Development of programmable front-end electronics for use with ultrasound hydrophone

Piezoelectric 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

Development of calibration techniques for ultrasonic hydrophone probes in the frequency range from 1 to 100 MHz

The 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

Simulation-based comparison of pull-push systems in motorcycle assembly line

To investigate the effects of adopting a pull system in assembly lines in contrast to a push system, simulation software called “ARENA” is used as a tool in order to present numerical results from both systems. Simulation scenarios are created to evaluate the effects of attributes changing in assembly systems, with influential factors including the change of manufacturing system (push system to pull system) and variation of demand. Moreover, pull system manufacturing consists of the addition attribute, which is the number of buffer storage. This paper will provide an analysis based on a previous case study, hence process time and workflow refer to the journal name “Optimising and simulating the assembly line balancing problem in a motorcycle manufacturing company: a case study” [2]. The implementation of the pull system mechanism is to produce a system improvement in terms of the number of Work-In-Process (WIP), total time of products in the system, and the number of finished product inventory, while retaining the same throughput

100 MHz sub-millimeter size fiber optic pressure sensors: a luxury or necessity?

Poster presented at Biomedical Technology Showcase 2006, Philadelphia, PA. Retrieved 18 Aug 2006 from http://www.biomed.drexel.edu/new04/Content/Biomed_Tech_Showcase/Poster_Presentations/Lewin_1.pdf.In the past decade, medical diagnostic ultrasound has become the primary noninvasive imaging modality because unlike CT or PET-scanners it does not use the ionizing radiation. In addition it is inexpensive in comparison with the MRI imaging and last but not least ultrasound imaging provides real-time information on the moving anatomical structures. Although diagnostic ultrasound safety record is impeccable and no side effects were reported in clinical applications, in general, the ultrasound exposure may lead to undesirable biological effects. Therefore, the acoustic output of the diagnostic ultrasound devices is regulated and cannot exceed prescribed limits. In the USA, these limits are established by the Food and Drug Administration's Center for Devices and Radiological Health, which requires the safety indicators such as Mechanical Index (MI) and Thermal Index (TI) to be displayed on the ultrasound imaging systems. Determination of these two indices requires precise characterization and measurements of the acoustic pressure-time waveforms produced by the imaging transducer. The objective of the research described here is to develop and optimize the calibration techniques for ultrasonic hydrophone probes capable of measuring acoustic fields at the frequencies beyond 20 MHz in particular beyond 60 MHz. Such techniques are currently unavailable and these high megahertz frequencies are gaining attention in skin, eye and intraluminal imaging as they offer enhanced sub-millimeter resolution. These objectives will be accomplished by development and implementation of two independent (acoustic and optic) measurement techniques that are capable of providing sensitivity versus frequency response of miniature ultrasonic probes over a wide, 100 MHz bandwidth. The innovative elements of the proposed research include implementing a 100 MHz fiber optic (FO) hydrophone probe with an active diameter of about 11 μm (microns) that will eliminate the need for spatial averaging correction and is sufficiently robust to measure fields generated by High Intensity Focused Ultrasound (HIFU) transducers. The intrinsically rugged characteristics of the fiber constitute an attractive feature as the existing probes are fragile and, in practice, cannot be used in therapeutic HIFU fields. Preliminary data indicate that once fully developed and calibrated, the acousto-optic system will form an important breakthrough in acoustic measurements of both diagnostic and therapeutic fields