dB In Simulation Research Articles

One hundred fifty GHz folded dipole antenna‐on‐chip based on artificial magnetic conductor structure

AbstractA folded dipole antenna using an artificial magnetic conductor (AMC) structure is proposed to improve the frequency bandwidth and reduce the size of the antenna on a chip. To change the distribution of the electromagnetic (EM) field, the proposed AMC structure shaped with square‐in‐square rings (SSRs) is arranged along the radiating metal of the folded dipole antenna and implemented on the lowermost metal layer of the backend oxide layers (BEOLs) between the radiating metal of the top layer of the BEOL and the ground plane of the bottom of the substrate. The SSR of the proposed antenna‐on‐chip (AoC) widens the frequency bandwidth by varying the electrical length to the ground and reduces the physical size of the radiating metal by increasing the effective permittivity. The 3D EM‐wave simulation shows that the proposed AMC structure changes the distribution of EM‐wave in the BEOL and Si substrate such that more EM fields are condensed around the radiating metal and the electrical length to the ground is nonuniform and longer. The AoC with the proposed AMC structure was fabricated using a 65‐nm standard complementary metal‐oxide semiconductor process with one‐poly and nine‐metal. Compared with the conventional 150‐GHz antenna that was implemented on the same die, the proposed differential antenna was measured to be a −10 dB bandwidth of 46 GHz, with a 1.12‐times improvement, and a size reduction of 20.4%. The measured gain of the proposed antenna was −5.99 dBi including the passive balun with an insertion loss of −1.36 dB in simulation.

Advancements in Flexible Antenna Design: Enabling Tri-Band Connectivity for WLAN, WiMAX, and 5G Applications

The use of flexible antennas has garnered significant interest in light of their wide-ranging applications inside contemporary wireless communication systems. The need for these antennas stems from the necessity for small, conformal, and versatile systems that can effectively function across many frequency ranges. The present study investigates designing and optimizing a universal triband antenna, focusing on meeting the distinct demands of Wireless Local Area Networks (WLAN), Worldwide Interoperability for Microwave Access (WiMAX), and 5G applications. The current methodologies often need help attaining maximum efficiency over a wide range of frequency bands, resulting in concerns such as subpar radiation patterns and restricted bandwidth. To address the obstacles, this research proposes a novel approach known as the Triband Antenna Design using the Artificial Neural Network (3AD-ANN) method. This method utilizes machine learning techniques to devise and enhance the attributes of the antenna effectively. The 3AD-ANN approach presents several notable characteristics, such as heightened adaptability, increased radiation patterns, and a condensed physical structure. The mean values for far-field radiation gain are around -37.4 dB in simulated scenarios and -39.9 dB in actual observations. The average return loss is roughly -23.8 dB in simulations and -25.8 dB in experimental measurements. The numerical findings illustrate the effectiveness of this methodology, exhibiting exceptional return loss and gain sizes over a range of frequencies, including WLAN, WiMAX, and 5G.

C- and O-Band Dual-Polarization Fiber-to-Chip Grating Couplers for Silicon Nitride Photonics.

Highly efficient coupling of light from an optical fiber to silicon nitride (SiN) photonic integrated circuits (PICs) is experimentally demonstrated with simple and fabrication-tolerant grating couplers (GC). Fully etched amorphous silicon gratings are formed on top of foundry-produced SiN PICs in a back-end-of-the-line (BEOL) process, which is compatible with 248 nm deep UV lithography. Metallic back reflectors are introduced to enhance the coupling efficiency (CE) from -1.11 to -0.44 dB in simulation and from -2.2 to -1.4 dB in experiments for the TE polarization in the C-band. Furthermore, these gratings can be optimized to couple both TE and TM polarizations with a CE below -3 dB and polarization-dependent losses under 1 dB over a wavelength range of 40 nm in the O-band. This elegant approach offers a simple solution for the realization of compact and, at the same time, highly efficient coupling schemes in SiN PICs.

A planar four-element modified L-shaped monopolar multiport antenna for sub-6 GHz applications

This paper presents and implements a four-element modified L-shaped multiport antenna for sub-6 GHz applications. The isolation between the antenna elements is improved by careful engineering in the ground plane. The proposed four-element modified L-shaped MIMO antenna has a footprint of 0.21897 λ02, where, λ0 is the wavelength of the lowest operating frequency. The fractional bandwidth of this antenna is 55.15% while operating between 3.9–6.87 GHz. The inter-element isolation is always above 16 dB in simulation and above 18 dB in measurements, with the simulated peak gain of 2.53 dBi over its operating frequency band. The measured Envelope Correlation Coefficient (ECC) is below 0.008 which makes it a potential candidate for IEEE 802.11a and sub-6 GHz wireless applications requiring compact and low-profile antennas with high inter-element isolation.

Source separation and noise reduction in single-pixel imaging

Degradation of imaging quality due to noise sources is one of the most essential problems for single-pixel imaging (SPI). This paper presents a method that separates, identifies, and reduces noise from the 1-D signal of the SPI before reconstructing the image. The proposed method raises the quality of the picture significantly, for example, PSNR from 9.14 dB to 30.29 dB and SSIM from 5.55% to 91.99% when SNR is -15 dB in simulation. This method has a strong robustness to a variety of noise types compared to the traditional filtering methods. The experimental results verified the proposed method's feasibility and improved the image's quality from a chaotic state to an acceptable stage. The method proposed in this paper can separate, identify and remove the noise component from the sources in SPI, which may open a branch by removing noise from sources rather than post-processing.

Generation of Flat Terahertz Noise by Mixing Incoherent Light Fields

Terahertz (THz) noise sources play an irreplaceable role in testing THz devices and evaluating THz application systems, and the flatness of their radio frequency (RF) spectra is an important technical parameter. In this paper, a scheme for generating flat THz noise by mixing multiple filtered incoherent light fields is proposed. A theoretical analysis is conducted to investigate the impact of different spectral linewidths and central wavelength differences of incoherent light fields on the noise power and RF spectrum flatness, and an optimized experimental scheme is obtained. The results show that the proposed method can generate a 280–380 GHz flat THz noise signal with an RF spectrum flatness of ±0.5 dB in simulation and ±2.7 dB in our experiments. This article provides an excellent technical solution to the demand for flat THz noise in the THz field.

On the design and manufacturing of miniaturized microstripline power splitters for driving multicoil transmit arrays with arbitrary ratios at 7T.

The purpose of the current study was to implement unequal microstrip power splitters for parallel transmission at 7 T that are optimized for size and loss and that can be configured for a wide range of power ratios. The splitters will enable the use of more transmit coils without a corresponding increase in the number of transmit channels or amplifiers to control specific absorption rate, shorten RF pulses, and shim inhomogeneous RF fields. Wilkinson unequal power splitters based on a novel microstrip network design were optimized to minimize their size under 8 cm in length and 9 cm in width, enabling them to be included in coil housing or cascaded in multiple stages. Splitters were designed and constructed for a wide range of output power ratios at 298 MHz. Simulations and bench tests were performed for each ratio, and a methodology was established to adapt the designs to other ratios and frequencies. The designs and code are open source and can be reproduced as is or reconfigured. The single-stage designs achieved good matches and isolations between output ports (worst isolation -15.9 dB, worst match -15.1 dB). A two-stage cascaded (one input to four outputs) power splitter with 1:2.5, 1:10, 1:3, and 1:6 ratio outputs was constructed. The worst isolation between output ports was -19.7 dB in simulation and the worst match of the three ports was -17.8 dB. The measured ratios for one- and two-stage boards were within 10% of the theoretical ratios. The power-handling capability of the smallest trace was approximately 70 W. Power loss for the one- and two-stage boards ranged from 1% to 3% in simulation compared with 5.1% to 7.2% on the bench. It was concluded that Wilkinson unequal microstrip power splitters can be implemented with a small board size (low height) and low loss, and across a wide range of output power ratios. The splitters can be cascaded in multiple stages while maintaining the expected ratios and low loss. This will enable the construction of large fixed transmit array-compression matrices with low loss.

Reconstruction for plane-wave ultrasound imaging using modified U-Net-based beamformer.

An image reconstruction method that can simultaneously provide high image quality and frame rate is necessary for diagnosis on cardiovascular imaging but is challenging for plane-wave ultrasound imaging. To overcome this challenge, an end-to-end ultrasound image reconstruction method is proposed for reconstructing a high-resolution B-mode image from radio frequency (RF) data. A modified U-Net architecture that adopts EfficientNet-B5 and U-Net as the encoder and decoder parts, respectively, is proposed as a deep learning beamformer. The training data comprise pairs of pre-beamformed RF data generated from random scatterers with random amplitudes and corresponding high-resolution target data generated from coherent plane-wave compounding (CPWC). To evaluate the performance of the proposed beamforming model, simulation and experimental data are used for various beamformers, such as delay-and-sum (DAS), CPWC, and other deep learning beamformers, including U-Net and EfficientNet-B0. Compared with single plane-wave imaging with DAS, the proposed beamforming model reduces the lateral full width at half maximum by 35% for simulation and 29.6% for experimental data and improves the contrast-to-noise ratio and peak signal-to-noise ratio, respectively, by 6.3 and 9.97dB for simulation, 2.38 and 3.01dB for experimental data, and 3.18 and 1.03dB for in vivo data. Furthermore, the computational complexity of the proposed beamforming model is four times less than that of the U-Net beamformer. The study results demonstrate that the proposed ultrasound image reconstruction method employing a deep learning beamformer, trained by the RF data from scatterers, can reconstruct a high-resolution image with a high frame rate for single plane-wave ultrasound imaging.

Generation of frequency 32-tupling millimeter-wave based on a dual-parallel polarization modulator.

A scheme to generate a frequency 32-tupling millimeter wave (mm-wave) is proposed, enabled by two dual-parallel polarization modulators (DP-PolMs) in cascade. By properly controlling the amplitude and the phase shift of the radio-frequency (RF) driving signal applied to two DP-PolMs, the main optical components at the output of the DP-PolM are ±16th order optical sidebands and the central carrier. After the central carrier is canceled by the polarization multiplexing structure, the ±16th order optical sidebands are beaten in the photodetector; then the frequency 32-tupling mm-wave can be achieved. The optical sideband suppression ratio (OSSR) and the radio-frequency spurious suppression ratio (RFSSR) of the generated signal are 52 and 47 dB in simulation, which are consistent with the theoretical analysis values 53.7 and 47.7 dB. The influence on the OSSR and RFSSR of the generated signal by the key parameters of devices deviating from the theoretical analysis value i are investigated.

Design of an Electrically Small 3-D Antenna With Quasi-Isotropic Radiation Pattern

An electrically small three-dimensional (3-D) antenna is proposed to generate a quasi-isotropic radiation pattern. The proposed antenna consists of a single layer conductor with bilateral symmetrical structure before being wrapped in a cylindrical foam. An H-shaped inductive coupling element is used to feed the antenna to obtain a magnetic dipole and a pair of short electric dipoles after the antenna is wrapped in a cylindrical foam. Therefore, by combining orthogonal complementary dipoles with the same radiation intensity and quadrature phase difference, a quasi-isotropic radiation pattern can be obtained. As a proof of this design, a 3-D antenna structure operating at 2.45 GHz is designed, fabricated and measured. It has been shown that the gain variation of the proposed electrically small antenna (ka = 0.48) in total space is 2.72 dB in simulation and 3.53 dB in measurement.

Performance improvement for compressive light field display based on the depth distribution feature.

Compressive light field (CLF) display using multi-layer spatial light modulators (SLMs) is a promising technique for three-dimensional (3D) display. However, conventional CLF display usually uses the reference plane with fixed depth, which does not consider the relationship between the depth distribution of the object and the image quality. To improve the quality of the reconstructed image, we further analyze the relationship between them in the paper. The theoretical analysis reveals that the object with a closer distance to the physical layer has a better reconstruction quality when the SLM layers have the same pixel density. To minimize the deviation between the reconstructed light field and the original light field, we propose a method based on the depth distribution feature to automatically guide the light field optimization without increasing the layered number or the refresh rate. When applied to a different scene, it could detect the dense region of depth information and map them as close to the physical layers as possible by offsetting the depth of the reference plane. Simulation and optical experiments with the CLF display are demonstrated to verify the proposed method. We implement a CLF display that consists of four-layer stacked display panels and the distance between two adjacent layers is 5cm. When the proposed method is applied, the peak signal-to-noise ratio (PSNR) is improved by 2.4dB in simulations and 1.8dB in experiments.

Broadband Metallic Fiber-to-Chip Couplers and a Low-Complexity Integrated Plasmonic Platform.

We present a plasmonic platform featuring efficient, broadband metallic fiber-to-chip couplers that directly interface plasmonic slot waveguides, such as compact and high-speed electro-optic modulators. The metallic gratings exhibit an experimental fiber-to-slot coupling efficiency of −2.7 dB with −1.4 dB in simulations with the same coupling principle. Further, they offer a huge spectral window with a 3 dB passband of 350 nm. The technology relies on a vertically arranged layer stack, metal–insulator–metal waveguides, and fiber-to-slot couplers and is formed in only one lithography step with a minimum feature size of 250 nm. As an application example, we fabricate new modulator devices with an electro-optic organic material in the slot waveguide and reach 50 and 100 Gbit/s data modulation in the O- and C-bands within the same device. The devices’ broad spectral bandwidth and their relaxed fabrication may render them suitable for experiments and applications in the scope of sensing, nonlinear optics, or telecommunications.

Denoising click-evoked otoacoustic emission signals by optimal shrinkage.

Click-evoked otoacoustic emissions (CEOAEs) are clinically used as an objective way to infer whether cochlear functions are normal. However, because the sound pressure level of CEOAEs is typically much lower than the background noise, it usually takes hundreds, if not thousands, of repetitions to estimate the signal with sufficient accuracy. In this paper, we propose to improve the signal-to-noise ratio (SNR) of CEOAE signals within limited measurement time by optimal shrinkage (OS) in two different settings: covariance-based optimal shrinkage (cOS) and singular value decomposition-based optimal shrinkage (sOS). By simulation, the cOS consistently enhanced the SNR by 1-2 dB from a baseline method that is based on calculating the median. In real data, however, the cOS cannot enhance the SNR over 1 dB. The sOS achieved a SNR enhancement of 2-3 dB in simulation and demonstrated capability to enhance the SNR in real recordings. In addition, the level of enhancement increases as the baseline SNR decreases. An appealing property of OS is that it produces an estimate of all single trials. This property makes it possible to investigate CEOAE dynamics across a longer period of time when the cochlear conditions are not strictly stationary.

Design and Analysis of Super Wideband Antenna for Microwave Applications.

In this article, a compact concentric structured monopole patch antenna for super wideband (SWB) application is proposed and investigated. The essential characteristics of the designed antenna are: (i) to attain super-wide bandwidth characteristics, the proposed antenna is emerged from a traditional circular monopole antenna and has obtained an impedance bandwidth of 38.9:1 (ii) another important characteristic of the presented antenna is its larger bandwidth dimension ratio (BDR) value of 6596 that is accomplished by augmenting the electrical length of the patch. The electrical dimension of the proposed antenna is ( corresponds to the lower end operating frequency). The designed antenna achieves a frequency range from 1.22 to 47.5 GHz with a fractional bandwidth of 190% and exhibiting S11 < −10 dB in simulation. For validating the simulated outcomes, the antenna model is fabricated and measured. Good conformity is established between measured and simulated results. Measured frequency ranges from 1.25 to 40 GHz with a fractional bandwidth of 188%, BDR of 6523 and S11 < −10 dB. Even though the presented antenna operates properly over the frequency range from 1.22 to 47.5 GHz, the results of the experiment are measured till 40 GHz because of the high-frequency constraint of the existing Vector Network Analyzer (VNA). The designed SWB antenna has the benefit of good gain, concise dimension, and wide bandwidth above the formerly reported antenna structures. Simulated gain varies from 0.5 to 10.3 dBi and measured gain varies from 0.2 to 9.7 dBi. Frequency domain, as well as time-domain characterization, has been realized to guide the relevance of the proposed antenna in SWB wireless applications. Furthermore, an equivalent circuit model of the proposed antenna is developed, and the response of the circuit is obtained. The presented antenna can be employed in L, S, C, X, Ka, K, Ku, and Q band wireless communication systems.

High-accuracy dual-slope-assisted chaotic Brillouin fiber dynamic strain measurement

Nowadays, distributed dynamic sensing technology based on stimulated Brillouin scattering has been widely employed in civil structure health monitoring, disaster warning, national defense, etc. In this paper, we propose and experimentally demonstrate a novel Brillouin optical correlation-domain analysis based-on gain-switch modulation and dual-slope assisted method for achieving high-accuracy large-range dynamic strain measurement. In single-slope assisted chaotic Brillouin sensing, the measurement accuracy of dynamic strain is deteriorated by the inherent characteristics of time delay signature and power stochastic fluctuations. First, the mechanism behind the acoustic field deterioration and principle of background noise suppression are analyzed theoretically. Then, the chaotic continuous pump light is modulated into pulsed light with a higher extinct ratio of 48.6 dB, where the electro-optical modulator is replaced by a gain switch. And thus, the noise peaks, induced by the secondary peaks and irregular basal oscillations of chaotic auto-correlation curve, are greatly restrained. Comparing with the electro-optical modulator-based system, the signal-to-noise ratio of stimulated Brillouin acoustic field is increased by 3.31 dB in simulation and the signal-to-background ratio of Brillouin gain spectrum is doubled in experiment. Consequently, the measurement accuracy of dynamic strain is improved from ± 40.2 με to ± 23.1 με and the relative error decreases from ± 5.0% to ± 2.9% in single-slope assisted system based-on gain switch modulation. In addition, a dual-slope assisted method is inspired to eliminate the detrimental effect caused by the intrinsic power fluctuations of chaotic laser. A verification experiment is pre-conducted that the dynamic strain could be correctly interrogated although a wide range pump power variation has been manually applied. The measurement accuracy is ultimately enhanced to ± 8.1 με and the relative error is ± 1% correspondingly, implying a higher stability. The dynamic range of this proposed system is retained at 800 με, which is approximately 5 times as large as the dynamic range of the traditional dual-slope assisted configurations. The 4-cm spatial resolution along 30-m FUT is also investigated and consistent with the result obtained previously. A larger measurement range and a higher vibration frequency would be further explored by using the multi-slope assisted method and piezoelectric ceramic oscillator respectively. The superior slope-assisted chaotic Brillouin optical correlation-domain analysis will provide a new solution for the accurate positioning and real-time monitoring of dynamic parameters in modern industry.

Bi-layer metasurface based on Huygens' principle for high gain antenna applications.

A planar isotropic unit cell based on Huygens' principle is presented for achieving transmission phase control. By tailoring overlapping electric and magnetic resonances with geometry of the proposed unit cell, the transmission phase ranging from 0 - 2π is achieved with high transmittance. The proposed unit cell is then employed to design a metasurface lens with center frequency at 9.3 GHz and a square shaped patch antenna is placed at the focal point of the designed lens to perform conversion from spherical wave front of the source antenna to planar wave front. The designed lens antenna is capable to realize pencil beam radiation pattern with a gain of 19.6 dB and side lobe levels less than -15 dB in simulation. To experimentally verify the proposed design, a prototype of the metasurface lens is fabricated and measured. The measurement results well validate the proposed design and its enhanced performance.

Non-metallic and angular-insensitive metasurface transmissive long-pass filter in the visible and near-infrared regions

In this Letter, we report on a non-metallic and angular-insensitive transmissive optical long-pass filter in the visible and near-infrared regions, which uses two sets of dielectric nanopillars grown on S i O 2 substrate with M g F 2 on the top. Coupled Mie resonances are generated from the two sets of dielectric nanopillars with different sizes so that high reflection and absorption are realized to steeply cut off the transmission in shorter wavelengths and to ensure a high transmission in longer wavelengths. A polarization-independent and wide-angular-insensitive (up to 60°) cutoff effect is realized within a surface layer that is only 399 nm thick. Double-beam ultraviolet interference lithography and sputter coating depositions are designed to efficiently fabricate the proposed metasurface with a multi-set of sub-nanostructures. Experimental results demonstrate that high isolation with an extinction ratio &gt; 16.53 d B (19.54 dB in simulation) and steep cutoff with a cutoff slope &gt; 0.013 n m − 1 ( 0.022 n m − 1 in simulation) in transmission can be achieved. The demonstrated device suggests an efficient way of designing and fabricating angular-insensitive optical filters with metasurfaces, which is of importance in applications such as the liquid crystal display, optical communication, and sensors.

Ridge Gap Waveguide Based Liquid Crystal Phase Shifter

In this paper, the gap waveguide technology is examined for packaging liquid crystal (LC) in tunable microwave devices. For this purpose, a line based passive phase shifter is designed and implemented in a ridge gap waveguide (RGW) topology and filled with LC serving as functional material. The inherent direct current (DC) decoupling property of gap waveguides is used to utilize the waveguide surroundings as biasing electrodes for tuning the LC. The bed of nails structure of the RGW exhibits an E-field suppression of 76 dB in simulation, forming a completely shielded device. The phase shifter shows a maximum figure of merit (FoM) of 70 °/dB from 20 GHz to 30 GHz with a differential phase shift of 387° at 25 GHz. The insertion loss ranges from 3.5 dB to 5.5 dB depending on the applied biasing voltage of 0 V to 60 V.

A High-Sensitivity Resonant Tangential E-Probe With Loaded Improved Dipole and Embedded Integrated Balun

In this paper, a high-sensitivity resonant probe for capturing tangential $E$ -field component is fabricated on a four-layer printed circuit board. The resonant probe consists of an improved dipole employed to further enhance sensitivity, a resonator made up of open- and short-circuit stubs achieving specific resonance, and an integrated Marchand balun used to transform the differential-mode voltage to the single-end output and match the instrument port impedance match. Compared with the referenced broadband probe, the relative sensitivity of the proposed resonant probe in terms of $\vert S_{12}\vert $ is enhanced by 13.21 and 14.82 dB for simulation and measurement, respectively. The absolute sensitivity in terms of the noise-equivalent field strength (NEFS) is 26.4 ${\mathrm{ dB}} \mu {\mathrm{ V}} ({\mathrm{ Hz}})^{1/2} $ . The measurements of the passive circuits (microstrip lines and coupled lines) and active circuit module are conducted to validate the resonant probe.

One-Dimensional Beam Scanning Transmitarray Lens Antenna Fed by Microstrip Linear Array

This paper proposed a one-dimensional beam scanning transmitarray lens antenna fed by a microstrip linear array antenna which owns a wide pattern in the plane orthogonal to the array axis and a narrow pattern in the plane that includes the array axis. The design principle of transmitarray lens aims to modulate a fan beam into a pencil beam by compensating phase shift of the linear array on the plane orthogonal to the array axis at X band. First, the Rotman lens feed network is used to implement nearly ±40° one-dimensional beam scanning for the linear array with 1 × 8 microstrip antenna elements. Then, a lowprofile transmitted element with only one-layer of the substrate is utilized to design the new transmitarray lens, which can reduce fabrication expense and difficulties. After adding the transmitarray lens, maximum gain increments of 7.81 and 7.65 dB in simulation and measurement can be obtained in quasi-boresight directions, and gain increment could be obtained within ±25° beam scanning range. Besides, the fan beams of the original linear array are smoothly transformed into pencil beams.