Resistive Microwires

Called resistive microwires based on alloys which are used for the manufacture of precision resistors.

The main requirements for resistive microwires are:

- close to zero temperature coefficient of resistance (TCR), at operating temperature range;

- high stability in time of resistivity;

- low thermal electromotive force in a pair of copper;

- high stability of resistivity after the impact of climate temperatures both high and low;

- stability in a variety of production environments – humidity, acids and alkalis, other aggressive environments.

 

Examples of resistive alloys for microwires:

Alloy

Chemical composition

Resistivity Ohm*mm2/m

Range of linear resistance

kOhm/m

TCR

Grad-1

Temperature range, С

Manganin

Cu-Ni-Mn-Si

0,45 - 0,5

1,5 - 50

±10*10-6

- 20 ÷ +90

DN(ДН)-1

Cu-Ni-Mn-Si

0,5 - 0,6

1,5 - 50

±5*10-6

- 60 ÷ +120

Alloy C(Ц)

Ni-Mn-Cr-Si  

1,4 – 1,5

5 - 250

±1*10-6

- 60 ÷ +280

70 NHS(НХС)

Ni-Cr-Si  

1,6 – 1,7

50 - 800

±1*10-6

- 60 ÷ +280

Magnetic Microwires

The new momentum in application of microwires leads the research results of microwire magnetic properties with amorphous and microcrystalline structure of microwire’s core.

Using developed alloys can be produced microwire with positive, negative or zero magnetostriction.

Axial, radial and tangential stresses, and also the value of magnetostriction form a wide variety of magnetic structures and magnetic properties.

At positive magnetostriction (alloys based on iron) direction of amgnetostatic and magnetoelastic anisotropy, and direction of easy magnetization, coincide with the axis of the microwire. Microwire has the property of bistability. Reversal magnetization takes with great leap Barkhausen.

                                                

 

Pulse of remagnetization and hysteresis loop of bistable micrwore

 

With negative magnetostriction, on alloys based on cobalt, magnetoelastic anisotropy creates an axis of easy magnetization directed perpendicular to the axis of the microwires. In a longitudinal magnetic field such microwires remagnetized with turn (rotation) of magnetization vector. The hysteresis loop has an inclined shape with very small coercive force (anhysteresis remagnetization).

 

Anhysteresis loop of remagnetization for microwires with negative magnetostriction

 

In microwires with near to zero (small negative) magnetostriction appear complex magnetic structures – “circular” or “helicoidally” with surface close domains.

On such microwires is achieved a great values of magnetic permeability (till 1000000) and magnetic impedance at high frequencies (till 800%).

 

         

Pulse of remagnetization and hysteresis loop of microwire with small negative magnetostriction

 

Stress sensing microwires

(microwires are sensitive to mechanical stress)

 As result of special thermomechanical treatment microwire changes the magnetization characteristics – rectangular hysteresis loop, usual for bistable microwire, becomes inclined.

Hysteresis loop of microwire, with positive magnetostriction, applied TMT (tension 500 MPa, (1) 300 ºС, 3 hour; (2) 280 ºС, 40 min.; (3) 265 ºС, 40 min.; (4) 235 ºС, 40 min.; (5) 215 ºС, 40 min.;)

 

By applying to such microwires tensile stress has the opposite phase transition - transformation of inclined loop to rectangular as in the original microwires.

Magnetic permeability, coercive force and pulse amplitude under the influence of tensile stress changes 50-100 times.

On the basis of such microwires can be made supersensitive sensors of stresses, displacements, stress sensitive composite materials.