Acoustic Center Research Articles

Experimental studies with parallel phase-shifting interferometry

One of the most popular of devices currently used for acousto-optic sensing is the laser Doppler vibrometer (LDV), an interferometer originally designed to measure the vibration velocity of objects. LDVs are a popular way to measure and visualize acoustic fields, however it requires scanning the laser, which limits the measurement sound field. Recently, as the camera captures 2D images of the sound field on thousands of pixels simultaneously, the sound fields that can be measured are no longer limited to those that can be repeated. A high-speed camera captures 2D sound fields with tens or hundreds of thousands of frames per second, making it possible to film a slow-motion video of propagating sound in real time. The parallel phase-shifting interferometry (PPSI) with polarized high-speed cameras has been developed and introduced in the acoustics field as well. It has demonstrated impressive visualizations of airborne acoustic phenomena due to its high sensitivity and spatiotemporal resolution. It has also found many applications in recent years. This paper presents our experimental studies, especially measurement of aerodynamic sound, sound radiated from fast-moving sources or musical instruments, determination of acoustic center, etc.

High-frequency surface-micromachined optical ultrasound transducer array for 3D micro photoacoustic computed tomography.

This Letter reports a new, to the best of our knowledge, high-frequency surface-micromachined optical ultrasound transducer (HF-SMOUT) array for micro photoacoustic computed tomography (µPACT). An 11 × 11 mm2 2D array of 220 × 220 elements (35 µm in diameter) is designed, fabricated, and characterized. The optical resonance wavelength (ORW) of ≥90% of the elements falls within a 6-nm range. The acoustic center frequency and bandwidth of the elements are ∼14 MHz and ∼18 MHz (129%), respectively. The noise equivalent pressure (NEP) is 161 Pa (or 18 m P a/H z) within a measurement bandwidth of 5-75 MHz. The standard deviation of the ORW drift is 0.45 nm and 0.93 nm within 25°C-55°C, respectively, and during a seven-day continuous water immersion. PACT experiments are conducted to evaluate the imaging performances of the HF-SMOUT array. The spatial resolution is estimated as 90 µm (axial) and 250-750 µm (lateral) within a 10 × 10 mm2 field of view (FoV) and the imaging depth of 16 mm. A 3D PA image of a knotted black hair target is also successfully acquired. These results demonstrate the feasibility of using the HF-SMOUT array for µPACT applications.

An Optically Transparent Focused P(VDF-TrFE) Transducer for Photoacoustic Microscopy (PAM)

This paper reports a new optically-transparent focused P(VDF-TrFE) (poly(vinylidene fluoride-co-trifluoroethylene)) transducer for photoacoustic microscopy (PAM), which is fabricated by a new process based on pre-cutting and direct-lamination. Compared with the previous fabrication process, it is simpler, and makes it possible to achieve a high numerical aperture (NA) without stretching the (brittle) piezoelectric film. For demonstration, a prototype transducer has been fabricated with a 10-μm-thick 70/30 P(VDF-TrFE) film laminated onto a plano-concave glass lens with an acoustic NA of 0.64. Experimental characterizations show that the transducer has an optical transmittance of 88.6% (@ 532 nm), an acoustic center frequency and -3 dB bandwidth of 24 MHz and 29 MHz, respectively. Using the new optically-transparent focused P(VDF-TrFE) transducer, a PAM setup has been built to carry imaging experiments on different targets. Based on the experimental results, it can be concluded that the optically-transparent focused P(VDF-TrFE) transducer could be useful for the development of new PAM systems for different imaging applications.

On the low-frequency acoustic center.

Acousticians typically consider the acoustic center of a source to be the point from which sound waves appear to diverge spherically. Many applications require the center's accurate determination, but its deeper significance and means of assessment have often remained ambiguous. This work revisits the acoustic center and shows how a low-frequency sound radiator with omnidirectional far-field directivity has a center defined by its dipole-to-monopole moment ratio. This definition yields conclusive results for several theoretical sources and highlights the limitations of characterizing the acoustic center only in terms of an equivalent point source.

Equivalent Size and Acoustic Center of Measuring Hydrophone

Equivalent Size and Acoustic Center of Measuring Hydrophone

Determination of microphone acoustic center from sound field projection measured by optical interferometry.

This article presents a method for determining the acoustic center of a microphone from a sound field measured by optical interferometry. The acoustic center defines the equivalent point source position of a microphone serving as a sound source where the spherical waveform starts to diverge. The value is used to determine the effective distance between microphones for free-field reciprocity calibration. Conventionally, it is determined from the inverse distance law properties of a point source using the transfer function method. In this study, the acoustic center was determined from the projection of the sound field of the microphone. Parallel phase-shifting interferometry was used to measure the line integration of the sound pressure from a microphone. The acoustic center is determined as the position where the squared error between the measured data and the projection model of a point source is minimized. Experiments with the B&K 4180 (Brüel & Kjær, Nærum, Denmark) microphone were performed for frequencies from 10 to 50 kHz. The best acoustic center estimation was obtained at a microphone distance of 0 mm, with a difference of 0.17 mm to the IEC 61094-3 value and 0.36 mm to the Barrera-Figueroa et al. [J. Acoust. Soc. Am. 120(5), 2668-2675 (2006)] result at a measurement frequency of 20 kHz.

Scaling of the simulated pass-by measurement based on the vehicle's acoustic centre

Preliminary work by the IPEK - Institute of Product Engineering at KIT has shown that the simulated pass-by measurement for exterior noise homologation of vehicles has relevant optimization potential: the measurement can be carried out in smaller halls and with a smaller measurement setup than required by the standard and thus with less building construction cost and measurement effort. A prerequisite for this, however, is the scaling of the entire setup. For the scaling to work correctly, the sound sources of the vehicle must be combined to a single point sound source - the acoustic centre. Therefore, in a preliminary work, the IPEK developed a method, with the help of which the dominant sound sources of a vehicle can be localized and combined to an acoustic centre. In this work, the method is applied exemplarily on two test vehicles and their acoustic centres are determined. Afterwards, the measurement setups for both vehicles are scaled based on the acoustic centres, Finally, the simulated pass-by measurement with the scaled measurement setup is performed on an acoustic roller test bench and the scaled sound pressure levels are determined. To verify the overall method, the results of the scaled pass-by measurements are compared with the unscaled one and with measurements on the test track.

The Acoustic Center of a Measuring Hydrophone

The Acoustic Center of a Measuring Hydrophone

The Acoustic Center of a Measuring Hydrophone

Various approaches to the formulation of the definition of an acoustic center of a transducer and the problems arising when using them for experimental determination of the acoustic-center position are considered. The reasons for which the formulation and the corresponding method for determining the position of the acoustic center of a microphone are not suitable for a hydrophone are discussed. An experiment is described that demonstrates the proposed method for experimentally determining the position of the acoustic center of a hydrophone during its phase calibration by the reciprocity method.

Experimental Determination of the Acoustic Center of a Measuring Hydrophone

Experimental Determination of the Acoustic Center of a Measuring Hydrophone

Equivalent size and acoustic center of measuring hydrophone

Equivalent size and acoustic center of measuring hydrophone

Experimental determination of the acoustic center of a measuring hydrophone

Experimental determination of the acoustic center of a measuring hydrophone

Method for localisation of sound sources and aggregation to an acoustic centre

Preliminary work by the IPEK - Institute of Product Engineering at KIT has shown that the simulated pass-by measurement for exterior noise homologation of vehicles has relevant optimization potential: the measurement can be carried out in smaller halls and with a smaller measurement setup than required by the norm and thus with less construction cost and effort. A prerequisite for this however is the scaling of the entire setup. For the scaling in turn, the sound sources of the vehicle must be combined to a single point sound source - the acoustic centre. Previous approaches for conventional drives assume a static centre in the front part of the vehicle. For complex drive topologies, e.g. hybrid drives, and unsteady driving conditions, however, this assumption is not valid anymore. Therefore, with the help of an acoustic camera, a method for localizing the dominant sound sources of the vehicle and a software-based application for summarizing them to an acoustic centre were developed. The method is able to take into account stationary, unsteady and sudden events in the calculation of the acoustic centre, which is moved as a result. Using substitute sound sources and two vehicles, the method and the used measurement technology were examined and verified for their applicability.

Acoustic-resolution photoacoustic microscopy based on an optically transparent focused transducer with a high numerical aperture.

This Letter reports acoustic-resolution-photoacoustic microscopy (AR-PAM) based on a new optically transparent focused polyvinylidene fluoride (PVDF) transducer with a high acoustic numerical aperture (NA) of 0.64. Owing to the improved fabrication process, the new transducer has a much higher NA (0.64) than the previously reported low-NA transducer (NA=0.23). The acoustic center frequency and (pulse-echo) bandwidth are also increased to 36 and 44 MHz, respectively, which provides a 38 µm acoustic focal spot size and 210 µm acoustic depth of focus. For demonstration, AR-PAM was conducted on a twisted wire target in water and chicken breast tissue, and in vivo on a mouse tail. The imaging results show that high acoustic resolution and sensitivity can be achieved with a simple and compact setup to resolve the target at different depths. Such capabilities can be useful for the development of new AR-PAM systems for handheld, wearable, and even endoscopic imaging applications.

Розпізнавання аварійних ситуацій роботи верстатів з ЧПК на основі штучного інтелекту

В рамках роботи було досліджено, що для розпізнання аварійнихситуацій потрібне зняття сигналів з джерел та подальша обробка керуючогосигналу. Тип датчика, як ключова роль в технологічній системі. Длярозпізнавання катастрофічних ситуацій можливе застосування датчиківвказаних типів. Стерео- й квадро- системи для зменшення перешкод та витримка умовдля акустичного центру. Рішення з приводу відсіювання частини перешкодпід час обробки сигналу: використання математичного апарату штучнихнейронних мереж та його подальше навчання під керівництвом верстатника. During the operation of the CNC machine there are serious problems and errors that lead to catastrophic failure of the cutting tool. We found that they occur for several reasons: errors in the initial adjustment of the CNC machine, low accuracy of the workpiece surfaces, errors in the configuration of the device, errors in control programs, failures in the CNC system and unfastening of workpieces during operation. As part of the work, it was investigated that the recognition of emergency situations requires the removal of signals from the cutting area and the subsequent generation of the control signal. The type of sensor plays a key role in such recognition systems. To detect catastrophic situations, it is possible to use acoustic sensors as the easiest to install in various CNC machines.The study of the capabilities of acoustic sensors and the subsequent processing of the received signal revealed significant shortcomings: low selectivity and noise immunity (vibration of the housing to which it is fixed; chip chips and noise of pouring coolant.Stereo and quad systems are offered to reduce interference signals by withstanding the conditions of the acoustic center. We have proposed a solution for the elimination of part of the interference during signal processing: the use of the mathematical apparatus of artificial neural networks and its further training under the guidance of a machine operator.The system has a ring signal recorder so that, if necessary, the machine operator activates the "Finish" functions for the neural network. This will help not to create the entire database of signals in the laboratory, but to complete the system of accident prevention directly in production.

Determination of the hydrophone phase-frequency response by its amplitude-frequency response

One of the tasks of the COOMET 786/RU/19 pilot comparisons is to check the correctness of the hydrophone model proposed in VNIIFTRI, consisting of an advance line and a minimum-phase part, including the effect of sound diffraction and resonance properties of the active element. This model makes it possible to use the Hilbert transform to obtain the phase-frequency response from the amplitude-frequency response as well as for inverse operation. The results of measuring experiments performed using facilities of the State Primary Standard GET 55-2017 are presented. For many practical tasks, it is not necessary to obtain the phase-frequency response for an acoustic center of the receiver. It is enough to determine the shape of the phase-frequency response using much less laborious methods. The question of which of the characteristics is expedient to determine during calibration - for an acoustic center, or for a point on the surface of an active element, deserves a discussion among specialists performing acoustic measurements.

Impact of using Double Layers Perforated Liners on the Acoustic Treatments of the Combustor Systems

The response of the combustor’s liner to the air-flow that passes through it is the key reason for the combustion chambers noise, hence the instabilities of those chambers that decreases the mechanical efficiency of such sections, by increased its mechanical vibrations, which increases the failure rate created during originating of the cracks spreading by the shakes producing by the series of high-level frequencies. Accordingly, any work debating the impact of the context of liners in the combustion chamber can provide grasping for the combustion noise generated by the undesirable vibrations, and benefits the industrial firms to design an ideal production procedure which increases the lifespan of the combustor. The goal of this work is to examine the influence of the acoustic treatment using a double layers cylindrical perforated liner on the acoustic transmission loss of gas turbines. The liners layout influences on this acoustic parameter was examined using an experimental data gained by the insertion of a full scale single and double patterns of perforated liners into the unique large scale acoustic wind tunnel at the acoustic research center at Hull University. The experimental tests under-designed acoustic signals were established firstly using 0m/s air cross-flow velocity, then by changed velocities with interval 5m/s ranging between 10m/s to 25m/s. MATLAB script was used to simulate, analyze, and figure out the data collected the insertion of single and double layer patterns of the perforated liner. The experiments demonstrated that, if the perforation acoustic treatments are applied, the acoustic transmission loss will decrease, particularly obvious at higher level frequencies. Further, the results exposed that the air tunnel with the insertion of the liner with double layers reveals an improved perforation acoustic treatment.

Acoustic source centering of musical instrument directivities using acoustical holography

The acoustic center of a source is commonly defined as the point from which spherical wavefronts appear to diverge. Measuring directivities of sound sources with a surrounding spherical array whose geometric origin is not aligned with the acoustic center of the source can lead to distortions in directivity patterns. Thus, a method is desired to obtain both the far-field directivity pattern and to determine the acoustic center of a source. This work illustrates how acoustical holography can identify the reference frame from which spherical waves diverge by studying various musical instruments' acoustic centers.

Effects of Spectral Resolution and Frequency Mismatch on Speech Understanding and Spatial Release From Masking in Simulated Bilateral Cochlear Implants.

Due to interaural frequency mismatch, bilateral cochlear-implant (CI) users may be less able to take advantage of binaural cues that normal-hearing (NH) listeners use for spatial hearing, such as interaural time differences and interaural level differences. As such, bilateral CI users have difficulty segregating competing speech even when the target and competing talkers are spatially separated. The goal of this study was to evaluate the effects of spectral resolution, tonotopic mismatch (the frequency mismatch between the acoustic center frequency assigned to CI electrode within an implanted ear relative to the expected spiral ganglion characteristic frequency), and interaural mismatch (differences in the degree of tonotopic mismatch in each ear) on speech understanding and spatial release from masking (SRM) in the presence of competing talkers in NH subjects listening to bilateral vocoder simulations. During testing, both target and masker speech were presented in five-word sentences that had the same syntax but were not necessarily meaningful. The sentences were composed of five categories in fixed order (Name, Verb, Number, Color, and Clothes), each of which had 10 items, such that multiple sentences could be generated by randomly selecting a word from each category. Speech reception thresholds (SRTs) for the target sentence presented in competing speech maskers were measured. The target speech was delivered to both ears and the two speech maskers were delivered to (1) both ears (diotic masker), or (2) different ears (dichotic masker: one delivered to the left ear and the other delivered to the right ear). Stimuli included the unprocessed speech and four 16-channel sine-vocoder simulations with different interaural mismatch (0, 1, and 2 mm). SRM was calculated as the difference between the diotic and dichotic listening conditions. With unprocessed speech, SRTs were 0.3 and -18.0 dB for the diotic and dichotic maskers, respectively. For the spectrally degraded speech with mild tonotopic mismatch and no interaural mismatch, SRTs were 5.6 and -2.0 dB for the diotic and dichotic maskers, respectively. When the tonotopic mismatch increased in both ears, SRTs worsened to 8.9 and 2.4 dB for the diotic and dichotic maskers, respectively. When the two ears had different tonotopic mismatch (e.g., there was interaural mismatch), the performance drop in SRTs was much larger for the dichotic than for the diotic masker. The largest SRM was observed with unprocessed speech (18.3 dB). With the CI simulations, SRM was significantly reduced to 7.6 dB even with mild tonotopic mismatch but no interaural mismatch; SRM was further reduced with increasing interaural mismatch. The results demonstrate that frequency resolution, tonotopic mismatch, and interaural mismatch have differential effects on speech understanding and SRM in simulation of bilateral CIs. Minimizing interaural mismatch may be critical to optimize binaural benefits and improve CI performance for competing speech, a typical listening environment. SRM (the difference in SRTs between diotic and dichotic maskers) may be a useful clinical tool to assess interaural frequency mismatch in bilateral CI users and to evaluate the benefits of optimization methods that minimize interaural mismatch.

A Focused Optically Transparent PVDF Transducer for Photoacoustic Microscopy

This papers reports the development of a novel focused optically-transparent ultrasound transducer with a wide bandwidth for photoacoustic microscopy (PAM). It consists of a 9- $\mu \text{m}$ -thick polyvinylidene fluoride (PVDF) film coated with Indium-tin oxide (ITO) and metal electrodes, which is laminated onto a concave glass lens. A new fabrication process was developed to ensure the formation of continuous ITO coatings on the curved transducer surface without fracturing. Both optical and acoustic experiments were conducted to characterize the performance of the transducer. The testing results show that the transducer has an optical transmittance of 60% (@ 532 nm), an acoustic center frequency of 24 MHz, and an acoustic bandwidth of 26 MHz. With an acoustic numerical aperture (NA) of 0.23, it provides a 0.13-mm acoustic focal spot and a 1.6-mm focal depth. For demonstration, a PAM setup was built for conducting PA imaging on different targets. In contrast to existing PAM systems, the use of the optically-transparent focused transducer allows a simpler and more compact configuration and easier alignment of the optical excitation and acoustic focal points. Such features are especially useful for the development of miniaturized PAM systems for handheld, wearable and even endoscopic applications.