S. Hashi

Wireless Magnetic Position-Sensing System Using Optimized Pickup Coils for Higher Accuracy

With the aim of improving the detection accuracy of a wireless magnetic position-sensing system using an LC resonant magnetic marker, a pickup coil with an optimal size (10 mm in diameter × mm thick), as calculated by a previous simulation study, was used and tested in this paper. Our study confirmed that positional errors were reduced to a submillimeter order in the area within y=120 mm from the pickup coil array. On the contrary, in the area outside y=130 mm from the pickup coil array, the errors increased by about 0.5-2 mm compared to the results for the previous pickup coil size (25 mm in diameter × 2 mm thick). Regardless of the size of the pickup coil, however, compensation can be made for these positional deviations, including the influence of the mutual inductance between the LC marker and the exciting coil. After application of the compensation process, the detection results were corrected approximately to the actual positions of the LC marker.

Effects of easy axis direction on the magnetoimpedance properties of thin films with uniaxial anisotropy

In this paper, we investigate the effects of easy axis direction against magnetoimpedance elements on stepped impedance properties. The angle between the easy axis and the element width is changed from 0° to 90°, and we examine the resulting impedance profiles. The magnetic field at which impedance is highest shifts to a lower field with increasing easy axis angles, which can be explained by a bias susceptibility theory. On the other hand, stepped impedance changes appear for the elements with an easy axis angle in the range of 35°–75°. We confirmed the stepped impedance property through our observations that those impedance jumps occur at transitional points of domain structure between single and multi domains by domain observations. The area where the impedance shows relatively low value and the element has multiple domains becomes narrower with increasing easy axis angles, which can be explained qualitatively on the basis of a simplified domain structure model.

Remote temperature sensing system using reverberated magnetic flux

A remote temperature sensing system was investigated. The system can measure the temperature by applying an external magnetic flux to the sensor and by receiving a flux at the resonant frequency corresponding to the temperature at the sensor. The sensor does not need a power supply within it and is only composed of a temperature sensitive ferrite core and a wound coil. The inductance of the core varied from about 8-18 mH in the temperature region of 35-55/spl deg/C. The induced voltage, /spl Delta/V by the sensor was about 10 mV for a 260 mm length between the transmitter and receiver. The system was successfully operated in our investigation.

Study on the deformation of 3%Si-Fe single crystal with magnetic field being deviated from [001]

We have investigated the magnetostriction and the magnetization process of 3%Si-Fe single crystal with (110) parallel to the surface, when the direction of magnetization is deviated from [001]. It was found that large contraction and expansion occurred as a result of magnetostriction in the magnetization process, even if the deviation angle was small. Complicated magnetic domain structures were observed with external field being applied. The behavior of magnetostriction corresponds to changes of magnetic domain structure. On the basis of the principle that no magnetic pole appears at domain walls, a model of domain structure is proposed. Using the model, the deformation behavior was explained well.

A Pushing Force Mechanism of Magnetic Spiral-type Machine for Wireless Medical-Robots in Therapy and Diagnosis

In this paper, we present a pushing force mechanism in a magnetic spiral-type machine for use in therapy and diagnosis. Non of the current spiral-type machines can create a pushing force. Thus, their locomotion or tasks are controlled by magnetic field strength and driving frequency. However, the proposed mechanism increases the thrust force on the robot itself in the working space without field controls. The developed pushing force mechanism uses a magnetic suspension structure based on two magnets between the two spiraltype machines. Through this mechanism, the two spiral-type machines act independently via a rotating magnetic field. Thus, the different thrust forces between the two machines create a variation of the magnetic repulsive force in the magnetic suspension. Therefore, the combination of the two thrust forces and the magnetic repulsive force become a total propulsive force. The prototype of the mechanism increased the total thrust force by approximately 3.6 times for locomotion and generated a maximum pushing force of 0.345 N.

Actuation of Novel Blood Pump by Direct Application of Rotating Magnetic Field

This paper presents a magnetic centrifugal pump, driven by an external rotating magnetic field, for use in artificial heart-assist blood pumps. The magnet rotor in the pump is synchronized to a rotating magnetic field, which then causes the fabricated impeller to produce a centrifugal force in the pump. Because the pump is driven by the direct application of an external rotating magnetic field, the proposed pump does not require a shaft or mechanical bearings. Thus, the proposed mechanism and external driving source give the pump the advantages of compact size; wireless, battery-free operation; heat-free operation; and minimal risk of bacterial infections. The pump weight, length, and diameter are 34 g, 35 mm, and 20 mm, respectively. The compact size and performance make the device suitable for use in pediatric cardiac assistance pumps.

Centrifugal Force Based Magnetic Micro-Pump Driven by Rotating Magnetic Fields

This paper presents a centrifugal force based magnetic micro-pump for the pumping of blood. Most blood pumps are driven by an electrical motor with wired control. To develop a wireless and battery-free blood pump, the proposed pump is controlled by external rotating magnetic fields with a synchronized impeller. Synchronization occurs because the rotor is divided into multi-stage impeller parts and NdFeB permanent magnet. Finally, liquid is discharged by the centrifugal force of multi-stage impeller. The proposed pump length is 30 mm long and19 mm in diameter which much smaller than currently pumps; however, its pumping ability satisfies the requirement for a blood pump. The maximum pressure is 120 mmHg and the maximum flow rate is 5000ml/min at 100 Hz. The advantage of the proposed pump is that the general mechanical problems of a normal blood pump are eliminated by the proposed driving mechanism.

A Method for Acquiring the Torque of a Magnetic Pump

A floating magnetic rotor is synchronized to a rotating magnetic field in the developed pump. We cannot measure or calculate the magnetic torque using a general measurement method because the angle theta (θ) represents the unknown factor between the magnetic field and the magnetic moment on the magnetic rotor. We have converted the relationship between the rotating magnetic field and the rotation of the magnetic rotor to an electrical signal using Faradays law. Converted signals have a phase difference that is converted to the angle theta (θ) in the magnetic torque. This has allowed us to calculate the magnetic torque.

Effects of DC Bias Current on Behavior and Sensitivity of Thin-Film Magnetoimpedance Element

We investigated the behaviors and sensitivity of thin-film magnetoimpedance elements having an easy axis angle of 0°–45° when applying dc bias current directly to the elements. All elements show symmetric impedance profiles with respect to the impedance axis without dc bias current, while their profiles become asymmetric with dc bias current. This appearance of the asymmetric property on the impedance profiles indicates that the shape of cross section of the element has asymmetric configuration. On the other hand, when the easy axis angle is relatively small, the sensitivity for field detection is enhanced with a small dc bias level, while a stronger bias level is required for the element with a larger easy axis angle. The obtained results show a potential to optimize the sensor properties by dc bias current with small intensity in case that design properties are not obtained in the fabrication process.

Position Sensing System of Nasogastric Tube Using Long LC Resonated Marker

A position-detecting system made up of a nasogastric tube using a wireless LC resonated magnetic marker has been developed. The marker, consisting of an inductor and a capacitor without battery or electric wires, was installed inside a commercial nasogastric tube. A positioning accuracy within 7.1mm was obtained when the marker inside the tube was parallel translation to 100mm. The marker inside the tube was roughly tracked in the esophagus and trachea of a human model.