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Polarization bandgaps and fluid-like elasticity in fully solid elastic metamaterials

View Article: PubMed Central - PubMed

ABSTRACT

Elastic waves exhibit rich polarization characteristics absent in acoustic and electromagnetic waves. By designing a solid elastic metamaterial based on three-dimensional anisotropic locally resonant units, here we experimentally demonstrate polarization bandgaps together with exotic properties such as ‘fluid-like' elasticity. We construct elastic rods with unusual vibrational properties, which we denote as ‘meta-rods'. By measuring the vibrational responses under flexural, longitudinal and torsional excitations, we find that each vibration mode can be selectively suppressed. In particular, we observe in a finite frequency regime that all flexural vibrations are forbidden, whereas longitudinal vibration is allowed—a unique property of fluids. In another case, the torsional vibration can be suppressed significantly. The experimental results are well interpreted by band structure analysis, as well as effective media with indefinite mass density and negative moment of inertia. Our work opens an approach to efficiently separate and control elastic waves of different polarizations in fully solid structures.

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Experimental set-ups.An electromagnetic shaker is used for transverse excitation in a; and longitudinal excitation in b. Rotational excitation is achieved by using an electric motor, which exerts a torque pulse about the meta-rod's axis (x axis), as shown in c. Accelerometers are used to obtain the elastic responses at different positions.
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f3: Experimental set-ups.An electromagnetic shaker is used for transverse excitation in a; and longitudinal excitation in b. Rotational excitation is achieved by using an electric motor, which exerts a torque pulse about the meta-rod's axis (x axis), as shown in c. Accelerometers are used to obtain the elastic responses at different positions.

Mentions: First, we excite sample-kz by a force perpendicular to the rod. This is realized by the experimental set-up shown in Fig. 3a. Simply put, the sample is uprightly fixated on an aluminum plate that is supported on low-friction sliding tracks, which confine their motion to one single direction. We then connect the aluminum plate to an electromagnetic shaker, whose vibration causes the plate to move back and forth along the tracks (see Methods for more details). For the meta-rod, this transverse excitation will excite flexural vibrations. We obtain the response function by dividing the acceleration (with direction along the excitation force) measured on the top of the sample with the one measured on the aluminum plate. This is plotted in Fig. 4a as a function of frequency (blue circles). A bandgap is clearly seen in ∼1.2–1.6 kHz. We further use a laser Doppler vibrometer to map the displacement parallel to the actuation direction on a facet of the meta-rod at 1,350 Hz, that is, inside the bandgap. The result is shown in Fig. 4b. It is seen that the displacement amplitude rapidly decays away from the actuation position (z=0 mm). This means that unlike ordinary elastic rods, transverse forces with frequencies inside the bandgap cannot excite the flexural vibration in our sample.


Polarization bandgaps and fluid-like elasticity in fully solid elastic metamaterials
Experimental set-ups.An electromagnetic shaker is used for transverse excitation in a; and longitudinal excitation in b. Rotational excitation is achieved by using an electric motor, which exerts a torque pulse about the meta-rod's axis (x axis), as shown in c. Accelerometers are used to obtain the elastic responses at different positions.
© Copyright Policy - open-access
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC5121349&req=5

f3: Experimental set-ups.An electromagnetic shaker is used for transverse excitation in a; and longitudinal excitation in b. Rotational excitation is achieved by using an electric motor, which exerts a torque pulse about the meta-rod's axis (x axis), as shown in c. Accelerometers are used to obtain the elastic responses at different positions.
Mentions: First, we excite sample-kz by a force perpendicular to the rod. This is realized by the experimental set-up shown in Fig. 3a. Simply put, the sample is uprightly fixated on an aluminum plate that is supported on low-friction sliding tracks, which confine their motion to one single direction. We then connect the aluminum plate to an electromagnetic shaker, whose vibration causes the plate to move back and forth along the tracks (see Methods for more details). For the meta-rod, this transverse excitation will excite flexural vibrations. We obtain the response function by dividing the acceleration (with direction along the excitation force) measured on the top of the sample with the one measured on the aluminum plate. This is plotted in Fig. 4a as a function of frequency (blue circles). A bandgap is clearly seen in ∼1.2–1.6 kHz. We further use a laser Doppler vibrometer to map the displacement parallel to the actuation direction on a facet of the meta-rod at 1,350 Hz, that is, inside the bandgap. The result is shown in Fig. 4b. It is seen that the displacement amplitude rapidly decays away from the actuation position (z=0 mm). This means that unlike ordinary elastic rods, transverse forces with frequencies inside the bandgap cannot excite the flexural vibration in our sample.

View Article: PubMed Central - PubMed

ABSTRACT

Elastic waves exhibit rich polarization characteristics absent in acoustic and electromagnetic waves. By designing a solid elastic metamaterial based on three-dimensional anisotropic locally resonant units, here we experimentally demonstrate polarization bandgaps together with exotic properties such as ‘fluid-like' elasticity. We construct elastic rods with unusual vibrational properties, which we denote as ‘meta-rods'. By measuring the vibrational responses under flexural, longitudinal and torsional excitations, we find that each vibration mode can be selectively suppressed. In particular, we observe in a finite frequency regime that all flexural vibrations are forbidden, whereas longitudinal vibration is allowed—a unique property of fluids. In another case, the torsional vibration can be suppressed significantly. The experimental results are well interpreted by band structure analysis, as well as effective media with indefinite mass density and negative moment of inertia. Our work opens an approach to efficiently separate and control elastic waves of different polarizations in fully solid structures.

No MeSH data available.


Related in: MedlinePlus