Miniaturized magnetometers. Magnetometers measure the direction and/or intensity of magnetic fields. They are used in space to monitor space weather — conditions in geospace where charged particles carried on the solar wind from the sun collide with Earth’s magnetic fields, sometimes producing solar storms capable of endangering satellites, bringing down power grids on Earth, and producing the phenomena known as auroras.

Joshua Semeter (ENG’92,’97), an ENG assistant professor of electrical and computer engineering, and Makhlouf Redjdal, an electrical and computer engineering research associate, are developing a new magnetometer, small and light enough to fly easily in space and sensitive enough to compete with the much bulkier fluxgate magnetometers that are the current industry standard.

The new magnetometers are based on the giant magneto-impedance (GMI) effect. Discovered in 1994, the GMI effect is observed in very small magnetic wires, about five one-thousandths of an inch in diameter. When a high-frequency current is passed through them in the presence of even a very small magnetic field, these wires produce very large changes in resistance.

The project uses GMI wires to design the next generation of magnetometers for space research. On Earth, these wires are used in automotive and transportations systems, industrial measurement, scientific applications, and health care. GMI wires are also being explored in research to separate biological molecules by binding them to magnetic microspheres. Ultimately, the wires may be incorporated into intravenous sensors to monitor cardiac health.

Semeter’s and Redjdal’s GMI magnetometers will use three wires at right angles to one another, enabling them to measure the direction, as well as the intensity, of magnetic fields. They will be packaged, along with the necessary electronics, in a box measuring about a half-inch by a half-inch by about three inches, and weighing only about 3.5 ounces. The researchers expect the cost of the smaller and more sensitive units to be about a hundredth that of current magnetometers.

The researchers will be collaborating with space scientists at the CAS Center for Space Physics to test the new magnetometers on sounding rockets. The research to build the prototype has been funded by one of this year’s SPRInG grants from the Office of the Provost.

Assessing tiny building blocks. First discovered in 1991, carbon nanotubes have become one of the most important building blocks of nanotechnology. Combining the strength of diamonds with the conductivity of graphite, carbon nanotubes can be envisioned as a sheet of graphite (a lattice of carbon atoms arranged in a hexagonal pattern) rolled into an incredibly thin cylinder one 30-thousandth the diameter of a human hair.

Although nanotubes have already been incorporated into new products, among them reinforced plastics, plastics that conduct electricity, high-resolution flat panel displays, novel semiconductor transistors, and sharper tips for atomic force microscopes, some characteristics of this new material remain poorly understood. Anna Swan, an ENG research assistant professor of electrical and computer engineering, is developing new methods to measure the optical and electronic properties of individual nanotubes. The ability to accurately characterize nanotubes will help scientists and engineers develop nano-photonic devices that use nanotubes to their full potential.

Swan proposes to study how light changes the electronic properties of nanotubes as the environment is systematically changed around them. Among the factors that will be varied are the refractive index, which measures the speed at which light moves through a material, the electrical charge of the medium in which the tubes are located, and the effects of stresses such as heat and strain.

Swan’s instrument will measure both the vibrational signature, using an optical technique known as Raman spectroscopy, and the fluorescence spectra emitted by the tubes. A sample patterned by electron beam lithography makes it possible to first locate tubes using atomic force microscopy, then later to reliably find the same tube using the optically visible pattern. A new microscope-compatible chamber will provide the means to control the environment.

Swan will be working closely with other members of the Center for Nanoscience and Nanobiotechnology as well as with collaborators at Harvard and MIT. The work is being supported by a recent SPRInG grant from the Office of the Provost.