19 research outputs found
Measurement of the field characteristics from High Intensity Focused Ultrasound transducer
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Development of calibration techniques for ultrasonic hydrophone probes in the frequency range from 1 to 100 MHz
Get PDFThe primary objective of this research was to develop and optimize the calibration techniques for ultrasonic hydrophone probes used in acoustic field measurements up to 100 MHz. A dependable, 100 MHz calibration method was necessary to examine the behavior of a sub-millimeter spatial resolution fiber optic (FO) sensor and assess the need for such a sensor as an alternative tool for high frequency characterization of ultrasound fields. Also, it was of interest to investigate the feasibility of using FO probes in high intensity fields such as those employed in HIFU (High Intensity Focused Ultrasound) applications. In addition to the development of a novel, 100 MHz calibration technique the innovative elements of this research include implementation of a prototype FO sensor with an active diameter of about 10 μm that exhibits uniform sensitivity over the considered frequency range and does not require any spatial averaging corrections up to about 75 MHz. The calibration technique provided the sensitivity of conventional, finite aperture piezoelectric hydrophone probes as a virtually continuous function of frequency and allowed the verification of the uniformity of the FO sensor frequency response. As anticipated, the overall uncertainty of the calibration was dependent on frequency and determined to be about ±12% (±1 dB) up to 40 MHz, ±20% (±1.5 dB) from 40 to 60 MHz and ±25% (±2 dB) from 60 to 100 MHz. The outcome of this research indicates that once fully developed and calibrated, the combined acousto-optic system will constitute a universal reference tool in the wide, 100 MHz bandwidth.Ph.D., Biomedical Engineering -- Drexel University, 200
Calibration of ultrasonic hydrophone probes in the frequency range from 250 kHz to 1 MHz
No full textDevelopment of programmable front-end electronics for use with ultrasound hydrophone
Get PDFPiezoelectric sensors are widely used in many bioengineering applications. However, the sensors exhibit high, on the order of MegaOhms, output impedance and, therefore, the signal generated at the output terminals of a sensor needs to be electronically conditioned prior to further use. Specifically, it is necessary to incorporate a high quality preamplifier between the sensor and analyzing equipment. Such preamplifiers are not commercially available. This work describes development of a programmable preamplifier tailored for use with miniature piezoelectric polymer hydrophones for characterization of acoustic output of ultrasound scanners. Such scanners are used in almost all medical fields and are becoming the preferred imaging modality in a variety of clinical situations. The preamplifier features 50 output impedance to eliminate transmission line phenomena, and high input resistance (1M) which minimizes loading of the hydrophone. The frequency response of the preamplifier was optimized to comply with the Food and Drug Administration (FDA) requirements; the circuit operates between 100 kHz and 40 MHz. To optimize the performance in terms of input impedance, frequency response and dynamic range, the preamplifier was implemented in two stages using application specific operational amplifiers. Visual Basic program was employed to automatically execute On/Off function of the buffer circuit. The implemented circuit topology allows fully automatic determination of key acoustic output parameters of diagnostic ultrasound scanners, which, in turn, determine the safety indicators such as Mechanical Index (MI) and Thermal Index (TI). To verify the performance of the programmable preamplifier, several ultrasound hydrophones were measured and calibrated with and without preamplifier. The measurement results are presented in terms of end-of-cable voltage sensitivity as a function of frequency. Also, the impedance of the preamplifier and programmable buffer circuit were determined as a function of frequency. In addition, the circuit’s scattering parameter S21 that is its transfer function versus frequency was measured. Future work will focus on extension of the preamplifier's bandwidth up to 100 MHz.M.S., Biomedical Engineering -- Drexel University, 200
Design and development of a smart continuous passive motion device for knee rehabilitation
No full textDesign and Development of the Ultrasound Power Meter with a Three Axis Alignment System for Therapeutic Applications
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