 A magnetoelastic material is a material that changes its dimensions when it is exposed to a magnetic field. A thin ribbon of a magnetoelastic material forms a magnetomechanical resonator and it can be viewed as a small tuning fork. Exposing the film to a short magnetic pulse excites the film and it starts to oscillate. The frequency, amplitude and damping of the vibration give information of the status of the sensor.
Properties of a media, such as its viscosity, density, pressure or flow speed can be determined by analyzing the response of a magnetoelastic film placed in the media. It is also possible to follow a dynamic event, for instance the curing process of glue and paint. The magnetoelastic film can be made sensitive to many physical properties by coating it with various materials, for instance a humidity sensor can be constructed by coating the film with a humidity absorbing material. When the humidity sensor is placed in a humid climate, the coating will absorb water and become heavier. Similarly, when the sensor placed in a dry climate, the coating will release water and become lighter. A heavy sensor will vibrate with a lower frequency than a light sensor. Imego’s sphere of expertise in this field covers magnetism, electronics, simulation, packaging and industrial design.
We have developed a Wireless Humidity Detection System (WHDS), which uses inexpensive sensors for wireless detection of humidity. The sensor is passive, so there is no need for batteries or other power sources. The WHDS can be applied to measure humidity in places that are hard to reach, for instance behind walls, in closed packages and for monitoring moisture in food, pulp and sand.
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We have built an experimental setup for investigating the time dependence of the moisture uptake and release in exterior panelling paint. The moisture uptake properties are believed to be important for the tendency for mould growth on a painted surface. In our setup, the paints under investigation are coated on a magnetoelastic film and the mass increase due to the moisture uptake of the paint is wirelessly measured using the magnetoelastic resonance method. Moisture absorption and desorption properties of different paints and thicknesses can be studied. The sensor method make it is possible to classify paints and to study their moisture absorption and desorption properties.
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Viscosity, hardening and curing | |
The viscosity and the hardening and curing process of a substance can be monitored in real-time using our magnetoelastic sensor. The magnetoelastic film can either be coated by a thin layer of the substance or (for a fluid) immersed in the substance. The properties of the substance are monitored by measuring the resonance frequency, the amplitude and the Q-value of the magnetoelastic film. With this method we can for instance follow a temperature dependent solidification process in real time and in great detail.
Curing process of paint measured with a magnetoelastic sensor. The magnetoelastic film was covered by a thin layer of paint and the resonance frequency and amplitude of the film was measured.
The magnetoelastic sensor can be used to make a sensitive non-contact thickness determination of a coating, for instance paint or finish. The thickness of the coating on a magnetoelastic film will give a corresponding shift in the resonance frequency.
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