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This paper describes a cantilevered magnetic actuator driven by magnetostriction in a low magnetic field. The dimensions of the two-layered actuator were 1 mm × 5 mm. Amorphous FeSiB was used as the magnetostrictive material, and polymide film with a thickness of 30 μm was used as the substrate for the experiment. The theoretical formulas for the amount of the displacement and for the force of the actuator were obtained. The calculated values of the displacement and the force were compared with experimental values, and were found to be in close agreement with them. It was also found that the obtained formulas were suitable for the design of the cantilevered actuator.

Improvement of the sensitivity of a high-frequency carrier-type (HFC-type) magnetic field sensor through the use of an edge extension structure is reported. The HFC-type magnetic field sensor is composed of a rectangular CoNbZr thin film with a coplanar-structure Cu thin film as an electrode. The edge extension structure causes reduction of the sensor's demagnetization field effect. A variation in the sensor impedance was obtained as a function of the external magnetic field for edge extension lengths ranging from X= 0 mm to X = 1 mm. The length of the sensor was 1 mm, the thickness was 2 μm, and the widths were 20 and 80 μm. It was demonstrated that the gain of an HFC-type magnetic sensor with an edge extension length of X = 1 mm was three times higher than that of a sensor with an edge extension length of X= 0 mm. This result shows that an edge extension structure improves the sensitivity of an HFC-type magnetic field sensor.

The high-frequency carrier-type (HFC-type) magnetic field sensor realizes very high sensitivity without any cooling apparatus for the sensor element. An important technique for obtaining high sensitivity is the use of a high-frequency current applied to the sensor element. The maximum sensitivity is obtained at frequencies up to the ferromagnetic resonance of the sensor magnetic thin film; for example, hundreds of megahertz for amorphous CoNbZr films. It is becoming important to study high-frequency circuits for driving HFC-type magnetic field sensors in order to achieve any practical applications such as nondestructive testing or biomedical applications. In this paper, a method of reflection signal measurement is studied in order to measure alternating magnetic fields with very small magnitude. A theoretical formula based on an equivalent circuit model was obtained for the relation between the sensor property and measurement sensitivity. An experimental confirmation was carried out by comparing this formula with experimental results. Finally, the measurement of a small alternating magnetic fields was effected by combining reflection signal measurement with the carrier-suppressing method.

This paper describes a cantilevered magnetic actuator driven in a low magnetic field. Magnetostriction was used as a driving principle in this study. We studied the displacement of the cantilevered magnetic actuator by the magnetostriction. FeSiB with the thickness of 0.7 μm was used as a magnetostrictive thin film. The dimensions of the cantilever were 1 mm×5 mm. We used polyimide films with thicknesses of 30 μm and 7.5 μm and Ni foil with a thickness of 5 mm as substrates. As a result, the cantilevered magnetic actuator was able to function in a magnetic field of 10 kA/m. The maximum displacement of the cantilevered magnetic actuator was about 40 μm with an Ni substrate.

Application of a magnetic actuator to a capsule endoscope is proposed. Capsule-type magnetic actuators were fabricated and their motion properties were investigated in a silicone tube and in the intestine of a pig. The dummy capsule is 11 mm in diameter and 40 mm in length. This magnetic actuator is composed of a permanent magnet inside the dummy capsule and spiral structures outside it. The permanent magnet is magnetized in the direction of the diameter. When a rotational magnetic field is applied, the magnetic actuator rotates and moves wirelessly. The velocity of capsules with top spirals was examined in a silicone tube. In addition, a motion test was conducted in the intestine of a pig. The actuator can pass through the small and the large intestines over distances of 450 mm and 400 mm, respectively, in less than 150 s. The capsule can pass out of the bag-shaped section of the large intestine. This result shows that the actuator has the potential to be used in the guidance system of a capsule endoscope.

A micropump with a spiral-type magnetic micromachine was fabricated. The magnetic micromachine was composed of a permanent magnet and a spiral coil. When a rotating magnetic field was applied, the machine rotated and produced a thrust force in a liquid. However, the machine remained still and pumped the liquid at the point of equilibrium between the thrust force and a force created by the field gradient. We experimentally examined the basic properties of the pump, such as the flow rate and pressure. As a result, we found that the latter two properties can be controlled by adjusting the frequency of the rotating magnetic field. The pump was able to produce a maximum pressure of 116 Pa and a flow rate of several ml/min.

A magnetic actuator for colon endoscope navigation was fabricated. We conducted motion tests of the actuator in the small intestine of a pig and the large intestine of a living dog. The actuator is composed of a permanent magnet and a spiral structure, and is attached to the pointed end of an imitation endoscope. When a rotational magnetic field is applied, the actuator rotates and moves in the intestine. It was able to draw the imitation endoscope forward without injuring and changing the shape of the intestine. This result shows that the actuator has the potential to be use for colon endoscope navigation.

By using a ferrite plating technique and stereolithography, we fabricated the medical magnetic micro-machines that plated ferrites on a spiral-structured resinous substrate. We plated a magnetite (Fe3O4) film with good biocompatibility and CoxFe3-xO4 films (CO0.39Fe2.61O4 or Co0.45Fe2.55O4) having large coercive force onto template bodies at 90°C for 5-8 hours, and fabricated solid-state-based ferrite-coated micro-machines with biocompatibility and light mass density. All the micro-machines were able to swim in water when an external rotational magnetic field was applied.

A magnetic micro-machine with a heating device, which can run in gel, was fabricated. The machine is composed of a screw tip, a rod-shaped NdFeB magnet, and a rod-shaped permalloy unit. The machine is 2 mm in diameter and 19 mm in length. The NdFeB magnet is magnetized to the direction of the diameter. When a rotational magnetic field with rotation frequency of 10 Hz is applied, the machine rotates and moves in agar. In addition, a machine placed in an alternating magnetic field, at 100kHz, produces heat by iron loss. It was demonstrated that the machine can move 20 mm and be heated above 50°C. This means a wireless heating mechanism could be obtained using an alternating magnetic field and a rotational magnetic field. This machine has the great possibilities for local medical operations for cancer.

The fundamental swimming properties of spiral-type magnetic micro-machines were investigated in detail by constructing four micro-machines with different structures. These micro-machines are able to swim in various liquids with kinematic viscosities ranging from 1.37 to 1000 mm2/s. This result suggests that the micro-machines have potential medical uses. In particular, they can swim against the stream in a liquid whose the velocity is comparable to the that of venous blood.