George K. Lewis Jr.,
Department of Biomedical Engineering,
William L. Olbricht,
Department of Bimolecular and Chemical Engineering,
Popular version of paper number 4aEA8
"Development of a portable therapeutic ultrasound system for military, medical and research use"
Presented at 10:05 a.m. on Thursday, November 13, 2008
156th Meeting of the Acoustical Society of America, Miami, FL
George Lewis, an NSF graduate research fellow in the Department of Biomedical Engineering at Cornell University, has developed the first pocket-size ultrasound system for commercial, military and research applications. The design is based on a novel approach that reduces the device’s size and cost compared with traditional ultrasonic devices. This transformative research has the potential to replace expensive shoe-box size systems with inexpensive compact cell-phone type devices and make ultrasound technology readily available for students, researchers and ultrasound practitioners.
Portable ultrasound system levitating and cavitating water at full power
Ultrasound is produced by using a piezoelectric transducer to convert electrical energy from an amplifier into sound energy. Traditionally, high power ultrasound is created by applying signals of 500 volts or more at the appropriate frequency across the piezoelectric transducer. The amplifier typically has an output impedance of 50-75 ohms, which matches that of the transducer in accord with the maximum power-transfer theorem: “To obtain maximum external power from a source with a finite internal impedance, the impedance of the load must be made the same as that of the source.” However, this results in a maximum energy transfer efficiency of 50%; in practice about 30% of the electrical energy is converted into ultrasound.
Lewis proposed reducing the amplifier source impedance to a small value, which could allow all of the electrical energy to be transferred to the transducer. Using a patent-pending design (Cornell Center for Technology Transfer D-4392), Lewis and his Cornell colleagues developed the first low-output impedance amplifier with a resistance of 0.3 ohms that transfers 95% of the source energy to the transducer. The low output impedance amplifier was incorporated into a portable battery-powered therapeutic system design described in “Development of a Portable Therapeutic and High Intensity Ultrasound System for Military, Medical and Research Use,” which will appear in the Review of Scientific Instruments (November 2008).
The system delivers acoustical energy at voltages that are lower than conventional ultrasound systems, which is inherently safer, and produces acoustic power over ranges typically seen in medical ultrasound systems. It is lightweight (6 lbs), portable, and powered by a rechargeable battery. The unit has been used for brain drug delivery experiments at Cornell, and surgeons at Weill Cornell Medical College will soon use the device in studies of ultrasound-enhanced wound healing and treatments for ischemia. The design also has potential to be incorporated into a myriad of ultrasonic applications.