Bandwidth Properties Research Articles

Design and Evaluation of a Pediatric Lower-Limb Exoskeleton Joint Actuator

Lower-limb exoskeletons have undergone significant developments for aiding in the ambulation of adults with gait impairment. However, advancements in exoskeletons for the pediatric population have comparatively been lacking. This paper presents a newly developed joint actuator designed to drive the hip and knee joints of a pediatric lower-limb exoskeleton. The performance requirements associated with the actuators were determined based on a target audience of children ages 6–11 years old. The developed actuators incorporate a hybrid belt-chain transmission driven by a frameless brushless DC motor. One actuator underwent benchtop testing to evaluate its performance with respect to their torque production, bandwidth properties, backdrivability in terms of inertia and friction characteristics, speed capabilities, and operational noise levels. As a preliminary validation, a set of actuators were placed in a prototype orthosis to move a pediatric test dummy in gait tracking via state-feedback control. The results showed that the newly developed actuators meet the design specifications and are suitable for use in the pediatric exoskeleton being developed.

Ultrawideband chromatic aberration-free meta-mirrors

Chromatic aberration-free meta-devices (e.g., achromatic meta-devices and abnormal chromatic meta-devices) play an essential role in modern science and technology. However, current efforts suffer the issues of low efficiency, narrow operating band, and limited wavefront manipulation capability. We propose a general strategy to design chromatic aberration-free meta-devices with high-efficiency and ultrabroadband properties, which is realized by satisfying the key criteria of desirable phase dispersion and high reflection amplitudes at the target frequency interval. The phase dispersion is tuned successfully based on a multiresonant Lorentz model, and high reflection is guaranteed by the presence of the metallic ground. As proof of the concept, two microwave meta-devices are designed, fabricated, and experimentally characterized. An achromatic meta-mirror is proposed within 8 to 12 GHz, and another abnormal chromatic meta-mirror can tune the reflection angle as a linear function. Both meta-mirrors exhibit very high efficiencies (85% to 94% in the frequency band). Our findings open a door to realize chromatic aberration-free meta-devices with high efficiency and wideband properties and stimulate the realizations of chromatic aberration-free meta-devices with other functionalities or working at higher frequency.

Design of a wideband random phase gradient metasurface by using line-shaped element

Based on phase randomization theory, a method for manufacturing metasurface with diffuse scatter performance is proposed. By using the line-shaped elements with random rotate angles and random distributing positions, the metasurface can achieve good diffusion scatter performance with polarization independent characteristic. This paper studies the effects of the length of line-shaped elements on the metasurface response frequency and the radar cross section (RCS) reduction bandwidth. The simulated result shows that the wideband properties of metasurface benefit from two different length line-shaped elements. The proposed metasurface can reduce the RCS significantly for both normal and oblique incident waves. The line-shaped element is suitable for all sizes of detected objects and it can be directly sprayed on the detected object surface. To demonstrate the effectiveness of the proposed method, the metasurface prototype is fabricated and measured. Experimental results show that the fabricated metasurface can effectively reduce RCS, and it has great application prospects in stealth technology.

Facile synthesis of Er3+/Tm3+ co-doped magnetic/luminescent nanosystems for possible bioimaging and therapy applications

Manganese-zinc ferrite is a kind of very important magnetic ferrite material. The properties of wide absorption band, sensitivity to ultraviolet (UV) light and tumor H2O2 promise it to be possibly used as a photothermal therapy (PTT), photodynamic therapy (PDT) and chemodynamic therapy (CDT) agent. Based on the unique advantages of rare-earth doped nanoparticles, an Er3+, Tm3+ co-doped upconversion-mediated nanosystem with manganese-zinc ferrite shell (named as UCNPS@M) was developed through a facile thermal co-decomposition method. The final nanosystems were surface-modified by using dopamine hydrochloride (DA) in order to warrant good biocompatibility (named as UCNPS@M@DA). Under irradiation of near-infrared (NIR) light, UCNPS emit both ultraviolet and visible light. The UV light is mostly absorbed by manganese-zinc ferrite shell to produce reactive oxygen species (ROS), which is essential to the potential PDT and CDT effect of nanosystems, and at the same time, Mn0.5Zn0.5Fe2O4 can further react with H2O2 to promote the efficiency of •OH-generation. It is expected that UCNPS@M@DA can act as upconversion luminescence imaging guidance due to the visible emission from UCNPS. In addition, the energy absorbed by the nanosystems can be transferred to heat to realize photothermal effect. Moreover, UCNPS@M@DA was successfully applied as a T1/T2-weighted magnetic resonance imaging (MRI) contrast agent due to the existence of Gd, Mn, and Fe elements. In light of the upconversion luminescence (UCL) imaging from the UCNPS as well as potential PTT, PDT, CDT effect mentioned above, this work provides a possibility to realize cancer multi-model bioimaging guided treatment by using an all-in-one diagnosis and therapy nanosystem through a simple yet powerful strategy.

The Impact of Multipath Information on Time-of-Arrival Estimation

Time-of-arrival (TOA) based localization plays a central role in current and future localization systems. Such systems, exploiting the fine delay resolution properties of wideband and ultra-wideband (UWB) signals, are particularly attractive for ranging under harsh propagation conditions in which significant multipath may be present. While multipath has been traditionally considered detrimental in the design of TOA estimators, it can be exploited to benefit ranging. This paper investigates the impact of a priori multipath information on TOA estimation. To this end, bounds on the performance of TOA estimation in dense multipath channels are provided and discussed under different operating conditions. The effects of channel dispersion and transmission bandwidth on ranging systems are investigated showing that, contrary to communication systems, diversity behavior is only exhibited in the medium signal-to-noise ratio regime.

Polarization-independent reflection grating in second-order Littrow for high laser resolving power

In order to obtain a grating solution for high laser resolving power, a multilayer fused-silica reflection grating is described with a silver layer embedded in the groove in second-order Littrow configuration instead of first-order mounting. Efficiencies of 96.17% and 96.14% can diffracted in −2nd order for TE and TM polarizations, which are greater than 96%. The new multilayer reflection grating with a silver layer embedded has good incident characteristics and process tolerances. Therefore, the high-efficiency output with polarization-independent and wideband property characteristics of the grating will be well applied to the laser field.

Wideband bandstop filters based on wideband 180° phase shifters

In this study, a class of wideband bandstop filters is proposed based on wideband 180° phase shifters. Different from traditional signal–interference-based bandstop filters, they make use of a 180° phase shifting in a wide operating band in principle. After numerical analysis of the phase responses of the two coupling-line paths, the optimal solutions for the largest 180° phase-shifting bandwidth or minimum impedance ratio can be obtained. Then, the wideband bandstop filter based on these two unique coupling lines is intensively analysed to reveal that three transmission zeros are generated in the stopband as the two paths have a 180° phase difference, thus exhibiting its wideband property. Moreover, by enlarging the impedance of the two paths, good out-of-band characteristics of the bandstop filter can be attained, while in-band performances are almost unchanged. Next, two types of bandstop filters with extended bandwidth are proposed by cascading an extra delay line for both paths, and they hold similar filtering characteristics as the aforementioned one. Finally, the design process and demonstration are provided. The measured results of the three fabricated filters show that Type-I, Type-II, and Type-III filters can satisfactorily obtain a 3 dB bandwidth of 108, 122, and 130% with 25, 14.7, and 11.6 dB rejection level, respectively.

Study on dynamic mechanical properties of viscoelastic damping materials based on finite element theory

The relationship between the vibration parameters and the dynamic mechanical properties of the rubber material is established through the vibration reduction experiment and the finite element theory of the ZN-35 silicon rubber damper, which provides a new method for the prediction of the wide-band dynamic mechanical properties of the viscoelastic damping material.

T-shaped reflective polarizer under second Bragg incidence

A T-shaped reflective grating device under the second Bragg angle is proposed for polarizer. This grating device is mainly made of fused silica with T-shaped ridges, which can diffract the energy of the TE-polarized light and the TM-polarized light to the −2nd order and the 0th order with the reflective efficiency of each order more than 95%. Normalized field magnitude distribution and overlap integral are analyzed to explain the physical mechanism and energy exchange. Based on the optimized results, the beam splitter exhibits high efficiency, good extinction ratio and optical properties of the incident bandwidth. Moreover, grating can have longer period for easy fabrication under second Bragg incidence compared to reported Bragg incidence. Therefore, the T-shaped reflective grating device should be useful for the future optical communication industry.

Structural and optical studies of TiO2:Ag2O nanocomposite by sol-gel method

Abstract As TiO2 is suitable for electronic and electrical applications, in the present work the authors have successfully modified TiO2 by adding silver (Ag) to form titanium oxide-silver oxide (TiO2:Ag2O) nanocomposite samples by using sol-gel technique. Characterizations of these composites have been performed using X-ray diffraction (XRD), atomic force microscopy (AFM), scanning electron microscopy (SEM) and UV-Vis spectroscopy. XRD study revealed that the crystal structure of the samples consisted of tetragonal and cubic phases. This study further showed an increment in the average crystallite size from 8 nm to 38 nm with an increase in Ag concentration. The increase in crystallite size has been confirmed additionally by SEM and AFM. The increment in the average particle size of the samples may be attributed to an increase in silver molarity in the TiO2 matrix. Significant red shift in the absorption edge has been observed, causing reduction in the energy bandgap of the composites from 3.89 eV to 3.46 eV with an increase in particle size which is evident from UV-Vis spectroscopic studies. This wide-band gap properties of the TiO2:Ag2O nanocomposite make it suitable for memory-storage devices and dielectric applications.

Wideband, Electrically Small, Near-Field Resonant Parasitic Dipole Antenna With Stable Radiation Performance

A wideband, electrically small, and near-field resonant parasitic (NFRP) dipole antenna with stable radiation performance is presented. Inspired by recent metasurface antennas (MSAs), a coax-fed dipole antenna is loaded with a specially-engineered interdigitated NFRP element. It exhibits identical operating mechanisms to a developed electrically large slot-fed MSA, i.e., it has the similar adjacent fundamental mode and antiphase mode, and thus has a wide bandwidth property and uniform radiation patterns. The electrically small prototype was fabricated and measured. The measured results, in good agreement with their simulated values, demonstrate a wide 14.4% −10 dB impedance bandwidth along with a stable realized gain of 1.4 dBi over the entire band. Moreover, stable and uniform radiation patterns together with high radiation efficiency values were also measured. These performance characteristics make the reported electrically small antennas attractive for wideband and space-limited applications.

Evaluation of the Frequency Bandwidth and Gain Properties of Antennas: Characteristics of Circularly Polarized Microstrip Antennas

Frequency bandwidth, gain, and dimensions are some of the most important characteristics of antennas. A comparison of the most important characteristics of circularly polarized microstrip antennas (CP MSAs) [1]-[33], using traditional methods, is accomplished in this article. The CP MSAs were chosen for the study because MSAs have been the most dynamically developing field of antennas over the last few decades [34], [35] and the CP is the more complex type of polarization than linear polarization (LP). The disadvantages of traditional methods of comparison, in which the antennas are practically compared according to only one characteristic, are indicated. Several criteria, simultaneously taking into account the effect of the frequency bandwidth, gain, and antenna dimensions, are proposed. These criteria can be used for a more complete evaluation of antenna characteristics.

Composite structure-based transparent ultra-broadband metamaterial absorber with multi-applications

In this paper, an approach is proposed to realize optically transparent metamaterial absorber (OTMA) with ultra-broadband absorption properties by using composite resonant structure. The indium tin oxide (ITO) resistive film is used to construct the resonant structure to induce high ohmic loss and broaden the bandwidth of the resonances, thus achieves more than 90% absorptivity in the wide bandwidth of 8–30.3 GHz, which can cover the X and Ku bands of the airborne and surveillance radar signal frequencies. The novelty of designed structure lies in the properties of larger absorption bandwidth (covering X, Ku, K and part of Ka bands), lower thickness, and absorption capacity over a wide range of incident angles. Moreover, by replacing the intermediate air spacer with polydimethylsiloxane (PDMS) and polymethyl methacrylate (PMMA) dielectrics, the OTMAs that can be used for conformal applications and rigid window glass of stealth armament are designed. This strategy provides more flexibility for the applications of broadband OTMA in different occasions, and has potential application prospects in radar stealth system, EM shielding and transparent RF equipment fields. The average optical transmittance of the whole structure in the visible light range exceeds 78%.

Serially concatenated extended CPM scheme based on TDRSS

Tracking and Data Relay Satellite System (TDRSS) can meet the needs of Low EarthOrbit (LEO) satellite real-time transmission, but it also has large Doppler shift, transmission delay and channel fading. Continuous Phase Modulation (CPM), with excellent properties of both bandwidth and energy efficient, are very suitable for nonlinear and/or fading channels such as satellite channel due to the constant envelope nature. In this paper, the CPE in the SCCPM scheme is replaced by the designed ECE to construct a new scheme called SCECPM scheme, in order to enhance the robustness of the signal. Compared with previous SCCPM scheme, the proposed system shows an improvement concerning the convergence threshold and bit-error-rate (BER).

IC 741 a nd IC AMP02FP Based Signal Conditioning Circuit f or Electrostatic Sensor u sing Multisim

The Electrostatic sensors are extensively used in military, radar and electronic applications which can sense the electric charge from the moving charged motes. The signal conditioning circuit for an electrostatic sensor is a voltage amplifier that can intensify a small input signal. This paper proposal is to design a low noise signal conditioning circuit using Multisim and to study the performance of its gain, bandwidth and noise properties.

High-Gain Metasurface in Polyimide On-Chip Antenna Based on CRLH-TL for Sub-Terahertz Integrated Circuits

This paper presents a novel on-chip antenna using standard CMOS-technology based on metasurface implemented on two-layers polyimide substrates with a thickness of 500 μm. The aluminium ground-plane with thickness of 3 μm is sandwiched between the two-layers. Concentric dielectric-rings are etched in the ground-plane under the radiation patches implemented on the top-layer. The radiation patches comprise concentric metal-rings that are arranged in a 3 × 3 matrix. The antennas are excited by coupling electromagnetic energy through the gaps of the concentric dielectric-rings in the ground-plane using a microstrip feedline created on the bottom polyimide-layer. The open-ended feedline is split in three-branches that are aligned under the radiation elements to couple the maximum energy. In this structure, the concentric metal-rings essentially act as series left-handed capacitances CL that extend the effective aperture area of the antenna without affecting its dimensions, and the concentric dielectric rings etched in the ground-plane act as shunt left-handed inductors LL, which suppress the surface-waves and reduce the substrates losses that leads to improved bandwidth and radiation properties. The overall structure behaves like a metasurface that is shown to exhibit a very large bandwidth of 0.350–0.385 THz with an average radiation gain and efficiency of 8.15dBi and 65.71%, respectively. It has dimensions of 6 × 6 × 1 mm3 that makes it suitable for on-chip implementation.

Comparative study of single- and double-layer BaFe12O19-Graphite nanocomposites for electromagnetic wave absorber applications

The development of stealth technology for military applications and increasing concerns of electromagnetic pollution have garnered interest to design microwave absorbing materials with wide absorption bandwidth and effective absorption properties. Two batches of samples as a potential radar absorbing material were prepared in this study: single-layer and double-layer nanocomposite mixtures of graphite and barium hexaferrite nanoparticles. Characterizations of electromagnetic and microwave absorbing properties were carried out in the frequency range of 8−12 GHz (X-band) and 12−18 GHz (Ku-band). Single-layer samples with thickness of 2 mm showed optimal absorption properties with minimum reflection loss of -20.5 dB at 11.8 GHz for X-band and -20.7 dB at 14.7 GHz for Ku-band, displaying bandwidths of 0.6 GHz for the former and 3.8 GHz for the latter at -10 dB. On the other hand, double-layer samples made of 1 mm thick barium hexaferrite matching layer and 2 mm thick graphite absorbing layer showed optimal absorption properties with minimum reflection loss of -30.0 dB at 9.2 GHz for X-band with narrower bandwidth of 0.6 GHz. The microwave absorption properties of these nanocomposites were attributed to combined effect of dielectric loss from graphite and magnetic loss from ferrite.

Automated design for a hybrid lumped and distributed dual‐band stub using aggressive space mapping

AbstractA dual‐band stub (DBS) in a hybrid lumped and distributed configuration is presented in this paper, which comprises one lumped kernel circuit unit cell (KCUC) centered between two uniform transmission lines. Image parameter theory is imposed to extract the DBS phase and impedance bandwidth properties. An odd‐even mode resonant frequency ratio is defined, capable of determining all the DBS element values as well as regulating the DBS size and its second working bandwidth. By converting the lumped KCUC into a quasi‐lumped microstrip topology, a purely planar DBS is automatically implemented by employing the aggressive space mapping (ASM). Through the customized ASM process, the finalized DBS dimensions can be generated within just a few full‐wave simulations. The relatively high accuracy and efficiency of the ASM are affirmed by comparing its performance to those of the traditional direct optimization algorithms. As an example, a DBS with WLAN dual frequencies and extended bandwidth is designed and fabricated. The measured results agree well with the simulated results, justifying the DBS properties and its ad hoc ASM optimization technique.

Differential phase shifters based on Schiffman type‐C and type‐F networks with wide phase shift range

This study proposes a class of differential phase shifters based on the Schiffman type-C and type-F networks with wide phase shift range. After the phase and bandwidth properties of these two distinct networks are numerically analyzed, two unique advantages of wide phase shift range and wide phase shift bandwidth are revealed. Next, the optimal design parameters for different phase shift values up to 405° are presented to allow for a quick design process. To verify the proposed approach, a 180° differential phase shifter is designed, fabricated and measured. Good performance is achieved with an impedance ratio of 1.959 and 3.7° phase deviation over a phase shift bandwidth of 61%.

Wideband Phase Shifters With Miniaturized Size on Multiple Series and Shunt Resonators: Proposal and Synthetic Design

In this article, a new class of wideband phase shifters with very compact size, large phase shift value, low insertion loss (IL), and low cost are presented and developed. The proposed phase shifter consists of N series and shunt resonators, which can achieve the magnitude and phase shift bandwidth of more than 120% thanks to N transmission poles. Besides the wideband property, the proposed phase shifter is able to achieve a small size of nearly 1/10 guided wavelength (λg), which has a size reduction of more than 90% as compared with conventional wideband phase shifters on printed circuit board (PCB). Meanwhile, insertion phases for the both series and shunt resonators are zero at their resonant frequencies; thus, the length of reference line can be also greatly reduced. What is more, a detailed synthesis method with closed-form equations is presented and employed to determine all circuit parameters of the proposed phase shifter with the specified in-band return loss (RL), phase shift value AΦ, and resonator number N. To validate the design concept, three design examples of 90° and 180° phase shifters on N = 3 and N = 5 are synthesized and tested. Theoretical, simulated, and measured results are in a fairly close agreement. In particular, the proposed phase shifters feature very low IL. The measured maximum in-band IL is only 0.38 dB for N = 3 (AΦ = 90°) and 0.50 dB for N = 5 (AΦ = 180°).