Meta-malzemelerin ses iletim kaybı davranışlarının incelenmesi
Investigation of sound transmission loss behaviors of meta-materials
Yazar: NİLÜFER DERİN
Danışman: PROF. DR. HALUK EROL
İstanbul Teknik Üniversitesi / Fen Bilimleri Enstitüsü / Makine Mühendisliği Ana Bilim Dalı / Makine Dinamiği, Titreşimi ve Akustiği Bilim Dalı
Derece: Yüksek Lisans, 2018
Konu: Makine Mühendisliği = Mechanical Engineering
Dizin: Endüstriyel gürültü = Industrial noise ; Gürültü yalıtımı = Noise isolation ; Ses iletim sistemleri = Voice transmission systems ; Ses yalıtımı = Sound insulation ; Sonlu elemanlar yöntemi = Finite element method ; Yalıtım malzemeleri = Insulating materials

Özet:
Teknolojinin gelişmesiyle birlikte, insanların hizmetine sunulmuş olan makina, alet ve ekipmanların sayısı hızla artmaktadır. Gündelik hayatta ve hatta iş ortamlarında insanların maruz kaldığı gürültü düzeyleri de aynı ölçüde artış göstermektedir. Kişilerin başta sağlığını olmak üzere, konforunu ve psikolojik karakterlerini olumsuz etkileyen gürültü problemlerini azaltmaya yönelik çalışmalar önem kazanmıştır. Çalışır durumdaki makina, ekipman ve aletlerinin gürültüleri, tasarım sayesinde belirli bir noktaya kadar iyileştirilebilmektedir. Sonraki adımda gürültüyü en az düzeye indirebilmenin yolu, sesin kaynaktan kullanıcıya doğru ilerlediği yol üzerinde bir takım önlemler almaktır. Söz konusu önlemler, ses yalıtımı olarak bilinmekte olup uygun yalıtım malzemeleri ve bunların tasarımları ile gerçekleştirilmektedir. 
Ses yalıtımı çalışmalarına başlamadan önce, ilgilenilen gürültü kaynağının karakteristiği ve uygulanacak yalıtım sisteminin performansı çok iyi bir şekilde analiz edilmelidir. Gürültü kaynaklarının, frekansa bağlı olarak incelendiği gibi, ses yalıtım amacıyla tasarlanan malzeme, plaka, bariyer veya tasarımların da frekans bantları bazında yalıtım performanslarının bilinmesi ve yorumlanması gerekmektedir. Gürültü kaynağının yorumlanmasında, yüksek ses gücü düzeylerine sahip frekans bantları tespit edilmektedir. Bu frekans bantları, kaynağın ses gücü düzeyini artıran noktalar olup, sönümlenerek veya yalıtılarak alıcıya iletiminin önlenmesi durumunda toplam ses düzeyi iyileştirilmiş olmaktadır. Bu bilgiler ışığında yapılan yalıtım sistemi tasarımları sayesinde başarılı bir biçimde gürültünün kontrolü sağlanmaktadır. 
Bu çalışmada, bünyesinde meta-yapılar barındıran meta-malzeme plaka sayesinde, istenilen frekans bantlarında, kaynaktan alıcıya ses iletimini önleyen tasarımlar ortaya konmuştur. Bahsi geçen meta-malzeme plakadan kasıt, düz bir plakaya belirli aralıklarla yerleştirilmiş olan birim meta-yapıların eklenmesi vasıtasıyla elde edilen, farklı frekans bantlarında durdurucu filtre gibi çalışan, kaynaktan alıcıya ses iletimini önleyen tasarımlardır. Bu meta-malzeme tasarımlarının ses iletim kaybı davranışlarının incelenmesi amacıyla, sayısal analiz modeli oluşturulmuştur. Bu nümerik model, literatür ve deneysel veri ile doğrulanmıştır. Sonrasında, söz konusu nümerik model üzerinden parametrik çalışmalar gerçekleştirilerek, farklı frekans bantlarında, ses iletim kaybı yüksek meta-malzeme plaka tasarımları oluşturulmuştur. Ayrıca bu çalışma, meta-malzeme tasarımında, odaklanılan frekans bantları için en uygun tasarımı gerçekleştirmeye yönelik izlenmesi gereken yöntem ve metodoloji hakkında bilgi vermeyi hedeflemektedir.

Abstract:
With the development of the technology, the number of machines, tools and equipments that are offered to people is rapidly increasing. In everyday life, and even in the industry environment, the sound levels that people are exposed to are also increasing at the same rate. Sound is defined as changes in pressure, sensed by the ear, in air, water, or similar media that radiate as a wave community. The phenomenon of sound propagation and propagation in the environment is due to the vibrations of the particles and their transmission into neighboring particles. The changes that the vibrating particles cause to the air pressure are transformed into electrical signals through the related units in the ear and the hearing activity is realized through the brain conduction. Studies aimed at reducing the noise problems, which negatively affect the comfort and psychological characteristics of the people, especially their health, have gained importance. The noise levels of working machines, equipment and tools can be improved to a certain point through design. The next step is to take some precautions on the way of the sound progresses from the source to the receiever. These studies are known as sound insulation and are realized with appropriate insulation materials and their designs.
According to regulations, standards, personal comfort criteria and health restrictions, the issue of noise control has become increasingly important and necessary. Products such as white goods and small household appliances must be optimally designed and optimized acoustically while delivering to the end user with respect to the restrictions imposed. The effectiveness and cost of the materials and designs used for noise control, especially in small household appliances and white goods, are the most important parameters in the cost optimization process and acoustic design process. These parameters are also becoming the most important criteria of the designer and the manufacturer while acoustically improving.
For this reason, it has become very important to create optimum designs for the optimization problem that exists directly between the product cost, weight and sound power level parameters, and studies on this issue are increasing day by day.
Before starting sound insulation studies, the characterization of the noise source concerned and the performance of the insulation system to be applied should be analyzed very well. It is necessary to know and interpret the insulation performances in terms of the frequency levels of the materials, plates, barriers or designs designed for sound insulation as well as the noise sources, acoustic spectra depending on the frequency. In the spectrum of the noise source, frequency bands with high sound power levels are detected. These frequency bands are points that increase the sound power level of the source and the total sound level is improved if the receiver transmission is prevented by damping or isolation. With this information, isolation system designs that are made in order to successfully control the noise are provided.
In this thesis, developed meta-material plate, designed to prevent the sound transmission from the source to the desired frequency bands is presented. The meta-material plate is a design that prevents the transmission of sound from the source to the receiver, acting as a band stop filter at desired frequency bands, obtained by adding unit resonant structures, called as meta-structure, spread periodically on a flat plate.
In literature, meta-material work has begun to be studied after 1990. For this reason, few studies are concerned. However, there are studies prepared with the same theoretical background. Literature research has been carried out on designs where the desired sound insulation performance is obtained in certain frequency bands. As a result of the research, different designs and applications have been examined and the design to be done within this study has been determined.
In order to solve the noise problems of the products such as white goods and small household appliances, a FEM model was created by using ANSYS to analyze the sound transmission loss (STL) of the meta-material plate designs with meta-structure in order to damp frequency bands which have high sound power level. Harmonic response analysis was performed by the coupled algorithm. During the analysis, the acoustic extension under the structural module is integrated into the program. Analyzes were performed in the range of 500 - 1000 Hz for the center frequency, the lower limit frequency and the upper limit frequency for each octave band in the 1/3 octave band. Parametric studies have been carried out using the numerical analysis model which has been verified by literature and experimental study. The experimental study was carried out by using twin alpha cabinet measurement system. The test setup contains two standard alpha cabins on the right and left. There is a sound source in one of the cabinets. Measurements are taken by the microphones in both cabinets. The test sample is fixed in the frame located in the middle section of the two cabinets. The sound transmission loss values are obtained by inserting the sample between the two enclosed volumes, for the panels and compartments, the source and the receiving room. The numerical analysis made with the meta-material was compared with the result of the sound transmission loss experiment performed on the twin alpha cabinet setup. The result of the numerical analysis and the result of the experimental work was overlapped.
While designing the meta-material, the most important criteria is the first natural frequencies of the added meta-structures. The first natural frequencies have been estimated by the finite element method. It is the fact that, first natural frequencies are close to the frequency bands where the sound transmission loss (STL) reaches the maximum value. According to this approach, meta-material design was changed parametrically. By means of parametric change, meta-materials designs, which have different natural frequency behaviors, were obtained. With parametrically modified designs, natural frequencies were estimated and acoustic analysis were performed, respectively. In this way, meta-material designs with different sound transmission loss behavior were obtained. It has been observed that each of these designs has superior sound transmission loss characteristics in different frequency bands. This result has allowed the presentation of meta-material designs that influence transmission of the frequency-based sound waves. As a result of the parametric studies, the sound transmission loss behaviors of the meta-materials were observed, interpreted. Suitable meta-material designs were decided according to the sound power level spectra of the interested products. 
In this study, the material type and characteristics were determined as DuraformPA. All numerical analysis, prototype production and experiments were carried out using this material type. Since, the aim is to examine the behavior of the transmission loss of meta-materials and to expand this work with parametric designs. Additionally, this study is carried out with only one meta-structure geometry. The critical dimensions of a fixed meta-structure geometry has changed, but its shape remains the same. 
In subsequent studies, this presented meta-material design study can be developed by examining for different types of materials and geometries.
In addition, this study aims to provide information about the method or methodology to be followed in designing the meta-material in order to implement the optimum design for the focused frequency bands.