Mahdi Haghzadeh

Design and Simulation of Fully Printable Conformal Antennas with BST/Polymer Composite Based Phase Shifters

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.

All-printed, flexible, reconfigurable frequency selective surfaces

We demonstrate a new fully printed, conformal, band-pass frequency selective surface (FSS) utilizing a novel interdigitated capacitor (IDC), in which the space between the fingers can be filled with dielectric materials with different dielectric constants. Every dielectric constant corresponds to a different resonance frequency for the FSS, leading to a bandpass performance that can be tuned in a static manner based on the dielectric choice. The 2-D FSS consists of a periodic array of non-resonant and subwavelength structures (i.e., a metallic square loop and a wire grid) printed on either side of a flexible polyimide film using direct-ink writing methodologies. The miniaturized-element nature of this metamaterial-inspired FSS results in localized frequency-selective properties with very low sensitivity to the angle of incidence. Moreover, its symmetric design makes it polarization independent. A multiphase barium strontium titanate/cyclic olefin copolymer (BST/COC) composite with two different BST loadin...

Fully printed varactors and phase shifters based on a BST/polymer ink for tunable microwave applications

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.

Microwave dielectric characterization of flexible plastic films using printed electronics

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.

Printed tunable miniaturized Frequency Selective Surface with BST/polymer composite filled interdigital capacitors

Summary form only given. We present an electrically tunable Frequency Selective Surface (FSS) at X-band utilizing a novel version of Interdigital Capacitors (IDCs), in which the space between fingers are filled with a ferroelectric composite of Barium Strontium Titanate (BST) suspended in a polymer. We also introduce a low temperature, printed fabrication process on flexible films. The literature suggests the use of varactors based on ferroelectric ceramics as the electrically tunable element in FSSs. These varactors have low Q factor and are expensive to fabricate. The ceramics are brittle in nature and require very high processing temperature (~1100°C). On the other hand, tunable ferroelectric polymers such as Polyvinylidene Fluoride (PVDF) are lossy and slow in switching at microwave frequencies. However, a BST-polymer composite promises both excellent ferroelectric characteristics of the BST in its paraelectric phase and flexible processing of the polymer. A composite by mixing micro and nano size particles of sintered Ba0.55Sr0.45TiO3 with a thermoplastic polymer, that has very low loss tangent at high frequencies, was prepared. It was found that when the key parameters - particle size and volume fraction - are tailored, high dielectric tunability up to 30% and low loss tangent are obtained for the composite, but the dielectric constant can be as low as 30 at microwave frequencies. To get around the low permittivity limitation, we introduced the filled IDC configuration that requires a dielectric constant as low as 20 for a frequency sweep range from 5.6 GHz to 12.8 GHz including full X-band (based on full-wave electromagnetic simulations), instead of the conventional IDCs with fingers on top of a BST ceramic layer that would require epsilon of few hundreds. Both computational and experimental results of the tunable filled IDC as well as the tunable FSS structure will be presented. Although, we demonstrate the implementation of this tunable filled IDC on FSS structures, this printable varactor can be utilized in various applications.

Patterns of Retinal Nerve Fiber Layer Loss in Different Subtypes of Open Angle Glaucoma Using Spectral Domain Optical Coherence Tomography.

Purpose of the Study:The purpose of the study was to determine whether there are different patterns of retinal nerve fiber layer (RNFL) thinning as measured by spectral domain optical coherence tomography (SD-OCT) for 4 subtypes of open angle glaucoma (OAG): primary OAG (POAG), normal tension glaucoma (NTG), pseudoexfoliation glaucoma (PXG), and pigmentary glaucoma (PDG) and to compare them with normal controls. Materials and Methods:SD-OCT RNFL thickness values were measured for 4 quadrants and for 4 sectors (ie, superior-nasal, superior-temporal, inferior-nasal, and inferior-temporal). Differences in RNFL thickness values between groups were analyzed using analysis of variance. Paired t tests were used for quadrant comparisons. Results:Two hundred eighty-five participants (102 POAG patients, 33 with NTG, 48 with PXG, 13 with PDG, and 89 normal patients) were included in this study. All 4 subtypes of OAG showed significant RNFL thinning in the superior, inferior, and nasal quadrants as well as the superior-temporal and inferior-temporal sectors (all P-values <0.0001) compared with normals. POAG and NTG patients had greater RNFL thinning inferiorly and inferior-temporally than superiorly (P-values: 0.002 to 0.018 and 0.006, respectively) compared with PXG patients. In contrast, PDG patients had greater RNFL thinning superiorly and superior-nasally than inferiorly compared with other OAG subtypes (ie, POAG, NTG, PXG groups, with P-values: 0.009, 0.003, 0.009, respectively). Of the 4 OAG subtypes, PXG patients exhibited the greatest degree of inter-eye RNFL asymmetry. Conclusions:This study suggests that SD-OCT may be able to detect significant differences in patterns of RNFL thinning for different subtypes of OAG.

All-printed conformai electronically scanned phased array

We present a novel fully printed, conformai phased array antenna with beam forming capability. Analog phase shifters with a left handed transmission line (LHTL) design are used at the feed lines of four patch subarrays. The microstrip LHTL phase shifter is made of series tunable capacitors and shunt inductive stubs. The voltage-variable capacitor (varactor) is an interdigitated capacitor (IDC) filled with a novel ferroelectric nanocomposite. The sinterless nanocomposite dielectric is made by suspending especially-engineered nanoparticles of ferroelectric Barium Strontium Titanate (BST) in a thermoplastic polymer. Direct-ink writing techniques are used to digitally print the conductive and ferroelectric features on flexible substrates. RF measurements on varactors showed up to 10% capacitance tunability at 2GHz. Preliminary radiation pattern measurements showed an electronic beam steering with up to 15° of scanning. The proposed phased array design has the potential for roll-to-roll fabrication of ultra-low-cost beamforming systems for communication and radar applications.

Printed electronics and additive packaging for microwave applications

There is growing interest in adopting additive technologies for the production of RF/microwave electronics. In addition to the ability for rapid prototyping, printed electronics can offer the manufacturing of electronics in nontraditional form factors-flexible, lightweight, conformable or wearable. Developing printed electronics for the RF/microwave/wireless domain is particularly challenging since the requisite materials, fabrication technologies (i.e., printing), device characterization and design methodolgies require higher performance than low frequency applications. In addition to use in DoD systems (e.g., radars, communications) this printing technology can be applied to commercial applications such as IoT and 5G telecommunication products and may benefit from expoiting additive technologies in microelectronic packaging.

Broadband microwave dielectric characterization method for printable dielectric inks

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 wideband printed technique and the banded waveguide technique.

Printed tunable frequency selective surface on a developed flexible functionalized ceramic-polymer based substrate

In this work, we demonstrate the development of a flexible, high-dielectric-constant substrate based on barium strontium titanate (BST)/thermoplastic cyclic olefin copolymer (COC) nanocomposites suitable for fully printable phased array applications. This functionalized BST/COC substrate is demonstrated to possess tunability as a function of an applied DC bias. This tunable substrate is implemented for a tunable frequency selective surface in the X-band frequency range.