MicroWire Sensors: GMI vs. RVmagnetics Principle

Glass-coated MicroWire is a unique form of material that has gained more and more attention in recent years, mainly due to its unique properties and the scalability of possible applications – mainly for sensorics. However, the MicroWire sensor by itself, is not utilisable and relies not only on the electronics for signal acquisition but also its “magic” is hidden on the microscopic level – chemical composition.

In previous articles the differences between MicroWires and different types of sensors were already clarified, but what about different types of MicroWire sensors? Depending on the employed physical phenomenon, two possible types of MicroWire sensors can be achieved: MicroWire sensors based on GMI (Giant Magnetoimpedance) effect, MicroWire sensors based on magnetic bistability (RVmagnetics’ sensors).

Introduction

To begin with, the MicroWire preparation is the most crucial thing. Every glass-coated MicroWire for any possible application is made via the Taylor-Ulitovsky method, from a bulk sample weighing ≈ 2 grams. With this method, it is possible to prepare kilometres of MicroWire in a few minutes time-span. The diameter of the metallic core is usually about 1 – 50 µm, and the glass coating can reach 2 – 20 µm thickness. The manufacturing process conditions can control these geometrical properties. Now, the manufactured MicroWire can be used for different applications, from special thermal sealants to electric conductors, actuators, and shape-memory materials to sensors.

GMI-based MicroWire Sensors

The sensors’ market offers several types of MicroWire sensors, one of them is a Giant Magnetoimpedance-based sensor of magnetic field. GMI is a physical phenomenon which takes place in specific materials and causes dramatic changes in electrical impedance with an applied external magnetic field. Strong dependence on the magnetic field allows its utilisation as a sensor of magnetic field, or indirectly as a displacement sensor of magnetic objects.

And what is electrical impedance? It is a more complex concept of electrical resistivity extended to AC electrical circuits. This form of explanation immediately gives the pros and cons of GMI sensors. The main advantage is the fast response of the sensor since high AC frequencies, in order of MHz scale, can be used to obtain information about the GMI effect. Also, the sensor can be tiny, only about 2 mm long. The disadvantage is the requirement of making electrical contacts on the MicroWire, in order to measure its impedance. Despite extraordinary sensitivity to the applied magnetic field with barely visible sensors, the necessity of electrical contacts is a significant shortcoming and limitation of the GMI sensors.

Magnetically Bistable MicroWire Sensors

On the other hand, magnetically bistable MicroWires are passive sensors without any need to make electrical contact directly with the MicroWire, which brings it to the forefront of MicroWire sensing. Comparable to the GMI sensor, the magnetic field sensing, altogether with the displacement sensing is viable up to a few centimetres (5 cm). However, magnetically bistable MicroWire is capable of wider utilisations (than GMI MicroWire sensor), as due to its magnetic principles, measurement of temperature, mechanical stress, vibrations, and more physical properties is possible.

While the GMI MicroWire sensor can work in the MHz frequencies, the bistable MicroWire operates in the range of audio-frequencies (kHz range), thus the response time is lower than in the case of GMI. This also extends to the power consumption requirements, as the excitation of bistable MicroWire needs more power due to the generation of the magnetic field, however, the power consumption is still low, just a few milliamperes per measurement. Moreover, the most significant difference between GMI and magnetically bistable MicroWire sensors lies in the passive character of the sensor, since it works purely on the magnetic principles. Moreover, the most significant difference between GMI and magnetically bistable MicroWire sensors lies in the passive character of the sensor, as magnetically bistable MicroWire communicates with data acquisition devices purely on magnetic principles. Therefore, no electrical contacts are necessary on the MicroWire, which allows its incorporation into otherwise inaccessible places. The correctly working length of the bistable MicroWire is from 1 cm up to 3 cm, which makes it easier to prepare for application and allows its use as a contactless passive strain sensor.

Conclusion

The market offers different types of sensors and different types of MicroWire sensors as well. Only your requirements will determine which type of sensor is the most suitable for your application.

If the contactless, tiny, passive sensor of various physical quantities can help you to solve your headaches – RVmagnetics have a fully tailor-made solution, fulfilling your needs. Are you intrigued? Contact us or visit the section discover possible applications.