Alkim Akyurtlu - Academia.edu (original) (raw)

Papers by Alkim Akyurtlu

The World Health Organization has estimated that 10% of the world's population (650 million p... more The World Health Organization has estimated that 10% of the world's population (650 million people) has a disability. Assistive Technology (AT) has the potential to improve function for individuals with disabilities. Research and development must to focus both on universal design approaches for the population, as well as customization to meet individual functional demands. This mini-symposium will present the trends driving the need for AT, case studies demonstrating solutions to functional challenges, and evidence-based policy measures that are being implemented to meet the needs of people with disabilities living in the community. Since 1991, UMass Lowell has operated an AT Program through which individuals with disabilities and community organizations meet with teams of students and faculty to design customized solutions. Symposium participants will discuss the development of population-level measures and examine indicators linking AT device use to psychosocial well-being: ul...

MRS Advances, 2022

In this work, we used nanosphere lithography to fabricate large area 2-D magnetic nanoparticle (M... more In this work, we used nanosphere lithography to fabricate large area 2-D magnetic nanoparticle (MNP) arrays on a flexible polyimide substrate (Kapton). Samples were fabricated by assembling polystyrene (PS) spheres on thin films of Co capped with Au. Etched PS spheres were used to mask Co-Au particle arrays. The MNP arrays were subjected to superconducting quantum interference device measurements; flat samples (10 nm Co coated with 10 nm Au) exhibited an M s of 117.3 emu g −1 , which was lower than the reported literature value for bulk Co (162.7 emu g −1). When compared to the flat film, coercivity, H c , increased in a linear fashion with respect to particle size. These preliminary results reveal that future investigations of the magnetic properties on flexible substrates should account for residual Co remaining in the polymeric material, the unique MNP shape, the effect of order (or lack or order) of the 2D array, and positioning with respect to the direction of the magnetic field.

Journal of Electronic Materials, 2021

Here, we report a previously unreported low-temperature curable barium strontium titanate (Ba X S... more Here, we report a previously unreported low-temperature curable barium strontium titanate (Ba X Sr 1−X TiO 3) or BST dielectric nanoparticle ink which shows a high dielectric tunability for printed electronics/additive manufacturing applications. The newly formulated BST ink is optimized to print in aerosol jet printers and can be cured at 150°C, which will allow the fabrication of tunable radio-frequency (RF) and microwave (MW) devices on a wide range of flexible substrates. Characterization of high-frequency dielectric properties showed a high dielectric tunability (~ 15% at 10 GHz with 10 V/µm) and a high dielectric constant (~ 16 at 10 GHz). The linear-reversible tunability, which is very important for tunable devices, was confirmed by the tunability testing at 10 GHz. Characterization of temperature-dependent dielectric properties found < 10% variations of the dielectric constant at 10 GHz from −50°C to 125°C for this BST ink. Detailed information on BST nanoparticle characterization, ink formulation and characterization of dielectric properties is discussed.

Flexible and Printed Electronics, 2020

Here, we report a previously un-reported printed electronics/additive manufacturing (AM) approach... more Here, we report a previously un-reported printed electronics/additive manufacturing (AM) approach to fabricate conductive/resistive features on novel insulating silver–barium strontium titanate (Ag–BST) printed composite films. Ag–BST composite functional ink was formulated by blending a conductive Ag nanoparticle ink and an insulating BST nanoparticle ink. The blending ratio of Ag and BST inks was optimized to obtain the insulating phase after the initial curing and the conductive/resistive phase following selective laser sintering under ambient conditions. Selective laser sintered Ag–BST resistors showed an ohmic behavior and the resistivity could be adjusted by varying the laser sintering parameters, such as the wavelength, power and the rastering speed/pitch of the laser. This insulator to conductor/resistor transitioning Ag–BST ink paves a new path for direct write printed electronics/AM applications. Proofs of concept for potential applications utilizing this functional ink ar...

2017 89th ARFTG Microwave Measurement Conference (ARFTG), 2017

This work presents a parameter-related, one-probe based microwave characterization method for det... more This work presents a parameter-related, one-probe based microwave characterization method for determining complex dielectric properties of various printable dielectric inks from 1–30 GHz. Dielectric constant and loss tangent of a material under test (MUT) are extracted utilizing the measured reflection 511-parameters and analyzed equivalent circuits of a cylindrical capacitor with and without the MUT. This method is also verified by HFSS simulations with predefined dielectric and loss tangent profiles. Both simulated and measured results show good agreement between the extracted data and predefined data. The method was implemented by microwave dielectric characterization of a commercially available dielectric ink. This commercial material was also characterized using a waveguide method developed by the National Institute of Standards and Technology (NIST) and a commercial based software. Results show good agreements between the complex dielectric properties obtained from our wideban...

International Symposium on Microelectronics, 2017

This paper describes efforts to apply Additive Manufacturing (AM) technologies to microelectronic... more This paper describes efforts to apply Additive Manufacturing (AM) technologies to microelectronic packaging of devices and subsystems for RF and microwave applications. This work, which was conducted at the Raytheon-University of Massachusetts Lowell Research Institute (RURI), is directed at a variety of applications such as 2D and 3D phased array antennas and tunable frequency selective surfaces (FSS). This paper will describe research on device modeling/simulation, formulation of novel functional inks, development of process/printing technologies and new material characterization techniques. Important elements of the additive packaging efforts include the integration of active die with printed components, replacement of wire bonds with printed chip interconnects and the development of integrated, printed connectors. Research on printed, tunable microwave components, such as varactors and phase shifters, are also discussed.

MRS Advances, 2020

The application of intense pulsed light (IPL) to printed copper nanoparticle (CuNP) films enables... more The application of intense pulsed light (IPL) to printed copper nanoparticle (CuNP) films enables rapid curing on low temperature substrates in ambient conditions. In this work, we printed CuNP ink on liquid crystal polymer (LCP; Vectra A resin) and then cured the films using a high energy density light pulse. High-resolution SEM images of the cured films revealed that the CuNPs on LCP were fused together. Optimal curing parameters were a 5 ms pulse, 75% duty cycle, and an energy density range of 4.2–5.2 J⋅cm-2. Sheet resistance, Rs, values as low as ~0.1 Ω⋅sq-1were obtained. The LCP substrate took on a yellowed appearance after the application of five pulses and exhibited a surface free energy increase. A filter that blocked wavelengths <450 nm was placed over the printed copper film on LCP. As expected, the presence of the filter decreased the total energy density and produced a cured film with high Rs; however, when the energy density was increased in the presence of the filte...

IEEE Transactions on Microwave Theory and Techniques, 2017

This paper presents all-printed varactors and phase shifters using direct-ink writing methodologi... more This paper presents all-printed varactors and phase shifters using direct-ink writing methodologies on flexible organic films. The key enabler is a novel ferroelectric nanoink that allows printing high dielectric constant, low loss, and electrostatically tunable dielectrics at extremely low temperatures. The dielectric is made by suspending nanoparticles of barium strontium titanate (BST) in thermoplastic cyclic olefin copolymer (COC) to create a multiphase BST/COC nanocomposite. Unlike conventional ferroelectric ceramics, this ferroelectric dielectric requires no sintering and can be printed on any substrate. After printing, it is cured at temperatures below 200°C. Careful stoichiometry and particle analysis of BST powders resulted in identifying conditions for achieving electrostatic tunability. A high relative permittivity of ε r = 38 and a very low dielectric loss of tan δ = 0.002 at f = 10 GHz were measured for the printed sinterless dielectric. The ink allows printing voltage-variable capacitors with a capacitance tunability up to 10% at microwave frequencies. The tunable capacitors were utilized in a left-handed transmission line design to create all-printed tunable phase shifters with up to a maximum phase shift of φ = 97°and a maximum figure of merit of 29°/dB at f = 10 GHz.

2016 IEEE MTT-S International Microwave Symposium (IMS), 2016

A fully printed varactor and a phase shifter using direct ink writing methodologies will be descr... more A fully printed varactor and a phase shifter using direct ink writing methodologies will be described. A novel ferroelectric ink was developed to print high dielectric constant, low loss, and electrostatically-tunable dielectrics on plastic substrates. The dielectric is based on multiphase Barium Strontium Titanate (BST)/polymer composite made by suspending nano/submicron-sized particles of BST in a thermoplastic polymer, namely Cyclic Olefin Copolymer (COC). After printing with the ink, a low temperature curing process was performed at temperatures below 200°C. RF measurements and characterizations showed that the sinter-less dielectric had a very high relative permittivity of εr = 42 and a very low dielectric loss of tanδ = 0.0005 at f = 10GHz. As a result, all-printed, voltage-variable capacitors with up to 10% capacitance tunability at microwave frequencies were realized. Subsequently, the tunable BST/COC ink was used in a left handed transmission line design to realize a printed tunable phase shifter.

Progress In Electromagnetics Research C, 2016

A fully printable and conformal antenna array on a flexible substrate with a new Left-Handed Tran... more A fully printable and conformal antenna array on a flexible substrate with a new Left-Handed Transmission Line (LHTL) phase shifter based on a tunable Barium Strontium Titanate (BST)/polymer composite is proposed and computationally studied for radiation pattern correction and beam steering applications. First, the subject 1 × 4 rectangular patch antenna array is configured as a curved conformal antenna, with both convex and concave bending profiles, and the effects of bending on the performance are analyzed. The maximum gain of the simulated array is reduced from the flat case level by 34.4% and 34.5% for convex and concave bending, respectively. A phase compensation technique utilizing the LHTL phase shifters with a coplanar design is used to improve the degraded radiation patterns of the conformal antennas. Simulations indicate that the gain of the bent antenna array can be improved by 63.8% and 68% for convex and concave bending, respectively. For the beam steering application, the proposed phase shifters with a microstrip design are used to steer the radiation beam of the antenna array, in planar configuration, to both negative and positive scan angles, thus realizing a phased array antenna.

2016 87th ARFTG Microwave Measurement Conference (ARFTG), 2016

This work describes the development of a wideband RF measurement technique using printed test str... more This work describes the development of a wideband RF measurement technique using printed test structures for characterizing the complex dielectric properties of flexible substrates at RF and microwave frequencies. This novel method is based on a single probe measurement using two concentric circular capacitors with different gap sizes that can be additively manufactured on the dielectric film under test. Three types of common, commercially-available substrates for flexible electronics were characterized: Polyimide (Kapton), Liquid Crystalline Polymer (LCP), and Polyethylene Terephthalate (PET). Their dielectric constant and loss tangent were measured from 50MHz up to 20GHz, and were compared to the data available from substrate vendors.

2015 USNC-URSI Radio Science Meeting (Joint with AP-S Symposium), 2015

Noble metals such as gold and silver demonstrate exotic optical properties and have been extensiv... more Noble metals such as gold and silver demonstrate exotic optical properties and have been extensively used in optical metamaterials. Unfortunately, these materials introduce high losses in the optical spectrum, which considerably restrict many applications of metamaterials where the required figure of merit needs to be very high. Several studies, both theoretical and experimental, have been conducted to suppress the optical losses. Examples include gain media, parametric second harmonic generation, and quantum optics approach. Nevertheless, the majority of this research is restricted to theoretical models or can be considered as optical laser-like amplifier more than an optical loss suppressor. Recently, a novel method has been introduced to reduce the optical losses in noble metals as well as in semiconductors. The technique is known as the parametric two-wave coherent coupling. The mechanism is based on the standard formalism of Boltzmann equation, and takes into account the wave coupling through the carriers in conduction band. The theoretical and analytical study of the mechanism has already been published, and the experimental proof of the mechanism in the Mid-IR frequency range has been reported as well. In the current work, the parametric two-wave coherent coupling technique consists of a support wave which is provided by a Nd-YAG laser at 1.064 µm, and the probe wave at 0.532 µm which is generated from the non-linear optical crystal Potassium Titanyl Phosphate (KTP) by means of the second harmonic generation technique. By adjusting the phase shift between the probe and support waves, and their amplitudes, the optical losses can be significantly suppressed. In this presentation, both the theoretical and experimental results for the reduction in losses in noble metals within the visible frequency range will be presented.

$Research paper thumbnail of Natural negative refraction index in polycrystalline Fe and Ni at optical frequencies$

Analysis of the photon-magnon interactions in Fe and Ni, 3d transition-metal ferromagnetics, demo... more Analysis of the photon-magnon interactions in Fe and Ni, 3d transition-metal ferromagnetics, demonstrating the coupling between the incident light and high-frequency spin waves with energy ( 0.2 -- 0.35 ) eV is presented. As a consequence, these metals in their polycrystalline form with nanoscale grains are found to possess a negative refraction index at optical frequencies, close to the high-frequency ferromagnetic resonance. The effect is due to the coexistence of the spin wave mode with the plasmonic mode, and both modes are activated by the e.m. field of the light, with simultaneous permittivity and permeability responses within some frequency band.

Terahertz Physics, Devices, and Systems, 2006

Materials that support strong, tunable magnetic and electric properties in the terahertz (THz) fr... more Materials that support strong, tunable magnetic and electric properties in the terahertz (THz) frequency range have a wide range of applications including sue in: security screening, medical imaging, bio-sensing, remote sensing, metrology, and spectroscopy. The main challenge in assembling metamaterials (MTM) aimed at higher frequency applications is the difficulty of the fabrication process. This is because metamaterials are composed of

2013 IEEE International Symposium on Phased Array Systems and Technology, 2013

A novel approach for the simulation of conformal microstrip patch antenna arrays is presented. 1×... more A novel approach for the simulation of conformal microstrip patch antenna arrays is presented. 1×2 and 1×4 microstrip arrays operating at 16 GHz were designed and their radiation characteristics were simulated and analyzed as a function of bending. The performance characteristics modeled include S-parameters, radiation patterns, 3-dB beamwidths, side lobe levels, VSWR and radiation efficiency. For the 1×2 array, the degradation in performance in observed for the bent arrays compared to the planar case. However, there is not a significant change in the parameters as there is an increase in the bending radius. As we increase the number of elements in the array, interelement coupling becomes more important. Although a better performance in gain and directivity is obtained for the 1×4 planar array compared to the 1×2 planar array, the performance parameters degrade more with respect to the bending of the array. A maximum gain of 13.65 dB with 16.7° 3-dB beamwidth was achieved at Ku-band. Furthermore, it is shown that the gain, resonance frequency, 3-dB beamwidth, radiation efficiency decreases as bending of the array structure increases. The proposed design can be used in many applications including telemetry, satellites, aircraft and medical operations. This modeling effort is a prelude to development of printed antennas on flexible substrates.

SPIE Proceedings, 2011

Novel mechanism of suppression losses in plasmonic subsystem in metals and semiconductors is sugg... more Novel mechanism of suppression losses in plasmonic subsystem in metals and semiconductors is suggested. If two parametrically coupled fields are applied to a metal plasma, a non-linearity of the transport equation affects the electric response, or the permittivity. If the coupling constant between the probe wave and the support wave is small, the permittivity, at the frequency of the probe wave, is still Drude-like, with the re-normalized plasmon frequency. In the case of a strong coupling, unusual response effects are possible (the induced transparency and the considerable suppression of the plasmon losses), with profoundly non-Drude permittivity function.

$Research paper thumbnail of Negative refraction in Cr doped Indium Oxide in the mid-infrared region$

2013 USNC-URSI Radio Science Meeting (Joint with AP-S Symposium), 2013

ABSTRACT form only given. The magnetic semiconductor, Indium Oxide doped with Chromium (In2-xCrxO... more ABSTRACT form only given. The magnetic semiconductor, Indium Oxide doped with Chromium (In2-xCrxO3-δ), is fabricated on Si substrate by DC-RF magnetron sputtering deposition technique at room temperature with low stoichiometric oxygen deficiency, δ [10-4-10-2], a carrier concentration of 1022cm-3, and doping concentration of x=3%. These isotropic films are uniformly homogenous and ferromagnetic at room temperature. The sputtered samples are grown using two targets - a d.c. magnetron sputtering gun for the Cr and an r.f. magnetron gun for the In2O3. The sputtering is performed in an Ar atmosphere of around 24 mT, while the oxygen concentration can be enhanced by the inclusion of a small partial pressure of oxygen at around ~0.3×10-3 mT. The structural study of the films were done by using the X-ray diffraction, Energy Dispersive Spectroscopy. The magnetic characterization was performed by Quantum Design Superconducting Quantum Interference Device (SQUID) magnetometer (MPSM XL and SVSM), and the optical properties of the films were investigated by measuring the relative transmission using Fourier Transformation Infrared Spectroscopy (FTIR) VERTEX 70-BRUKER. Based on the method of the transmitted beam shifting, the films were shown, experimentally, to demonstrate negative refraction in the mid-infrared region by measuring. Here, we introduced the blade method as it is described in A. Boltasseva's paper [Proc. Natl. Acad. Sci. USA 5 June 2012: 8834-8838.] and measured the relative transmission for the angles 5 to 35 degrees.

2014 USNC-URSI Radio Science Meeting (Joint with AP-S Symposium), 2014

This work discusses a metamaterial based dual band absorber operating at mid infrared regime. The... more This work discusses a metamaterial based dual band absorber operating at mid infrared regime. The design is composed of periodic resonant pattern that mainly utilizes U-shaped and cut wire resonators as a building block for the single unit cell. The simulated results are obtained using the full electromagnetic wave simulation package CST MWS. The absorber is designed to possess two distinct absorption bands centered at 9.57 and 4 lm. The two bands are well separated with a first to second band ratio of 2.39. The sub-wavelength period size is measured to be 0.19 and 0.45 k with respect to the first and second bands respectively. High absorption is also observed for wide range of incident angles. Samples of this design were fabricated and tested. The measured response shows two absorption peaks with better than 80 % absorption for both peaks.

$Research paper thumbnail of Negative refractive index in ferromagnetic semiconductors: experimental verification$

SPIE Proceedings, 2012

ABSTRACT In this work, we show that natural crystals, or magnetic semiconductor, Cr-doped indium ... more ABSTRACT In this work, we show that natural crystals, or magnetic semiconductor, Cr-doped indium oxide, has a negative refractive index at ~ 27.8 micron wavelength. The effect was predicted by two of us a few years ago (A.G. Kussow and A. Akyurtlu, Phys. Rev. B, 78, 205202 (2008)). Our result seriously undermines wide-spread opinion that only composite artificial metamaterials can demonstrate negative refractive index. Thin ferromagnetic films of ICO were fabricated by original post-annealing sputtering method. FTIR R and T measurements were processed to extract refractive index within the range of interest. The extracted from combined transmittance and reflectance FTIR data negative refractive index band parameters are found to be close to expected one.