A recoverable composite auxetic absorber optimized for low-energy impacts

In this paper, a composite strategy has been developed to achieve continuous absorption coverage from the ultrahigh-frequency (UHF) band to the Ku band. Based on this strategy, an ultrawideband lightweight composite metamaterial absorber is fabricated and measured. The composite absorber comprises two cascaded parts operating in separated frequency bands. First, we design a polarization-insensitive tunable absorber in the UHF band based on the equivalent circuit model. The measured results indicate that the tunable UHF absorber obtains a tunable −10 dB reflection coefficient from 0.88 to 1.48 GHz. Furthermore, a lightweight 3D absorber is applied to cascade with the tunable UHF absorber to constitute a ultrawideband composite absorber. The composite absorber achieves an ultrawideband absorption ranging from 0.78 to 18 GHz with a reflection coefficient below −10 dB. The overall composite structure is extremely lightweight with a surface density below 0.2897 g cm−2. This composite absorber also exhibits good angular stability, low profile, and polarization insensitiveness. We think this work is of great application potential for military and civilian applications.

Micro-perforated panel (MPP) backed by a rigid cavity is a widely used clean sound absorber; however, its application at low frequency is limited because a deep cavity is required to achieve good sound absorption in the low frequency range. In the present paper, a composite absorber composed by an MPP and a shunted loudspeaker is proposed. The loudspeaker is installed at the back wall of the air cavity and the acoustic impendence can be optimized by adjusting the parameters of the loudspeaker and the electronic components in the shunt to improve the sound absorption performance. The prediction model of such a finite-sized composite absorber is established based on the mode analysis solution and the equivalent circuit of the loudspeaker. Both numerical simulations and experiments show that the thickness of the proposed composite absorber can be much smaller than that of traditional MPP constructions.

In this paper, an innovative concept is proposed, based on the hexachiral auxetic frames filled with foams with enhanced energy absorption capabilities. Numerical assessments of the composite foam-filled auxetic absorbers, of pure foam blocks and unfilled auxetic frames for metallic and polymeric material combinations were accomplished considering a case of localized impact. The energy absorbed by the composite absorbers are found superior to the sum of the energies absorbed by constituent elements tested separately with clear advantages also at the level of the specific energy absorbed per unit mass. The interactions between the two constituents are analyzed and discussed. An experiment considering a 3D-printed polymeric hexachiral frame filled with open-cell soft polyurethane foam under localized impact is conducted to validate the numerical approach. Eventually, a parametric sensitivity study is conducted numerically to illustrate the effects of geometrical parameters on the energy absorption capacity. Overall, the results confirm the potential and the great design flexibility of the concept, provides the guidelines to design advanced energy absorbing system, underlies the importance of the combination between the frame and foam properties and the effect of the main geometrical parameters on the performance.

Micro-perforated panel (MPP) backed by a rigid cavity is a widely used clean sound absorber; however, its application at low frequency is limited because a deep cavity is required to achieve good sound absorption in the low frequency range. In the present paper, a composite absorber composed by an MPP and a shunted loudspeaker is proposed. The loudspeaker is installed at the back wall of the air cavity and the acoustic impedance can be optimized by adjusting the parameters of the loudspeaker and the electronic components in the shunt to improve the sound absorption performance. The prediction model of such a finite-sized composite absorber is established based on the mode analysis solution and the equivalent circuit of the loudspeaker. Both numerical simulations and experiments show that the thickness of the proposed composite absorber can be much smaller than that of traditional MPP constructions.

The objective of the present study was to investigate the mechanism by which the fluid transported across the small intestine becomes isoosmotic with the mucosal solution. The osmolality of the mucosal solution of a unilateral preparation (the serosal side was not bathed) was increased with water soluble, nonelectrolyte solutes of different Staverman reflection coefficients (σ), and the composition of the undiluted absorbate was studied. The solutes ('hyperosmotic agents') used were formamide, urea, erythritol, and mannitol. In a series of separate experiments, utilizing a method based on potential difference depression, we found that the σ's of these solutes in the hamster small intestine were 0.26, 0.85, 0.93, and 1.00, respectively. Our data on transport across the unilateral preparation showed that when the intestine was incubated in an isotonic mucosal solution (Krebs–Ringer bicarbonate solution containing 10 mM glucose, 292 mosmol/kg), the absorbate was essentially isotonic, although its composition was significantly different from that of the mucosal solution. When the osmolality of the mucosal solution was increased to 342, 392, or to 442 mosmol/kg with any of the hyperosmotic agents, the absorbate was always isoosmotic with the mucosal solution. With formamide (low σ) as the hyperosmotic agent, the concentration of electrolytes and glucose in the absorbate was the same as that in the absorbate of the control preparation (incubated in the isotonic mucosal solution), and the transported fluid became isoosmotic with the mucosal solution exclusively due to the presence of formamide in the absorbate. When the osmolality of the mucosal solution was increased with urea, erythritol, or mannitol, the concentration of these hyperosmotic agents in the absorbate decreased linearly with the increase in their σ, and the absorbate became isoosmotic with the mucosal solution due to a linear increase in the concentration of electrolytes and glucose. In addition, we found that the transport of fluid, solutes, and fluid/solute (ml/mmol per gram dry intestine) decreased linearly with the increase in σ of the hyperosmotic agents. Further calculation of the data showed that the increase in the concentration of electrolytes and glucose with the increase in σ of the hyperosmotic agents was almost exclusively due to a linear decrease in fluid/solute transport.

This work uses topology optimization methods to interactively design the plasma and metasurface loaded by resistance film, and obtains a composite absorber with good absorption effect. Genetic algorithm is used to find the minimum reflectivity of the composite absorber of plasma and metasurfaces, and after decoding, determine the corresponding topological structure of metasurface units and the optimal values of other parameters of the composite absorber. The optimized composite absorber maintains an absorption rate of over 95% in a wide frequency range of 5 GHz–18 GHz. This broadband absorption effect is caused by the superposition of the absorption performance of plasma and metasurface. In addition, due to the central symmetric configuration of the metasurface unit, the composite absorber has good polarization insensitivity characteristics, and it still has broadband absorbing ability in the case of TE polarized waves and TM polarized waves obliquely incident. Thus, the proposed composite absorber designed based on topology optimization method has a wide frequency band, wide incidence angle, high absorption rate, and polarization insensitive absorbing effect. The topology optimization method is used for the design of the proposed composite absorber composed of plasma and metasurface, which does not overly rely on design experience of designer and provides an intelligent design method for stealth skin design in complex scattering media such as plasma.

Low-profile broadband microwave absorber based on magnetic coating and artificial electromagnetic structures

In this paper, we present the design and experimental results of wide-band composite microwave absorber fabricated using thermoplastic polyurethane, carbon fibers, glass microballoons, micro and nano size magnetic materials. Ni-Zn ferrite and carbonyl iron powders of nano and micrometer size particles were used along with carbon fibers and microbaloons for the development of the absorber. It is found that both Ni-Zn ferrite and carbonyl iron powders and their ratio in the composite plays critical role in the absorber performance. Measured results show that a reflectivity reduction of 15 dB from 5 to 18 GHz is possible using this composite absorber.

Optimization of constrained composite absorbers using simulated annealing

Preparation and characterization of carbonyl iron/glass composite absorber as matched load for isolator

The performance of PAN-based composite absorbers was evaluated in dynamic experiments at flow rates ranging from 25--100 bed volumes (BV) per hour. Composite absorbers with active components of ammonium molybdophosphate (AMP) PAN and K-Co ferrocyanide (KCoFC) PAN were used for separating Cs from a 1 M HNO{sub 3} + 1 M NaNO{sub 3} + 2 {times} 10{sup {minus}5} M CsCl acidic simulant solution. KCoFC-PAN and two other FC-based composite absorbers were tested for separating Cs from alkaline simulant solutions containing 0.01 M to 1 M NaOH and 1 M NaNO{sub 3} + x {times} 10{sup {minus}4} M CsCl. The efficiency of the Cs sorption on the AMP-PAN absorber from acidic simulant solutions was negatively influenced by the dissolution of the AMP active component. At flow rates of 50 BV/hr, the decontamination factor of about 10{sup 3} could be maintained for treatment of 380 BV of the feed. With the KCoFC-PAN absorber, the decontamination factor of about 10{sup 3} could be maintained for a feed volume as great as 1,800 BV. In alkaline simulant solutions, significant decomposition of the active components was observed, and the best performance was exhibited by the KCoFC-PAN absorber. Introductory experiments confirmed that Cs may be washed out of the composite absorbers. Regeneration of both absorbers for repetitive use was also found to be possible. The main result of the study is that PAN was proven to be a versatile polymer capable of forming porous composite absorbers with a large number of primary absorbers. The composite absorbers proved to be capable of withstanding the harsh acidic and alkaline conditions and significant radiation doses that may be expected in the treatment of US DOE wastes. A field demonstration is proposed as a follow-on activity.

A micro-perforated panel (MPP) absorber with a single shaped micro-perforation has a large backed air cavity and a narrow absorption bandwidth in the low frequency range. To address this issue, based upon the absorption principle of the MPP absorber and the coordination of multiple detuned absorption cells, we propose a composite MPP absorber with different shaped micro-perforations where the circle, the equilateral triangle, the square and the narrow slit shaped micro-perforations will be involved to broaden the absorption bandwidth. The theoretical model of the composite MPP absorber is firstly established by the electro-acoustic analogy circuit. The sound absorption characteristics of the MPP absorbers with a single shaped micro-perforation are analyzed to meet the research objective of which the various shaped micro-perforations are perforated on a uniform thickness panel to form the proposed composite MPP absorber. The sound absorption characteristics of the composite MPP absorber with the same shaped micro-perforations but different perforation distributions as well as those with two different shaped micro-perforations are further discussed. No matter the type of the different shaped micro-perforation distributions, the composite MPP absorbers would depict the similar sound absorption curve as long as the combination of the resonance frequency remains the same. The effect of the area ratio of each shaped micro-perforation on the sound absorption coefficient is discussed. Finally, the experimental measurements of the composite MPP absorber samples are in good agreement with their theoretical predictions. The composite MPP absorber with different shaped micro-perforations can exhibit a significantly broader absorption bandwidth than the MPP absorber with a single shaped micro-perforation, providing a reference for the design of novel wideband absorber.

Micro-perforated panel (MPP) absorber with a single uniform air cavity is regarded as a promising sound-absorbing structure; however, MPP absorption performance remains unfortunately limited due to the Helmholtz resonance mechanism, which results in more and more attention being placed on composite MPP absorbers. This study focuses on acoustic properties of different composite MPP absorbers, including three types of composite MPP absorbers which are coupled in serial, parallel and serial–parallel modes. Their mathematical models of the normal absorption coefficient are established by utilizing the acoustic electric analogy method. The single-cavity MPP absorber and three composite MPP absorbers are preliminarily designed to verify the equivalent circuit models and perform a pilot analysis of their sound absorption characteristics. Moreover, the particle swarm optimization algorithm is selected to optimize the absorbers so that optimal combination of structure parameters within a prescribed frequency range can be obtained. In addition, the absorbers are made based on the optimized parameters for experimental investigation. The results show that a wider absorption bandwidth may be achieved by composite MPP absorbers through introducing additional absorption peaks with reference to that for the conventional single-cavity MPP absorber, and there are more absorption peaks for the serial–parallel-coupled MPP absorber rather than the simply serial- or parallel-coupled MPP absorber so that better sound absorption effect may be achieved.

An optimized NiZn ferrite absorber for the whole P-band (230 –1000 MHz) is proposed by inserting cross-shaped metamaterial. Effective absorption bandwidth below − 10 dB for the composite absorber covers the frequency range 210 MHz–1000 MHz. Electromagnetic wave attenuation mechanisms are revealed by surface current distribution and power loss density distribution. The increased absorption bandwidth of the composite absorber is attributed to the overlap effect of three absorption peaks originated from the multilayer cross-shaped metamaterial absorbers. Results indicate that the proposed composite absorber can be utilized in the P-band with relatively less thickness compared to the traditional NiZn ferrite absorber.

Both cementation and vitrification was shown by preliminary experiments to be applicable for treatment of the spent composite absorbers with polyacrylonitrile binding matrix for final disposal. Loadings of cement mix with composite absorbers up to 5–9% (w/w) were achieved Admixtures of natural clinoptilolite were found to improve compressive strength of the samples. The presence of PAN binding polymer was found not to disqualify the composite absorber tested from final treatment by vitrification.