Never Be Heard: Nonreciprocal Acoustic Circulator Blocks Sound Waves From Travelling Back

By lookng at how an electronic circulator works, University of Texas at Austin researchers have adapted the concept and applied it to develop a non-reciprocal acoustic circulator. The device allows sound waves to travel one way and not travel back, basically a one-way road for sound. The circulator transmits these acoustic waves in one direction but block them in the other, in a linear and distortion-free way.

The device is similar in concept to a one way mirror. The acoustic circulator allows one to listen but not be heard.

Communications devices and radars use electronic circulators that manage transmission of microwaves and radio signals in three ports. These signals are transmitted in a sequential way from one port to the next. The unused port acts as an isolator to allow the signals to travel to the other port but not back.

Using this technology, the researchers adapted it to sound waves. This development can lead to advances in noise control, sonars and sound communication systems, and components for acoustic imaging and sensing.

The image is the non-reciprocal acoustic circulator as shown on the cover of Science. The device creates one way communication channels for sound letting sound in but not in the opposite direction. The arrows show the acoustic signals travelling through the device albeit in a non-reciprocal manner.

Nanoplasmonic Bubble Lens Controls Focus and Direction of Light

Credit: Tony Jun Huang, Penn State

Scientists have developed a reconfigurable plasmofluidic lens using nanoplasmonics that can control light waves at the nanoscale. The nanoscale light beam is modulated by surface plasmon polaritons (SPP) which are short electromagnetic waves. The light wave is controlled by the bubble lens which can control the focus and direction of light.

Nanoplasmonics is a new field of science that deals with the behavior of metal particles at the nanoscale and its optical properties. At the nanoscale, light or electromagnetic waves approaches half the size of its wavelength. At this level, the electrical field of light displaces the metal's electrons producing an oscillating field or what is called a surface plasmon. By using certain metal nanoparticles such as gold or silver and manipulating its size and shape, the surface plasmons can be modulated.

Ancient stained glass windows (which contains gold and silver particles) use nanoplasmonic properties to attain its deep vibrant colors when light passes through it.

Currently, manipulating and reconfiguring the focus and direction of these light waves have been difficult. But with the development of reconfigurable plasmofluidic lens, which are essentially tiny bubbles, scientists have found a way to control, switch, and modulate light.

Applications for nanoplasmonics can be found in photovoltaics and optical plasmonic systems. In photovoltaic systems, plasmons can be used to modify the opto-electronic properties for fast photo-detectors and effective photocells. With optical plasmonic systems, devices can be developed that manipulate the optical properties which may lead to the development of inexpensive, fast and small active optical elements.

Transformational Optics Metamaterial Leads To Development Of Improved Invisibility Cloak

A new metamaterial based on transformational optics has been engineered that can successfully split light waves around an object. This can lead to advancements in fiber optics as well as in the development of a more advanced cloaking device or as it is popularly known, an invisibility cloak.

Nanophotonics Allow Color Manipulation A Few Atoms Wide With Opaque Objects

Nanophotonics is the study that has anything to do with light at the nanoscale level. The nanoscale level is usually around 1-100 nanometers (nm); a nanometer is one billionth of a meter.

Using nanophotonics, researchers at Harvard have discovered that color can be manipulated at the nanoscale even with opaque objects. These kind of objects are impenetrable by light and are believed cannot exhibit thin-film interference effects.

Thin film interference effects happen when light waves interfere with each other as they pass through a medium and are reflected back out. As they are reflected back, some colors come out brighter while others are lost. An example of this would be rainbow like colors reflected back from an oily puddle on the street.

MIT News: Bending Light To Cloak Objects Lead To Better Electron Transfer For Thermoelectric Devices

A new approach that allows objects to become “invisible” has now been applied to an entirely different area: letting particles “hide” from passing electrons, which could lead to more efficient thermoelectric devices and new kinds of electronics.

Diagram shows the 'probability flux' of electrons, a representation of the paths of electrons as they pass through an 'invisible' nanoparticle. While the paths are bent as they enter the particle, they are subsequently bent back so that they re-emerge from the other side on the same trajectory they started with — just as if the particle wasn't there.
Image courtesy Bolin Liao et al.

The concept — developed by MIT graduate student Bolin Liao, former postdoc Mona Zebarjadi (now an assistant professor at Rutgers University), research scientist Keivan Esfarjani, and mechanical engineering professor Gang Chen — is described in a paper in the journal Physical Review Letters.