K. Mohri

Review on recent advances in the field of amorphous-metal sensors and transducers

Recent researches and developments of applications of amorphous ribbons and wires to sensors and transducers are reviewed. Various sensitive and quick response magnetic sensors with very small amorphous cores have been developed corresponding to strong demands in the fields of information devices, automobiles, power motor drives, industrial robots, and industrial measurement instruments. Relationship between amorphous material properties and the suitable applications to sensors and transducers, the basic principle of amorphous sensor constitutions, and the advantageous points of amorphous sensors are represented.

Large Barkhausen effect and Matteucci effect in amorphous magnetostrictive wires for pulse generator elements

The mechanisms producing the sensitive large Barkhausen effect and the Matteucci effect in as-prepared amorphous magnetostrictive wires are investigated using colloid technique domain observations and Sixtus-Tonks domain propagation characteristics. Theoretical analysis of the pulse height of induced voltage at the pick-up windings and between both ends of the wire are made. This analysis is compared with experimental results. The Matteucci effect was remarkably improved by twisting or twisting then annealing the as-prepared wires. Jitter-less pulse generation is realized in the latter case.

Jitter-less pulse generator elements using amorphous bistable wires

New jitter-less pulse generator elements are presented using amorphous magnetostrictive wires. These elements induce sharp voltage pulses with ∼ 6V/cm2.Oe.turn due to the large Barkhausen jumps and with ∼ 6V/cm3.Oe due to the Matteucci effect using external ac fields of more than 0.1 Oe at frequencies between 0.01 Hz - 10 k Hz. Jitter of the pulse inducing phase is less than 1/10 and the pulse height is about twice that of Wiegand wires, respectively. The critical field of the large Barkhausen jump is controlled by heat treatment, etching, or twisting the wires. These wires are expected to be useful for high-performance pulse generator elements for high resolution rotary encorders by combining them with magnet ring, torque sensors, proximity sensors and magnetometers.

Large Barkhausen discontinuities in Co‐based amorphous wires with negative magnetostriction

Magnetic properties, such as domain patterns and anisotropy, were measured for negative magnetostrictive Co‐Si‐B amorphous wires exhibiting large Barkhausen discontinuities and the results are compared to those of Fe‐Si‐B wires with positive magnetostriction. The Co‐based wire was found to have a bamboolike domain structure at the wire surface. It was also shown that the amorphous wires prepared by the in‐water quenching technique store tensile stress in the radial direction. The magnetostrictive anisotropy due to residual stress will produce an axial component of magnetization in conjunction with the two‐dimensional geometry of wires making both Co‐ and Fe‐based wires exhibit large Barkhausen discontinuities along the axis of the wire.

Bistable magnetization reversal in 50 µm diameter annealed cold-drawn amorphous wires

Amorphous magnetostrictive 50 μm diameter Fe 77.5 Si 7.5 B 15 wires exhibiting square and bistable hysteresis loops have been obtained by field-tension annealing and flash annealing treatments of cold-drawn as-quenched wires. Highest switching field, 1.3 Oe, and domain drive field, 0.5 Oe, for annealing temperature 330 C , time 30 min, axial tension 150 Kg/mm2and axial field 200 Oe are an order of magnitude improvement over the as-quenched (AQ) state. Corresponding induced peak voltage is 0.5 mV/turn with exciting sinusoidal field 2 Oe and 60 Hz. Shorter pulse generation elements (≈ 2 cm) than for AQ wires (≈ 6 cm) were realized with 0.5 mV/turn peak voltage. Maximum squareness ratio is close to unity, twice that of AQ (125 μm) wires.

Sensitive force transducers using a single amorphous core multivibrator bridge

New sensitive linear-type force transducers are presented using a single amorphous core multivibrator bridge with a dc output. These amorphous-core transducers, in which annealed Metglas 2605A ribbon-wound cores with lumped windings are used, have high linearity (0.5 %FS), high stability against temperature variation (0.02 %FS/°C), high maximum operating temperature (200°C), and high output voltage (350 mV) compared with conventional unbonded resistance wire strain gages and semiconductor transducers. The amorphous-core force transducers are considered to be suitable for application in industrial automatic control under high temperature and high noise level conditions.

Dynamics and relaxation of large Barkhausen discontinuity in amorphous wires

Domain wall processes (domain wall configuration, propagation, and collapse) in magnetostrictive amorphous wires of the composition Fe/sub 77.5/Si/sub 7.5/B/sub 15/ were investigated. The wires were held under tensile stress (up to 1700 MPa in the case of as-quenched). The domain wall length and normal mobility (or damping) as functions of applied stress were found experimentally and from an ellipsoidal domain model. This allows the losses to be separated into eddy current and spin relaxation contributions. It was demonstrated that the spin relaxation contribution to the total damping parameter becomes dominant with increase of tension and leads to a dramatic decrease of the wall mobility. This is the reason cold-drawn and then tension-heated wires with high residual stress exhibit a much lower mobility in spite of the smaller diameter. The process of domain collapse at a collision of two domain walls is accompanied by a very sharp voltage pulse. It is shown that during the collapse the domain is affected by a growing internal magnetic field connected with an excess of domain surface energy in comparison with magnetostatic energy. >

Misch metal-Fe-B melt spun magnets with 8 MGOe energy product

The magnetic and structural properties of melt spun MM-Fe-B ribbons, where MM stands for misch metal, were examined. It has been shown that the MM 16 Fe 75 B 9 ribbon can exhibit a coercive force of 9.4 kOe and an energy product of 8.1 MGOe when it was quenched at the optimum rate of 20 m/sec, in terms of quenching wheel surface velocity. Microstructural and X-ray analysis revealed that the optimum-quenched ribbons consist of grains with size from less than 10 nm to 300 nm, and have c-axis orientation in the free surface. The plastic magnets made of the optimum-quenched ribbons have been shown to exhibit a coercive force of 7.6 kOe and an energy product of 4.4 MGOe, which compare favorably to anisotropic ferrite magnets.

Magnetometers using two amorphous core muitivibrator bridge

Accurate and quick-response type magnetometers are presented using two-amorphous-core multivibrator bridge with a dc output. As-prepared zero-magnetostrictive amorphous ribbons of Fe 4.7 Co 70.3 B 15 Si 10 with 1 mm width are used in straight form for sensing of absolute value of fields or field difference. In these two-core type magnetometers, sensitivity is about eight times that of one-core type magnetometers and the minimum detectable field is about 10-5Oe. Temperature stability and flux change stability are high due to that the flux reversals occur in mainly rotational magnetization regions, in which Barkhausen noises and iron losses are low and aging of flux changes is very small. The maximum frequency or cut-off frequency of detected sinusoidal fields is as high as about 4 kHz which is about four times that in Supermalloy core flux gate magnetometers. The two-core type magnetometers are useful for applications to non-contact type dc and ac current sensors, motor leakage flux sensors, and dynamic displacement sensors for medical electronics, because that only effective field signals are accurately detected by cancelling uniform magnetic disturbances in the two cores.

Accurate mechanocardiogram sensors using amorphous star-shaped core multivibrator combined with a magnet

New non-contact type accurate mechanocar-diogram sensors are presented using an amorphous star-shaped core multivibrator combined with a small magnet. These sensors can detect magnet displacement from 0.02 μm to 15 mm. Accurate mechanocardiograms (heartbeat cardiogram, phonocardiogram, and blood-vessel pulsation) are stably detected by fixing a small magnet on the chest wall or the blood-vessel position. A prototype sensor is fablicated with a microchipped multivibrator circuit and a filter which uses a 3 volts and 9 mA power source.