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This paper describes a GHz range magnetic field measurement of a coplanar waveguide (CPW) by using a magnetic force microscope (MFM) tip to explore a beat signal between a CPW with a 5-μm-wide signal line and a 50-μm-wide ground line and a semicircular exciting coil with a 100 μm diameter. The beating field is produced by supplying a signal current to the CPW and a reference current to the exciting coil. The signal current is fixed at a specific frequency between 0.1 and 7.0 GHz, while the reference is adjusted to produce a beat with a frequency near the cantilever resonance frequency. As the MFM tip is excited by the beat, the gradient of magnetic field can be successfully observed above the CPW surface for a signal frequency up to 7.0 GHz. The gradient of magnetic field is minimized near the two gaps, but is maximized near the center of the signal line. These results demonstrate that the tip interacts closely with the RF magnetic near-field of the CPW through the beating field, and exploring a reference RF field can detect the distribution of RF magnetic fields radiated from an RF circuit component with a very high spatial resolution.

We present a 3-D magnetic-near-field scanner and a magnetic-near-field probe with a sensor head consisting of a 60 × 60 μm2 on-chip coil. The 3-D scanner consists of an XY stage that positions the device under test with an accuracy of 10 μm and a Z stage that positions the probe and provides yaw-, pitch-, and roll-angle adjustment. The probe outputs are measured by a spectrum analyzer. Furthermore, we demonstrate and clarify the performance of a 1-μm-thick Co85Zr3Nb12 soft magnetic film as a noise suppressor. The film is integrated into a test element group (TEG) chip for next-generation cell phone handsets. The TEG chip is based on a long-term-evolution class complementary metal-oxide-semiconductor radio-frequency integrated circuit receiver. The CoZrNb film suppresses radiated emission by more than 15 dB. These results demonstrate the expected performance of the scanner and probe and the usefulness of the 1-μm-thick CoZrNb film as a noise suppressor.

This paper describes our study on high-resolution measurements of the distribution of the radio frequency (RF) magnetic near field from a coplanar waveguide (CPW) with a size similar to power and ground lines in radio frequency integrated circuit chips using a magnetic force microscope tip and amplitude modulation of the line current. Cantilever resonance frequency modulation of approximately 25 kHz supplies the CPW with current and carrier frequencies up to 0.1 GHz. The CPW has a signal line width of 3 μm and a ground line width of 50 μm. The oscillation amplitudes of the tip with and without a DC magnetic field indicates that the distribution of the RF magnetic near field in the proximity of the CPW can be observed for a carrier frequency up to 0.1 GHz. This result also suggests that this method has potential as a new technique for high-resolution RF field measurements.

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.

We have developed a transmission-line thin-film sensor by using a ceramic substrate with high permittivity (er=115) and amorphous CoNbZr film. We fabricated a coplanar line type sensor with CoNbZr film (25 x 25 mm and 8 μm in thickness). A phase change of 150 degrees/Oe was achieved, which was more than a 10-fold improvement compared with that for a previously reported sensor using a Teflon substrate (er=5). The signal-to-noise ratio improved and was about 3 times higher than that for the previous sensor when a small AC field (270 pT, 11 Hz) was applied.

We have developed a very sensitive transmission line-type thin film sensor. The sensor, consisting of a coplanar line, SiO2 film, and amorphous CoFeSiB film, was fabricated by sputtering, lift-off, and lithography processes. A phase change of 45 degrees/Oe was obtained at 1 GHz. We arranged two-dimensional stepping motors and developed a scanning system for the sensor. Aluminum samples with through holes were examined by using the eddy current method. Aluminum wires with small Fe balls as impurities were tested by measuring the DC field.

We have developed a jaw tracking system with wireless resonated markers. The system consists of two resonated markers, driving coil, 40 pickup coils, DA converter, and AD converters. The two resonated markers were composed of a coil with NiZn ferrite and tip condenser. We attached to one marker on the incisor and the other on the forehead. Position accuracy of within 1 mm was achieved when the fabricated jaw model was moved about 40 mm. This system is available for tracking of reasonable jaw movement of normal subjects without disturbing the physiology.

A detection technique having an accuracy of better than 1 mm is required for body motion analysis in the field of medical treatment. A wireless magnetic motion capture system is one such effective detection technique. We propose a candidate system using an LC resonant magnetic marker (LC marker). Previous studies have showed that the system is capable of repeatable position detection accuracy of better than 1 mm if the system has an adequate signal-to-noise (S/N ratio). However, there are some cases in which the detection results include unignorable errors because some approximations, e.g. a magnetic dipole assumption of the LC marker, are applied to solve the inverse problem to determine the position and orientation of the LC marker. Therefore, a numerical analysis is employed to realize a motion capture system having a high detection accuracy. To elucidate the problem of detection error, the influence of variations in the sizes of the LC marker and the pick-up coil are considered in the numerical simulation. After studying the analysis, the main cause of detection error is determined to be the size of the pick-up coil rather than the size of the LC marker. It was also is found that a pick-up coil measuring 10 mm in diameter with a wound coil width of 1 mm achieves a detection accuracy of better than 0.1 mm.

We developed a very sensitive high-frequency carrier-type thin film sensor with a sub-pT resolution using a transmission line. The sensor element consists of Cu conductor with a meander pattern (20 mm in length, 0.8 mm in width, and 18 μm in thickness), a ground plane, and amorphous CoNbZr film (4 μm in thickness). The amplitude modulation technique was employed to enhance the magnetic field resolution for measurement of the high-frequency field (499 kHz), a resolution of 7.10×10−13 T/Hz1/2 being achieved, when we applied an AC magnetic field at 499 kHz. The phase detection technique was applied for measurement of the low frequency field (around 1 Hz). A small phase change was detected using a dual mixer time difference method. A high phase change of 130°/Oe was observed. A magnetic field resolution of 1.35×10−12 T/Hz1/2 was obtained when a small AC field at 1 Hz was applied. We applied the sensor for magnetocardiogram (MCG) measurement using the phase detection technique. We succeeded in measuring the MCG signal including typical QRS and T waves, and compared the MCG with a simultaneously obtained conventional electrocardiogram (ECG) signal.

We developed a very sensitive high-frequency carrier-type magnetic-field sensor with a sub-pT resolution using a transmission-line-type sensor. Meander-type sensor elements using amorphous CoNbZr films (4μm in thickness), Cu conductor with a meander pattern (30 mm in length, 1.0 mm in width, 18 μm in thickness), and a ground plane were fabricated. We obtained a magnetic field resolution of 9.1×10-13 T/Hz1/2 at 1 Hz. The detectable magnetic field was limited by the 1/f noise. We detected a magnetocardiogram (MCG) signal of heartbeats with the sensor.

We visualized electromagnetic-energy flows by using newly developed electro-optic probes, which cause little interference with the surrounding electromagnetic fields. Amplitudes and phases of all electric- and magnetic-field components were measured near a coupled line and a patch antenna by the probes. The time-varying Poynting vectors near the objects were evaluated with the data and were visualized. The energy flows that are caused by crosstalk of the coupled line and that are radiated from the antenna are presented. This is the first visualization of Poynting vectors that are evaluated with only experimental data in near-field regions.

The present paper reports the principle of a wireless magnetic motion capture system that uses multiple LC resonant magnetic markers and demonstrates its application. Small and lightweight markers (4 mm in diameter, 10 mm in length, and 0.63 g in weight) use a soft ferrite core and a coil, representing a minimal LC circuit with no battery, driven wirelessly by electromagnetic induction. The markers are given respective resonant frequencies ranging from 150 to 450 kHz. The magnetic signal of the marker is detected by a pick-up coil array consisting of 25 pick-up coils. The markers are excited by a superposed wave corresponding to all of the resonant frequencies, while the voltage signals induced through pick-up coils are separated in a frequency spectrum by FFT analysis. Regardless of the number of markers, the voltage amplitude for each resonant frequency can be easily obtained simultaneously, and thus the proposed system can detect multiple markers. In addition, the positional error of the system caused by a mutual inductance between the exciting coil and the LC marker was examined. The impedance change of the exciting coil due to a resonance of the LC marker was found to perturb the strength of the magnetic field used for marker excitation. The closer a marker approaches the exciting coil, the larger it becomes. This fluctuation induces an error in the marker signal, which is measured by the pick-up coils and is necessary for positional calculation. Then, considering the mutual inductance, a compensatory process was employed for positional calculation in order to improve the positional accuracy. After compensation, the absolute positional accuracy was determined to be less than 2 mm within 140 mm of the pick-up coil array.

We developed a very sensitive high-frequency carrier-type magnetic field sensor with a pT resolution using a transmission-line-type sensor. Meander-type sensor elements using amorphous CoNbZr films were fabricated. We obtained a magnetic field resolution of 3.0 x 10-12 T/Hz1/2 at 1 Hz. The detectable magnetic field was limited by the 1/f noise. We detected the magnetocardiogram (MCG) signal by using the sensor.

We describe a new permeameter to evaluate all components of a permeability tensor. The permeameter consists of a shorted microstrip line and a revolving coil, which can operate well up to 300 MHz. All muij r (i, j = x, y, and z) of a relative permeability tensor of a magnetic thin film were evaluated by the permeameter. The measurements show that the sample has large off-diagonal components compared with diagonal ones, indicating that the examination of such off-diagonal components by the permeameter can be used to design new devices with high accuracy.

A micropump with spiral-type magnetic micromachine was fabricated. When a rotating magnetic field was applied, the machine rotated and pumped a surrounding liquid. We experimentally examined the basic properties of this pump. We found that the pressure and the flow rate could be controlled by the rotating frequency, and this pump could work under wide range kinematic viscosity. In addition, we proposed a disposable pump system using the machine. When a plate installed a fluid channel and the machine was set on a stage for generating a rotating magnetic field, the machine worked as the pump.

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.

We developed a very sensitive high-frequency carrier-type magnetic field sensor with a sub-pT resolution using a resonating transmission line. Meander-type sensor elements using amorphous CoNbZr films were fabricated. We obtained a magnetic field resolution of 7.4 x 10-13 T/Hz1/2 at 501 kHz. The detectable magnetic field was limited bythe noise caused by nonlinear magnetic excitation. We analyzed the quality factor of the resonance for enhancementof the signal-to-noise ratio.

A giant magnetoimpedance sensor with a step-like impedance property was obtained in the case of amorphous Co85Nb12Zr3 soft magnetic thin film in a rectangle shape with an in-plane uniaxial easy axis in a direction nearly 60 degrees relative to the width direction of the element. It was shown experimentally that the magnetic field in which the step-like impedance change occurs has an almost constant value with a standard deviation in the microtesra (μT) range. The magnetic field in which the step-like change occurs includes information on the external magnetic field. To realize a magnetic field sensor with an accuracy of nT/Hz1/2 by using this step-like phenomenon, a differential circuit was studied in combination with an alternating bias field in the kilohertz (kHz) frequency range. The aim of the differential circuit was to make the driving circuit into a digital logic circuit, by using pulse signals timed to coincide with the step-like changes. The alternating bias field increases the sampling number, because of the step-like changes in the bias frequency. The aim of the ac bias is to improve the sensor accuracy by using an averaging effect. This paper reports a first trial of the method. As a result, a high-linearity sensor without hysteresis was obtained, which had a linearity error of less than 0.5% in the range of ±100 μT. A measurement accuracy of 460 nT was achieved with a 20 Hz time constant of the output low pass filter (LPF).

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.

This paper presents a new type of optical magnetic field probe designed to detect magnetic near-fields with high accuracy up to 15 GHz. The probe head consists of a loop antenna element and CdTe electrooptic crystals. The probe using CdTe has a resonant frequency higher than that of a previous probe using LiNbO/sub 3/ because CdTe has a dielectric constant lower than that of LiNbO/sub 3/. Through an optical technique, a probe doubly loaded with CdTe can work as a conventional double-loaded loop probe without metallic cables or an electrical hybrid junction. We examined probe characteristics up to 20 GHz. We confirmed that the probe could measure magnetic fields near a microstrip line with high accuracy in the gigahertz range.

A novel motion capture system using magnetically coupled LC resonant marker have been developed. This system composed from the LC marker, a driving coil and a pickup coil array. The marker consists only of an inductor and a capacitor without battery or electric wires, and driven wirelessly by the action of electromagnetic induction. The position accuracy was around 2 mm when the marker was located within the space of 50 mm apart from the pickup coil array. The system is applicable for highly accurate motion capturing without magnetic shielding because the system is free from the earth field. Additionally, it has a possibility of a multi-point motion capturing because the system allow markers to have an individual frequency band.

We designed high-frequency-carrier-type thin-film sensors to obtain high sensitivity. We consider the relation between the sensor form and the sensor to be characteristic. When the sensor area was fixed to 5 mm × 5 mm, and the sensor interval was 30 μm, the width of the sensor with the best sensitivity was set to 200-400 μm. We fabricated a meander-type sensor element, and compared the calculated and measured result. It was found that-they mostly in agreed.

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.

We propose a new type of optical probe designed to detect magnetic near-fields with high accuracy up to the gigahertz range. Its probe head consists of a loop antenna element doubly loaded with electrooptic crystals. Using optical technology, it realizes hybrid operation of a conventional double-loaded loop probe and requires no metallic cables or electrical hybrid junction. We examined probe characteristics for magnetic field detection up to 10 GHz. We confirmed that the probe can measure magnetic fields near a microstrip line with high accuracy in the gigahertz range and can suppress influence of electric fields.

We developed a jaw-tracking system consisting of two magnets and biaxial fluxgate sensors. One magnet is fastened to a tooth in the bottom jaw of the subject and another is fastened to the subject’s forehead. The system can naturally detect movement of the jaw as a rigid body. We fabricated sensor arrays with separate upper and lower parts in order to obtain good position accuracy. Positional accuracy to within 0.1 mm was achieved as a rigid body using a jaw model. Six degrees of freedom and 100 Hz sensing cycles were achieved using one rigid marker (composed of two magnets), and achieved position accuracy to within 0.3 mm.

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.

The swimming properties of a spiral-type magnetic micro-machine were analyzed theoretically using 3D finite volume method. The basic equations of incompressible viscous fluid flow were integrated. The flow field around the micro-machine was calculated to estimate the swimming velocity, thrust, drag, and load torque of a spiral-type magnetic micro-machine. Good agreement was obtained between the experimental and theoretical results in a low Reynolds number. Therefore, the 3D analysis method without any fitting parameters was judged to be established.

We developed a new system to capture jaw movement. It consists of two magnets and biaxial fluxgate sensors. A magnet is fixed to a tooth in the bottom jaw of the subject and another is fixed to the subject's forehead. The system can naturally detect movement of the jaw as a rigid body, because it does not require such attachments as a clutch inside the mouth or a magnetic field sensor array in contact with the head. In this paper, we investigate five error sources of the jaw-tracking system, using a jaw model, and report the achievement of a positional accuracy of 1.5 mm and an axial accuracy of 2 degrees. Positional accuracy within 2 mm is achieved as a rigid body.

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.

Electro-deposition of Fe–Tb–O films was attempted using ac currents with low frequency. The film composition, especially Tb content of films, was found to be sensitive to the concentration of complex agent, KNaC 4 H 4 O 6 : when KNaC 4 H 4 O 6 =283.47 mM, plated films with very high Tb content reaching 29 at.% were obtained, in spite of the difficulty in electro-deposition of Tb owing to its very low catalytic activity. Coercivity H c and squareness ratio M r / M S of films varied considerably depending strongly on the intensity of ac current i : when i =0.67 A/dm 2 , films with relatively soft magnetic properties of H c =29O e and M r / M S =0.93 were realized.

We have developed a new planar flux sensing coil using multilayer printed wiring board fabrication technique. The coil is useful for high frequency magnetic flux sensing because the coil is sensitive to the magnetic field and insensitive to the electric field. A 1 MHz–3.5 GHz broad bandwidth thin-film permeance meter is developed by using parallel plates with short plate and shielded loop pickup coil combination. We investigated the upper frequency limit of permeance measurement is given by the minimum value of standing wave position at the center of pickup coil.

A remote temperature sensing system was investigated for use, local such as inside the human body. The system was divided into a magnetic generating part, temperature sensing and temperature information generating part, and temperature information receiving part. A ferrite having a low Curie temperature was used in the temperature sensing part. To receive and transmit the temperature information effectively, LC resonance circuits were used in the system. The resonance frequency of 145 kHz to 220 kHz was varied in the range of 58°C to 66°C. From this experiment, we determined that temperature could be measured at the local site using this system.

Improvement of magnetic thin-film inductors for RF monolithic microwave integrated circuits (MMICs) is discussed. Surface planarization reduced the surface roughness down to R/sub a/=1.2 nm, which enhanced the quality factor by 14% over a nonplanarized inductor. The orthogonal bar slit pattern was the best among the fabricated slit patterns, L=7.55 nH (+12% of the air core), R=6.80 /spl Omega/ and Q=7.09 (+9%) were obtained for the orthogonal bar slit pattern (slit width=0.75 /spl mu/m) with surface planarization.

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.

Amorphous FeCoSiB films with high saturation magnetostriction and excellent soft magnetic properties were studied to determine their strain sensitivity. The films were subjected to strain by bending of their substrates, which caused a change in the magnetic anisotropy of films via magnetoelastic coupling. The films exhibited a figure of merit F ≡ (θμ/θe)/μ (change in film permeability μ per unit of strain e) of 1.2 × 105, which is comparable to that of amorphous ribbons. To study the use of the magnetostrictive films as strain sensor elements, we prepared meander-patterned films by means of the photolithography and ion milling processes. The impedance change in the patterned films when strain was applied was measured in the frequency range from 1 MHz to 1 GHz. Reflecting the large value of F, the high-frequency impedance of the films was changed considerably: a change in impedance of 46% was observed at 100 MHz when a strain of 300 × 10-6 was applied. It is also demonstrated that, by using the strain-dependent impedance, a small strain of 1 × 10-7 can be detected by means of the film pattern.

This study reports the performance of a high-frequency carrier-type thin-film magnetic field sensor that uses impedance change at high frequencies. To obtain high resolution, we reduced environmental electromagnetic noise and used high resolution instruments. A voltage change ratio (similar to the MR ratio) of 26.7% was achieved when ac carrier frequency was 400MHz. The resolution of the sensor was dc 2 × 10-4 Oe and ac 8 × 10-5 Oe, respectively.

A wireless magnetic motion capture system using an LC resonant magnetic marker was developed and has been studied. The positional error of the system caused by mutual inductance between the exciting coil and the LC marker was examined. It has been found that the impedance change of the exciting coil due to a resonance of the LC marker perturbs the strength of the magnetic field which is used for marker excitation. The more a marker approaches the exciting coil, the larger it becomes. This fluctuation induces an error in the marker signal which is measured by the pickup coils and is necessary for positional calculation. Then, the compensatory process in consideration of the mutual inductance has been employed for positional calculation in order to improve the positional accuracy. From the compensation, the absolute positional accuracy is less than 2 mm within 140 mm of the pickup coil array