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Simple, Less Expensive Ultrasound Probe Developed

Polymer ultrasound team

Developers of polymer ultrasound device, L-R: Robert Rohling, Carolos Gerardo, and Edmond Cretu (Clare Kiernan, University of British Columbia)

12 September 2018. Engineers designed a device that sends and receives ultrasound signals with polymer plastics instead of silicon-based circuits, which can lower the cost of medical images. A team at University of British Columbia in Vancouver describes its device in yesterday’s issue of the journal Microsystems and Nanoengineering.

Researchers led Carlos Gerardo, a doctoral candidate in electrical and computer engineering at UBC, are seeking new methods for producing ultrasound images used in common devices for monitoring pregnancies and diagnosing heart disease, as well as other organs and blood flow inside the body. Ultrasound can be used non-invasively from outside the body and does not employ X-rays, which can be harmful. An ultrasound probe sends sound waves through the skin from a probe called a transducer, which then receives the signals that bounce back. A digital system collects and assembles the received signals and converts them to visual images, often in real time.

Transducer probes today are made from chips fabricated on silicon using piezoelectric crystals that generate electrical charges from mechanical stresses, in this case from sound waves, much like voice-recognition devices on smartphones. Gerardo, with UBC engineering professors Edmond Cretu and Robert Rohling developed an alternative transducer probe made from a type of polymer plastic. The plastic in this case is known as SU-8, a polymer used in microelectronics, which surrounds electrodes in a membrane. The polymer membranes react and vibrate, which are captured and transmitted through the electrodes.

To prove the concept, Gerardo and colleagues tested their device called polymer capacitive micro-machined ultrasound transducers, or polyCMUTs, in a tank of mineral oil as a simulated medium. The device, about the size of a band-aid, accurately captured images of 12 aluminum wires suspended in the oil. The researchers say the images produced by polyCMUTs are at least as sharp as those produced by today’s piezoelectric crystals.

A key advantage of polyCMUTs is their lower cost and simpler fabrication. “Transducer drums have typically been made out of rigid silicon materials that require costly, environment-controlled manufacturing processes, and this has hampered their use in ultrasound,” says Gerardo in a university statement. “By using polymer resin, we were able to produce polyCMUTs in fewer fabrication steps, using a minimum amount of equipment, resulting in significant cost savings.”

Cretu adds that their device’s lower power and flexible materials could make ultrasound more widely available. “Since our transducer needs just 10 volts to operate,” Cretu notes, “it can be powered by a smartphone, making it suitable for use in remote or low-power locations. And unlike rigid ultrasound probes, our transducer has the potential to be built into a flexible material that can be wrapped around the body for easier scanning and more detailed views, without dramatically increasing costs.”

The university filed for a patent on the technology. The researchers believe the costs for producing polyCMUTs can be reduced even further with production in a vacuum environment and using roll-to-roll manufacturing methods, enabling ultrasound to become a ubiquitous imaging process.

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