Resonant Bridges Research Articles

Research on High-Precision Resonant Capacitance Bridge Based on Multiple Transformers.

The Taiji program is dedicated to the detection of middle and low-frequency gravitational waves, targeting the 0.1 mHz to 1 Hz frequency band. The project requires an acceleration residual sensitivity of 3 × 10-15 ms-2/Hz1/2, which necessitates a capacitance sensing resolution of 1 aF/Hz1/2 for the capacitive sensing system within the specified frequency range. The noise level of the resonant bridge significantly influences the resolution. Addressing the challenges in enhancing transformer performance parameters in existing resonant capacitance bridges and the constraints on improving the characteristics of resonant capacitance bridges, this study introduces a novel approach to reduce bridge thermal noise without optimizing existing parameters. The simulation results demonstrate that this scheme can reduce the noise to 0.7 times the original level and further reduce bridge thermal noise when other parameters affecting noise are optimized. This not only mitigates the demands for other performance parameters but also increases the range of maximum acceptable resonant frequency deviations and reduces its sensitivity to such variations. Experimental validation confirms that the proposed scheme effectively reduces noise by 0.7 times and improves the resolution of capacitance sensing to 0.6 aF/Hz1/2, thereby advancing the Taiji program gravitational wave detection capabilities.

Dynamic behaviour of railway poles built on bridges under train passage in high-speed railways and a simple evaluation method

There have been studies on increased dynamic response of bridges for high-speed railways (HSRs) and damage to the overhead contact line system (OCS), including wires supported by railway poles placed on resonant bridges. However, the dynamic behavior of the poles installed on bridges under train passages, which is considerably related to the damage to the OCS, has not been systematically examined. This study aims to examine the dynamic behaviour of poles installed on bridges and provide a simple calculation method or guidelines for bridge design and OCS maintenance considering pole vibration. First, a field test of a HSR bridge with poles was conducted, and numerical simulations using a finite element model of pole and bridge were validated. Next, a parametric study using the validated numerical model was conducted. The results demonstrated that the multiple resonances observed when the excitation frequency of travelling train matches the bridge and pole frequencies can cause dominant vibration of the poles built at the bridge edge, thus posing a risk of OCS wire fatigue. In addition to the understanding of the basic dynamic behavior, a simple calculation approach based on a theoretical model considering the interaction between the bridge and poles installed at the bridge edge is developed for practical use. The proposed model clarifies train-induced pole top displacements with standard bridge and pole specifications in Japanese HSRs. Using the bridge/pole frequency ratio and bridge span length, the results are presented in the form of a pole response map that can be used to calculate the pole top displacement. Finally, an example of bridge frequency guidelines is provided for extracting and evaluating poles that may require attention for maintaining the OCSs.

Drive-by methodology to identify resonant bridges using track irregularity measured by high-speed trains

Resonance of railway bridges is a matter of major concern in high-speed railways because it reduces riding comfort, damages the attached structures, and decreases the strength of girder bodies. Although this abnormal behavior can be inspected using in situ displacement measurements taken from the ground, its investigation is tedious and, consequently, is very expensive. In this study, authors developed a novel drive-by system for high-speed railways to detect resonant bridges; the difference between two track irregularities at the same position using devices mounted on the first and last vehicles of a train was measured. This is based on the idea that the response of the last vehicle passing through the resonant bridge is attributed to the superposition of track irregularities and abnormal bridge displacement because of resonance mechanisms. However, the response of the first vehicle primarily arises from track irregularities since the resonance phenomenon is not yet sufficiently excited. The Resonance Detection Index (RDI), defined as the difference between the track irregularities measured by the devices mounted on the first and last vehicles, is used to emphasize the component excited by vehicle length to propose a methodology for detecting resonant bridges.Numerical simulations clarify that bridge span and track irregularity have greater effects on the RDI than either measurement noise or positioning error. Track irregularity may cause the RDI to vary by ± 2 mm depending on vehicle length wave component of the track irregularity. Consequently, this study demonstrates that resonant bridges with spans between 20 and 60 m can be detected using the proposed RDI.Finally, the proposed method was applied to track irregularity measurements using actual high-speed trains operating in Japan. More than ten bridges, out of more than 800 bridges, were detected as resonant bridges according to RDI. In situ displacement measurements were performed for three of these bridges, demonstrating the presence of resonance phenomenon and thereby validating the proposed method.

Extended-State-Observer Based Model Predictive Control of a Hybrid Modular DC Transformer

Due to the power interaction between the phase-shifted dual active bridges (PSDABs) and series resonant dual active bridges (SRDABs) in the hybrid modular dc Transformer (HMDCT), it is difficulty to optimize current stress based on the transferred power. An extended-state-observer based model predictive control (ESO-MPC) strategy with the extended phase shift (EPS) is proposed to optimize the current stress of the PSDABs in the HMDCT. The MPC is employed to calculate the optimal transferred power of the PSDABs. Moreover, a first-order ESO is introduced to observe the uncertain output current of the PSDABs. Based on the calculated transferred power, the optimal phase-shifted duty ratios of each PSDAB under EPS, which achieves optimal current stress, are obtained by the Lagrange multiplier method. Because of the ESO-MPC strategy, it enables to achieve the current sensorless control of the HMDCT. Simulations on a four-cell 3kV/500V HMDCT and the extensive experiments of a downscale laboratory platform, using DSP OMPL138 -EZW + FPGA XC7A75T as the core controller, validate the feasibility of the proposed control strategy.

New results on orbital resonances.

Perturbative analyses of planetary resonances commonly predict singularities and/or divergences of resonance widths at very low and very high eccentricities. We have recently reexamined the nature of these divergences using non-perturbative numerical analyses, making use of Poincaré sections but from a different perspective relative to previous implementations of this method. This perspective reveals fine structure of resonances which otherwise remains hidden in conventional approaches, including analytical, semi-analytical and numerical-averaging approaches based on the critical resonant angle. At low eccentricity, first order resonances do not have diverging widths but have two asymmetric branches leading away from the nominal resonance location. A sequence of structures called "low-eccentricity resonant bridges" connecting neighboring resonances is revealed. At planet-grazing eccentricity, the true resonance width is non-divergent. At higher eccentricities, the new results reveal hitherto unknown resonant structures and show that these parameter regions have a loss of some - though not necessarily entire - resonance libration zones to chaos. The chaos at high eccentricities was previously attributed to the overlap of neighboring resonances. The new results reveal the additional role of bifurcations and co-existence of phase-shifted resonance zones at higher eccentricities. By employing a geometric point of view, we relate the high eccentricity phase space structures and their transitions to the shapes of resonant orbits in the rotating frame. We outline some directions for future research to advance understanding of the dynamics of mean motion resonances.

Bayesian time–frequency analysis of the vehicle–bridge dynamic interaction effect on simple-supported resonant railway bridges

Abstract Monitoring the conditions or damages of bridges under train passages demands a high-accuracy modal-characteristic identification method that separates the apparent fluctuations caused by vehicle–bridge dynamic interaction (VBI) effects from other fluctuations. This study proposes a novel method based on a time-varying autoregressive model, which is solved using a hierarchical Bayesian estimation approach. The VBI effect is estimated from the displacement response of the railway bridges as temporal fluctuations of the natural frequency and modal damping ratio. The exogenous variable is the train load, expressed as an external force. Numerical experiments verified the higher accuracy of the proposed method than the existing method. The influences of train speed and rail irregularity on the VBI effects are clarified by the application of the proposed method to various VBI simulations. The proposed method was applied to the measured resonance responses of actual bridges and succeeded in empirically demonstrating the decreased natural frequency and the increased modal damping ratio under train passage. Additionally, using the proposed method, modal characteristics variation due to VBI effect calculated using VBI model simulation was verified by comparing with those estimated from the measured results.

A Feasibility Study of the Drive-By Method for Damage Detection in Railway Bridges

Damage identification and localization in railway bridges is a widely studied topic. Strain, displacement, or acceleration sensors installed on the bridge structure are normally used to detect changes in the global behavior of the structure, whereas approaches like ultra-sonic testing, acoustic emission, and magnetic inspection are used to check a small portion of structure near localized damage. The aim of this paper is to explore another perspective for monitoring the structural status of railway bridges, i.e., to detect structural damage from the dynamic response of the train transiting the bridge. This approach can successfully be implemented in the case of resonant bridges, thanks to the high level of acceleration generated, but its application becomes more challenging when the excitation frequencies due to train passage do not excite the first mode of vibration of the bridge. The paper investigates the feasibility of the method in the latter case, through numerical simulations of the complete train-track-bridge system. Accelerations on axleboxes and bogies are processed through suitable algorithms to detect differences arising when the train crosses a defective bridge or a healthy one. The results outline the main operational parameters affecting the method, the best placement for sensors, and the best frequency range to be considered in the signal processing, also addressing the issues that are related to track irregularity. Good performance can be achieved in the case of short bridges, but a few practical issues must be tackled before the method could be tested in practice.

Modeling of Soft-Switching Losses of IGBTs in High-Power High-Efficiency Dual-Active-Bridge DC/DC Converters

Soft-switching techniques are very attractive and often mandatory requirements in medium-voltage and medium-frequency applications such as solid-state transformers. The effectiveness of these soft-switching techniques is tightly related to the dynamic behavior of the internal stored charge in the utilized semiconductor devices. For this reason, this paper analyzes the behavior of the internal charge dynamics in high-voltage (HV) semiconductors, giving a clear base to perform overall converter optimizations and to understand the previously proposed zero-current-switching techniques for insulated-gate bipolar-transistor (IGBT)-based resonant dual active bridges. From these previous approaches, the two main concepts that allow switching loss reduction in HV semiconductors are identified: 1) shaping of the conducted current in order to achieve a high recombination time in the previously conducting semiconductors; and 2) achieving zero-voltage-switching (ZVS) in the turning-on device. The means to implement these techniques in a triangular-current-mode dual-active-bridge converter, together with the benefits of the proposed approaches, are analyzed and experimentally verified with a 1.7-kV IGBT-based neutral-point-clamped (NPC) bridge. Additionally, the impact of the modified currents in the converter's performance is quantified in order to determine the benefits of the introduced concepts in the overall converter.

Soil–structure interaction in resonant railway bridges

This paper explores dynamic soil–bridge interaction in high speed railway lines. The analysis was conducted using a general and fully three-dimensional multi-body finite element–boundary element model formulated in the time domain to predict vibrations caused by trains passing over the bridge. The vehicle was modelled as a multi-body system, the track and the bridge were modelled using finite elements and the soil was considered as a half-space by the boundary element method. The dynamic response of bridges to vehicle passage is usually studied using moving force and moving mass models. However, the multi-body system allows to consider the quasi-static and dynamic excitation mechanisms. Soil–structure interaction was taken into account by coupling finite elements and boundary elements. The paper presents the results obtained for a simply supported short span bridge in a resonant regime under different soil stiffness conditions.

Reliability and stability of thin-film amorphous silicon MEMS resonators

The stability of the resonance frequency (fres) characteristics of MEMS resonators upon long-term cycling is crucial for many applications. Thin-film silicon MEMS have been developed to take advantage of their low-temperature processing and large area deposition characteristics. A reliability and stability study of thin-film-doped hydrogenated amorphous silicon (n+-a-Si:H)-aluminum MEMS resonators fabricated on glass substrates at a maximum processing temperature of 110 °C is presented. Long-term cycling of thin-film silicon microbridge resonators with different top electrode configurations was performed in vacuum and in air using electrostatic actuation. The number of cycles to failure, the fres stability, the quality factor (Q) stability and the effect of measurement temperature are studied. The resonant bridges withstand the industry standard of 1011 continuous cycles at high load with no failure reported both in vacuum and air with fres shifts which depend on the resonator top electrode configuration. No Q degradation was observed. Frequency stability better than ±20 ppm was observed in vacuum after long-term cycling.

Reliability and stability of thin-film amorphous silicon MEMS on glass substrates

ABSTRACTIn this work, we present a reliability and stability study of doped hydrogenated amorphous silicon (n+-a-Si:H) thin-film silicon MEMS resonators. The n+-a-Si:H structural material was deposited using radio frequency plasma enhanced chemical vapor deposition (RF-PECVD) and processed using surface micromachining at a maximum deposition temperature of 110 ºC. n+-a-Si:H resonant bridges can withstand the industry standard of 1011 cycles at high load with no structural damage. Tests performed up to 3x1011 cycles showed a negligible level of degradation in Q during the entire cycling period which in addition shows the high stability of the resonator. In measurements both in vacuum and in air a resonance frequency shift which is proportional to the number of cycles is established. This shift is between 0.1 and 0.4%/1x1011 cycles depending on the applied VDC. When following the resonance frequency in vacuum during cyclic loading, desorption of air molecules from the resonator surface is responsible for an initial higher resonance frequency shift before the linear dependence is established.

Microelectromechanical systems for biomimetical applications

An etch release process capable of releasing long resonant gate transistor bridges from a sacrificial layer has been studied as a step towards developing a system to mimic the cochlear mechanism inside the human ear. The developed etch release process involves the use of a gentle etch tool that is capable of a clean and damage-free etch release. The influence of temperature and oxygen/nitrogen gas flow rates on the undercut etch rates and the profiles of photoresist and polyimide sacrificial layers have been investigated. An array of aluminum bridges of length 0.278–1.618 mm, which cover the frequencies from 1 to 33.86 kHz, has been designed and released from a sacrificial layer. The resonating beams have been measured.

Design and investigation of micromechanical bridge structures for an optical pressure sensor with temperature compensation

Abstract For fibre-optical sensor systems, a frequency-encoded sensor signal is of great interest due to its immunity against attenuation effects along the fibre-optic transmission line. A possible approach for such sensors is the use of silicon micromechanical bridges with optothermal excitation and an interferometric measuring technique. A problem with such sensors is the cross-sensitivity to other parameters, especially to temperature. We have designed and realized a structure with two resonant bridges made of silicon nitride to allow temperature compensation of a pressure measurement. By this method it is possible to reduce the temperature dependence of the pressure sensor to less than 1% within the temperature range used.

Improved DC/AC interface inverter for high-frequency space applications

A DC/AC interface inverter for a high-frequency space power distribution system that uses dual asymmetrical resonant bridges is examined. Compared to the conventional approach in which two symmetrical bridges are used, the asymmetrical bridges arrangement offers better use of the installed kVA rating and efficiency of the inverter system. A simplified approach for modeling the inverter system in steady-state is presented, and a criteria to select the resonant components is given. A detailed simulation is performed for the following: a symmetrical inverter system with a resistive load, an asymmetrical inverter system with a resistive load, and an asymmetrical inverter system with the type-1A AC/DC converter load. >

Resonant-bridge two-axis microaccelerometer

This paper describes a two-axis silicon microaccelerometer consisting of two pairs of polysilicon resonant bridges orthogonally attached to a silicon proof mass. Acceleration in the plane of the substrate causes differential axial loads on opposing microbridges in each pair, thereby shifting their resonant frequencies. The acceleration component aligned with a pair is measured by the difference in resonant frequencies. The device has a 1.45 mg proof mass and 250 μm long, 100 μm wide, 1.6 μm thick polysilicon bridges. To suppress rotation and vertical displacement of the proof mass, it is also supported on the backside of the wafer by eight, 8 μm thick silicon bridges. Initial measurements indicate a sensitivity to inline acceleration of 160 Hz/g.

Microdyanmics

Microdynamics, the science, technology, and design of moving micromechanical devices and mechanisms, has become the focus for a widening scope of research. Microdynamic structures made with technology derived from IC processes show promise for the design of high-performance sensors and actuators and can be combined with on-chip circuits. This development may lead to a new class of microsystems having significant impact on engineering design. Polycrystalline silicon and silicon nitride can be applied as mechanical materials in a process in which microstructures are freed from the substrate by etching a sacrificial layer of silicon dioxide. This technology, first demonstrated as a means to produce electrostatically driven resonant bridges, has been extended to make rotating and sliding structures, gears, springs, and recently micromotors. Research on the mechanical properties of the electrical materials forming microdynamic structures (which previously had exclusively electrical uses), on the scaling of mechanical design, and on the effective uses of computer aids is needed to provide the engineering base that will make it possible to exploit fully this technology.