Toroid Cavity Imagers/Detectors

A family of rugged, versatile imaging devices, easy to make and simple to use

View Toroid Cavity Imager "Family Tree"

Argonne's award-winning toroid cavity imager is suited to a wide range of uses, from "seeing" into packages to monitoring nuclear waste. In an experiment to quantify the amount of water in nuclear-waste stimulant (silicon oxide, the white material in the photo at left), the imager detected 0.056 wt% water, illustrating a sensitivity level equivalent to the most sensitive nondestructive evaluation methods currently being considered for nuclear-waste monitoring.

Scientists in Argonne's Chemical Engineering Division have invented a device — a toroid cavity imager that uses nuclear magnetic resonance (NMR) technology to reveal the location and characteristics of materials inside sealed metal containers. Moisture, degradation products, and other chemical reaction products, can be detected and measured nondestructively. The device's high resolution and sensitivity make it attractive for nuclear-waste monitoring, as well as for nondestructive evaluation of commercial packaged goods, and safety and security applications.

The inexpensive imaging device could point the way to improved ceramics, alloys, composites and coatings and could permit more detailed observations than ever before of the chemical near the surface of electrodes in batteries, fuel cells and similar devices.

How Does It Work?

The "toroid cavity imager" is based on magnetic resonance imaging (MRI) methods similar to those used in hospitals to peer inside the human body. Connected to a computer, it provides an image of sample materials with up to 10 times better detail than conventional MRI methods.

In fluids, the imager has the potential to detect objects as small as 0.0002 inches (5 micrometers). In solids and polymers (long-chained molecules), it can see films that are only 0.00004 inches (1 micrometer) thick. The current version of the imager can be used at 500 times normal atmospheric pressure and at temperatures as high as 480 degrees Fahrenheit (250 degrees Celsius).

The toroid cavity imager is a simple, rugged device easily machined from metals and alloys like silver, gold, copper, beryllium-copper and titanium-aluminum. It costs about $10,000, far less than other MRI imaging cavities that provide less detailed information. Fully equipped functional devices can be made for as little as $500 for certain applications.. Argonne's toroid cavity imager is a hollow cylinder, about 1 and a half inches long and half an inch in diameter, with an electrode running down its center. It is the central electrode, or principal detector element, that makes the device unique.

Like conventional MRI devices, the Argonne cavity maps the internal chemical and physical properties of materials by surrounding them with a strong magnetic field that lines up the nuclei in the material's atoms like tiny compass needles. Next, a strong pulse of radio-frequency signals disturbs the alignment.

After the pulse, the atom's nuclei relax and realign, giving off radio-frequency signals in the process. These signals give information about the locations and identities of the atoms that make up the material.

Conventional MRI imagers surround a sample material with a uniform radio frequency magnetic field. By comparison, Argonne's cavity produces an inhomogeneous magnetic field that is stronger at the central electrode but weaker at distances further from the electrode. This variation in magnetic field strength gives detailed information unavailable with a static magnetic field.

The procedure for recording an image is simple.. A series of snapshots is recorded for a series of longer RF pulse lengths.. The snapshots are processed and rendered mathematically to produce. the images.

The invention won a 1994 R&D 100 Award. R&D 100 awards are given annually by R&D Magazine for the "100 most significant technical products of the year."

Argonne's toroid cavity imaging technology comprises 9 issued patents and is available for licensing.

Printer friendly (pdf)

For More Information

For more information on Argonne's Toroid Cavity Imager, contact Jerry Rathke (630-252-4549, rathke@cmt.anl.gov).. For information on licensing agreements and collaborative arrangements, contact William Ingle, 630-252-4694, wingle@anl.gov .

Research funded by U.S. Department Of Energy, Office of Basic Energy Sciences, Division of Chemical Sciences