Desired Frequency Research Articles

Design of a MIMO Antenna with High Gain and Enhanced Isolation for WLAN Applications

A multi-input multi-output (MIMO) antenna for wireless local area network (WLAN) applications operating in 2.4 GHz and 5.8 GHz frequency bands is proposed in this paper. The proposed dual-band MIMO antenna is composed of two symmetrical radiation elements, and the isolation performance is improved by adopting parasitic elements and a defective ground plane. The measured reflection coefficients are less than −10 dB in the bandwidth range of 2.12–2.8 GHz and 4.95–6.65 GHz, respectively. The measurements show excellent isolation of −21 dB and −15 dB in both desired frequency bands, respectively. The total peak gain is greater than 4.8 dBi. The calculated envelope correlation coefficients (ECC), based on the measured S-parameters, are smaller than 0.01 and 0.024 in the lower and higher frequency bands, respectively. The dimension of the presented antenna occupies 50 × 40 × 1.59 mm3. It is suitable for IEEE 802.11 a/b/g/n (2.4–2.4835 GHz, 5.15–5.35 GHz and 5.725–5.85 GHz) WLAN applications.

A Method to Minimize the Effort for Damper–Blade Matching Demonstrated on Two Blade Sizes

A method called PCR (Platform Centered Reduction) is designed to more effectively perform complex iterative and nonlinear calculations required for the dynamic response of turbine blades damped by dry friction contacts between rigid dampers and airfoil-to-neck platform. The key feature of PCR is to represent all nonlinear forces on the blade platform by means of only six degrees of freedom at a point located within the platform volume, regardless of the number of damper–platform contact elements. Despite reducing the effort and computational time by more than one order of magnitude, the method proves to be fully accurate by a check against the corresponding nonlinear Finite Elements (FE) calculation. It is also shown that the limit exciting force, indicating the upper capability to dampen vibrations, can be calculated with a simple linear modal analysis. In order to search for the best blade–damper match, the preferred graph represents relevant bending stresses on the airfoil against excitation forces. A detailed application of the method concerns two significantly different blade sizes, by varying parameters such as neck length and damper centrifugal force. Finally, it is emphasized that a final check by a complete FE analysis is still possible as a purely linear solution fed by sets of contact forces previously determined through the PCR at any desired frequency and excitation.

Self-excited oscillations in an inverted cart–pendulum based on the two-relay approach

Solving the orbital stabilization of a class of underactuated systems near its open-loop unstable equilibrium point is a challenging task but useful in repetitive tasks. This paper addresses the control problem of an inverted cart–pendulum’s motion driven by a two-relay controller. This controller is tuned to set the desired amplitude and frequency using the locus of the perturbed relay system, which is a frequency-domain method. We solved the periodic motion of the pendulum occurring in its open-loop unstable equilibrium point. The experimental results showed that the proposed two-relay controller forced the pendulum into a periodic motion around the upright position.

A Compact Diplexer Using Coupled π-CRLH Zeroth Resonators

ABSTRACT This paper presents a new diplexer design of a new-coupled composite right/left-handed (CRLH) resonator to serve the LTE applications. The realization of the diplexer is designed as coupled two zeroth order π-CRLH resonators to represent with zero electrical length and hence attaining a significant size reduction. The filters are designed to achieve a desired frequency bandwidth of 4% ∼16.7 Q-factor and ∼0.066 coupling coefficient at a centre frequency of 2.1 and 2.6 GHz with transmission zeros. The diplexer exhibits a rejection level of 15–20 dB while maintaining insertion loss of 1 dB for the Tx and Rx bands. The circuit design concepts are verified using equivalent circuit simulations, full electromagnetic simulations and experimental measurements. In conclusion, a good agreement is perceived between the measured and simulated data with size compactness of 30 × 60 mm2.

Frequency Control of a Resonant Radio Absorber with a Free Space

Abstract—Numerical calculations of the matching of a resonant radio absorber (RA) have confirmed that the ideal matching of such an RA with free space can be realized using practically any dielectrics with losses at any desired frequency. The conditions are considered that provide the widest matching band of the RA, and it is shown that the ratio of the bandwidth to the RA thickness (bandwidth to thickness ratio) is about 3.7, i.e., more than for the usual single-layer Dallenbach RA (about 3.2).

Aortic Valve Status Detection for Heart Failure Patient with LVAD Using Deep Neural Networks

Purpose Continuous flow left ventricular assist devices (LVADs) can change aortic valve (AoV) biomechanics, which can result in reduced or lack of AoV opening. This can increase the risk of thrombotic events, gastrointestinal bleeding and denovo aortic incompetence. Therefore, detection of AoV opening and adjusting pump speed corresponding to the AoV status play a vital role for heart failure (HF) patients with LVADs. Although current assessment of AoV rely on supine resting echocardiography, this method cannot be applied outside of hospital. This study presents a deep neural network model for noninvasive detection of AoV opening for Heartware patients in different patient states. Methods 18 patients supported by a continuous flow HeartWare HVAD underwent transthoracic echocardiography for parasternal M‐mode images of the AoV. A continuous recording of 2 minutes at rest, immediately following by 1-minute Valsalva maneuver and then followed by leg‐raising exercise for 1-minute. A deep neural network model was trained and validated through 10-fold cross validation to detect AoV status based on the 200 samples (four seconds) of pump flow. The developed model performance was assessed using several performance metrics such as accuracy, sensitivity, specificity and receiver operating characteristic (ROC) curve area (AUC). Results The deep neural networks model was able to detect AoV opening/closing accurately across 10-fold cross validation based on the pump flow. The results show the accuracy of 86.59 %, sensitivity 81.39 %, specificity of 89.55 % and AUC of 0.928. However, including more patients on training and validation process of deep neural networks model can improve these performance metrics. Conclusion The deep neural network model would be useful for real-time detection of AoV opening which can be employed to adjust pump speed in HF patients to promote at least intermittent AV opening. Implementation of the proposed AoV detection in real-time mode could be integrated into a “smart pump” control system to automatically adjust LVADs speed to ensure a desired frequency of AV opening.

Robust H∞ Loop Shaping Controller Synthesis for SISO Systems by Complex Modular Functions

In this paper, a loop shaping controller design methodology for single input and a single output (SISO) system is proposed. The theoretical background for this approach is based on complex elliptic functions which allow a flexible design of a SISO controller considering that elliptic functions have a double periodicity. The gain and phase margins of the closed-loop system can be selected appropriately with this new loop shaping design procedure. The loop shaping design methodology consists of implementing suitable filters to obtain a desired frequency response of the closed-loop system by selecting appropriate poles and zeros by the Abel theorem that are fundamental in the theory of the elliptic functions. The elliptic function properties are implemented to facilitate the loop shaping controller design along with their fundamental background and contributions from the complex analysis that are very useful in the automatic control field. Finally, apart from the filter design, a PID controller loop shaping synthesis is proposed implementing a similar design procedure as the first part of this study.

Automated wide-ranged finely tunable microwave cavity for narrowband phase noise filtering.

Narrowband microwave filters have wide ranging applications, including the reduction in phase noise of microwave sources within a given frequency band. The prospect of developing an automated filter that tunes itself to an arbitrary desired frequency at maximum extinction promises many experimental advantages such as an enhanced efficiency in performing fine frequency detuning scans and saving time and effort as compared to manual tuning. We design, construct, and program such an automated system and present its hardware and software for reproducibility. It consists of a cylindrical cavity filter and two motors, which change the cavity length and the coupling strength of the microwave field into the cavity, respectively. By measuring the cavity response, an algorithm implemented in Python optimizes these two parameters to achieve the tuning of the filter cavity to the desired frequency with a precision of around 20 kHz, which is significantly better than the cavity linewidth (∼1 MHz). We also demonstrate the suppression of phase noise at the desired frequency by more than 10 dB.

Wide-band switching-mode power amplifier using varactor-based reconfigurable output matching network

Switch Mode Power Amplifiers (SMPAs) have attracted significant attention due to their high efficiency, thus, designing a reconfigurable SMPA, which can operate efficiently in a wide frequency range, is of great merit. Here, a reconfigurable SMPA with excellent performance was designed. A compact reconfigurable Band-Pass Filter (BPF) network was proposed for the Output Matching Network (OMN) which resulted in optimum matching at operating frequencies for maximum power, Power Added Efficiency (PAE) and gain. A wide-band BPF with microstrip lines was used in the OMN design. It was selected using a set of varactor diodes to meet a desired frequency band. The reconfigurable BPF was connected to the transistor drain using four microstrip lines (as an impedance matching). Through changing the reverse bias voltage of the varactor diodes, the central frequency of BPF can shift between 850 MHz and 1.8 GHz of the bandwidth. The ability to select the desired frequency in PA using a BPF was shown by two modes, lumped and distributed elements. The proposed wideband PA in the frequency band of 850 MHz-1.8 GHz was designed using a GaN CGH40010F. Simulation results showed an 11.6 – 14.5 dB gain with 59–83% Drain Efficiency (DE), and an output power of 41.15 – 41.9 dBm across the frequency band.

Choosing the frequency of volatility components within the Double Asymmetric GARCH–MIDAS–X model

The Double Asymmetric GARCH–MIDAS (DAGM) model has the advantage of modelling volatility as the product of two components: a slow–moving term involving variables sampled at lower frequencies and a short–run part, each with an asymmetric behavior in volatility dynamics. Such a model is extended in three directions: first, by including a market volatility index as a daily lagged variable in the short–run component (the so-called “–X” term); second, by adding the same variable in the long–run component as variations of data aggregated at any desired frequency; third, by proposing a data-driven method to find the optimal number of lags to be included in the positive and negative parts of the long–run component. The resulting model, labelled as DAGM–X–2K, is extensively evaluated under several alternative configurations, producing satisfactory evidence when applied to the S&P 500 and NASDAQ indices. The out–of–sample results show that the “–X” addition significantly improves the performance, making the proposed DAGM–X–2K model enter the Model Confidence Set, even for large forecasting horizons (for 1 to 60 days).

Infinity Shell Shaped MIMO Antenna Array for mm-Wave 5G Applications

In this paper, a novel single layer Multiple Input–Multiple Output (MIMO) antenna for Fifth-Generation (5G) 28 GHz frequency band applications is proposed and investigated. The proposed MIMO antenna operates in the Ka-band, which is the most desirable frequency band for 5G mm-wave communication. The dielectric material is a Rogers-5880 with a relative permittivity, thickness and loss tangent of 2.2, 0.787 mm and 0.0009, respectively, in the proposed antenna design. The proposed MIMO configuration antenna element consists of triplet circular shaped rings surrounded by an infinity-shaped shell. The simulated gain achieved by the proposed design is 6.1 dBi, while the measured gain is 5.5 dBi. Furthermore, the measured and simulated antenna efficiency is 90% and 92%, respectively. One of the MIMO performance metrics—i.e., the Envelope Correlation Coefficient (ECC)—is also analyzed and found to be less than 0.16 for the entire operating bandwidth. The proposed MIMO design operates efficiently with a low ECC, better efficiency and a satisfactory gain, showing that the proposed design is a potential candidate for mm-wave communication.

Performance Analysis of Slotted Monopole Antenna with Pin Diodes for Wireless Applications

This paper deals with Performance Analysis of slotted monopole antenna with pin diodes for wireless applications. The antenna is designed on a 1.6 mm thick FR4 substrate with the dielectric constant ( ) of 4.4. Antenna is electrically reconfigured incorporating pin diodes as switching elements to tune desired frequency and to achieve frequency reconfigurability. The antenna parameters like return loss, bandwidth, radiation pattern, directivity and gain are simulated and characterized in this paper. The proposed antenna covers resonating frequencies ranging from the 3.7-13.4GHz. The proposed microstrip monopole frequency reconfigurable antenna can be considered as electrically small, low weight, low profile. The design and analysis of the proposed antenna is accomplished through HFSS EM simulator.

Anchor Loss Reduction of Lamb Wave Resonator by Pillar-Based Phononic Crystal.

Energy leakage via anchors in substrate plates impairs the quality factor (Q) in microelectromechanical system (MEMS) resonators. Most phononic crystals (PnCs) require complicated fabrication conditions and have difficulty generating a narrow bandgap at high frequency. This paper demonstrates a pillar-based PnC slab with broad bandgaps in the ultra high frequency (UHF) range. Due to Bragg interference and local resonances, the proposed PnC structure creates notably wide bandgaps and shows great advantages in the high frequency, large electromechanical coupling coefficient () thin film aluminum nitride (AlN) lamb wave resonator (LWR). The dispersion relations and the transmission loss of the PnC structure are presented. To optimize the bandgap, the influence of the material mechanical properties, lattice type, pillar height and pillar radius are explored. These parameters are also available to adjust the center frequency of the bandgap to meet the desirable operating frequency. Resonators with uniform beam anchors and PnC slab anchors are characterized. The results illustrate that the Q of the resonator improves from 1551 to 2384, and the mechanical energy leakage via the anchors is significantly decreased using the proposed PnC slab anchors. Moreover, employment of the PNC slab anchors has little influence on resonant frequency and induces no spurious modes. Pillar-based PnCs are promising in suppressing the anchor loss and further improving the Q of the resonators.

A novel three‐phase buck‐boost inverter controlled by an open‐loop assisted closed‐loop hybrid control method

SummaryA novel general purpose three‐phase buck‐boost inverter without need of additional filtering units is presented in this study. The proposed inverter topology is built with moderate numbers of elements in terms of the operation advantages and qualities. The buck‐boost converter‐based structure provides obtaining wide‐range output voltage amplitudes lower or higher than the input voltages. A novel hybrid control method that is open‐loop assisted closed‐loop control is proposed for the inverter operation to improve the response performance on various input and output operation conditions. The wye‐connected modular structure of the proposed inverter topology also enables unbalanced three‐phase operation and single‐phase operation for each phase with independent phase voltages and frequencies. An experimental laboratory setup is built for the proposed three‐phase inverter for 0–50 Hz, 0–100 Vp, and 1.5 kW operation values for real‐time application tests. Simulation tests are also applied for the inverter. The obtained results for both the simulation and the experimental tests show that the presented inverter with the proposed hybrid control method is capable of operating in balanced/unbalanced three‐phase and independent single‐phase modes while producing close to sine wave output voltages under 5% THD levels with wide range desired amplitudes and frequencies on different operating points.

28nm FDSOI Ultra Low Power 1.5–2.0 GHz Factorial-DLL Frequency Synthesizer

This brief presents the design of an ultra-low-power frequency synthesizer based on a feedback loop composed of an improved version of the Factorial Delay-Locked Loop (F-DLL). Its output frequency is controlled by a set of current-starved delay units tuned by a standard DLL feedback loop and a set of logic circuits to generate an RF output frequency proportional to the reference. The objective of this circuit is to achieve a power consumption in the micro-watt range to generate the desired output frequency proportional to the reference frequency between 1.5 and 2.0 GHz, being capable of supporting a wide range of input frequencies with a low phase noise (lower than −90 dBc/Hz at 1 MHz offset) and $370~\mu \text{W}$ of power consumption. In order to ensure the locking state of the feedback loop and to reduce the phase noise, a modification of the biasing circuit for the voltage-controlled delay line (VCDL) is used to improve the linearity of the frequency response of the output using a complementary feedback loop architecture. The circuit was designed and fabricated using the 28 nm FDSOI technology from STMicroelectronics and the measurement results are presented.

A Wideband Fast Start-Up Multi-Core VCO With Auto-Frequency Control in 0.18 μm CMOS

A 2.8 – 4.6 GHz wideband multi-core VCO with a fast start-up scheme is presented in this brief. The proposed multi-core VCO uses a successive approximation register based auto frequency control (SAR-AFC) loop with the embedded 2/3 Judge to ensure the desired output frequency. To benefit a wider application, the VCO provides radio and low frequency outputs. A prototype of the multi-core VCO is implemented in 180-nm CMOS, and consumes 20 mA from a 3.3-V supply voltage with an active area of 4.8 mm2. Measured results indicate that the multi-core LC VCO is capable of providing the phase noise of −120 dBc/Hz at 1-MHz offset from 4.6 GHz frequency. One of the attractive merits from the proposed LC VCO is that the response time could be saved 45% over the traditional VCO architecture.

Texture Analysis using wavelet Transform

In this research application of wavelet based multiscale image analysis methods for texture analysis has been highlighted. These methods are based on multiresolution properties of the two-dimensional wavelet transform, which is used to extract the features needed to discriminate and differentiate various textures more accurately then existing methods, we also took into account the texture model, the noise distribution, and the inter-dependence of the texture features which further help in discriminating factor. Multiresolution approach is nothing but a modified wavelet transform called the tree-structured wavelet transform or wavelet packets for texture analysis and classification. This approach is motivated by the observation that a large class of natural textures can be modeled as quasi-periodic signals whose dominant frequencies are located in the middle frequency channels. With the transform, we are able to zoom into any desired frequency channels for further decomposition and thus we could extract more texture features as compared to other methods.

Guided modes and terahertz transitions for two-dimensional Dirac fermions in a smooth double-well potential

The double-well problem for the two-dimensional Dirac equation is solved for a family of quasi-one-dimensional potentials in terms of confluent Heun functions. We demonstrate that for a double well separated by a barrier, both the energy-level splitting associated with the wave-function overlap of well states and the gap size of the avoided crossings associated with well and barrier state repulsion can be controlled via the parameters of the potential. The transitions between the two states comprising a doublet, as well as transitions across the pseudogaps are strongly allowed, highly anisotropic, and, for realistic graphene devices, can be tuned to fall within the highly desirable terahertz frequency range.

Effect of polydextrose-containing beverage on bowel habits and gastrointestinal symptoms of constipated subjects: a pilot study

Introduction: Indonesians have a low intake of dietary fibre, a key component for an increased incidence in constipation. Available data have documented the benefits of polydextrose (PDX) in healthy subjects. However, data on constipated subjects are lacking. This study aimed to investigate the effect of consuming a PDX (prebiotic) beverage on bowel habits and gastrointestinal symptoms of constipated subjects over seven days. Methods: This was a randomised, non-blinded, nonplacebo-controlled parallel design study involving 24 subjects, divided equally into two groups. Group A (active control group) consisted of 12 subjects, consuming one serving size of 6g PDX beverage. While Group B (intervention group) consisted of 12 subjects, consuming two servings of the same product, containing 12g PDX beverage. Changes in bowel habits (constipation score, stool frequency and stool consistency) and gastrointestinal symptoms (abdominal pain, bloating and flatulence) were monitored. Results: Within seven days, Group B showed 4.9% more reduction in overall constipation mean score than that of Group A. Positive improvement in gastrointestinal symptoms were reported: i.e. abdominal pain (∆M = -0.08±0.43), bloating (∆M = -0.29±0.37) and flatulence (∆M = -0.17±0.47). Majority of subjects had desirable stool frequency (87.5%, >3 defecations/week) and stool consistency (58.3%, type 4). These improvements were due to the fact that PDX provides physiological effects consistent with prebiotic fibre, which alters the gut microbiota composition during the fermentation cycle in the large intestine. Conclusion: Findings of this study suggested that daily PDX beverage consumption effectively improved bowel habits, with fewer constipated subjects reporting of gastrointestinal symptoms.

Compact Dual-Band Rectenna Based on Dual-Mode Metal-Rimmed Antenna

This paper proposes the design of a dual-band integrated rectenna. The rectenna has compact size of 0.4 × 0.3 × 0.25 cm3 and operates at 925 MHz and 2450 MHz bands. In general, the rectenna consists of two main parts, the metal-rimmed dual-band antenna used for harvesting the radio frequency (RF) signals from the environment and the rectifier circuit to convert these receiving powers to the direct current (DC). Because of the dual resonant structure of the antenna, the rectifier circuit can be optimized in terms of size and the frequency bandwidth, while the conversion efficiencies are always obtained 60% at the RF input power −2.5 dBm and −1 dBm for the lower band and the higher band, respectively. Measured results show that the metal-rimmed antenna exhibits −10 dB reflection coefficient in both desired frequency bands. Moreover, the antenna achieves 47% and 89% of total efficiency respectively at 925 MHz and 2450 MHz, which confirms that the proposed rectenna is well applicable in most of the miniaturized wireless sensor networks and IoT systems.