In recent years metamaterials gained a lot of attention due to their superior noise and vibration insulation properties, be it at least in some targeted and tuneable frequency ranges, referred to as ...stopbands. These are frequency zones for which free wave propagation is prevented throughout the metamaterial, resulting in frequency zones of pronounced wave attenuation. Metamaterials are achieved due to addition of an, often periodic, grid of resonant structures to a host material or structure. The interaction between resonant inclusions and host structure can lead to a performance which is superior to the ones of any of the constituent materials. A key element in this concept is that waves can be affected by incorporating structural resonant elements of sub-wavelength sizes, i.e. features that are actually smaller than the wavelength of the waves to be affected. This paves the way towards compact and light vibro-acoustic solutions in the lower frequency ranges. This paper discusses the numerical design and experimental validation of acoustic insulation based on the concept of metamaterials: a hollow core periodic sandwich structure with added local resonant structures. In order to investigate the sensitivity to specific parameters in the metamaterial design and the robustness of the design, a set of variations on the nominal design are investigated. The stop bands are numerically predicted through unit cell modelling after which a full vibro-acoustic finite element model is applied to predict the insertion loss of the demonstrator. The results of these analyses are compared with measurements; both indicate that this metamaterials concept can be applied to combine light weight, compact volume and good acoustic behaviour.
•Design and analysis of resonant metamaterials for acoustic insulation.•Numerical simulation of and experimental validation on a set of enclosures.•Increased insertion loss through resonant inclusion in hollow core sandwich structure.
This paper investigates a metamaterial solution for efficient vibration attenuation and acoustic radiation reduction of an aluminum pipe. To this end, using unit cell predictions, locally resonant ...structures are designed to have a pronounced flexural resonance frequency at the vicinity of a dominant vibration mode of the pipe. A direct approach of the Bloch-Floquet theorem is adopted to provide the dispersion relation representing wave motion in an infinite metamaterial pipe. Using these wave dispersion relations, the frequency range of the stopband zone created by the metamaterial solution is predicted. The dynamic behavior of the finite counterpart is predicted using the Finite Element Method (FEM). The resonant structures are produced from polymethyl methacrylate (PMMA) panels and are added to the host structure. In order to properly characterize both the vibrational behavior of the metamaterial pipe and the acoustic radiation from its wall, impact tests using roving hammer technique is performed on the pipe and both accelerations and acoustic pressures are measured at different locations. The experimental results show a pronounced stopband zone created by the addition of a few rows of resonant structures. Moreover, comparisons between the measurements and numerical predictions show a good agreement.
To enhance the sound insulation performance of double panel partitions at their mass-air-mass resonance frequency, novel compact and low-mass solutions are sought. This paper investigates the use of ...the locally resonant vibro-acoustic metamaterial concept as a possible solution. The metamaterial solution is applied to one panel of a double panel partition in order to enhance the sound transmission loss at the mass-air-mass resonance. To design the metamaterial solution and predict its sound transmission loss performance, an extension of the multiple reflection theory is proposed, incorporating the dynamic mass of a metamaterial panel. The latter is obtained from the metamaterial plate dispersion curves, calculated using finite element based unit cell modeling. The designed metamaterial solution is manufactured and its insertion loss is measured. The novel design outperforms the original double panel and an equivalent total mass double panel configuration in the targeted mass-air-mass resonance frequency region. The predictions obtained with the proposed method are in good agreement with the experimentally obtained results. This demonstrates the potential of the metamaterial solution to enhance the acoustic insulation at the mass-air-mass resonance and indicates that the proposed method allows a fast, simple and representative indication of their acoustic insulation performance.
•Double panel STL is enhanced at the mass-air-mass frequency using locally resonant metamaterials.•A unit cell based dynamic mass calculation based on the dispersion curves is proposed.•Fast STL prediction method is proposed using the multiple reflection theory combined with the dynamic mass.•A transparent metamaterial double panel partition is designed, manufactured and tested experimentally.•Good agreement between proposed method and experimental results.
This paper deals with the extraction of wave features in elastic media. An inverse approach is proposed for the identification of wave dispersion characteristics (e.g. k-space) in one- and ...two-dimensional structures (1D, 2D). The proposed method is similar to the ESPRIT algorithm and the Prony series method and can be considered as an extension of the latter, specifically when applied to 1D problems. By using a convolution framework, the method is extended to the 2D case for which it allows the estimation of the full k-space by solving a linear problem. The method is called INverse COnvolution MEthod (INCOME). The formulation of INCOME is first detailed and mathematically justified. Both the 1D and 2D cases are detailed and explained. Then several examples are presented for assessing the validity domain of INCOME. These numerical tests clearly show the relevance of INCOME for structured inputs with periodic characteristics.
•We introduce a new wavenumber extraction method for 1D and 2D wave propagation.•The proposed method is exact in both 1D and 2D cases.•In the 2D case, a full continuous k-space is retrieved in a coherent manner.•The proposed technique resembles the WFEM and can be considered an inverse WFEM.
•STL improvement of foam core double panels using resonant metamaterials.•Mass-spring-mass STL deterioration effect is attenuated using resonant metamaterials.•Fast STL prediction method using ...Heckl’s model and metamaterials dynamic mass.•Good agreement between numerical predicted and experimental results.
Double panel partitions with a foam core suffer a poor sound transmission loss at their mass-spring-mass resonance frequency. This paper considers the use of vibro-acoustic resonant metamaterials to improve the acoustic insulation performance at the frequency region of this resonance while adding only 8% of mass to the double panel, hence maintaining its lightweight characteristics. To design the metamaterial, dispersion curves are calculated through finite element unit cell analysis to predict the stop band frequency region. The resulting sound transmission loss due to the stop band effect is predicted using Heckl’s model combined with the equivalent dynamic mass of the metamaterial, which is obtained from the dispersion curves analysis. This method allows taking into consideration complex resonator geometries and locally reacting material interlayers in the hosting panel. The designed metamaterial double panel is realised, and its experimentally measured insertion loss surpasses the insertion loss of the bare and equivalent mass addition double panels in the targeted frequency region. The predicted insulation agrees well with the measured performance, validating the proposed method.
Novel diagnostic stewardship in infectious disease consists of interventions that modify ordering, processing, and reporting of diagnostic tests to provide the right test for the right patient, ...prompting the right action. The interventions work upstream and synergistically with traditional antimicrobial stewardship efforts. As diagnostic stewardship continues to gain public attention, it is critical that antimicrobial stewardship programmes not only learn how to effectively leverage diagnostic testing to improve antimicrobial use but also ensure that they are stakeholders and leaders in developing new diagnostic stewardship interventions within their institutions. This review will discuss the need for diagnostic and antimicrobial stewardship, the interplay of diagnostic and antimicrobial stewardship, evidence of benefit to antimicrobial stewardship programmes, and considerations for successfully engaging in diagnostic stewardship interventions. This article is part of the
Special Issue: https://www.drugsincontext.com/special_issues/antimicrobial-stewardship-a-focus-on-the-need-for-moderation.
Resonant metamaterials are emerging as novel concepts to reduce noise levels in targeted frequency zones, so-called stop bands. The metamaterial concept improves acoustic behaviour through an ...increase of the insertion loss. This paper concerns a first investigation on the absorption capabilities of a resonant metamaterial when thermo-viscous effects are incorporated via the addition of microslits. In a previous work, a resonant metamaterial was obtained through the inclusion of resonating structures into cavities of an open honeycomb assembly. In this study, the air gap of the honeycomb structure is reduced so as to provide viscous losses for the travelling waves. Considering that the created resonant structures with open cavities are rigid, an equivalent fluid model is used to calculate the acoustical properties of a so called microslit metamaterial. It is demonstrated that the unit cell structure can be divided into parallel elements for which the acoustic impedance can be computed via the transfer matrix approach TMM in parallel and series. Likewise, it is shown that the structural response can be predicted by FEM models allowing studying the structural effects separately from the viscous–thermal effects predicted by the equivalent fluid model. Moreover, the combined effect of both approaches is shown experimentally where it is observed that: (i) The absorption of the resonant metamaterial is increased by the addition of microslits, (ii) the modes of the test sample appear as small peaks on the absorption curve of the microslit metamaterial, (iii) the structural modes are grouped below and above the stop band and, (iv) the resonant structures do not lead to additional absorption in the stop band region. Analytical models are compared to experimental measurements to validate the models and to show the potential of this material assembly.
•A metamaterial that provides insertion loss and acoustic absorption is proposed.•The absorption and structural stop band effects are modelled separately.•The acoustic impedance is obtained by a TMM approach in series and/or parallel.•FEM and Unit Cell models predict the structural response and the stop bands.•Absorption and structural effects are observed jointly in the measurements.
Polymer gel dosimeters offer a wide range of applications in the three-dimensional verification of complex dose distributions such as in intensity-modulated radiotherapy. One of the major ...difficulties with polymer gel dosimeters is their sensitivity to oxygen, as oxygen inhibits the radiation-induced polymerization reaction. For several years, oxygen was removed from the gels by bubbling the sol with inert gases for several hours during the gel fabrication. Also, the gel had to be poured in containers with low oxygen permeability and solubility. Recently, it was found that these technical difficulties can easily be solved by adding an antioxidant to the gel. These gels are called 'normoxic' gels as they can be produced under normal atmospheric conditions. In this study several properties of polymer gel dosimeters have been investigated: the dose sensitivity, the temporal and spatial stability of the gel, the sensitivity of the dose response to temperature during irradiation and during MR imaging, the energy dependence and the dose-rate dependence. This study reveals that the normoxic polymer gel dosimeter based on methacrylic acid (nMAG) studied in this work has inferior radiation properties as compared to the polyacrylamide gelatine (PAG) gel dosimeters. It is shown that from the three different gel dosimeters investigated in this study, the nPAG gel dosimeter results in a less sensitive gel dosimeter but with superior radiation properties as compared to the nMAG gel dosimeter. The importance of investigating relevant radiation properties of gel dosimeters apart from the radiation sensitivity-prior to their use for dosimetric validation experiments-is illustrated and emphasized throughout this study. Other combinations of monomer and gelling agent may result in more reliable normoxic polymer gel dosimeters.
•Analytical formulas are derived for derivatives in the WFEM framework.•An algorithm using line search and an ellipsoid trust-region method is implemented.•Parameter estimation is carried out in a ...unit cell modeling framework.•The vibroacoustic performance of metabeams are optimized using an SQP algorithm.•The diffuse field STL of a metapanel is optimized near the acoustic coincidence.
This paper presents a second order optimization method based on the WFEM framework that enables the optimization of finite 1D periodic structures and 2D infinite ones. While optimization at the unit cell level has been done in previous studies, it did not account for the boundary conditions and excitation on the system, which might have an important influence on its dynamics. The proposed methodology exploits semi-analytical derivatives in an optimization algorithm that combines line search and trust region methods. It is tested and validated in a parameter identification procedure and subsequently used to minimize the mean square velocity of metabeams with clamped free boundary conditions. Finally, it is applied to the optimization of the sound transmission loss of a metapanel in the structural-acoustic coincidence region. The proposed scheme is versatile and can be used in a wide range of applications including, model updating, homogenization, design optimization and possibly damage detection.
Purpose of Review
Urinary tract infections (UTIs), including catheter-associated UTIs, are among the most common bacterial infections in both inpatient and outpatient settings. Diagnosis of true UTI ...remains a clinical challenge, and excessive antimicrobial treatment of asymptomatic bacteriuria (ASB) or contaminated urine cultures is common.
Recent Findings
Challenges with the appropriate diagnosis of UTIs include the lack of specific signs and symptoms, no definitive diagnostic criteria, high incidence of ASB, contamination of samples, and frequent lack of indications for ordering urine cultures. Promising interventions include education and feedback, indication requirements when ordering cultures, and use of reflex culture policies that limit urine cultures.
Summary
Antimicrobial and diagnostic stewardship interventions can work synergistically to decrease ordering of urine cultures without clear indication and prevent excessive antimicrobial administration in patients without clearly defined UTI.
PDF
