Broadband Operation of Acoustic Collimated Beam Source [Slides]
Abstract not provided.
36 MATERIALS SCIENCE↗
Engineering topics
Chillara, Vamshi
Publications and source records attributed to Chillara, Vamshi.
On the Bandwidth and Beam Profile Characteristics of a Simple Low-Frequency Collimated Ultrasound Beam Source
We numerically investigate the bandwidth and collimation characteristics of ultrasound beams generated by a simple collimated ultrasound beam source that consists of a piezoelectric disk operated near its radial mode resonances. We simulate the ultrasound beam generated in a fluid medium as a function of the excitation frequency for two cases: (1) free piezoelectric disk that corresponds to zero-traction along the lateral edge and (2) fixed piezoelectric disk that corresponds to zero-displacement along the lateral edge. We present and discuss the physical mechanism underpinning the frequency-dependent collimation and bandwidth properties of the ultrasound beams. We observe that the collimated beam generated by the free disk repeatedly lengthens/shortens and also extends/retracts sidelobes with increasing frequency. Alternatively, fixing the piezoelectric disk results in a consistent beam profile shape across a broad range of frequencies. This facilitates generating broadband signals such as a Gaussian pulse or chirp, which are common in ultrasound imaging. Thus, the fixed piezoelectric disk finds application as a collimated ultrasound beam source in a wide range of applications including medical ultrasound imaging, scanning acoustic microscopy, sonar detection, and other nondestructive ultrasound inspection techniques.
47 OTHER INSTRUMENTATION↗
The effect of a transducer’s spatial averaging on an elastodynamic guided wave’s wavenumber spectrum
Elastodynamic guided waves propagate in an elastic solid which makes it difficult, if not impractical, to place a receiving transducer in the direct path of the propagating wave (as one would for an acoustic wave in a fluid medium). Thus, to account for this, receiving transducers are often placed on the surface of the solid waveguide such that the transducer surface is parallel to the wave propagation direction. This transducer orientation introduces spatial averaging, which causes the received signal to have an altered signal amplitude and mode bias. We investigate both of these effects and present a simple model from which we derive a scaling-ratio expression that describes the effects of spatial averaging. Furthermore, we then test its performance using finite-element simulations that incorporate “real-world” assumptions (e.g., transient waves, piezoelectric effects, etc.). The results from the simulations demonstrate that the scaling-ratio can characterize the effects resulting from spatial averaging. The scaling-ratio expression will be particularly useful when designing experiments involving high frequency (small wavelength) guided waves. Lastly, the proposed scaling-ratio expression could be applied to other sensing methods, like Laser Doppler Vibrometry (LDV) or piezoelectric waveguides with inter-digitated transducers, because of its generality. However, the authors are careful to note that the scaling-ratio expression is not intended as a replacement of multi-physics analysis or good experimental design, and the effects of spatial averaging should be avoided whenever possible.
2DFFT↗
High-Resolution 3D Acoustic Borehole Integrity Monitoring System [Slides]
Develop a high-resolution 3D imaging system for improved wellbore diagnostics and integrity assessment
47 OTHER INSTRUMENTATION↗
Ultrasonic waves from radial mode excitation of a piezoelectric disc on the surface of an elastic solid
In this work, we discuss the ultrasonic wave propagation characteristics in an isotropic elastic solid due to the radial mode excitation of a piezoelectric disc actuator bonded to its surface. Finite element simulations using coupled electromechanical modeling is employed to investigate the wave propagation behavior. We find that the radial mode vibrations on the surface of the elastic solid generates all the three types of ultrasonic waves: longitudinal, shear, and surface waves. The waves in the solid are comprised of a central lobe and multiple side lobes based on the frequency of the radial mode excitation. The central lobe is predominantly composed of longitudinal waves and the side lobes are composed of shear waves. While the longitudinal waves have a strong central lobe and weak side lobes that are not fully developed, shear waves consists of fully developed side lobes. In addition, we observe that the longitudinal waves have fewer side lobes inside the solid compared to the shear waves. A semi-analytical approach is presented to explain the above observations. The interface traction boundary condition between the piezoelectric disc and the elastic solid is approximated as a truncated 'Bessel' excitation over the area of the piezoelectric disc in contact with the solid. A Fourier–Bessel series expansion technique is used to investigate the wave propagation behavior from the above traction boundary condition. The results obtained explain the observations from the finite element simulations with regard to the number and distribution of side lobes pertaining to the longitudinal and shear waves generated from the radial modes of the piezoelectric disc. The proposed semi-analytical approach is general and can be applied to any arbitrary axisymmetric excitations on the surface of an elastic solid.
36 MATERIALS SCIENCE↗
Ultrasonic Bessel beam generation from radial modes of piezoelectric discs
We present comprehensive analytical and experimental investigations on ultrasonic Bessel beam generation from radial modes of piezoelectric disc transducers. The Bessel vibration pattern of the radial modes was experimentally measured using Laser Doppler Vibrometry and was found to be in very good agreement with those obtained from numerical simulations. Ultrasonic beam profiles from the first four radial modes of the piezoelectric disc were measured using a hydrophone in a water tank. The results obtained from the experimental scans were compared to the predictions from an analytical model and were found to be in very good agreement. Also, the Bessel beams generated from the radial modes (except the first) of the piezoelectric discs were found to have narrow beam width for the central lobe compared to those from an ideal piston source of same size. The proposed approach of using radial modes for Bessel beam generation finds applications in imaging, acoustic particle manipulation and trapping, and acousto-optics.
47 OTHER INSTRUMENTATION↗
ACCObeam: Acoustic Collimated Ultrasonic Beam
A passive, linear arrangement of a sonic crystal-based apparatus and method including a 1D sonic crystal, a nonlinear medium, and an acoustic low-pass filter, for permitting unidirectional broadband ultrasound propagation as a collimated beam for underwater, air or other fluid communication are described. The signal to be transmitted is first used to modulate a high-frequency ultrasonic carrier wave which is directed into the sonic crystal side of the apparatus.
36 MATERIALS SCIENCE↗
Powering Implants Using Sound
This report describes design approaches and specifics for biomedical applications.
42 ENGINEERING↗