Reduction In Resonant Frequency Research Articles

Flexible Wearable Pre-fractal Antennas for Personal High-Temperature Monitoring

This paper proposed a new flexible and wearable antennas design based on teragon pre-fractal geometry until the third level, for monitoring high-temperature in humans for wireless body area network operating band. The antennas were built in polyamide laminate dielectric material, which has suitable thermal and mechanical resistance characteristics for application in wearable antennas. The antenna’s structure was generated by teragon pre-fractal geometry using a MATLAB code and simulated with commercial software ANSYS. The application of teragon geometry allows controlling the resonance frequencies and radiation characteristics in comparison to simple square geometry. Teragon level 3 has provided maximum resonance frequency reduction, about 142.4%. In comparison of simulated and measured results on-body we noted that variation of resonance frequency is directly proportional to the fractal level, with the increase of fractal level there is greater variation in the difference between the simulated and measured resonance frequency, close results of gain, and higher simulated SAR value of 0.0653 mW/kg (K = 2), being within standard indicated by international institutions such as FCC and IEEE.

Mesoporous Silica Microspheres Composited with SBA-15s for Resonance Frequency Reduction in a Miniature Loudspeaker

Microspheres composited with mesoporous SBA-15 particles and silica were investigated as fillers in miniature loudspeakers to study the factors influencing the resonance frequency offsets(RFOs). Mesoporous silica microspheres(MSMs) were prepared by self-assembling SBA-15 mesoporous silica in a microemulsion synthesis system. The formation process involved the fabrication of a stable O/W microemulsion of tetrabutyl orthosilicate(TBOS) and hexadecyltrimethylammonium bromide(C16TAB) and encapsulation of SBA-15s. The RFO increased and then decreased with increasing particle size(in the length range of 0.7–5.5 µm and in the width range of 0.2–0.45 µm), increased with increasing pore size(in the range of 7.0–9.4 nm) of SBA-15s, and increased with decreasing particle size(105–900 µm) of MSMs.

Association Between Bedroom Particulate Matter Filtration and Changes in Airway Pathophysiology in Children With Asthma

Fine particles (particulate matter 2.5 μm [PM2.5]), a ubiquitous air pollutant, can deposit in the small airways that play a vital role in asthma. It appears to be unknown whether the use of a PM2.5 filtration device can improve small airway physiology and respiratory inflammation in children with asthma. To discover what pathophysiological changes in the small airways are associated with using a PM2.5-removing device in the bedrooms of children with asthma. Children with mild or moderate asthma were enrolled in this double-blind, crossover study. The participants used a true filtration device and a sham filtration device in their bedrooms in a random order for 2 weeks each with a 2-week washout interval. The study was conducted in a suburb of Shanghai, China, during a low-ozone season. Ozone and PM2.5 were measured inside bedrooms and outside a window. Impulse oscillometry, spirometry, and fractional exhaled nitric oxide were measured at the beginning and the end of each intervention. Peak expiratory flow was measured twice daily at home. Forty-three children (5-13 years old; 26 boys [60%]) participated. Outdoor 24-hour mean PM2.5 concentrations were moderately high, ranging from 28.6 to 69.8 μg/m3 (median, 53 μg/m3). During true filtration, bedroom PM2.5 concentrations were a mean (SD) of 63.4% (35.9%) lower than during sham filtration. Compared with sham filtration, true filtration was significantly associated with improved airway mechanics, reflected in a 24.4% (95% CI, 11.8%-37.1%) reduction in total airway resistance, a 43.5% (95% CI, 13.7%-73.3%) reduction in small airway resistance, a 22.2% (95% CI, 2.2%-42.2%) reduction in resonant frequency, and a 73.1% (95% CI, 0.3%-145.8%) increase in airway reactance. True filtration was also associated with significant improvements in fractional exhaled nitric oxide (a 27.6% [95% CI, 8.9%-42.4%] reduction) and peak expiratory flow (a 1.6% [95% CI, 0.8%-2.5%] increase). These improvements were significantly associated with bedroom PM2.5 reduction. Improvements in small airway function were nonsignificant (8.4% [95% CI, -1.4% to 18.3%]) in all participants but significant (13.2% [95% CI, 1.2%-25.1%]) in participants without eosinophilic airway inflammation at baseline. No improvements were observed for forced vital capacity, forced expiratory volume during the first second, and the ratio of these in all participants or subgroups. Per these results, indoor PM2.5 filtration can be a practical method to improve air flow in an asthmatic lung through improved airway mechanics and function as well as reduced inflammation. This warrants a clinical trial to confirm. ClinicalTrials.gov Identifier: NCT03282864.

An Essential Cause of Stall Stagnations in Compressor Surges

The author has proposed in the preceding study on the behaviors of infinitesimal perturbations of surge in simplified compressor systems that the occurrences of stagnations could be closely related with the travelling wave conditions of the surge oscillations through the phase-differences and the propagations along the flowpaths. The concept was applied to real situations of systems of compressors and flowpaths in the present study. It resulted in a non-dimensional parameter named flowpath-average reduced resonance frequency, fSUBRav/SUB, which is an equivalent of the phase-propagation parameter proposed in the preceding study. It is finally a product of the resonance frequency of the system and the time required for the fluid particles to pass through the whole flowpath, namely, the total number of excitations that the fluid particles suffer in the time. A number of numerical experiments on compressor surges have demonstrated that the fSUBRav/SUB parameter could explain the cause of surge stagnations very simply and clearly. It has values of 1.5 – 3 at the stagnation boundaries for variations in flowpath configurations and compressors having a single-stage to nine stages. It means that the stagnations occur for the total number of the excitation cycles less than 1.5-3. It could be the most essential cause of the stagnations. In other words, deep surges could develop only after the fluid particles have experienced more number of cycles of the excitations in the passing time. In further, the fSUBRav/SUB parameter is made more comprehensive by multiplication of the compressor tip Mach number Mt, i.e., fSUBRav/SUB×MSUBt/SUB, which gives a nearly constant value of 1.5 over a wide range of flowpath configurations and tip speeds of compressors, for relatively small number of stages. Those parameters not only suggest the essential cause of surge stagnations, but also are the simplest and clearest measurers of stagnation boundaries. It is much easier to apply in real situations of the systems than any of the parameters proposed so far. However, for multi-stage compressors in long delivery flowpaths and in off-design operations, the parameters appear to deviate somewhat from the constant value.

Miniaturized dual‐band slot antenna design for GPS, amateur radio and WLAN applications

In this article, miniaturization of dual-band slot antenna design for GPS, WLAN and amateur radio applications is presented. The proposed dual-band miniaturized antenna is achieved using slits, rectangular split ring and metallic strips fed by 50 Ω microstrip feed. The first resonant frequency is achieved by loading reference antenna with eight slits that is antenna 1 and the second resonant frequency is achieved by loading with one center slits and rectangular split ring that is antenna 2. Dual-band antenna is achieved by loading reference slot antenna with nine slits and rectangular split ring which resonates at frequency of 1.52 and 3.03 GHz respectively. As a result, it is achieved 53.79% reduction in first band resonant frequency with 76.07% improvement in −10 dB bandwidth and 7.90% reduction in second band resonant frequency compared to reference slot antenna. Further, this dual-band antenna is miniaturized by metallic strips which are placed on the bottom of the substrate. This results in 61.39% reduction in first band resonant frequency with 32.07% improvement in −10 dB bandwidth and 26.13% reduction in second band resonant frequency in comparison with reference slot antenna topology.

Effect of seismic mass thickness on the resonance frequency of cantilever type piezoelectric energy harvester

Piezoelectric energy harvesters find applicability in remote area of application because of simple design and operation. Micro-electromechanical system (MEMS) process technology is utilized to fabricate these cantilever based structures. Piezoelectric layer length and thickness are the key parameters for controlling the resonance frequency. However, for further lowering the resonance frequency and having optimal output a seismic mass is introduced at the tip of the cantilever structure. In this paper, the effect of increasing the thickness of the seismic mass on the resonance frequency of the cantilever structure has been investigated. Finite Element Method (FEM) results have been obtained using Coventorware software by varying the thickness of the seismic mass 10–20 µm. It has been observed the variation of the thickness of the seismic mass has an effect on the resonance frequency of the cantilever. As the thickness increases, the volume of the seismic mass increases and the resonance frequency of the cantilever decreases. The base of the cantilever is Silicon; Aluminum Nitride (AlN) piezoelectric material has been selected of 3 µm thickness. The length of the silicon cantilever is varied from 1600 to 2500 µm and the resonance frequency is obtained. At a length of 1600 µm, variation of seismic mass thickness from 10 to 15 µm results in reduction in resonance frequency by 17.27% whereas when seismic mass is varied from 15 to 20 µm the resonance frequency is reduced by 12.63%.

T-Shaped Piezoelectric Structure for High-Performance MEMS Vibration Energy Harvesting

In the recent decades energy harvesting from ambient vibration by the micro-electromechanical systems (MEMS) has been recognized as a promising solution to boosting lifespan of low-power electronic devices. Apparently, highly efficient MEMS vibration harvesters with lower operational frequencies are advantageous. In this paper we propose a new mechanical structure to aim for energy conversion efficiency enhancement and operational frequency reduction for the piezoelectric MEMS vibration energy harvesters. The proposed structure has a T-shaped geometry with integration of two identical proof masses at the T-segment. Thanks to two degrees-of-freedom, in this structure both bending and torsional mode frequencies can be located close to each other. Its analytic model of frequency response is derived and then validated by finite element modeling (FEM) simulations and prototype measurements. Compared to the conventional straight cantilever configuration, our proposed T-shaped piezoelectric cantilever structure can help distribute mechanical strain in broader areas with higher magnitude and lower resonant frequency. Our analytical, numerical, and experimental studies show that the normalized power density of the proposed T-shaped harvester is 4.8 times higher than that of the conventional one, in addition to 36% resonant frequency reduction. [2019-0146]

MEMS meander harvester with tungsten proof-mass

Using current battery technology the life-time of a leadless pacemaker is approximately 6-10 years, with a large portion of the pacemaker occupied by the battery. This paper investigates the possibility to use a MEMS piezoelectric harvester as a complementary energy source in leadless pacemakers. The challenge is to combine the low resonance frequency required to harvest energy from a heartbeat with the small volume of 20×4×3 mm3 available, with the corresponding harvester displacement restricted to 2 mm. Due to the displacement restriction the selected structure was a double clamped bridge in order to reduce the mass displacement, with various meander-type designs simulated to reduce resonance frequency. To further reduce resonance frequency large proof-masses of tungsten were attached by gluing. Two types of tungsten proof-masses were added to four different harvesters, 16.4 mg and 16.6 mg on sample 1 and 2 and 502 mg and 492 mg proof-mass on sample 3 and 4. The structures have 2 µm patterned PZT (deposited by sol-gel technique) and Pt metal electrodes for d31 mode harvesting. The power output measured from one of the two PZT/electrodes was 0.13 nW with 50 µm deflection at 100 k Ω optimal load resistance and 9.1 mVpp at 232 Hz.

Piezoelectric Composite Vibrator with a Bilaminated Structure for Bending Vibration

A piezoelectric composite vibrator with a bilaminated structure is designed and fabricated, in this work by applying bending vibration to increase vibration displacement and reduce resonance frequency. The finite element software ANSYS (ANSYS, Inc. USA) is used to simulate the 2-2 and 1-3 piezoelectric composite bilaminated vibrators under free boundary condition and optimize their design. Simulation results show that the vibration displacement of the 2-2 vibrator is higher than that of the 1-3 vibrator, and the resonance frequency of the former is lower than the latter. Five pieces each of the 2-2 and piezoelectric ceramic vibrators are prepared. In addition, simulation and experimental results indicate that the vibration displacement of the 2-2 vibrator increases by 2.3 times, whereas its resonance frequency decreases by nearly 100 Hz, in comparison with those of the piezoelectric ceramic bilaminated vibrator.

Resonant Frequency Reduction of Piezoelectric Voltage Energy Harvester by Elastic Boundary Condition

ABSTRACTMost vibration-based energy harvesters, including piezoelectric harvester system, perform efficiently at only its resonant frequency as linear resonators, usually at very high frequency which are out of the range of frequency of interest. In real life applications, these linear resonators are impractical since real ambient vibrations are simply having varying lower frequencies. Hence, design a tuneable vibration energy harvester at a lower and useful frequency range of interest are essential in allowing promising energy output to meet intended power input at a more practical approach. In this paper, the piezoelectric voltage energy harvester (PVEH) was designed with a flexible fixture with the aim to reduce its first fundamental natural frequency. Two thickness of elastic fixtures were applied to generate power on PVEH. Three experimental techniques were used to measure the vibration characteristics of PVEH. First, the full-field optical technique, amplitude-fluctuation electronic speckle pattern interferometry (AF-ESPI) measured simultaneously the resonant frequencies and mode shapes. This is followed by the pointwise measurement system, laser Doppler vibrometer (LDV) in which the resonant frequencies were measured by dynamic signal swept-sine analysis. The resonant frequencies and anti-resonant frequencies were also obtained by impedance analysis. The results obtained from experimental measurements were compared with finite element numerical calculation. It is found that the boundary conditions under the elastic fixtures can effectively reduce the resonant frequency of the PVEH with a reasonable voltage output. The fundamental natural frequency of PVEH with the thickness of 0.58-mm elastic fixture is reduced to 37 Hz maintaining at 7.1 volts (1.2 mW), in comparison with the natural frequency on cantilevered PVEH at 78 Hz that produces 7.7 volts (6.5 mW).

Dimensional dependence of the radiation damage in microelectromechanical system resonators

The effect of 10 keV x-ray and 255 nm UV radiation on MEMS resonators of different sizes were tested. The change in resonance frequency of the resonator during and after radiation was tracked, and a dimensional dependent resonance frequency reduction was observed for both x-ray and UV irradiation. The dimensional dependence of the resonance frequency shift indicates that surface effects are an important factor in both types of radiation damage. We propose two theoretical models that successfully explain the dimensional dependencies of x-ray and UV radiation damage. The x-ray model is based on hydrogen diffusion in silicon and the UV model is based on radiation induced charging of the native oxide. The models show that larger surface-to-volume ratio devices are more susceptible to radiation and need to be considered when scaling MEMS devices.

Further slot antenna miniaturization and bandwidth enhancement

In this work, antenna miniaturization using slits and metallic strips fed by microstrip line has been demonstrated. It has been noticed that slot antenna fed by microstrip line provides more miniaturization and in some cases enhanced bandwidth in comparison with the slot antenna fed by other feeding mechanism, keeping the same length and width of the radiating slots, slits and metallic strips. We have achieved 51.67% reduction in resonant frequency and 74.72% improvement in −10 dB bandwidth compared with 37.73% and no bandwidth improvement of either side slits loaded slot antenna topology. Further, it has been shown 63.52% reduction in resonant frequency and 2.23% improvement in −10 dB bandwidth in comparison with 42.33% reduction in resonant frequency of only one side slits loaded slot antenna topology. The current work highlighted not only greater miniaturization and enhanced bandwidth but also almost unperturbed radiation pattern compared to reference antenna topology and low cross-pol level even slot antenna loaded by only one side slits, which was not demonstrated in earlier works.

Extremely compact EBG‐backed antenna for smartwatch applications in medical body area network

This paper presents design of a compact interdigital electromagnetic band gap unit cell (IDE) for wearable applications in the medical body area network (MBAN) band. The uniqueness of the proposed cell is in its ability to achieve lower resonant frequency in spite of very compact size of 14.3 mm × 14.5 mm. The cell has adjacent fingers connected in such a way that the net inductance contributed by the metallic strips increases and this aids in the reduction of resonant frequency. An equivalent lumped circuit model supports the analysis of the proposed cell. The evaluation of the developed model is assessed by comparing the reflection phase response obtained from the circuit model and full wave analysis. The proposed design, even though slightly asymmetric, possess polarisation stability and this has been validated using the reflection phase parameter for a plane wave polarised along x -and y -axes. Subsequently, a reflector consisting of 2 × 2 IDE-unit cell to be integrated with monopole antenna of overall size 36 mm × 38 mm × 3.12 mm is designed. The design exhibits a very good agreement between the experimental and the simulated results whereby it is able to provide gain and efficiency of 5.3 dB and 85% respectively at the MBAN frequency.

A Polymer-based Piezoelectric Vibration Energy Harvester with a 3D Meshed-Core Structure.

In this study, we fabricated a flexible 3D mesh structure with periodic voids by using a 3D lithography method and applying it to a vibration energy harvester to lower resonance frequency and increase output power. The fabrication process is mainly divided into two parts: three-dimensional photolithography for processing a 3D mesh structure, and a bonding process of piezoelectric films and the mesh structure. With the fabricated flexible mesh structure, we achieved the reduction of resonance frequency and improvement of output power, simultaneously. From the results of the vibration tests, the meshed-core-type vibration energy harvester (VEH) exhibited 42.6% higher output voltage than the solid-core-type VEH. In addition, the meshed-core-type VEH yielded 18.7 Hz of resonance frequency, 15.8% lower than the solid-core-type VEH, and 24.6 μW of output power, 68.5% higher than the solid-core-type VEH. The advantage of the proposed method is that a complex and flexible structure with voids in three dimensions can be relatively easily fabricated in a short time by the inclined exposure method. As it is possible to lower the resonance frequency of the VEH by the mesh structure, use in low-frequency applications, such as wearable devices and house appliances, can be expected in the future.

On wave diffraction of two-dimensional moonpools in a two-layer fluid with finite depth

This paper studies the wave diffraction problem of two-dimensional moonpools in a two-layer fluid by using domain decomposition scheme and the method of eigenfunction expansion. Wave exciting forces, free surface and internal wave elevations are computed and analyzed for both surface wave and internal wave modes. The present model is validated by comparing a limiting case with a single-layer fluid case. Both piston mode and sloshing mode resonances have been identified and analyzed. It is observed that, compared with the solutions in surface wave mode, the wave exciting forces in internal wave mode are much smaller, and show more peaks and valleys in low-frequency region. As the wave frequency increases, the bandwidth of sloshing mode resonances decreases. Extensive parametric studies have been performed to examine the effects of moonpool geometry and density stratification on the resonant wave motion and exciting forces. It is found that, for twin bodies with deep draft in surface wave mode, the decreasing density ratio has little effects on the sloshing mode resonance frequencies but can somehow suppress the horizontal wave exciting forces and surface wave elevations around piston mode resonance region. In addition, the presence of lower-layer fluid can lead to the reduction of piston mode resonance frequency.

Fabrication and Sensitivity Analysis of Guided Beam Piezoelectric Energy Harvester

This paper reports the fabrication of MEMS-based guided two-beam piezoelectric energy harvester for low-frequency operation. A highly c-axis-oriented zinc oxide thin film of 2.5- $\mu \text{m}$ thickness covered with 0.5- $\mu \text{m}$ plasma-enhanced chemical vapor deposition SiO2 is sandwiched between the aluminum electrodes to form split electrodes on the two beams. A pyramidal-shaped seismic mass that gives a higher electric potential is realized by bulk micromachining using CMOS compatible 25 wt% tetramethyl ammonium hydroxide wet etching. The thickness of the beams is optimized using deep reactive-ion etching to achieve a low-frequency operation. COMSOL Multiphysics has been used to study the stress distribution to optimize the dimension and placement of the split electrodes. The optimized split electrodes give a reduced resonance frequency by 4.2% when compared with previously used electrode pattern ensuring maximum electric potential generation for guided two-beam structure. The resonance frequency of the device measured experimentally using laser Doppler vibrometer comes to be 466 Hz. The packaged device exhibits a maximum sensitivity of 1.5089 mV/m/s2 in the frequency range from 160 to 1000 Hz.

Sandwich piezoelectric energy harvester: Analytical modeling and experimental validation

Piezoelectric energy harvesting from ambient vibration sources has great potential for powering microelectronic devices and wireless sensors. Almost all the conventional piezoelectric energy harvesters (CPEHs) in the literature have been designed with a single metallic layer as substrate along with the piezoelectric material bonded over it. In this work, a novel sandwich structure is used as substrate for designing harvester. The substrate structure comprises of a soft-core material sandwiched between metallic layers. The proposed sandwich piezoelectric energy harvester (SPEH) has lower resonant frequency and generates higher voltage output than the CPEH with the same geometrical dimension. Furthermore, the SPEH offers high design flexibility in terms of tuning the resonant frequency through selection of materials and geometric parameters for the core and metal layers. The mathematical formulation of a generalized electromechanical model of the SPEH is developed using the Lagrange approach. The natural frequencies, displacement and voltage frequency response functions of the harvester are obtained analytically. A single-degree-of-freedom model for the SPEH is also derived. Subsequently, the analytical modeling is validated by finite element simulations and experimental results. When excited at 0.1 g, the SPEH generates 18.8% more voltage output at resonance as compared with a CPEH with the same geometrical dimension and tip mass accompanied by 24% reduction in resonant frequency. At 30 Hz resonance frequency, CPEH generates open-circuit voltage 17.6 V using 15 g of tip mass whereas SPEH uses only 8.2 g of tip mass to generate 16.6 V. SPEH generates 130.8 μW, 426.6 μW and 1158.0 μW at base accelerations 0.05 g, 0.1 g and 0.2 g with optimal resistance, respectively. Finally, the influence of geometric and material properties of core and metallic layers on the performance of SPEH are analyzed comprehensively. The proposed novel SPEH together with its analytical modeling is intended to serve as a basis for future sandwich harvester designs.

Interdigitated cantilever array topology for low frequency MEMS vibration energy harvesting

Micro-fabricated vibration energy harvesters enable merits such as miniaturisation, economies of scale for manufacturing, and ease of integration with semiconductor IC technologies. However, the frequency range of ambient vibration is generally low (10’s Hz to 100’s Hz). Existing MEMS vibration energy harvesters that target these frequencies typically are in the centimetre scale range. This sacrifices the miniaturisation aspect as well as introducing new challenges in packaging and integration for the unconventionally large MEMS devices. This paper proposes a new interdigitated fork cantilever array topology, which allows for up to about a third reduction in resonant frequency compared to the classical cantilever topology, for the same design area and without compromising on power optimisation. Further resonant frequency reduction is also possible, but at the expense of power optimisation. This opens up design flexibility to achieve low frequency MEMS resonators that are more suitable to practically target ambient vibration, without sacrificing the aforementioned merits of MEMS technology.

Influence of Crack on Modal Parameters of Cantilever Beam Using Experimental Modal Analysis

In this paper, the dynamic behavior of a cantilever beam without and with crack is observed. An elastic Aluminum cantilever beams having surface crack at various crack positions are considered to analyze dynamically. Crack depth, crack length and crack location are the foremost parameters for describing the health condition of beam in terms of modal parameters such as natural frequency, mode shape and damping ratio. It is crucial to study the influence of crack depth and crack location on modal parameters of the beam for the decent performance and its safety. Crack or damage of structure causes a reduction in stiffness, an intrinsic reduction in resonant frequencies, variation of damping ratios and mode shapes. The broad examination of cantilever beam without crack and with crack has been done using Numerical analysis (Ansys18.0) and experimental modal analysis. To observe the exact higher modes of beam, discretize the beam into small elements. An experimental set up was established for cantilever beam having crack and it was excited by an impact hammer and finally the response was obtained using PCB accelerometer with the help sound and vibration toolkit of NI Lab-view. After obtaining the Frequency response functions (FRFs), the natural frequencies of beam are estimated using peak search method. The effectiveness of experimental modal analysis in terms of natural frequency is validated with numerical analysis results. This paper contains the study of free vibration analysis under the influence of crack at different points along the length of the beam.

Frequency selective surface using meander line inclusions

A frequency selective surface (FSS) composed of a periodic arrangement of meander line inclusions is numerically analysed. The study is presented with respect to the number of meanders and is a generalization of the U-shape (1-meander). A y-polarized incident wave is used to illuminate the structure. The results are obtained by the finite element method. By investigating the transmission coefficient, in this letter, it is seen that several stopbands may be exhibited within the operating frequency band and resonant frequency reduction can be associated with the number of meanders. For an incident wave with linear polarization, our findings suggest that the shift at the resonant frequency is also due to the increase in the effective length in the polarization direction of the incident wave. The validation of our model is performed by U-shape simulation already experimentally tested in other letters. A very good agreement has been achieved.