Electrical engineering uses electricity in practical applications. Many of these applications also draw on expertise from other disciplines, such as aeronautical, hydraulic, and mechanical engineering, and sometimes materials science and theoretical physics. The scale of electrical engineering covers an enormous range: from microcircuitry in computers, where distances are measured in microns, to power systems that span whole continents. This article presents some of the recent advances and current research in electrical engineering.
Advances in electric motors
The electric motor is a mainstay of electrical engineering. In its most basic form, it has changed little for well over a century: a motor consists of coils, called windings, wrapped around a rotor—a shaft that rotates between magnets. Currents in the coils produce magnetic dipoles that interact with the magnetic field to produce a turning force that spins the rotor. The windings of the motor are fed with electricity one after another through a commutator—a set of contacts at one end of the rotor. The commutator contacts slip between two feeder contacts, called brushes, and this action is a major cause of mechanical wear and eventual motor failure.
A new type of motor eliminates the need for a commutator—and avoids the risk of its failure—by using electronic switches to feed current to the appropriate winding at any given rotor position. Commutatorless motors are more reliable than their conventional counterparts, and they operate efficiently over greater ranges of speed and load.
The use of electronic switching also revolutionized a less conventional motor: the reluctance motor. This type of motor has a cog-shaped soft-iron rotor wheel. Fixed coils around the edge of the wheel are fed with current in sequence to provide a rotating magnetic field that drags the rotor around. In 1842, Robert Davidson of Aberdeen, Scotland, used a reluctance motor to provide traction for a primitive battery-powered locomotive. However, Davidson’s motor used a rotating commutator to switch power between the coils of the motor, and the resulting loss of mechanical energy made his motor too inefficient to gain widespread acceptance. Electronic switching eliminates these losses, resulting in compact motors that are efficient and easily controlled. In the 1980s, switched reluctance motors acquired acceptance as drives for flexible-cycle washing machines, high-speed machine tools, and lightweight, easily controlled traction motors.
Magnetic micromotors
In 1991, the Japanese Toshiba company developed a reluctance motor with a potentially wide range of applications owing to its microscopically small size. The Toshiba micromotor measured less than 0.03 in. (0.8 mm) in diameter.
A variety of reluctance micromotors have been built since the Toshiba model. Their rotors are typically 0.004 to 0.006 in. (0.1–0.15mm) in diameter, with coils fixed in rings some 1.5 times the diameter of the rotor. Such motors have maximum speeds of around 150,000 rpm, can operate continuously at 20,000 rpm for a day or more, and produce more than 1 × 10–9 Nm of torque. The high rotor speed would necessitate a miniature transmission for many applications; nevertheless, it is thought that micromotors will one day be used to remove plaque from the inner walls of clogged arteries in human beings, for example.
