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Better Ultrasound Imaging and Sonar Through Samarium

Samarium can nearly double the performance of piezoelectric crystals used in many sensors

2 min read
A doctor administers an ultrasound exam on a pregnant woman.
Photo: iStockphoto

Piezoelectric crystals are the key ingredient in many kinds of sensors that detect vibrations, and can be found in underwater sonars and medical ultrasound imaging systems. The crystals’ performance can be dramatically improved, according to a team of researchers at Xi'an Jiaotong University in China, by adding trace amounts of a rare-earth element.

Piezoelectric materials can convert mechanical oscillations to electrical signals and vice versa. Currently, the most advanced piezoelectric devices often use a perovskite oxide crystal known as PMN-PT, which outperforms other common piezoelectric materials by roughly a factor of three in terms of efficiency. However, despite much research, progress toward improving the performance of these crystals has been slow over the past two decades, researchers say.

Now scientists have discovered that introducing relatively minuscule amounts of samarium into PMN-PT—adding about one atom per thousand atoms of the parent crystals—could greatly enhance its performance. Regular PMN-PT crystals generate about 1,200 to 2,500 picocoulombs of charge per newton of force, but the new doped crystals could generate 3,400 to 4,100 picocoulombs per newton, they say.

The researchers found that the samarium atoms make the orderly crystalline structure of the PMN-NT more heterogeneous on the atomic and nanometer scales. This in turn disrupts the orderly arrangement of its dipole moments— spots in the material where electric charges are polarized. This disruption makes the crystal “much more sensitive and responsive to an applied electric field, leading to high piezoelectricity,” says study lead author Fei Li.

The scientists also discovered that samarium doping led to more uniform piezoelectric properties throughout the crystals by counteracting variations in the crystal's electrical properties as it was grown. The doping also led to bigger crystals, potentially helping reduce production costs and waste, they note.

The researchers suggest their work could one day lead to medical-imaging devices with improved resolution, sensitivity and efficiency, as well as more powerful piezoelectric actuators for use in a wide range of industrial applications. They detailed their findings in the 19 April issue of the journal Science

The Conversation (0)
Illustration showing an astronaut performing mechanical repairs to a satellite uses two extra mechanical arms that project from a backpack.

Extra limbs, controlled by wearable electrode patches that read and interpret neural signals from the user, could have innumerable uses, such as assisting on spacewalk missions to repair satellites.

Chris Philpot

What could you do with an extra limb? Consider a surgeon performing a delicate operation, one that needs her expertise and steady hands—all three of them. As her two biological hands manipulate surgical instruments, a third robotic limb that’s attached to her torso plays a supporting role. Or picture a construction worker who is thankful for his extra robotic hand as it braces the heavy beam he’s fastening into place with his other two hands. Imagine wearing an exoskeleton that would let you handle multiple objects simultaneously, like Spiderman’s Dr. Octopus. Or contemplate the out-there music a composer could write for a pianist who has 12 fingers to spread across the keyboard.

Such scenarios may seem like science fiction, but recent progress in robotics and neuroscience makes extra robotic limbs conceivable with today’s technology. Our research groups at Imperial College London and the University of Freiburg, in Germany, together with partners in the European project NIMA, are now working to figure out whether such augmentation can be realized in practice to extend human abilities. The main questions we’re tackling involve both neuroscience and neurotechnology: Is the human brain capable of controlling additional body parts as effectively as it controls biological parts? And if so, what neural signals can be used for this control?

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