Amir Abas Mohammadzadeh Galehdar

Antenna Efficiency Calculations for Electrically Small, RFID Antennas

Radio frequency identification (RFID) antenna efficiency is an important component of link budget design. A method of moments technique based on the summation of segment currents compares favorably with two different results obtained using the finite element method (radiation pattern integration and Wheeler cap). The efficiency of a resonant dipole was found to be proportional to the inverse square root of the conductivity. For a typical RFID meander line antenna in free space the relationship is more severe

Using ant colony optimisation to construct meander-line RFID antennas

A method increasingly used to uniquely identify objects (be they pieces of luggage, transported goods or inventory items in shops and warehouses), is Radio Frequency IDentification (RFID). One of the most important components of RFID systems is the antenna and its design is critical to the utility of such tracking systems. Design engineers have traditionally constructed small antennas using their knowledge and intuition, as there is no simple analytical solution relating antenna structure to performance. This, however, does not guarantee optimal results, particularly for larger, more complex antennas. The problem is ideally suited to automated methods of optimisation. This chapter presents an overview of the automatic design of antennas using the meta-heuristic known as Ant Colony Optimisation (ACO). Apart from a description of the necessary mechanics ACO needs to effectively solve this problem, a novel local search refinement operator and a multi-objective version of the problem are also described. The latter is used to optimise both antenna efficiency and resonant frequency. Computational results for a range of antenna sizes show that ACO is a very effective design tool for RFID antennas.

Using Ant Colony Optimisation to Improve the Efficiency of Small Meander Line RFID Antennas

Increasing the efficiency of meander line antennas is an important real-world problem within radio frequency identification (RFID). Meta-heuristic search algorithms, such as ant colony optimisation, are very efficient at solving problems that require paths to be constructed. This search technique is adapted to solve the grid based path problem for meander line antennas and incorporates the NEC evaluation suite. The results for grid sizes up to 10 times 10 grid indicates that ant colony optimisation is extremely effective at this real-world problem.

Efficiency variations in electrically small, meander line RFID antennas

Not all meander line dipole antennas (MLDAs) plotted on the same grid necessarily have similar characteristics. MLDAs can be optimized for best efficiency, lowest resonant frequency or highest impedance. Different structures were investigated using a 5 times 10 array of rectangular grid points in 4times9 mm2 area and, all symmetrical MLDA that incorporate all grids points were modeled to determine the resonant frequency and efficiency. Based on the NEC simulation results for all possible family members, the range in resonant frequencies was 3.51 to 4.71 GHz and the range in efficiencies was 58.48% to 83.17%. The most efficient structure and the structure with the lowest resonant frequency were determined from the entire population of 1072 different antenna structures. The most efficient antennas have identical structures close to the feed point and all have an efficiency of greater than 83%.

Optimising efficiency and gain of small meander line RFID antennas using ant colony system

Radio Frequency IDentification (RFID) technology is increasingly being used to uniquely identify objects. An important component of RFID systems is the design of the antenna - which usually takes the form of a compacted meander line. This task becomes an optimisation problem as different designs will have different efficiencies and resonant frequencies. In this paper, we explore the use of a multi-objective version of ant colony system. This constructive meta-heuristic, as shown, is highly suitable for this problem.

Local search for Ant colony system to improve the efficiency of small meander line RFID antennas

The efficient design of meander line antennas for RFID devices is a significant real-world problem. Traditional manual tuning of antenna designs is becoming impractical for larger problems. Thus the use of automated techniques, in the form of combinatorial search algorithms, is a necessity. Ant colony system (ACS) is a very efficient meta-heuristic that is commonly used to solve path construction problems. Apart from its own native search capacity, ACS can be dramatically improved by combining it with local search strategies. As shown in this paper, applying local search as a form of structure refinement to RFID meander line antennas delivers effective antenna structures. In particular, we use the operator known as backbite, that has had previous application in the construction of self-avoiding walks and compact polymer chains. Moreover, we apply it in a novel, hierarchical manner that allows for good sampling of the local search space. Its use represents a significant improvement on results obtained previously.

Design Methods for 3D RFID Antennas Located on a Conducting Ground Plane

Based on 2D meander line methods, 3 times 3 times 3 point, symmetrical, 3D dipole antennas structure was investigated exhaustively to identify those configurations with the highest efficiency and lowest resonant frequency for a fixed length. Maximum efficiency and input impedance occurs when adjacent high current segments in the antenna are oppositely directed. The optimal antenna structure was compressed and the effect of a nearby conducting plane was investigated. The meander line structure greatly improves antenna performance with a resonant frequency of 498 MHz and an efficiency of 62% when located on a conducting ground plane.

Optically transparent frequency selective surfaces on flexible thin plastic substrates

A novel 2D simple low cost frequency selective surface was screen printed on thin (0.21 mm), flexible transparent plastic substrate (relative permittivity 3.2). It was designed, fabricated and tested in the frequency range 10-20 GHz. The plane wave transmission and reflection coefficients agreed with numerical modelling. The effective permittivity and thickness of the backing sheet has a significant effect on the frequency characteristics. The stop band frequency reduced from 15GHz (no backing) to 12.5GHz with polycarbonate. The plastic substrate thickness beyond 1.8mm has minimal effect on the resonant frequency. While the inner element spacing controls the stop-band frequency, the substrate thickness controls the bandwidth. The screen printing technique provided a simple, low cost FSS fabrication method to produce flexible, conformal, optically transparent and bio-degradable FSS structures which can find their use in electromagnetic shielding and filtering applications in radomes, reflector antennas, beam splitters and polarizers.

Flexible, light-weight antenna at 2.4GHz for athlete clothing

Linearly polarized rectangular patch antennas printed on light-weight cotton clothing are subject to both convex and concave bending. Changes in resonant frequency resulting from H plane bending are explained in terms of changes in effective length. Agreement between theory, practical and simulation results was observed. The resonant frequency changed by up to 8% for extreme bending although the bandwidth remains essentially unchanged at 4.5%. A 16.8% bandwidth was achieved using a double U-Slotted patch which minimized the problem.

Tapered Meander Line Antenna for Maximum Efficiency and Minimal Environmental Impact

The environmental impact of mass produced, disposable antennas is a major consideration in such areas as RFID, cellular telephones and keyless entry devices. The selection of environmentally benign materials and low energy manufacturing impacts the efficiency of antennas. This letter outlines a design methodology based on tapering printed meander line antennas to gain maximum efficiency within a fixed area. The strategy involves an iterative optimization technique in which the thickness of each segment is changed proportionally with the current in each segment of the line. At 860 MHz, the same efficiency can be achieved with 50% of the conductive material. Alternatively, the efficiency can be increased without increasing the volume of conducting material.