Minimum Resonant Frequency Research Articles

Optimal Design of the Modular Joint Drive Train for Enhancing Cobot Load Capacity and Dynamic Performance

Automation advancements prompts the extensive integration of collaborative robot (cobot) across a range of industries. Compared to the commonly used design approach of increasing the payload-to-weight ratio of cobot to enhance load capacity, equal attention should be paid to the dynamic response characteristics of cobot during the design process to make the cobot more flexible. In this paper, a new method for designing the drive train parameters of cobot is proposed. Firstly, based on the analysis of factors influencing the load capacity and dynamic response characteristics, design criteria for both aspects are established for cobot with all optimization design criteria normalized within the design domain. Secondly, with the cobot in the horizontal pose, the motor design scheme is discretized and it takes the joint motor diameter and gearbox speed ratio as optimization design variables. Finally, all the discrete values of the optimization objectives are obtained through the enumeration method and the Pareto front is used to select the optimal solution through multi-objective optimization. Base on the cobot design method proposed in this paper, a six-axis cobot is designed and compared with the commercial cobot. The result shows that the load capacity of the designed cobot in this paper reaches 8.4 kg, surpassing the 5 kg load capacity commercial cobot which is used as a benchmark. The minimum resonance frequency of the joints is 42.70 Hz.

Measurement of Complex Permittivity for Rapid Detection of Liquid Concentration Using a Reusable Octagon-Shaped Resonator Sensor

Substrate-integrated waveguides (SIWs) are widely used in microwave systems owing to their low cost and ease of integration. In this study, an SIW-based resonator that reacts to the complex permittivity variation of solutions with dimensions of 79.2 mm × 59.8 mm is introduced. This octagon-shaped sensor can be installed on a preliminary monitoring system to test water quality by observing the parameter variations caused by external factors. The resonant structure was used to test different concentrations of ethanol-water and acetone-water mixtures for verification. The resonant frequency and quality factor (Q-factor) were found to vary with the relative complex permittivity of the liquid in the S-band, and the electric field distribution varied when liquid droplets were placed in the center of the substrate. The designed sensor operates at 2.45 GHz in the air, and the observed minimum resonant frequency shift with liquid was 15 MHz. The measurement error was approximately 3.1%, and the results reveal a relationship between the resonant frequency and temperature as well. Considering the observed sources of error, the measured relative permittivity is consistent with the actual values. The proposed sensor is economically convenient and suitable for various test environments.

Tank acoustics substantially distort broadband sounds produced by marine crustaceans.

Marine crustaceans produce broadband sounds that have been mostly characterized in tanks. While tank physical impacts on such signals are documented in the acoustic community, they are overlooked in the bioacoustic literature with limited empirical comparisons. Here, we compared broadband sounds produced at 1 m from spiny lobsters (Panulirus argus) in both tank and in situ conditions. We found significant differences in all sound features (temporal, power, and spectral) between tank and in situ recordings, highlighting that broadband sounds, such as those produced by marine crustaceans, cannot be accurately characterized in tanks. We then explained the three main physical impacts that distort broadband sounds in tanks, respectively known as resonant frequencies, sound reverberation, and low frequency attenuation. Tank resonant frequencies strongly distort the spectral shape of broadband sounds. In the high frequency band (above the tank minimum resonant frequency), reverberation increases sound duration. In the low frequency band (below the tank minimum resonant frequency), low frequencies are highly attenuated due to their longer wavelength compared to the tank size and tank wall boundary conditions (zero pressure) that prevent them from being accurately measured. Taken together, these results highlight the importance of understanding tank physical impacts when characterizing broadband crustacean sounds.

Tapered substrate thickness to enhance the performance of a piezoelectric energy harvester

In this paper, the improvement of the performance of a piezoelectric (PZ) cantilever beam using a non-uniform substrate thickness is presented. This reduces the resonant frequency, improves the stress distribution and generates more output voltage and power. Both analytical and finite-element method analyses were performed to investigate the effect of a tapered substrate thickness on a PZ cantilever beam. A tapered substrate thickness was used in rectangular and trapezoidal cantilever structures. All of the designed cantilever structures had the same fabrication area, and their performance was evaluated and compared using an excitation acceleration of 1g (9.8 m/s2). The tapered-down trapezoidal cantilever achieved a minimum resonant frequency of 62.41 Hz, which was 48.83% less than the resonant frequency of the uniform rectangular cantilever beam. The output peak voltage and average power of the proposed tapered-down trapezoidal cantilever beam were 12.36 V and 21 μW, respectively, which were improved by 44 and 74.48%, respectively, compared with those of the uniform rectangular cantilever structure.

Ternary optimization for designing metasurfaces

A fully automated approach for designing metasurfaces whose unit cell may include metallic vias is proposed. Towards this aim, a ternary version of the particle swarm optimization (PSO) algorithm is employed in order to find the optimal metallic pattern and via-hole positions simultaneously. In the proposed design method, the upper surface of the unit cell is first pixelated. One of the possible three states of a metallic covered pixel, an uncovered etched pixel and a pixel containing a centered metalized via-hole is assigned to each pixel. The optimal state of each pixel is then determined by utilizing a ternary PSO algorithm to achieve favorable design goals. This method can be used for designing various metasurfaces as well as other via-assisted electromagnetic structures. As a proof of concept, the proposed method was applied to design two surfaces: a frequency selective surface with a minimum resonance frequency, and a linear-to-circular polarization converter with a maximum polarization conversion bandwidth. Comparison of the results with previous works confirms the efficiency and capability of the proposed method to design diverse metasurfaces in an automated fashion without the need for any theoretical or physical model.

Multi-domain ferromagnetic resonance in magnetic van der Waals crystals CrI3 and CrBr3

Two-dimensional (2D) magnetic van der Waals crystals have received great attentions recently owing to their novel electronic and magnetic properties and rich potentials for low-dimensional and high-density spintronic devices. We investigated the magnetization dynamics of CrI3 and CrBr3 bulk single crystals by utilizing broadband ferromagnetic resonance (FMR) in a frequency range of 1 – 40 GHz and over a wide temperature range of 10 – 300 K. Complex features observed in the FMR spectra are quantitatively described by the multi-domain FMR theory. The minimum resonance frequency fmin in FMR spectra was recognized and analyzed as characteristics of the transition of the domain structure. Micromagnetic simulation on the domain structure and spin dynamics explains that the multi-domain structure exists under strong in-plane magnetic field for CrI3 and CrBr3 and significantly influences the magnetic dynamics properties. Our results also suggest that the linewidths of FMR spectra in CrI3 and CrBr3 are dominated by the magnetic inhomogeneous broadening.

Modal Analysis of Bus Body Structure using Finite Element Analysis Technique

Present work deals with evaluation of dynamic characteristics of a bus body structure. The bus under consideration is a sleeper non-air conditioned vehicle for a passenger capacity of thirty and it is designed adhering to automotive industry standards. Modal analysis of the proposed bus design is carried using Ansys Workbench. With the aid of modal analysis ten mode shapes of the bus are postulated, corresponding frequencies and deflections are estimated. Mesh generator is used to mesh the complex bus model. The deflection and frequency magnitudes of proposed bus model is found with the help of Finite Element Analysis (FEA) technique and they are in good agreement with experimental results available in literature. Engine being the prime source of excitation, it’s frequency is compared with the frequencies determined by FEA of the proposed bus body and it is observed that the frequencies of the bus body for ten different modes are far less than the minimum resonant engine frequency.

Multi-factors analysis on the energy harvesting performance of PEH under multiple-frequency excitation

The piezoelectric energy harvesters (PEHs) undergoing coupled bending-torsional vibrations were designed by crossbeam-offset and asymmetric mass, and the maximum output peak voltage at the first mode (Up-max1) and the minimum resonance frequency difference between the first and second modes (Δf0) were 81.5 V and 16.0 Hz chosen as the optimization objectives in the multi-factors analysis based on the orthogonal test method. The geometrical parameters including the crossbeam length, mass ratio, substrate thickness and primary beam length are correspondingly determined, before the PEHs were fabricated to investigate the optimum resistance and energy harvesting efficiency. The PEHs were constructed as the series connection structure, and the mechanical vibration experiments were performed to measure output peak voltage vs frequency curve. When the load resistance is applied from 47 to 1000 kΩ, all of the optimum resistances are about 470 kΩ for the PEHs with the offset ratio 1.23 and mass ratio 4. The errors are at the ranges of 5.0%–16.4% for Up-max and 1.1%–6.5% for f0, and the measurement reliability is acceptable. The sums of half-power bandwidths are regarded as the energy harvesting characteristic to evaluate the efficiency, and they are broaden by 133% and 180% for the PEHs with crossbeam-offset and asymmetric mass under multiple-frequency excitation. PEH undergoing coupled bending-torsion vibrations could harvest more electrical power at multiple resonance frequencies in nature environment.

Fabrication, Structure and Mechanical and Ultrasonic Properties of Medical Ti6Al4V Alloys Part I: Microstructure and Mechanical Properties of Ti6Al4V Alloys Suitable for Ultrasonic Scalpel.

Ti6Al4V alloy has been considered as a key component used in ultrasonic scalpels. In this series of papers, the fabrication, structure, and mechanical and ultrasonic properties of medical Ti6Al4V alloys suitable for ultrasonic scalpel are studied systemically. These alloys with low elastic modulus and present a typical bimodal microstructure with relatively high β phase content (~40%) and lamellar α thickness of ≤ 0.9 µm. In the first paper, the relationship between the microstructure and mechanical properties of hot-rolled Ti6Al4V alloys treated by heating treatment is discussed. In the second paper, the dependence of the ultrasonic properties on the microstructure of the heat-treated Ti6Al4V alloys is reported. With increasing solid solution temperature, the content and size of the primary α phase decrease. In contrast, the content and size of the lamellar α phase increase. Additionally, the β phase content first increases and then decreases. The microstructure of Ti6Al4V alloys could be slightly changed by aging treatment. When the solid solution treatment temperature increases to 980 °C from 960 °C, the average size of the lamellar α phase in the alloys increases by 1.1 µm. This results in a decrease in the average yield strength (93 MPa). The elastic modulus of alloys is mainly controlled by the β phase content. The microstructure of alloys by solution-treatment at 960 °C shows the highest β phase content and lowest average elastic modulus of 99.69 GPa, resulting in the minimum resonant frequency (55.06 kHz) and the highest average amplitude (21.48 µm) of the alloys at the length of 41.25 mm.

Fabrication, Structure, and Mechanical and Ultrasonic Properties of Medical Ti6Al4V Alloys Part II: Relationship between Microstructure and Mechanical Properties and Ultrasonic Properties of Ultrasonic Scalpel.

In this study, the ultrasonic resonance parameters of Ti6Al4V alloys under different heat treatments are measured by an impedance analyzer. The amplitude of the specimens is measured experimentally by means of optical microscope and image analysis software. These results show that the ultrasonic properties of Ti6Al4V alloys are closely related to β phase content and elastic modulus of the alloys. The highest volume fraction of the β phase appears in the specimen treated by solid solution treatment at 960 °C is 40.2%. These alloys present the lowest average elastic modulus (~99.69 GPa) and the minimum resonant frequency (55.06 kHz) and the highest average amplitude (21.48 µm) when the testing sample length is 41.25 mm. These findings can be used to guide the design of medical Ti6Al4V alloys for ultrasonic scalpels.

Development of dissipative elastic metamaterials based on the layered cantilever-in-mass structure for attenuating the broad spectrum vibrations

In this paper, the layered cantilever-in-mass structures (LCIMs) will be theoretically investigated to reveal the effects of the layered structures on band gaps, which have great potential to bring in many useful material properties without much increasing the manufacturing difficulty by stacking the damped layers or other different component layers. Firstly, the negative effective mass model of LCIMs is derived based on the mass-in-mass model, which is applied to analyze the effective parameters of band gaps in terms of the geometrical features and material properties, the analytical results indicate the negative effective masses of LCIMs depend highly on the material parameter and thicknesses of each constituent layers. Then the LCIMs consist of the same thickness layers are further researched, which has found that their resonance frequency are independent on the layer thickness, and the numeric values of resonance frequencies are between the maximum and minimum local resonance frequency of their constituent layers. To validate the above analytical model, the three-dimensional model and the two-dimensional shell model of LCIMs are constructed in COMSOL Multiphysics. The obtained results show well agreement with the derived model in both the three-dimensional model and shell model. Finally, the dissipative LCIMs modeled by stacking the damped layers and metal layers are studied and discussed.

Printing of Wearable Antenna on Textile

A wearable antenna which is meant to be a part of the clothing used for communication purposes includes tracking, navigation and mobile computing has been seen in demand due to the recent miniaturization of wireless devices. Printing of conductive ink provides flexibility properties on electronics thus allowing it to be used on conformal surfaces. However, the current printing techniques mostly suffer from ink incompatibility and limited of substrates to be printed with. Hence, this paper intend to discloses the printing of wearable antenna using alternative technique via syringe-based deposition system with conductive ink on textile. A validation between simulation and measurement of return loss, (S11) and radiation pattern of the antenna printed is also performed. It was found that a functional antenna is successfully printed on textile since the performances obtained are as expected. The antenna resonated at a minimum resonant frequency of 1.82 GHz which the S11 gathered at-18.90 dB. The radiation pattern for both simulation and measurement is as predicted since both have a larger magnitude of the main lobe than the side lobe. The magnitude of the main lobe from measurement was observed to be 8.83 dB higher than the magnitude of the main lobe of the simulation which is only 3.77 dB. It is proven that the syringe-based deposition system is capable of printing functional antenna on textile.

Of Own and Forced Vibrations of Dissipative Inhomogeneous Mechanical Systems

In the work, the problems of proper and forced oscillations of dissipative mechanical systems, consisting of rigid and deformable bodies are solved. To quantify the dissipative properties of the system, two values are proposed: the minimum resonance frequency of natural oscillations and the maximum resonant amplitude. In the study of the problem of dissipative inhomogeneous mechanical systems, a nonmonotonic dependence of the damping coefficients on the parameters of the system was observed. The concepts are derived Global damping factor, which characterizes the Damping properties of the dissipative mechanical system as a whole.

Investigation of a serially coupled double microsphere resonator to expand resonance frequency spacing of microsphere resonators

A serially coupled double microsphere resonator is investigated to reduce the nonfundamental resonances and therefore expand the resonance frequency spacing in microsphere resonator systems. Coupled-mode theory is used to model the system and investigate the resonator parameters as coupling efficiency. As a result, it is shown that the nonfundamental resonances in the output spectrum of a single 225 μm microsphere are reduced noticeably and therefore its minimum resonance frequency spacing is expanded from 5.2 pm to 0.6 nm by serially coupling to a 50 μm radius microsphere. Furthermore, it is shown that the quality factor of this resonator can reach 2.14×108, which is on the same order of a single 225 μm microsphere resonator. The model is verified by comparing the results of the model with the experimental results published by other groups to investigate induced transparency in the coupling of two microspheres.

Elliptical ultrasonic–assisted turning tool with longitudinal and bending vibration modes

Ultrasonic-assisted turning is a machining process in which a vibrational displacement (usually in ultrasonic frequencies) is superimposed with the machining displacements in the cutting direction (one-dimensional ultrasonic-assisted turning) or in the cutting direction along with the radial direction (two-dimensional ultrasonic-assisted turning or elliptical ultrasonic–assisted turning). In this research, an elliptical ultrasonic–assisted turning tool is designed in ABAQUS software, in which the longitudinal and bending vibration modes have the minimum resonance frequency difference, so that the resonance of both the vibration modes can be achieved in a definite frequency. A set of half-ring piezoelectric stacks is employed for excitement of the bending mode, and a set of ring-shaped piezoelectric stacks is used for the excitement of the longitudinal mode. There is a phase shift with the amount of π/2 between the longitudinal and bending vibration modes to produce an elliptical vibration. The manufactured tool is employed for machining of copper, which resulted in better surface finish and lower cutting forces.

Microbead-assisted high resolution microwave planar ring resonator for organic-vapor sensing

A microbead-assisted planar microwave resonator for organic vapor sensing applications is presented. The core of this sensor is a planar microstrip split-ring resonator, integrated with an active feedback loop to enhance the initial quality factor from 200 to ∼1 M at an operational resonance frequency of 1.42 GHz. Two different types of microbeads, beaded activated carbon (BAC) and polymer based (V503) beads, are investigated in non-contact mode for use as gas adsorbents in the gas sensing device. 2-Butoxyethanol (BE) is used in various concentrations as the target gas, and the transmitted power (S21) of the two port resonator is measured. The two main microwave parameters of resonance frequency and quality factor are extracted from S21 since these parameters are less susceptible to environmental and instrumental noise than the amplitude. Measured results demonstrate a minimum resonance frequency shift of 10 kHz for a 35 ppm concentration of BE exposure to carbon beads and 160 kHz for the polymer based adsorbent at the same concentration. The quality factor of the resonator also changed for different concentrations, but a distinguishable variation is observed for the BAC adsorbents. The high quality factor of the sensor provides the opportunity of real time monitoring of the adsorbent behaviors in remote sensing mode with very high resolution.

MODELING OF A 4DOF PRECISE POSITIONING STAGE BY FINITE ELEMENT METHOD

This paper proposes a novel 4DOF precise positioning stage on the rotational platform for the calibration of the rotary encoder’s raster scales. The 4DOF precise positioning stage is featured with flexure-based joints and mechanical actuation mechanisms. The flexure-based joints for required motion were optimised. Their performances in terms of maximum and minimum output displacements, maximum stress and resonant frequency have been evaluated via finite element analysis approach, using SolidWorks Simulation software package. DOI: http://dx.doi.org/10.5755/j01.mech.18.4.2331

Effects of scaling and geometry on the performance of piezoelectric microphones

Recent advances in microfabrication and nanofabrication techniques have allowed for the construction of ever-smaller sensors for the measurement of acoustic signals. The physics of sensor transduction and acoustics however place fundamental constraints on performance and limit the benefits of continual reductions in size. Key operating parameters such as sensitivity, minimum detectable signal (MDS) and resonant frequency are directly affected by device scale. Besides overall scale, relative sensor geometry (e.g. thickness ratio) can drastically alter performance. Through finite element and lumped element modeling, we study the effects of sensor geometry and scale on the sensitivity and noise performance of a piezoelectric microphone. The results indicate optimal relative geometric parameters for maximum performance and demonstrate the strong dependence on device geometry.

Size effect of Fe nanoparticles on the high-frequency dynamics of highly dense self-organized assemblies

Molded Fe nanoparticle (NP) assemblies 4 mm × 8 mm × 0.3 mmt in size were fabricated by a uniaxial press from Fe NPs 3 nm to 22 nm in diameter, and their high-frequency dynamics and static properties were investigated. The freezing temperature of the magnetic moment of the assemblies increased from 25 K to over 400 K with an increasing Fe NP diameter, and for particles larger than 8.1 nm, the Fe NP assemblies showed ferromagnetic behavior even at room temperature. For particles smaller than 8.1 nm, on the contrary, the assemblies showed superparamagnetism at room temperature. From the complex magnetic susceptibility spectra of the assemblies normalized by the volume of the Fe NPs, χ′Fe, and χ″Fe, the minimum ferromagnetic resonance frequency, fr (106 MHz), and maximum χ′Fe at 1 MHz (123) were obtained at 8.1 nm. The fr of the Fe NP assembly increased because of an enhanced magnetostatic interaction field between NPs larger than 8.1 nm. For NPs smaller than 8.1 nm, in the superparamagnetic phase, the thermal magnetic field increasingly dominated the effective magnetic field with a decreasing NP diameter. This indicates the existence of a critical diameter for the thermal fluctuation of the moment, which competes with the magnetostatic interactions between the Fe nanoparticles.

Mathematical Modeling, Equivalent Circuit Analysis and Genetic Algorithm Optimization of an N-sided Regular Polygon Split Ring Resonator (NRPSRR)

In this paper, a mathematical model is proposed to estimate the resonant frequency of a N-sided Regular Polygon Split Ring Resonator (NRPSRR), which is extended to the Circular Split Ring Resonator (CSRR) for N tending to infinity. The model also predicts the variation in the resonant frequency with the angle of rotation (skew) between the inner and the outer polygon. It is mathematically shown that the minimum resonant frequency is obtained at zero skew. Genetic Algorithm Optimization is used over the independent parameters deciding the geometry of the NRPSRR to optimize them for a particular desired resonant frequency by minimizing the relative error between the calculated and desired frequency. NRPSRR metamaterial loaded microstrip antenna could be used to obtain highly directional beam pattern and increased gain for miniaturized (electrically small) antenna systems in the microwave regime.