CHAPTER 1 INTRODUCTION. the sectors of industrial and customer products [5]. The first ever concept of nanotechnology

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1 CHAPTER 1 INTRODUCTION 1.1 General Introduction: Nanotechnology is defined as the application of nanoscience in technological devices/processes/products. It is fast promising technology capable of impacting almost all the sectors of industrial and customer products [5]. The first ever concept of nanotechnology was introduced by the famous professor of physics Dr. Richard P. Feynman in Invention of scanning tunneling microscope in 1981 by IBM which is used to manipulate individual atoms and molecules, and discovery of fullerene in 1985 leads to the emergence of nanotechnology. The term nanotechnology was defined by Professor Norio Taniguchi of Tokyo University of Science in 1974 paper which as follows: Nano-technology mainly consists of the processing of separation, consolidation, and deformation of materials by one atom or by one molecule Nanotechnology is a highly multidisciplinary field drawing from material science, applied physics, electrical engineering, mechanical engineering, information technology, chemical engineering, biotechnology, etc. as illustrated in Fig.1.1. The early 2000 saw the beginning of commercial applications of nanotechnology in surface coatings, aerospace and vehicle manufacturing etc., although these were limited to bulk application of nanomaterials. There is a great demand for Nanoscience and Nanotechnology in drug delivery, energy sector including battery, bio-defense, biotechnology, electronics, solar cells, metallurgy and materials, communication, chemicals, fertilizers, pesticides, agriculture, healthcare including water purification system, food technology and cosmetics. Fig. 1.2 illustrates applications of nanotechnology. 1

2 Fig. 1.1: Nanotechnology-Multidisciplinary field Fig. 1.2: Applications of Nanotechnology 2

3 Some of the most revolutionary nanotechnology applications are communications systems, nano functional electronics, nano embedded systems, nano functional textiles, semiconductor materials, nanomagnets, fuel cell electrodes, sensors (gas, chemical, and bio etc.), solar cell and photonic materials etc. [2]. Nanotechnology represents a very broad area and is composed of nanomaterials, nanotools, and nanodevices. Nanomaterials represent a class of materials characterized by a feature size in the range nm. While nanodevices will certainly have to be made from nanomaterials, nanomaterial itself impacts area beyond nanotechnology. It is important that bringing the feature size to 1 to 100 nm results in significant enhancement of strength, toughness or electrical, electronic, optical and magnetic properties. The achievements in the synthesis of nanostructured materials enabled researchers to explore the physical, chemical, and electronic properties for various applications in the field of nanoelectronics, nanooptics, energy conversion, and chemical sensing. Chemical sensors have important applications in the area of environmental monitoring, public security, automotive application, and medical diagnosis. In general, the advantages of nanomaterial based sensors are fast response, small size, high selectivity, and portability compared to existing large sensors. While many different approaches to gas detection like infrared, electromechanical, paramagnetic, catalyst based etc. are available, metal oxide, copper oxide, tin oxide based nano sensors are widely used for a range of species [4] [6] [9]. Many researchers have reported nano electronic nose approach having great potential for detecting and discriminating between variety of gases including explosive ones and nerve agents [7-8]. In research paper [1], authors have developed a low cost wireless embedded CO sensor system based on tin oxide nano sensor to detect CO and LPG. Another area of interest is study of nanotechnology enabled electronics in developing applications based on magnetic nanomaterials, nano films, carbon nanotube, and graphene. 3

4 The electronic applications include microwave antennas, filters, inductors, chokes, coreshaped transformers, ultra high frequency telecommunications, power converters, high density data storage etc. In our research we focus mainly on design, modelling, simulation and prototype fabrication of electronic microstrip patch antenna (MPA) using nanotechnology. Further, theoretical study is made on carbon nanotube (CNT) radio frequency (RF) model and its applications in antenna development. The nanotechnology materials and antenna are modeled in Mentor Graphics IE3D simulator version [116]. IE3D is an electromagnetic simulator used to model and simulate antennas and filters. IE3D simulator is a method of moments (MoM) based full wave electromagnetic simulator used for the design of general 3D and 2D planar structures like patch antennas. It solves Maxwell s equation and its solutions include discontinuity effects, wave effects, coupling effects, and radiation effects. The modeled and simulated antennas are fabricated using conventional tools and nanotechnology tools. The conventional tools used are AutoCAD drawing and photolithography process. Nanotechnology tools used are RF-sputtering, physical vapor deposition, magnetic stirrer and screen printer. For thickness and uniform deposition confirmation, scanning electron microscopy (SEM) is used. 1.2 Motivation and Goals of Research In electronic RF wireless communication systems, antenna is an integral part for radiating or receiving radio waves [30]. Antennas are commonly used for commercial telecommunication applications like personal communication systems and cellular. An antenna comes in variety of shapes and sizes and EM computational equations are used to design their geometry for specific applications. Various antenna types are: wire antennas, aperture antennas, microstrip antennas, lens antennas, reflector antennas and array antennas etc [22]. Among these microstrip patch antennas are increasingly becoming popular as size 4

5 and weight reduction are important factor in a system where demand is for device miniaturization. In addition, large bandwidth, tenability and mechanical flexibility of the antennas are all desirable properties. In high performance aircraft, spacecraft, satellite and missile applications, where cost, size, weight, ease of installation, performance, and aerodynamic profile have limitations, require low profile antennas. There are many other private, governmental and commercial business applications such as mobile devices and wireless systems that have similar requirements. To meet these, microstrip antennas are used. Microstrip antennas are low profile, conformable to planar and non planar surfaces, simple and inexpensive to manufacture using modern printed circuit board technology, mechanically robust when mounted on rigid surfaces, compatible with monolithic microwave integrated circuit designs. When the particular patch shapes are chosen, antennas are very versatile in terms of polarization, resonant frequency, pattern and impedance. The current technologies use bulk and thick film forms of materials in fabricating patch antennas. As antenna sizes gets smaller, losses due to EM dissipation in materials increase and directly affect the performance by reducing the bandwidth and gain. Presently there is a major R&D thrust in developing antennas using novel geometric design where the miniaturization can be improved, but at the cost of reducing the bandwidth and high quality factor (Q). However, there has been little effort in improving the material technology in antennas and other communication devices. Our approach to address the above issues is to study and develop nano-material based antenna to have enhanced electromagnetic properties in particular size reduction and bandwidth enhancement. Nano structured material with grain sizes in 1 to 100 nm range shown to have number of desirable electromagnetic and mechanical properties that play a significant role in improving antenna parameters like size reduction, bandwidth and impedance matching [6] [40]. Electromagnetic properties can be controlled by changing the particle size 5

6 distribution in nano materials and application specific, tailored materials can be produced. Eddy current and magnetic losses can be minimized using nano material (ultrathin patch) in antenna structure [53-55]. In this research work, we focus on developing antennas structures based on nano materials that exhibit improved characteristics. There will be a large effort on synthesis and processing of nano materials using nanotechnology tools, techniques and measurement systems. A few key aspects that make nano materials very attractive candidates for antenna development are: physical properties different from bulk and often superior, better control of microstructure and selective enhancement of desirable parameter etc. In coming days, if proven to be effective, nano materials will replace the current materials used in all the antennas devices. The biggest impact of nanotechnology in the coming days is impact on almost all the application sectors of wireless industry. Thus, technological innovations that result in major breakthroughs will impact on health care, defense, agriculture, satellite, mobile communication, wireless sensor network etc. 1.3 Antenna Miniaturization (Size Reduction) Techniques The art of antenna size reduction is an art of compromise. One has to develop an antenna as small as possible that is still suitable for a given application with respect to its radiation characteristics. In addition to miniaturization one has to look for the best trade-off among volume, bandwidth, gain etc. The best trade-off is usually obtained when the complete volume (size) is used. There are several antenna size reduction technique used at present, but each of them might affect the antenna performance differently. Dielectric loading: The use of high permittivity substrate allows reducing the size of an antenna with the disadvantage of field confinement around the high permittivity region. The high permittivity increases the concentration of reactive 6

7 energy within the substrate and therefore increases the Q factor, which reduces the available bandwidth of the antenna. Examples of antennas that exploit this technique are patch antenna and PIFA antennas [12] [17]. The use of high dielectric materials is often restricted to antennas such as GPS and Bluetooth operating at a single narrow band. Geometry Modifications: This approach tries to lengthen the current path while reducing the overall dimension of the antenna. The strategies are multilayered structures, folding, meandering, slots etc. For example, introducing slots in patch force surface currents to lengthen the patch, thus artificially increasing the antennas electrical length without modifying its original dimensions. However, this approach increases reactive impedance and reduce its radiation resistance. Many RFID antennas use this technique. Use of shorting plane: This technique uses shorting plane to force excitation of a given current mode on an antenna, in such a way that the part of the antenna becomes redundant and can be removed. Monopole and PIFA antenna uses this technique. Lumped Elements Loading: The simplest way to reduce the size of antenna than its resonant size. The antenna smaller than half-wave length will have strong reactive input impedance which has to be compensated by loading it with a capacitor. However, the effect of this loading will reduce the efficiency and bandwidth of the antenna. Use of superstrate: This technique uses high dielectric substrate as superstrate on conducting patch of the antenna for miniaturization, but at the cost of decreased bandwidth. 7

8 1.4 New Materials from Nanotechnology: Magneto-Dielectrics Magneto-dielectric (MD) materials are artificial materials that present EM properties unavailable in nature. The MD material is one kind of dielectric material whose value of permeability can be varied easily above one [19]. It is different from conventional dielectric material in which the permeability is one. MD material is suggested to use instead of high permittivity dielectric substrate because high permittivity substrate causes antenna to have narrow bandwidth and low efficiency [14]. Magneto-dielectric material use reduces the electric and magnetic imbalance which enhances system bandwidth automatically by increasing the magnetic energy as major energy storage for a pure dielectric which is capacitive [19] [25]. Also, magneto-dielectrics have advantage of magnetic fine tuning and lower eddy current losses if nano-ferrite is used. MD material can be processed by nanotechnology that includes nano ferrite in the dielectric composite material [40]. The antennas designed on magneto-dielectric materials thus have higher bandwidths and lower Q. In addition, the surface waves excitation is significantly minimized thus resulting in low coupling losses in array antennas [38]. It is reported that magneto-dielectric substrate can be synthesized and processed using nanotechnology tools and techniques. In material science engineering elements like Cobalt, Zink and Garnets like hexaferrite and Yitrium Iron Garnet have considerable permeability values at GHz frequencies [48]. Miniaturized antennas based on Nickel-Cobalt-Ferrite and Nickel-Zink-Ferrite magneto-dielectric substrates are reported in research papers [21] [28] [31] [42]. 1.5 Nanofilm (Ultra-Thin Patch) Antennas The present antennas use bulk rolled copper on substrates as radiating patch suffers from skin effect problem. Because of skin depth, currents in a microstrip antenna flow mainly in the patch s inner and outer surfaces. The inner surface of the patch attached to the dielectric substrate faces the ground plane. The current on the outer surface is lower than the 8

9 current on the inner surface. However, it is mainly the outer surface of patch radiates or receives the signal. Currents on the inner surface of patch are not capable of radiating because of the conductor portion of the patch between the outer and inner surface not allows radiation which the current at the inner surface may produce. This limits the bandwidth and efficiency [53-54]. In order to overcome above situation, using nanotechnology we fabricate radiating patch on substrate, where its thickness is in the range nm, which is less than many times of skin depth thickness [55].In our research work, the bulk thickness patch and nano thickness patch on dielectric substrate are modeled and simulated in IE3D simulator for copper and silver metals. The antennas are fabricated by depositing nano thickness metal patch on Flame Retardant (FR4 substrate) glass epoxy keeping other parts of antenna like substrate and feedline in bulk form. The nanofilm antennas are investigated for bandwidth enhancement in WLAN and X band frequency applications. 1.6 Carbon Nanotube (CNT) Antennas With the recent developments in medical electronics, security systems etc, antennas are becoming integral part of these systems. Since these systems operate in THz frequency range, antenna dimension reduces to micron/nano thickness size. Under these circumstances it is very difficult to fabricate antennas with conventional metals like copper, aluminum etc. The reason is that when standard metal reduces to nano size, its conducting property changes to very low conductivity, since metal surface offers higher surface resistance [52] [57] [60] [66] [97]. Under this condition the nano size antenna may not be realizable as antenna. The above problem with metals at nano level dimension can be solved by replacing them with carbon nanotubes. Carbon nanotubes are 1-dimensional structures that can be obtained by rolling up a crystalline structure of carbon atoms in a hexagonal pattern called grapheme [102] [106]. There is an ongoing research on carbon nanotube applications ranging from CNTFET, 9

10 biomedical applications, sensing applications to nano antenna applications [109] [112] [114]. The interest in carbon nanotube for antenna applications arises from the potential miniaturization capabilities that are observed from the study of their electronic structure, and how they interact with electromagnetic waves [ ]. In chapter 6 we study in detail about CNT architecture, RF model and its applications in antenna development. 1.7 Nanotechnology Tools There are many nanotechnology tools available where nanomaterials are realized into functional devices with high performance. Normally device fabrication requires deposition of either nano composites (mix of metals, oxides etc) or pure metals on some kind of dielectric materials based on applications. For example thermal physical vapor deposition (PVD) system, radio frequency sputtering (RF-sputter), chemical vapor deposition (CVD) system to name few tools which are used for deposition of metal oxides or metals in nano thickness level on other materials like substrates, plastics, metals, silicon wafer etc. Some other nanotechnology tools are simple screen printing system, spray deposition, spin coating, dip coating technique, electro-spinning, inkjet printing etc are used to deposit nano composites for sensor and other device fabrications. There are nanotechnology measurements tools such as transmission electron microscopy (TEM), scanning electron microscopy (SEM), atomic force microscope (AFM) etc. are used to measure and analyze nano particle thickness, layer uniformity, thin film uniformity etc at nano level. For electrical characterization such as permittivity, permeability, conductivity, AC and DC resistance of fabricated device tools such as four probe technique, impedance analyzer, network analyzer etc are used. For nanotechnology enabled electronic device fabrication, many material simulation tools are available. For example COMSOL multi-physics simulation software is used to model and analyze nano material behavior with respect to external factors such as temperature, pressure, stress etc at atomic and molecular level. 10

11 1.8 Benefits of Nanotechnology Enabled Antenna Development Miniaturization without affecting other parameters like radiation efficiency, directivity etc. Increasing bandwidth in multiple folds. Reducing density of antenna structure. Nano materials are best known for their highly superior mechanical properties linked with the increased material surface area contribution. This can be directly exploited in antenna technology to produce antennas fabricated on flexible substrates such as cotton, plastic and curved materials. It has been established in several nano-materials that mechanical properties like yield strength, tensile strength, fatigue etc show remarkable improvement over bulk materials. These desirable properties can be selectively exploited in the development of mechanically robust electromagnetic sensors that operate effectively in harsh environments. Nanotechnology helps to deposit nanofilm for antenna sensor applications on rigid surface substrates. Following are the few important aspects that make the nano-materials very attractive candidate for planar antenna development: Physical and electrical properties different from bulk Selective enhancement of desirable parameter Better control of micro/nano structure porosity for ex: antenna sensors Novel nano-composite is possible Superior mechanical properties 11

12 In our work we study antenna using magneto-dielectric substrate, nanofilm (ultra-thin) patch based antenna and carbon nanotube based antennas. 1.9 Application and Market Potential Nano materials with superior electromagnetic properties will have high impact on defense, health care, cellular etc. In coming days, the biggest research in the commercial sector will be in the wireless and communication industry. Let us consider the case of analog cellular communication systems. The projected market for upgrading existing antennas and communication systems will be in several millions $ per year Organization of the Thesis The research study presented here mainly consists of seven chapters. Each chapter has been organized with same format beginning with an introduction for the concerned chapter and detailed explanation related to the research study. Chapter 1 discusses the concept of nanotechnology and its applications in electronic wireless communication system in particularly RF device antenna. It starts with how conventional antenna can be miniaturized with currently available techniques like high permittivity dielectric loading, use of geometry modification etc. But these conventional techniques increases quality factor Q of an antenna and reduces bandwidth. In this section we discuss how the conventional antenna size reduction techniques reduces antenna narrow bandwidth, and how to overcome this problem by utilizing nanotechnology processed materials like magneto-dielectric. It also briefs thin film technology (nanofilm) for antenna development. The motivation and goal for the present work is described in this chapter. Chapter 2 describes elaborate review of literature survey made on past work carried out in the field of antenna using nanotechnology in wireless communication systems. The literature review covers the period from 1934 to till date in detail. The formulation of problem is also described in this chapter for proposed work to carry out. 12

13 In chapter 3, we describe the methodology, experimental and radiation pattern measurement setups. It explains block diagram of Vector Network Analyzer (VNA). This chapter also gives brief idea about nano materials modelling in IE3D for nanotechnology enabled antenna development. A technical note on electromagnetic simulation package IE3D is presented in this chapter. Chapter 4 deals with design, theoretical modelling, simulation, fabrication, and radiation measurements of patch antenna based on Magneto-dielectric substrate. The probefed and aperture coupled patch antennas are loaded with synthesized magneto-dielectric material. Antenna loaded with magneto-dielectric film is investigated for antenna miniaturization and bandwidth enhancement. Chapter 5 deals with design, theoretical modelling, simulation, fabrication and radiation measurements of nano thickness (ultra-thin in nm range) radiating patch based antennas. In this we fabricate aperture coupled and proximity coupled feeding antennas using photolithography. The thin-film patches are fabricated using nanotechnology tools like vapor deposition system and RF-sputtering. The nanofilm patches are fabricated on FR4 substrate from pure silver and copper bulk material. In this chapter mainly we study on antenna bandwidth enhancement without affecting resonant frequency. In chapter 5, we also discuss application of thin-film for co-planar patch antenna by designing, modelling and simulation. In this we study nanofilm patch antenna on FR4 and silicon substrate. Through simulation we analyze nanofilm coplanar antenna with bulk patch coplanar antenna for bandwidth, return loss and radiation pattern. Chapter 6 deals with theoretical study of carbon nanotube, RF-circuit model and its applications in antenna development. Rapid advances in nanotechnology have made it possible to develop carbon nanotubes. In this chapter we study how CNTs are modeled as antenna at high frequencies and its effect on antenna parameters such as miniaturization (size 13

14 reduction), resonant frequency, input impedance, bandwidth and efficiency etc. The CNT based dipole antenna is studied in detail. In chapter 7, we discuss the conclusion and remarks drawn from the preceding chapters. This chapter also includes the futuristic scope for further study and investigation. The references, list of publications of the author and subject index are also given at the end of this thesis. 14