Scientists control super fast frequencies by using high temperature superconductors

Apr 18, 2005
Scientists control super fast frequencies

Imagine an imaging technology that could see deep into human tissue without the harmful side effects of radiation. Super-fast oscillations of radio waves, called terahertz (THz) have that promise, but so far, controlling them has been beyond reach.
But now, by using layered high temperature superconductors, researchers at the University of Michigan and RIKEN, Japan have proposed a way to cherry pick these ultra-fast waves, letting only certain waves pass through, similar to how we tune a radio.

Image: The array of green cylinders inside the sample, forming a so-called photonic crystal, span the width of the sample. These cylinders contain a magnetic field, and act somewhat similarly to bumpers in a pinball machine, scattering the incident electromagnetic waves, shown in red. Only red waves with certain frequencies can propagate through the crystal, resulting in the outgoing transmitted wave shown in green. The rest bounce back, shown as the reflected blue waves.

This tunable filter uses a superconducting material with a regular array of spaghetti-shaped magnetic field lines, known as a Josephson vortex lattice, said U-M Physicist Franco Nori, one of the principal investigators on the project. The filter works similarly to the way bumpers on a pinball machine deflect the ball. The result is that the arrangement of "bumpers" creates frequency gaps that the waves can't penetrate. These band gap structures are referred to as "terahertz photonic crystals."

Scientists are able to "tune" the bumpers by changing an externally applied electromagnetic field, thus selecting which frequencies to let through, and which to keep out, similar to how a radio dial selects some frequencies and weeds out others.

This sort of "tuning" is important to developing coherent images with high-frequency radio waves.

Terahertz waves—a trillion oscillations per second—occupy a large portion of the electromagnetic spectrum between the infrared and microwave bands. Although they are considered the next frontier in imaging science, no reliable means of harnessing and controlling this high frequency has been developed, said Nori.

"To push beyond the gigahertz range of frequencies has been very difficult because the waves oscillate so fast that most electronics can't keep up," Nori said. "Indeed if you look at standard computer chips, it is hard to go beyond a few gigahertz. When you go beyond 100 gigahertz, you approach the terahertz range, the next frontier. The poor circuits just can't keep up."

Terahertz radiation represents the last unexplored frontier of the radio wave and light spectrum, Nori said. Terahertz waves can penetrate deep into many organic materials—such as tissue—without the damage associated with ionizing radiation such as X-rays. Also, terahertz radiation can be used to distinguish between materials with varying water content, such as fat versus lean meat. These properties lend themselves to applications in biomedical imaging, as well as quality control. Terahertz radiation can also help scientists understand the complex dynamics involved in materials.

"This is an exciting new frontier, with new research centers on this being started in different parts of the world," Nori said.

A paper on the research, "Using Josephson Vortex Lattices to Control THz Radiation: Tunable Transparency and THz Photonic Crystals," is to appear in the April 29 Physical Review Letters. Collaborators are Sergey Savel'ev and A.L. Rakhmanov from The Institute of Physical and Chemical Research (RIKEN), Japan.

Source: University of Michigan

Explore further: Seeking 'absolute zero', copper cube gets chillingly close (Update)

add to favorites email to friend print save as pdf

Related Stories

'T-rays' to shed light on nuclear fusion

Oct 09, 2014

In the race to secure clean energy in the future, Lancaster University Engineers are reinventing a piece of technology which so far has only been used in labs to diagnose cancer, detect explosives, and even analyse grand ...

New quantum probe enhances electric field measurements

Oct 07, 2014

Researchers at the National Institute of Standards and Technology (NIST) and the University of Michigan have demonstrated a technique based on the quantum properties of atoms that directly links measurements ...

Recommended for you

Backpack physics: Smaller hikers carry heavier loads

17 hours ago

Hikers are generally advised that the weight of the packs they carry should correspond to their own size, with smaller individuals carrying lighter loads. Although petite backpackers might appreciate the ...

Extremely high-resolution magnetic resonance imaging

18 hours ago

For the first time, researchers have succeeded to detect a single hydrogen atom using magnetic resonance imaging, which signifies a huge increase in the technology's spatial resolution. In the future, single-atom ...

'Attosecond' science breakthrough

19 hours ago

Scientists from Queen's University Belfast have been involved in a groundbreaking discovery in the area of experimental physics that has implications for understanding how radiotherapy kills cancer cells, among other things.

User comments : 0