I. Sasada

A new torque transducer using stress sensitive amorphous ribbons

A new torque transducer of the noncontact type employing the magnetostrictive effect is presented. In this torque transducer, two stress-sensitive amorphous ribbons are glued to a torsion bar which is used as a part of the shaft. Unidirectional magnetoelastic magnetic anisotropy is created in each ribbon in such a manner that one of the anisotropies lies along 45° to the shaft axis and another along -45°. The applied torque is detected as a difference in permeability between the amorphous ribbons by an ac bias field. The amorphous ribbon used in experiments is of Fe-Si-B system whose saturation magnetostriction \lambda_{s} \simeq 24\times10^{-6} and I_{s} \simeq 1.5 T. With this torque transducer, instantaneous torque as well as static torque is detected with sufficient accuracy. Due to the easy-to-mount structure, this torque transducer is well suited for the torque control application.

Torque transducers with stress-sensitive amorphous ribbons of chevron-pattern

In this paper, a simplified assembling method is presented by which a reliable and compact torque transducer exhibiting wide dynamic range and good linearity is obtained. The only modification applied to the shaft to obtain the torque transducer is to glue several pairs of stress-sensitive amorphous ribbons of rectangular form or of parallelogram form to the shaft in a chevron-pattern. Experiments are carried out on torque transducers with the nonmagnetic torsion bar to comfirm the theoretical prediction and with the magnetic steel torsion bar to examine the output characteristics and the dynamic response.

Effective shielding for low‐level magnetic fields

An effective method of shielding slowly varying low‐level magnetic fields is presented. The key of this method is the use of soft magnetic materials with a highly rectangular B‐H loop and the application of the shaking field to them. Metglas 2705M amorphous ribbon of about 22 μm in thickness was used in the experiments since it has almost vertical flanks in the dc B‐H loop in as‐prepared state and small coercivity Hc∼0.5 A/m. A shielding factor of the cylindrical case with a copper pipe inside (diameter : 60 mm; length : 100 mm) and with two crossed layers of the ribbon outside was measured against low‐level disturbing fields of 10 Hz applied transversely to the case. Although the shielding factor was as small as 3.5 without shaking, it became higher than 150 under the shaking field of 1 kHz, 2.9 A/m(rms). This value is far better than that with Mumetal or 4‐79 Mo‐Permalloy. A shaking frequency as high as 1 kHz or higher makes it easy to suppress the leakage of the shaking field into the shielded space.

Reduction of Noise in Fundamental Mode Orthogonal Fluxgates by Optimization of Excitation Current

Reduction of noise is a major issue for orthogonal fluxgates, since the main drawback of this kind of sensor is higher noise than parallel fluxgates. Fundamental mode orthogonal fluxgates were successfully proposed to reduce the noise level, thanks to dc bias added to the excitation current. It has been shown that the main reason for noise suppression in fundamental mode orthogonal fluxgates is the reduction of Barkhausen noise obtained with a large dc bias, which makes the excitation current unipolar and avoids reversal of magnetization. Thus, one might believe that a low ac current and a large dc bias are always advantageous. In this paper we will show that this is not always true when this sensor is used in a magnetometer operated in feedback mode. For a given dc bias the 1/f noise will drop when we increase the ac current due to the increment of sensitivity inside the loop. The 1/f noise will reach a minimum level, and then if we further increase the ac current it will rise back up because the increment of Barkhausen noise becomes predominant over the increment of sensitivity. The minimum point is also verified by measurement of circumferential flux-current loop. By properly choosing excitation current parameters, we achieved a 2.5 pT/√Hz noise floor and 7 pT/√Hz noise at 1 Hz. A general rule is finally proposed to easily minimize the noise.

Planar coil system consisting of three coil pairs for producing a uniform magnetic field

A planar coil system that produces a uniform field and consists of three coil pairs has been designed and constructed. The design process involves the numerical solution of an equation based on the filamentary coil current and the truncation of the ratio of coil currents. This process makes it possible to realize the ratio by the coils’ number of turns and then modifying the geometrical parameters to make allowances for the practical cross sections of coil conductors. Although design parameters obtained using this process may not be optimum, the uniformity of the calculated magnetic field is satisfactory for most practical situations. The uniformity of the magnetic field was confirmed by constructing a coil system with an outer diameter equal to 1 m. The predicted area of uniformity (less than 0.01% error), for the proposed design, was six times larger than that obtained using a conventional Helmholtz coil of the same diameter.

Noncontact torque sensors using magnetic heads and a magnetostrictive layer on the shaft surface - application of plasma jet spraying process

A noncontact torque sensor using magnetic heads and a magnetostrictive layer deposited uniformly on the shaft surface is presented. To realize the torque sensor, a new circuit is developed. Using a Ni layer deposited by the plasma jet spraying process, fundamental characteristics of the torque sensor are investigated, and possibility of detecting instantaneous value of the applied torque is demonstrated.

Fine grained Mn–Zn ferrite for high frequency driving

A Mn–Zn ferrite with a grain size of about 2 μm has been developed for the transformer driven at around 1 MHz. The developed ferrite exhibits considerably lower core losses than a conventional Mn–Zn ferrite with a grain size of about 10 μm at a frequency of 0.5 to 2 MHz. The thin-type transformer using the developed ferrite driven at 1 MHz shows a high efficiency of more than 95% at an output power of 10 to 17 W and a much lower surface temperature rise than the transformer using the conventional ferrite.

Planar Inductors Using NiZn Ferrite Thin Plates And The Application To High-freouency Dc-to-dc Converters

New structure planar inductors are developed for miniaturized DC-DC converters. A thin gap is introduced into the sandwich-structured planar inductors between a pair of magnetic plates, in one of which a meander coil is embedded. Due to the thin air gap introduced, the flux density in the magnetic plates becomes uniform, resulting in low iron loss. Planar inductors using NiZn ferrite thin plates are successfully applied to a 10-W-class buck converter operated at 2 MHz. The efficiency is higher than 82%, and the effective volume of the inductor is 0.2 cm/sup 3/ (1 cm square and 2 mm thick). >

High Sensitive Orthogonal Fluxgate Magnetometer Using a Metglas Ribbon

In this paper, performance of an orthogonal fluxgate magnetometer with the use of a narrow Metglas 2714A ribbon is presented. The magnetometer operates in a fundamental mode. In this mode, a direct current bias is added to the alternating current excitation which increases a sensors performance. Experimental results are shown for the U-shaped sensor head of 5 cm length constructed using a 1-mm-wide ribbon. Results are compared with the performance of the sensor head built using an amorphous wire of a similar cross section. High sensitivity as well as a good linearity of the input-output characteristic is observed. The electronic circuit for driving magnetometer is presented where direct current bias switching for reducing offset and drift is implemented to the circuit. Preliminary results of the sensors performance driven by the circuit are presented

Compensation of the thermal drift in the sensitivity of fundamental-mode orthogonal fluxgates

A method is suggested that reduces the temperature coefficient of the sensitivity of fundamental-mode orthogonal fluxgates by an order of magnitude. For the background magnetic fields greater than 20μT, the method provides even better reduction, down to 100ppm∕°C, which is comparable with the temperature coefficient of conventional parallel-type fluxgates operated in closed-loop configuration. The fluxgate prototype has demonstrated a 20-fold reduction of the thermal drift in its sensitivity. The suggested method is solely based on the processing of signals generated by fundamental-mode orthogonal fluxgates in open-loop configuration and does not require any additional hardware. This makes the open-loop fundamental-mode orthogonal fluxgates competitive with closed-loop parallel-type ones in terms of both resolution and accuracy, while still keeping them simpler than the parallel fluxgates.