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In the article, in order to effectively detect unmanned aerial vehicles and create an effective radar location, a mathematical model of covering the dead zone of radiolocation stations with an electro-optical system installed on an automatically operating bench placed on a visual observation post, opened in the direction of the likely flight of the enemy, was built and a comparison was made on concrete examples. The aim of the research work is to build a mathematical model of the monitoring of the dead zone of the radiolocation station with the help of an electro-optical system mounted on an automatically operating bench placed on a visual observation post. The following problems are solved in the article: analysis of the characteristics of the radiolocation area; development of a mathematical model for evaluating the dead zone of radiolocation stations with an automatically operating electro-optical system mounted on a bench; assessment of the probability of the unmanned aerial vehicle passing through the field of view of the electro-optical system without detection. The following research methods are used to solve problems: synthesis, theoretical analysis, mathematical modeling, comparative analysis. The following results were obtained: an electro-optical system automatically operating with a rotation period of T=10 [sec] mounted on a bench will detect the UAV traveling a distance of 27 km, for 138 times in 23 minutes, with a rotation period of T=20 [sec] mounted on a bench will detect the UAV covering a distance of 18 km, for 27 times in 9 minutes, with a rotation period of T=20 [sec] mounted on a bench will detect the UAV covering a distance of 3 km 3 times in 1 min. From the comparison of the obtained numbers and the reports made on the basis of the obtained mathematical algorithm, it can be concluded that it is possible to detect unmanned aerial vehicles by means of 1 automatically operating electro-optical system installed on the bench. [ABSTRACT FROM AUTHOR]

The standard model reference adaptive control (MRAC) application to the Dual Active Bridge (DAB) converter has proven to achieve excellent dynamic and tracking responses under parametric uncertainty. However, it is sensitive to bounded non-parametric uncertainty caused by measurement noise and ripples in the output voltage produced in the electronic device. When left unchecked, it affects the system’s performance and may lead to instability. This paper investigates two robust modifications to the standard MRAC, namely the projection operator and dead zone techniques, to tackle the issue of the bounded noise to the dual active bridge with constant power loading (CPL). It further develops an improved form of the dead zone-based MRAC, which ensures better transient and steady-state output voltage when compared with the traditional dead-zone-based MRAC.

Abstract This study proposes an accurate dead zone compensation control method for electro-hydrostatic actuators (EHAs) under low-speed conditions. Specifically, the nonlinear dead zone characteristics under low-speed conditions are summarized based on numerous EHA experiments. An adaptive compensation function (ACF) is then constructed for the dead zone. Next, this study proposes an adaptive dead zone compensation control method for EHAs by integrating the ACF with a virtual decomposition controller (VDC) based on the established EHA model. The stability of the proposed control method is also proven. Finally, the proposed control method is verified using an EHA platform. The test results show that the dead zone trajectory tracking errors of EHAs are significantly reduced when combined with the ACF. Furthermore, since most EHAs are controlled by adjusting the motor speed, the method presented in this study is simpler and easier to use than methods that employ flow compensation.

This study proposes an accurate dead zone compensation control method for electro-hydrostatic actuators (EHAs) under low-speed conditions. Specifically, the nonlinear dead zone characteristics under low-speed conditions are summarized based on numerous EHA experiments. An adaptive compensation function (ACF) is then constructed for the dead zone. Next, this study proposes an adaptive dead zone compensation control method for EHAs by integrating the ACF with a virtual decomposition controller (VDC) based on the established EHA model. The stability of the proposed control method is also proven. Finally, the proposed control method is verified using an EHA platform. The test results show that the dead zone trajectory tracking errors of EHAs are significantly reduced when combined with the ACF. Furthermore, since most EHAs are controlled by adjusting the motor speed, the method presented in this study is simpler and easier to use than methods that employ flow compensation. [ABSTRACT FROM AUTHOR]

A novel, precise disturbance rejection dynamic inversion control algorithm has been proposed. In the high-order dynamic surface control system, an innovative approach utilizes a monotonically increasing inverse hyperbolic sine function to construct an extended state observer, which estimates the uncertain functions at each step. The monotonicity of the inverse hyperbolic sine function simplifies the system stability analysis. Additionally, being a smooth function, it avoids the disturbances caused by piecewise functions at their breakpoints in conventional observer construction, thereby enhancing system stability. The accurate prediction capability of the new observer improves the system's disturbance rejection performance. To address the inherent differential explosion phenomenon in traditional dynamic inversion control schemes, this paper ingeniously employs a tracking signal observer as a substitute for traditional filters, thus avoiding the differential explosion that may occur with first-order filters. Finally, comparative simulations were conducted to validate the effectiveness of the proposed method. The results show that both the observer and the controller possess high-gain characteristics, and the closed-loop system exhibits a fast convergence rate. [ABSTRACT FROM AUTHOR]

Three-phase motor current information is essential for vector and torque control of motors. The use of dc-link single shunt has cost and size advantages and can reduce torque ripples caused by offset and scale differences. However, dc-link single shunt can measure the current only when an active voltage vector is applied, which will result in a large immeasurable region. Various current reconstruction schemes have been developed to eliminate immeasurable regions. Conventional solutions are effective only in specific immeasurable regions and limited in their ability to eliminate all the immeasurable regions and require complex calculations. This study proposes an optimal current reconstruction strategy that can be used in all immeasurable regions. The method divides the immeasurable region into three segments and selectively applies various pulsewidth modulation (PWM) techniques, including the proposed edge-aligned PWM method, which requires only simple calculations. The method can reduce the complexity and successfully eliminate all the immeasurable regions. The experiment results confirm the effectiveness and feasibility of the proposed method. [ABSTRACT FROM AUTHOR]

This work focuses on the issue of neural networks-based adaptive output-feedback control for nonlinear systems with dead zone output and immeasurable states. Radial basis function neural networks (RBFNN) are utilised to approximate the unknown functions and an input-driven filter is used to estimate the immeasurable states. Nussbaum function is employed to address the issue of uncertain virtual control coefficient, which is brought by the dead zone in the output mechanism, and the presented control scheme requires only one adaptive law, making the structure of the controllers very realistic. Based on the approximation capabilities of NNs and the backstepping method, an adaptive controller is designed. Based on the Lyapunov stability theory, all signals in closed-loop systems are semi-globally uniformly ultimately bounded (SGUUB), and the tracking error converges to a small area near the origin. The effectiveness of the proposed adaptive control method is proved with the help of two examples. [ABSTRACT FROM AUTHOR]

ObjectiveA local dynamic collision avoidance algorithm based on an improved fast-marching square (IFMS) method is proposed to solve the multi-vessel collision avoidance problem of unmanned sailboats in open water. MethodsConsidering the uncontrollable speed of a sailboat, its collision avoidance behavior is transformed into a heading control problem, with the direction of the total potential field gradient decreasing as the desired collision avoidance heading. When sailing without risk of collision or downwind, a temporal potential field is constructed to avoid all stationary irregular obstacles and reach the target point. When the sailboat has sailing constraints, Gaussian likelihood functions are designed for specific encounter situations to dynamically construct obstacle potential fields according to the convention on the international regulations for preventing collisions at sea (COLREGS), while the local wind potential field is introduced to consider the dead zone of a sailboat and realize the application requirements of combining dynamic collision avoidance with a zigzag sailing strategy. ResultsThe results show that the proposed algorithm can enable an unmanned sailboat to successfully achieve collision avoidance operations with other sailboats and restricted motor vessels in various encounter situations, while complying with collision avoidance rules and avoiding navigational dead zones. Compared with the original fast-marching square (FMS) algorithm, the upwind sailing time is significantly reduced and the planned collision avoidance trajectory is safer and more reasonable.ConclusionThe proposed method complies with the characteristics of sailboat motion and collision avoidance rules, has high safety and robustness in complex environments, and possesses scientific value regarding the development of autonomous obstacle avoidance technology for unmanned sailboats.

The Northern Gulf of Mexico hosts a severe dead zone, an oxygen-depleted area spanning 1,618,000 hectares, threatening over 40% of the U.S. fishing industry and causing annual losses of USD 82 million. Using a System Dynamics (SD) approach, this study examined the Mississippi–Atchafalaya River Basin (MARB), a major contributor to hypoxia in the Gulf. A dynamic model, developed with Vensim software version 10.2.1 andexisting data, represented the physical, biological, and chemical processes leading to eutrophication and simulated dead zone formation over time. Various policies were assessed, considering natural system variability. The findings showed that focusing solely on nitrogen control reduced the dead zone but required greater intensity or managing other inputs to meet environmental goals. Runoff control policies delayed nutrient discharge but did not significantly alter long-term outcomes. Extreme condition tests highlighted the critical role of runoff dynamics, dependent on nitrogen load relative to flow volume from upstream. The model suggests interventions should not just reduce eutrophication inputs but enhance factors slowing down the process, allowing natural denitrification to override anthropogenic nitrification. [ABSTRACT FROM AUTHOR]

In this paper, an adaptive back-stepping control scheme based on the command filter is proposed for the servo system with current constraints and non-symmetric dead zone. First, a novel system transformation scheme is designed to transform the servo system with current constraints into the equivalent "unconstrained". A security boundary is incorporated into the designed strategy to restrict the activation state of the constraint mechanism. Second, the asymmetric dead zone nonlinearities can be represented into a parameterized form by using a continuous piecewise linear neural network (CPLNN). Moreover, an adaptive law with guaranteed convergence is used to online update the CPLNN weights so as to derive the dead zone characteristic parameters and then compensate for the asymmetric dead zone. Then, the command filter is introduced into the back-stepping control strategy to avoid the complexity explosion. The stability analysis of the closed-loop system is proved by the Lyapunov stability theory. Finally, the effectiveness and feasibility of the proposed control scheme are validated through the real-time experiments on a permanent magnet synchronous motor (PMSM) platform. [ABSTRACT FROM AUTHOR]

Summary: In this study, couple inductor‐based buck power factor correction (PFC) converter is designed to mitigate dead zones of the converter. To minimize switching losses, all switches are controlled using a soft switching method, eliminating the need for snubber circuits. The circuit is controlled by an analog UC3843 pulse width modulation (PWM) integrated circuit (IC), providing natural PFC capability, which simplifies control and offers advantages in terms of size and cost compared to conventional ones. Simulation studies and prototype implementation are carried out to evaluate performance of the topology. The converter operates within a voltage range of 90–280 Vrms and has a power rating of 150 W. The results from both simulation and experimental analyses indicate that power factor (PF) of the circuit exceeds 98% and total harmonic distortion (THD) of the input current is found to be below 5% under various input voltage and load conditions. Furthermore, proposed topology demonstrated high efficiency, with measurements of 93% at full load and 95.6% at half load under 220 Vrms input voltage and 80 Vdc output voltage conditions. Outcomes highlight that the proposed topology achieves pure sinusoidal input current and exhibits competitive performance compared to other topologies used in the industry. [ABSTRACT FROM AUTHOR]

This article proposes an improved adaptive finite time command filtered controller for high-precision motion control of electro-hydraulic servo systems. During the controller design process, the effects of parameter uncertainty, unmodeled disturbances, and dead zone uncertainty in the system are effectively addressed by integrating parameter adaptive laws and disturbance estimation laws. By extending the system states, this strategy eliminates the need for the controller to rely on the first-order derivative of the tracking trajectory, making it applicable in tracking non smooth curves. Through Lyapunov stability analysis and comparative simulation experiments, it is shown that even in the presence of unmodeled disturbances, unknown system parameters, and unknown dead zone characteristics in the system, the developed controller can still achieve adjustable neighborhood tracking errors around the origin in a finite time. • A controller for an electro-hydraulic servo system that comprehensively considers multiple nonlinear factors is proposed. • Improved instruction filtering controller, weakened derivative requirements, and expanded application scenarios. • The proposed controller can achieve tracking error convergence within the specified error band within a finite time. • This article considers the nonlinear factors caused by the dead zone of the servo valve in the system. [ABSTRACT FROM AUTHOR]

This paper investigates a neural network adaptive controller design method for turbo‐generator of power systems with external disturbance, unknown system dynamic, prescribed performance, and unknown actuator dead zone. First, the unknown system dynamic is estimated and overcome through a neural network. Using the implicit function theorem, the unknown asymmetric dead‐zone behavior of the actuator is overcome by another static neural network. Second, the external disturbance and the reconstruction error of neural networks are handled by a robust term updated online. Moreover, there is no requirement to pre‐know or off‐line estimate the reconstruction error of neural networks and the upper bound of the system external disturbance. Third, based on Lyapunov theory, the smooth control law is proposed. In the meantime, the uniform ultimate boundedness of the networks weights is strictly proved. Furthermore, the system state error satisfies the prescribed transient performance and can converge to a small neighborhood around zero. Finally, a numerical simulation shows the effectiveness of the proposed method. [ABSTRACT FROM AUTHOR]

The paper focused on the distributed tracking problem for a specific class of multi-agent systems, characterized by bandwidth constraint and dead zone actuators, where the bandwidth limitations exist in neighbor agents and the dead zone nonlinearity refers to a generalized mathematical model. Initially, a series of event-triggered mechanisms with relative thresholds were established for neighbor agents, ensuring that control signals were transmitted only when necessary. Next, the generalized dead zone models were decomposed into two parts: indefinite terms with control coefficients and disturbance-like terms, resulting in unpredictability and damaging effects. Subsequently, based on the backstepping procedure, final consensus controllers with multiple polynomial compensators were constructed. These controllers offset the coupling coefficients caused by event-triggered mechanisms and dead zone non-smooth. Stability analysis was given to substantiate the theoretical correctness of this method and support the claim of Zeno behavior avoidance. Finally, simulation studies were performed for the feasibility of our proposed methodology. [ABSTRACT FROM AUTHOR]

The fractional-order controllers (FOCs) have recently had a significant impact on control applications. However, they still need further research for feedback systems with hard nonlinearities, such as dead zones. The above compelling evidence motivates the design of a new robust FOC to avoid limit cycles caused by dead zones in the control loops. The proposed FOC consists of the cascade of two shifted in frequency, fractional-order lead networks. They provide high-value and sufficiently flat phase leads in sufficiently large frequency intervals. In this way, the linear part of the control loop can be easily shaped to achieve avoidance of limit cycles. The article applies classical concepts, such as the Nyquist plot and describing function method, to derive guidelines for designing the free parameters of the FOC. Moreover, a realization algorithm and a parameter setting procedure make the new FOC easily implementable in engineering practice.

In this paper, a waterwheel-handling robot based on funnel control was proposed for loading and unloading particles in docks and ports by optimizing the control method and modifying the controller. It can solve the problems of the high procurement cost of large-scale handling equipment and the low efficiency of small-scale handling equipment. Common handling equipment has low positioning accuracy, operating speed, and trajectory accuracy because of the existence of dead zone, friction, unmodeled dynamics, parameter uncertainty, external disturbances, environmental and human factors and other factors. In comparison with traditional proportional integral derivative control, even with initial errors and various disturbances, this robot adopted improved funnel control, which can still guarantee fast convergence of trajectory and speed, as well as keep tracking errors within the funnel-boundary range. Therefore, the operating accuracy and efficiency of the waterwheel-handling robot are significantly improved based on this research.

The attitude tracking control problem of an overdriven quadrotor aircraft experimental platform is studied. The platform has unknown input disturbances and angular velocity cannot be measured, and the motor also has dead zone and saturation nonlinear characteristics. First, a linear perturbed double-integral model of the platform is established. Afterwards, an attitude-tracking robust controller including a proportional-integral-derivative nominal controller and an adaptive extended state observer (AESO) is designed. Among them, the nominal controller is used to ensure the asymptotic stability of the nominal closed-loop system, and AESO is used to estimate the angular velocity and disturbance information of the experimental platform to solve the problem of no velocity measurement and disturbance suppression. Moreover, the overdrive control allocation problem is solved by using the pseudo-inverse matrix method. In addition, an auxiliary system is constructed to weaken the influence of the motor’s dead zone and saturated nonlinear characteristics. Finally, the simulation and experiments verify that the proposed control strategy can effectively solve the problems caused by the dead zone and saturation characteristics of the motor, and can simultaneously take into account the transient overshoot and steady-state error performance of the closed-loop system.

Ultrasonic time-of-flight diffraction (TOFD) technique is a means of defect detection adopting the diffracted longitudinal waves from flaw tips. However, the dead zone is induced by the coupling between tip-diffracted longitudinal wave and lateral wave or longitudinal back-wall wave. In this paper, the methods for reducing dead zone are reviewed from parameter optimization, alternative TOFD techniques and signal processing techniques. The principles, effects and influencing factors of different methods are analyzed and compared in sequence. Finally, the future challenges focus on the multiple overlapped signals (N ≥ 3) from shallow subsurface defects in thin plates and the change of dead zone induced by irregular structure. [ABSTRACT FROM AUTHOR]

In this paper, the event-triggered control problem is investigated using backstepping techniques for nonlinear systems with dead-zone input. The external disturbance and unknown parameters are also considered in the controller's design. It is well known that errors in input signal measurements are inevitable. In event-triggered control, such errors will directly affect whether the control signal is updated. This measurement error can be seen in the form of interference to the threshold. Therefore, unlike traditional event-triggered control, the existence of threshold disturbance is considered in the controller's design. The proposed controller can not only compensate for the uncertainties caused by external disturbance and unknown parameters but can also suppress the unknown effects caused by threshold interference. In addition, to obtain a continuous controller, a smooth function is constructed to approximate the discontinuous sign function. In this way, Zeno behavior is successfully avoided. The boundedness of all signals and the tracking performance of the system can be guaranteed by the proposed control scheme. Numerical simulation and actual system simulation demonstrate the effectiveness of the proposed control scheme. The comparative simulation results also verify this event-triggered controller's advantages, including better tracking performance and fewer trigger times. [ABSTRACT FROM AUTHOR]

In order to clarify the action law of the swirl oxygen lance jet on the melt pool of the converter and to determine the optimal swirl angle of the swirl oxygen lance for the 120t converter, this study establishes the gas-liquid two-phase flow model of the oxygen lance with different swirl angles based on the realizable k-e model and the VOF multiphase flow model. The gas-liquid interface behavior during the interaction between the jet and the molten pool was analyzed, and the flow pattern of molten steel in the molten pool was mainly investigated. The results show that compared with traditional oxygen lance, the rotating oxygen lance jet enhances the stirring of the melt pool and intensifies the fluctuation of the melt pool liquid level. The depth of the impact cavity decreases with the increase of the swirl angle, but the diameter of the impact cavity increases with the increase of the swirl angle. When the jet with a swirl angle of 10 ° impacts the surface of the melt pool, the turbulence energy obtained by the molten steel is the highest, the average flow velocity inside the melt pool is the highest, and the molten steel is stirred more thoroughly, achieving better melting effects. [ABSTRACT FROM AUTHOR]

The Northern Gulf of Mexico hosts a severe dead zone, an oxygen-depleted area spanning 1,618,000 hectares, threatening over 40% of the U.S. fishing industry and causing annual losses of USD 82 million. Using a System Dynamics (SD) approach, this study examined the Mississippi–Atchafalaya River Basin (MARB), a major contributor to hypoxia in the Gulf. A dynamic model, developed with Vensim software version 10.2.1 andexisting data, represented the physical, biological, and chemical processes leading to eutrophication and simulated dead zone formation over time. Various policies were assessed, considering natural system variability. The findings showed that focusing solely on nitrogen control reduced the dead zone but required greater intensity or managing other inputs to meet environmental goals. Runoff control policies delayed nutrient discharge but did not significantly alter long-term outcomes. Extreme condition tests highlighted the critical role of runoff dynamics, dependent on nitrogen load relative to flow volume from upstream. The model suggests interventions should not just reduce eutrophication inputs but enhance factors slowing down the process, allowing natural denitrification to override anthropogenic nitrification.

The objective of this study is to numerically investigate the effects of electrohydrodynamics (EHD) on coupled free convective thermocapillary flow. The study focuses on a free-surface cavity filled with a hybrid nanofluid (MWCTN- Fe3O4-thermal oil) and containing a hot rigid obstacle. An electric field is applied between the obstacle and the lower cavity wall to induce additional instabilities in this region. This technique aims to eliminate the dead zone typically present in traditional natural convection and is expected to greatly improve heat transfer efficiency. To achieve this objective, the equations governing the EHD phenomenon, as well as the equations defining the physicochemical properties of the hybrid nanofluid, are solved using the finite volume method (FVM) coupled with a blocked-off region procedure. A parametric study is conducted, involving the Marangoni number (surface tension), the thermal Rayleigh number (buoyancy force), the electrical Rayleigh number (electrical force), the nanoparticle concentration, the size and the position of the obstacle. It has been demonstrated that applying of an electric field to the convective-thermocapillary flow of the nanofluid (combining two enhancement techniques) significantly enhances heat transfer, resulting in a more than 230 % increase in the Nusselt number.

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This paper expresses a novel adaptive fault-tolerant control (FTC) method for a robotic manipulator with dead zones and actuator faults in the task space. To specify, the actuator faults are the partial loss of effectiveness of actuators. The partial loss of effectiveness and the break-points of dead zone are estimated by the novel adaptive laws. Establishing an anti-singularity terminal sliding surface ensures the finite time convergence of the tracking errors to zero. The correctness of this method is proved by the Lyapunov criterion. Despite the fact that the proposed adaptive FTC method belongs to the passive group, it does not require any robust component which makes large-magnitude chattering phenomena to deal with the actuator faults. Instead, they are handled by a unique technique. The comparative simulation results illustrate the merit and efficiency of the proposed method. [ABSTRACT FROM AUTHOR]

Variants of quadrature receiver of signals of continuous automatic train signaling (CATS) with nonlinear transformation are proposed, the noise immunity and safety of which are assessed in comparison with those of a receiver of CATS signals with amplitude detection. To suppress impulsive noise, it is proposed to use a combined noise suppressor (noise killer), which is a combination of an alternately operating blanking circuit and a wideband filter, limiter, and narrowband filter scheme. Analysis of the effectiveness of using correlation techniques and nonlinear processing of CATS signals was performed. The results show that the greatest noise immunity and safety is provided by the quadrature receiver of CATS signals with a combined noise suppressor and a block with a dead zone. [ABSTRACT FROM AUTHOR]

The results of a study of the noise immunity of a receiver of a continuous automatic locomotive signaling channel under the influence of sinusoidal interference from power lines are presented. It is shown that the use of a block with an insensitivity zone in the receiver makes it possible to effectively combat sinusoidal interference from power lines in the automatic locomotive signaling channel. As a result of the use of such a block, the interference interval from the power line was reduced from 11.7 to 4.5 s. [ABSTRACT FROM AUTHOR]

Herein, the distribution of sulfur and iron compounds (dissolved sulfide: H2S and HS−, iron sulfide: FeS, and ionized iron: Fe2+ and Fe3+) in sediments (0–15 cm depth) at four stations in Mikawa Bay, Japan, was evaluated from April 2015 to March 2016. The maximum dissolved sulfide concentrations in the upper part of the sediment porewater (0–4 cm depth) (within 1.4–8.1 mmol·L−1) varied among stations located in a waterway of a large-scale port with a significant dead zone. Moreover, the iron sulfide and ionized iron concentrations in the upper part were highest at a station where the dissolved sulfide concentration was relatively low compared with that of the other sites. Analysis of the theoretical and hypothetical accumulation of particulate oxidized iron (FOOH) at the stations located in the dead zone revealed that the estimated particulate oxidized iron accumulation was higher (2303 mmol·m−2) at a station in which the dissolved sulfide concentration was low compared with the other stations (142–384 mmol·m−2). Altogether, these findings suggest that the sulfur–iron cycling can determine the amount of dissolved sulfides that accumulate in sediments. Hence, artificially adding iron compounds to the seabed may help mitigate free sulfides accumulation and prevent extreme hypoxia. [ABSTRACT FROM AUTHOR]

This paper presents a PAM-4 receiver (RX) for CMOS image sensor (CIS) link. A robust baud-rate PAM-4 phase detector (PD) is proposed, which alleviates the dead zone issue encountered in the conventional sign-sign Mueller-Muller (SS-MM) PD when combined with an adaptive decision feedback equalizer (DFE). An optimum and unique locking point is reached by using a sign-sign minimum mean squared error (SS-MMSE) PD with a biased state which exhibits a constant probability for all phase error ranges. The proposed PD with the biased state evades the dead zone and prevents wandering. Furthermore, the phase-detecting transitions of the proposed SS-MMSE PD are 1.5 times higher compared to the conventional SS-MM PD. The proposed solution is verified with a prototype PAM-4 RX chip using 40-nm CMOS technology. It demonstrates a bit error rate (BER) of less than $10^{-9}$ with a 15.8 dB loss channel. The total power consumption is 46.6 mW at 12 Gb/s, achieving a figure of merit (energy efficiency per channel loss at Nyquist frequency) of 0.24 pJ/b/dB.

The dead zone in ultrasonic time-of-flight diffraction (TOFD) restricts the quantitation of near-surface defects. Alternative TOFD techniques introduce other tip-diffracted/scattered waves with longer propagation times to implement defect detection, but the applicability is influenced due to ignoring the change of acoustic path of the diffracted shear wave in wedge. In this paper, the mode-converted wave (MCW) method is exemplified to analyze the propagation path of diffracted shear wave and the change of the received point in wedge. On this basis, the corrected MCW method is proposed by establishing the relationship between the propagation time of MCW and defect depth according to Fermat's principle. The simulation and experiments show that the depth of near-surface dead zone is reduced by 60% with the corrected MCW method. The positioning errors of the defects in the aluminum alloy sample with a thickness of 20.0 mm are no more than 0.15 mm by using the TOFD probes with 10 MHz center frequency and 40 mm probe center spacing (PCS) and the 60° wedges. Compared to the conventional MCW method, the corrected method widens the range of applicable TOFD signals in B-scan images and reduces the measurement errors of defect depths to within 3.5% under ideal conditions. [ABSTRACT FROM AUTHOR]

The ball screw feed system of CNC machine tools is a typical mechatronic motion mechanism. During the operation of the machine tool, not only the dynamic characteristics of the mechanical structure will affect its performance, but also the electrical characteristics of the servo system will affect the movement of the worktable, which will lead to displacement fluctuation and bring adverse effects on the precision of the machine tool and even the quality of the processed parts. Therefore, the electrical system and the mechanical system are strongly coupled to each other due to their high integration. In this paper, the fluctuation of current, torque, and displacement during the motion of the worktable is studied. Firstly, the mechatronic model of the ball screw feed system, which not only consists of all components of the feed system but also takes different nonideal characteristics of each component into consideration, is established to realize the physical simulation of the whole system. Then, with the consideration of the impacts of inverter dead zone, motor cogging torque, rotor mixed-eccentricity, winding asymmetry, and collecting error of feedback current, the frequency components of fluctuations caused by the nonlinear electrical characteristics of inverter and servo motor in the servo drive system are obtained. Finally, the influences of load, feedrate, servo parameters, and dynamic characteristics of mechanical structure on fluctuation are analyzed in the time domain and frequency domain. The phenomenon of displacement fluctuation of the worktable caused by the electrical characteristics of the servo system indicates that it is necessary and meaningful to build the integrated model to study the ball screw feed system from the view of the whole system. • Ball screw feed system integrated model including control system, inverter, motor, mechanical system. • Physical simulation of feed system considering nonlinear electrical characteristics of servo system. • Feed system fluctuation due to nonlinear electrical characteristics of servo system is studied. • Low frequency components of servo system harmonics can pass through mechanical system. • Analysis of impact of load, feedrate, servo parameter, mechanical system dynamic characteristics on fluctuation. [ABSTRACT FROM AUTHOR]

In mobile applications such as geomagnetic surveying, two major effects hamper the use of optically pumped magnetometers: dead zones, sensor orientations where the sensors signal amplitude drops; and heading errors, a dependence of the measured magnetic field value on the sensor orientation. We present a concept for an omnidirectional magnetometer to overcome both of these effects. The sensor uses two cesium vapor cells, interrogated by circularly-polarized amplitude-modulated laser light split into two beams propagating perpendicular to each other. This configuration is experimentally investigated using a setup wherein the laser beam and magnetic field direction can be freely adjusted relative to each other within a magnetically shielded environment. We demonstrate that a dead-zone-free magnetometer can be realized with nearly isotropic magnetic-field sensitivity. While in the current configuration we observe heading errors emerging from light shifts and shifts due to the nonlinear Zeeman effect, we introduce a straightforward approach to suppress these systematic effects in an advanced sensor realization. [ABSTRACT FROM AUTHOR]

In this paper, we present the high-speed phase frequency detector where the phase characteristics are enhanced. This PFD has a simple structure where the dead zone is annihilated and blind zone is highly reduced. This PFD generates UP and DN signal only when it gets the distinct phase difference. With the reduction of the reset time, the proposed PFD function is in the order of 1.5 M H z − 4 G H z operating frequency. The design shows the improvement by completely eliminating the dead zone. However, the blind zone is minimised to 74.6 p s in the phase characteristics which improves the output phase noise as −132.9 d B c / H z at 1 M H z offset frequency. The power consumption is minimised upto 417.3 μ W @ 4 G H z operating frequency. The design is simulated in standard 0.18 \mum CMOS technology node with 1.8 V power supply. Furthermore, the achieved frequency band is applicable for high-speed and low-power PLL application such as Zigbee, Wifi, Bluetooth and 4 G communication. [ABSTRACT FROM AUTHOR]