The Experts below are selected from a list of 62601 Experts worldwide ranked by ideXlab platform
John T W Yeow - One of the best experts on this subject based on the ideXlab platform.
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Lumped element modeling of air-coupled capacitive micromachined ultrasonic transducers with annular Cell Geometry.
Ultrasonics, 2016Co-Authors: Lawrence L P Wong, Albert I H Chen, Mirek Macecek, John T W YeowAbstract:Air-coupled capacitive micromachined ultrasonic transducers (CMUTs) based on annular Cell Geometry have recently been reported. Finite element analysis and experimental studies have demonstrated their significant improvement in transmit efficiency compared with the conventional circular-Cell CMUTs. Extending the previous work, this paper proposed a lumped element model of annular-Cell CMUTs. Explicit expressions of the resonance frequency, modal vector, and static displacement of a clamped annular plate under uniform pressure were first derived based on the plate theory and curve fitting method. The lumped model of an annular CMUT Cell was then developed by adopting the average displacement as the spatial variable. Using the proposed model, the ratio of average-to-maximum displacement was derived to be 8/15. Experimental and simulation studies on a fabricated annular CMUT Cell verified the effectiveness of the lumped model. The proposed model provides an effective and efficient way to analyze and design air-coupled annular-Cell CMUTs.
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Capacitive micromachined ultrasonic transducers based on annular Cell Geometry for air-coupled applications.
Ultrasonics, 2016Co-Authors: Albert I H Chen, Lawrence L P Wong, Mirek Macecek, John T W YeowAbstract:A novel design of an air-coupled capacitive micromachined ultrasonic transducer (CMUT) with annular Cell Geometry (annular CMUT) is proposed. Finite element analysis shows that an annular Cell has a ratio of average-to-maximum displacement (RAMD) of 0.52-0.58 which is 58-76% higher than that of a conventional circular Cell. The increased RAMD leads to a larger volume displacement which results in a 48.4% improved transmit sensitivity and 127.3% improved power intensity. Single-Cell annular CMUTs were fabricated with 20-μm silicon plates on 13.7-μm deep and 1.35-mm wide annular cavities using the wafer bonding technique. The measured RAMD of the fabricated CMUTs is 0.54. The resonance frequency was measured to be 94.5kHz at 170-V DC bias. The transmit sensitivity was measured to be 33.83Pa/V and 25.85Pa/V when the CMUT was excited by a continuous wave and a 20-cycle burst, respectively. The receive sensitivity at 170-V DC bias was measured to be 7.7mV/Pa for a 20-cycle burst, and 15.0mV/Pa for a continuous incident wave. The proposed annular CMUT design demonstrates a significant improvement in transmit efficiency, which is an important parameter for air-coupled ultrasonic transducers.
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A CMUT array based on annular Cell Geometry for air-coupled applications
2016 IEEE International Ultrasonics Symposium (IUS), 2016Co-Authors: Lawrence L P Wong, Albert I H Chen, Mirek Macecek, John T W YeowAbstract:An annular Cell has been reported with improved transmit sensitivity over a conventional circular Cell for air-coupled CMUTs. The particular Geometry of an annular Cell also allows multi of them to be arranged in a concentric layout such that high-intensity ultrasound can be focused in the depth direction. This paper presents a 9.3-mm-diameter CMUT array consisting of four concentric annular Cells. The wafer-bonded CMUT has a plate thickness of 18.3 μm and Cell width of 930 μm. Under atmospheric pressure, the ratio of average-to-maximum displacement (RAMD) of the annular Cells was measured to be 0.53 using a profilometer. At 200-V DC bias and 20-Vpp AC actuation voltage, the frequency response of the maximum displacement was measured using a laser Doppler vibrometer, and a resonance frequency of 182.5 kHz was observed. At the same DC bias, the resonance frequency of the array was also measured to be 182.5 kHz using a vector network analyzer. Based on the frequency response, the acoustic filed of the CMUT array was simulated to have an 11.4-mm natural focal depth with -3-dB beam width of 3.14 mm. This study demonstrates the potential of using concentric annular-Cell CMUT array to generate focused ultrasound in air.
Jochen Küpper - One of the best experts on this subject based on the ideXlab platform.
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optimized Cell Geometry for buffer gas cooled molecular beam sources
Physical Review A, 2018Co-Authors: Vijay A. Singh, Amit K Samanta, Nils Roth, Daniel Gusa, Tim Ossenbruggen, Igor Rubinsky, Daniel A Horke, Jochen KüpperAbstract:We have designed, constructed, and commissioned a cryogenic helium buffer-gas source for producing a cryogenially-cooled molecular beam and evaluated the effect of different Cell geometries on the intensity of the produced molecular beam, using ammonia as a test molecule. Planar and conical entrance and exit geometries are tested. We observe a three fold enhancement in the NH$_3$ signal for a Cell with planar-entrance and conical-exit Geometry, compared to that for a typically used `box'-like Geometry with planar entrance and exit. These observations are rationalized by flow-field simulations for the different buffer-gas Cell geometries. The full thermalization of molecules with the helium buffer-gas is confirmed through rotationally-resolved REMPI spectra yielding a rotational temperature of 5 K.
Arri Priimagi - One of the best experts on this subject based on the ideXlab platform.
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a bifacial colour tunable system via combination of a cholesteric liquid crystal network and hydrogel
Journal of Materials Chemistry C, 2020Co-Authors: Owies M Wani, Albertus P H J Schenning, Arri PriimagiAbstract:We present a colour tunable system obtained by combining a humidity-responsive cholesteric liquid crystal network and hydrogel coatings, in a diligently designed Cell-Geometry. The design enables sensitive colour tuning via temperature-induced changes in humidity inside the Cell. Uniquely, the system exhibits a bifacial response, causing either a blue- or red-shift in the reflected color when heated from opposite sides.
Vijay A. Singh - One of the best experts on this subject based on the ideXlab platform.
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optimized Cell Geometry for buffer gas cooled molecular beam sources
Physical Review A, 2018Co-Authors: Vijay A. Singh, Amit K Samanta, Nils Roth, Daniel Gusa, Tim Ossenbruggen, Igor Rubinsky, Daniel A Horke, Jochen KüpperAbstract:We have designed, constructed, and commissioned a cryogenic helium buffer-gas source for producing a cryogenially-cooled molecular beam and evaluated the effect of different Cell geometries on the intensity of the produced molecular beam, using ammonia as a test molecule. Planar and conical entrance and exit geometries are tested. We observe a three fold enhancement in the NH$_3$ signal for a Cell with planar-entrance and conical-exit Geometry, compared to that for a typically used `box'-like Geometry with planar entrance and exit. These observations are rationalized by flow-field simulations for the different buffer-gas Cell geometries. The full thermalization of molecules with the helium buffer-gas is confirmed through rotationally-resolved REMPI spectra yielding a rotational temperature of 5 K.
Albert I H Chen - One of the best experts on this subject based on the ideXlab platform.
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Lumped element modeling of air-coupled capacitive micromachined ultrasonic transducers with annular Cell Geometry.
Ultrasonics, 2016Co-Authors: Lawrence L P Wong, Albert I H Chen, Mirek Macecek, John T W YeowAbstract:Air-coupled capacitive micromachined ultrasonic transducers (CMUTs) based on annular Cell Geometry have recently been reported. Finite element analysis and experimental studies have demonstrated their significant improvement in transmit efficiency compared with the conventional circular-Cell CMUTs. Extending the previous work, this paper proposed a lumped element model of annular-Cell CMUTs. Explicit expressions of the resonance frequency, modal vector, and static displacement of a clamped annular plate under uniform pressure were first derived based on the plate theory and curve fitting method. The lumped model of an annular CMUT Cell was then developed by adopting the average displacement as the spatial variable. Using the proposed model, the ratio of average-to-maximum displacement was derived to be 8/15. Experimental and simulation studies on a fabricated annular CMUT Cell verified the effectiveness of the lumped model. The proposed model provides an effective and efficient way to analyze and design air-coupled annular-Cell CMUTs.
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Capacitive micromachined ultrasonic transducers based on annular Cell Geometry for air-coupled applications.
Ultrasonics, 2016Co-Authors: Albert I H Chen, Lawrence L P Wong, Mirek Macecek, John T W YeowAbstract:A novel design of an air-coupled capacitive micromachined ultrasonic transducer (CMUT) with annular Cell Geometry (annular CMUT) is proposed. Finite element analysis shows that an annular Cell has a ratio of average-to-maximum displacement (RAMD) of 0.52-0.58 which is 58-76% higher than that of a conventional circular Cell. The increased RAMD leads to a larger volume displacement which results in a 48.4% improved transmit sensitivity and 127.3% improved power intensity. Single-Cell annular CMUTs were fabricated with 20-μm silicon plates on 13.7-μm deep and 1.35-mm wide annular cavities using the wafer bonding technique. The measured RAMD of the fabricated CMUTs is 0.54. The resonance frequency was measured to be 94.5kHz at 170-V DC bias. The transmit sensitivity was measured to be 33.83Pa/V and 25.85Pa/V when the CMUT was excited by a continuous wave and a 20-cycle burst, respectively. The receive sensitivity at 170-V DC bias was measured to be 7.7mV/Pa for a 20-cycle burst, and 15.0mV/Pa for a continuous incident wave. The proposed annular CMUT design demonstrates a significant improvement in transmit efficiency, which is an important parameter for air-coupled ultrasonic transducers.
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A CMUT array based on annular Cell Geometry for air-coupled applications
2016 IEEE International Ultrasonics Symposium (IUS), 2016Co-Authors: Lawrence L P Wong, Albert I H Chen, Mirek Macecek, John T W YeowAbstract:An annular Cell has been reported with improved transmit sensitivity over a conventional circular Cell for air-coupled CMUTs. The particular Geometry of an annular Cell also allows multi of them to be arranged in a concentric layout such that high-intensity ultrasound can be focused in the depth direction. This paper presents a 9.3-mm-diameter CMUT array consisting of four concentric annular Cells. The wafer-bonded CMUT has a plate thickness of 18.3 μm and Cell width of 930 μm. Under atmospheric pressure, the ratio of average-to-maximum displacement (RAMD) of the annular Cells was measured to be 0.53 using a profilometer. At 200-V DC bias and 20-Vpp AC actuation voltage, the frequency response of the maximum displacement was measured using a laser Doppler vibrometer, and a resonance frequency of 182.5 kHz was observed. At the same DC bias, the resonance frequency of the array was also measured to be 182.5 kHz using a vector network analyzer. Based on the frequency response, the acoustic filed of the CMUT array was simulated to have an 11.4-mm natural focal depth with -3-dB beam width of 3.14 mm. This study demonstrates the potential of using concentric annular-Cell CMUT array to generate focused ultrasound in air.