THE NEXT STEP IN ENGINEERING

Smart structures can sense changes in their environment and respond accordingly. These adaptive structures can autonomously modify their shapes to perform the desired task regardless of the particular environmental disturbance.

"It's difficult to bet on technology-you cannot always pick the winners, but it looks like smart materials would be the next step in engineering design," says Craig A. Rogers, director of Virginia Tech's Center for Intelligent Systems and Structures.

By using smart materials instead of adding mass, engineers can endow structures with built-in responses to a myriad of contingencies. In their various forms, these materials can perform as actuators, which can adapt to their environments by changing such characteristics as shape and stiffness, or as sensors, which provide actuators with information about structural and environmental changes.

Smart structures have numerous applications, among them the following:

SPACE STRUCTURES

Large space structures are subject to a variety of dynamic perturbations produced by the crew, the docking of other spacecraft, transient thermal states during the orbit, micrometeorities, and so on. The vibration amplitude of the perturbations has to be dampened in time to avoid further nonstability in the space structure.

In addition to that, the dampening of the flexible models is a necessary ingredient in achieving robust attitude control of the spacecraft.

AIRPLANES

Smart wings. Airplanes that have smart wings will control surfaces that can reshape themselves on the fly. Airplane wings will flex themselves like fish tails. With the help of smart structures, airfoil will be shaped and the aircraft's lift will be improved. This improved lift will help to get a single-engine fighter off the deck of an aircraft carrier without a catapult.

Replacing current (and heavy) hydraulic control systems with light-weight, high-performance smart materials could increase aircraft payloads by as much as 30 percent and flight range by 50 percent.

Adaptive surfaces would replace stiff structures designed as a compromise among ideal wing shapes for various maneuvers. Eventually vertical tails, ailerons, and stiff structures could be eliminated.

HELICOPTERS

Active helicopter blades that adjust shape continuously to respond to vibration-engendering pressure changes in the air. These fluctuations knock the machinery out of alignment and cause a lot of down time. A helicopter's maintenance schedule is approximately 15 percent of its time. In the helicopter project, piezoelectric patches on blade surfaces function both as sensors and as actuators, or as generators of counter-force.

Flutter suppression is a particularly important problem. Recent experiments in NASA wing tunnels with unoptimized smart structure designs have shown a 70 percent decrease in displacement and a 20 percent increase in blade speed by utilizing active vibration control concepts.

Active noise suspension for helicopter cabins promise greatly decreased acoustic noise/vibration intensities. This reduces stress upon crew members involved in increasingly longer duration missions.

SUBMARINES

Stealth submarines using smart skins. Smart materials technology may result in stealth submarines. Their acoustically hypersensitive smart skins would detect the pressure of an incoming sonar wave, and then automatically generate an equal but opposite counter-pressure to cancel out the ping. With nothing reflected back to enemy boat, the submarine would be invisible.

CARS

The automotive industry also is eager to incorporate intelligent materials technology. Some of the areas where smart material will be used are:

Smart car seats. Researchers are working on an industry-sponsored project to develop smart car seats that can identify primary occupants and adapt to their preferences for height, leg room, back support, and so forth.

Maintenance information. The technology exists to enable cars to tell owners how much air pressure tires have, when oil changes are needed, and other maintenance information.

Suspension and transmission. Smart materials that can change their viscosity (inherent thickness or resistance to flow) when exposed to electric or magnetic fields. This kind of smart material will lead to new kinds of auto suspensions and transmissions.

SKIS

A revolutionary piezo control module, developed by Active Control eXperts, Inc. (ACX), serves as "the brain inside the ski."

The ACX "brain" is a small, thin, rectangular card containing piezoelectric smart materials and control circuits, which are embedded while the skis are being made. These materials detect unwanted vibrations in the skis and convert them into useful electrical energy. The control circuitry then uses the energy to smooth out the vibrations, putting the skis back on the snow. The result is a smoother ride, more responsive turning, and "solid stability."

SOUND

Ultra-high-fidelity stereo speakers. Using piezoelectric actuators, such speakers can expand and contract in thousandths of a second in response to applied voltage. Speaker speakers in their homes and cars to achieve maximum musical effects. Their cars and houses will offer built-in surround-sound.

BUILDINGS

New bridge systems using fiber-optic lines and other sensors as strain indicators. Embedded in building materials, these devices would generate telltale optical or electrical signals when the system is stressed. Eventually, earthquake-resistant structures could be made using materials that would alter their stiffness in response to the ground's motion, much as horseback riders flex their legs while riding.

Earthquake resistant structures. Smart structures will shake the building to cancel the effect of the earthquake.

Early warning. Smart structures will help determine possible structural damages due to the onset of structural degradation.