| 1. |
- Argyri, Smaragda Maria, 1994, et al.
(författare)
-
Customized and high-performing acoustic levitators for contact-free experiments
- 2024
-
Ingår i: Journal of Science: Advanced Materials and Devices. - 2468-2284 .- 2468-2179. ; 9:3
-
Tidskriftsartikel (refereegranskat)abstract
- Acoustic levitators are becoming an increasingly common research instrumentation for contact-free, lab-in-a-droplet studies. Recently, levitators that employ multiple, small, ultrasonic transducers have gained popularity, given their low price, temperature and spatial stability, low voltage, and accessibility. Yet, the current state-of-the-art device, TinyLev, presents limitations for certain applications in terms of stability, strength, and compactness. Herein, we developed three new levitators and evaluated the effect of the construction parameters (e.g., distance of opposing arrays, number and arrangement of transducers, etc.) on their performance. Compared to TinyLev, the best performing levitator from this work had half the number of transducers while presenting 1.7 and 3.5 times higher levitation capacity along the horizontal and vertical configurations, respectively, while the horizontal and vertical stability of a levitated object was improved 4.7 and 2.0 times, respectively. Additionally, we present a direct means to evaluate the acoustic radiation net force acting on a deformable object for uniaxial levitators, without the use of a microphone or a schlieren deflectometer for this type of levitators. The theoretical and experimental observations provide insights for adapting the acoustic levitator design for specific applications. Finally, we developed an open-source software which allows the evaluation of the acoustic pressure field generated by customized designs and provides the necessary files for 3D printing the scaffold of the levitator. This study aims to increase accessibility and promote further developments in contact-free experiments.
|
|
| 2. |
- Ahrens, Jens, 1978, et al.
(författare)
-
Auralization of acoustic spaces based on spherical microphone array recordings
- 2017
-
Ingår i: Acoustics ’17, Boston, MA.
-
Konferensbidrag (övrigt vetenskapligt/konstnärligt)abstract
- Microphone arrays can capture the physical structure of a sound field. They are therefore potentially suited to capture and preserve the sound of acoustic spaces within given physical limitations that are determined by the construction of the array. Especially spherical microphone arrays have received considerable attention in this context. Superposed onto the limitations of the microphone array are the limitations caused by the auralization system. We present results from user studies on the perceptual differences between spherical microphone array recordings that are auralized with headphones as well as with a circular 56-channel loudspeaker array and headphone auralization based on dummy head measurements of the same spaces. Head-tracking was applied in all cases in which headphones were used.
|
|
| 3. |
- Ahrens, Jens, 1978, et al.
(författare)
-
Authentic Auralization of Acoustic Spaces Based on Spherical Microphone Array Recordings
- 2018
-
Ingår i: Proceedings of the Institute of Acoustics. - 1478-6095. ; 40:3, s. 303-310
-
Konferensbidrag (refereegranskat)abstract
- Many approaches for the capture and auralization of real acoustic spaces have been proposed over the past century. Limited spatial resolution on the capture side has typically been the factor that caused compromises in the achievable authenticity of the auralization. Recent advancements in the field of spherical microphone arrays provide new perspectives for both headphone-based and loudspeaker-based auralization. It has been shown that a bowling-ball-size spherical array of around 90 microphones allows for creating signals at the ears of the listener that are perceptually almost indistinguishable from the ear signals that arise in the original space. Head-tracked headphone auralization, i.e. playback that adapts to the instantaneous head orientation of the listener, has been shown to provide the best results. In the present contribution, we provide an overview of the technology and demonstrate the latest research advancements and remaining challenges.
|
|
| 4. |
- Ahrens, Jens, 1978, et al.
(författare)
-
Perceptual evaluation of headphone auralization of rooms captured with spherical microphone arrays with respect to spaciousness and timbre
- 2019
-
Ingår i: Journal of the Acoustical Society of America. - : Acoustical Society of America (ASA). - 1520-8524 .- 0001-4966. ; 145:4, s. 2783-2794
-
Tidskriftsartikel (refereegranskat)abstract
- A listening experiment is presented in which subjects rated the perceived differences in terms of spaciousness and timbre between a headphone-based headtracked dummy head auralization of a sound source in different rooms and a headphone-based headtracked auralization of a spherical microphone array recording of the same scenario. The underlying auralizations were based on mea- sured impulse responses to assure equal conditions. Rigid-sphere arrays with different amounts of microphones ranging from 50 to up to 1202 were emulated through sequential measurements, and spherical harmonics orders of up to 12 were tested. The results show that the array auralizations are partially indistinguishable from the direct dummy head auralization at a spherical harmonics order of 8 or higher if the virtual sound source is located at a lateral position. No significant reduction of the perceived differences with increasing order is observed for frontal virtual sound sources. In this case, small differences with respect to both spaciousness and timbre persist. The evaluation of lowpass-filtered stimuli shows that the perceived differences occur exclusively at higher frequen- cies and can therefore be attributed to spatial aliasing. The room had only a minor effect on the results.
|
|
| 5. |
|
|
| 6. |
- Ahrens, Jens, 1978, et al.
(författare)
-
Tutorial on scaling of the discrete fourier transform and the implied physical units of the spectra of time-discrete signals
- 2020
-
Ingår i: 148th Audio Engineering Society International Convention.
-
Konferensbidrag (refereegranskat)abstract
- The combination of the time-discrete property of digital signals together with the commonly employed definition of the discrete Fourier transform (DFT) can cause ambiguity when interpreting magnitude spectra with respect to the physical unit of the signal under consideration. Standardized scaling of spectra increases the comparability of frequency-domain data that are published in scientific articles or data sheets of commercial products. We present and discuss in this tutorial a collection of the most relevant scaling options for DFT spectra to yield amplitude spectra, power spectra, and power density spectra, and we illustrate how an implied physical unit of the underlying signal is reflected by the magnitude of the spectrum. The tutorial is accompanied by Matlab/Octave scripts that demonstrate the different cases.
|
|
| 7. |
- Andersson, Carl, 1992, et al.
(författare)
-
A Method for Simultaneous Creation of an Acoustic Trap and a Quiet Zone
- 2018
-
Ingår i: Proceedings of the IEEE Sensor Array and Multichannel Signal Processing Workshop. - 2151-870X. ; 2018-July, s. 622-626
-
Konferensbidrag (refereegranskat)abstract
- An acoustical levitation trap can be created by max- imizing the Laplacian of the Gor’kov potential and minimizing the pressure at a given location. Marzo et al. have successfully used Broyden-Fletcher-Goldfarb-Shanno minimization to find the phases to be imposed on the elements of an ultrasonic transducer array to create the required pressure field. We extend this method to create a field with one acoustical trap and a quiet zone at a different location. This can be used to, for example, create an independent second trap at the location of the quiet zone. We show through numerical simulations that it is possible to create such sound fields using ultrasonic arrays, and we demonstrate the advantages of the proposed approach over the direct design of a sound field with more than one trap. Our method can create a quiet zone extending almost two wavelengths without affecting the levitation trap.
|
|
| 8. |
- Andersson, Carl, 1992, et al.
(författare)
-
Acoustic Levitation from Superposition of Spherical Harmonics Expansions of Elementary Sources: Analysis of Dependency on Wavenumber and Order
- 2019
-
Ingår i: IEEE International Ultrasonics Symposium, IUS. - 1948-5719 .- 1948-5727. ; 2019-October, s. 920-923
-
Konferensbidrag (refereegranskat)abstract
- Acoustic levitation of spherical objects in mid-air is a technique that is gaining traction in various human computer interaction applications such as data visualization or interactive displays. The commonly used hardware platforms are phased ultrasonic transducer arrays, used to levitate small spheres of polystyrene. Previous works have used angular spectrum decomposition of the incident sound field to derive the radiation force exerted on an arbitrary sphere. We show an alternate formulation more suited to sound fields from transducer arrays, based on direct spherical harmonics expansions of the sound fields from the individual transducer elements in the array. Finally we investigate how the truncation order of the spherical harmonics expansion influence the calculated force, for varying sphere sizes.
|
|
| 9. |
- Andersson, Carl, 1992
(författare)
-
Acoustic levitation of multi-wavelength spherical bodies using transducer arrays of non-specialized geometries
- 2022
-
Ingår i: Journal of the Acoustical Society of America. - : Acoustical Society of America (ASA). - 1520-8524 .- 0001-4966. ; 151:5, s. 2999-3006
-
Tidskriftsartikel (refereegranskat)abstract
- Recently, acoustic levitation of a wavelength-sized spherical object using a general-purpose ultrasonic transducer array was demonstrated. In this article, the possibility of extending the capabilities of such arrays to levitate multi-wavelength-sized objects is explored. The driving signals for the elements in the array are determined via numerical optimization of a physics-based cost function that includes components for trap stabilization. The cost function is balanced with an improved approach, mimicking dynamical de-weighting of the included components to avoid over-optimization of each individual component. Sound fields are designed and analyzed for levitation of objects with diameters up to 50 mm for various general-purpose simulated array configurations. For a 16 x 16 element transducer array, simulations predict levitation of spheres with diameters up to 20 mm (2.3 wavelengths), which is verified experimentally.
|
|
| 10. |
- Andersson, Carl, 1992, et al.
(författare)
-
Creation of Large Quiet Zones in the Presence of Acoustical Levitation Traps
- 2021
-
Ingår i: IEEE International Ultrasonics Symposium, IUS. - 1948-5719 .- 1948-5727.
-
Konferensbidrag (refereegranskat)abstract
- We propose a method to generate an acoustical levitation trap at the same time as suppressing the sound in a multi-wavelength region of space. The method uses a spherical basis expansion of the sound field in the quiet zone, calculated by translating individual source expansions of elements in a transducer array. We show that it is possible to control the size of the quiet zone with the truncation order of the expansion, and explain the trade-off between field suppression in the quiet zone and stiffness loss of the levitation trap. Measurements of a generated sound field show the existence of a region of lower sound pressure. Simulations demonstrate a contrast up to 50 dB and sizes up to 60 mm for a 256 element array.
|
|
