Shift In Operating Frequency Research Articles

The Impact of Bending on Radiation Characteristics of Polymer-Based Flexible Antennas for General IoT Applications

Flexible wearable wireless devices have found practical uses as their cost has fallen and Internet of Things applications have gained further acceptance. These devices are gaining further use and acceptance in the consumer and wearable space for applications such as logistical tracking and maintaining sensor information, including temperature, humidity, and location. In such applications, antennas are exposed to bending and crumbling. Therefore, flexible substrate antennas for use with polymer-based flexible devices are an important area of research that needs to be addressed. In this study, the bending capabilities of flexible polymer substrate antennas for general IoT applications were practically analyzed by fabricating flexible antennas on Polyethylene Terephthalate (PET), Polytetrafluoroethylene (PTFE) Teflon, and Polyvinylchloride (PVC) substrates operating at 2.45, 4.45, and 7.25 GHz frequencies. The basic premise was to investigate the flexibility and bending ability of polymer materials, and their tendency to withstand deformation. In the current paper, we start by providing an equivalent model for the flexible microstrip patch antenna under bent conditions, followed by outlining the process of designing flexible antennas on polymer substrates. Finally, the fabricated flexible antennas were tested in an anechoic chamber for various radiation characteristics such as reflection coefficients, operating frequency shifts, and impedance mismatch with the transmission line, under bending conditions up to 7 mm. The practical outcomes were then compared with our recent investigation on flexible polymer substrate antennas for wearable applications. This study provides a means to select a suitable polymer substrate for future wearable sensors and antennas with high bendability.

Investigation of methanol contaminated local spirit using metamaterial based transmission line sensor

A metamaterial-based transmission line sensor was designed to determine the amount of methanol in methanol-contaminated local spirit samples both numerically and experimentally. The proposed sensor consists of a square split-ring resonator and a transmission line. The dielectric constants of four different types of branded local spirit samples were measured. Electric field distribution has been given when the sample holder was filled with branded local spirit. Then the results were compared to show that they have almost the same characteristics. After different percentages of methanol were added to the chosen branded local spirit samples their dielectric characteristics were observed. Numerical and experimental sensing studies were conducted in these methanol-branded local spirit mixtures. As the methanol content increases in the local spirit samples, the operating frequency shifts linearly. The proposed sensor has 150 MHz bandwith and is capable of determining the level of methanol content in the branded local spirit sample.

Ohmic loss analysis for coaxial cavities of high-power high-frequency gyrotrons

Coaxial cavities are the main interaction structures of high-power high-frequency gyrotrons at present. With the increase of operating frequency and output power, ohmic loss becomes to be a vital issue needed to be analyzed compulsorily for coaxial-cavity gyrotron. It would lead to operating frequency shift and efficiency decline. In addition, the long pulse operation would be deteriorated to a large extent as a consequence of rather severe ohmic losses. Therefore, it is of great meaning to analyze the ohmic losses of coaxial cavity more accurately. In this paper, a new method is introduced to analyze the influence of the ohmic losses on coaxial cavities and TE34,11 mode operating at 170 GHz is taken as an example to compare this method with other two methods. The results show that this method can be used to analyze the coaxial cavity with higher accuracy and fewer restrictions.

Development of frequency-tunable multiple-band terahertz absorber based on control of polarization angles.

Controlling and tuning the spectral absorption response of metamaterial absorbers fabricated by arranging a set of resonators in a regular array is challenging. Polarization tunable multi-band terahertz resonant absorbers were developed using anisotropic microstructure arrays. The unit cell consisted of four pairs of H-shaped resonators of different sizes and a metallic ground plane separated by a dielectric layer. Discrete operating frequency shifts and dynamic amplitude tuning were observed by changing the polarization angle. The effect of the polarization angle on the absorption amplitude was evaluated. This work provides a concise approach to realize tunable absorption characteristics, which can be applied in sensors, detectors, and switches.

High power folded waveguide traveling wave tube based on variable-width technology

Variable-width technology applied to the folded waveguide traveling wave tube (FW-TWT) is proposed in this paper to suppress the lower band-edge oscillation and to expand the operating bandwidth when the operating frequency shifts toward the lower band for obtaining larger output power. Changes in the width of the slow wave structure (SWS) determine the variation of the lower-cutoff-frequency (LCF), which makes the LCF's distribution a frequency range rather than a specific frequency-point. The lower band-edge oscillation will not be focused on a special position but distributed in a frequency-band range in which multiple oscillation modes compete with each other near the LCF. The lower band-edge oscillation can be suppressed by mode competition to some extent. In addition, the width variation of SWS also results in the phase-velocity variation, and thus, the operating bandwidth of FW-TWT can be further improved by the optimized design of variable-width-SWS parameters. Beam-wave interaction simulations predicted that power and bandwidth improvements have been achieved without the lower band-edge oscillation. Meanwhile, four solutions are given for further certifying the effectiveness of the variable-width method in lower band-edge oscillation suppression and bandwidth widening. An output power level of over 350 W in a frequency range of 85–90 GHz (5 GHz) is obtained, with a maximum power of ∼648 W and an electron efficiency of ∼12.1% at 88 GHz with a beam current of 260 mA and a beam voltage of 20.5 kV.

High‐power DC–DC converter utilising Scott transformer connection

To obtain a resilient and flexible DC grid, reliable means for interfacing its parts operating under different voltage levels must be ensured. This paper proposes bidirectional, isolated, DC-DC converter designed to connect either high/medium voltage bipolar DC grid or two separate high/medium voltage DC grids with another DC grid of similar or different voltage level. In order to achieve galvanic separation among converter stages, while providing redundancy in case of the converter parts malfunction or a DC feeder loss, Scott transformer connection is employed. So far, Scott transformer connection has mostly been used in the railway applications, implying low-frequency operation, in order to obtain two single-phase voltages from a symmetrical three-phase grid. However, its use in the field of the DC-DC conversion has never been analysed in the literature. Further, this paper emphasises operating frequency shift towards the medium frequency range, following the trend of the solid-state transformers which have drawn the attention of both academia and industry worldwide. To control the converter power flow, phase shift control principles are adopted. Consequently, control simplicity is retained, while achieving system complexity reduction. At last, in order to evaluate proposed converter performance, simulation results of a 40 kV/1.5 kV, 10 MW converter are presented, illustrating excellent operating performances.

A Mie resonant antenna with high sensitivity for force and strain measurement

We demonstrate the experimental and simulated performances of a Mie resonant antenna for force sensing with high sensitivity for compressive force and strain measurements inside soft materials. The proposed sensor is compatible with biological specimens and has small dimensions. It comprises a pair of dielectric cubes and an elastic layer of silicone rubber. The applied force is determined by measuring the redshift of the operating frequency when a mechanical load applied. Both simulated and experimental results demonstrate that the relationship between the frequency shift of the sensor and the applied compressive load could be fitted well using a quadratic equation with a maximum fitting error less than 17%, which enables highly sensitive telemetric force measurements to be performed inside structures by observing the operating frequency shift. The proposed design provides a simple and low-cost approach to realizing highly-efficient telemetric measurement inside soft materials such as biological tissues.

Demonstration of a Three-dimensional Negative Index Medium Operated at Multiple-angle Incidences by Monolithic Metallic Hemispherical Shells

We design and construct a three-dimensional (3D) negative index medium (NIM) composed of gold hemispherical shells to supplant an integration of a split-ring resonator and a discrete plasmonic wire for both negative permeability and permittivity at THz gap. With the proposed highly symmetric gold hemispherical shells, the negative index is preserved at multiple incident angles ranging from 0° to 85° for both TE and TM waves, which is further evidenced by negative phase flows in animated field distributions and outweighs conventional fishnet structures with operating frequency shifts when varying incident angles. Finally, the fabrication of the gold hemispherical shells is facilitated via standard UV lithographic and isotropic wet etching processes and characterized by μ-FTIR. The measurement results agree the simulated ones very well.

Transparent all-dielectric gradient index waveplates with compact profiles

Purely dielectric waveplates overcome problems typically associated with metals, e.g., corrosion. However, they are often bulky and/or lossy, substantially reducing their applicability. As the operating frequency shifts towards lower frequencies where compactness is a sought after quality, these problems become even more severe. In this letter, we theoretically demonstrate how to combine axially varying gradient index materials with form birefringence to realize nearly transparent and compact dielectric waveplates. The waveplate is subsequently studied considering a discrete distribution of indexes of refraction. Our results indicate that the number of discretization levels required to perform as the continuous gradient index case is small, which would simplify significantly the fabrication process. As an example, a 0.65λ-thick quarterplate with less than 0.1 dB insertion loss at ∼34 GHz is designed and compared with full-wave simulations, proving an excellent agreement.

Engineering spectrum and dispersion with filters for high-sensitivity radio frequency detections

We demonstrate that engineering spectrum and dispersion with filters are an effective approach to boost sensor sensitivities for various radio-frequency (RF) sensing applications. A low-pass filter with a ∼2 GHz cutoff frequency and a band-pass filter with a ∼3 GHz center frequency are designed and incorporated into an interferometer to achieve ultra-high sensitivity RF detections. Compared with coplanar waveguides, the filters have up to 10-times longer group delays and 9-times stronger localized RF E-fields. Thus, the interactions between RF fields and material-under-test, which is a slab of polydimethylsiloxane in this work, are significantly enhanced. The interferometer sensitivities are boosted by up to 11 times for operating frequency shifts and 25 dB for magnitude change at frequencies up to 12 GHz.

Ferrite film growth on semiconductor substrates towards microwave and millimeter wave integrated circuits

It is widely recognized that as electronic systems’ operating frequency shifts to microwave and millimeter wave bands, the integration of ferrite passive devices with semiconductor solid state active devices holds significant advantages in improved miniaturization, bandwidth, speed, power and production costs, among others. Traditionally, ferrites have been employed in discrete bulk form, despite attempts to integrate ferrite as films within microwave integrated circuits. Technical barriers remain centric to the incompatibility between ferrite and semiconductor materials and their processing protocols. In this review, we present past and present efforts at ferrite integration with semiconductor platforms with the aim to identify the most promising paths to realizing the complete integration of on-chip ferrite and semiconductor devices, assemblies and systems.

Smart Switch Metamaterials for Multiband Radio Frequency Antennas

We investigate metal–matrix composite metamaterials with embedded electrical switches made of shape memory nickel–titanium (Ni–Ti) for use in broadband radio frequency (RF) antennas. Experiments show that a Ni–Ti ribbon can form an electrical contact that opens and closes depending on the Ni–Ti phase being austenite or martensite. Finite element modeling of thermal gradients illustrates the phase change within the ribbon. Ultrasonic additive manufacturing (UAM), a solid-state additive manufacturing process, was utilized for embedding a Ni–Ti switch in an aluminum matrix. The aluminum matrix must have structural-grade strength for use in load-carrying antennas; thus, mechanical testing was conducted to quantify the longitudinal tensile, transverse tensile, and shear strength of the UAM matrix. Reconfiguration using a Ni–Ti switch was proven using a shape memory switch on a monopole RF antenna producing an operating frequency shift from 270 to 185 MHz when the switch is connected. A planar microstrip line was used to demonstrate signal transmission and reflection efficiency in a smaller, second switch. Transmission tests yielded less than −10 dB signal reflection proving the feasibility of reconfigurable planar antenna arrays using smart switches.

Developing a nanotube-based electromechanical-device for measuring angular velocity

We propose an angular-velocimeter with a carbon nanotube resonator for sensing the angular velocity of a rotating body. When centrifugal force exerted by the rotation of the system causes an elongation of the carbon nanotube resonator due to the centrifugal force, the frequency spectra of centrifugal force is dependent on the angular velocity of the rotating plate, and feedback sensing is then achieved via operating frequency shift. Such a nanoelectromechanical device is investigated via molecular dynamics simulations and the classical continuum theory. The model of the classical continuum theory is in good agreement with the results obtained from the classical molecular dynamics simulations.

α-SiC nanoscale transit-time diodes: performance of the photo-irradiated terahertz sources at elevated temperature

The effects of elevated junction temperature on the terahertz (THz) frequency characteristics of α-(hexagonal, 4H and 6H) silicon carbide (SiC) based double-drift region (DDR, p++ p n n++ type) impact ionization avalanche transit-time (IMPATT) devices are studied and compared for the first time through simulation experiments. This study reveals that at 300 K < T < 600 K, a 4H-SiC IMPATT diode may yield 3.5 W of output power (efficiency (η) ∼ 8.6%) at 1.3 THz, while its 6H-SiC counterpart can deliver 3 W of output power (η = 6.3%) at 1.2 THz. It is interesting to observe that at elevated temperature, the performance of a 6H-SiC IMPATT diode degrades more in comparison with its 4H-SiC counterpart. These comparative analyses reveal the superiority of 4H-SiC diodes over their 6H-SiC counterparts, and thus establish the potential of the former as a high-power THz IMPATT oscillator even in harsh environments. Mobile space charge effects and the effect of positive series resistance on the high-temperature performance of the THz devices are also simulated, and it is found that series resistance reduces the output power level of the diodes by at least 15.0%. Moreover, the effects of increased junction temperature on the photo-sensitivity of top mounted (TM) and flip chip (FC) α-SiC IMPATTs are also investigated using a modified simulation technique. The device operating frequencies, under TM illumination configuration, shifts upward by at least 40.0 GHz, whereas the operating frequency shifts upward by at least 100.0 GHz under FC illumination configuration. The simulation results and the proposed experimental methodology presented here may be used for realizing optically controlled α-SiC transit-time devices for application in THz communication.

Metamaterial based telemetric strain sensing in different materials

We present telemetric sensing of surface strains on different industrial materials using split-ring-resonator based metamaterials. For wireless strain sensing, we utilize metamaterial array architectures for high sensitivity and low nonlinearity-errors in strain sensing. In this work, telemetric strain measurements in three test materials of cast polyamide, derlin and polyamide are performed by observing operating frequency shift under mechanical deformation and these data are compared with commercially-available wired strain gauges. We demonstrate that hard material (cast polyamide) showed low slope in frequency shift vs. applied load (corresponding to high Young's modulus), while soft material (polyamide) exhibited high slope (low Young's modulus).

Operating frequency tracking of single phase driving type piezoelectric motors

We developed a multi (or mixed) mode excitation type piezoelectric motor that uses a rectangular bar type piezoelectric multilayer stator as the vibrating element. The stator has a first longitudinal vibration mode in a direction of longest length and second flexural mode in a direction of thickness. During operation of the motor, these two modes are coupled so at the two end surfaces, elliptical motions are generated. The elliptical motion at one end of the stator is transferred to a moving element through frictional contact. This paper introduces structure and operating principal of the piezoelectric multilayer stator. An equivalent circuitry model for the free stator and a frequency tracking method to operate the motor at its optimum operating frequency are also proposed. The frequency tracking method not only finds the best operating frequency, it also tracks the frequency variations from sample to sample and operating frequency shift due to temperature change.

Non-Parametric Identification of Nonlinear Electromagnetic and Squeeze-Film Devices, Application for On-Line Monitoring

Coupled electromechanical systems are often treated near an operating point ignoring the change of natural frequencies due to external loading or environmental variations. This paper deals with systems that are efficient energy transformers converting electrical energy into mechanical work by keeping the system in high admittance state (in resonance). The first difficulty one encounters is the identification of the non-linear manner by which the optimal operating frequency shifts with the change of the operating conditions. In this paper we present two approaches: (1) an off-line characterization method that is suitable for non-linear vibration system identification that uses the Hilbert transform in time domain. The objective, in this part, was to propose a methodology to identify how a natural frequency changes with the amplitude and to detect various types of non-linearity from measured response data. (2) an adaptive tracking algorithm that uses a parametric model of the response in the vicinity of the operating frequency combined with an optimization strategy. The proposed identification methodology concentrates on the signal envelope and the instantaneous frequency. It enables us to estimate non-linear instantaneous dynamic parameters of the system, including its non-symmetric elastic force static characteristics. With the Hilbert based approach, a precise calibration of a nonlinear device can be performed. This calibration serves for an initial setting of the operating point allowing us to apply a more accurate local tracking approach with a combination of an extended Kalman filter with a nonlinear optimization method. Modelling examples of vibrations of non-linear non-symmetric elastic force characteristics are included. The obtained results of vibration analysis reconstruct the initial “soft᾿ non-symmetric elastic force static characteristics of the system. A tracking algorithm is outlined and some simulation results with a piezoelectric-driven squeeze-film levitation system are shown.