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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.

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 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.

By the sterolithography technique and the ferrite plating, we fabricated three types of magnetic micromachines which coated Fe3O4, Co0.39Fe2.61O4, and Co0.45Fe2.55O4, respectively. The stereolithography technique enables one to form the spiral-shape resinous templates and the ferrite plating enables one to coat the ferrites uniformly onto these templates from an aqueous solution. The total machine weight is light because a resin of the template body is almost the same density as water. We verified that the machines swim freely and wirelessly in water by applying a rotational magnetic field. As these machines coated with ferrites have the biocompatibility, there is the possibility of medical microrobots which swim in the human body for medical operations.

A magnetic micro-machine, a minuscule device composed of a cylindrical body with a magnet and spiral blade, swims in liquid under the force of a rotational magnetic field. To obtain a machine capable of swimming through organs and blood vessels for medical applications, it must be designed on a scale below the mm order and retain its swimming capability under highly varied conditions. The swimming properties of a spiral-type magnetic micro-machine were examined under various Reynolds number conditions by altering the kinematic viscosity of the liquid. The machine could swim in liquids with kinematic viscosities ranging from 1.37 to 5/spl times/10/sup 5/ mm/sup 2//s, which translates into a Reynolds number from 430 to 6/spl times/10/sup -7/. The Reynolds number of blood flow is within this range. In addition, the load torque for swimming was studied theoretically and experimentally. The results obtained suggested great promise for the development of a micro-machine that can be put to work inside the human body.