ABSTRACT
The detectors of the laser interferometer gravitational-wave observatory (LIGO) are broadly limited by the quantum noise and rely on the injection of squeezed states of light to achieve their full sensitivity. Squeezing improvement is limited by mode mismatch between the elements of the squeezer and the interferometer. In the current LIGO detectors, there is no way to actively mitigate this mode mismatch. This paper presents a new deformable mirror for wavefront control that meets the active mode matching requirements of advanced LIGO. The active element is a piezo-electric transducer, which actuates on the radius of curvature of a 5 mm thick mirror via an axisymmetric flexure. The operating range of the deformable mirror is 120±8 mD in vacuum and an additional 200 mD adjustment range accessible out of vacuum. Combining the operating range and the adjustable static offset, it is possible to deform a flat mirror from -65 mD to -385 mD. The measured bandwidth of the actuator and driver electronics is 6.8 Hz. The scattering into higher-order modes is measured to be <0.2% over the nominal beam radius. These piezo-deformable mirrors meet the stringent noise and vacuum requirements of advanced LIGO and will be used for the next observing run (O4) to control the mode-matching between the squeezer and the interferometer.
ABSTRACT
In this paper, we present a bearingless motor with a novel segmented dipole interior permanent magnet (IPM) slice rotor. The segmented dipole IPM rotor contains a unique pattern of interior permanent magnets arranged to generate a dipole air gap flux pattern. The magnets are encapsulated within an electrical steel rotor structure. The stator contains a three-phase, four-pole winding for suspension and a three-phase, two-pole winding for rotation. We present analyses of several candidate rotor designs. The analyses indicate that the segmented dipole IPM rotor achieves a reduced trade-off between force and torque capacity and relatively symmetric force dynamics as compared to prior art designs and alternate topologies. Symmetric and decoupled force dynamics allow a simple force decoupling algorithm to be used. We designed, constructed, and tested a prototype system. We experimentally demonstrate that the prototype system can achieve stable levitation and open-loop rotation.
ABSTRACT
We report the design and testing of a compression-biased thermally-actuated deformable mirror that has a dynamic range larger than the limit imposed by pure-bending stress, negligible higher-order-mode scattering, and a linear defocus response and that is vacuum compatible. The optimum design principles for this class of actuator are described and a mirror with 370 mD dynamic range is demonstrated.
ABSTRACT
We present a new configuration of bearingless slice motor that levitates and rotates a ring-shaped solid steel reluctance rotor. The rotor is 50 mm in diameter and has salient features on the outer surface. Symmetric sets of Halbach magnet arrays, mounted on the tips of stator teeth, establish a homopolar bias flux around the rotor. The bias flux passively stabilizes the rotor in the out-of-plane tilts and axial translation, whereas the rotor's radial translations are actively stabilized by feedback control. The rotor saliencies spatially modulate the air-gap bias flux such that the resulting torque-current relationship is similar to that of permanent-magnet synchronous machines. We have designed, built, and tested a prototype bearingless motor and control system. The prototype system achieves a torque constant of 14.9mNm/A, maximum speed of 5500 rpm, and suspension bandwidth of 84 Hz with a phase margin of 11.3 deg. The rated torque and speed are 26.8 mNm and 3486 rpm, and the axial and tilting passive stiffnesses are 15.3 N/mm and 34.4 mNm/deg.
ABSTRACT
We present a new concept of bearingless slice motor that levitates and rotates a ring-shaped solid rotor. The rotor is made of a semi-hard magnetic material exhibiting magnetic hysteresis, such as D2 steel. The rotor is radially biased with a homopolar permanent-magnetic flux, on which the stator can superimpose 2-pole flux to generate suspension forces. By regulating the suspension forces based on position feedback, the two radial rotor degrees of freedom are actively stabilized. The two tilting degrees of freedom and the axial translation are passively stable due to the reluctance forces from the bias flux. In addition, the stator can generate a torque by superimposing 6- pole rotating flux, which drags the rotor via hysteresis coupling. This 6-pole flux does not generate radial forces in conjunction with the homopolar flux or 2-pole flux, and therefore the suspension force generation is in principle decoupled from the driving torque generation. We have developed a prototype system as a proof of concept. The stator has twelve teeth, each of which has a single phase winding that is individually driven by a linear transconductance power amplifier. The system has four reflective-type optical sensors to differentially measure the two radial degrees of freedom of the rotor. The suspension control loop is implemented such that the phase margin is 25 degrees at the cross-over frequency of 110 Hz. The prototype system can levitate the rotor and drive it up to about 1730 rpm. The maximum driving torque is about 2.7 mNm.
ABSTRACT
OBJECTIVE: An infant born with long-gap esophageal atresia has its esophagus separated into two pouches, and typically undergoes multiple open-chest surgeries for esophageal reconstruction. In this paper, we study a possible approach for less invasive correction of long-gap esophageal atresia. METHODS: Our technique utilizes a magnet-tipped catheter with a piston on the end to push the esophageal pouch from the inside. The attractive magnetic force helps the catheter stretch the esophageal pouches, while the hydraulic piston prevents the magnet from applying too large force. The piston also enables estimation of the esophageal tension based on the hydraulic pressure measurement. RESULTS: We have built a prototype system and performed bench-level tests on an esophageal mock-up. A hydraulic dither is applied to the piston to average out seal friction, thereby improving the tension estimation performance. CONCLUSION: The bench-level tests demonstrate that the prototype bougienage system gives a reliable low-frequency estimate of the esophageal tension in real-time, and also enables longitudinal bougienage by a desired amount of load, e.g., 2N, for various gap sizes. SIGNIFICANCE: This study provides a foundation for the next step of designing a system for use on actual patients.