Stanislav Sergeev

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Ultrabroadband sound control with deep-subwavelength plasmacoustic metalayers

Romain Christophe Rémy Fleury, Hervé Lissek, Stanislav Sergeev

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.

2023

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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.

2022

Chargement

Plasma-based Electroacoustic Actuator for Broadband Sound Absorption

Stanislav Sergeev

Environmental noise, mostly related to human activities, has an immense impact on public health. The development of noise reduction technologies is paramount in addressing this problem. Because of practical and economic reasons, a compact, broadband, lightweight, and mechanically robust solution is often compulsory. Existing noise reduction methods typically fall short meeting these requirements. Passive absorbers are bulky and inefficient in the low frequency range or present only a narrowband performance. Active noise reduction methods, including active noise cancellation and acoustic impedance control, appear more promising as they allow extending the bandwidth of operation and remain small compared to a wavelength. An electrodynamic loudspeaker is conventionally a favourable choice for a controlled transducer. However, it limits efficient technology application due to its fragile diaphragm, relatively high weight, and inherent resonant nature, bounding the bandwidth of control.This thesis is devoted to the development of a fundamentally different plasma-based electroacoustic transducer for active sound control applications. The acoustic field is manipulated by the partial ionisation of a thin air layer with an atmospheric corona discharge and its further control with an alternating electrical field. The transducer consists of a set of high voltage wires, separated with a grounded mesh by an air gap. Analytical and numerical models are first developed to design and characterise the corona discharge actuator. Several feedback impedance control strategies are adapted and implemented with the corona discharge actuator, resulting in achieving broadband impedance and sound absorption. A prototype of a plasma-based active acoustic liner for noise reduction under grazing sound incidence is proposed and assessed experimentally in laboratory facilities. A model-based feedforward approach for broadband control of acoustic impedance is then developed. Exploiting the unique physics of the corona discharge actuator with the help of the analytical model, perfect sound absorption and tunable acoustic reflection under normal incidence are achieved over two frequency decades, from several Hz to the kHz range. Such unprecedented bandwidth and compactness of the developed system, along with the simplicity of construction, lightweight, and flexible design, opens new doors in noise control applications, and acoustic metamaterials, among others.

EPFL2022

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