6/19/2021 0 Comments Ultrasonic Power Amplifier
Because the output impedance of the drive circuitry and metal-oxide-semiconductor field-effect transistor (MOSFET) switching loss is negligible compared with the ultrasound transducers impedance, little energy is lost as heat.Published online 2008 Nov 11.PMCID: PMC2596633 NIHMSID: NIHMS76471 PMID: 19045903 Development of a portable therapeutic and high intensity ultrasound system for military, medical, and research use George K.Lewis, Jr. 1, a) and William L.
Olbricht 2, b) George K. Lewis, Jr. 1 Department of Biomedical Engineering, Cornell University, Ithaca, New York 14853, USA Find articles by George K. Lewis, Jr. William L. Olbricht 2 School of Chemical and Biomolecular Engineering, Cornell University, Ithaca, New York 14853, USA Find articles by William L. Olbricht Author information Article notes Copyright and License information Disclaimer 1 Department of Biomedical Engineering, Cornell University, Ithaca, New York 14853, USA 2 School of Chemical and Biomolecular Engineering, Cornell University, Ithaca, New York 14853, USA a) Electronic mail: moc.embllenrocegroeg. Received 2008 Aug 7; Accepted 2008 Oct 17. Copyright 2008 American Institute of Physics This article has been cited by other articles in PMC. Abstract We have developed a portable high power ultrasound system with a very low output impedance amplifier circuit (less than 0.3 ) that can transfer more than 90 of the energy from a battery supply to the ultrasound transducer. The system can deliver therapeutic acoustical energy waves at lower voltages than those in conventional ultrasound systems because energy losses owing to a mismatched impedance are eliminated. The system can produce acoustic power outputs over the therapeutic range (greater then 50 W) from a PZT-4, 1.54 MHz, and 0.75 in diameter piezoelectric ceramic. It is lightweight, portable, and powered by a rechargeable battery. The portable therapeutic ultrasound unit has the potential to replace plug-in medical systems and rf amplifiers used in research. The system is capable of field service on its internal battery, making it especially useful for military, ambulatory, and remote medical applications. Thus, the development of a cost-effective, portable system for delivering ultrasound could greatly enhance the use of ultrasound across a broad range of medical therapies. In the late 1920s initial studies of the biological effects of ultrasound were performed by Wood and Loomis. Since then, researchers have proposed systems to produce high power ultrasound. In 1942 Lynn et al. Ultrasonic Power Amplifier Driver For BiologicalHz high voltage (30006000 V) low current (900 mA) ultrasound driver for biological research, which was based on vacuum tube technology and radio transmitter design. Since in-house power and very high voltages were used in this design, precautions were taken to avoid electrical shock and rf interference. Lynns system and power outputs were measured crudely by measuring the rise of a conical oil cone from the radiation force exerted by the focused ultrasound energy. Fry et al. 18 in 1986 presented a focused ultrasound system for tissue volume ablation of brain tumors. The power of the system was supplied by a 990 kHz tuned (impedance matched) 2 kW amplifier with preamplifying circuitry. Lee et al. 19 in 1999 introduced a 64-channel rf driving unit with phase control to produce local hyperthermia in vitro and in vivo. The amplifier stage of the system used transistor-transistor-logic (TTL) timing with an unspecified in-house built circuit to amplify the drive signal. The 8.0 MHz array Lee et al. The system provided 140 W of acoustic energy from a 70 efficient lead zirconate titanate (PZT) transducer with 33 mm diameter and 55 mm radius of curvature. Owen et al. 15 compared the device with products on the market at the time and found their device favorable because of its light weight and ability to cause hemostasis and tissue necrosis. Commercially available ultrasound drivers and rf amplifiers are generally built with a 50 output impedance that has high voltage amplification and switching of the applied ac signal. To date, many of the developed ultrasound drivers have been impedance matched to enhance power transfer as stated in 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. The 50 output impedance is matched to the transducer using special impedance-matching circuitry to maximize power transfer and minimize reflections from the ultrasound transducer. From voltage division, the voltage across the transducer is inversely related to the impedance of the source. Therefore, if the source has a 50 output impedance and the transducer has a 10 purely resistive impedance, only 17 of the energy from the source will be supplied to the transducer. When impedance-matching circuitry is used, one-half of the power from the source is transferred, and the driver becomes more efficient. In matching the characteristic impedance of the driver to the ultrasound probe, which generally has complex impedance, automatic tuning devices are used that add to the cost and bulk of the system. We have developed a plug-free portable high power ultrasound system with a very low output impedance amplifier circuit (less than 0.3 ) that is capable of transferring more than 95 of the voltage from the battery supply to the transducer.
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