Hysteresis Bearingless Slice Motors with Homopolar Flux-biasing

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 two-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 six-pole rotating flux, which drags the rotor via hysteresis coupling. This six-pole flux does not generate radial forces in conjunction with the homopolar flux or two-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 12 teeth, each of which has a single-phase winding that is individually driven by a linear transconductance power amplifier. The system has four reflectivetype 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° at the cross-over frequency of 110 Hz. The prototype system can levitate the rotor and drive it up to about 1730 r/min. The maximum driving torque is about 2.7 mNm

Closed-loop feedback control for microfluidic systems through automated capacitive fluid height sensing

Precise fluid height sensing in open-channel microfluidics has long been a desirable feature for a wide range of applications. However, performing accurate measurements of the fluid level in small-scale reservoirs (<1 mL) has proven to be an elusive goal, especially if direct fluid-sensor contact needs to be avoided. In particular, gravity-driven systems used in several microfluidic applications to establish pressure gradients and impose flow remain open-loop and largely unmonitored due to these sensing limitations. Here we present an optimized self-shielded coplanar capacitive sensor design and automated control system to provide submillimeter fluid-height resolution (∼250 μm) and control of small-scale open reservoirs without the need for direct fluid contact. Results from testing and validation of our optimized sensor and system also suggest that accurate fluid height information can be used to robustly characterize, calibrate and dynamically control a range of microfluidic systems with complex pumping mechanisms, even in cell culture conditions. Capacitive sensing technology provides a scalable and cost-effective way to enable continuous monitoring and closed-loop feedback control of fluid volumes in small-scale gravity-dominated wells in a variety of microfluidic applications.United States. Defense Advanced Research Projects Agency (Award W911NF-12-2-0039

Enhancing the dynamic range of deformable mirrors with compression bias

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

A MAGNETICALLY SUSPENDED, SPHERICAL PERMANENT MAGNETIC DIPOLE ACTUATOR

The attitude control system (ACS) of a spacecraft contains a minimum of three reaction wheels to rotate the spacecraft in 3 degrees of freedom (DoF), but typically contains additional reaction wheels for both redundancy and improved pointing accuracy. Each wheel rotates the spacecraft about its axis by imparting an equal-and-opposite torque when the spacecraft accelerates the wheel. Since space, weight, and power (SWaP) are a premium on a spacecraft, reaction spheres, which impart an equal-and-opposite torque about an arbitrary axis when the spacecraft accelerates the sphere about that axis, have been proposed to reduce the ACS down to a single device. While NASA first proposed reaction spheres over a half century ago, limitations with previous designs have kept the technology from commercialization. These designs can be generalized into two categories: asynchronous, induction-type actuators and synchronous actuators similar to DC and hysteresis motors. The induction-type designs are difficult to model and suffer from eddy current losses in the rotor while the synchronous designs often have rotors constructed from multiple magnets which presents fabrication, strength, and balance issues. To incorporate the best of both worlds, the mechanical simplicity of an induction motor with the efficiency and simple model of a brushless DC motor, a spherical permanent magnetic dipole rotor actuated by a stator of surrounding soils has been considered. This paper presents the modeling, design, and vertical suspension of a prototype permanent magnetic dipole reaction sphere depicted in Figure 1

The US Program in Ground-Based Gravitational Wave Science: Contribution from the LIGO Laboratory

Recent gravitational-wave observations from the LIGO and Virgo observatories have brought a sense of great excitement to scientists and citizens the world over. Since September 2015,10 binary black hole coalescences and one binary neutron star coalescence have been observed. They have provided remarkable, revolutionary insight into the "gravitational Universe" and have greatly extended the field of multi-messenger astronomy. At present, Advanced LIGO can see binary black hole coalescences out to redshift 0.6 and binary neutron star coalescences to redshift 0.05. This probes only a very small fraction of the volume of the observable Universe. However, current technologies can be extended to construct "3rd Generation" (3G) gravitational-wave observatories that would extend our reach to the very edge of the observable Universe. The event rates over such a large volume would be in the hundreds of thousands per year (i.e. tens per hour). Such 3G detectors would have a 10-fold improvement in strain sensitivity over the current generation of instruments, yielding signal-to-noise ratios of 1000 for events like those already seen. Several concepts are being studied for which engineering studies and reliable cost estimates will be developed in the next 5 years

Hydraulically controlled magnetic bougienage for correction of long-gap esophageal atresia

Thesis: S.M., Massachusetts Institute of Technology, Department of Mechanical Engineering, 2014.This electronic version was submitted by the student author. The certified thesis is available in the Institute Archives and Special Collections.Cataloged from student-submitted PDF version of thesis.Includes bibliographical references (pages 133-135).About one in 4000 babies in the United States is born with their esophageal disconnected and separated by a gap, which is called esophageal atresia. Esophageal atresia with a relatively short gap can be directly corrected with surgery, whereas babies with a relatively long gap requires a treatment over several weeks to stretch the esophageal pouches. In this thesis, we have designed and developed a hydraulically controlled bougienage system as a case study for correction of long-gap esophageal atresia. We insert two magnetic bougies into the esophageal pouches and applying stretching force. The key idea is to employ the magnetic force between the two bougies. The bougie is designed based on a piston mechanism, which consists of a barrel and a magnetic plunger. The plunger has a through hole in the center, so that we can push water into the piston to extend the barrel. A catheter is connected to the bougie to transfer the water. Also, the catheter is driven using a friction drive placed near the mouth, which adjusts the neutral gap size between the two magnets. A syringe pump pushes water through the catheter to extend the tip of the bougie. Therefore, the system can stretch the esophageal pouch without changing the gap size between the two magnets, which helps to apply the stretching force in a controllable manner. The piston mechanism also enables measurement of the stretching force while the bougienage is being performed. A prototype bougienage system is built and integrated on a test bench, in which surgical rubber tubing is used as a mock-up of the esophagus. We have experimentally demonstrated that the prototype bougienage system can stretch the mock-up by a desired amount of force. Also, we have shown that the bougie can reliably measure the stretching force when the O-ring friction is compensated with dither. This bench level experiment shows promising results and forms the basis for further efforts towards utilization in patients.by Minkyun Noh.S.M

Homopolar bearingless slice motors with magnet-free rotors for extracorporeal life support

Thesis: Ph. D., Massachusetts Institute of Technology, Department of Mechanical Engineering, 2018.Cataloged from PDF version of thesis. Pages 224, 230 and 231 in the original document contain text that runs off the edge of the page.Includes bibliographical references (pages 257-262).Extracorporeal life support (ECLS) is a medical therapy that uses an external blood pump and oxygenator to provide cardiac or cardiopulmonary support. One common system-related challenge is to reduce blood damage, e.g., hemolysis, which is primarily caused by the stress and heat from the pump impeller's bearing surface. Another challenge is to reduce the cost of the impeller module that is disposed after each use and therefore incurs a repeated cost. This thesis presents two types of new homopolar bearingless slice motors that levitate and rotate disk-shaped solid iron rotors. Our first bearingless motor uses a ring-shaped D2 steel rotor which generates a driving torque via hysteresis coupling. Our second bearingless motor uses a low-carbon steel rotor with surface saliencies which, in conjunction with a homopolar bias flux, makes the resulting torque-current relation similar to that of permanent-magnet synchronous machines. For both machines, permanent magnets are located on the stator to provide a homopolar bias flux to the magnet-free rotors. The bias flux passively stabilizes the rotor's axial translation and out-of-plane tilts, thereby reducing the required number of sensors and power electronics. In particular, the second bearingless motor stator includes Halbach magnet arrays for homopolar flux-biasing, which significantly improves the passive stiffness and also simplifies the design of the flux-biasing structure. The rotor's radial translation is actively stabilized by superposing a two-pole suspension flux on the homopolar bias flux. The homopolar bias flux enables us to design a winding scheme that physically decouples the torque generation and suspension force generation mechanisms. This characteristic reduces the complexity of the control algorithms. We have built the two bearingless motor prototypes, developed the associated control systems, and conducted performance tests, including pumping tests with water saline, and bovine blood. The first prototype driving a D2 steel rotor achieves a maximum rotational speed of 1730 rpm in air, where the limit comes from the position sensor's noise and the resulting power amplifier saturation and suspension failure. The second prototype driving a reluctance rotor achieves a maximum rotational speed of 5500 rpm in air, where the limit comes from the power amplifier bus voltage saturation. Based on functional requirements for ECLS, we have chosen the second bearingless motor for integration into a prototype pump module. Pumping tests are conducted with various liquids including water, saline water, and freshly obtained bovine blood. With the bovine blood, the prototype pump achieves a maximum flowrate of 2.17 L/min and maximum pump head of 120 mmHg at low flow. The blood sampled after a circulation test at 1 L/min demonstrated satisfactory hemodynamic performance including low levels of hemolysis. Integrated into extracorporeal blood pumps, the levitated magnet-free rotors are advantageous to develop low-cost disposable pump modules exhibiting a low level of hemolysis. Also, the ruggedness of the magnet-free rotors shows promise in high-speed applications, such as centrifuges and turbo-molecular pumps, and high-temperature applications, such as steam turbines and turbochargers in vehicles.by Minkyun Noh.Ph. D

Stereo-Selective Pharmacokinetics of Ilimaquinone Epimers Extracted from a Marine Sponge in Rats

An ilimquinone (IQ) mixture isolated from Hippiospongia metachromia, consisting of IQ and epi-ilimaquinone (epi-IQ), exerts anti-HIV, anti-microbial, anti-inflammatory, and anti-cancer effects. An HPLC-MS/MS method was developed for simultaneous determination of the two epimers in rat plasma, separating them using a biphenyl column. Ascorbic acid is added during the sample preparation to ensure the stability of both isomers. The plasma concentrations of the isomers were monitored following intravenous and oral administration of the IQ mixture in rats as well as the individual epimers that were separately orally administered. Compare to IQ, epi-IQ was much more stable in rat plasma, likely due to its configurations of decalin. Both substances decayed in more than bi-exponential pattern, with an elimination rate constant of 1.2 h&minus;1 for IQ and 1.7 h&minus;1 for epi-IQ. The epi-IQ was distributed more widely than IQ by about two-fold. Consequently, the clearance of epi-IQ was greater than that of IQ by about three-fold. The oral absolute bioavailability for IQ was 38%, and, that for epi-IQ, was 13%. Although the systemic exposure of IQ was greater than that of epi-IQ by ~8.7-fold, the clearance of each isomer was similar when administered either orally or intravenously, when normalized for bioavailability. The stereo-specific behavior of the isomers appears to originate from differences in both their tissue distribution and gastrointestinal permeability