Development of a universal ultrasonic scanner system for nondestructive evaluation (NDE) of material degradation will allow the NDE users to utilize various scanning methods with a one stop system. Some ultrasonic scanning requires, water e.g. C-scan, Guided wave scan, some requires gel, e.g. hand held Pulse-echo and Phased Array, and some performs scan in air using air-coupled ultrasound. Additionally, in recent years development of new theories of wave propagation in phononic crystal and metamaterials demand scans of the systems using acoustic waves for fundamental understanding. There are many NDE system that can perform individual scans with specific objective. However, in addition to ultrasonic NDE scanning, acoustic scanning, guided wave scanning, biological sample inspection and many other forms of scanning e.g. Raman spectroscopy scanning to find material composition at various special spots of a material, may demand different setup and different mechanism. In this research we developed an ability to have a system that can utilize these various mechanisms and methods and unify them under one umbrella that can serve many applications in both research and commercial use. In this article, the discussion of the development and success of such a system will be elaborated on further as testing for various ultrasonic and acoustic methods on a variety of different materials (metal, composite, phononic crystals, metamaterials) have been proven successful. Tests using ultrasonic in both air and water and dry coupled scan was performed on various materials, yielding data to create ultrasonic images. These tests show the ease of use with the system and how simple it is to convert the scanner to utilize a different method as module of ultrasonic scanning. This scanner supports the use of various transducers at any frequency, Transmit and receive (T/R) mode and through mode with signal conditioning, and the ability to configure the resolution and size of the scan. This universal scanner has the protentional to be an all-around solution for NDE and acoustic research.
Elastic wave propagation in anisotropic media is of great interest in various branches of engineering and applied sciences. In this study, an anisotropic wave propagation behavior in isotropic material with orthogonal surface perturbation is presented. The conventional method of estimating dispersion equations for isotropic material is to apply Helmholtz decomposition on the potential functions for Rayleigh-Lamb wave and Shear Horizontal (SH) waves. However, the presence of isotropic material with orthogonal surface perturbations in two coordinate directions, which is known as doubly corrugated wave guide, can significantly affect the wave propagation behavior. This is because of the direction dependency of the wave propagation in the doubly corrugated structure, and hence, the Helmholtz decomposition of the potential functions cannot be applied to derive the dispersion equations. To validate the direction dependency of the wave propagation in isotropic material with doubly corrugated geometry, a time domain simulation is performed by the Finite Element Method using a tone burst signal to excite the wave guide. A similar baseline time domain study is also performed for a flat wave guide using the same material property without corrugation in any directions. The displacements of the particles of these two studies are compared at multiple time steps and analyzed for the direction dependency of wave propagation. The preliminary results show that the wave propagation in doubly corrugated structure is highly dependent on the corrugation parameters.
In this work, reduced order nonlinear state of Lamb wave propagation due to stress-relaxation of composites was experimentally observed. Residual stresses in the composites are developed under tensile-tensile fatigue loading, which reduce over time during relaxation process due to viscoelastic behavior of the polymer matrix. To investigate reduction in nonlinearity of Lamb wave during stress-relaxation, fatigue loading on the composite specimens were conducted at an interval of 75k until 225k cycles for different cyclic frequencies (i.e., 2Hz, 5Hz and 10Hz), and relaxation experiments were conducted for a duration of 8hrs between two successive fatigue loading sequence. Experimental results show a 6-20% reduction acoustic nonlinearity of Lamb wave during relaxation. Reduction in nonlinearity is mainly contributed by stress redistribution at fibers and recovery of plastic strain during relaxation. This technique is imperative to explore long-term performances and conditions of advanced composite structures.
Accidental degeneracy is the only known reason behind the degeneration of 3 or more modes, giving a Dirac cone or Dirac-like cone, depending on the position of the occurrence. The generation of triply degenerate points at the center of the Brillouin zone (where the wave number k→ = 0) is rare and only happens accidentally. In this article, it is proposed to execute triple degeneracy using the simplest geometric microarchitecture of phononic crystals (PnCs). The modulation of the crystals can be performed to demonstrate multiple Dirac-like cones at Γ point by using the nondispersive deaf band obtained from the periodic structure. Thus, a deaf band based predictive model of PnCs can be realized, by proving the existence of the deaf band both numerically and experimentally. The claims have been proved and validated using a squared array of cylindrical polyvinylchloride (PVC) inclusions in an air matrix. This phenomenon yields multiple wave guiding patterns that can be practically used in many research fields.
This article presents the recent study in guiding acoustic waves by creating frequency band gaps and harvesting energy simultaneously from the vibration of the structure using split ring metamaterial. Traditionally, conventional materials are unable to create frequency stop bands. So, split ring metamaterial has been used which has shown the ability to filter acoustic waves in a certain frequency range by creating frequency stop bands. In this article, a 3D unit cell of aluminum with continuous periodicity and certain split ring resonator pattern is discussed. PVDF film is used in the structure as a piezoelectric material. Here, a wide range of frequency (0-30kHz) is studied to demonstrate the ability of the cell to create stop bands within the study range. From the study, it can be seen that this unit cell is capable of creating stop bands and at the same time harvest ~2.4μW of energy simultaneously under 10kΩ resistive load.
A high percentage of failures and damage propagation in materials and sensors employed in harsh industrial environments and airborne electronics is due to mechanical failure under tension and compression loads. Therefore, it is of paramount importance to test equipment reliability and ensure its survival in long missions in the presence of physical fluctuations. Mechanical testing systems (MTS) employ mechanical load in laboratories and all the scanning tests are performed after removing the sample from MTS machine. However, more precise tracking of failures and damages is possible only the moment the material is under loads. Hence, to systematically characterize and fully understand damage’s behavior, a system capable of Realtime scanning is required. The primary objective of this study is design, fabrication, and testing of a Realtime ultrasonic scanning using hydraulic arms (RUSH), which provides mechanical loads using hydraulic arms on the specimen and simultaneously scans it with ultrasonic scanning system. RUSH consists of two hydraulic pistons (for mechanical loading) and a main control unit that accurately calculates and sets the actuators’ input signals in order to generate desired load on the materials. In this paper, the system’s architecture, its mechanical structure, and electrical components are described. In addition, to verify RUSH’s performance, various experiments are carried out using unidirectional composites.
Extracting improved mechanical properties such as high stiffness-high damping and high strength-high toughness are being investigated recently using high symmetry interlocking micro-structures. On the other hand, development of artificially engineered composite metamaterials has significantly widen the usability of such materials in multiple acoustic applications. However, investigation of elastic wave propagation through high symmetry micro-structures is still in trivial stage. In this work, a novel interlocking micro-architecture design which has been reported previously for the extraction of improved mechanical properties has been investigated to explore its acoustic responses. The finite element simulations are performed under dynamic wave propagation load at multiple scales of the geometry and for a range of material properties in frequency domain. The proposed composite structure has shown high symmetry which is uncommon in fiber-reinforced polymer composites and a desirable feature for isotropic behavior. The existence of multiple acoustic features such as band gap and near-isotropic behavior have been established. An exotic wave propagation feature, wave trapping and attenuation, has shown energy encapsulation in a series of repeating structures in a frequency range of 0.5 kHz to 2 kHz.
Nonlinear ultrasonic techniques have shown the prominent potential for assessing progressive damage occurred in the composite materials in their fatigue life cycles. Stress relaxation in composite material is being measured in two ways, in-situ analysis (on-line technique) using Lamb waves and Off-line technique using pressure wave (Scanning Acoustic Microscope). In this article, the progressive damage was investigated by a set of fatigue loading experiments on woven composite samples followed by a specific duration of stress relaxation in room temperature condition. A quantitative measure of stress relaxation is determined using Scanning Acoustic Microscope for a fatigue cycle of 225000 with the loading frequency of 10 Hz. To prove this claim, a well-established reduced order nonlinear state of Lamb wave due to stress-relaxation was compared with SAM data analysis. A good agreement between these two techniques is reported herein.
The unique phenomena in acoustic metamaterial at the Dirac-like cone, and at the exceptional spawning ring could transform the field of engineering with multiple new applications that was never possible before. Formation of localized conical dispersion (Dirac cone) at the Brillouin boundaries are the well-known facts, which exhibits many intriguing phenomena. However, Dirac cone like dispersion at the center of Brillouin zone (k ⃗=0) is rare and only happens due to accidental degeneracy at finite frequencies in two-dimensional periodic crystals (PCs), with or without microarchitectures. Additionally, a possible deformation of a Dirac cone instigates a degenerated state called spawning ring or exceptional ring, where two resonant modes coincides over a zonal wave numbers. The point of exceptional ring is called exceptional point, and known as parity-time symmetry breaking point. Exploiting the behaviors of Dirac cones and spawning rings at the origin and boundaries of the Brillouin zone, a directional and bifurcation lens were designed which will propagate sound wave in specific directions at multiple frequencies. In this article, PCs having a square array of cylindrical polyvinylchloride (PVC) inclusions in air media are studied numerically, that exhibits Dirac-like points and exceptional points simultaneously at k ⃗=0 by modulating the physical parameter of the cylindrical inclusions (PVC) in fixed lattice constant. Detailed numerical study of 2D PCs showed that by adjusting the system parameter, an accidental triple degeneracy of dispersion at Γ point can be achieved. The authenticity of the claim is demonstrated by simulating the phenomena in a designed zero-refractive index material.
Recent development of artificially engineered metamaterial has significantly widened the range of acoustic responses found in nature. Propagation of elastic waves through such composite materials unveils many applications most of which are acoustic analogue of electromagnetic metamaterials. While holographic imaging using electromagnetic metamaterials is visually indistinguishable from original object, hologramic acoustic imaging is still in a trivial stage. In this article, a conceptual design of butterfly shaped engineered metamaterial consisting of an array of full ring resonators at multiple-length scales embedded in a polymer matrix is reported. Wave propagation in the proposed media is largely affected by the geometrical anisotropy and the anisotropic constituent materials. Introduction of local anisotropy made this engineered structure a suitable candidate for ultrasonic wave bifurcation and convergence. A numerical simulation confirms the negative refraction phenomenon near 37.3 kHz and explores the superlensing capability. Wave dispersion and transmission were analyzed, which showed the formation of acoustic image at a distance away from the source. While superlensing capability is found primarily in electromagnetic metamaterials, local anisotropy in this butterfly design causes negative refraction that results in acoustic hologramic image formation. As the negative refraction leads to a richness of diversified material properties, the proposed acoustic metamaterial will have important applications in biomedical devices, ultrasonic imaging, wave guiding and marine transportations.
Access to the requested content is limited to institutions that have purchased or subscribe to SPIE eBooks.
You are receiving this notice because your organization may not have SPIE eBooks access.*
*Shibboleth/Open Athens users─please
sign in
to access your institution's subscriptions.
To obtain this item, you may purchase the complete book in print or electronic format on
SPIE.org.
INSTITUTIONAL Select your institution to access the SPIE Digital Library.
PERSONAL Sign in with your SPIE account to access your personal subscriptions or to use specific features such as save to my library, sign up for alerts, save searches, etc.