Dispersion characteristics of broadside coupled dielectric image guide at millimeter wave frequencies

Dispersion characteristics and wave impedance for the even and odd modes of the broad side coupled dielectric image guides are computed by using mode matching techniques. Dispersion curves for broadside image guide are plotted for various dielectric materials and dimensional parameters as a function of frequency. Normalized electric field for dominant electric field component E of TM even and odd modes for various half spacings between two dielectric slabs of broadside coupled image guide have been plotted. Polysterene (∈ r=2.56) and Stycast (∈ r=3.4) have been used as dielectric materials in fabricating broadside coupled image guide. This broadside coupled dielectric guide is very convenient as compared to the other dielectric guides. Since in case of broadside coupled image guide the dielectric slab can be bonded to the side metallic walls using some low loss adhesive material, while in other coupled dielectric guides the dielectric slab have to be supported by some low dielectric constant material (Eccofoam with ∈ r=1.02) to maintain the proper distance of side metallic walls from the dielectric slab. Since this structure is symmetrical, this configuration can be analysed in terms of even and odd mode phase velocities. The difference in these even and off mode phase velocities can be used to determine the coupling between coupled dielectric slab. Various couplers in this configuration can be realised.     

Directional couplers in trapped image guide configuration

Dispersion characteristics and wave impedance of trapped coupled image guides are computed by using mode matching techniques. Dispersion curves for trapped coupled image guide are plotted for various dielectric materials and dimensional parameters. The hybrid directional couplers in the above configuration have been theoretically designed by computing the normalization propagation constant.     

Hallow Image Guide and Overlayed Image Guide Coupler

A dielectric waveguide structure, hollow image guide, is described. This structure has several interesting characteristics useful for millimeter-wave applications. Dispersion characteristics and field distributions are theoretically and experimentally studied. The structure can also be considered as two parallel image guides coupled strongly by a dielectric overlay. Coupling characteristics between two image guide arms are studied numerically and experimentally.     

Tailoring the microwave permittivity and permeability of composite materials

The microwave permittivity (?_r) and permeability (µ_r) of composite materials are tailored by adding various loading agents to a host plastic and are subsequently modeled using the Maxwell Garnett theory and second order polynomials. With the addition of manganese zinc ferrite, strontium ferrite, nickel zinc ferrite, barium tetratitanate and graphite powders, materials with values of ?′, e″, µ′, µ″ as high as 22, 5, 2.5 and 1.7 have been obtained. Permittivity and permeability data are calculated at 2.0245 GHz from reflection and transmission measurements performed in a 7 mm coaxial test line. The Maxwell Garnett (MG) theory successfully models ?_r if the filling factor is less than 0.30 and ratio |?₁| (host)/ |?₂| (powder) is greater than 0.04. As this ratio decreases, the MG theory is shown to be independent of ?₂ and second order polynomials are used to effectively model the dielectric constant. Polynomials are also used for the ferrite composites because it was determined that the MG theory was unable to model µ_r. This deficiency is attributed to the difference of domain structures that exist in powdered and sintered ferrites.     

Non-radiative phenomenon in couple dielectric guide

The solutions of electromagnetic field equations for non-radiative coupled dielectric guides are derived using mode matching technique. Dispersion curves are plotted for various dielectric materials and dimensional parameters. The non-radiative phenomenon in the coupled dielectric guide has been discussed in detail. The hybrid directional couplers in the above configuration have been theoretically designed by computing the normalized propagation constants. The superiority of such directional couplers is discussed.     

Structure and dielectric properties of Ba<Subscript>1−x</Subscript>Sr<Subscript>x</Subscript>ZnTi<Subscript>7</Subscript>O<Subscript>16</Subscript> hollandite ceramics

Hollandite-type Ba_1−xSr_xZnTi₇O₁₆ (x=0, 0.2, 0.4, 0.6, 0.8, and 1) ceramics have been synthesized by the conventional solid-state ceramic route. The phase purity and microstructure of these compositions have been characterized using x-ray diffraction (XRD) and scanning electron microscopy (SEM). The XRD analysis shows that an increase in strontium concentration in the A-site causes pairing of vacant tunnel sites, and hence the structure becomes unstable due to the collapse of the tunnel walls. The dielectric properties such as dielectric constant (ε_r), loss tangent (tan δ), and temperature variation of dielectric constant (τε_r) have been measured up to the 13 MHz region. The present study shows that zinc hollandites have relatively high dielectric constant and low loss tangent. The temperature variation of dielectric constant studies reveal that Ba-rich compositions have high positive τε_r and Sr-rich compositions have high negative τε_r in the 0–100°C region. Proper tailor making of these compositions has been attempted to arrive at near-zero temperature variation of the dielectric constant.     

Duplexer designed on the basis of microstrip filters using high dielectric constant substrates

A microstrip duplexer for a modification of a PCS communication system operating at frequencies of 1.84?C1.87 and 1.75?C1.78 GHz is described. The duplexer containing microstrip bandpass filters on high dielectric constant substrates (? _r = 92) are compared with duplexers manufactured on microwave ceramic materials with high values of ? _r . The microstrip bandpass filters use stepped-impedance resonators placed one near another with a gap of 0.1?C0.2 mm. It is shown that the microstrip duplexer has slightly lower insertion loss and occupies smaller volume than a duplexer using coaxial dielectric resonators having a rectangular cross section of 3 × 3 mm and ? _r = 92.     

Effect of substrate thickness and metallization thickness on dispersion characteristics of CPW

Approximate conformal mapping techniques have been used for analysing the effect of finite substrate thickness on coplanar wave guide (CPW). Calculations for impedance and effective dielectric constant are presented for CPW's with finite substrate thicknesses. Analytical formulation are presented for calculations. Network analytical methods of electromagnetic fields are employed to evaluate the effect of thick metal coating on CPW. Dispersion characteristics of CPW have been plotted for various metallization thicknesses. Effect of thick metal coating on guide wavelength is also plotted. Increase in metallization thickness of CPW causes an increase in wavelength. Due to this fact characteristic impedance and effective dielectric constant decreases.     

Ultrahigh Energy Storage Capacitors Based on Freestanding Single-Crystalline Antiferroelectric Membrane/PVDF Composites

Inorganic/organic dielectric composites are very attractive for high energy density electrostatic capacitors. Usually, linear dielectric and ferroelectric materials are chosen as inorganic fillers to improve energy storage performance. Antiferroelectric (AFE) materials, especially single-crystalline AFE oxides, have relatively high efficiency and higher density than linear dielectrics or ferroelectrics. However, adding single-crystalline AFE oxides into polymers to construct composite with improved energy storage performance remains elusive. In this study, high-quality freestanding single-crystalline PbZrO₃ membranes are obtained by a water-soluble sacrificial layer method. They exhibit classic AFE behavior and then 2D–2D type PbZrO₃/PVDF composites with the different film thicknesses of PbZrO₃ (0.1-0.4 µm) is constructed. Their dielectric properties and polarization response improve significantly as compared to pure PVDF and are optimized in the PbZrO₃(0.3 µm)/PVDF composite. Consequently, a record-high energy density of 43.3 J cm⁻³ is achieved at a large breakdown strength of 750 MV m⁻¹. Phase-field simulation indicates that inserting PbZrO₃ membranes effectively reduces the breakdown path. Single-crystalline AFE oxide membranes will be useful fillers for composite-based high-power capacitors.     

Influence of the annealing temperature on the ferroelectric properties of niobium-doped strontium–bismuth tantalate

Characteristics of ferroelectric thin films of niobium-doped strontium–bismuth tantalate (SBTN), which were deposited by magnetron sputtering on Pt/TiO₂/SiO₂/Si substrates, are investigated. To form the ferroelectric structure, deposited films were subjected to subsequent annealing at 700–800°C in an O₂ atmosphere. The results of X-ray diffraction showed that the films immediately after the deposition have an amorphous structure. Annealing at 700–800°C results in the formation of the Aurivillius structure. The dependences of permittivity, residual polarization, and the coercitivity of SBTN films on the modes of subsequent annealing are established. Films with residual polarization 2P_r = 9.2 µC/cm², coercitivity 2E_c = 157 kV/cm, and leakage current 10^–6 A/cm² are obtained at the annealing temperature of 800°C. The dielectric constant and loss tangent at frequency of 1.0 MHz were ε = 152 and tan δ = 0.06. The ferroelectric characteristics allow us to use the SBTN films in the capacitor cell of high density ferroelectric random-access non-volatile memory (FeRAM).     

Effects of Interfacial Dielectric Layers on the Electrical Performance of Top‐Gate In‐Ga‐Zn‐Oxide Thin‐Film Transistors

We investigate the effects of interfacial dielectric layers (IDLs) on the electrical properties of top‐gate In‐Ga‐Zn‐oxide (IGZO) thin film transistors (TFTs) fabricated at low temperatures below 200°C, using a target composition of In:Ga:Zn = 2:1:2 (atomic ratio). Using four types of TFT structures combined with such dielectric materials as Si₃N₄ and Al₂O₃, the electrical properties are analyzed. After post‐annealing at 200°C for 1 hour in an O₂ ambient, the sub‐threshold swing is improved in all TFT types, which indicates a reduction of the interfacial trap sites. During negative‐bias stress tests on TFTs with a Si3N4 IDL, the degradation sources are closely related to unstable bond states, such as Si‐based broken bonds and hydrogen‐based bonds. From constant‐current stress tests of Id = 3 µA, an IGZO‐TFT with heat‐treated Si₃N₄ IDL shows a good stability performance, which is attributed to the compensation effect of the original charge‐injection and electron‐trapping behavior.     

Shielded suspended dielectric guide

The dispersion characteristics of a shielded suspended dielectric are computed using mode matching technique. From the dispersion characteristics the dielectric and conductor loss, quality factor and wave impedances are derived. The dimensions of shielded suspended dielectric are same as that of a rectangular metallic wave guide at K_a band.     

Metal wave-guide to dielectric image guide transition using exponential taper

A unique metal wave guide to dielectric image guide transition has been developed using exponential taper in dielectric wave guide. The propagation characteristics have been computed theoretically and taper impedance for the different cross-sections have been evaluated, so as to match it with the metal wave guide for efficient mode conversion. Transmission loss and return loss for triangular and exponentail taper with frequency for same dimensional parameters have been measured.     

Development of Electronic and Electrical Materials from Indian Ilmenite

Some new complex electronic materials have been prepared by mixing bismuth oxide (Bi₂O₃) and ilmenite in different proportions by weight, using a mixed-oxide technique. Room-temperature x-ray diffraction analysis confirms the formation of a new compound with trigonal (rhombohedral) crystal structure with some secondary phases. Studies of dielectric parameters (ε _r and tan δ) of these compounds as a function of temperature at different frequencies show that they are almost temperature independent in the low-temperature range. They possess high dielectric constant and relatively small tangent loss even in the high-temperature range. Detailed studies of impedance and related parameters show that the electrical properties of these materials are strongly dependent on temperature, showing good correlation with their microstructures. The bulk resistance, evaluated from complex impedance spectra, is found to decrease with increasing temperature. Thus, these materials show negative temperature coefficient of resistance (NTCR)-type behavior similar to that of semiconductors. The same has also been observed from their I–V characteristics. Complex electric modulus analysis indicates the possibility of a hopping conduction mechanism in these systems with nonexponential-type conductivity relaxation. The nature of the variation of the direct-current (dc) conductivity with temperature confirms the Arrhenius behavior of these materials. The alternating-current (ac) conductivity spectra show a typical signature of an ionic conducting system, and are found to obey Jonscher’s universal power law.     

在45°入射时间接测量置于空气中的介质复折射率的方法

光在45°入射时,通过置于空气中的介质表面的反射强度,可用偏振的数学描述来表达.结合光在两透明电介质分界面上的反射时的菲涅耳反射系数的复振幅rs、rp与折射介质对入射介质的介电常数ε之问有一个数学表达式:(rs-rp)/(1-rs·rp)(1-ε)/(1+ε),即可推导出介质的复数折射率表达式为:N=(rs2+1)/(rs+1)2.     

Fullerene Adducts Bearing Cyano Moiety for Both High Dielectric Constant and Good Active Layer Morphology of Organic Photovoltaics

Power conversion efficiency (PCE) of organic photovoltaics (OPVs) lags behind of inorganic photovoltaics due to low dielectric constants (ε _r) of organic semiconductors. Although OPVs with high ε _r are attractive in theory, practical demonstration of efficient OPV devices with high‐ε _r materials is in its infancy. This is largely due to the contradiction between the requirements of high ε _r and good donor:acceptor blend morphology in the bulk heterojunction. Herein, a series of fullerene acceptors is reported bearing a polar cyano moiety for both high ε _r and good donor:acceptor blend morphology. These cyano‐functionalized acceptors (ε _r = 4.9) have higher ε _r than that of the widely used acceptor, [6,6]‐phenyl‐C₆₁‐butyric acid methyl ester (PC₆₁BM) (ε _r = 3.9). The high ε _r is realized without decrease of electron mobility and change of the lowest unoccupied molecular orbital/highest occupied molecular orbital (LUMO/HOMO) energy levels. Although the cyano‐functionalized acceptors have increased polarity, they still exhibit good compatibility with the typical donor polymer. Polymer solar cells based on the cyano‐functionalized acceptors exhibit good active layer morphology and show better device performance (PCE = 5.55%) than that of PC₆₁BM (PCE = 4.56%).     

Stripe delay filters

There are considered constructions of microsized stripe delay filters, which are realized on a basis of ceramic materials with high dielectric permittivity. Delay time of non-minimal phase filters is 7–12 ns at frequencies of 1900 MHz with relative bandwidth of 3.6–3.85%. Filters dimensions are comparable with ones used in portable communication devices. Dimensions of researched three-resonator filter at frequency of 1900 MHz are 8.4×5×2mmwith material dielectric permittivity ε_r = 92, and 5-resonator filter ones are 9.2×8.6×2 mm. Filters are different from traditional delay filters. Two filters of considered ones contain odd resonator number and the third one contains four resonators and it has two cross couplings. The basis of the filters is amount of step-impedance stripe resonators pairs located close to each others whose electromagnetic coupling behavior is capacitive. There are represented the results of frequency characteristics simulation for different delay filters.     

Polymers as masks for Ion implantation

Polymers such as polyimides and photoresists, commonly used in semiconductor processing, have been investigated as high resolution masks for ion implantation. Thin films consisting of these materials were subjected to various implant doses of H⁺, Ne⁺ and Ar⁺ ions and the post implantation surface morphologies investigated. Polyimides maintained their integrity under severe H⁺ and Ne⁺ implant doses as high as 2.4 × 10¹⁶ cm⁻² and 1.0 × 10¹⁶ cm⁻², respectively, whereas photoresists began to degrade at implant doses of 9.6 × 10¹⁵ cm⁻² and 1.9 × 10¹⁵ cm⁻², respectively. When polyimide was H⁺ implanted with doses up to 10¹⁶ cm⁻² its dielectric constant and breakdown strength remained unchanged at 3.5 and 150 V/μm, respectively. However, a gradual increase in the dielectric constant was observed for doses above this level. It was also observed that under the influence of H⁺ implants with beam current densities exceeding 10⁻⁷ A-cm⁻² a hardening of the polyimide occurs, resulting in reduction of the etching rate in an O₂ plasma. The stopping powers of various polymers for H⁺ implants have been measured. The results show that the experimental energy loss rate for protons in these materials lies between 75–100 keV/μm.     

Quasioptical dielectric resonators in millimeter-wave band experiments

New results of theoretical and experimental investigations of non-uniform dielectric resonators with the higher order azimuthal waves (whispering gallery modes) have been presented. Their application for study of various materials (dielectric, high-T_c superconductor) and for generation obtaining of millimeter wave oscillations has been considered.     

An efficient image guide mode launcher

A three section efficient mode launcher for converting TE₁₀ mode of rectangular wave guide to dielectric image guide mode has been designed and tested experimentally. The transmission loss of the trapped image guide and insulated trapped image guide are also evaluated experimentally using this transition.