K. J. Vinoy

On the relationship between fractal dimension and the performance of multi-resonant dipole antennas using Koch curves

This paper relates for the first time, multiple resonant frequencies of fractal element antennas using Koch curves to their fractal dimension. Dipole and monopole antennas based fractal Koch curves studied so far have generally been limited to certain standard configurations of the geometry. It is possible to generalize the geometry by changing its indentation angle, to vary its fractal similarity dimension. This variation results in self-similar geometry which can be generated by a recursive algorithm. Such a variation is found to have a direct influence on the input characteristics of dipole antennas. The primary resonant frequency, the input resistance at this resonance, and the ratio of first two resonant frequencies, have all been directly related to the fractal dimension. Curve-fit expressions can also be obtained for the performance of antennas at their primary resonance, in terms of fractal iteration and fractal dimension. The antenna characteristics have been studied using extensive numerical simulations and are experimentally verified. These findings underscore the significance of fractal dimension as an important mathematical property of fractals that can be used as a design parameter for antennas. The use of these ideas would not only reduce the computational intensity of optimization approaches for design of fractal shaped antennas, but also help antenna designers approach the problem systematically. Design formulation for antennas based on other fractal geometries can be similarly obtained after identifying suitable parameters of variation. This would therefore help analytical design of multiband and multifunctional antennas using fractal geometries.

Broadband Suspended Microstrip Antenna For Circular Polarization

In this paper we propose a circularly polarized (CP) microstrip antenna on a suspended substrate with a coplanar capacitive feed and a slot within the rectangular patch. The antenna has an axial ratio bandwidth (< 3 dB) of 7.1%. The proposed antenna exhibits a much higher impedance bandwidth of about 49% (S11 < -10 dB) and also yields return loss better than -15 dB in the useful range of circular polarization. Measured characteristics of the antenna are in good agreement with the simulated results. The radiation patterns indicate good cross polarization rejection and low back lobe radiations. The design proposed here can be scaled to any frequency of interest.

MICROSTRIP SQUARE RING ANTENNA FOR DUAL- BAND OPERATION

This paper presents a generalized approach to design an electromagnetically coupled microstrip ring antenna for dual-band operation. By widening two opposite sides of a square ring antenna, its fractional bandwidth at the primary resonance mode can be increased significantly so that it may be used for practical applications. By attaching a stub to the inner edge of the side opposite to the feed arm, some of the losses in electrical length caused by widening can be regained. More importantly, this addition also alters the current distribution on the antenna and directs radiations at the second resonant frequency towards boresight. It has also been observed that for the dual frequency configurations studied, the ratio of the resonant frequencies (center dot r(2)center dot center dot r(1)) can range between 1.55 and 2.01. This shows flexibility in designing dual frequency antennas with a desired pair of resonant frequencies.

Resonant frequency of Hilbert curve fractal antennas

An approximate formulation for the resonant frequency of a dipole Hilbert curve fractal antenna (HCFA) is derived here. These can be used as small resonant antennas, useful in VHF/UHF communication. The formulas presented here can be appropriately inverted to obtain the design equations for the antenna, for a given resonant frequency.

Smart material systems and MEMS : design and development methodologies

Preface. About the Authors. PART 1: FUNDAMENTALS. 1. Introduction to Smart Systems. 1.1 Components of a smart system. 1.2 Evolution of smart materials and structures. 1.3 Application areas for smart systems. 1.4 Organization of the book. References. 2. Processing of Smart Materials. 2.1 Introduction. 2.2 Semiconductors and their processing. 2.3 Metals and metallization techniques. 2.4 Ceramics. 2.5 Silicon micromachining techniques. 2.6 Polymers and their synthesis. 2.7 UV radiation curing of polymers. 2.8 Deposition techniques for polymer thin films. 2.9 Properties and synthesis of carbon nanotubes. References. PART 2: DESIGN PRINCIPLES. 3. Sensors for Smart Systems. 3.1 Introduction. 3.2 Conductometric sensors. 3.3 Capacitive sensors. 3.4 Piezoelectric sensors. 3.5 Magnetostrictive sensors. 3.6 Piezoresistive sensors. 3.7 Optical sensors. 3.8 Resonant sensors. 3.9 Semiconductor-based sensors. 3.10 Acoustic sensors. 3.11 Polymeric sensors. 3.12 Carbon nanotube sensors. References. 4. Actuators for Smart Systems. 4.1 Introduction. 4.2 Electrostatic transducers. 4.3 Electromagnetic transducers. 4.4 Electrodynamic transducers. 4.5 Piezoelectric transducers. 4.6 Electrostrictive transducers. 4.7 Magnetostrictive transducers. 4.8 Electrothermal actuators. 4.9 Comparison of actuation schemes. References. 5. Design Examples for Sensors and Actuators. 5.1 Introduction. 5.2 Piezoelectric sensors. 5.3 MEMS IDT-based accelerometers. 5.4 Fiber-optic gyroscopes. 5.5 Piezoresistive pressure sensors. 5.6 SAW-based wireless strain sensors. 5.7 SAW-based chemical sensors. 5.8 Microfluidic systems. References. PART 3: MODELING TECHNIQUES. 6. Introductory Concepts in Modeling. 6.1 Introduction to the theory of elasticity. 6.2 Theory of laminated composites. 6.3 Introduction to wave propagation in structures. References. 7. Introduction to the Finite Element Method. 7.1 Introduction. 7.2 Variational principles. 7.3 Energy functionals and variational operator. 7.4 Weak form of the governing differential equation. 7.5 Some basic energy theorems. 7.6 Finite element method. 7.7 Computational aspects in the finite element method. 7.8 Superconvergent finite element formulation. 7.9 Spectral finite element formulation. References. 8. Modeling of Smart Sensors and Actuators. 8.1 Introduction. 8.2 Finite element modeling of a 3-D composite laminate with embedded piezoelectric sensors and actuators. 8.3 Superconvergent smart thin-walled box beam element. 8.4 Modeling of magnetostrictive sensors and actuators. 8.5 Modeling of micro electromechanical systems. 8.6 Modeling of carbon nanotubes (CNTs). References. 9. Active Control Techniques. 9.1 Introduction. 9.2 Mathematical models for control theory. 9.3 Stability of control system. 9.4 Design concepts and methodology. 9.5 Modal order reduction. 9.6 Active control of vibration and waves due to broadband excitation. References. PART 4: FABRICATION METHODS AND APPLICATIONS. 10. Silicon Fabrication Techniques for MEMS. 10.1 Introduction. 10.2 Fabrication processes for silicon MEMS. 10.3 Deposition techniques for thin films in MEMS. 10.4 Bulk micromachining for silicon-based MEMS. 10.5 Silicon surface micromachining. 10.6 Processing by both bulk and surface micromachining. 10.7 LIGA process. References. 11. Polymeric MEMS Fabrication Techniques. 11.1 Introduction. 11.2 Microstereolithography. 11.3 Micromolding of polymeric 3-D structures. 11.4 Incorporation of metals and ceramics by polymeric processes. 11.5 Combined silicon and polymer structures. References. 12. Integration and Packaging of Smart Microsystems. 12.1 Integration of MEMS and microelectronics. 12.2 MEMS packaging. 12.3 Packaging techniques. 12.4 Reliability and key failure mechanisms. 12.5 Issues in packaging of microsystems. References. 13. Fabrication Examples of Smart Microsystems. 13.1 Introduction. 13.2 PVDF transducers. 13.3 SAW accelerometer. 13.4 Chemical and biosensors. 13.5 Polymeric fabrication of a microfluidic system. References. 14. Structural Health Monitoring Applications. 14.1 Introduction. 14.2 Structural health monitoring of composite wing-type structures using magnetostrictive sensors/actuators. 14.3 Assesment of damage severity and health monitoring using PZT sensors/actuators. 14.4 Actuation of DCB specimen under Mode-II dynamic loading. 14.5 Wireless MEMS-IDT microsensors for health monitoring of structures and systems. References. 15. Vibration and Noise-Control Applications. 15.1 Introduction. 15.2 Active vibration control in a thin-walled box beam. 15.3 Active noise control of structure-borne vibration and noise in a helicopter cabin. References. Index.

Coplanar Capacitively Coupled Probe Fed Microstrip Antennas for Wideband Applications

The design and analysis of a coplanar capacitive fed microstrip antenna suspended above the ground plane is presented. It is demonstrated that the proposed approach can be used for designing antennas with impedance bandwidth of about 50% and a good gain to operate in various microwave bands. The model of the antenna incorporates the capacitive feed strip which is fed by a coaxial probe using equivalent circuit approach, and matches simulation and experimental results. The capacitive feed strip used here is basically a rectangular microstrip capacitor formed from a truncated microstrip transmission line and all its open ends are represented by terminal or edge capacitances. The error analysis was carried out for validity of the model for different design parameters. The antenna configuration can be used where unidirectional radiation patterns are required over a wide bandwidth.

ZnFe2O4: Rapid and sub-100 °C synthesis and anneal-tuned magnetic properties

Nanocrystalline zinc ferrite (ZFO) has been synthesized from metal acetylacetonates by microwave irradiation for 5 min in the presence of a surfactant. The as-prepared material is ZFO and has been subjected in air to conventional furnace annealing and to rapid annealing at different temperatures. Both annealing protocols lead to well-crystallized ZFO, with crystallite sizes in the range ∼8–20 nm, which is ferrimagnetic, even at room temperature, with magnetization attaining saturation. While the magnetization MS of conventionally annealed ZFO varies with crystallite size in the expected manner, rapid annealing leads to high MS even when the crystallite size is relatively large. The coercivity is greater in the conventionally annealed ZFO. Thermal and magnetic measurements suggest that the inhomogeneous site cationic distribution within each crystallite caused by rapid annealing can be used to tailor the magnetic behaviour of nanocrystalline ferrites.

Design Studies of Ultra-Wideband Microstrip Antennas with a Small Capacitive Feed

The design of an ultra-wideband microstrip patch antenna with a small coplanar capacitive feed strip is presented. The proposed rectangular patch antenna provides an impedance bandwidth of nearly 50%, and has stable radiation patterns for almost all frequencies in the operational band. Results presented here show that such wide bandwidths are also possible for triangular and semiellipse geometries with a similar feed arrangement. The proposed feed is a very small strip placed very close to the radiator on a substrate above the ground plane. Shape of the feed strip can also be different, so long as the area is not changed. Experimental results agree with the simulated results. Effects of key design parameters such as the air gap between the substrate and the ground plane, the distance between radiator patch and feed strip, and the dimensions of the feed strip on the input characteristics of the antenna have been investigated and discussed. As demonstrated here, the proposed antenna can be redesigned for any frequency in the L-, S-, C-, or X-band. A design criterion for the air gap has been empirically obtained to enable maximum antenna bandwidth for all these operational frequencies.

Design of reconfigurable fractal antennas and RF-MEMS for space-based systems

In this paper, design concepts of reconfigurable and electronically steered antennas based on a new fractal antenna and RF-MEMS devices are presented. As modern telecommunications extend towards higher frequencies, the advantages of employing RF-MEMS switches, phase shifters, and miniaturized fractal antennas become more significant. The input characteristics of the Hilbert curve fractal antenna can be made frequency agile by incorporating RF switches along its length. In addition, due to the large number of connected segments in this antenna geometry, reconfigurable radiation characteristics can be obtained by adding just a few additional line segments to interconnect these through semiconductor or RF-MEMS switches. The beam peak direction can be shifted by 63° and the beam width can be changed by up to 25° by this approach. An electronically steered antenna with micromachined phase shifters using tunable ferroelectric barium strontium titanate thin film is also discussed. These MEMS-based antenna systems find applications in communications satellites and electronically scanned arrays for space-based radars.

An integrated wideband multifunctional antenna using a microstrip patch with two U-slots

In this paper, a multifunctional microstrip antenna is designed, fabricated and experimentally verifled for operation in AWS, GSM, WiMAX and WLAN bands. This microstrip patch antenna has two U-shaped slots to achieve the dual wideband operation required to meet these speciflcations. The dimensions and locations of the U- slots are designed appropriately. The thick substrate used here helps in integrating the antenna with the existing aircraft panel material while achieving wide bandwidths. Experimental results of this single feed antenna indicate that it meets all current requirements for in-cabin wireless communication needs.