Attempts to perform synthesis of a passive vibroinsulation two-mass system intended for the simultaneous reduction of machine frame vibrations and forces transmitted to foundations by supporting elements were undertaken in the study. In view of the variable frequency of the machine operation, it was necessary for the frequency interval, encompassed by the vibroinsulation system operation, to be within given limits. On the grounds of properties of the linear massive-elastic system formulated in the works of Genkin and Ryaboy (1998), the problem of vibroinsulation system synthesis was formulated in the parametric type optimisation approach with equality and inequality limitations. For piston compressor vibroinsulation, the mass and elasticity matrices of the vibroinsulating system, as well as its physical structure, were determined. Its operation was verified on the basis of simulation investigations, taking into account the system loss and transient states.

A metamaterial absorber (MA) based sensor is designed and analysed for various important applications including pressure, temperature, density, and humidity sensing. Material parameters, as well as equivalent circuit model have been extracted and explained. After obtaining a perfect absorption (PA) at around 6.46 GHz and 7.68 GHz, surface current distributions at resonance points have been explained. Since bandwidth and applicability to different sensor applications are important for metamaterial sensor applications, we have realized distinctive sensor demonstrations for pressure, temperature, moisture content and density and the obtained results have been compared with the current literature. The proposed structure uses the changes on the overall system resonance frequency which is caused by the sensor layer’s dielectric constant that varies depending on the electromagnetic behaviour of the sample placed in. This model can be adapted to be used in sensor applications including industrial, medical and agricultural products.

We report on the absorption properties of polarization-insensitive transmissive and reflective metamaterial absorbers based on two planar aluminium periodic structures and SU-8 epoxy resist. These absorbers were investigated using numerical simulation and experimental methods in the terahertz range (below 2 THz). SU-8 is a very promising organic material for dielectric layers in planar metamaterials, because its application simplifies the process of fabricating these structures and significantly reduces the fabrication time. The experimental absorption of the metamaterial absorbers has narrowband characteristics that were consistent with the numerical simulations. Power flow analysis in the transmissive metamaterial unit cell shows that the absorption in the terahertz range occurs primarily in the SU-8 layer of the absorber.

For building applications, woven fabrics have been widely used as finishing elements of room interior but not in particular aimed for sound absorbers. Considering the micro perforation of the woven fabrics, they should have potential to be used as micro-perforated panel (MPP) absorbers; some measurement results indicated such absorption ability. Hence, it is of importance to have a sound absorption model of the woven fabrics to enable us predicting their sound absorption characteristic that is beneficial in engineering design phase. Treating the woven fabric as a rigid frame, a fluid equivalent model is employed based on the formulation of Johnson-Champoux-Allard (JCA). The model obtained is then validated by measurement results where three kinds of commercially available woven fabrics are evaluated by considering their perforation properties. It is found that the model can reasonably predict their sound absorption coefficients. However, the presence of perturbations in pores give rise to inaccuracy of resistive component of the predicted surface impedance. The use of measured static flow resistive and corrected viscous length in the calculations are useful to cope with such a situation. Otherwise, the use of an optimized simple model as a function of flow resistivity is also applicable for this case.

The proposed paper discusses the design and characterization of a soft miniature Magneto-Rheological (MR) shock absorber. In particular, the final application considered for the insertion of the designed devices is a controllable variable stiffness sole for patients with foot neuropathy. Such application imposes particularly challenging constraints in terms of miniaturization (cross-sectional area ≤ 1.5 cm2, height ≤ 25 mm) and high sustainable loads (normal loads up to 60 N and shear stresses at the foot/device interface up to 80 kPa) while ensuring moderate to low level of power consumption. Initial design considerations are done to introduce and justify the chosen novel configuration of soft shock absorber embedding a MR valve as the core control element. Successively, the dimensioning of two different MR valves typologies is discussed. In particular, for each configuration two design scenarios are evaluated and consequently two sets of valves satisfying different specifications are manufactured. The obtained prototypes result in miniature modules (external diam. ≤ 15 mm, overall height ≤ 30 mm) with low power consumption (from a minimum of 63 mW to a max. of 110 mW) and able to sustain a load up to 65 N. Finally, experimental sessions are performed to test the behaviour of the realized shock absorbers and results are presented.

The theoretical estimation of sound absorption coefficient of a surface may give very different results. This will depend on the type of sound field assumed in the theoretical model used for the estimation of its sound absorption coefficient. Absorption coefficients for normal and diffuse sound fields are widely known, although they may be far from the absorption values given by an absorbing material when it is finally installed inside a room or enclosed space, where a sound field closer to a spherical wavefront is more likely to be found. This work presents a theoretical study, which is addressed at obtaining a mathematical expression to calculate the sound absorption coefficient for a variable range of incidence angles, called αs. The presented method uses a circular sound field incidence as an approximation to a spherical incidence. The estimation of this coefficient αs is based on obtaining the incident and reflected sound fields for a surface located facing a lineal source. The advantage of this calculation method over others lies on its capability to give results for circular, normal and random wave incidence depending on the range of incidence angles considered in the calculation.

Noise reduction inside waveguide systems has gained momentum owing to a great interest in it. To attenuate the sound in a broad frequency range, this study aims to compare the effects of two acoustic liners, a perforated plate backed by an air cavity (PP-Air cavity), or by a porous material (PP-PM), on the acoustic behaviour of lined ducts using a numerical model to compute the multimodal scattering matrix. From this matrix, the reflection and the transmission coefficients are computed and therefore the acoustic power attenuation is deduced. Moreover, the effects of geometry of ducts with and without changes in the section are investigated. The numerical results are obtained for five configurations, including cases of narrowing and widening of a duct portion with sudden or progressive discontinuities. Accordingly, numerical coefficients of reflection and transmission as well as the acoustic power attenuation show the relative influence of acoustic liners in each type of configuration.

In the present work, the radiation of sound waves from a coaxial duct is considered. This coaxial duct has an inner wall which is infinite and has piecewise acoustically absorbent material, while the outer wall is semi-infinite and rigid. The analytical solution of the problem is found by means of the Wiener-Hopf technique. Applying the Fourier transformation to the boundary value problem, the explicit expression for the scattered field is obtained. In the end, some numerical results are displayed for different parameters and compared to rigid case.

Natural fibres are attractive as the raw material for developing sound absorber, as they are green, eco-friendly, and health friendly. In this paper, pineapple leaf fibre/epoxy composite is considered in sound absorber development where several values of mechanical pressures were introduced during the fabrication of absorber composite. The results show that the composite can absorb incoming sound wave, where sound absorption coefficients α _n > 0.5 are pronounced at mid and high frequencies. It is also found that 23.15 kN/m^2 mechanical pressure in composite fabrication is preferred, while higher pressure leads to solid panel rather than sound absorber so that the absorption capability reduces. To extend the absorption towards lower frequency, the composite absorber requires thickness higher than 3 cm, while a thinner absorber is only effective at 1 kHz and above. Additionally, it is confirmed that the Delany-Bazley formulation fails to predict associated absorption behavior of pineapple leaf fibre-based absorber. Meanwhile, a modified Delany-Bazley model discussed in this paper is more useful. It is expected that the model can assist further development of the pineapple leaf composite sound absorber.

We demonstrated a tunable Q-switched ytterbium-doped fiber laser (YDFL) using MoWS₂/rGO nanocomposite as passive saturable absorber. Further, the Mo_1−xWxS₂/rGO nanosheets, with x proportion of 0.2, are synthesized using hydrothermal exfoliation technique. The proposed nanocomposite-PVA based thin film is fabricated by mixing the MoWS₂/rGO nanosheets with polyvinyl alcohol (PVA). The fabricated thin film is sandwiched between two fiber ferrules to realize the proposed saturable absorber (SA). Further, the proposed MoWS₂/rGO-PVA based thin film SA exhibits a fast relaxation time and a high damage threshold which are suitable to realize a Q-switched pulsed laser with a tunable wavelength range of 10  nm that extends from 1028 nm to 1038 nm. For the highest pump power of 267.4 mW, the generated Q-switched pulses exhibit a narrow pulse width of 1.22 μs, the pulse repetition rate of 90.4 kHz, the highest pulse energy of 2.13  nJ and its corresponding average power of 0.193 mW. To the best of author’s knowledge, this is the first realization of a tunable Q-switching fiber laser in a 1 μm wavelength using MoWS2/rGO nanocomposite saturable absorber.