Effect Of Frequency Detuning Research Articles

Chaos secure communication based on free-running VCSEL system

Abstract In this paper, we propose a parallel injection chaotic system involving three free-running 
vertical-cavity surface-emitting lasers (VCSELs). First, the chaotic synchronization 
performance of the system is evaluated using the cross-correlation function. Then, we analyze 
in detail the effects of injection strength, frequency detuning, and parameter mismatch on the 
chaotic synchronization and information transmission of the system. Numerical studies 
indicate that the proposed parallel injection chaotic system based on three VCSELs can 
achieve high-quality chaotic synchronization over a wide bandwidth and a broad range of 
input parameters. Furthermore, even in the case of parameter mismatch, high-quality chaotic 
synchronization and communication can still be achieved. Additionally, with appropriate 
injection strength, the system can compensate for the efficiency reduction caused by 
parameter mismatch.

Optical injection effects in electrically pumped semiconductor nano-laser arrays

A theoretical analysis is performed on the response of electrically pumped nano-laser arrays to external optical injection. The response to both continuous wave and modulated optical injection is explored. Continuous wave injection is shown to excite several varieties of dynamical behaviour in the array elements including regular dynamics and quasi-periodic behaviour. The strength of the optical injection, the frequency detuning between the injected light and the target laser, and the magnitude of the Purcell spontaneous emission enhancement factor are shown to markedly affect the dynamics. When subject to modulated optical injection, the effects of frequency detuning and optical injection strength are the focus of attention. It is shown that the elements of the array subject to modulated optical injection exhibit oscillatory behaviour over broad regimes determined by the optical injection strength and the frequency detuning.

Применение каскадных последовательностей в инфокоммуникационных системах

The article discusses the question of direct spectrum expansion with sequences formed by cascading other sequences. The effect of sampling frequency detuning and local oscillator frequency on the possibility of receiving a noise-like signal of a given duration is analyzed. Expressions are given for the critical values of frequency detuning depending on the duration of the spreading sequence and the carrier frequency of the signal. A cascade method for generating a spreading sequence is proposed, along with transmitter and receiver circuits for its implementation. The results of modeling the circuit operation, when a differential encoder and a differential decoder are added, are presented. The economy of hardware resources when implementing the proposed scheme in comparison with a conventional matched filter, the stability of the communication system to noise, and frequency detuning are analyzed.

Theoretical investigations of population trapping phenomena in atomic four-color, three-step photoionization scheme

The four-color three-step selective photoionization process of atom is very important in laser isotope separation technology. The population trapping phenomena and their influences are studied theoretically in monochromatic and non-monochromatic laser fields based on the density matrix theory in this work. Time evolutions of the photoionization properties of the four-color, three-step process are given. The population trapping effects occur intensely in monochromatic excitation, while it gradually turns weak as the laser bandwidth increases. The effects of bandwidth, Rabi frequency, time delay, and frequency detuning on the population trapping effect are investigated in monochromatic and non-monochromatic laser fields. The effects of laser process parameters and atomic parameters on the effective selective photoionization are also discussed. The ionization probability and selectivity factors, as evaluation indexes, are difficult to improve synchronously by adjusting systematic parameters. Besides, the existence of metastable state may play a negative role when its population is low enough.

Compact hybrid EBG microstrip antenna for wearable applications

Abstract A novel strip line fed, circularly polarized (CP), annular slotted dual band antenna using hybrid electromagnetic band gap (EBG) structure for Global Positioning System (GPS) has been herein designed, analyzed, and investigated for wearable applications. Adjusting the radii of the annular slots on the radiating patch excellent circular polarized (CP) radiation and impedance matching is achieved. The design demonstrates Kapton based flexible, robust, and low-profile solution with permittivity of 3.4 to meet the requirements of wearable applications. Due to the high losses of the animal body, the electromagnetic band gap (EBG) structure is used to reduce back radiation and the effect of frequency detuning. The proposed antenna structure also enhances the front-to-back ratio (FBR) by 10 dB. This antenna with dimensions 0.56λ 0 × 0.4913λ 0 × 0.002λ 0 analyzed using a flexible Kapton substrate. Optimized hybrid EBG structure provides an excellent Specific Absorption Rate (SAR) along with all other antenna parameters, within acceptable for GPS-based wearable applications at 1.13 GHz and 1.157 GHz frequency band. Therefore the proposed antenna is a suitable candidate for GPS-based tracking and wireless body area network (WBAN) applications. The proposed antenna was also tested upon fabrication and the measured results agree with simulated results.

Multiple quantum interrogation to determine the position of an object in a serial array of ring resonators

We propose quantum interaction-free measurements to determine not only whether an object exists, but also where it is situated among possible interrogation positions. In the first configuration, the object exists at one of several possible positions, and the other positions are empty. We regard this as multiple quantum trap interrogation. In the second configuration, the object does not exist in any possible interrogation position, but other positions are occupied by objects. We refer to this as multiple quantum loophole interrogation. It is possible to determine the position of a trap or loophole with almost 100% certainty, without any real interaction between the photon and the objects. We performed a preliminary experiment using a serial array of add-drop ring resonators and confirmed that multiple trap and loophole interrogations are possible. We discuss the detuning of resonators from the critical coupling condition, the loss effects in the resonator, the frequency detuning effect of incident light, and the effect of object semitransparency on the interrogation systems.

Numerical studies of isotopic selective photoionization of ytterbium in a three-step ionization scheme

Selective photoionization of ytterbium isotope is studied numerically based on a three-step photoionization scheme, 4f146s2 1S0 (0 cm−1) → 4f146s6p 3P1 (17992.008 cm−1) → (4f136s26p) (7/2, 3/2)2 (35196.98 cm−1) → auto-ionization state (52353 cm−1) → Yb+, by the density matrix theory with the consideration of atomic hyperfine structures and magnetic sublevels. To examine the physical model, the numerical isotopic abundance of ytterbium is compared with that from mass spectroscopy experiment, showing that they are in good agreement with each other. The excitation process and ionization process of ytterbium, especially for odd isotopes, are discussed and analyzed in detail on this basis. The effects of frequency detuning, power densities, spectral bandwidths, polarization of two excitation lasers, and atomic Doppler broadening on the total ionization yield and isotopic abundance are investigated numerically and the optimal excitation conditions for 176Yb enrichment are identified semi-quantitatively.

Characteristic Study on Parallel Reservoir Computation Based on VCSEL Dynamics With Optoelectronic Feedback

We proposed a new reservoir computation (RC) structure using polarization dynamics of vertical cavity surface emitting lasers (VCSELs) with optoelectronic feedback. Santa-Fe time-series prediction and nonlinear channel equalization were used to evaluate its parallel processing capability. We numerically discussed the effects of feedback strength, injection strength, frequency detuning, injection current and scaling factors on the RC performance of the system. The results show that, the operation range of negative feedback is larger than that of positive feedback; under appropriate feedback and lager injection strengths, good RC performance can be achieved for a wider injection current; with continuous variation of feedback strength from negative to positive values, the optimized location for frequency detuning moves from positive to negative values. We also evaluated the processing rate of proposed RC structure. The related study is helpful for the design and optimization of VCSEL-based RC under optoelectronic feedback.

Enhanced prediction performance of a time-delay reservoir computing system based on a VCSEL by dual-training method.

In this paper, a new dual-training method for a time-delay reservoir computing (RC) system based on a single vertical-cavity surface-emitting laser (VCSEL) is proposed and demonstrated experimentally for the first time. The prediction performance of the RC system by using the dual-training method has been experimentally and numerically investigated. Here, the dual-training method is defined as performing a further RC based on the difference between the target value and the predicted value of the traditional single training. It is found that enhanced prediction performance of the RC system can be obtained by employing the dual-training method, compared to the traditional single training method. More specifically, the NMSE values of the RC system with the dual-training method applied can be improved to 760% compared with the single training method in experiments. Besides, the effects of injection power, bias currents, feedback strength, and frequency detuning are also considered. The proposed dual-training method is of great significance to the performance enhancement of the RC and has an important promotion effect on the application of the RC in the future.

Coherent population transfer of Rydberg atoms in a dual-microwave driven five-level configuration

We report the coherent population transfer (CPT) of Rydberg atoms with a 5S1/2-5P3/2-57D5/2-58P3/2-58S1/2 level configuration of 85Rb using a dual-microwave driven four-step excitation scheme. The electromagnetically induced transparency, Autler–Townes splitting, and CPT are experimentally observed with different energy level configurations. The effects of power and frequency detuning of microwave fields are investigated to demonstrate plentiful population dynamics. To comprehend the entire coherent mechanism, a theoretical model based on the density-matrix is proposed and numerically solved with the steady-state condition. Compared with the mono-microwave-assisted coherent process of Rydberg atoms, dual-microwave results, which are the optimal coherent transfer evolution of atom population with multiple tunable parameters, are presented in this scheme. This work lays the foundation for studying multi-level coherence effects and manufacturing multi-channel quantum sensors.

Towards durable and efficient antenna with SAR reduction analysis for on-body applications

Abstract This paper is focused on providing a viable solution to wearable antenna performance disconcertment caused by the underlying human body. Direct placement of the antenna on the body yields undesired results owing to the frequency detuning effect. The simplest possible way out is to make use of a metallic reflector. Hence, a reflector backed antenna is presented for 5.8 GHz ISM band with total lateral dimensions of 28 × 28 × 13.58 mm3. The reflector makes use of a conformal high dielectric laminate coated with a thin copper layer owing to which the assembled design achieves low SAR (Specific Absorption Rate). The prototype provides excellent results at the cost of some extra volume occupation in an off-body direction. Another AMC (Artificial Magnetic Conductor) backed technique is followed and implemented separately to have the structural compactness lacking in the former case. The antenna at hand is backed by a 2 × 2 array of AMC unit cells. The overall design dimensions are reduced. The reflector backed design achieves 8.2 dB gain, above 90% efficiency, and 99% bandwidth overlap with the primary antenna. The AMC backed design provides good spectrum coverage from 5.73 to 5.94 GHz with high gain. Free space response, on-body performance, and investigation of SAR analysis of the proposed designs substantiate effective wireless data transfer in body-centric communication.

Design of a wideband patch antenna and performance enhancement using an AMC reflector surface for on-body communication at 2.45 GHz

ABSTRACT Wireless biotelemetry enables the formation of communication link from living body to an external monitoring device. Isolation of near field electromagnetic (EM) waves from body tissue, and wide bandwidth to avoid frequency detuning in different biological environments are the important parameters of on-body antennas. In this paper, a conformal defected ground patch antenna with artificial magnetic conductor (AMC) is introduced for on-body communication. Initially, a quarter wave wide band antenna with a shorting pin is designed to operate at 2.45 GHz. It resonates effectively on body tissue but most of the near field EM radiations are absorbed by tissue. Poor radiation efficiency of 10% and high specific absorption rate (SAR) value of 7.73 W/Kg were obtained. Thus, to reduce the effect of tissue loading on antenna performance an AMC-based structure is added. Better impedance matching, high efficiency (65%) and directivity (7.3 dBi) is achieved with AMC structure. Furthermore, unidirectional radiation pattern with SAR value of 1.43W/Kg is attained. Wide bandwidth of 600 MHz on phantom enables the antenna to withstand frequency detuning effect due to body postures and movements. Antenna robustness is analysed by bending the structure at different radii along X-axis and Y-axis.

Nonlinear rotational inertial double-tuned mass damper for reducing human-induced floor vibration with frequency detuning

This study proposes a novel nonlinear rotational inertial double-tuned mass damper (NRIDTMD), which introduces a cubic stiffness element into the inerter-based passive control system RIDTMD, by exploiting the frequency insensitivity of nonlinear energy sink to overcome the frequency detuning problem in human-induced floor vibration control. Due to its nonlinear nature, the complexification-averaging technique is adopted to obtain the approximate steady-state response of the coupled floor-NRIDTMD system, and the number of the solutions and stability of the responses are discussed. Based on the genetic simulated annealing algorithm, the design parameters of the proposed NRIDTMD are optimized, and the empirical design formulation and response prediction equation are further proposed. Considering the effect of frequency detuning caused by human-structure interaction, floor stiffness degradation and mass increase, a numerical model of an experimental floor is used to verify the vibration mitigation performance of the proposed NRIDTMD, and compared with those of TMD and RIDTMD. The results reveal that the empirical formulation and prediction equation exhibit excellent accuracy and applicability, and the proposed NRIDTMD can minimize the acceleration response increment of the floor in frequency detuning, exhibiting better frequency robustness than those of conventional linear dampers.

The Flow-Structure Couplings of Fluidelastic Instability and the Effect of Frequency Detuning in Triangular Tube Bundles Subjected to a Two-Phase Flow

Abstract For decades, fluidelastic instability (FEI) has been known to cause dramatic mechanical failures in tube bundles. Therefore, it has been extensively studied to mitigate its catastrophic consequences. Most of these studies were conducted in controlled experiments where significant simplifications to the geometry and flow conditions were utilized. One of these simplifications is the assumption that all tubes have the same dynamic characteristics. However, in steam generators with U-bend tube configuration, the natural frequencies of tubes are nonuniform due to manufacturing tolerances and tubes' curvature in the U-bend region. Thus, this investigation aims to understand the rule of frequency variation (detuning) on FEI in two-phase flow. This includes investigating the effect of detuning on transverse and streamwise FEI for air–water mixture flow. The role of FEI damping and stiffness couplings was investigated over the entire range of air void fraction, or equivalently, the mass-damping parameter. It was found that frequency detuning could elevate the stability threshold caused by either coupling at high air void fraction in the case of transverse FEI. Furthermore, the frequency detuning had a marginal effect on the stability threshold for water flow. It was observed that the mass-damping parameter has a critical impact on FEI under detuning conditions.

Analysis on Bending Performance of the Electro-Textile Antennas With Bandwidth Enhancement for Wearable Tracking Application

Frequency detuning issues in antenna operation due to structural deformation have become a concern, especially for flexible devices such as a textile antenna. Under deformed conditions such as during bending, the antenna might not operate at the desired frequency, causing performance degradation. Therefore, a 1.575 GHz textile antenna for GPS tracking application with defected ground structure is proposed in this paper to alleviate the frequency detuning issues and is demonstrated under two bending conditions, H-plane and E-plane. The implementation of DGS is expected to minimize the frequency detuning by increasing the bandwidth. Hence, the frequency detuning effects could be minimized under bent conditions with broader bandwidth and acceptable antenna performance. In this paper, a planar textile-based antenna with the dimension of 90mm ( <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$L$ </tex-math></inline-formula> ) <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\times100$ </tex-math></inline-formula> mm ( <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$W$ </tex-math></inline-formula> ) was designed, and three rectangular slots were applied at the ground to create DGS. A self-developed electro-textile and polyester were used as the antenna conductive material and substrate. Through the study, a detailed analysis was conducted for both antennas, with and without DGS. The significance of DGS in the proposed design is evaluated and clarified by comparing electric and magnetic field intensities in non-radiating and radiating edges. The detailed performance comparison were observed and analyzed through S-parameter, gain, radiation pattern, and current distribution. The technical performance of the proposed technique is validated through simulation and measurement. DGS implementation has improved the antenna bandwidth from 4.04% to 12.20%, with 1.45dB gain and 23.75% radiation efficiency. As a result, the antenna can operate at the desired frequency under both bending conditions. DGS method provides simplicity in its design, and this method has been widely used in conventional antennas previously. However, the detailed behaviour of field intensity around the non-radiating and radiating edges have not been demonstrated and analyzed. Therefore, the validation of the proposed design through a detailed analysis of E-field and H field intensity concerning antenna configurations; with and without DGS becomes the main contribution of this paper. In addition, the study of bending on different bending radius is also conducted in this paper.

Flat Broadband Chaos Generation Using a Semiconductor Laser Subject to Asymmetric Dual-Path Optical Feedback

A method of generating flat broadband chaos by using a semiconductor laser subject to asymmetric dual-path optical feedback is proposed and demonstrated experimentally. In the asymmetric dual-path optical feedback, one path is connected with an optical band-pass filter (OBPF) to form filtered path, and the other is a traditional optical feedback path named non-filtered path. Through the beating frequency effect between the filtered mode and the non-filtered chaos mode, a chaotic signal with the standard bandwidth of 36.1 GHz and the spectrum flatness of 5.8 dB is generated experimentally. Furthermore, the effects of filter frequency detuning, filter bandwidth and feedback strength on the bandwidth and flatness of chaos are investigated. The results show that the bandwidth enhancement and the flat spectrum can be achieved simultaneously in a wide range of operating parameters.

Subnanoliter Sensing of Dielectric Properties of Liquid-in-Flow at 190 GHz

Dielectric properties (permittivity and loss tangent) of various liquids (water, methanol, propanol, acetone, and isopropanol) are determined by analyzing the frequency detuning effects of different millimeter-wave resonators exposed by the liquid-under-test. Alumina ceramic spherical dielectric resonators, fed from a thin-film circuit, form a resonator fixture operating at 190 GHz. Subnanoliter amount of liquid, carried in a glass tube, is exposed to the resonator. Analysis of the setup by means of electromagnetic field simulations reveals the liquid’s dielectric properties. Extracted data match well with properties obtained from Debye models. Measurement sensitivity is discussed with respect to frequency shift, sensed volume, and dielectric contrast. Obtained sensitivity figure-of-merit outperforms alternative techniques at such high frequency.

Effects of Frequency Detuning and Excitation Quantum Number on the Dynamics of Entanglement in the Jaynes-Cummings Polariton Model

Effects of Frequency Detuning and Excitation Quantum Number on the Dynamics of Entanglement in the Jaynes-Cummings Polariton Model

Dynamics of a delayed Duffing-type energy harvester under narrow-band random excitation

In this paper, a Duffing-type energy harvester with time delay circuit under narrow-band random excitation is studied by using the method of multiple scales. The analytical expressions of the steady-state responses near the principal resonance and their stable conditions are derived. Results show that the phenomenon of stochastic jump is found, and the operational bandwidth of the nonlinear energy harvester can be extended. The effects of frequency detuning, noise intensity, time delay, piezoelectric coupling, and time constant ratio on the dynamical behaviors are discussed. From the viewpoint of improving system performance and optimizing harvester design, a proper choose of time delay and feedback gain is proposed by the power conversion efficiency and the RMS voltage. It indicates that the negative feedback gain is favorable for an energy harvester to provide more electrical output power and miniaturize design. Moreover, the Monte Carlo simulations are given to verify the validity of the theoretical method.

RF Near-Field Coupling System Using Reverse PDN and Considering Electromagnetic Effects

One of the more intriguing applications of wireless power transfer is power delivery for low-power Internet of Things (IoT) devices. By utilizing RF near-field coupling (NFC), an improved combination of small receiver coil area and system efficiency can be achieved, as is ideal for wireless charging for low-power IoT platforms. However, utilizing high efficiency RF NFC comes with a cost—various electromagnetic effects can lead to detuning of the resonant frequency if not properly modeled. In addition, integrating power regulation with high frequency ac–dc conversion can create large ripple voltage supply to a power distribution unit (PDU). This paper investigates the system level issues that arise in efficient, regulated RF NFC systems for milliwatt-scale output power. A method for modeling the various electromagnetic, frequency detuning effects is presented, as well as a selection process for the circuit component values in the design. Furthermore, a reverse power distribution network is designed to integrate the rectifier with a PDU, introducing a target impedance and phase considerations for an RF rectifier. The modeling and integration solutions are experimentally verified through two different RF NFC systems. The systems have measured peak efficiency of 68.4% at 3.3 V output and 58.6% for 1 V output with less than 100 mm $^2$ receiver coil area, demonstrating a unique combination of small coil area and high efficiency compared to other NFC systems to better support low-power IoT devices.