Excitation Signal Research Articles

Pure flexural guided wave excitation in pipes using cross-exciting circumferential phased arrays

ABSTRACT Flexural guided waves that preserve the circumferential focusing characteristics provide insights into the structural integrity and thus have great application potential. An improved transducer called cross-exciting circumferential phased array is proposed for generating pure flexural mode in pipes. It is divided into two cross-exciting sub-arrays, with opposing excitation angles with respect to the pipe axis, forming a standing wave in the circumference and thereby a clear circumferential focus. The excitation response of the proposed transducer is theoretically analyzed with the normal mode expansion method. Finite element simulations of flexural mode excitation with the proposed transducer and a conventional circumferential array are further compared. The simulation results agree well with the theoretical predictions. Pure flexural modes of circumferential order of one are successfully generated. The excited signals are comprehensively analyzed. Furthermore, purity improvements are investigated with respect to the excitation frequency, element number, element width, and axial length. The excitation frequency should be appropriately chosen to suppress the unwanted modes. The element number should be sufficiently large to prevent the excitation of high circumferential order modes. The element width has negligible effect on the target flexural mode purity, whereas the element axial length significantly should be carefully chosen.

The effects of surface tension on spherical oscillatory indentation of viscoelastic materials

Abstract The oscillatory indentation has become an attractive approach to characterizing the viscoelastic properties of soft biological solids. However, the influences of surface tension on oscillatory responses are ignored, which might lead to an inaccurate measurement of mechanical properties. In this work, the influences of surface tension on spherical oscillatory indentation for viscoelastic materials are investigated through the finite element method. The viscoelasticity of solids is characterized by the standard linear solid model and a sinusoidal displacement is applied as the excitation signal. During an entire cycle at the steady state of oscillation, both the average value of contact radius and the dissipated energy decrease due to the presence of surface tension. For the oscillatory responses at various frequencies, the existence of surface tension results in an increase of average force but a decrease of phase angle. The force amplitude at low frequencies becomes higher when surface tension is considered. For the evaluation of the complex modulus, neglecting the surface tension would lead to a significant overestimation of storage modulus at low frequencies and an obvious underestimation of loss modulus when the normalized frequency approaches 1. Our results provide a comprehensive understanding of the effects of surface tension on the mechanical responses of oscillation and the determination of viscoelastic properties through oscillatory indentation.

High Impedance Microstrip Resonators and Transceiver Arrays for Ultrahigh Field 10.5T MR Imaging.

Multichannel transceiver coil arrays are needed to enable parallel imaging and B1 manipulation in ultrahigh field MR imaging and spectroscopy. However, the design of such transceiver coils and coil arrays often faces technical challenges in achieving the required high operating frequency at the ultrahigh fields and sufficient electromagnetic (EM) decoupling between resonant elements. In this work, we propose a high impedance microstrip transmission line resonator (HIMTL) technique that has unique high frequency capability and adequate EM decoupling without the use of dedicated decoupling circuits. To validate the proposed technique for the ultrahigh field 10.5T applications, a two-channel high impedance microstrip array with the element dimension of 8cm by 8cm was built and tuned to 447 MHz, Larmor frequency of proton at 10.5T, for signal excitation and reception. Bench tests and numerical simulations were performed to evaluate its feasibility and performance. The results show that the proposed high impedance microstrip technique can be a simple and robust way to design high frequency transceiver coils and coil arrays for ultrahigh field MR applications.

Integrated scanning electrochemical cell microscopy platform with local electrochemical impedance spectroscopy using a preamplifier.

Local electrochemical impedance spectroscopy (LEIS) has emerged as a technique to characterize local electrochemical processes on heterogeneous surfaces. However, current LEIS heavily relies on lock-in amplifiers that have a poor gain effect for weak currents, limiting the achievements of high-spatial imaging. Herein, an integrated scanning electrochemical cell microscopy is developed by directly collecting the alternating current (AC) signal through a preamplifier. The recorded local current (sub nA-level) is compared with the initial excitation signal to get the parameters for Nyquist plotting. By integrating this method into scanning electrochemical cell microscopy (SECCM), an image of LEIS at the Indium Tin Oxide/gold (ITO/Au) electrode is obtained with a spatial resolution of 180 nm. The established SECCM platform is integrated such that it could be positioned into the limited space (e.g. glove box) for real characterization of electrodes.

Influence of the Transducer-Mounting Method on the Radiation Performance of Acoustic Sources Used in Monopole Acoustic Logging While Drilling.

Transducers used in acoustic logging while drilling (ALWD) must be mounted on a drill collar, and their radiation performance is dependent on the employed mounting method. Herein, the complex transmitting voltage response of a while-drilling (WD) monopole acoustic source was calculated through finite-element harmonic-response analysis. Subsequently, the acoustic pressure waveform radiated by the source driven by a half-sine excitation voltage signal was calculated using the complex transmitting voltage response. The calculation results were compared with those obtained using finite-element transient analysis to verify the accuracy of the calculation method. The influence of transducer-mounting methods on the radiation performance of the monopole acoustic source was examined by modifying the material and structural dimensions of the coupling medium between the transducer and drill collar as well as the material and thickness of the protective cover. Numerical simulations were performed, and a transducer-mounting method suitable for ALWD was proposed based on the simulation results. Results showed that soft rubber (as the coupling material; thickness = 2 mm) enabled the WD monopole acoustic source to radiate robust acoustic energy in an infinite fluid. Increasing the height of the coupling material enhanced the radiated acoustic energy and reduced axial vibrations on the drill collar. The radiated acoustic pressure signal was unaffected by a steel protective cover (thickness = 0.5 mm). Conversely, increasing the cover thickness reduced the energy of the radiated acoustic signal. With increasing pulse width of the half-sine excitation voltage signal, the amplitude of the radiated acoustic pressure of the transducer initially increased and then declined, reaching a maximum at a pulse width that was 0.6 times the resonant period. Overall, the findings help in designing acoustic-source structures and excitation signals for ALWD tools.

Research on Structural Optimization and Excitation Control Method Using a Two-Dimensional OWPT System for Capsule Robots Based on Non-Equivalent Coils.

The rapid development of wireless power transfer (WPT) technology has provided new avenues for supplying continuous and stable power to capsule robots. In this article, we propose a two-dimensional omnidirectional wireless power transfer (OWPT) system, which enables power to be transmitted effectively in multiple spatial directions. This system features a three-dimensional transmitting structure with a Helmholtz coil and saddle coil pairs, combined with a one-dimensional receiving structure. This design provides sufficient internal space, accommodating patients of various body types. Based on the magnetic field calculation and finite element analysis, the saddle coil structure is optimized to enhance magnetic field uniformity; to achieve a two-dimensional rotating magnetic field, a phase difference control method for the excitation signal is developed through the analysis of circuit topology and quantitative synthesis of non-equivalent magnetic field vectors. Finally, an experimental prototype is built, and the experimental results show that the one-dimensional transmitting coil achieves a minimum received voltage stability of 94.5% across different positions. When the three-dimensional transmitting coils operate together, a two-dimensional rotating magnetic field in the plane is achieved at the origin, providing a minimum received power of 550 mW with a voltage fluctuation rate of 7.68%.

Application of Pulse Gas-Discharge Electroacoustic Transducer for Non-Destructive Testing

This paper presents the results of a gas-discharge electro acoustic transducer of two configurations, operating on the basis of a pulsed discharge in air at atmospheric pressure. The influence of the electrode configuration on the acoustic characteristics of the transducer is considered. It is shown that a change in the volume of the discharge chamber and the inter electrode gap have a significant effect on the radiation intensity of the transducer. The features that arise when using open and closed type electro acoustic transducers in flaw detection problems are revealed. It is shown that an open type gas-discharge electroacoustic transducer is a sufficiently powerful broadband source of the excitation signal and has prospects for use in non-destructive testing. A closed type gas-discharge electroacoustic transducer has advantages when testing materials with special requirements for surface cleanliness or the magnitude of the applied external electric field.

Method of oscillation excitation for investigation of inconsistency of coating deposition on long parts

A method is proposed for studying the uniformity of electrochemical coating on the outer wall of a thin metal rod by determining the parameters of natural oscillations of this rod, which is clamped on one side. The parameters are studied by analyzing the natural frequencies of the rod. The uneven coating of the rod wall causes a change in the frequency of transverse modes and the shape of the bending line of the rod axis. The mechanical vibrations of the rod are excited by the interaction of an external magnetic field with the Ampere force arising from the current flowing through the rod. A method of adaptive tuning of the spectral components of the excitation current is developed by modifying the coefficients of a digital filter through which a noise-like signal pass. The coefficients of the digital filter are changed adaptively, based on the analysis of the signal spectrum obtained in response to the excitation in the first step. The oscillation is excited by mixing the noise-like signal and the signal received in response to the excitation in the previous step after averaging with a sliding window, the coefficients of which are obtained from the resonance characteristics of the mechanical oscillatory system. A gradual change in the ratio of the amplitude of the noise-like and stationary components of the excitation signal causes a smooth increase in the amplitude of oscillation at a frequency approaching the frequency of the rod's natural oscillations. A numerical and full-scale experiment is carried out to excite mechanical vibrations of a thin metal rod, the end of which is clamped on one side.

Towards affordable biomedical imaging: Recent advances in low-cost, high-resolution optoacoustic microscopy.

This short review discusses the recent developments in low-cost, high-resolution optoacoustic microscopy systems, integrating laser diodes for signal excitation, which are 20-40 times cheaper than the typically employed Q-switched nanosecond laser sources. The development of laser diode-based microscopes can substantially improve not only cost efficiency, but also multispectral capabilities, robustness, portability and overall imaging performance of the optoacoustic technique. To this end, we demonstrate relevant implementations in both time and frequency domain, highlighting their representative applications in biomedical research such as microvasculature imaging, oxygen saturation assessments, hybrid and multiview microscopy of model organisms and tissues and Doppler flow speed measurements. Finally, we analyse the benefits and limitations of each approach, identifying the respective application contexts where they achieve optimum performance.

Dynamic modeling and parameters optimization of parallel – suspension type inertially stabilized platform

The development of a new generation platform stability system has broken through limitations in its core architecture. The system has both rapid response performance while retaining vibration isolation capability. However, there is an imperative requirement for model mechanism analysis and properties research on new systems. Accordingly, this research proposes a novel parallel – suspension type dynamics model of stabilized platform, and optimizes the key parameters. Concretely, spring elements considering columnar instability phenomenon are applied to isolators to create a parallel – suspension, which replaces the traditional series – gimbals configuration. Furthermore, a 3-DOF dynamic model of the inner frame of the stabilized platform is established, and the optimal parameters are obtained from a constraint index function presented by genetic algorithm. The numerical results show that the vibration isolation effect of the system attenuates the excitation signal energy by more than 70%, and still maintains the steering performance and stability simultaneously. The feasibility and superiority of the model and the parameter optimization method are tested by dynamics software, simulation signal and flight data respectively.

Modeling nonlinear behavior of piezoelectric actuators using improved WT-GRU neural network

The coupling of hysteresis and low damping vibration in a piezoelectric actuator results in low modeling accuracy and adversely affects output motion precision. To mitigate this problem, this paper proposes an improved wavelet transform gated recurrent unit (WT-GRU) model. This model integrates a convolutional layer with WT-GRU to enhance its capability to express complex relationships. Firstly, the input voltage sequence undergoes wavelet transform to decompose it into a set of frequency subsequences. Then, using the feature extraction and representation ability of the convolutional layer, significant features are extracted from subsequences to construct a time series feature vector. Finally, a gated recurrent unit is trained to predict the output displacement sequence accurately. Statistical metrics such as mean absolute error (MAE), root mean square error (RMSE), and coefficient of determination ( R2) were utilized to evaluate the model performance. Additionally, experimental tests were conducted with frequency excitation signals at 80–120 Hz. Experimental results show that the proposed model achieves a MAE of 0.0102 mm, an RMSE of 0.0148 mm, and an R2 value of 0.9478. This model exhibits a significant advantage in accurately predicting the output displacement of piezoelectric actuators, thereby providing a reliable foundation for designing piezoelectric actuator control systems.

Study of the Characteristics of Second-Order Underdamped Unsaturated Stochastic Resonance System Driven by OFDM Signals

Aiming at the issue of suboptimal demodulation performance in OFDM signal enhancement processes due to slow response speeds in first-order overdamped stochastic resonance systems, this paper designs an OFDM signal enhancement and demodulation system based on second-order underdamped unsaturated bistable stochastic resonance (SUUBSR). Firstly, a nonsaturated bistable potential function model is constructed by combining a traditional monostable potential function with a Gaussian potential function, and a damping coefficient is introduced simultaneously to build the SUUBSR system. Subsequently, the transient and steady-state output response analytical expressions of the SUUBSR system under OFDM signal excitation are derived, the energy loss of OFDM symbol waveforms caused by the transient response of the system is discussed, and the relationship between the damping coefficient and the steady-state output response of the system is explored. Finally, simulations are conducted to evaluate the enhancement and demodulation process of OFDM signals using the SUUBSR system. The simulation results show that at an input signal–noise ratio of 2 dB, compared to the first-order unsaturated bistable stochastic resonance (FUBSR) system, the proposed system reduces the system response time by 3.956% of a symbol period and decreases the demodulation bit error rate for OFDM signals by approximately 35%.

Real-time spectroscopic tracking of efficient intersystem crossing triggered by the heavy-atom effect in di-heteroatomic organic phosphorescent molecules.

The development of efficient and long-lived halogen-free organic phosphorescent molecules remains a challenge. For the single-heteroatomic 9,10-dihydroacridine (AcH2), the evolution of singlet and triplet excited state absorption signals reveals an intersystem crossing (ISC) lifetime of 8.2 ns and a triplet state lifetime of 0.52 µs. In contrast, the ISC lifetimes of di-heteroatomic phenoxazine (PXZ) and phenothiazine (PTZ) are significantly accelerated to 1.7 ns and 1.1 ns, respectively, while the triplet state lifetimes are extended to 0.72 µs and 4 µs. These results confirm that the introduction of di-heteroatomic synergistic effects enhances ISC efficiency while simultaneously prolonging the triplet state lifetimes. Notably, these two critical factors are further improved in PTZ due to the heavy-atom effect of sulfur atom. The work emphasizes the di-heteroatomic synergistic effect, particularly the role of heteroatoms with large atomic numbers, which is crucial for the design of halogen-free organic phosphorescent materials.

A Novel Simulation Model of Shielding Performance Based on the Anisotropic Magnetic Property of Magnetic Shields.

To achieve a near-zero magnetic field environment, the use of permalloy sheets with high-performance magnetic properties is essential. However, mainstream welding processes for magnetically shielded rooms (MSRs), such as argon arc welding and laser welding, can degrade the magnetic properties of the material. Additionally, neglecting the anisotropy of permalloy sheets can introduce unpredictable errors in the evaluation of MSR performance. To address this issue, this paper proposes a modified model for calculating the shielding factor (SF) of MSRs that incorporates the anisotropic magnetic characteristics of permalloy sheets. These characteristics were measured using a two-dimensional single sheet tester (2D-SST). A high-precision measurement system was developed, comprising a 2D-SST (to generate two-dimensional magnetic fields and sense the induced B and H signals) and a control system (to apply in-phase 2D excitation signals and amplify, filter, and record the B and H data). Hysteresis loops were tested at low frequencies (0.1-9 Hz) and under different magnetization states (0.1-0.6 T) in two orientations-parallel and perpendicular to the annealing magnetic field-to verify anisotropy under varying conditions. Initial permeability, near-saturation magnetization, and basic magnetization curves (BM curves) were measured across different directions to provide parameters for simulations and theoretical calculations. Based on these measurements and finite element simulations, a mathematical model was developed to adjust the empirical coefficient λ used in theoretical SF calculations. The results revealed that the ratio of empirical coefficients in different directions is inversely proportional to the ratio of magnetic permeability in the corresponding directions. A verification group was established to compare the original model and the modified model. The mean squared error (MSE) between the original model and the finite element simulation was 49.97, while the MSE between the improved model and the finite element simulation was reduced to 0.13. This indicates a substantial improvement in the computational accuracy of the modified model.

The de-icing method using synthesized envelope modulation signals from resonance low-frequency and ultrasonic signals

This paper proposes a method of combining low-frequency resonance signals and ultrasonic signals through envelope modulation to form an excitation signal for de-icing. Modulated signals are applied to a single type of actuator for de-icing, aiming to simplify the equipment required for de-icing and reduce power consumption. The envelope modulation signal is generated by combining low-frequency signals with ultrasonic signals using amplitude modulation, the Hamming window function, and the Hanning window function, respectively. The de-icing excitation effects of the modulation signals generated by different modulation methods at various initial phases on the ice-covered leading edge of the blade are calculated through numerical simulations. Simulations show that the modulation method and initial phase have a significant impact on the de-icing excitation effect. Experiments are conducted to explore the de-icing effectiveness and power consumption under different envelope modulation signal excitations. The results indicate that the envelope modulation signal de-icing method can simplify equipment and reduce power consumption, showing promising development and application prospects.

Hall effect thruster impedance characterization in ground-based vacuum test facilities

Hall effect thrusters (HETs) are typically regarded as DC electric propulsion devices as they are operated with isolated DC power supplies. However, it is well known that the HET’s discharge current possesses oscillations of varying magnitudes and frequencies and is thus a function of time with AC characteristics. The observed oscillations are caused by plasma processes associated with ion, electron, and neutral particle dynamics that occur inside the HET’s discharge channel and in the plume as the HET electrically interacts with its local operating environment. The extent to which plasma oscillations impact HET discharge dynamics is difficult to quantify due to the complexity of analyzing AC signals, given that the HET is a nonlinear, time-variant electrical load. In this work, we overcome the challenge of nonlinearity and time-variance of HETs by conducting a small-signal impedance analysis to characterize the effective resistance and reactance of the HET discharge with a novel and versatile impedance measurement diagnostic. The impedance magnitude and phase of a 7-kW class HET were measured from 100 Hz to 300 kHz with an excitation signal of ± 2 Vpk for two discharge operating conditions on krypton: 4.5 kW, 15 A and 6 kW, 20 A. The results were used to quantify resistive, capacitive, and inducive characteristics present within the HET discharge signature. For the 4.5 kW, 15 A thruster operating condition, the breathing mode capacitance was estimated to be 12.6 µF with an inductance of 15.3 µH. Furthermore, the impedance characteristics of the breathing mode are within ± 2.4 kHz of the power spectral density plots independently generated by time-resolved oscilloscope traces indicating good agreement in the frequency domain. Thus, the impedance measurement tool is a new diagnostic for characterizing the impedance and associated AC characteristics of HETs.

Parametric optomechanics

We investigate two-phonon parametric opto-mechanical generation in a solid state optical cavity pumped with two resonant counter-propagating coherent optical fields. We show that the optical frequencies of the fields must differ by more than the characteristic frequency of the stimulated Brillouin scattering in the material to support the parametric process. The optical harmonics associated with the subsequent optical scattering over the sound waves can be utilized for the excitation of low noise microwave signals.

Oscillation Suppression Method of Digital Proportional Valve Based on Fuzzy Intelligent PID Control

A digital proportional valve is constituted by the main spool and a high-speed on/off valve bridge acting as the pilot stage. However, the main spool will generate oscillation during movement under the control of the pilot stage. This results in poor stability, slow response speed, low control accuracy, and even the potential loss of control of the valve. To tackle this issue, an oscillation suppression method based on fuzzy intelligent proportional-integral-derivative (PID) control is put forward. The movement state of the main spool is determined in accordance with its movement position and velocity. Thereafter, the fuzzy control parameters of the controller are calculated on the basis of the determined movement state of the main spool. Different PID parameters are adopted to eliminate the control effect difference caused by the structural asymmetry of the two pilot control chambers of the main valve. The performance and robustness of the proposed control method are verified by comparison with the PID controller based on full-bridge and half-bridge control. The results demonstrate that the proposed control method can effectively suppress the oscillation of the main spool of the digital proportional valve, improve the control accuracy, and reduce the response time. When the excitation signal takes the form of a step signal, the overshoot of the control method put forward in this paper is diminished by 26.2% in comparison with that of the PID control. Under stable operating conditions, the maximum tracking error is less than 3.1%. Moreover, compared with simply using the PID control method, this error is reduced by 41%.

Strong hole-photon coupling in planar Ge for probing charge degree and strongly correlated states

Semiconductor quantum dots (QDs) in planar germanium (Ge) heterostructures have emerged as front-runners for future hole-based quantum processors. Here, we present strong coupling between a hole charge qubit, defined in a double quantum dot (DQD) in planar Ge, and microwave photons in a high-impedance (Zr = 1.3 kΩ) resonator based on an array of superconducting quantum interference devices (SQUIDs). Our investigation reveals vacuum-Rabi splittings with coupling strengths up to g0/2π = 260 MHz, and a cooperativity of C ~ 100, dependent on DQD tuning. Furthermore, utilizing the frequency tunability of our resonator, we explore the quenched energy splitting associated with strong Coulomb correlation effects in Ge QDs. The observed enhanced coherence of the strongly correlated excited state signals the presence of distinct symmetries within related spin functions, serving as a precursor to the strong coupling between photons and spin-charge hybrid qubits in planar Ge. This work paves the way towards coherent quantum connections between remote hole qubits in planar Ge, required to scale up hole-based quantum processors.

Dynamic modelling and mechanical analysis of an inertial linear piezoelectric actuator with double stators

Abstract To achieve higher output performance in precision applications, and in order to gain deeper insight into operation principle, a dynamic model is established including the transmission relationship between the stators, the driving shaft, and the mover based on a slip-slip type inertial linear piezoelectric actuator with double stators. The influence of stator material and symmetry ratio of the excitation signal on the vibration characteristics of the stator and the output performance are investigated. This study reveals the relationship between these factors through a combination of simulations and experiments. Prototypes using several materials are machined and assembled, and the vibration characteristics and output performance are rigorously tested. The results obtained from the experimental measurements are consistent with the simulation results, confirming the validity and rationality of the dynamic model. The experimental results of the stator, as well as the actuator, are analyzed. It can be concluded that the actuator is able to output a larger effective displacement in one motion period with the increased symmetry ratio of the triangular wave signal, applied with a higher operating frequency, resulting in a higher output velocity of 42 mm/s and a larger load of 300 g with the steel stator, and a higher displacement resolution of 18 nm can be achieved using the AL alloy stator. This research not only provides an effective method for enhancing and selecting the desired output performance for the researched actuator but also can be extended to other slip-slip type inertial linear piezoelectric actuators.