon in weighed increments of approximately 20 kg. We also determined the mass macoust of argon in the BBB by measuring the pressure, the acoustic resonance frequencies facoust of 3 modes, and using the known thermophysical properties of argon. The values of macoust were within ±0.03 % of the gravimetrically determined masses. In a typical application, the BBB will never be isothermal. Nevertheless, the acoustic resonance frequencies quickly and accurately determine the average temperature and mass of the gas in the BBB despite significant, long-lived thermal gradients that are created by pressure changes. A theoretical model for effect of temperature gradients on the acoustic resonance frequencies is presented.

Experimental Investigation for Effects of Steam Wetness and Static Pressure on Acoustic Resonance Frequency at Side Branch Piping under Wet Steam Flow

Flow-induced acoustic resonances in steam piping with closed side branches cause severe structural vibration and fatigue damage of piping and components in many industrial applications such as power plants. The steam state in the steam piping of power plants is not only dry steam but also wet steam. From our previous experiments under low-pressure wet steam flow, the resonance frequencies, which is important parameter to predict acoustic resonance, under wet steam obtained by the theoretical equation and assuming a saturated sound speed were within ±6% of the measured values. However, the static pressure in practical steam piping is often higher than that in our previous experiments. In this study, we conducted experiments on acoustic resonance in a single side branch under a high-quality wet steam flow with the static pressure as parameters to investigate the effects of the static pressure on acoustic resonance frequency under wet steam flow.

Electronic frequency tuning of the acousto-optic mode-locking device of a laser

The effect of the electronic tuning of the acoustic resonances in an acousto-optic mode-locking device of a laser is investigated theoretically and experimentally. The problem of the excitation of a Fabry–Perot acoustic resonator by a plate-like piezoelectric transducer (PET) is solved in the approximation of plane acoustic waves taking into consideration the actual parameters of an RF generator and the elements for matching the PET to the generator. Resonances are tuned by changing the matching inductance that was connected in parallel to the transducer of the acousto-optic cell. The cell used in the experiment was manufactured from fused silica and included a lithium niobate PET. Changes in the matching inductance in the range of 0.025 to 0.2 μH provided the acoustic-resonance frequency tuning by 0.19 MHz, which exceeds the acoustic- resonance half-width.

Measurement of the Boltzmann Constant in a Quasispherical Acoustic Resonator

Frequencies of acoustic and electromagnetic resonances were measured in a quasispherical acoustic resonator at the temperature of the triple point of water. The resonator was filled with helium 4He. Based on the analysis of experimental data, a value for the Boltzmann constant of kB = 1.380651·10–23 J·K–1 with uncertainty of 2.4 ppm was obtained.

Acoustically actuated ultra-compact NEMS magnetoelectric antennas

State-of-the-art compact antennas rely on electromagnetic wave resonance, which leads to antenna sizes that are comparable to the electromagnetic wavelength. As a result, antennas typically have a size greater than one-tenth of the wavelength, and further miniaturization of antennas has been an open challenge for decades. Here we report on acoustically actuated nanomechanical magnetoelectric (ME) antennas with a suspended ferromagnetic/piezoelectric thin-film heterostructure. These ME antennas receive and transmit electromagnetic waves through the ME effect at their acoustic resonance frequencies. The bulk acoustic waves in ME antennas stimulate magnetization oscillations of the ferromagnetic thin film, which results in the radiation of electromagnetic waves. Vice versa, these antennas sense the magnetic fields of electromagnetic waves, giving a piezoelectric voltage output. The ME antennas (with sizes as small as one-thousandth of a wavelength) demonstrates 1–2 orders of magnitude miniaturization over state-of-the-art compact antennas without performance degradation. These ME antennas have potential implications for portable wireless communication systems.

An efficient low-frequency acoustic energy harvester

Here, an efficient acoustic energy harvester is proposed that is suitable for low-frequency bands. It is composed of a tunable Helmholtz resonator with a flexible bottom, with affixed piezo disk and proof mass. The proof mass can lower the mechanical resonance frequency of the bottom, while increasing the harvested sound power. The proposed Helmholtz resonator was designed for sound pressure amplification. Furthermore, it is tunable, enabling adjustment of the acoustic resonance frequency to the mechanical resonance frequency. The designed tunable Helmholtz resonator has been fabricated and its function was experimentally verified. Furthermore, the acoustic energy harvesting study was conducted under 100dB sound pressure level excitation. Experimental results show that the proposed harvester can generate 3.49μW (at optimal load) when both resonance frequencies are matched, and the energy conversion efficiency can reach up to 38.4%.

Development of an acoustic measurement protocol to monitor acetabular implant fixation in cementless total hip Arthroplasty: A preliminary study

In cementless total hip arthroplasty (THA), the initial stability is obtained by press-fitting the implant in the bone to allow osseointegration for a long term secondary stability. However, finding the insertion endpoint that corresponds to a proper initial stability is currently based on the tactile and auditory experiences of the orthopedic surgeon, which can be challenging.This study presents a novel real-time method based on acoustic signals to monitor the acetabular implant fixation in cementless total hip arthroplasty. Twelve acoustic in vitro experiments were performed on three types of bone models; a simple bone block model, an artificial pelvic model and a cadaveric model. A custom made beam was screwed onto the implant which functioned as a sound enhancer and insertor. At each insertion step an acoustic measurement was performed.A significant acoustic resonance frequency shift was observed during the insertion process for the different bone models; 250 Hz (35%, second bending mode) to 180 Hz (13%, fourth bending mode) for the artificial bone block models and 120 Hz (11%, eighth bending mode) for the artificial pelvis model. No significant frequency shift was observed during the cadaveric experiment due to a lack of implant fixation in this model. This novel diagnostic method shows the potential of using acoustic signals to monitor the implant seating during insertion.

A magnetoelectric sensor of threshold DC magnetic fields

A multiferroic magnetic field sensor capable of producing an output for threshold magnetic fields has been fabricated and characterized. The sensor consists of a trilayer composite of piezoelectric X-cut lanthanum gallium tantalate and magnetostrictive Metglas placed inside a solenoid and a wide-band amplifier. The composite plays two distinct roles in the device; it forms the feedback loop of an oscillator and sets the frequency of sustained oscillations. The sensor generated an output of 2.5 V at the longitudinal acoustic resonance frequency of 87.5 kHz for the trilayer for DC magnetic fields H = 0.3 to 50 Oe parallel to the composite plane. The device functions as a threshold magnetic field sensor for this H-interval, and the threshold ON and OFF H-values for an ac voltage output could be controlled electronically or with a proper choice of the ferromagnetic phase in the composite.

Low frequency mechanical resonance of the vocal tract in vocal exercises that apply tubes

Abstract Phonation into a tube that lowers the acoustic vocal tract resonance frequency and increases vocal tract impedance is used in voice therapy to establish effortless voice production. Additionally, keeping the distal end of the tube in the water results in the water bubbling and a consequent oscillation of oral pressure. This may feel like a massage of the vocal tract and larynx. A low frequency mechanical resonance of the vocal tract, F m , could enhance the effect of tube therapy in two ways: 1) by lowering the first acoustic resonance closer to the fundamental frequency of phonation, and 2) by introducing a coalescence of F m with the water bubbling frequency. A mathematical model of acoustic-structural interaction is introduced to clarify F m in the context of phonation into a tube with the distal end in air and in water. The numerical results from the model are compared with the resonance frequencies measured in a male subject phonating on the vowel [u:] into a glass resonance tube with the distal end in air and at 2 cm and 10 cm under water. The effects of phonation through the tube are demonstrated by registering oral air pressure and electroglottography, and by synchronous high‐speed filming of the water bubbling. The first computed acoustic resonance frequency decreased from F 1 = 200 Hz for the tube end in air down to about F 1 = 175 Hz for the tube end in water, which roughly agrees with the first formant frequency of c. 179 Hz that was experimentally found for the human vocal tract. Considering the mechanical resonance F m of the vocal tract to be c. 66 Hz, as previously estimated from measurements of a closed vocal tract, then according to the mathematical model for the vocal tract prolonged by a rigid glass tube, this frequency drops to 23 Hz. When the tube is submerged in water, F m drops further to F m = 8 Hz for the resonance tube and to about F m = 10 Hz for a longer and wider silicon Lax Vox tube. The results thus show that the mechanical resonance can be near the measured water bubbling frequency F b = 11–11.5 Hz. The results suggest that the mechanical resonance of the vocal tract tissues enhances the effects of the tube during voice therapy.

Experimental and Numerical Study on Pressure Pulsations Under Various Acoustic Boundary Conditions in Piping Systems

To improve design and troubleshooting techniques of piping systems for operating power plants, it is necessary to investigate, by experiment and simulation, the behavior of fluid inside the piping system in detail. This study was conducted using full-scale piping system under conditions that could seriously threaten the plant operation, by matching pressure pulsations, acoustic resonance, and piping natural frequency. Although piping vibration is reported to influence fluid pressure pulsations, there were no such examples of influence in this experiment. Knowing that the opening ratio of the pressure control valve affects the boundary condition for acoustic resonance, experiment and simulation at different opening ratios were conducted. It has been suggested that the cases in which a valve partially open at 25% or less should not be taken as a closed end. This finding conflicts with such a widespread design assumption.

Evaluation of the myringosclerotic tympanic membrane with wideband tympanometry

Objective: The purpose of this study is to evaluate the effects of myringosclerosis (MS) localized to the tympanic membrane (TM) on the mechano-acoustics of hearing using wideband tympanometry (WBT). Materials and Methods: In this prospective case-controlled study, 86 ears of 54 patients who were found to have MS localized to the TM were compared to 40 healthy eardrums in 20 patients. Thirty-seven ears which had a MS ratio to the whole TM of 50% were classified as Group 3. Peak acoustic compliance, resonant frequency (RF), and frequency-specific absorbance results of WBT were compared among the MS groups and the control group. Results: When the amplitudes of peak acoustic compliance of the MS groups and control group were compared, the MS groups were found to have lower amplitudes, and the difference was statistically significant (P 0.05). The RF of Groups 1, 2, and 3 were 1062, 1154, and 1166 Hz, respectively, and the RF of the control group was 1077 Hz. There was no significant difference among the groups with regard to resonant frequencies. Conclusion: This study showed that although MS localized to the TM decreased the amplitude of peak acoustic compliance of the tympanogram, it did not affect the RF or the wideband acoustic absorbance.

Energy accommodation coefficient extracted from acoustic resonator experiments.

We review values of the temperature jump coefficient ζT determined from measurements of the acoustic resonance frequencies facoust of helium-filled and argon-filled, spherical cavities near ambient temperature. We combine these values of ζT with literature data for tangential momentum accommodation coefficient (TMAC) and the Cercignani-Lampis model of the gas-surface interaction to obtain measurement-derived values of the normal energy accommodation coefficient (NEAC). We found that NEAC ranges from 0 to 0.1 for helium and from 0.61 to 0.85 for argon at ambient temperature for several different surfaces. We suggest that measurements of facoust of gas-filled, cylindrical cavities and of the non-radial modes of quasi-spherical cavities might separately determine TMAC and NEAC. Alternatively, TMAC and NEAC could be determined by measuring the heat transfer and momentum transfer between parallel rotating discs at low pressure.

Probing the acoustic vibrations of complex-shaped metal nanoparticles with four-wave mixing.

We probe the acoustic vibrations of silver nanoprisms and gold nano-octahedrons in aqueous solution with four-wave mixing. The nonlinear optical response shows two acoustic vibrational modes: an in-plane mode of nanoprisms with vertexial expansion and contraction; an extensional mode of nano-octahedrons with longitudinal expansion and transverse contraction. The particles were also analyzed with electron microscopy and the acoustic resonance frequencies were then calculated by the finite element analysis, showing good agreement with experimental observations. The experimental mode frequencies also fit with theoretical approximations, which show an inverse dependence of the mode frequency on the edge length, for both nanoprisms and nano-octahedrons. This technique is promising for in situ monitoring of colloidal growth.

Acoustic resonances greatly improve detection of leaks from large pressure vessels

We measured the pressure p and the acoustic resonance frequency fa of argon gas in a 300 L tank. We then used the ratio p/fa2 (proportional to the mass M of gas) to determine the fractional leak rate (dM/dt)/M ≈ −13×10−6/hr of gas from the tank. The tank was filled with argon at 450 kPa and was exposed to sunshine-driven temperature and pressure fluctuations as large as (dT/dt)/T ≈ (dp/dt)/p ≈ 5×10-2 h-1 (i.e., 1000× larger) in a 24-hour record. This leak could not be detected in a 72-hour record of p/T. Theory predicts that the resonance frequencies are insensitive to linear temperature gradients; however, we do not have a detailed understanding of why the acoustic frequencies are insensitive to asymmetric, time-dependent heating of the tank. From auxiliary measurements and information from the literature, we believe that convective currents near the tank's walls carry most of the heat between the hot and cool regions, leaving a linear temperature gradient in the majority of the gas's volume. We plan to report preliminary measurements for a much larger (1800 L) tank. We expect that the results of this investigation will lead to effective acoustic methods for flow calibrations and leak detection in large volumes.