| 1. |
- Plessky, Victor, et al.
(författare)
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Two Resonances of Different Nature in STW Resonators With Aperture-Weighted Metallization
- 2015
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Ingår i: IEEE Transactions on Ultrasonics, Ferroelectrics and Frequency Control. - 0885-3010 .- 1525-8955. ; 62:4, s. 766-770
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Tidskriftsartikel (refereegranskat)abstract
- In a narrowband 2-port resonator on 37 degrees-cut quartz with Al electrodes (h(Alu) = 100 nm) exploiting surface transverse waves (STW), we have observed parasitic ripples which have been attributed to transverse modes unusually situated on the left side of the main resonance. To suppress these modes, we have used metallization coefficient weighting across the aperture, with more metal in the middle and reduced metallization close to the busbars. The parasitic modes indeed disappeared, but at significantly higher frequency, we have found an additional strong response which does not exist in a resonator with uniform electrode metallization. 3-D simulations showed that the structure has another very different mode, with the wave propagating mainly along the edge of the busbars, but excited with the interdigital electrode system.
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| 2. |
- Sheikh, Rafi, et al.
(författare)
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Clinical translation of a novel photoacoustic imaging system for examining the temporal artery
- 2019
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Ingår i: IEEE Transactions on Ultrasonics, Ferroelectrics and Frequency Control. - 0885-3010. ; 66:3, s. 472-480
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Tidskriftsartikel (refereegranskat)abstract
- The objective was to provide a clinical setup for photoacoustic imaging (PAI) of the temporal artery in humans and to describe the challenges encountered and methods of overcoming them. The temporal artery was examined in 7 patients with suspect giant cell arteritis (GCA), both in vivo and ex vivo, and the results were compared to that of histology. To adapt PAI to human studies, the transducer was fixed to an adjustable arm to reduce motion artifacts and a stepping motor was developed to enable 3D scanning. Risks associated with the use of lasers, ultrasound, and electrical equipment were evaluated by measuring energy levels, and safety precautions were undertaken to prevent injury to the patients and staff. The PAI spectra obtained clearly delineated the artery wall, both in vivo and ex vivo, although the latter were of higher quality due to the lack of artifacts. The results could be compared to that of histology. The energy levels involved were found to be below limits given in regulatory standards. Eye protectors prevented irradiation of the patient’s eyes, and visual function after the procedure was found not to be affected. The patients reported no discomfort during the investigations. PAI provides images of the temporal artery wall that may be used for the future diagnosis of GCA in humans. The technique could be further refined by addressing the specific problems of motion artefacts and interference from blood and other chromophores. This study paves the way for other clinical applications of PAI.
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| 3. |
- Sjöstrand, Sandra, et al.
(författare)
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Design and fabrication of a conceptual arterial ultrasound phantom capable of exhibiting longitudinal wall movement
- 2017
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Ingår i: IEEE Transactions on Ultrasonics, Ferroelectrics and Frequency Control. - 0885-3010. ; 64:1, s. 11-18
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Tidskriftsartikel (refereegranskat)abstract
- The longitudinal movement of the arterial wall of large human arteries has shown promise to be an independent indicator of vascular health. Despite growing interest in this movement, its nature, causes, and implications are not fully understood, and existing phantoms have failed to show a pure longitudinal movement that is not secondary to the distension. An often overlooked aspect of the arterial wall is the interaction between the different layers. The longitudinal movement of the innermost layers, the intima and media, can be several hundred micrometers in the direction of flow during early systole. This is markedly larger than that of the adventitia, indicating that sliding occurs between the two layers. This feature was incorporated into a phantom by casting it in two parts. The molds were developed in-house using mainly a 3-D printer, a versatile and easy production method. Additionally, the phantom contains a tapered region. Using the phantom, we were able to demonstrate a pure longitudinal movement; when it was subjected to a pulsatile pressure, the wall displaced 220 μm (SD 40) radially and 560 μm (SD 74) longitudinally distal to the tapering. The motion followed the pressure variations. This paper serves as a guide for phantom production, explaining each step of the process.
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| 4. |
- Vorobiev, Andrei, 1963, et al.
(författare)
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Composite Ferroelectric FBARs That Are Switchable Between the First and Second Harmonics: Experimental Demonstration
- 2015
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Ingår i: IEEE Transactions on Ultrasonics, Ferroelectrics, and Frequency Control. - : Institute of Electrical and Electronics Engineers (IEEE). - 0885-3010. ; 62:3, s. 565-575
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Tidskriftsartikel (refereegranskat)abstract
- Digital switching between the first and second harmonics, in a composite thin-film bulk acoustic wave resonator (FBAR), is demonstrated experimentally. The FBAR consists of two 180-nm-thick paraelectric-phase Ba0.25Sr0.75TiO3 films separated by a 50-nm-thick SrRuO3 conducting layer. The resonant frequency of this composite resonator (with Pt bottom and Al top electrodes) is switched from 3.6 GHz to 7.6 GHz, where the polarity of the 5 V dc bias is reversed on one of the ferroelectric films. The frequency switching ratio (f(2)/f(1) >= 2) depends on the thickness of the electrodes. Some adjustment of f(2)/f(1) is possible by changing the applied dc bias.
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