ABSTRACT MEMS scanners are useful for medical applications as optical coherence tomography and la... more ABSTRACT MEMS scanners are useful for medical applications as optical coherence tomography and laser microsurgery. Although widespread design of MEMS scanners have been presented, their behavior is not well known, and thus, their motions are not easily and efficiently controlled. This deficiency induces several difficulties (limited resolution, accuracy, cycle time, etc.), and to tackle this problem, this article presents the modeling of an ISC electrothermally actuated MEMS mirror and the experimental characterization for the piston motion. Modeling and characterization are important to implement the control. A multiphysic model is proposed, and an experimental validation is performed with a good correspondence for a voltage range from 0 V to 3.5 V with a maximum displacement up to 200 µm and with a relative tilting difference of 0.1°. The article also presents a simple and efficient experimental setup to measure a displacement in dynamic and static mode, or a mirror plane tilting in static mode.
Mechanical property data for brain tissue are needed to understand the biomechanics of neurologic... more Mechanical property data for brain tissue are needed to understand the biomechanics of neurological disorders and response of the brain to different mechanical and surgical forces. Most studies have characterized mechanical behavior of brain tissues over large regions or classified tissue properties for either gray or white matter regions only. In this study, spatially heterogeneous viscoelastic properties of ex vivo rat brain tissue slices were measured in different anatomical regions including the cerebral cortex, caudate/putamen, and hippocampus using an optical coherence tomography (OCT) indentation system. Cell viability was also tested to observe neuronal degeneration and morphological changes in tissue slices and provide a proper timeline for mechanical tests. Shear modulus was estimated by fitting normalized deformation data (D/ti), which was defined as the ratio of deformation depth (D) to initial thickness of the tissue slice (ti), to a viscoelastic finite element model. The estimated shear modulus decayed nonlinearly over 10min in each anatomical region, and the range of instantaneous to equilibrium shear modulus was 3.8-0.54kPa in the cerebral cortex, 1.4-0.27kPa in the hippocampus and 1.0-0.17kPa in the caudate/putamen. Although these regions are all gray matter structures, their measured mechanical properties were significantly different. Accurate measurement of inter-regional variations in mechanical properties will contribute to improved understanding organ-level structural parameters and regional differential susceptibility to deformation injury within CNS tissues.
ABSTRACT MEMS scanners are useful for medical applications as optical coherence tomography and la... more ABSTRACT MEMS scanners are useful for medical applications as optical coherence tomography and laser microsurgery. Although widespread design of MEMS scanners have been presented, their behavior is not well known, and thus, their motions are not easily and efficiently controlled. This deficiency induces several difficulties (limited resolution, accuracy, cycle time, etc.), and to tackle this problem, this article presents the modeling of an ISC electrothermally actuated MEMS mirror and the experimental characterization for the piston motion. Modeling and characterization are important to implement the control. A multiphysic model is proposed, and an experimental validation is performed with a good correspondence for a voltage range from 0 V to 3.5 V with a maximum displacement up to 200 µm and with a relative tilting difference of 0.1°. The article also presents a simple and efficient experimental setup to measure a displacement in dynamic and static mode, or a mirror plane tilting in static mode.
Nonmechanical steering of optical beams will enable revolutionary systems with random access poin... more Nonmechanical steering of optical beams will enable revolutionary systems with random access pointing, similar to microwave radar phased arrays. An early approach was birefringent liquid crystals writing a sawtooth phase profile in one polarization, using 2� resets. Liquid crystals were used because of high birefringence. Fringing fields associated with voltage control required to implement the 2� resets have limited the
Scanning fiber tips provides the most convenient way for forward-viewing fiber-optic microendosco... more Scanning fiber tips provides the most convenient way for forward-viewing fiber-optic microendoscopy. In this paper, a distal fiber scanning method based on a large-displacement MEMS actuator is presented. A single-mode fiber is glued on the micro-platform of an electrothermal MEMS stage to realize large range non-resonantscanning. The micro-platform has a large piston scan range of up to 800 µm at only 6V. The tip deflection of the fiber can be further amplified by placing the MEMS stage at a proper location along the fiber. A quasi-static model of the fiber-MEMS assembly has been developed and validated experimentally. The frequency response has also been studied and measured. A fiber tip deflection of up to 1650 µm for the 45 mm-long movable fiber portion has been achieved when the MEMS electrothermal stage was placed 25 mm away from the free end. The electrothermally-actuated MEMS stage shows a great potential for forward viewing fiber scanning and optical applications.
A new design of high-full-factor(HFF)micromirror array(MMA) has been proposed, fabricated and tes... more A new design of high-full-factor(HFF)micromirror array(MMA) has been proposed, fabricated and tested. Optical-phased-array (OPA) beam steering based on the HFF MMA has also been demonstrated. This unique HFF MMA design consists of large sub-apertures (i.e., mirror pixels). The flatness of the mirror surface is provided by a 80 micrometers-thick single-crystal silicon layer. The MMAs are fabricated using a single-wafer fabrication process without any wafer bonding, and the devices are surface-mountable right after the batch fabrication. A fabricated 4 4 MMA achieves a combined optical aperture of 6.4mm 6.4mm with ~90% fill factor and > 25 degree scan range in two axes at 4V DC. A static piston of 320 micrometers is achieved at less than 8V. The measured piston and rotation resonance modes are 247Hz and 320Hz, respectively. It is experimentally shown that the spot size from a rectangular aperture consisting of two consecutive sub-apertures is significantly reduced compared to that ...
ABSTRACT MEMS scanners are useful for medical applications as optical coherence tomography and la... more ABSTRACT MEMS scanners are useful for medical applications as optical coherence tomography and laser microsurgery. Although widespread design of MEMS scanners have been presented, their behavior is not well known, and thus, their motions are not easily and efficiently controlled. This deficiency induces several difficulties (limited resolution, accuracy, cycle time, etc.), and to tackle this problem, this article presents the modeling of an ISC electrothermally actuated MEMS mirror and the experimental characterization for the piston motion. Modeling and characterization are important to implement the control. A multiphysic model is proposed, and an experimental validation is performed with a good correspondence for a voltage range from 0 V to 3.5 V with a maximum displacement up to 200 µm and with a relative tilting difference of 0.1°. The article also presents a simple and efficient experimental setup to measure a displacement in dynamic and static mode, or a mirror plane tilting in static mode.
Mechanical property data for brain tissue are needed to understand the biomechanics of neurologic... more Mechanical property data for brain tissue are needed to understand the biomechanics of neurological disorders and response of the brain to different mechanical and surgical forces. Most studies have characterized mechanical behavior of brain tissues over large regions or classified tissue properties for either gray or white matter regions only. In this study, spatially heterogeneous viscoelastic properties of ex vivo rat brain tissue slices were measured in different anatomical regions including the cerebral cortex, caudate/putamen, and hippocampus using an optical coherence tomography (OCT) indentation system. Cell viability was also tested to observe neuronal degeneration and morphological changes in tissue slices and provide a proper timeline for mechanical tests. Shear modulus was estimated by fitting normalized deformation data (D/ti), which was defined as the ratio of deformation depth (D) to initial thickness of the tissue slice (ti), to a viscoelastic finite element model. The estimated shear modulus decayed nonlinearly over 10min in each anatomical region, and the range of instantaneous to equilibrium shear modulus was 3.8-0.54kPa in the cerebral cortex, 1.4-0.27kPa in the hippocampus and 1.0-0.17kPa in the caudate/putamen. Although these regions are all gray matter structures, their measured mechanical properties were significantly different. Accurate measurement of inter-regional variations in mechanical properties will contribute to improved understanding organ-level structural parameters and regional differential susceptibility to deformation injury within CNS tissues.
ABSTRACT MEMS scanners are useful for medical applications as optical coherence tomography and la... more ABSTRACT MEMS scanners are useful for medical applications as optical coherence tomography and laser microsurgery. Although widespread design of MEMS scanners have been presented, their behavior is not well known, and thus, their motions are not easily and efficiently controlled. This deficiency induces several difficulties (limited resolution, accuracy, cycle time, etc.), and to tackle this problem, this article presents the modeling of an ISC electrothermally actuated MEMS mirror and the experimental characterization for the piston motion. Modeling and characterization are important to implement the control. A multiphysic model is proposed, and an experimental validation is performed with a good correspondence for a voltage range from 0 V to 3.5 V with a maximum displacement up to 200 µm and with a relative tilting difference of 0.1°. The article also presents a simple and efficient experimental setup to measure a displacement in dynamic and static mode, or a mirror plane tilting in static mode.
Nonmechanical steering of optical beams will enable revolutionary systems with random access poin... more Nonmechanical steering of optical beams will enable revolutionary systems with random access pointing, similar to microwave radar phased arrays. An early approach was birefringent liquid crystals writing a sawtooth phase profile in one polarization, using 2� resets. Liquid crystals were used because of high birefringence. Fringing fields associated with voltage control required to implement the 2� resets have limited the
Scanning fiber tips provides the most convenient way for forward-viewing fiber-optic microendosco... more Scanning fiber tips provides the most convenient way for forward-viewing fiber-optic microendoscopy. In this paper, a distal fiber scanning method based on a large-displacement MEMS actuator is presented. A single-mode fiber is glued on the micro-platform of an electrothermal MEMS stage to realize large range non-resonantscanning. The micro-platform has a large piston scan range of up to 800 µm at only 6V. The tip deflection of the fiber can be further amplified by placing the MEMS stage at a proper location along the fiber. A quasi-static model of the fiber-MEMS assembly has been developed and validated experimentally. The frequency response has also been studied and measured. A fiber tip deflection of up to 1650 µm for the 45 mm-long movable fiber portion has been achieved when the MEMS electrothermal stage was placed 25 mm away from the free end. The electrothermally-actuated MEMS stage shows a great potential for forward viewing fiber scanning and optical applications.
A new design of high-full-factor(HFF)micromirror array(MMA) has been proposed, fabricated and tes... more A new design of high-full-factor(HFF)micromirror array(MMA) has been proposed, fabricated and tested. Optical-phased-array (OPA) beam steering based on the HFF MMA has also been demonstrated. This unique HFF MMA design consists of large sub-apertures (i.e., mirror pixels). The flatness of the mirror surface is provided by a 80 micrometers-thick single-crystal silicon layer. The MMAs are fabricated using a single-wafer fabrication process without any wafer bonding, and the devices are surface-mountable right after the batch fabrication. A fabricated 4 4 MMA achieves a combined optical aperture of 6.4mm 6.4mm with ~90% fill factor and > 25 degree scan range in two axes at 4V DC. A static piston of 320 micrometers is achieved at less than 8V. The measured piston and rotation resonance modes are 247Hz and 320Hz, respectively. It is experimentally shown that the spot size from a rectangular aperture consisting of two consecutive sub-apertures is significantly reduced compared to that ...
Uploads
Papers by Huikai Xie