Putting Confidence in Ultrasound

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Publications by Onda Staff

    Acoustics and Vibration

  1. Hydrophone Handbook
    Publication: October 2015
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  2. A Novel Device for Total Acoustic Output Measurement of High Power Transducers
    Authors: S. Howard, R. Twomey, H. Morris, C. I. Zanelli
    Publication: 8th International Symposium on Therapeutic Ultrasound, 2009
    [PDF]
    Abstract>

    A Novel Device for Total Acoustic Output Measurement of High Power Transducers

    Authors: S. Howard, R. Twomey, H. Morris, C. I. Zanelli
    Publication: 8th International Symposium on Therapeutic Ultrasound, 2009.

    The objective of this work was to develop a device for ultrasound power measurement applicable over a broad range of medical transducer types, orientations and powers, and which supports automatic measurements to simplify use and minimize errors. Considering all the recommendations from standards such as IEC 61161, an accurate electromagnetic null-balance has been designed for ultrasound power measurements. The sensing element is placed in the water to eliminate errors due to surface tension and water evaporation, and the motion and detection of force is constrained to one axis, to increase immunity to vibration from the floor, water sloshing and water surface waves. A transparent tank was designed so it could easily be submerged in a larger tank to accommodate large transducers or sidefiring geometries, and can also be turned upside-down for upward-firing transducers. A vacuum lid allows degassing the water and target in situ. An external control module was designed to operate the sensing/driving loop and to communicate to a local computer for data logging. The sensing algorithm, which incorporates temperature compensation, compares the feedback force needed to cancel the motion for sources in the “on” and “off” states. These two states can be controlled by the control unit or manually by the user, under guidance by a graphical user interface (the system presents measured power live during collection). Software allows calibration to standard weights, or to independently calibrated acoustic sources. The design accommodates a variety of targets, including cone, rubber, brush targets and an oil-filled target for power measurement via buoyancy changes. Measurement examples are presented, including HIFU sources operating at powers from 1 to 100.



  3. Characterization of a HIFU Field at High Intensity
    Authors: S. Howard and C. Zanelli
    Publication: 2007 IEEE Ultrasonics Symposium
    [PDF 237K]
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    Characterization of a HIFU Field at High Intensity

    Authors: S. Howard and C. Zanelli
    Publication: IEEE Ultrasonics Symposium, 2007. Pgs. 1301-1304

    Accurate quantification of HIFU fields has been hampered by the inability of traditional hydrophones to survive the high pressures encountered. We present a set of data at high intensities taken with a hydrophone capable of surviving this environment, which included 5 MPa maximum rarefactional pressure, pulse-average-spatialpeak intensity of 3760 W/cm2, and a total power of 101 Watts. Comparisons are made to predictions of a KZK model and an independent measurement of total power via radiation force balance, and are found to be favorable. Beamplots show more than 50% reduction in the –3 dB beam area measured at low power, in agreement with KZK predictions.



  4. HIFU Transducer Characterization Using a Robust Needle Hydrophone
    Authors: S. Howard and C. Zanelli
    Publication: 6th International Symposium on Therapeutic Ultrasound, 2007
    [PDF]
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    HIFU Transducer Characterization Using a Robust Needle Hydrophone

    Authors: S. Howard and C. Zanelli
    Publication: 6th International Symposium on Therapeutic Ultrasound, 2007. Pgs. 8-14

    A robust needle hydrophone has been developed for HIFU transducer characterization and reported on earlier [1]. After a brief review of the hydrophone design and performance, we demonstrate its use to characterize a 1.5 MHz, 10 cm diameter, F-number 1.5 spherically focused source driven to exceed an intensity of 1400 W/cm^2 at its focus. Quantitative characterization of this source at high powers is assisted by deconvolving the hydrophone's calibrated frequency response in order to accurately reflect the contribution of harmonics generated by nonlinear propagation in the water testing environment. Results are compared to measurements with a membrane hydrophone at 0.3% duty cycle and to theoretical calculations, using measurements of the field at the source's radiating surface as input to a numerical solution of the KZK equation. vailable specific services in microscopic assembly, thin-film metalization and Parylene coating.



  5. A Robust Hydrophone for HIFU Metrology
    Authors: C. Zanelli and S. Howard
    Publication: American Institute of Physics, Therapeutic Ultrasound, 2006
    [PDF 268K]
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    A Robust Hydrophone for HIFU Metrology

    Authors: C. Zanelli and S. Howard
    Publication: Therapeutic Ultrasound: 5th International Symposium on Therapeutic Ultrasound, 2006, Pgs. 618-622

    The high acoustic intensities generated by HIFU systems cause conventional hydrophones to fail before measurements can be reliably made. To address this challenge, we present a new piezoelectric needle hydrophone, which is resistant to cavitation while possessing a flat frequency response (+/- 3 dB from 1 to 10 MHz) and a small effective aperture (400 micron effective diameter). This hydrophone has been used in high intensity field (1.5 MHz tone burst of 30 microseconds and a 3% duty cycle, with rarefactional pressures exceeding 4 MPa and positive pressures exceeding 15 MPa) without degradation in the hydrophone's performance, as indicated in before-and-after calibration checks of the device.

    [ Copyright (2006) American Institute of Physics. This article may be downloaded for personal use only. Any other use requires prior permission of the author and the American Institute of Physics. ]
    [ This article appeared in Therapeutic Ultrasound: 5th International Symposium on Therapeutic Ultrasound, Clement, MacDonald, and Hynynen, eds., Boston, MA, 2005 and may be found at: ]
    [ American Institute of Physics Link ]



  6. Imaging of High-Intensity Focused Ultrasound-Induced Lesions in Soft Biological Tissue using Thermoacoustic Tomography
    Authors: X. Jin, Y. Xu, L. Wang, Y. Fang, C. Zanelli and S. Howard
    Publication: Medical Physics, Vol. 32, No. 1, January 2005
    [PDF 492K]
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    Imaging of High-Intensity Focused Ultrasound-Induced Lesions in Soft Biological Tissue using Thermoacoustic Tomography

    Authors: X. Jin, Y. Xu, L. Wang, Y. Fang, C. Zanelli and S. Howard
    Publication: Medical Physics, Vol.. 32, No. 1, January 2005

    An imaging technology, thermoacoustic tomography (TAT), was applied to the visualization of high-intensity focused ultrasound (HIFU)-induced lesions. A single, spherically focused ultrasonic transducer, operating at a central frequency of approximately 4 MHz, was used to generate a HIFU field in fresh porcine muscle. Microwave pulses from a 3 GHz microwave generator were then employed to generate thermoacoustic sources in the tissue sample. The thermoacoustic signals were detected by an unfocused ultrasound transducer that was scanned around the sample. To emphasize the boundaries between the lesion and its surrounding tissue, a local-tomography-type reconstruction method was applied to reconstruct the TAT images of the lesions. Good contrast was obtained between the lesion and the tissue samples confirming the TAT images. This work demonstrates that TAT may potentially be used to image HIFU-induced lesions in biological tissue.



  7. Characterization and FEA Simulation for a HIFU Phantom Material
    Authors: S. Howard, J. Yuen, P. Wegner and C. Zanelli
    Publication: IEEE Ultrasonics Symposium, 2003, P. 1270-1273.
    [PDF 746K]
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    Characterization and FEA Simulation for a HIFU Phantom Material

    Authors: S. Howard, J. Yuen, P. Wegner and C. Zanelli
    Publication: IEEE Ultrasonics Symposium, 2003

    Results are presented for a new formulation of HIFU phantom material made with polyacrylamide gel and Bovine Serum Albumin. This formulation closely matches the acoustic attenuation as well as the velocity and impedance of tissue, while providing a uniform and optically transparent medium. The phantom material turns permanently opaque whenever the material achieves a temperature greater than 70 degrees C. Computer simulations of the formation and growth of opaque lesion-mimicking regions in the phantom material were performed, and good agreement with experiment was obtained. This material holds some promise both as (i) a controllable, quantitative tool for development of HIFU systems, and (ii) as a quality assurance tool for such systems.



  8. Electrochemistry in the Presence of Convective Flow Generated by Acoustic Streaming from a Focused Ultrasound Source
    Authors: I. Stefan, Y. Mo, C. Zanelli and D. Scherson
    Publication: Analytical Chemistry, Vol. 73, No. 17, September 2001.
    [PDF 164K]
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    Electrochemistry in the Presence of Convective Flow Generated by Acoustic Streaming from a Focused Ultrasonic Source

    Authors: Ionel C. Stefan, Yibo Mo, Claudio I. Zanelli, and Daniel A. Scherson
    Publication: Analytical Chemistry, Vol. 73, No. 17, September 1, 2001

    Limiting currents for the reduction of hexacyanoferrate-(III),i-lim, in aqueous solutions have been recorded in the presence of convective flow generated by a focused acoustic source with its main axis placed normal to the surface of a circular Au electrode embedded in a coplanar Teflon shroud. THe results obtained could be fitted to a formula of the type - i-lim = a(Uz^ss)^b, where Uz^ss is the axial velocity of the fluid along the center line of the lens evaluated at the focal point using computer simulation routines developed by Kamakura and co-workers (Kamakura, T.; Matsuda, K; Kumamoto, Y.; Breazeale, M.A.J. Acoust. Soc. Am. 1995, 97,2740-2746). The fit yielded a value of b ~0.5 in agreement with that of rotating disk and impinging jet electrodes.



  9. Noninvasive Transcutaneous Low-Frequency Ultrasound Enhances Thrombolysis in Peripheral and Coronary Arteries
    Authors: R Siegel, S. Atar, M. Fishbein, A. Brasch, T. Peterson T. Nagai, D. Pal, T. Nishioka, J.S. Chae, Y.Birnbaum, C. Zanelli and H. Luo
    Publication: Echocardiography, Vol. 18, No. 3, April 2001
    [PDF 732k]
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    Noninvasive Transcutaneous Low-Frequency Ultrasound Enhances Thrombolysis in Peripheral and Coronary Arteries

    Authors: Robert J. Siegel, MD; Shaul Atar, MD; Michael C. Fishbein, MD; Andrea V. Brasch, MD; Thomas M. Peterson, MBA; Tomoo Nagai, MD; Dharmendra Pal, MS; Toshihiko Nishioka, MD; Jang-Seong Chae, MD, PhD; Yochai Birnbaum, MD; Claudio Zanelli, PhD; Huai Luo, MD
    Publication: Echocardiography, Vol. 18, No. 3, April 2000

    Previous studies have shown that external ultrasound with low frequencies and high intensities can enhance thrombolytic drug-induced clot dissolution during in vitro experiments. In this series of studies, we evaluated the efficacy of peripheral and coronary thrombolysis in vivo in animals by using noninvasive transcutaneous ultrasound combined with thrombolytic drugs (streptokinase and tPA) and/or microbubbles agents (dodecafluoropentane [DDFP] and perfluorocarbon-exposed sonicated dextrose albumin [PESDA]). Thrombotic occlusions were induced in 74 rabbit iliofemoral arteries and 24 canine left anterior descending (LAD) coronary arteries in this in vivo study. By using the combination of transcutaneous ultrasound and streptokinase, the angiography patency rate in rabbit iliofemoral arteries was higher (56%-100%) than with ultrasound (6%; P <= 0.0036) and streptokinase alone (6%; P <= 0.0012). Also, with transcutaneous ultrasound and microbubbles, the angiographic patency rates were (9%, P <= 0.0001). In the canine study of acute myocardial infarction, thrombolysis in myocardial infarction (TIMI) grade flow at 90 minutes in the tPA alone group was 0.92 +- 1.4 as compared with 2.42 +- 1.9 in the tPA plus transthorasic ultrasound group (P = 0.006). There was much improved reperfusion with tPA plus ultrasound as compared with tPA alone. In vivo animal studies demonstrate that noninvasive transcutaneous ultrasound can greatly enhance the effect of clot dissolution with thrombolytic drugs and/or microbubbles, and has the potential for clinical application as an adjunctive method to improve arterial thrombolysis.



  10. Wideband Spherically Focused PVDF Acoustic Sources for Calibration of Ultrasound Hydrophone Probes
    Authors: A. Selfridge and P. Lewin
    Publication: IEEE Transactions on Ultrasonics, Ferroelectrics, and Frequency Control, Vol. 47, No. 6, Pg. 1372, November 2000
    [PDF 288k]
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    Wideband Spherically Focused PVDF Acoustic Sources for Calibration of Ultrasound Hydrophone Probes

    Authors: A. Selfridge and P. Lewin
    Publication: IEEE Transactions on Ultrasonics, Ferroelectrics, and Frequency Control Vol. 47, No. 6, Pg. 1372

    Several broadband sources have been developed for the purpose of calibrating hydrophones. The specific configuration described is intended for the calibration of hydrophones in a frequency range of 1 to 40 MHz. All devices use 25 µm film of PVDF bonded to a matched backing. Two had radii of curvatures (ROC) of 25.4 and 127 mm with f numbers of 3.8 and 19, respectively. Their active element diameter was 0.26 in (6.60 mm). The active diameter of the third source used was 25 mm, and it had an ROC of 254 mm and an f number of 10. The use of a focused element minimized frequency-dependent diffraction effects, resulting in a smooth variation of acoustic pressure at the focus from 1 to 40 MHz. Also, using a focused PVDF source permitted calibrations above 20 MHz without resorting to harmonic generation via nonlinear propagation.



  11. Silicon Substrate Ringing in Microfabricated Ultrasonic Transducers
    Authors: I. Ladabaum, P. Wagner, C. Zanelli, J. Mould, P. Reynolds and G. Wojcik
    Publication: IEEE Ultrasonics Symposium, October 2000
    [PDF 157k]
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    Silicon Substrate Ringing in Microfabricated Ultrasonic Transducers

    Authors: Igal Ladabaum, Paul Wagner, Claudio Zanelli, John Mould, Paul Reynolds and Greg Wojcik
    Publication: IEEE Ultrasonics Symposium, 2000

    Experimental and theoretical evidence of silicon substrate ringing in microfabricated ultrasonic transducers in presented. This ringing is clearly observed in immersion transducers with a 650 um thick substrate at 7 MHz and harmonics. An analytical model of the ringing is introduced and simulations based on the model are shown to agree with experimental observations. Experimental results are further compared to simulations carried out in time-domain, large-scale PZFlex models and qualitative agreement is demonstrated. The insights gained from the simulations and experiments are used to design and fabricate a device whose ringing mode is eliminated with a backing layer.



  12. Noninvasive, Transthoracic, Low-Frequency Ultrasound Augments Thrombolysis in a Canine Model of Acute Myocardial Infarction
    Authors: R Siegel, S. Atar, M. Fishbein, A. Brasch, T. Peterson T. Nagai, D. Pal, T. Nishioka, J.S. Chae, Y.Birnbaum, C. Zanelli and H. Luo
    Publication: Circulation, May 2000
    [PDF 221k]
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    Augments Thrombolysis in a Canine Model of Acute Myocardial Infarction

    Authors: Robert J. Siegel, MD; Shaul Atar, MD; Michael C. Fishbein, MD; Andrea V. Brasch, MD; Thomas M. Peterson, MBA; Tomoo Nagai, MD; Dharmendra Pal, MS; Toshihiko Nishioka, MD; Jang-Seong Chae, MD, PhD; Yochai Birnbaum, MD; Claudio Zanelli, PhD; Huai Luo, MD
    Publication: Circulation May 2, 2000

    Coronary thrombolysis reduces mortality and preserves ventricular function, but it results in angiographic TIMI 3 flow in only 40% to 60% of patients. The procedure is further complicated by major bleeding in 5% of patients. Consequently, an enhancement of thrombolysis without promoting bleeding is desirable. We evaluated the augmentation of coronary thrombolysis with intravenous tissue-type plasminogen activator (t-PA) and noninvasive, transthoracic, low frequency (27 kHz) ultrasound.



  13. Wave Field Visualization using Scanned Hydrophone Measurements
    Author: A. Selfridge
    Publication: Proc. SPIE, vol. 3664, Ultrasonic Transducer Engineering, K. Shung, Editor, p. 202-209, June 1999
    [PDF 1.29M]
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    Wave Field Visualization with Scanned Hydrophone Measurements

    Author: Alan R. Selfridge
    Publication: Proc. SPIE, vol. 3664, Ultrasonic Transducer Engineering, K. Kirk Shung, Editor, June 1999, p. 202-209.

    A simple yet novel method has been developed which is useful for visualizing pressure distributions in acoustic wave fields. The method utilizes a computer to store entire waveforms from the numerous points interrogated in a planar scan. The most useful type of planar scan for the concept is made in the xz plane, where the z-axis corresponds to the beam axis of a transducer and the x-axis is an arbitrary axis normal to it. The technique yields moving images of instantaneous acoustic pressure in the xz plane. The concept of looking down at the surface of a body of water, with ripples moving away from a wave generator, is a good analogy.



  14. Dynamic Response and Wave Propagation in Plane Trusses and Frames
    Authors: Y. Pao, D. Keh and S. Howard
    Publication: AIAA Journal, 1999
    [PDF 863k]
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    Dynamic Response and Wave Propagation in Plane Trusses and Frames

    Authors: Y.-H.Pao, D.-C.Keh, S.M.Howard
    Publication: AIAA Journal, Vol 37, Num 5, P. 594-603, May 1999

    The dynamics of planar frames and trusses is analyzed in terms of the propagation of axial (longitudinal) and flexural (transverse) stress waves being structural members. The waves are multiscattered at the joints, and scattering coefficients representing the reflection and transmission of both types of waves at each joint are derived from the dynamics and compatibility conditions of the joint. The complex multireflected waves within the structure are evaluated in the frequency domain by a newly developed reverberation matrix, which is formulated from scattering coefficients and propagating phase factors. Transient waves are then analyzed by Fourier synthesis and evaluated by a fast Fourier transform algorithm. Transient responses for the axial and bending strains in all structural members are calculated over a long duration for a model truss with rigid joints. Comparison to experimental data of the model truss under a step loading shows good agreement for the early as well as considerably long time responses.



  15. Analysis and Experiments on Stress Waves in Planar Trusses
    Authors: S. Howard and Y. Pao
    Publication: Journal of Engineering Mechanics, 1998
    [PDF 714k]
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    Analysis and Experiments on Stress Waves in Planar Trusses

    Authors: Y.-H.Pao, D.-C.Keh, S.M.Howard
    Publication: Journal of Engineering Mechanics, August 1988

    The dynamics of planar trusses are investigated in terms of axial (longitudinal) stress waves, which propagate along structural members and scatter at the joints. The scattering coefficients represent the reflection and transmission of axial waves at each joint are derived from the dynamics and compatibility conditions of the joint. The complex multiple reflections of waves within the structure are evaluated in the frequency domain with a newly developed reverberation matrix, which is formulated from the scattering coefficient and propagating phase factors. Transient waves are then derived by Fourier synthesis, and evaluated by a Fast Fourier Transform algorithm. Experimental results of propagating broad band pulses are presented for a truss model excited by a step loading. Comparison between theoretical results and transient wave records indicate that the axial wave theory is valid only for the response at the very early time. The discrepancy is much reduced if the scattering coefficients are modified to allow mode conversion from axial to flexural waves at the joint.



  16. Spectrogram Analysis of Components of a Central Javanese Gamelan
    Authors: R.Mohn, R. Chivers, M. Hatch, S. Howard and W. Sachse
    Publication: Acoustic Letters, 1998
    [PDF 2.06M]
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    Spectrogram Analysis of Components of a Central Javanese Gamelan

    Authors: R. Mohn, R.C. Chivers, M. Hatch, S.M. Howard and W. Sachse
    Publication:Acoustic Letters, Vol. 12, No. 1, 1988

    Some preliminary spectrographic measurements are reported on elements of the bonang and kenong instruments from a Central Javanese gamelan. Although the elements from the two instruments are of different sizes and shapes, they seem to exhibit few characteristic acoustical differences. The second mode, which is always less than an octave above the fundamental, appears to play an important role in the musical behavior of the devices.



  17. Spot Poled Reflector Style Hydrophone for Shock Wave Measurements
    Author: R. Bedi and A. Selfridge
    Publication: IEEE Ultrasonic Symposium, 1991
    [PDF 461K]
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    Spot Poled Reflector Style Hydrophone for Shock Wave Measurements

    Authors: R. Bedi and A. Selfridge
    Publication: 1991 Ultrasonics Symposium

    The membrane tryle hydrophone commonly used to calibrate lithotriptors is found to have a fast rise time, mediocre sensitivity but a very short life span. We propose a new style of hydrophone here that overcomes the longevity problem by employing a spot poled ceramic active element backed by a matched acoustic impedance. This robust hydrophone is shown to have a fast rise time (<50 nS) together with a high sensitivity. It has been successfully used to measure pressures in excess of 100 MPa for over five thousand shots without any serious degradation in sensitivity or pulse shape. Furthermore, it is shown that such a hydrophone reproduces negative (rarefactional) pressures faithfully. By adopting this technique, we also gain the benefit of having well defined and potentially very small (less than 0.5 mm diameter) active areas.



  18. Approximate Material Properties in Isotropic Materials
    Author: A. Selfridge
    Publication: IEEE Transaction on Sonics and Ultrasonics, Vol. SU-32, No. 3, May 1985
    [PDF 285K]
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    Approximate Material Properties in Isotropic Materials

    Author: Alan R. Selfridge
    Publication: IEEE Transactions on Sonics and Ultrasonics, Vol. SU-32, No. 3, May 1985

    A very important part of the design of ultrasonic transducers and ultrasonic measurement systems is the selection of materials. Typically, materials must be screened on the basis ofof their acoustic velocity, impedance, and attenuation. The final selection of a material is based upon many other factors, such as how well it adheres to epoxy, its linearity, or how much water it absorbers. This paper is intended to aid in the initial screening process. Some single techniques for approximating these material properties are presented, and then an extensive table of the materials that have been measured or whose properties have been obtained from the references is given.



  19. KLM Transducer Model Implementation Using Transfer Matrices
    Authors: A. Selfridge and S. Gehlbach
    Publication: IEEE Ultrasound Symposium, 1985
    [PDF 256k]
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    KLM Transducer Model Implementation Using Transfer Matrices

    Authors: A Selfridge and S. Gehlbach
    Publication: 1985 Ultrasonics Symposium

    The Krimholtz, Leedom, and Matthaei transmission line model for acoustic transducers has been implemented on an IBM PC-XT computer using transfer, or "ABCD" matrices. Use of matrices formalism makes the programs easy to understand and allows quantities such as voltage, stress, strain and current to be readily calculated anywhere in the model. Previously difficult to model cases, such as open circuit receivers, are much simpler to treat with the new formalism. Furthermore, an accurate account of total linear phase is made, and acoustic and electrical loss is properly treated to first order.



  20. Approximate Material Properties in Isotropic Materials
    Authors: A. Selfridge
    Publication: IEEE Ultrasound Symposium, 1985
    [PDF]
    Abstract>

    Approximate Material Properties in Isotropic Materials

    Authors: A. R. Selfridge
    Publication: 1985 Ultrasonics Symposium

    A very important part of the design of ultrasonic transducers and ultrasonic measurement systems is the selection of materials. Typically, materials must be screened on the basis of their acoustic velocity, impedance, and attenuation. The final selection of a material is based upon many other factors, such as how well it adheres to epoxy, its linearity, or how much water it absorbs. This paper is intended to aid in the initial screening process. Some simple techniques for approximating these material properties are presented, and then an extensive table of the materials that have been measured or whose properties have been obtained from the references is given.


  21. Ultrasonic Characterization of Porosity in Powder Metals
    Authors: S. Howard, J. Tani, H. Arnold, H. Schwetlick and W. Sachse
    Publication: Proceedings of the ASM Metals Congress; ASM International, 1984
    [PDF 474k]
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    Ultrasonic Characterization of Porosity in Powder Metals

    Authors: S. Howard, J. Tani, H. Arnold, H. Schwetlick, Wolfgang Sachse
    Publication: Proceedings of the 1984 ASM Metals Congress; ASM International, Materials Park, OH 44073-0002

    We present preliminary results of a project aimed at investigating ultrasonic techniques to measure the bulk density, pore size, and spatial variation of porosity in powder metal specimens. Specific techniques considered are ultrasonic wavespeed, attenuation and wave dispersion measurements, and the identification of spectral features in the amplitude spectra. Also discussed is the inverse medium problem for reconstructing the acoustic impedance profile along the direction of wave propagation in a specimen.



  22. The Design of Ultrasonic Transducers and Transducer Arrays
    Author: A. Selfridge
    Publication: Ph.D. Dissertation, Stanford University, 1983

  23. Computer-Optimized Design of Quarter-Wave Acoustic Matching and Electrical Matching Networks for Acoustic Transducers
    Authors: A. Selfridge, R. Baer, B. Khuri-Yakub and G. Kino
    Publication: Ultrasonics Symposium, 1981.
    [PDF 359k]
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    Computer-Optimized Design of Quarter-Wave Acoustic Matching and Electrical Matching Networks for Acoustic Transducers

    Authors: A.R. Selfridge, R. Baer, B.T. Khuri-Yakub and G.S. Kino
    Publication: Ultrasonics Symposium, 1981

    We have developed an iterative computer program to optimize the parameters for the acoustic matching layer(s) and the electrical matching network of a transducer for a minimum length of the impulse response. By including the interactions between electrical and acoustic matching in our model, we have been able to significantly improve the quality of our transducers.
    A 3.65 MHz center frequency transducer, made of Murata PZT, was constructed to verify the computer results. The impulse response was approximately 2-1/2 cycles long with a round trip insertion loss of 10.9 dB at the center frequency, and the 40 dB ringdown time was 1.5 usec when working into a water load.



  24. Contacting Transducers and Transducer Arrays for NDE
    Authors: R. Baer, A. Selfridge, B. Khuri-Yakub and G. Kino
    Publication: Ultrasonics Symposium, 1981.
    [PDF 397k]
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    Contacting Transducers and Transducer Arrays for NDE

    Authors: R. Baer, A Selfridge, B. Khuri-Yakob and G. Kino
    Publication: 1981 Ultrasonics Symposium

    We have designed and built longitudinal wave and several shear wave contacting arrays for the nondestructive evaluation of aluminum. The arrays each have 32 elements and operate at a center frequency of 3 MHz. Side drilled holes and EDM slots of different orientations (all of which are in aluminum sample blocks) are imaged using these arrays in a real-time synthetic aperture imaging system.

    Following a suggestion of H. D. Williams of the CEGB (England), the coupling problem between the arrays and the aluminum block under test has been alleviated by using natural bee honey with bulk wave transducers in the frequency range of 3 MHz to 300 MHz. Our initial experiments indicate that honey is a superior couplant to any of the other available couplants.



  25. A Theory for the Radiation Pattern of a Narrow-Strip Acoustic Transducer
    Authors: A. Selfridge, G. Kino and B. Khuri-Yakub
    Publication: Applied Physics Letters, American Institute of Physics, July 1980.
    [PDF 131K]
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    A Theory for the Radiation Pattern of a Narrow-Strip Acoustic Transducer

    Authors: A.R. Selfridge, G.S. Kino, and B.T.Khuri-Yakub
    Publication: Applied Physics Letters 37(1), American Institute of Physics, 1 July 1980

    An important criterion in the design of transducer array elements for acoustic imaging is the angular response, or the far-field radiation pattern, of a single element. In this letter, we show that the widely accepted formula for the angular response function is inadequate and must be multiplied by cos(theta). Good agreement with experiment is then obtained.



  26. Fundamental Concepts in Acoustic Transducer Array Design
    Authors: A.R. Selfridge, G.S. Kino and B. Khuri-Yakub
    Publication: Ultrasonics Symposium, 1980.
    [PDF 331k]
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    Fundamental Concepts in Acoustic Transducer Array Design

    Authors: A.R. Selfridge, G.S. Kino and B.T. Khuri-Yakub
    Publication: Ultrasonics Symposium, 1980

    Ceramic strip resonators with rectangular cross-section have been made with aspect ratios (width to height ratios) from 0.1 to 30. The short and open circuit resonant frequencies have been plotted as a function of aspect ratio and show good agreement between experiment and a simple coupled mode theory.

    The effect of loading these resonators acoustically with solids and liquids has also been examined. The resonators we have measured had a center frequency of near 3 MHz and widths down to 0.12 wavelengths in water at this frequency. We have demonstrated for the first time that when the resonators are less than a wavelength in width, a complex acoustic load impedance must be used to accurately predict the electrical impedance of the resonator which is measured.



  27. The Design of Broadband and Efficient Acoustic Wave Transducers
    Authors: C.H. Chou, J.E. Bowers, A.R. Selfridge B.T. Khuri-Yakub and G.S. Kino
    Publication: Ultrasonics Symposium, 1980.
    [PDF 298k]
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    The Design of Broadband and Efficient Acoustic Wave Transducers

    Authors: C. Chou, J. Bowers, A Selfridge, B. Khuri-Yakob and G. Kino
    Publication: 1980 Ultrasonics Symposium

    The basic design criteria for SAW transducers is typically a flat frequency response. The basic design criteria for bulk wave transducers in nondestructive evaluation and medical imaging is the compactness of the impulse response. This criteria is different from the usual flat frequency response criteria because a flat bandwidth does not necessarily imply a compact impulse response. An iterative optimization program, based on a least mean square algorithm, has been developed and used to simultaneously optimize the matching networks and acoustic parameters to achieve either of the above design criteria. The optimization is first illustrated in the frequency domain for an IDT transducer. Then the optimization is done in the time domain for a bulk wave transducer with the criterion of reducing the length of the impulse response. The impulse response is thus reduced from about 15 cycles to 3 cycles and has an almost Gaussian frequency response. The increase in the round trip insertion loss of the transducer due to the tuning is of the order of a few dB. Transducers have been constructed at 5 and 35 MHz with a backing of epoxy (Z = 3 kg/m^2-sec) and no front matching layer. The agreement between theory and experiment is excellent.



  28. An Edge-Bonded Surface Acoustic Wave Transducer Array
    Authors: H.C. Tuan, A.R. Selfridge, J. Bowers, B.T. Khuri-Yakub and G.S. Kino
    Publication: Ultrasonics Symposium, 1979.
    [PDF 315k]
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    An Edge-Bonded Surface Acoustic Wave Transducer Array

    Authors: H.C. Tuan, A.R. Selfridge, J. Bowers, B.T. Khuri-Yakub and G.S. Kino
    Publication: Ultrasonics Symposium, 1979

    A new type of transducer array has been designed and built for imaging surface defect in metals such as aluminum. The array is formed by edge-bonding a piece of piezoelectric material to a substrate of the same material as the sample to be tested. The individual elements in the array are formed by photolithography, and each element acts as an edge-bonded surface wave transducer. The array has 32 elements resonant at a center frequency of 3.1 MHz with a round trip 6 dB and a +-35-deg, 3 dB acceptance angle at its center frequency. A theory has been developed which predicts the angular response of the array accurately.



  29. Computer-Controlled System for Measuring Two-Dimensional Acoustic Velocity Fields
    Authors: D.B.Ilic, G.S. Kino, A.R. Selfridge and F.E. Stanke
    Publication: Ultrasonics Symposium, 1979.
    [PDF 395k]
    Abstract>

    Computer-Controlled System for Measuring Two-Dimensional Acoustic Velocity Fields

    Authors: D.B. Ilic, G.S. Kino, A.R. Selfridge and F.E. Stanke
    Publication: Ultrasonics Symposium, 1979

    An automatic system is described for measuring two-dimensional acoustic velocity in solid samples. The measurement is performed by a computer-controlled, mechanically-scanned transducer in a liquid bath and is based on measuring the phase delay of the acoustic wave by a two-pulse echo method. Applications include measuring stress fields due both to externally-applied and residual stresses, and microstructure studies of solid samples.



  30. Highly Efficient Transducer Arrays Useful in Non destructive Testing Applications
    Authors: C.S. Desilets, A.R. Selfridge and G.S. Kino
    Publication: Ultrasonics Symposium, 1978.
    [PDF 457k]
    Abstract>

    Highly Efficient Transducer Arrays in Nondestructive Testing Applications

    Authors: C. Desilets, A Selfridge and G. Kino
    Publication: 1978 Ultrasonics Symposium Proceedings, IEEE Cat. #78CH 1344-1SU

    Two types of highly efficient transducer arrays are described which couple acoustic energy into the samples imaged in nondestructive testing applications. The first type of array utilizes fully slotted, double quarter-wave matched elements to couple the acoustic energy from the high impedance ceramic to water, which is used as the transmitting medium. One such 180 element linear array operating at a center frequency of 3.5 MHz has 11 dB return loss, 45% 3 dB bandwidth, and +-13-deg 3 dB acceptance angle. Experimental results with an improved double quarter-wave matched, fully slotted array are described including 9 dB return loss, 65% 3 dB bandwidth, and +-44-deg 3 dB acceptance angle.

    A second type of high efficiency array uses un-slotted ceramic permanently attached to a high impedance buffer block which is coupled directly to the load. Individual array elements are formed by deposition of electrodes on the monolithic slab of ceramic. One longitudinal wave test array mounted on aluminum is reported with a half power beamwidth of +-37-deg.

    Schlieren

  1. Schlieren Metrology for High Frequency Medical Ultrasound
    Authors: C. Zanelli and S. Howard
    Publication: Ultrasonics, August 2006
    [PDF 187k]
    Abstract>

    Schlieren Metrology for High Frequency Medical Ultrasound

    Authors: Claudio I. Zanelli and Samuel M. Howard
    Publication: Ultrasonics, August, 2006

    The increased use of medical ultrasound above 40 MHz poses the challenge of measuring beam features that may be less than 40 um. We have successfully used the optical Schlieren technique for transducers operating as high as 110 MHz. After a brief discussion of the technique, results are presented, including comparisons to state-of-the-art hydrophones and wire targets.



  2. A Novel, Rapid Method to Measure the Effective Aperture of Array Elements
    Authors: E. LeDet and C. Zanelli
    Publication: IEEE Ultrasonics Symposium, 1999
    [PDF 264k]
    Abstract>

    A Novel, Rapid Method to Measure the Effective Aperture of Array Elements

    Authors: Earl G. LeDet and Claudio I. Zanelli
    Publication: IEEE Ultrasonics Symposium, 1999

    Effective aperture is a commonly used measure of the amount of acoustic or electrical crosstalk between elements in ultrasonic arrays. It is also important to assess element-to-element uniformity and quality of the separation between the elements. This parameter is obtained from the beam profile obtained by pulsing each individual element with a known excitation function. The traditional method, using hydrophones, presents many challenges that are overcome by the proposed method.

    Using a quantitative schlieren system, we imaged the acoustic burst from an array element. Automated processing allows determination of the average intensity over the burst at all angles (angular beam profile) and its width is used to determine the effective aperture for that element. Examples are presented for floating and purposefully coupled neighboring elements, and the results are in good agreement with those obtained with a hydrophone. The algorithm used for image analysis is also described.



  3. Quantitative 2D and 3D Schlieren Imaging For Acoustic Power and Intensity Measurements
    Authors: T. Charlebois and R. Pelton
    Publication: Medical Electronics 1995
    [PDF 2.29MB] [PDF 7.35MB]
    Abstract>

    Quantitative 2D and 3D Schlieren Imaging for Acoustic Power and Intensity Measurements

    Authors: Thomas F. Charlebois and Roger C. Pelton
    Publication: Medical Electronics, June, 1995

    Ultrasound imaging manufacturers are required to conduct hundreds of thousands of measurements of transducer power and intensity for research, development, regulatory compliance (FDA/IEC), and production quality assurance. This can delay new product introductions and force trade-offs between product performance and testing costs. High-resolution schlieren imaging provides real-time, 2D visualization and quantification of the acoustic beam and total acoustic power output, but not intensity. Tomographic reconstruction allows computing full 3D pressure and intensity maps throughout the acoustic field, and automatic determination of maximum intensity value and location in minutes, instead of the hours needed for conventional hydrophone scanning techniques.



  4. Measurements of Acoustic Pressure in Non-Linear Range in Water Using Quantitative Schlieren
    Authors: C. Zanelli and M. Kadri
    Publication: IEEE Ultrasonics Symposium (p. 1765) 1994
    [PDF 322k]
    Abstract>

    Measurements of Acoustic Pressure in Non-Linear Range in Water Using Quantitative Schlieren

    Authors: C. I. Zanelli, M. M. Kadri
    Publication: IEEE Ultrasonics Symposium (p. 1765) 1994

    The schlieren method, based on Raman-Nath scattering by ultrasonic waves, is extended to pressures up to 8.8x10 Pa (about 5KW/cm for 4 MHz CW waves) by capturing up to the 16th order diffraction harmonics in water. Given the high spatial resolution ( 100 &microm), this kind of measurement is not possible with conventional hydrophones. Working under partially applicable Raman-Nath regime (thin grating, Q = 0.016 <<2pi but 0<v<2000), the theoretical description fails beyond the first few orders. However, we demonstrate that an empirical calibration is possible as long as plane waves are used and the short integration length is maintained. Examples of beams and measurements are presented and compared with the basic theory.



  5. Design and Characterization of a 10 cm Annular Array Transducer for High Intensity Focused Ultrasound (HIFU) Applications
    Authors: C. Zanelli, C. Hennige and N. Sanghvi
    Publication: IEEE Ultrasonics Symposium (p. 1887) 1994
    [PDF 348k]
    Abstract>

    Design and Characterization of a 10 cm Annular Array Transducer for High Intensity Focused Ultrasound (HIFU) Applications

    Authors: C. I. Zanelli, C. W. Hennige, N. T. Sanghvi
    Publication: IEEE Ultrasonics Symposium (p. 1887) 1994

    A large transducer to generate high intensity focused ultrasound (HIFU) for surgery via tissue ablation is described. Designed to address the need for therapeutic applications into deep tissue, the device operates at 1.25 MHz. In order to increase focus-to-entrance intensity ratios, the design was optimized to have a natural focal distance of 10 cm at f/1.0. Variable focus is achieved by phasing the array, and particular care was exercised to maximize the range of focal distances that can be achieved with a limited number of amplifiers and elements, using a constant-phase delay design. Design approach and tradeoffs are discussed, with emphasis in comparing theoretical calculations with test performance.



  6. Beam Forming for Therapy with High Intensity Focused Ultrasound(HIFU) Using Quantitative Schlieren
    Authors: C. Zanelli, S. DeMarta, C. Hennige and M. Kadri
    Publication: IEEE Ultrasonics Symposium, (p. 1233), 1993
    [PDF 448k]
    Abstract>

    Beam Forming for Therapy with High Intensity Focused Ultrasound (HIFU) Using Quantitative Schlieren

    Authors: C. I. Zanelli, S. DeMarta, C. W. Hennige, M. M. Kadri
    Publication: IEEE Ultrasonics Symposium, pg 1233, 1993

    The requirements for beam forming in high intensity focused ultrasound (HIFU) for tissue destruction are substantially different than those for diagnostic imaging. High numerical aperture and CW efficiency are desirable for tissue destruction, while depth of focus and broadband sensitivity are key to good imaging. When the same transducer must be used for ablation and imaging some compromised must be made, resulting in non-ideal beam patterns. Predicting the dosage in tissue that results from actual beam patterns becomes a key element in designing such systems. Quantitative schlieren images in CW mode are used to provide fast, high dynamic range field maps in water. The image data are then corrected for attenuation, resulting in simulated beam profiles and absorbed dose rates for tissue.



  7. Quantitative Real-time Pulsed Schlieren Imaging of Ultrasonic Waves
    Publication: IEEE Ultrasonics Symposium, (p. 1223), 1991
    [PDF 387k]
    Abstract>

    Quantitative Resal-time Pulsed Schlieren Imaging of Ultrasonic Waves

    Authors: A. Hanafy and C. I. Zanelli
    Publication: IEEE Ultrasonics Symposium, pg 1223, 1991

    A pulsed Schlieren system based on Raman-Nath scattering by ultrasonic waves in water is described. High powered, monochromatic infrared pulsed light is used conjunction with axial optics and a video camera to visualize the acoustic field. Projection beam profiles in any plane parallel or orthogonal to the direction of acoustic propagation are demonstrated. Controlled delay between acoustic pulse and light flash allows scrutinizing wave fronts at variable delay after launching. The method is applicable with reasonable repetition rates to broadband acoustic pulses with intensities in the medical diagnostic range. Quantification of the pressure density by analysis of the video signal is shown using a single-point calibration against a total acoustic power measurement by the force balance method, without a priori assumptions about the beam structure.

Other Useful References

    Acoustics

  1. Acoustic Waves, Devices, Imaging, & Analog Signal Processing
    Author: G. Kino
    Publication: ISBN 0-13-003-47-3, Prentice-Hall, Inc. 1987

  2. Fundamentals of Acoustics
    Authors: L. Kinsler, A. Frey, A. Coppens and J. Sanders
    Publication: ISBN 0-471-02933-5, 3rd edition, John Wiley & Sons, 1982

  3. Onda Hydrophone Handbook
    [View with eReader]

    Schlieren

  1. Schlieren Photography in Physics a Schlieren System
    Authors: M. Breazeale
    Publication: SPIE 1998
    [PDF 2052k]
    Abstract>

    Schlieren Photography in Physics

    Author: M. A. Mreazeale
    Publication: SPIE, 1998

    Schlieren photography has been used many years in physics; however it has proven to be exceptionally valuable in the study of ultrasonic waves in liquids. Part of the reason for its value is that many of the ultrasonic phenomena studied have their optical analogues. Thus, when one studies ultrasonic images he actually is studying a general wave phenomenon from a perspective that is impossible with light alone. Examples are given of ultrasonic schlieren photographs as are conclusions possible from their study.



  2. Quantitative Analysis of Pulsed Ultrasonic Beam Patterns Using a Schlieren System
    Authors: B. Schneider and K. Shung
    Publication: IEEE Transaction on Ultrasonics Vol 43, No 6, November 1996
    [PDF 561k]
    Abstract>

    Quantitative Analysis of Pulsed Ultrasonic Beam Patterns Using a Schlieren System

    Authors: Byron Schneider and K. Kirk Shung, Fellow, IEEE
    Publication: IEEE Transactions on Ultrasonics Vol 43, No 6, Part II, November 1996

    The acoustic output from pulsed ultrasonic transducers has traditionally been analyzed with a hydrophone. Recently, a new faster technique has been developed using the principles of optical diffraction. This schlieren method allows the direct two-dimensional visualization of the ultrasonic beam as a pulse train. In order to obtain quantitative information in the form of temporal-average acoustic intensity, however, tomographic reconstruction has to be performed. In this study, tomographic reconstruction was achieved by acquiring 250 images over a 180 degree angle. Automation of the measurement was obtained by using a frame grabber, a stepper motor, and digital delays all controlled by an IBM-compatible computer. Comparisons of the schlieren results to those obtained by using a hydrophone are made in terms of both the -3 dB beamwidths and axial profiles. The results demonstrate that the schlieren method may be a more time efficient alternative for the characterization of ultrasonic transducers.



  3. Tomographic Schlieren Imaging for Measurement of Beam Pressure and Intensity
    Authors: T. Pitts, J. Greenleaf, J. Lu and R. Kinnick
    Publication: IEEE Ultrasonics Symposium (p. 1665) 1994
    [PDF 485k]
    Abstract>

    Tomographic Schlieren Imaging for Measurement of Beam Pressure and Intensity

    Authors: Todd Pitts, James Greenleaf, Jian-Yu Lu, Randy Kinnick
    Publication: IEEE Ultrasonics Symposium (p. 1665) 1994

    The visualization of ultrasonic fields via acousto-optic interaction is an old technique. Shadowgraph and schlieren imaging produce data representing a line integral related to pressure and time-average intensity, respectively. These "projections" can be used in computed tomography. We have compared the reconstructed pressure distribution in a plane obtained via tomographic inversion with those obtained by mechanically scanning a 0.5mm calibrated hydrophone through the same plane. Schlieren methods result in the reconstruction of a time average intensity approximation. Shadowgraph methods reconstruct pressure at a given point in time. The advantage of the tomographic methods is that they can be done quickly. A fully automated system could produce a three-dimensional image of an ultrasound beam in a few minutes.



  4. Quantitative Schlieren Method Axisymmetrical [PDF 287k]

  5. Experimental Study Cavitation Shock Waves [PDF 338k]

  6. Numerical Procedure for Calculating Acoustooptic Effect [PDF 1056k]

  7. Comparison of Acousto-optic and Radiation Force Method of Measuring Ultrasonic Power
    Authors: M. Haran, B. Cook and H. Stewart
    Publication: J. Acoust. Soc. Am. Vol 57, No 6, Part II, June 1975
    [PDF 351k]
    Abstract>

    Comparison of Acousto-optic and Radiation Force Method of Measuring Ultrasonic Power

    Authors: Michael E. Haran, Bill D. Cook, Harold F. Stewart
    Publication: J. Acoust. Soc. Am. Vol 57, No 6, Part II, June 1975

    During the interim period while nationally acceptable methods of measurement and referential standards for ultrasonic power are being developed, comparisons are needed among measurement techniques currently used. This is particularly necessary for determining the acoustic power from ultrasonic medical devices. These comparisons are an important step toward a referential measurement method. Current techniques include calorimetric radiation force, piezoelectric, and optical methods. A recently published comparison determined the ultrasonic pressure amplitude using several methods. This paper presents a comparison between an optical and a radiation force technique for measuring ultrasonic power. The optical technique employs the basic Raman-Nath theory in which it is assumed that the sound presents a phase grating to a normally incident beam of plane, monochromatic light. Based on a theoretical investigation of the integrated optical effect of sound form a circular plane piston source, a correction was made for the axial distance from the face of the transducer to point sampled by the light. This correction eliminated the need to know the path length of the light in the sound for the calculation of acoustic power. The radiation force system is patterned after one developed by the Federal Institute of Physical Technology (West Germany) for the evaluation and certification off medical ultrasonic instruments. It consists of a conically shaped air-based reflector, the displacement of which is proportional to the incident acoustic power.



  8. The Diffraction of Light by High Frequency Ultrasonic Waves
    Authors: C. Raman and N. Nath
    Publication: Proc. Indian Acad. Sci II, 406 (1935)

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