Browsing by Author "Erturk, V. B."
Now showing 1 - 9 of 9
- Results Per Page
- Sort Options
Item Open Access Analysis of input impedance and mutual coupling of microstrip antennas on multilayered circular cylinders using closed-form green's function representations(Institute of Electrical and Electronics Engineers Inc., 2014) Karan, S.; Erturk, V. B.Closed-form Green's function (CFGF) representations for cylindrically stratified media are developed and used in conjunction with a Galerkin method of moments (MoM) in the space domain for the analysis of microstrip antennas on multilayered circular cylinders. An attachment mode is used in the MoM solution procedure to accurately model the feeding of probe-fed microstrip antennas. The developed CFGF representations are modified in the source region (where two current modes can partially or fully overlap with each other during the MoM procedure) so that singularities can be treated analytically and hence, the proposed CFGF representations can be safely used in this region. Furthermore, accurate CFGF representations for the probe-related components (necessary for probe type excitations including the attachment mode) are obtained when the radial distance between the source and field points is electrically small or zero. Numerical results in the form of input impedance of various microstrip antennas and the mutual coupling between two antennas are presented showing good agreement when compared to the available published results as well as the results obtained from CST Microwave Studio.Item Open Access Analytic expressions for the ultimate intrinsic signal-to-noise ratio and ultimate intrinsic specific absorption rate in MRI(Wiley, 2011-03-09) Kopanoglu, E.; Erturk, V. B.; Atalar, ErginThe ultimate intrinsic signal-to-noise ratio is the highest possible signal-to-noise ratio, and the ultimate intrinsic specific absorption rate provides the lowest limit of the specific absorption rate for a given flip angle distribution. Analytic expressions for ultimate intrinsic signal-to-noise ratio and ultimate intrinsic specific absorption rate are obtained for arbitrary sample geometries. These expressions are valid when the distance between the point of interest and the sample surface is smaller than the wavelength, and the sample is homogeneous. The dependence on the sample permittivity, conductivity, temperature, size, and the static magnetic field strength is given in analytic form, which enables the easy evaluation of the change in signal-to-noise ratio and specific absorption rate when the sample is scaled in size or when any of its geometrical or electrical parameters is altered. Furthermore, it is shown that signal-to-noise ratio and specific absorption rate are independent of the permeability of the sample. As a practical case and a solution example, a uniform, circular cylindrically shaped sample is studied. CopyrightItem Open Access Applications of hybrid discrete Fourier transform moment method to the fast analysis of large rectangular dipole arrays printed on a thin grounded dielectric substrate(Wiley, 2002) Chou, H.-T.; Ho, H.-K.; Civi, O. A.; Erturk, V. B.Recently a discrete Fourier transform-method of moments (DFT-MoM) scheme was developed for fast analysis of electrically large rectangular planar dipole arrays, which has been shown to be very efficient in terms of number reduction of unknown variables and computational complexity. The applications of this DFT-MoM to treat dipole arrays printed on a grounded dielectric substrate are examined in this Letter. Numerical results are presented to validate its efficiency and accuracy.Item Open Access Efficient computation of surface fields excited on a dielectric-coated circular cylinder(IEEE, 2000-10) Erturk, V. B.; Rojas, R. G.An efficient method to evaluate the surface fields excited on an electrically large dielectric-coated circular cylinder is presented. The efficiency of the method results from the circumferentially propagating representation of the Green’s function as well as its efficient numerical evaluation along a steepest descent path. The circumferentially propagating series representation of the appropriate Green’s function is obtained from its radially propagating counterpart via Watson’s transformation and then the path of integration is deformed to the steepest descent path on which the integrand decays most rapidly. Numerical results are presented that indicate that the representations obtained here are very efficient and valid even for arbitrary small separations of the source and field points. This work is especially useful in the moment-method analysis of conformal microstrip antennas where the mutual coupling effects are important.Item Open Access Novel microstrip fed mechanically tunable combline cavity filter(IEEE, 2013) Kurudere, S.; Erturk, V. B.A novel configuration for mechanically tunable combline bandpass filters is proposed, where the classical resonating rod-tuning screw combination is replaced with a simple printed circuit-tuning screw combination. Moreover, because a printed circuit structure that uses metal vias forms the bottom part of the cavity, the coaxial type feeding and the coaxial to cavity matching of classical combline filters are also replaced with a microstrip feeding. Consequently, the proposed configuration provides smaller size, less weight, integration with other printed circuits and significant simplification in the fabrication process. A prototype filter is designed and fabricated for verification. The measured results are in good agreement with the simulation, and the filter exhibits very good harmonic suppression.Item Open Access Optical antenna of comb-shaped split ring architecture for increased field localization in NIR and MIR(Optical Society of America, 2013) Kilic, V. T.; Erturk, V. B.; Demir, Hilmi VolkanWe propose and demonstrate novel designs of optical antennas based on comb-shaped split ring architecture that display multi resonance field intensity enhancement spectrum. These nanoantennas achieve substantially increased field localization at longer wavelengths than that of a single or an array of dipoles with the same side length. With these optical antennas, localizing near infrared (NIR) and mid infrared (MIR) lights within a region of tens of nanometers at an intensity enhancement level of the order of thousands of magnitude can be accomplished. (C)2013 Optical Society of America.Item Open Access Three-dimensional study of planar optical antennas made of split-ring architecture outperforming dipole antennas for increased field localization(Optical Society of America, 2012-01-09) Kilic, V. T.; Erturk, V. B.; Demir, Hilmi VolkanOptical antennas are of fundamental importance for the strongly localizing field beyond the diffraction limit. We report that planar optical antennas made of split-ring architecture are numerically found in three-dimensional simulations to outperform dipole antennas for the enhancement of localized field intensity inside their gap regions. The computational results (finite-difference time-domain) indicate that the resulting field localization, which is of the order of many thousandfold, in the case of the split-ring resonators is at least 2 times stronger than the one in the dipole antennas resonant at the same operating wavelength, while the two antenna types feature the same gap size and tip sharpness.Item Open Access Wireless displacement sensing enabled by metamaterial probes for remote structural health monitoring(Multidisciplinary Digital Publishing Institute, 2014-01-17) Ozbey, B.; Unal, E.; Ertugrul, H.; Kurc, O.; Puttlitz, C. M.; Erturk, V. B.; Altintas, A.; Demir, Hilmi VolkanWe propose and demonstrate a wireless, passive, metamaterial-based sensor that allows for remotely monitoring submicron displacements over millimeter ranges. The sensor comprises a probe made of multiple nested split ring resonators (NSRRs) in a double-comb architecture coupled to an external antenna in its near-field. In operation, the sensor detects displacement of a structure onto which the NSRR probe is attached by telemetrically tracking the shift in its local frequency peaks. Owing to the NSRR's near-field excitation response, which is highly sensitive to the displaced comb-teeth over a wide separation, the wireless sensing system exhibits a relatively high resolution (<1 mu m) and a large dynamic range (over 7 mm), along with high levels of linearity (R-2 > 0.99 over 5 mm) and sensitivity (>12.7 MHz/mm in the 1-3 mm range). The sensor is also shown to be working in the linear region in a scenario where it is attached to a standard structural reinforcing bar. Because of its wireless and passive nature, together with its low cost, the proposed system enabled by the metamaterial probes holds a great promise for applications in remote structural health monitoring.Item Open Access Wireless Measurement of Elastic and Plastic Deformation by a Metamaterial-Based Sensor(2014-10-20) Ozbey, B.; Demir, Hilmi Volkan; Kurc, O.; Erturk, V. B.; Altintas, A.We report remote strain and displacement measurement during elastic and plastic deformation using a metamaterial-based wireless and passive sensor. The sensor is made of a comb-like nested split ring resonator (NSRR) probe operating in the near-field of an antenna, which functions as both the transmitter and the receiver. The NSRR probe is fixed on a standard steel reinforcing bar (rebar), and its frequency response is monitored telemetrically by a network analyzer connected to the antenna across the whole stress-strain curve. This wireless measurement includes both the elastic and plastic region deformation together for the first time, where wired technologies, like strain gauges, typically fail to capture. The experiments are further repeated in the presence of a concrete block between the antenna and the probe, and it is shown that the sensing system is capable of functioning through the concrete. The comparison of the wireless sensor measurement with those undertaken using strain gauges and extensometers reveals that the sensor is able to measure both the average strain and the relative displacement on the rebar as a result of the applied force in a considerably accurate way. The performance of the sensor is tested for different types of misalignments that can possibly occur due to the acting force. These results indicate that the metamaterial-based sensor holds great promise for its accurate, robust and wireless measurement of the elastic and plastic deformation of a rebar, providing beneficial information for remote structural health monitoring and post-earthquake damage assessment.