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Wearable Compact Fractal Antennas for 5G and Medical Systems
Published in Albert Sabban, Wearable Systems and Antennas Technologies for 5G, IOT and Medical Systems, 2020
Euclidean antennas are typically desired to operate within a narrow range (e.g., 10%–40%) around a central frequency fc which in turn dictates the size of the antenna (e.g., half or quarter wavelength). When the size of a Euclidean antenna is made much smaller than the operating wavelength (λ), it becomes very inefficient because the antenna’s radiation resistance decreases and becomes less than its ohmic resistance (i.e., it does not couple electromagnetic excitations efficiently to free space). Instead, it stores energy reactively within its vicinity (reactive impedance Xc). These aspects of Euclidean antennas work together to make it difficult for small Euclidean antennas to couple or match to feeding or excitation circuitry and cause them to have a high Quality (Q) factor (lower bandwidth). Q factor may be defined as approximately the ratio of input reactance Xin to radiation resistance Rr,Q=Xin/Rr.
Multi-Folded and Multi-Level Antennas
Published in Boris Levin, Antenna Engineering, 2017
Further, we pass to Q-factor. Q-factor (quality) is an important electrical characteristic of the antenna. It defines in particular the frequency band within which one may obtain the given level of matching an antenna with a cable without a change of a tuning. Q-factor characterizes the rate of changing the antenna input impedance as the result of the influence of various external factors and can be used to quantify the sustainability of the antenna tuning, if the sustainability is understood as the preservation of the results of the antenna tuning. From this standpoint, the higher the quality factor, the worse the stability, and vice versa.
Reactors
Published in Leonard L. Grigsby, Electric Power Transformer Engineering, 2017
Richard F. Dudley, Michael Sharp, Antonio Castanheira, Behdad B. Biglar
Various levels of electrical damping are required in a number of reactor applications including harmonic filters, shunt capacitor banks, and series capacitor banks. All are inductive or capacitive circuits and damping is usually governed by the resistive component of the reactor impedance. If this is insufficient, then other means of providing damping must be employed. The required level of damping in a harmonic filter depends on system parameters. In the case of harmonic filter, shunt capacitor bank, and series capacitor bank applications, the required level of damping is system design driven. Damping is usually required at a specific frequency. The Q-factor is a measure of the damping; the lower the Q the higher the damping. The Q-factor is the ratio of reactive power to active power in the reactor at a specific frequency. In cases requiring high damping, the natural Q-factor of the reactor is usually too high. However, there are methods available to reduce the Q of a reactor by increasing the stray losses through special design approaches, namely, increasing conductor eddy loss and mechanical clamping structure eddy loss. In the case of reactors for shunt capacitor banks and series capacitor bank applications this method is usually sufficient. In the case of reactors for harmonic filter applications other more stringent approaches may be necessary. One traditional method involves the use of resistors that, depending on their rating, can be mounted in the interior of the reactor or on the top of the reactor or separately mounted. Resistors are usually connected in parallel with the reactor. Figure 11.43 shows a tapped filter reactor, separately mounted resistor arrangement for an AC filter on an HVDC project.
Investigation on material variants and fabrication methods for microstrip textile antennas: A review based on conventional and novel concepts of weaving, knitting and embroidery
Published in Cogent Engineering, 2022
Rameesh Lakshan Bulathsinghala
The Q factor analysis of textile-based antennas is essential since power losses of textile antennas are higher than their metallic counterparts due to the anisotropic nature of textile materials and fabrication limitations. Therefore, material variants and fabrication variants should be considered based on power losses as mentioned in Equation (1) while fabricating each component of the textile antenna. The Q factor is the ratio between electric energy stored and radiated by the conductive material, which is a measure of power loss in a microwave system. The Q-factor determines the bandwidth of the microstrip antennas. The total Q-factor (QT) is a combination of Q-factor due to lateral radiation loss (Qrlateral), Q-factor due to space wave radiation loss (Qrspace) Q-factor due to conduction loss (Qc), Q-factor due to dielectric loss (Qd) and the Q-factor due to surface wave propagation loss (Qs). The total Quality factor in terms of these Q factors is given below in Equation (1).
Effect of coil design parameters on performance of electromagnetic forming process
Published in Materials and Manufacturing Processes, 2022
Manoj Soni, Meraj Ahmed, Sanjay Kumar Panthi, Surendra Kumar
= coil inductance (Lc), RAC = frequency dependent resistance; r1 = inner radius of coil (mm); α and β are the form factors; η = effective number of turns; π = 3.141 radian; Rcoil = resistance of coil at constant current; N = Nominal/total number of turns; ξ = filling factors; ρ = resistivity (Ω mm); = permeability of vacuum (H/m); = skin depth of coil (mm); = thickness of turn (mm);(α, β) = self-inductance factor; ρ coil = resistivity of coil. Various others terms associated with efficiency of coil and EMF process are Q-factor, skin depth, frequency, and current pulse and they are discussed below in brief. Quality factor (Q) represents the loss of energy into the coil and is given by the ratio of stored energy to the energy dissipated. Q can be optimized by changing inductive and resistive parameters. It is given as follows[43]:
Analysis of the quality factor of micro-beam resonators based on heat conduction model with a single delay term
Published in Journal of Thermal Stresses, 2019
Harendra Kumar, Santwana Mukhopadhyay
Based on modern technology, the Micro-Electro-Mechanical Systems (MEMS) and Nano- Electro-Mechanical Systems (NEMS) are being developed due to their various applications in fields of engineering and science such as sensors, micro pumps, accelerometers, charge detectors, radio frequency (RF) filters, and so forth. One of the important application of MEMS is micromechanical resonators for their high sensitivity and fast response. For resonators, it is possible to construct and design systems with very little loss of energy dissipation during vibration. It has been observed that one of the import energy loss factors during vibration is thermoelastic damping in very small structure in size. In order to minimize energy dissipation during the vibration, we need to construct a system with high-quality factor. The quality factor is a dimensionless parameter of a micro resonator and defined as the ratio of the stored energy in the resonator and the dissipated energy by the resonator per cycle of vibration. Quality factor is also commonly termed as the Q-factor. A high value of the quality factor indicates the low rate of energy loss and therefore in such case, oscillations will gradually reduce. This implies that oscillations will ring or vibrate for a long time.