Unit 3 Mars rovers set to scale heights

A ROBOTIC mountaineer that could one day climb cliffs on Mars and even help rescue earthquake victims has taken its first steps. The spider-like robot, called Lemur, was developed by engineers at Stanford University and NASA's Jet Propulsion Laboratory (JPL) in California, as a prototype for a fully autonomous rock climber. It can already follow a human climber up an irregular surface without any guidance from a controller. And it has a spookily human gait.

JPL is better known for its twin Mars rovers, Spirit and Opportunity, which have roamed the Red Planet. The rovers have transmitted images of the planet's surface and gleaned much information from soil and rock samples. But Tim Bretl, the lead engineer on the project at Stanford's robotics laboratory, says Lemur's technology could take planetary exploration to another level.

While other climbing robots are designed to scale the sides of flat structures using suction cups or magnets for grip, tackling uneven geological surfaces is a far more difficult task. With a central body and four triple-jointed limbs, Lemur’s gait resembles that of a human rock climber as it maneuvers up an indoor climbing wall at Stanford. At the moment, the robot cannot stick to a sheer wall. But on uneven surfaces it can use a claw at the end of each limb to hook into a foothold. For the moment Lemur cannot “see” its footholds, so a computer model of the wall, containing coordinates of the footholds, has to be fed into its onboard computer before it starts climbing. From this it figures out an ideal route up and works out how to manoeuver itself for each step of the ascent.

The ultimate goal is for Lemur to read a scene and calculate its own best path up a cliff. The route would be modified as it climbed, using information from its own video cameras and touch sensors. At the moment, the sensors are used only to make sure that each foothold is secure.

After Lemur moves one of its limbs to a new foothold, it must simultaneously shift its weight by repositioning the other three limbs to maintain balance. Future incarnations of Lemur are likely to have grippers for a more secure foothold, and more joints in the articulated limbs, giving them a greater range of movement. It will also be taught how to react if it unexpectedly loses its grip.

Unit 4 Piezoelectric materials

Piezoelectric materials have two unique properties which are interrelated. When a piezoelectric material is deformed, it gives off a small but measurable electrical discharge. Alternately, when an electrical current is passed through a piezoelectric material it experiences a significant increase in size (up to a 4% change in volume).

Piezoelectric materials are most widely used as sensors in different environments. They are often used to measure fluid compositions, fluid density, fluid viscosity, or the force of an impact.

Piezoelectricity is the charge which accumulates in certain solid materials (notably crystals, certain ceramics, and biological matter such as bone, DNA and various proteins) in response to applied mechanical stress. The word piezoelectricity means electricity resulting from pressure.

It is derived from the Greek piezo or piezein, which means to squeeze or press, and electric or electron, which stands for amber, an ancient source of electric charge. Piezoelectricity is the direct result of the piezoelectric effect.

The first practical application for piezoelectric devices was sonar, first developed during World War I. In France in 1917, Paul Langevin and his coworkers developed an ultrasonic submarine detector. The detector consisted of a transducer, made of thin quartz crystals carefully glued between two steel plates, and a hydrophone to detect the returned echo. By emitting a high-frequency chirp from the transducer, and measuring the amount of time it takes to hear an echo from the sound waves bouncing off an object, one can calculate the distance to that object.

The use of piezoelectricity in sonar, and the success of that project, created intense development interest in piezoelectric devices. Over the next few decades, new piezoelectric materials and new applications for those materials were explored and developed.