Pub Date : 2002-12-01DOI: 10.1109/ULTSYM.2002.1193370
K. Uehara, H. Nakamura, H. Nakase, K. Tsubouchi
We have successfully developed (00/spl middot/1) AlN film with atomically flat surface on (00/spl middot/1) sapphire substrate using metalorganic chemical vapor deposition (MO-CVD) method. The atomically flat surface of less than Ra=2/spl Aring/, Ra means mean roughness measured by atomic force microscope (AFM), within the thickness of 1.7 /spl mu/m has been achieved, whose conditions are high substrate temperature of 1200/spl deg/C, low pressure of 30Torr, low V-III ratio of 500 and the numerous flow rate of trimethylaluminum (TMA)-back-up H/sub 2/ gas of 5.0slm The temperature-coefficient-of-delay (TCD) of the fabricated surface-acoustic-wave (SAW) device on (00/spl middot/1)AlN/ (00/spl middot/1) Al/sub 2/O/sub 3/ combination with atomically flat surface are found to be 44.5 ppm//spl deg/C at kH=2.25 and 28.5 ppm//spl deg/C at kH=3.32, where kH is the normalized thickness by wave number, k is wave number and H is AlN film thickness. These measured TCD are agreed with simulated curve. AlN/Al/sub 2/O/sub 3/ combination with atomically flat surface has a potential for zero-TCD at kH=4.5.
{"title":"AlN epitaxial film with atomically flat surface for GHz-band SAW devices","authors":"K. Uehara, H. Nakamura, H. Nakase, K. Tsubouchi","doi":"10.1109/ULTSYM.2002.1193370","DOIUrl":"https://doi.org/10.1109/ULTSYM.2002.1193370","url":null,"abstract":"We have successfully developed (00/spl middot/1) AlN film with atomically flat surface on (00/spl middot/1) sapphire substrate using metalorganic chemical vapor deposition (MO-CVD) method. The atomically flat surface of less than Ra=2/spl Aring/, Ra means mean roughness measured by atomic force microscope (AFM), within the thickness of 1.7 /spl mu/m has been achieved, whose conditions are high substrate temperature of 1200/spl deg/C, low pressure of 30Torr, low V-III ratio of 500 and the numerous flow rate of trimethylaluminum (TMA)-back-up H/sub 2/ gas of 5.0slm The temperature-coefficient-of-delay (TCD) of the fabricated surface-acoustic-wave (SAW) device on (00/spl middot/1)AlN/ (00/spl middot/1) Al/sub 2/O/sub 3/ combination with atomically flat surface are found to be 44.5 ppm//spl deg/C at kH=2.25 and 28.5 ppm//spl deg/C at kH=3.32, where kH is the normalized thickness by wave number, k is wave number and H is AlN film thickness. These measured TCD are agreed with simulated curve. AlN/Al/sub 2/O/sub 3/ combination with atomically flat surface has a potential for zero-TCD at kH=4.5.","PeriodicalId":378705,"journal":{"name":"2002 IEEE Ultrasonics Symposium, 2002. Proceedings.","volume":"2 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2002-12-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"132677756","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2002-12-01DOI: 10.1109/ULTSYM.2002.1192629
S. Umemura, T. Azuma, Y. Miwa, K. Sasaki, T. Sugiyama, T. Hayashi, H. Kuribara
In imaging with a microbubble contrast agent, which tends to make irreversible changes by transmission even at a low intensity, both transmission beamwidth and number of transmission per frame must be minimized. A transmission focusing technique based on a noncylindrical delay, which is applicable to a one-dimensional array, is proposed. Unlike X waves, the main beam propagates always coherently with the waves transmitted from the central part of the aperture. The non-cylindrical focusing delay was calculated by assuming a local focal length along the aperture, which increases gradually as the distance from the center increases. Numerical simulation of wave propagation predicted a large depth of field for a reasonably narrow main beam having longitudinally uniform intensity. The noncylindrical focusing was employed in a prototype beamformer, and the large depth of transmission field was confirmed with Shrielen measurements.
{"title":"Non-cylindrical transmission focusing for large depth of field","authors":"S. Umemura, T. Azuma, Y. Miwa, K. Sasaki, T. Sugiyama, T. Hayashi, H. Kuribara","doi":"10.1109/ULTSYM.2002.1192629","DOIUrl":"https://doi.org/10.1109/ULTSYM.2002.1192629","url":null,"abstract":"In imaging with a microbubble contrast agent, which tends to make irreversible changes by transmission even at a low intensity, both transmission beamwidth and number of transmission per frame must be minimized. A transmission focusing technique based on a noncylindrical delay, which is applicable to a one-dimensional array, is proposed. Unlike X waves, the main beam propagates always coherently with the waves transmitted from the central part of the aperture. The non-cylindrical focusing delay was calculated by assuming a local focal length along the aperture, which increases gradually as the distance from the center increases. Numerical simulation of wave propagation predicted a large depth of field for a reasonably narrow main beam having longitudinally uniform intensity. The noncylindrical focusing was employed in a prototype beamformer, and the large depth of transmission field was confirmed with Shrielen measurements.","PeriodicalId":378705,"journal":{"name":"2002 IEEE Ultrasonics Symposium, 2002. Proceedings.","volume":"270 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2002-12-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"120895211","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2002-12-01DOI: 10.1109/ULTSYM.2002.1192518
A. Hladky-Hennion, D. Markley, R. Newnham, R. Meyer, W. Hughes
This paper describes the design and the development of transducer arrays fabricated from miniature piezoceramic hollow spheres, the BBs. After the presentation of the fabrication procedure of the transducers, it presents the numerical tools used to model 2/spl times/2 and 4/spl times/4 transducer arrays in water. Numerical calculations give good agreement with the experimental results and provide physical insight for understanding the acoustic observations.
{"title":"Analysis of transducers arrays from piezoelectric hollow spheres","authors":"A. Hladky-Hennion, D. Markley, R. Newnham, R. Meyer, W. Hughes","doi":"10.1109/ULTSYM.2002.1192518","DOIUrl":"https://doi.org/10.1109/ULTSYM.2002.1192518","url":null,"abstract":"This paper describes the design and the development of transducer arrays fabricated from miniature piezoceramic hollow spheres, the BBs. After the presentation of the fabrication procedure of the transducers, it presents the numerical tools used to model 2/spl times/2 and 4/spl times/4 transducer arrays in water. Numerical calculations give good agreement with the experimental results and provide physical insight for understanding the acoustic observations.","PeriodicalId":378705,"journal":{"name":"2002 IEEE Ultrasonics Symposium, 2002. Proceedings.","volume":"33 3","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2002-12-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"113974329","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2002-12-01DOI: 10.1109/ULTSYM.2002.1192597
Z. M. Benenson, A. B. Elizarov, T. Yakovleva, W. O’Brien
A technique is proposed that generates a depth-independent and narrow beamwidth 3D ultrasonic image. A high-frequency, wide-bandwidth spherical transducer is scanned in 2D along Cartesian coordinates. The received wideband ultrasonic pulses are dynamically focused by means of correcting the spatial spectrum of signals for various temporal frequencies. The main procedures of the algorithm consist in the direct and inverse fast Fourier transforms by time and by two spatial Cartesian coordinates.
{"title":"Depth-independent narrow beamwidth 3D ultrasonic image formation technique","authors":"Z. M. Benenson, A. B. Elizarov, T. Yakovleva, W. O’Brien","doi":"10.1109/ULTSYM.2002.1192597","DOIUrl":"https://doi.org/10.1109/ULTSYM.2002.1192597","url":null,"abstract":"A technique is proposed that generates a depth-independent and narrow beamwidth 3D ultrasonic image. A high-frequency, wide-bandwidth spherical transducer is scanned in 2D along Cartesian coordinates. The received wideband ultrasonic pulses are dynamically focused by means of correcting the spatial spectrum of signals for various temporal frequencies. The main procedures of the algorithm consist in the direct and inverse fast Fourier transforms by time and by two spatial Cartesian coordinates.","PeriodicalId":378705,"journal":{"name":"2002 IEEE Ultrasonics Symposium, 2002. Proceedings.","volume":"21 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2002-12-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"134569736","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2002-12-01DOI: 10.1109/ULTSYM.2002.1192560
B. C. Tran, Jongbum Soo, J. Fowlkes, C. Cain
The presence of ultrasound contrast agent (stabilized microbubbles) during high intensity focused ultrasound insonation can reduce both the exposure intensity and duration required for producing macroscopic tissue damage. In this paper, we evaluate the enhancement produced by Optison/spl reg/ infusion at concentrations of 0, 0.1, 0.3, 1, 3, and 10 /spl mu/L/kg/min. Acute canine kidneys were surgically externalized and insonified with single ultrasound exposures. The probability of tissue damage production was determined with respect to exposure intensity and duration for each concentration. As microbubble concentration increased from 0 to 10 /spl mu/L/kg/min, the requisite intensity and the requisite duration both gradually decreased. The results indicate that microbubble introduction up to 10 /spl mu/L/kg/min is effective for aiding ultrasound therapy.
{"title":"The effect of microbubble concentration on thresholds for tissue damage produced by single bursts of high intensity ultrasound during continuous Optison/spl reg/ infusion","authors":"B. C. Tran, Jongbum Soo, J. Fowlkes, C. Cain","doi":"10.1109/ULTSYM.2002.1192560","DOIUrl":"https://doi.org/10.1109/ULTSYM.2002.1192560","url":null,"abstract":"The presence of ultrasound contrast agent (stabilized microbubbles) during high intensity focused ultrasound insonation can reduce both the exposure intensity and duration required for producing macroscopic tissue damage. In this paper, we evaluate the enhancement produced by Optison/spl reg/ infusion at concentrations of 0, 0.1, 0.3, 1, 3, and 10 /spl mu/L/kg/min. Acute canine kidneys were surgically externalized and insonified with single ultrasound exposures. The probability of tissue damage production was determined with respect to exposure intensity and duration for each concentration. As microbubble concentration increased from 0 to 10 /spl mu/L/kg/min, the requisite intensity and the requisite duration both gradually decreased. The results indicate that microbubble introduction up to 10 /spl mu/L/kg/min is effective for aiding ultrasound therapy.","PeriodicalId":378705,"journal":{"name":"2002 IEEE Ultrasonics Symposium, 2002. Proceedings.","volume":"21 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2002-12-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"127001608","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2002-12-01DOI: 10.1109/ULTSYM.2002.1192614
Z. M. Benenson, A. B. Elizarov, T. Yakovleva, W. O’Brien
The paper proposes a method to form 3D images with improved resolution and significantly decreased frame rates. The method is based on a linear phased array with a cylindrical lens that is moving in the direction perpendicular to the electronic scanning plane. The theory, the algorithms of the dynamic focusing in 3D space, the results of simulation and physical experiment results are given.
{"title":"Moving linear array technique: improved lateral resolution with decreased scan time to form a 3D image","authors":"Z. M. Benenson, A. B. Elizarov, T. Yakovleva, W. O’Brien","doi":"10.1109/ULTSYM.2002.1192614","DOIUrl":"https://doi.org/10.1109/ULTSYM.2002.1192614","url":null,"abstract":"The paper proposes a method to form 3D images with improved resolution and significantly decreased frame rates. The method is based on a linear phased array with a cylindrical lens that is moving in the direction perpendicular to the electronic scanning plane. The theory, the algorithms of the dynamic focusing in 3D space, the results of simulation and physical experiment results are given.","PeriodicalId":378705,"journal":{"name":"2002 IEEE Ultrasonics Symposium, 2002. Proceedings.","volume":"96 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2002-12-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"127056815","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2002-12-01DOI: 10.1109/ULTSYM.2002.1192484
A. Safari, M. E. Ebrahimi, S. Turcu, A. Hall, R. Brennan, N. M. Hagh
Layered Manufacturing (LM) technology has been implemented to prototype novel piezoelectric ceramics and composites for sensor and actuator applications. Piezoelectric actuators in the form of tubes, telescoping, spirals and ovals have been manufactured. Among actuators, spirals have shown giant tangential displacements up to several millimeters at moderate electric field. Multimaterials actuators have also been prototyped to study field-induced strain in these structures. In addition to actuators, piezocomposite sensors with oriented 2-2 and 3-3 composites were prototyped, in which the ceramic phase was oriented with respect to the poling direction. Various piezoelectric properties were measured and calculated. The hydrostatic figure of merit at an orientation angle of 45 degrees was significantly (50-80 times) larger than those of the conventional piezocomposites. Recently, we have fabricated net shape grain-oriented/single crystal components by integration of LM and Templatcd Grain Growth techniques. Grain oriented PMN-PT, bismuth titanate, and lead niobate components were also made using LM feedstock containing small amounts of platelet or needle-like seeds, resulting in improved piezoelectric properties.
{"title":"Layered manufacturing for prototyping of novel transducers","authors":"A. Safari, M. E. Ebrahimi, S. Turcu, A. Hall, R. Brennan, N. M. Hagh","doi":"10.1109/ULTSYM.2002.1192484","DOIUrl":"https://doi.org/10.1109/ULTSYM.2002.1192484","url":null,"abstract":"Layered Manufacturing (LM) technology has been implemented to prototype novel piezoelectric ceramics and composites for sensor and actuator applications. Piezoelectric actuators in the form of tubes, telescoping, spirals and ovals have been manufactured. Among actuators, spirals have shown giant tangential displacements up to several millimeters at moderate electric field. Multimaterials actuators have also been prototyped to study field-induced strain in these structures. In addition to actuators, piezocomposite sensors with oriented 2-2 and 3-3 composites were prototyped, in which the ceramic phase was oriented with respect to the poling direction. Various piezoelectric properties were measured and calculated. The hydrostatic figure of merit at an orientation angle of 45 degrees was significantly (50-80 times) larger than those of the conventional piezocomposites. Recently, we have fabricated net shape grain-oriented/single crystal components by integration of LM and Templatcd Grain Growth techniques. Grain oriented PMN-PT, bismuth titanate, and lead niobate components were also made using LM feedstock containing small amounts of platelet or needle-like seeds, resulting in improved piezoelectric properties.","PeriodicalId":378705,"journal":{"name":"2002 IEEE Ultrasonics Symposium, 2002. Proceedings.","volume":"147 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2002-12-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"124710210","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2002-12-01DOI: 10.1109/ULTSYM.2002.1192686
Y. Yamakoshi, Y. Ozawa, N. Masuda
When the micro-bubble oscillates under the ultrasonic wave, the bubble radiates secondary waves around it. This wave generates secondary Bjerknes force between the neighboring bubbles and the force assists inherent bubble movements such as bubble aggregation inside the ultrasonic wave field. In this paper, a novel technique to characterize the secondary ultrasonic wave from the bubbles is proposed. This method is based on the observation of fringe like pattern produced around the bubble of interest. This pattern is produced by micro bubbles which are trapped inside the interference wave field of incident wave and the secondary wave. The experiments are carried out by an ultrasonic wave contrast agent "Levovist" (SCHERING A.G. Germany). The fringe like patterns are observed for relative large aggregated bubbles.
{"title":"Holographic visualization of secondary ultrasonic waves radiated from micro-bubbles","authors":"Y. Yamakoshi, Y. Ozawa, N. Masuda","doi":"10.1109/ULTSYM.2002.1192686","DOIUrl":"https://doi.org/10.1109/ULTSYM.2002.1192686","url":null,"abstract":"When the micro-bubble oscillates under the ultrasonic wave, the bubble radiates secondary waves around it. This wave generates secondary Bjerknes force between the neighboring bubbles and the force assists inherent bubble movements such as bubble aggregation inside the ultrasonic wave field. In this paper, a novel technique to characterize the secondary ultrasonic wave from the bubbles is proposed. This method is based on the observation of fringe like pattern produced around the bubble of interest. This pattern is produced by micro bubbles which are trapped inside the interference wave field of incident wave and the secondary wave. The experiments are carried out by an ultrasonic wave contrast agent \"Levovist\" (SCHERING A.G. Germany). The fringe like patterns are observed for relative large aggregated bubbles.","PeriodicalId":378705,"journal":{"name":"2002 IEEE Ultrasonics Symposium, 2002. Proceedings.","volume":"75 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2002-12-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"132460529","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2002-12-01DOI: 10.1109/ULTSYM.2002.1192566
H. Yao, P. Phukpattaranont, E. Ebbini
It has long been recognized that thermal lesions formed using high-intensity focused ultrasound (HIFU) exhibit nonlinear behavior that can be detected in pulse-echo ultrasound. Second harmonic imaging of freshly formed thermal lesions have consistently shown significant enhancement in their visualization confirming this nonlinear behavior. In this paper, we describe a post-beamforming nonlinear filtering algorithm based on a second-order Volterra filter (SVF) model that separates the linear and quadratic components of the echo signal leading to significant enhancement of lesion visualization. Images from ex vivo tissue samples are shown to demonstrate the level of contrast enhancement achieved with the SVF-based quadratic filter compared with standard echo and 2nd harmonic imaging results.
{"title":"Detection and mapping of thermal lesions using dual-mode ultrasound phased arrays","authors":"H. Yao, P. Phukpattaranont, E. Ebbini","doi":"10.1109/ULTSYM.2002.1192566","DOIUrl":"https://doi.org/10.1109/ULTSYM.2002.1192566","url":null,"abstract":"It has long been recognized that thermal lesions formed using high-intensity focused ultrasound (HIFU) exhibit nonlinear behavior that can be detected in pulse-echo ultrasound. Second harmonic imaging of freshly formed thermal lesions have consistently shown significant enhancement in their visualization confirming this nonlinear behavior. In this paper, we describe a post-beamforming nonlinear filtering algorithm based on a second-order Volterra filter (SVF) model that separates the linear and quadratic components of the echo signal leading to significant enhancement of lesion visualization. Images from ex vivo tissue samples are shown to demonstrate the level of contrast enhancement achieved with the SVF-based quadratic filter compared with standard echo and 2nd harmonic imaging results.","PeriodicalId":378705,"journal":{"name":"2002 IEEE Ultrasonics Symposium, 2002. Proceedings.","volume":"7 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2002-12-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"121205284","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2002-12-01DOI: 10.1109/ULTSYM.2002.1192555
T. Bigelow, W. O’Brien
Due to regulatory reasons, the output levels of ultrasound sources for use in medical applications must be known. Currently, this is done by making focal pressure measurements for a very large number of drive voltage amplitudes and then linearly derating the measured pressure levels. In order to reduce calibration times, some have proposed to linearly extrapolate pressures rather than perform direct measurements. However, nonlinear propagation effects corrupt the linear extrapolation and derating procedure. Thus, a reliable indicator of nonlinearity is needed to identify when linear extrapolation/derating would be valid. In this study, eight different nonlinearity indicators were evaluated experimentally in terms of their correspondence to the linear extrapolation error. Spherically focused ultrasound transducers were selected and excited to test the indicators sensitivity to frequency (3 - 8 MHz), f/# (1 and 2), transducer diameter (1.905 and 5.08 cm), pulse duration (1 and 3 cycles), and pulse phase (0/spl deg/ and 180/spl deg/). None of the eight nonlinearity indicators yielded consistent results. The lack of consistency resulted from the competing effects of nonlinear absorption and asymmetric distortion, which have yet to be combined into a unified theory.
{"title":"Experimental evaluation of some possible nonlinearity indicators","authors":"T. Bigelow, W. O’Brien","doi":"10.1109/ULTSYM.2002.1192555","DOIUrl":"https://doi.org/10.1109/ULTSYM.2002.1192555","url":null,"abstract":"Due to regulatory reasons, the output levels of ultrasound sources for use in medical applications must be known. Currently, this is done by making focal pressure measurements for a very large number of drive voltage amplitudes and then linearly derating the measured pressure levels. In order to reduce calibration times, some have proposed to linearly extrapolate pressures rather than perform direct measurements. However, nonlinear propagation effects corrupt the linear extrapolation and derating procedure. Thus, a reliable indicator of nonlinearity is needed to identify when linear extrapolation/derating would be valid. In this study, eight different nonlinearity indicators were evaluated experimentally in terms of their correspondence to the linear extrapolation error. Spherically focused ultrasound transducers were selected and excited to test the indicators sensitivity to frequency (3 - 8 MHz), f/# (1 and 2), transducer diameter (1.905 and 5.08 cm), pulse duration (1 and 3 cycles), and pulse phase (0/spl deg/ and 180/spl deg/). None of the eight nonlinearity indicators yielded consistent results. The lack of consistency resulted from the competing effects of nonlinear absorption and asymmetric distortion, which have yet to be combined into a unified theory.","PeriodicalId":378705,"journal":{"name":"2002 IEEE Ultrasonics Symposium, 2002. Proceedings.","volume":"59 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2002-12-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"133945198","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
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