Electromagnetic Inspired Acoustic Metamaterials

This thesis deals with electromagnetic inspired acoustic metamaterials, enabling sound-matter interactions in different wave scenarios that include propagation, guided-waves, radiation, refraction, reflection and transmission. To this end, a particular emphasis is placed on introducing novel applications for acoustic metamaterials operating on each one of the aforementioned wave scenarios. A few years ago, metamaterials have been introduced as a new class of composite artificial materials, engineered to produce unusual effective material properties not readily available in nature. Electromagnetic metamaterials are probably the oldest class of metamaterials, being nowadays in the process of reaching maturity and being proposed for interesting commercial applications. On the other hand, as in most young but not yet mature emerging fields of science, acoustic metamaterials are still providing lots of fertile and unexplored ground for research and study. Despite many inherent physical differences, the propagation of electromagnetic and acoustic waves are both governed by a similar mathematical model, the so-called Helmholtz wave equation. The main purpose of this work is to leverage this amazing similarity by translating recent advances in electromagnetic metamaterials into their corresponding, previously unseen, applications in acoustics. The first contribution of this thesis is to adapt the classic electromagnetic transmission-line theory to allow the design of acoustic metamaterials. The proposed circuit-based theory finds a direct application in the design of composite right/left hand transmission-line metamaterials, which yield novel guided-wave applications for acoustic metamaterials. Then, the developed theory is leveraged to model and achieve optimal design of different acoustic metamaterial-based devices, such as leaky-wave antennas and reflector-type metasurfaces. The second part of the thesis spins around acoustic leaky-wave antennas and their different functionalities, showing that they are able to act as acoustic dispersive prisms in the refraction mode and as acoustic single sensor direction finder in the radiation mode. Studying reflection phenomena in sound-metasurface interactions constitutes the next part of this thesis, where a membrane-capped cavity is introduced performing as an ultra-thin unit-cell for reflective acoustic metasurfaces. This leads to exciting applications of the concept, like acoustic reflectarray antennas and acoustic metasurface skin-cloaks Finally, the last part of this thesis deals with transmission phenomena in acoustic metasurfaces and, especially, in orbital angular momentum metasurfaces. This concept results in the design of an innovative labyrinthine-type helicoidal unit-cell that is used for phase coding a surface and transforming impinging acoustic wavefronts into transmitted helical wavefronts.

Optimization of an acoustic leaky-wave antenna based on acoustic metamaterial

Sami Driss Karkar, Hervé Lissek, Seyyed Hussein Seyyed Esfahlani

In recent years, an increasing number of pioneering studies have been carried out in the field of acoustic metamaterials, following the path of electromagnetic metamaterials. These artificial engineered materials are designed in such a way so as to achieve new macroscopic properties, like negative refraction, that are not readily present in nature. While the design and the fabrication of these artificial materials is a hot topic among scientists in different fields of physics such as photonic, electromagnetic, acoustic and recently mechanic, an important part of the scientific research is now oriented towards the identification of actual applications for these structures. As the novel idea of metamaterial was first developed in the electromagnetic realm and for the microwave frequency range, it is somehow more mature in these fields than in acoustics. Metamaterial applications are now widely developed in electromagnetics especially for the design of new antenna. Among other examples, metamaterial concepts are aiming at reducing the coupling between two adjacent radiating elements of the array and increasing the operating bandwidth of radiating elements. It is also used for phase compensation in microwave transistors, and many more applications are rising in the recent literature. In year 2009, in analogy with electromagnetic transmission line metamaterial, our group proposed a concept of acoustic transmission line metamaterial, consisting of a waveguide periodically loaded with membranes along the duct, and transverse open channels (denoted “stubs”). Based on our proposed structure and in analogy with applications of transmission line electromagnetic metamaterials, researchers proposed the idea of an acoustic counterpart to the “backward wave antenna”. These antennas or radiating devices have a very special property such that the radiation angle or the directivity changes with the frequency. In this article, a comprehensive, step by step, design methodology for acoustic backward wave antenna is presented. For this purpose we use the model proposed in our 2009 publication for acoustic transmission line metamaterial, but we focus the discussion on the optimization of the antenna performance. We also propose some closed form formulas for the practical design of such devices, and a formal validation of the structure is proposed using Comsol Multiphysics.

2013

Acoustic dispersive prism

Sami Driss Karkar, Hervé Lissek, Juan Ramon Mosig, Seyyed Hussein Seyyed Esfahlani

The optical dispersive prism is a well-studied element, which allows separating white light into its constituent spectral colors, and stands in nature as water droplets. In analogy to this definition, the acoustic dispersive prism should be an acoustic device with capability of splitting a broadband acoustic wave into its constituent Fourier components. However, due to the acoustical nature of materials as well as the design and fabrication difficulties, there is neither any natural acoustic counterpart of the optical prism, nor any artificial design reported so far exhibiting an equivalent acoustic behaviour. Here, based on exotic properties of the acoustic transmission-line metamaterials and exploiting unique physical behaviour of acoustic leaky-wave radiation, we report the first acoustic dispersive prism, effective within the audible frequency range 800 Hz - 1300 Hz. The dispersive nature, and consequently the frequency-dependent refractive index of the metamaterial are exploited to split the sound waves towards different and frequency-dependent directions. Meanwhile, the leaky-wave nature of the structure facilitates the sound wave radiation into the ambient medium.

2016

Power line communications

Emmanuel Marthe

With the deregulation of the electricity and telecommunications markets, a great deal of new operators providing some innovative services have appeared. In the telecommunications' field, the promise of broadband Internet access with easy installation procedure at low cost may help to win new customers. The Power Line Communications (PLC) technology is a way to fulfil this function. PLC uses the low voltage (LV) and the medium voltage (MV) networks as communication support. It consists in an additional signal carrying data information and superimposed to the 50 Hz power wave. As PLC is easy to install, it can be used to extend the Internet coverage to areas that are still badly covered by the other broadband technologies, or to provide high speed Internet access to every power socket of a building. This thesis, done as a part of research project called Digital Power Line Access, is devoted to the study of electromagnetic compatibility (EMC) aspects involved with the PLC. There are still a certain number of problems due to the fact that PLC, which is a quite recent technology, has not been regulated yet. Among these problems, all the aspects associated with the radiation created by the transmission of PLC signals over unshielded conductors and their potential disturbances are very significant. The aim of this thesis is the analysis of PLC data transmission over the low voltage network and the related EMC problems, mainly the radiation due to the transmission of PLC signals. The measurement and the analysis of these radiations lead us to develop a method to reduce these radiations. The mitigation of radiation created by the use of PLC within buildings is still an important EMC challenge, because there are no possibilities for network conditioning. The first two chapters of this thesis present a state of the art of PLC, its regulation and the related EMC problems. The second chapter describes the working of PLC and emphasizes the hostile nature of its environment. The problems (filtering, attenuation, generation of noise,...) caused by the use of a signal in the [1 – 30 MHz] band over a channel designed for a 50 Hz power wave are presented. On the other hand, the various technologies used to allow the PLC to work (suitable modulation scheme, use of repeater,...) are illustrated. An analysis of the different PLC concepts and of the successful and unfruitful commercial deployment ends this chapter. In the third chapter, we present the technical criterion (use of the PLC as a multi-purpose port: as a main port and as a telecommunication port) that we have to consider and the evolution of the conducted and radiated limits that we have to respect. The pollution of the radio amateur band, which could be the result of a massive deployment of PLC, is the subject of tremendous discussions and proves that if according to some persons the current limits are too permissive, for the PLC manufacturer they are already too restrictive. The coexistence of the PLC with other broadband technologies (xDSL, CA-TV, Wireless,...) is also addressed and we show that only the coexistence with an alternative of the DSL – VDSL – could be problematic. The main original contributions of this thesis are presented in chapters 4 to 6. We concentrated on the problems related to the electromagnetic radiations associated with PLC signals, especially in indoor environment. The reason for this is that the emission of electromagnetic noise, which can interfere with services such as public and amateur radio, remains an obstacle to the development of PLC. Furthermore, to the best of our knowledge, the mitigation of indoor radiation has not been addressed in the literature. In chapter 4, we present a complete characterization of the problems resulting from the use of PLC in an indoor environment. Two approaches are presented for the measurement of electromagnetic fields. The first one consists in the injection of a reference signal in the network and the measurement of the resulting radiations. The second one deals with the measurements of interferences due to the work of real PLC equipments. These two approaches enlight several aspects. The main aspect is the strong dispersion of the measurements, resulting from the influence of the position of the observation point and of the power network load. Measurements on real PLC networks show excessive radiations, which confirm that the limits are, at this time, too restrictive. We also present and discuss PLC radiated emissions in typical indoor environments. In particular, we analyze the field levels resulting from PLC signals with magnitudes given by EN55022/CISPR22 limits and compare them with various proposals for PLC radiated field limits. Thus, we show that the resulting fields exceed, for a wide range of frequencies, some of the current emission limits such as the German NB30, which is considered as a very strict limit. In this same chapter, we present a technique for the analysis of power line communication (PLC) signals, based on the formalism of the scattering parameters. This technique allows an efficient and fast characterization of any transmission medium of a power network. The analysis of the variations of the magnitude and phase of the scattering parameters gives useful insights on the increasing of the losses with frequency and confirm the need of a technique to reduce impedance mismatch at both injection and reception ports. The chapter 5 presents the modelling of the PLC environment and the computation of its radiations using a commercial code, the Numerical Electromagnetics Code (NEC), which solves the electric field integral equation in the frequency domain using the method of moments. We present some comparisons between the NEC simulations and the experimental data for the total magnetic field presented in the previous chapter. The simulations of simple models give results in good agreement with the experimental data and therefore allow the validation of certain principles. Unfortunately, the simulations on a model of increasing complexity give less satisfactory results. Because of the difficulty to respect the topology of the network and to take into account all of the components of the network coupled with the constraints of NEC, it is extremely difficult to obtain accurate results on the complete PLC band. The strong electromagnetic radiations appeared as the major problem of this technology. Therefore, the development of a method of mitigation was the logical continuation of this work, especially because there is still no solution to this problem. We developed a technique, which is presented in chapter 6, aiming at reducing the electromagnetic field radiated by indoor PLC signals. This technique is the major original contribution of this thesis and led us to file a patent. The central idea is to take advantage of the additional ground conductor and inject a signal similar to the PLC signal into the ground-neutral line, but with a reversed phase. As a result, the overall antenna mode current is significantly reduced, as well as the radiated electromagnetic fields. The method is specifically developed for indoor applications and applies to uni-directional and bi-directional data transmission systems with an implementation using switches. Experimental data obtained on a test network have shown that the use of the proposed technique implies a significant reduction (up to 20 dB) of the PLC electromagnetic radiation in the considered frequency range. It is also shown that the performance of the proposed technique increases when the ground-neutral line is terminated by an impedance equal to the one of the PLC modem. Other tests performed on 230 V network confirm this trend but show that further work is needed in this direction. This work could consist in the development of a system allowing the synchronisation of the real PLC signal and the auxiliary signal according to the behavior of the PLC channel, in order to optimise the performances for any frequency used by the PLC.