Figure - available from: Journal of Physics D: Applied Physics
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Three dimensional directivity patterns of the CD actuator at frequencies at 1000 Hz (left) and 8000 Hz (right). Units are indicated in dB SPL re 20 µPa. The calculation is performed at the distance of 1 m from the actuator center. U DC = 8.2 kV, u AC = 300 Vrms.
Source publication
Conventional loudspeakers generate sound through the vibration of a diaphragm, attached to a rigid frame through elastic suspensions. Although such construction is satisfactory for sound diffusion in steady environments, it is likely to fail in harsh conditions, which is often the case for active noise control applications. Plasma-based actuators a...
Citations
... For example, EPFL (École Polytechnique Fédérale de Lausanne, Switzerland) researched the possibility of using plasma actuators to absorb the broadband low frequency noise. This solution achieved an absorption of broadband noises as a result of a partial ionization of a thin air layer with an atmospheric corona discharge and its control with an alternating electrical field [3][4][5]. ISVR (Institute of Sound and Vibration Research, Southampton) uses slanted perforated plates introduced in the resonance cavities of acoustic liners to absorb an even broader spectrum of noise frequencies [6]. ...
This paper presents the technological advancement of using friction powders to increase the absorption of acoustic liners used in the reduction of tonal noise generated by aero-engines or for other applications related to Helmholtz resonators used in noise absorption of low frequencies. The experimental research was conducted during the European project ARTEM (2017–2022), and after. This concept was inspired by the discovery made by several historians of narrow neck bottles filled with ash in the old Christian churches. These artifacts were made with the purpose of absorbing low frequency noises. Based on this creative idea, the present authors proposed a new method of noise absorption capabilities of acoustic liners filled with various types and quantities of natural and artificial powders. Considering the positive results the ARTEM project offered, COMOTI continued testing this concept by using even finer cork powders manufactured with a new technology. Measurements in Kundt tubes showed that noise absorption increased significantly in broadband for low frequencies (over 0.9 at high frequencies and 0.6 at low frequencies, 500 Hz). Some of the researched powders can be used in the field of bladed machines to reduce the aerodynamic noise of an aircraft or in the automotive industry where the reduction of low frequency noises is necessary.
... These two phenomena can be included as sound source terms in the acoustic wave equation. Derivation of equations ((1)-(2)) and their contributions to the total generated pressure in free field are discussed in the previous work 23 . In 24 , an attempt was made to control the corona discharge transducer, where it was used as a generic transducer to absorb sound, without benefiting from the physics of the corona discharge. ...
Controlling audible sound requires inherently broadband and subwavelength acoustic solutions, which are to date, crucially missing. This includes current noise absorption methods, such as porous materials or acoustic resonators, which are typically inefficient below 1 kHz, or fundamentally narrowband. Here, we solve this vexing issue by introducing the concept of plasmacoustic metalayers. We demonstrate that the dynamics of small layers of air plasma can be controlled to interact with sound in an ultrabroadband way and over deep-subwavelength distances. Exploiting the unique physics of plasmacoustic metalayers, we experimentally demonstrate perfect sound absorption and tunable acoustic reflection over two frequency decades, from several Hz to the kHz range, with transparent plasma layers of thicknesses down to λ/1000. Such bandwidth and compactness are required in a variety of applications, including noise control, audio-engineering, room acoustics, imaging and metamaterial design.
... To generate a sinusoidal sound wave at frequency ω, one should apply a voltage difference in the form U = U DC + u AC sin(ωt), with u AC being only a few percents of U DC . In the linear approximation, the magnitude of the AC part of the force source in the plasmacoustic metalayer with geometry illustrated in Figure 1 can be expressed as follows [23]: ...
... where d is the interelectrode distance and µ i is the effective ion mobility in the air. The heat power is assumed to be the total Joule losses in the discharge H(t) ≈ U (t)I(t), and its AC linear component in the frequency domain can be written as [23]: ...
... For this purpose, let us mount the plasmacoustic metalayer right before the termination of an air-filled duct of same cross-section ( Figure 2a). Since the corona discharge is homogeneous along the transverse directions [23] and the interelectrode distance is limited to a few millimeters, force and heat can be considered, at low frequencies, as two collocated acoustic point sources. The termination of the duct is represented by an impedance Z l at distance l from the center of the metalayer, which is a large real number in the case of a rigid termination. ...
Controlling audible sound requires inherently broadband and subwavelength acoustic solutions, which are to date, crucially missing. This includes current noise absorption methods, such as porous materials or acoustic resonators, which are typically inefficient below 1 kHz, or fundamentally narrowband. Here, we solve this vexing issue by introducing the concept of plasmacoustic metalayers. We demonstrate that the dynamics of small layers of air plasma can be controlled to interact with sound in an ultrabroadband way and over deep-subwavelength distances. Exploiting the unique physics of plasmacoustic metalayers, we experimentally demonstrate perfect sound absorption and tunable acoustic reflection over more than two frequency decades, from several Hz to the kHz range, with transparent plasma layers of thicknesses down to $\lambda/1000$. Such unprecedented bandwidth and compactness opens new doors in a variety of applications, including noise control, audio-engineering, room acoustics, imaging and metamaterial design.
... Consequently, they are light, mechanically robust, with a short response time to an electrical signal. In [24], the acoustic properties of an electroacoustic actuator based on the atmospheric corona discharge in a wire-to-mesh geometry have been investigated. Its non-resonant frequency response, satisfactorily low harmonic distortion, along with the abovementioned properties of plasma-based actuators make it an appealing candidate for active noise control applications. ...
... The previous study [24] introduced simple analytical model of a corona discharge (CD) actuator sound radiation in free space with far field approximation. Nonetheless, it does not describe the near field behaviour when the system is enclosed. ...
... The experimental prototype of the corona discharge actuator used for both control strategies has been built in a wire-to-mesh geometry ( Fig. 2) according to the design proposed in [24]. The first electrode is made of nichrome wire with 0.1 mm diameter strung on a plastic frame, forming a pattern of thin parallel wires in one plane. ...
In the majority of active sound absorbing systems, a conventional electrodynamic loudspeaker is used as a controlled source. However, particular situations may require an actuator that is more resistant to harsh environments, adjustable in shape, and lighter. In this work, a plasma-based electroacoustic actuator operating on the atmospheric corona discharge principle is used to achieve sound absorption in real-time. Two control strategies are introduced and tested for both normal in the impedance tube and grazing incidence in the flow duct. The performance of plasma-based active absorber is competitive with conventional passive technologies in terms of effective absorption bandwidth and low-frequency operation, however, it presents some inherent limitations that are discussed. The study reveals that the corona discharge technology is suitable for active noise control in ducts while offering flexibility in design, compactness, and versatility of the absorption frequency range.
... The corona actuator is lightweight and does not include any moving parts, which makes it robust. The previous work of the authors introduced the corona discharge actuator in the wire-to-mesh geometry and analyzed its physical principles of sound generation [12]. This work presents the actuator for use as an active sound absorber. ...
... Some basic acoustic characteristics of the sound source such as frequency response, directivity pattern and harmonic distortion have been assessed for the CD actuator. For these measurements, we built a prototype with thickness of 7 mm in the wire-to-mesh geometry, as this configuration leads to the corona discharge operation in the range of DC voltages 6.5-10 kV [12]. The discharge is produced on the area of 50x50 mm 2 ( Fig. 1 on the left). ...
This work focuses on the development of a plasma-based electroacoustic transducer for active noise control applications. The transducer is based on the atmospheric corona discharge in a wire-to-mesh geometry. The main motivation for plasma technology is its simple robust design and absence of moving parts in the actuator, which could be advantageous when used in harsh environments. We characterize the corona discharge as an electroacoustic source. Further, we describe the active impedance control strategy for sound absorption by means of this type of discharge. The system is implemented experimentally in an impedance tube under normal sound incidence. The achieved sound absorption demonstrates the potential of the corona discharge actuators for use in active noise control systems, as an alternative to conventional electrodynamic transducers.
... In [24], the acoustic properties of an electroacoustic actuator based on the atmospheric corona discharge in a wire-to-mesh geometry have been investigated. The transducer was found to be a potential candidate for active noise control applications. ...
... Previous study [24] introduced simple analytical model of a corona discharge (CD) actuator sound radiation in free space with far field approximation. Nonetheless, it does not describe the near field behaviour when the system is enclosed. ...
... The experimental prototype of the corona discharge actuator used for both control strategies has been built in a wire-to-mesh geometry ( Figure 2) according to the design proposed in [24]. The first electrode is made of nichrome wire with 0.1 mm diameter strung on a plastic frame, forming a pattern of thin parallel wires in one plane. ...
In the majority of active sound absorbing systems, a conventional electrodynamic loudspeaker is used as a controlled source. However, particular situations may require an actuator that is more resistant to harsh environments, adjustable in shape, and lighter. In this work, a plasma-based electroacoustic actuator operating on the atmospheric corona discharge principle is used to achieve sound absorption in real-time. Two control strategies are introduced and tested for both normal in the impedance tube and grazing incidence in the flow duct. The performance of plasma-based active absorber is competitive with conventional passive technologies in terms of effective absorption bandwidth and low-frequency operation, however, it presents some inherent limitations that are discussed. The study reveals that the corona discharge technology is suitable for active noise control in ducts while offering flexibility in design, compactness, and versatility of the absorption frequency range.
Acoustic resonances in open systems, which are usually associated
with resonant modes characterized by complex eigenfrequencies,
play a fundamental role in manipulating acoustic wave radiation and
propagation. Notably, they are accompanied by considerable feld
enhancement, boosting interactions between waves and matter,
and leading to various exciting applications. In the past two decades,
acoustic metamaterials have enabled a high degree of control over
tailoring acoustic resonances over a range of frequencies. Here,
we provide an overview of recent advances in the area of acoustic
resonances in non-Hermitian open systems, including Helmholtz
resonators, metamaterials and metasurfaces, and discuss their
applications in various acoustic devices, including sound absorbers,
acoustic sources, vortex beam generation and imaging. We also
discuss bound states in the continuum and their applications in
boosting acoustic wave–matter interactions, active phononics and
non-Hermitian acoustic resonances, includi
A surface corona actuator for flow control, already tested in wind tunnel experiments, is here characterized at the bench in still air. The anodic electrode is provided with periodic triangular tips and is operated with a pulsed waveform. The operating stability and voltage range turn out to be wider than for dc operation. The actuator is characterized by means of several measurements as a function of the frequency, including power absorption and ionic wind measurements in different locations. The ionic wind is measured first by a micropitot probe obtaining time-averaged values, then by a hot wire anemometer obtaining instantaneous velocities and turbulence spectra. The behavior of the actuator is interpreted accounting for the creation and removal of charges in the gap subject to a periodic excitation.
