Transducer Design

Design of modern transducers is shifting away from being a standalone technical premise and becoming more of an interdisciplinary area of study. This shift has been further expedited during recent years by introduction of the multiphysics simulation platforms. In the area of transducer design there are several unanswered research questions which are either purely theoretical or need minimal laboratory instruments. This include designing bone conduction transducers for wearable electronics and  military applications and also vibration and acoustic sensors for health monitoring of manufacturing machines.

On the other hand, in some other fields, while computer simulations are a necessary and obvious step for evaluating the design, computer simulations alone are often not considered to be sufficient for proof-of-concept. It is rather with performing validating tests under near-real-life working conditions that a proposed design or methodology can stand out as a viable solution. During my career I have had the opportunity to closely collaborate with world class designers and physicists as well as working with real-time simulation setups. These experimental setups enable the researcher to simulate testing environments very similar to real-life conditions.

Material Characterization Using Ultrasound

There are several research areas in this field. Throughout my work at INL I have been involved in various researches concerning:

  • Measuring internal friction of metals with a novel and accurate method.
  • A novel technique to measure crystal orientation throughout a single crystal metal.
  • Developing new theoretical methods for evaluating elastic and anelastic properties of materials.

All these researches have been performed using laser ultrasound. The non-contact nature of laser ultrasound – both on the excitation and the detection side – makes it a suitable choice for in situ measurements and also remote access environments such as nuclear reactors. While nuclear industries are specifically interested in this research, it has applications in several other areas including military and automotive industries

Using Eigenmodes to Perform the Inverse Problem Associated with Resonant Ultrasound Spectroscopy Laser resonant ultrasonic spectroscopy (LRUS) uses lasers to excite and detect resonant modes. This experimental approach makes possible a new method for performing the inverse problem that employs eigenmodes. The crystallographic orientation of a copper sample determined using (top) the traditional eigenfrequency method is compared with (bottom) the eigenmode method.  Image courtesy of Farhad Farzbod and David Hurley, the Materials Science and Engineering Department, Idaho National Laboratory, Idaho Falls, ID. For further reading, please see the accompanying article on pages 2470–2475 of this issue.

Periodic Structures

Structures with periodic features are widely utilized in the nature and also in the technical world. From an engineering point of view, the main interest of their characteristics is their simple manufacturing, significant impact and high temperature tolerance, and high strength-weight ratios. In addition, because of the vibration patterns of periodic structures, they provide manageable wave propagation characteristics which make them excellent candidates for the design of wave guides, frequency filters, or heat insulators. On the macro scale, examples of periodic structures include multi-span bridges, multi-blade turbines, chemical pipelines,stiffened plates and shells in aerospace and ship structures. On the other hand, any crystal (e.g. phononic crystals) can be thought of as a periodic structure in the micro scale order.The mathematical tool to investigate the wave propagation in these structures is mainly derived from Bloch theorem. In part of my PhD research, I developed and derived Bloch theorem rigorously in such a way that makes it suitable to address damping and energy dissipation in aperiodic structure. This research would pave the way for exciting new applications including design of new materials and methods to filter acoustic noises, harvest vibration energy in a wide range of frequencies, focusing ultrasound, and acoustic metamaterials with negative refraction index to overcome diffraction limit of acoustic imaging.  

In the area of macroscopic periodic systems, FEA is a vital tool for simplification of the model and saving time of computation. However, there are some theoretical issues with regard to FE methods in wave propagation analysis. There are several unanswered research questions on how to design periodic structures with certain band gaps. This theoretical part of research needs knowledge of vibration analysis and also mathematical tools such as functional analysis. This is one of the research areas in which I have deep understanding of the subjects and adequate background to do novel works. 

On the experimental part of this research, we need to verify theorems and make prototypes for real world applications. The geometry of a unit cell in a periodic structure in theory could be really complicated, making them difficult for manufacturing and prototyping. However, recent progress in additive manufacturing provides unprecedented opportunities for prototyping these materials. Currently it is possible to 3D print plastics and metals, ceramics and composites are also emerging. This research is an excellent application of additive manufacturing technologies providing exciting materials for aerospace applications.

Symmetry Lines and contour graph of dispersion surface
for a 2D-two-mass system with damping [1]