Electrical Characterization Method for Resonance Performance of Photo-Elastic Modulators

As a kind of resonant device, the modulation efficiency of the photo-elastic modulator (PEM) is determined by its inherent resonance characteristics, including the resonance frequency and quality factor (Q-factor). The existing methods used to characterize the resonance performance of the PEM are mainly based on the optical method to measure the vibration parameters, but these methods are more complex, have a high cost, and are not able to accurately measure the quality factor. Therefore, this paper proposes an electrical characterization method based on impedance measurement. In this method, an equivalent circuit model for the PEM is established. By measuring the impedance vs. frequency curve of the PEM and using the equivalent circuit model for fitting analysis, we can obtain the parameters of the equivalent circuit model. With these parameters, we can eventually calculate the natural resonance frequency and quality factor. The above method was applied to some commercial PEM products for experimental verification. The experimental results show that this method can accurately measure the natural resonance frequency and quality factor of the PEM, and the error is less than 0.03%.

Electromagnetic Vibration Energy Harvester with Tunable Resonance Frequency Based on Stress Modulation of Flexible Springs

This paper presents a compact electromagnetic vibrational energy harvester (EVEH) with tunable resonance frequency. The resonance frequency of the EVEH is tuned by adjusting the axial stress in the flexible polymeric springs, which is realized by physically pulling and pushing the springs. The stress tuning functionality is realized with a compact structure with small volume. The total frequency tuning range of the proposed EVEH is 56 Hz (74 Hz–130 Hz), which is 64% of the natural resonance frequency of the EVEH (88 Hz). It is found that the tensile stress increases the resonance frequency of the EVEH, while the compressive stress firstly reduces the resonance frequency and then increases the resonance frequency due to buckling.

Design and simulation of acoustics for the home theatre

As a typical acoustics room, the sound quality of home theatre is an important standard to evaluate its design. Qualified acoustics design is the guarantee of good sound quality. The volume of home theatre is generally small, so the room size is similar to the low-frequency wavelength. Then the resonance will occur when the excitation of the sound source frequency acts on the natural resonance frequency of the room. At the same time, the secondary reflection of the room also interferes the direct sound emitted by the speaker, thus destroying the sound image. In order to solve the above problems, this paper took a home theatre as an example, analyzed the normal modes of the room by the theory of wave acoustics, and then made an acoustics design and simulation. The simulation results showed that the reverberation time was up to the relevant standards and the room acoustic quality environment was improved obviously after the acoustic design.

Numerical and experimental investigation of the dynamics of ultrasound contrast agents excited at higher multiples of their natural resonance frequency

In this work the Hoff model for microbubble oscillations was used together with bifurcation diagrams to investigate microbubble behavior for a range of the system control parameters (driving frequency and pressure, microbubble size and shell parameters). We have shown that if the microbubble sizes are optimized so that their resonance frequency is a fraction of the sonication frequency (1/3, 1/4...), above a certain pressure threshold, the microbubbles can emit higher order subharmonics at (1/3, 2/3...) of the sonication frequency. Experimental results (using Artenga and in-house made lipid microbubbles with a 25 MHz, 30 cycle pulse using 0.1-2.5 MPa pressures) showed subpopulations of the microbubbles that were able to show this behaviour by scattering ultrasound according to the theoretical predictions (e.g. having two frequency maxima for subharmonics at f/3 and 2f/3). The ring-down analysis of the natural free oscillations of these microbubbles confirmed the theoretical resonance predictions.

Numerical and experimental investigation of the dynamics of ultrasound contrast agents excited at higher multiples of their natural resonance frequency

In this work the Hoff model for microbubble oscillations was used together with bifurcation diagrams to investigate microbubble behavior for a range of the system control parameters (driving frequency and pressure, microbubble size and shell parameters). We have shown that if the microbubble sizes are optimized so that their resonance frequency is a fraction of the sonication frequency (1/3, 1/4...), above a certain pressure threshold, the microbubbles can emit higher order subharmonics at (1/3, 2/3...) of the sonication frequency. Experimental results (using Artenga and in-house made lipid microbubbles with a 25 MHz, 30 cycle pulse using 0.1-2.5 MPa pressures) showed subpopulations of the microbubbles that were able to show this behaviour by scattering ultrasound according to the theoretical predictions (e.g. having two frequency maxima for subharmonics at f/3 and 2f/3). The ring-down analysis of the natural free oscillations of these microbubbles confirmed the theoretical resonance predictions.

Analysis and Research on the Comprehensive Performance of Vehicle Magnetorheological Regenerative Suspension

Magnetorheological (MR) regenerative suspension system can not only achieve excellent comprehensive suspension performance but also effectively recover and utilize vibration potential energy, which has been a research hotspot in the field of vehicle engineering. In this paper, for the 1/4 vehicle’s MR regenerative suspension system parallel with a tubular permanent magnet linear motor (TPMLM), the dynamic model of the MR semi-active suspension system and the TPMLM finite element model are established separately to form a joint simulation platform. The simulation analysis of the comprehensive suspension performance and regeneration performance under different road excitations is performed. The results show that installing TPMLM does not change the natural resonance frequency of the suspension system, which ensures good driving comfort and handling stability. At the same time, it has considerable regeneration power. This research can provide a reference for the stability analysis and popularization of the vehicle’s MR regenerative suspension system.

RESEARCH OF THE RESONANCE PROPERTIES OF HELMHOLTZ RESONATORS

The object of research. Process of oscillation of the Helmholtz resonators. Investigated problem. Differences between some formulas for the calculation of the resonant frequency of the Helmholtz resonator and the most accurate of them were established. The effect of acoustic design on the Helmholtz resonator frequency value and influence of the attached air mass between the neck of the Helmholtz resonator and free field were investigated. The main scientific results. As a result of a numerical experiment, analytical ratios were obtained that allow obtaining the most accurate results. One of them is the most optimal for calculating the resonator resonant frequency in a free field, and in this case, less than 1 % inaccuracy level can be achieved, given that r/R<0.25. Other one allows to achieve the same low inaccuracy level for a resonator located in an acoustically rigid shield, given that r/R<0.25. Research has shown that the location of the resonator in an acoustically rigid shield leads to significant changes in natural resonance frequency value. The area of practical use of the research results. The detailed research of previously unexplored properties of resonators will make it possible to improve the algorithms for the development of metamaterials, to discover additional parameters with which it is possible to control the characteristics of the metamaterial. Scope of the innovative technological product. Such resonators are used as the basic elements in metamaterials, as structural elements of the sound-absorbing panels, in acoustic mufflers.

Is there a Seasonality of the Martian Seismic Event Rate?

&lt;p&gt;We analyze the sequence of seismic events of different types as recorded by the SEIS instrument of the InSight mission. After several weeks without any detection, event counts started to increase at the end of May 2019. The majority of recorded events belongs to the class of 2.4 Hz events, which prominently excite a continuously observed natural resonance frequency.&lt;/p&gt;&lt;p&gt;After a sudden onset of seismic detections by the end of May 2019 (about sol 180, L&lt;sub&gt;S&lt;/sub&gt;&amp;#8776;32&amp;#176;), especially the combined event rate of the High Frequency, Very High Frequency, and 2.4 Hz family of events increased from 3.6 events/sol in June 2019 to more than 9 events/sol until late August 2019, i.e. increased by a factor of about 3.&lt;/p&gt;&lt;p&gt;Estimating event rates as if events are the result of a constant-rate Poisson process leads to contradictions with the statistical properties of those, either in the cumulative event count or in the lag time distribution. These contradictions can be overcome by assuming a step-wise increase of the event rate.&lt;/p&gt;&lt;p&gt;Any deviation from a purely random occurrence of quakes, in both time and space, requires a mechanism to suppress or support the source process. The seismic activity of the Moon is mainly controlled by tidal deformation, at least in terms of source time. What controls the event rate of Martian high frequency events is currently elusive.&lt;/p&gt;