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In this paper, design and realization of a Low Profile Archimedean Spiral Antenna is presented. The Low Profile Archimedean Spiral Antenna is printed on a substrate. The bidirectional radiation patterns of the antenna are converted to unidirectional using uniplanar EBG reflector. This uniplanar EBG ground plane is designed with modification in Compact Uniplanar Photonic Band Gap (UC-PBG) structure. The modified version of UC-PBG ground plane provides much wider bandwidth. This ground plane is tested for its electrical characteristics over the frequency band and used as a reflector with spiral antenna. An Archimedean Spiral antenna is designed and simulated in the frequency band of 0.5–6 GHz. The frequency band of operation for the EBG ground plane/ reflector is of the same order. The physical parameters of the antenna are studied for its electrical characteristics and these parameters are optimized for better electrical characteristics of the antenna. Antenna performance is also compared with conventional Metallic (PEC) reflector. The simulated results are validated with measurement. Comparisons of these results are presented. In this design, the height of the antenna is reduced by 86% compared to conventional cavity backed Spiral Antennas. The bandwidth of proposed EBG cell is 171.4%. For spiral antenna integrated with EBG reflector; the impedance and radiation patterns bandwidth are 169%, on axis axial bandwidth is 169% and off-axis axial ratio bandwidth is 163.6%. [ABSTRACT FROM AUTHOR]

Antenna operates at single frequency can be wielding for any one application. If the antenna has to be wield for multiple operations the number of antennas will increase, which in turn increases system size. The proposed printed antenna with novel spiral shaped slot having circular dumble shaped defective structure results in multiple bands can overcome the stated limitation. Printed patch antenna is designed and simulated using High Frequency Structure Simulator software using Glass epoxy substrate. The proposed antenna has a dimensions of 3.34 × 2.47 × 0.16 cm with low cost substrate shows five different working frequencies with good return loss having impedance bandwidth of 7.93% with highest gain of 9.92 dB and virtual size reduction of 28.33%. The proposed antenna is resonating between 4.36 and 15.89 GHz which covers L, C, Ku and K band application. [ABSTRACT FROM AUTHOR]

A high-power source of ultrawideband radiation with elliptical polarization based on a 64-element array of spiral antennas was developed. The array was excited by a bipolar voltage pulse with an amplitude of up to 240 kV and a duration of 1 ns at a repetition rate of 100 Hz. Radiation pulses with an ellipticity coefficient of 0.64 and a peak field strength of 250 kV/m at a distance of 10 m were obtained. [ABSTRACT FROM AUTHOR]

As we know, valley-Hall kink states or pseudospin helical edge states are excited by polarized-momentum-locking [left-handed circular polarization (LCP) and right-handed circular polarization (RCP)] because the valley-Hall kink modes or pseudospin polarized modes have intrinsic and local chirality, which is difficult for these states to achieve phase modulation. Here we theoretically design and study a compatible topological photonic system with coexistence of photonic quantum Hall phase and pseudospin Hall phase, which is composed of gyromagnetic photonic crystals with a deformed honeycomb lattice containing six cylinders. A typical kind of hybrid topological waveguide states with pseudospin-characteristic, magnetic field-dependent, and strong robustness against backscattering and perfect electric conductor (PEC) is realized in the present system. Furthermore, we re-design a structure with intersection-liked, achieve splitting for one-way pseudospin quantum Hall edge states by using phase modulation. Robustness of the one-way pseudospin-quantum Hall edge states in splitting has been demonstrated as well. Additionally, PEC inserted in transport channel brings optical path difference in waveguide transmission, which would influence splitting for hybrid topological waveguide states in phase difference modulation. This work not only provides a new way for manipulation (i.e., phase modulation) of hybrid topological waveguide states in compatible topological photonic system from distinct topological classes but also has potential in various applications, such as sensing, signal processing, and on-chip communications. [ABSTRACT FROM AUTHOR]

The development of stretchable electronic devices is a critical area of research for wearable electronics, particularly electronic textiles (e-textiles), where electronic devices embedded in clothing need to stretch and bend with the body. While stretchable electronics technologies exist, none have been widely adopted. This work presents a novel and potentially transformative approach to stretchable electronics using a ubiquitous structure: the helix. A strip of flexible circuitry ('e-strip') is twisted to form a helical ribbon, transforming it from flexible to stretchable. A stretchable core—in this case rubber cord—supports the structure, preventing damage from buckling. Existing helical electronics have only extended to stretchable interconnects between circuit modules, and individual components such as printed helical transistors. Fully stretchable circuits have, until now, only been produced in planar form: flat circuits, either using curved geometry to enable them to stretch, or using inherently stretchable elastomer substrates. Helical e-strips can bend along multiple axes, and repeatedly stretch between 30 and 50%, depending on core material and diameter. LED and temperature sensing helical e-strips are demonstrated, along with design rules for helical e-strip fabrication. Widely available materials and standard fabrication processes were prioritized to maximize scalability and accessibility. [ABSTRACT FROM AUTHOR]

Investigators are looking at radio frequency ranges that may suit cellular data consumers' growing requirements. Terahertz's (THz) frequency range is vital for high-speed data communication in wireless gadgets and has indignant the interest of researchers. A novel spiral-shaped patch and diffracted ground-based MIMO antenna structure are presented. The overall dimensions of the structure are 600 µm by 800 µm. The polyamide material is used as a substrate. The analysis among 1 × 1, 1 × 2, 2 × 1 and 2 × 2 MIMO antenna structures are carried out. Performance in reflectance response, Bandwidth, gain, radiation pattern and directivity are analyzed. The proposed structure provides the multiband response with a minimum reflectance response of − 30.51 dB, a bandwidth of 10 THz, peak isolation of 36.99 dB, a maximum normalized directivity of 1030 and a peak gain of 39 dB. ECC TARC, CCL and D.G. were considered for the performance observation. A comparison of the presented structure with other articles is included in the manuscript. The proposed work suits biomedical imaging, short-distance communication, healthcare and WBAN applications. [ABSTRACT FROM AUTHOR]

This article presents a 3D-printed cylindrical dielectric resonator antenna operating at 5.8 GHz that achieves circular polarization by integrating a fully dielectric parasitic helix with a higher permittivity than the cylindrical resonator. The antenna polarization can be right-handed or left-handed depending on the turning sense of the helix. An extensive parametric study was done for the helix design to evaluate the effects of the dimensions and dielectric constant of the helix over the matching and axial ratio of the antenna. The manufacturing is made using low-loss dielectric filaments and a low-cost 3D printer. Simulation and measurement results show that both antennas are well-matched and operate with the corresponding circular polarization, with an axial ratio bandwidth compatible with UAV applications. [ABSTRACT FROM AUTHOR]

Because of their superior mechanical properties, preformed helical fittings are widely used in UHV transmission lines. However, they easily slip and become loose under extreme environments, so it is very important to study the fastening characteristics of preformed helical fittings. According to the stress characteristics of preformed helical fittings, a parametric finite element model including a core and preformed armor rods was established. Finally, the finite element model calculation was verified by comparing it with the test results. In this paper, the influences of the preformed armor rod diameter, pitch, length and forming aperture on the fastening characteristics were investigated. The numerical simulation results showed that the smaller the forming aperture of preformed armor rods, the larger the grip force. However, a small forming aperture is inconvenient to install, and too large of a grip force on the core easily leads to core damage. With the increase in the preformed armor rod length, the grip force increased gradually and linearly, and the increase slowed after the pitch number reached 9. The larger the pitch, the smaller the grip force of the preformed helical fittings. The fastening characteristics of preformed armor rods with slightly larger diameters were better and the fourth power of the diameter of the preformed armor rods has a linear relationship with the grip force. [ABSTRACT FROM AUTHOR]

Here, optimization of a quadrafilar helical antenna is presented to compare the performances of objective function pairs adapted from mathematical models by using DEA with fixed weight objective function structure and SPEA2 with variable weight objective function structure from 2 different competitive multi-objective algorithms. The most important purpose in optimization problems is to find the result with the lowest cost. For this, the selection of the appropriate objective function pair is very important. The most important aim in this study is to determine the optimum objective function pair model. For this purpose, five different objective function models were derived by using nonlinear mathematical models. These objective functions are adapted from polynomial, power, exponential, gaussian and fourier mathematical models. In order to determine the most successful model without question, the objective functions adapted from the mathematical models are compared separately in both evolutionary algorithms by using different algorithm parameters and different weight coefficients. According to the results obtained, it is seen that the objective function adapted from the power mathematical model has the lowest cost. This proposed adaptation technique, which is the novelty of the study, is an efficient and reliable method to find the most appropriate objective function and the lowest cost result in optimization problems. It can also be quickly adapted to any optimization problem. [ABSTRACT FROM AUTHOR]

We report on the analysis of pure gadolinium oxide (Gd2O3) and its detection when mixed in surrogate nuclear debris using microwave-enhanced fiber-coupled micro-laser-induced breakdown spectroscopy (MWE-FC-MLIBS). The target application is remote analysis of nuclear debris containing uranium (U) inside the Fukushima Daiichi Nuclear Power Station. The surrogate nuclear debris used in this study contained gadolinium (Gd), cerium (Ce), zirconium (Zr), and iron (Fe). Ce is a surrogate for U, and Gd2O3 is an excellent hazard index because it is incorporated into some fuel rods. Gd detection is essential for assessing debris prior to the retrieval process. Surrogate debris was ablated by an 849 ps 1064 nm micro-laser under atmospheric pressure conditions while a helical antenna propagated 2.45 GHz 1.0 kW microwaves for 1.0 ms into the laser ablation, which was then characterized by a high-speed camera and high-resolution spectrometers. The results showed that microwave-induced plasma expansion led to enhanced emission signals of Gd I, Zr I, Fe I, Ce I, and Ce II. No self-absorption of Gd emissions was evident from the detection limit calibration graphs. Moreover, microwave irradiation decreased the standard deviations of the Gd and Ce emissions and lowered the Gd detection limit by 60%. [ABSTRACT FROM AUTHOR]

This work presents the results from the experimental evaluation of a quantum random number generator circuit over a period of 300 minutes based on a single chip fabricated on the InP platform. The circuit layout contains a gain switched laser diode (LD), followed by a balanced Mach Zehnder Interferometer for proper light power distribution to the two arms of an unbalanced MZI incorporating a 65.4 mm long spiral waveguide that translates the random phase fluctuations to power variations. The LD was gain-switched at 1.3 GHz and the chip delivered a min-entropy of 0.5875 per bit after removal of the classical noise, resulting a total aggregate bit rate of 6.11 Gbps. The recoded data set successfully passed the 15-battery test NIST statistical test suite for all data sets. [ABSTRACT FROM AUTHOR]

Sintering of silver (Ag) nanoparticles (NPs) using carboxylic acid vapors was introduced for conductive patterns applicable for flexible radio-frequency identification (RFID) tag application. The printed Ag NP patterns on flexible polyimide sheets were sintered in the atmosphere selected from air, N2, or N2-bubbled carboxylic acids. The sintering temperature was chosen from 80, 140, and 200 °C. Microstructures, organic residues, and electrical and mechanical properties of the sintered Ag patterns were compared, depending on sintering atmospheres. The Ag NP patterns sintered in N2-bubbled formic acid (FA) atmosphere revealed an effective decomposition of organic materials in the patterns, resulting in lower electrical resistance and improved mechanical hardness. The Ag pattern sintered in FA showed relatively low resistances with 0.029–0.039 Ω for all temperatures. Upon folding tests, the Ag NP pattern sintered in FA showed the smallest change in the resistance. The Ag NP pattern sintered in FA at 140 °C had its highest hardness of 3.59 N/mm2. Sintering conditions in FA at 140 °C for 1.5 min were chosen for the fabrication of flexible RFID tags with two different shapes of squared and spiral antennas. The quality factor (Q-factor) was in the range of 7.775–34.817 and 7.241–78.156, for squared and spiral antennas, respectively. [ABSTRACT FROM AUTHOR]

The release of GNSS raw measurement acquisition privileges on Google Android makes high-precision positioning on the low-cost smart devices possible. However, influenced by the inner linearly polarized antenna, the pseudorange and carrier phase noises of the smart device are much larger than those of the geodetic receiver. As a result, only meter-level positioning accuracy can be obtained based on the smart device's original antenna. With the external survey-grade antenna enhancing, positioning accuracy of decimeter-level to centimeter-level can be obtained, but it still takes tens of minutes to converge and fix the ambiguity. However, a PPP-RTK method is proposed to achieve rapid integer ambiguity resolution (AR) with the regional atmospheric augmentation. In this contribution, an uncombined PPP-RTK model is developed using Android GNSS raw measurements with an external antenna, after carefully considering the coexistence of single- and dual-frequency signals on smart devices. A low-cost helical antenna is employed to enhance the Android GNSS data as it is capable to provide observation data of comparable quality with the survey-grade antenna and has several advantages of low weight, low-power consumption, and portability. Moreover, a series of quality control methods in the data preprocessing and ambiguity resolution are proposed for smartphone-based PPP-RTK to enhance the positioning results. To validate the proposed method, several experiments are carried out using raw measurements of Xiaomi Mi8 with an external low-cost helical antenna. The result shows that the ambiguity fixed solution can be obtained within 3 min in both static and kinematic scenarios. After the ambiguity resolution, centimeter-level positioning accuracy of (1.7, 2.1, 4.1) cm and (7.2, 4.5, 8.1) cm for the east, north, and up components can be achieved in static and kinematic scenarios, respectively. [ABSTRACT FROM AUTHOR]

This article proposed a compact dual-element MIMO (multiple-input-multiple-output) antenna system working in 1.575 GHz (Global Positioning System)/4.5 GHz (5G)/5.8 GHz (Wireless Local Area Network)/6.4 GHz (Satellite communication) with relatively high isolation. The proposed antenna element consists of compact inverted-F antenna with meandered arm. One side of the T-shaped monopole antenna is extended and meandered while the other side is grounded to form the IFA structure. Meandering of the arm is responsible for the quad-band response. The proposed structure is simulated and fabricated on a FR4 substrate with an overall dimension of (0.23 λ0 × 0.09 λ0 × 0.004 λ0) and edge-to-edge separation of the two patches is 0.04 λ0, where λ0 is the wavelength at lower resonating frequency (1.575 GHz) of the proposed antenna. The high isolation is achieved by incorporating two inverted L-shaped strips and a narrow slot in the ground plane. Envelope correlation co-efficient (ECC) and channel capacity loss (CCL) are within their acceptable limits. Other different diversity parameters are evaluated and the results are satisfactory for MIMO applications. [ABSTRACT FROM AUTHOR]

A low profile wideband spiral antenna array is presented for global mid-band 5G beam steering applications. In the global rollout of mid-band 5G, different frequencies have been licensed within each region (e.g. 3.4–3.8 GHz in the EU and 3.7–5 GHz in the USA). Therefore, antenna arrays must be able to cover a bandwidth of 3.3 GHz to 5 GHz to provide true global coverage. Initially, this work presents the design of a wideband compressed spiral antenna that provides an axial beam throughout its operational bandwidth of 3.3 GHz to 5 GHz, enabling beam steering functionality. Then, this antenna has been placed in a 4 × 4 array with a triangular lattice. The proposed spiral antenna array can provide a scanning range of − 40° ≤ θ ≤ + 40° in all azimuth directions with an average back lobe level of less than − 9.5 dB. This development will allow for low-cost integration of 5G systems for global use, such as passenger aircraft, UAVs, drones, and marine and ground vehicles. [ABSTRACT FROM AUTHOR]

Dynamic electric field frequency actuated helical and spiral structures enable a plethora of attributes for advanced photonics and engineering in the contemporary era. Nevertheless, leveraging the frequency responsiveness of adaptive devices and systems within a broad dynamic range and maintaining restrained high-frequency induced heating remain challenging. Herein, we establish a frequency-actuated heliconical soft architecture that is quite distinct from that of common frequency-responsive soft materials. We achieve reversible modulation of the photonic bandgap in a wide spectral range by delicately coupling the frequency-dependent thermal effect, field-induced dielectric torque and elastic equilibrium. Furthermore, an information encoder prototype without the aid of complicated algorithm design is established to analogize an information encoding and decoding process with a more convenient and less costly way. A technique for taming and tailoring the distribution of the pitch length is exploited and embodied in a prototype of a spatially controlled soft photonic cavity and laser emission. This work demonstrates a distinct frequency responsiveness in a heliconical soft system, which may not merely inspire the interest in field-assisted bottom-up molecular engineering of soft matter but also facilitate the practicality of adaptive photonics. Frequency responsiveness within a broad dynamic range in adaptive systems while also reducing high-frequency induced heating remains a challenge for advanced photonics. Here, authors report a frequency-actuated heliconical soft architecture with reversible modulation of the photonic bandgap in a wide spectral range. [ABSTRACT FROM AUTHOR]

In this paper, a spiral array is designed to estimate two-dimensional direction of arrival (DOA), which allows a larger spacing between adjacent antennas of the array. The fourth-order cumulant is also utilized to create more virtual antennas, further enlarging the array aperture. The noise resistance of the high-order cumulant can help to construct an improved propagator, and there is no need for any priori knowledge of the source number to estimate the DOAs. With the help of the cumulant, a convex optimization is introduced to improve the estimation accuracy, which can overcome the estimation bias caused by the finite snapshots. Simulation results demonstrate the effectiveness of the proposed estimator. [ABSTRACT FROM AUTHOR]

To optimally coordinate the operational safety, manoeuvrability, positioning reliability, and space expansibility of deep-sea stations, this study proposed a segmented spiral pressure hull with reference to the geometry of worm snails. The design addresses the disadvantages of existing ring-stiffened cylinder, segmented sphere, and circular toroid structures. This study numerically and experimentally examined the buckling performance of segmented spiral pressure hulls. The numerical, experimental, and analytical data exhibited satisfactory agreement. The proposed pressure hulls exhibited a favourable space expansibility and buckled in a nonlinear manner. The buckling loads varied slightly after the threshold number of segments. All the post buckling modes were local dents. The current findings may serve as a reference for the research and development of original deep-sea stations. [ABSTRACT FROM AUTHOR]

We present the design and analysis of 28 GHz CMOS power amplifiers using miniature coupled-line-based power combiners, which adopt single spiral structure with symmetrical layout to achieve miniature area and small amplitude imbalance (AI) and phase difference (PD). Coupled-line-based two power combiners and one 6-bit phase shifter (covering the 360° tuning range with excellent linearity) are designed and implemented. The first power combiner using two-turn spiral structure (combiner-1) achieves S21 of −3.93 dB and S31 of −3.97 dB at 28 GHz, corresponding to AI of 0.04 dB and PD of 0.11°. The second power combiner using three-turn spiral structure (combiner-2) achieves S21 of −3.9 dB and S31 of −3.86 dB at 28 GHz, corresponding to AI of −0.04 dB and PD of 0.02°. Three 28 GHz power amplifiers using the power combiners are designed and implemented. Excellent results are achieved. For instance, the third power amplifier (PA3) with combiner-2 comprises two ways of cascode input stage with wideband LC input matching network, followed by a common-source output stage with wideband LC inter-stage and output networks. PA3 occupies a chip area of 0.74 mm2 and achieves prominent output power (Pout) of 16.4 dBm, power gain of 22.1 dB, and power-added efficiency (PAE) of 32.6%. The eminent results of the power combiners, phase shifter, and power amplifiers indicate that they are suitable for 5G communication systems. [ABSTRACT FROM AUTHOR]

We present the design and analysis of noninverting single-spiral Ka-band (26.5–40 GHz) CMOS Wilkinson power dividers and their deriving quadrature couplers (QCs) and baluns. For the power dividers, a parallel capacitor is included at the input port (port 1) for input matching, and a parallel RC network is connected between the output ports (ports 2 and 3) for input matching and isolation. Noninverting single-spiral structure with transmission-line (TL) length of about λ/12 is adopted to achieve miniature area and small amplitude imbalance (AI) and phase difference (PD). To realize QC and balun, negative/positive phase-shift TLs with phase-shift of − 45°/45° and − 90°/90°, respectively, can be included at ports 2/3 of the power divider. Two power dividers and their deriving two QCs and two baluns are designed and implemented. Prominent result is obtained. For example, the miniature QC achieves excellent S11 of − 13.5 dB, S22 of − 14.5 dB, S33 of − 19.4 dB, S32 of − 10.5 dB, S21 of − 4.713 dB, and S31 of − 4.731 dB at 28 GHz. The corresponding AI and PD are 0.018 dB and − 0.1°, respectively. Moreover, S11 is smaller than − 10 dB from 10.4 GHz to over 50 GHz, corresponding to a fractional bandwidth (FBW) larger than 141.4%. The QC occupies a normalized chip area of 6.1 × 10–4 λ02, one of the smallest normalized chip areas ever reported for millimeter-wave QCs. [ABSTRACT FROM AUTHOR]

The article discusses the temperature regimes of transit pipelines for steam and hot water movement. A new device for thermal insulation of high-temperature pipelines with a spiral-bent hose is proposed. The most effective control is a visual examination during routine technical inspections to detect timely leakage defects. Transparent thermal insulation enables to visually monitor the state of the protected pipeline without dismantling the thermal insulation. The article presents a criterion equation for the similarity of convective heat transfer of a spiral-bent hose filled with air and an equation for reducing the temperature of the cooling agent. [ABSTRACT FROM AUTHOR]

We propose a power divider comprising of two parallel λ/4 coupled lines with a shared input signal line. An isolation resistor R is included to enhance the output-port reflection coefficients (S22 and S33) and the isolation between the output ports (S32 and S23). In theory, the power divider can achieve perfect input-port reflection coefficient (S11) and equal power coupling from the input to the outputs (i.e. S21 = S31). To achieve compact chip area, three prototyped power dividers with single-spiral- structure are designed and implemented. Tapered width from 8 to 3 μm is used at the output port transmission lines (TLs) (the first power divider) or the input port TL (the second and the third power dividers) to compensate for the single spiral structure for its non-ideality. This leads to enhancement of the reflection coefficients, and amplitude imbalance (AI) and phase difference (PD) of S21 and S31 of the power dividers. Prominent results are obtained. For instance, the second power divider (divider-2) occupies a chip area of 0.02 mm2 (i.e. 2.4 × 10–4λ02), one of the smallest normalized chip areas ever reported for millimeter-wave power dividers. At 33 GHz, divider-2 achieves decent S11 of −13.4 dB, S22 of −17.6 dB, S33 of −22.1 dB, S32 of −17.1 dB, S21 of − 4.68 dB, S31 of − 4.37 dB, AI of −0.31 dB, and PD of − 1.1°. The remarkable results of the power divider indicate that it is suitable for Ka-band communication systems. [ABSTRACT FROM AUTHOR]

The kinetic characteristics of a two-phase fluid system in a screw centrifugal sedimenter stem from the effect on the phases of forces from the screw that initiate pressure-free (gravity) spiral flow movement inside the rotor and from the effect on the mixture components of centrifugal inertial forces that induce the sedimentation process. As the suspension flows out of the feed pipe into the conical section of the cylindroconical rotor, it is transformed under the action of the force factors into two oppositely directed flows: a wet sediment flow moving along the rotor wall and a liquid flow moving near the feed pipe counter to the sediment flow. In this work, considering the specific features of the liquid mixture treatment conditions (pressure-free steady slow movement of the fluid system components in the mobile system), in selecting a physicomathematical model, we proceeded from the scientific premises of hydrodynamics of interpermeating and interacting multiphase fluid. In this context, the characteristics of the solid sedimentation process in the working space of the centrifuge were theoretically substantiated and calculated. The characteristics disclosed by use of the obtained relationships and parameters of the fluid system separation process can be used for designing and calculating suspension clarification process in innovative centrifugal equipment prototypes. [ABSTRACT FROM AUTHOR]

Two pairs of spiral-shape parasitic elements are proposed to improve the bandwidth of a microstrip patch antenna for simultaneous transmit and receive in 2.4–2.5 GHz ISM band. The antenna has two low-cost FR4 substrate layers and a ground plane between the layers. The top layer consists of the patch and parasitic spirals, and a modified 180° rat-race hybrid coupler is printed on the bottom layer. Adding the parasitic spirals enhance the antenna bandwidth by 15–25 MHz in both transmit and receive modes based on simulation and measured results. The hybrid coupler is used to maintain the high isolation between transmit and receive operations of the antenna. The antenna offers low-cross polarization for both modes at boresight (near 20 dB on the x–z plane and larger than 40 dB on the y–z plane). The design also has high self-interference cancellation, a spherical directional radiation pattern, good impedance matching, and reasonable gain values. [ABSTRACT FROM AUTHOR]

We present the design and analysis of G-band CMOS Wilkinson power dividers and dual balun for G-band communication and imaging systems. Miniature spiral and U-shaped four-way Wilkinson power dividers, which are based on three two-way Wilkinson power dividers, are designed and implemented. Miniature spiral dual balun, which is equivalent to an upper balun and a lower balun in parallel, is also designed and implemented for comparison. These devices are planar and symmetrical, and their main structure is implemented by the 2.34-µm-thick topmost metal to minimize the resistive loss. This leads to low insertion loss, and small amplitude imbalance (AI) magnitude and phase difference (PD) deviation. For instance, the spiral four-way Wilkinson power divider occupies 0.033 mm2 chip area and achieves S11 of − 11.4 dB, S21 of − 6.271 dB, S31 of − 6.445 dB, S41 of − 6.676 dB, and S51 of − 6.111 dB at 180 GHz, one of the smallest chip areas and lowest insertion losses for four-way power dividers with similar operation frequency. The corresponding AI magnitude and PD deviation are 0.565 dB and 3.2°, respectively. Moreover, the spiral dual balun occupies 0.026 mm2 chip area and achieves S11 of − 10.6 dB, S21 of − 7.549 dB, S31 of − 7.1 dB, S41 of − 7.598 dB, and S51 of − 7.352 dB at 180 GHz. The corresponding AI magnitude and PD deviation are 0.498 dB and 5.7°, respectively. The prominent results of the spiral and U-shaped four-way Wilkinson power dividers, and the spiral dual balun indicate that they are suitable for power division/combination in G-band systems. [ABSTRACT FROM AUTHOR]

A novel, wireless, passive, extra-arterial implantable blood pressure monitoring system was designed, fabricated, and tested. The measurement system is composed of an implantable sensor in-vivo and a readout system in-vitro. It was designed to balance the measurement accuracy and arterial invasiveness in continuous blood pressure monitoring. The passive LC resonant circuit was formed by a variable parallel-plate capacitance and a planar spiral inductor. It was fabricated and implanted in the necks of the rats to detect blood pressure changes. The variation of blood pressure was transduced into a change of the capacitance value of the variable parallel-plate capacitor, which caused a variation of the resonant frequency of the LC circuit. A readout probe with inductor coil was then used to measure the change of the resonant frequency of the LC circuit, and therefore indirectly measure the variation of blood pressure wirelessly. By measuring the resonant frequency with electromagnetic coupling of the implanted LC resonant sensor and the external inductor coil, a sensitivity of 8.53 kHz/mmHg for blood pressure measurement had been successfully achieved. The sensing distance is longer than 22 mm, which is enough for implementation of the wireless measurement. The overall size of the implantable sensor is 5 mm × 1.1 mm. The wireless implantable blood pressure sensor may be used in biomedical research for continuous, accurate and arterial trauma free blood pressure monitoring. [ABSTRACT FROM AUTHOR]

We propose and experimentally investigate a spiral-polished single-multi-single-mode (SP-SMS) fiber sensor for the simultaneous measurement of strain and temperature. This special spiral shape on a multimode fiber is fabricated by a high-frequency CO2 laser, which excites higher order cladding modes in the interference process and leads to high strain sensitivity. Experimental results show that the strain sensitivity for the proposed structure in the transmission spectrum of two marked interference dips is − 17 pm/με and − 1 pm/με in the range of 0–600 με. Moreover, temperature sensitivities of 10 pm/℃ and 13.3 pm/℃ are obtained in the range of 30–150 ℃. Furthermore, the proposed sensor is inexpensive, is easy to fabricate and has a compact structure. [ABSTRACT FROM AUTHOR]

Several methods have been proposed in the literature for the calculation of self and mutual inductance. These methods include the use of complex integral analysis, the necessity of having primary and secondary coils with the same dimensions and the limitations of the ratio of the coil dimension to the distance between the coils. To overcome these restrictions, a new semi-analytical estimation method has been proposed in this paper. Calculation the self and mutual inductance by using the same basic formula which is based on Biot Savart Law prevents the formation of complex integrals and helps create a simple solution method. In order to verify the results obtained with the analytical approach, two hexagonal coils with 10 and 20 cm outer side lengths were produced by using litz wire with a conductive cross section of 1.78 mm2. The results obtained with the new approach are compared with the finite element analysis, other work presented in the literature and experimental results in order to prove the accuracy of the proposed method. [ABSTRACT FROM AUTHOR]

In this paper, in order to amplify terahertz output pulses and achieve higher frequency peaks, a scheme of spiral lines is proposed to be used in the electrodes of photoconductive dipole antennas. This scheme is simulated with the help of the CST software. At first, a photoconductive antenna is simulated and compared with the experimental results. In order to improve the effectiveness of the antenna, certain changes are made in its shape. These changes are necessary because the intensity and frequency bandwidth of terahertz radiation in photoconductive antennas are less effective than other sources of terahertz waves and the shape of electrodes plays a fundamental role in the output of the radiation. As a result, adding spiral lines to antenna electrodes increases the intensity of terahertz radiation and shifts the frequency peak of that radiation toward higher frequencies. [ABSTRACT FROM AUTHOR]

In the current research, viscosity and thermal conductivity of hybrid Cu/CNTs water-based nanofluids were investigated at various concentrations of nanofluid and temperatures. The results demonstrated that although increasing the concentration leads to enhance the thermal conduction coefficient and viscosity, the increase in temperature followed the expected results of increasing thermal conductivity and decreasing viscosity. For the objective of evaluating the function of the U-shaped heat exchanger system, exergy variations concerning different operation conditions of three nanofluid concentrations (0.1, 0.2, and 0.5%) and three different pitches of the spiral strip (2, 3, and 4) were considered. The results showed that in all cases, a rise in Reynolds number would increase heat transfer. Additionally, the presence of a spiral strip resulted in much more increase in turbulent flow; subsequently, an impressive effect on the thermal performance can be obtained. The findings of the exergy efficiency for the U-shaped heat exchanger using hybrid nanofluid in different scenarios indicated that it is improved to 9–17%, and exergy improvement with the ratio of 4 is 23–26% and, for the ratio of 4, obtained 10–12.7%. For predicting the exergy efficiency of the heat exchanger, the designed neural network presented a three-layer model (one input layer, one hidden layer, and one output layer) containing seven neurons in the hidden layer and the leading algorithm of backpropagation Levenberg–Marquardt that anticipates the behavior of the system with a precision of R2 = 0.9967. The investigation of error distribution indicated that the model follows a normal distribution. [ABSTRACT FROM AUTHOR]

In this paper, a new application of dipole and chiral elements and structures based on them as one of the reflectors of a Fabry–Perot resonator located in the meta-interferometer is presented. It is experimentally shown that this application allows controlling multichannel microwave filtration in the range of 3–6 GHz. The influence of controlled resonance effects in the elements on the resonator spectrum and interferogram dynamics is demonstrated. The features related to the application of different elements and structures are studied: a "butterfly" dipole loaded with a varactor or stationary butterfly capacitor, a row of three single rings with two gaps loaded with two varactors, and arrays of spiral elements with 1.5 turns and double split rings. The theoretical study was carried out on an example of a meta-interferometer with a meta-structure in the form of a bianisotropic waveguide layer accounting for the possibility of implementing both direct wave and back wave modes. [ABSTRACT FROM AUTHOR]

In this paper an optimized helical antenna is proposed for heating ablation (Hyperthermia) of uterus, ovarian and colon cancers. This antenna is designed in such a way that can be easily insert into the intra cavities, due to its size and flexible shape. Various characteristics of the proposed helical applicator are investigated and optimized for best created specific absorption rate (SAR). After optimizations, the special proposed helical antenna is able to process the maximum symmetry radiation beams and this is an important feature because the cavity which the antenna is located must have capability to heat same in all directions. Finally, measured results of the constructed applicator are presented by the accuracy of simulated results. [ABSTRACT FROM AUTHOR]

Comparative experimental investigations of combined and helical ultra-wideband antennas are performed. The antennas are optimized to be excited by the 1 ns bipolar voltage pulses. The antenna matching with the feeder is studied in the frequency domain. The antenna patterns by the peak value of the radiated field are studied in the time domain for E- and H-planes. The effective potential values in the boresight radiation direction are studied as well with the same exciting voltage pulse at the antenna inputs. A probability is found for the effective potential of the helical antenna to be larger than that of the combined antenna in the case of an arbitrary orientation of the receiving linearly-polarized antenna. The effective potential of both antennas was registered in the pattern maxima at the same distances. This probability is equal to 0.6. [ABSTRACT FROM AUTHOR]

We analyse the use of a tunable dual wavelength Y-branch DBR laser diode for THz applications. The laser generates electrically tunable THz difference frequencies in the range between 100 and 300 GHz. The optical beats are tuned via current injection into a micro-resistor heater integrated on top of one of the distributed Bragg reflector (DBR) section of the diode. The laser is integrated in a homodyne THz system employing fiber coupled ion-implanted LT-GaAs log spiral antennas. The applicability of the developed system in THz spectroscopy is demonstrated by evaluating the spectral resonances of a THz filter as well as in THz metrology in thickness determination of a polyethylene sample. [ABSTRACT FROM AUTHOR]

A reconfigurable wideband circularly polarized plasma helical antenna is designed for wireless applications in the frequency band from 6 to 12 GHz. The proposed antenna structure is suitable to be integrated with electronic circuits for different applications. An optimization for different parameters of the antenna for wideband end-fire radiation characteristics is investigated. The antenna has matching impedance bandwidth of 48% with maximum gain of 8.5 dBi and wideband circular polarization of 31%. The antenna gain and bandwidth for different numbers of helix turns are increased with varying the plasma frequency. An improvement in the antenna gain and radiation efficiency is achieved via loading the antenna with dielectric lenses of different shapes. The end-fire directional gain is improved to 11.5 dBi for hemispherical lens and 10.5 dBi for quarter spherical lens with HPBW of 40°. [ABSTRACT FROM AUTHOR]

This paper introduces a proposed design of a circularly polarized quadfilar or octafilar helical antenna (QFHA or OFHA) dedicated for wireless in-body capsule endoscopy applications at 2.4 GHz. The use of a circularly polarized antenna permits a freedom in capsule orientation during endoscopy process. A multi-layered cylindrical model and homogenous cubic model for the human body tissues are studied and compared. The radiation characteristics of the QFHA and OFHA are encapsulated and placed inside the human model. Both the QFHA and the OFHA in capsule module are designed to resonate at 2.4 GHz with an impedance matching wide bandwidth of 125 MHz. The effect of the capsule ordination on the performance of the endoscopy process is studied. The response of the OFHA with and without capsulation is studied and introduced. The electrical length of an implantable antenna increases due to the high permittivity of the surrounding body tissues. The radiation characteristics of the QFHA and OFHA antennas in different cases are fully analysed and investigated using the finite integral technique. [ABSTRACT FROM AUTHOR]

Abstract: Helical magnets which violated space inversion symmetry have rather peculiar topological defects. In isotropic helical magnets with exchange and Dzyaloshinskii-Moriya interactions, there are only three types of linear defects: ±π and 2π-disclinations. Weak crystal anysotropy suppresses linear defects on large scale. Instead, planar defects appear: domain walls that separate domains with different preferential directions of helical wavevectors. The appearance of such domain walls in the bulk helical magnets and some of their properties were predicted in the work [1]. In a recent work by an international team of experimenters and theorists [2], the existence of new types of domain walls on crystal faces of helical magnet FeGe was discovered. They have many features predicted by theory [1], but display also unexpected properties, one of them is the possibility of arbitrary angle between helical wavevectors. Depending on this angle, the domain walls observed in [2] can be divided in two classes: smooth and zig-zag. This article contains a mini-review of the existing theory and experiment. It also contains new results that explain why in a system with continuous orientation of helical wavevectors domain walls are possible. We discuss why and at what conditions smooth and zig-zag domain walls appear, analyze spin textures associated with helical domain walls, and find the dependence of their width on the angle between helical wavevectors. [ABSTRACT FROM AUTHOR]

Ultrawideband elliptically polarized radiation is numerically and experimentally studied. The analysis is performed for the axial radiation of a cylindrical helical antenna that is excited by a bipolar voltage pulse with a duration of 2 ns. The results are used for construction of a source of high-power ultrawideband pulses with elliptical polarization. The radiation pulses with an effective potential of 300 kV are generated at an amplitude of the bipolar voltage pulse of 200 kV and a repetition rate of 100 Hz. [ABSTRACT FROM AUTHOR]

A novel multi frequency printed antenna is presented in this article. This type of antennas is very useful for the wireless world of today. The proposed antenna covers the low frequency biomedical band as well as various mobile wireless bands such as GSM bands, Bluetooth, ZigBee, Wi-Fi, WLAN and LTE bands etc. The antenna has multi resonating point between 0.5 and 5.6 GHz. The antenna is compact and its size is 32 × 40 × 1.6 mm. Coplanar waveguide (CPW) feed is used to excite this antenna. CPW feed improves the bandwidth of every resonating point between the above said frequency range. A detailed parametric study of the proposed prototype is presented in this paper. The results show that gain is improved from low frequency to high frequency range. The radiation pattern is directional, which is the most important need of biomedical and specific mobile wireless applications, and radiation efficiency is also good. The prototype is designed and simulated using HFSS. Further measured and simulated results are compared and a good impedance match is found between them. Overall this antenna can be used as a module with bunch of wireless applications. [ABSTRACT FROM AUTHOR]

A high-power source of ultrawideband radiation with elliptical polarization was developed on the basis of exciting a conical helical antenna by a bipolar voltage pulse with a length of 1 ns. The antenna parameters were preliminarily estimated using analytical formulas and then optimized via numerical simulation. The results of low-voltage test measurements were compared with the data that were obtained using a program that was developed on the basis of the finite-difference method in the time domain. In high-voltage measurements, the energy efficiency of the radiator was 0.85 and the coefficient of the hodograph ellipticity measured along the antenna axis was 0.9. The effective radiation potential of the source at an amplitude of bipolar voltage pulses of 190 kV was 270 kV, while the efficiency with respect to the peak field strength was 1.35. The high-power source of ultrawideband radiation operated at a pulse repetition frequency of 100 Hz. [ABSTRACT FROM AUTHOR]

Increasing mobility, safety and passenger comfort are very strong motivations for implementation of Intelligent Transportation Systems (ITS) in practice. The role of wireless communications in ITS has become compelling, both for industry and research community. Wireless communications technologies provide a platform for the exchange of data among the vehicles. A penta-band printed spiral antenna with tapered feed is proposed for vehicular communication system, facilitating vehicle-to-vehicle (V2V) and infrastructure to vehicle (I2V) communication. The antenna covers the navigational frequencies viz., 1.2, 1.5 GHz and Wireless Communication frequencies viz., 2.45, 3.3 GHz and Dedicated Short Range Communication frequency, 5.8 GHz for vehicular communications. Further, radio link characterization of I2V and V2V propagation channel is carried out using Electromagnetic propagation tool, and compared with empirical path loss models of ITU, two-ray reflection and inter-vehicle models. [ABSTRACT FROM AUTHOR]

An antenna in form of a dense multifilar helix of thin metal ribbons on a spherical surface with lower order transverse-electric and transverse-magnetic modes is considered. Averaged boundary conditions taking into account the capacitances between the edges of ribbons are formulated. Formulas for calculating the angle of inclination of ribbons and the required inter-edge capacitance from a given resonance frequency and approximate ellipticity coefficient are obtained. The inclination of the axes of the polarization ellipse and an improved ellipticity coefficient are determined. The fractional bandwidth of the antenna is expressed via the improved limits of the fractional bandwidth of linearly polarized antennas. The limits of the fractional bandwidth of circularly polarized antennas are found. It is established that the maximum fractional bandwidth is reached if the ellipticity coefficient is slightly different from unity. [ABSTRACT FROM AUTHOR]

Bolometer sensor is a good candidate for THz imaging due to its compact system, low cost, and wideband operation. Based on infrared microbolometer structures, two kinds of antenna-coupled microbridge structures are proposed with different spiral antennas: spiral antenna on support layer and spiral antenna with extended legs. Aiming at applications in detection and imaging, simulations are carried out mainly for optimized absorption at 2.52 THz, which is the radiation frequency of far-infrared CO lasers. The effects of rotation angle, line width, and spacing of the spiral antenna on THz wave absorption of microbridge structures are discussed. Spiral antenna, with extended legs, is a good solution for high absorption rate at low absorption frequency and can be used as electrode lead simultaneously for simplified manufacturing process. A spiral antenna-coupled microbridge structure with an absorption rate of more than 75% at 2.52 THz is achieved by optimizing the structure parameters. This research demonstrates the use of different spiral antennas for enhanced and tunable THz absorption of microbridge structures and provides an effective way to fabricate THz microbolometer detectors with great potential in the application of real-time THz imaging. [ABSTRACT FROM AUTHOR]

Dust emission is used in space applications for star-formation characterization normally acquired by different detectors operating at Infrared (IR) and sub-millimeter wave (sub-mm wave) frequencies. An integrated dual band detector working at both frequency ranges is described in this paper. The proposed configuration implements a spiral antenna working at sub-millimeter wave frequencies whose design is based on Fresnel zones theory. At the same time, this spiral antenna is used as Fresnel lens to focus IR power (12 μm) into an IR detector. The paper describes the influence of implementing a sub-mm wave spiral antenna based on square Fresnel zones. In particular, the effects on the focal distance and the focal gain at IR frequencies and the radiation features at sub-mm wave frequencies are studied. Furthermore, the importance of the number of Fresnel zones used in the design of the sub-mm spiral antenna is also determined. [ABSTRACT FROM AUTHOR]

This article discusses alternative designs of helical antennas used in space vehicles. The dependence of the beam shape on the number of approaches and the mode of excitation of helical antennas is shown. [ABSTRACT FROM AUTHOR]

Power limitations in CW THz generation imposed by conventional photomixers ('antenna emitters', AEs) are the major drawbacks on THz generation. From the antenna point of view, two different strategies are proposed to increase the generated power: optimized arrays and lenses arrangements and the use of new dielectric horn antennas. Then, using multiple small lenses, one per each single element, instead of a large one, bigger than the array, makes the generated power much higher. In addition, horn antennas etched in the substrate are considered in order to reduce the energy distribution scattering. Finally, some manufacturing issues are discussed. [ABSTRACT FROM AUTHOR]

This paper presents a method to improve the circular polarization of an Archimedean spiral antenna placed over a radial Artificial Magnetic Conductor (AMC). Results have been compared with the same radiating element over a more classical AMC reflector. A prototype of an Archimedean two-wire spiral antenna has been built to operate from 0.5 GHz to 6 GHz. Measurement results with this radial AMC give a relative bandwidth of 79 %, in which the broadside RHCP gain is improved. In this bandwidth the axial ratio of Archimedean spiral antenna placed over a radial AMC is less than 2 dB whereas it is higher than 3 dB with a classical cartesian shape of AMC reflector. [ABSTRACT FROM AUTHOR]

In this paper, the effect of coupling two kinds of metamaterial cells with a coil to achieve Magnetic Resonance Imaging (MRI) is investigated. Both an array of four spirals then a single spiral-shaped metamaterial are put on the top of the coil antenna. These metamaterial based resonant structures are designed to work at 63 MHz. They are intended to increase the sensitivity of the whole system and to improve the homogeneity of the RF magnetic field pattern. The spiral-shaped metamaterials added on the top of the antenna gave very promising numerical results. The calculated magnetic fields are homogeneous and their magnitudes are multiplied by factor of 4 up to 6. We are fabricating both structures using microfabrication techniques because of the small size of the structures. [ABSTRACT FROM AUTHOR]

The results of the development of an integrated high-performance antenna-type microbolometer and a computer experiment to investigate its expected parameters and characteristics are presented. It is shown that the use of a metamaterial in the heat-sensitive element, which is the load of a double-threaded spiral antenna, enables the main parameters of the receiver, which determine its practical suitability, to be improved. [ABSTRACT FROM AUTHOR]

In the paper, the hybrid backed-cavity with EBG (Electromagnetic Band-Gap) structure and PEC (Perfect Electronic Conductor) is proposed for Archimedean spiral antenna, which can make the spiral antenna work over the 10:1 bandwidth, without the loss introduced by absorbing materials. Based on the AMC characteristic (Artificial Magnetic Conductor), the EBG is placed in the outer region of backed-cavity to improve the blind spot gain in the low frequency. The PEC at the center of the structure is used to obtain high gain at high frequency. The better antenna performances are achieved in the low profile spiral antenna. A typical spiral antenna with hybrid backed cavity is numerically studied. The novel spiral antenna design with hybrid backed cavity is validated by simulated results. [ABSTRACT FROM AUTHOR]