| Multiferroic materials are special materials that exhibit two or more kinds of iron sequences,such as ferroelectricity,ferromagnetism and ferroelasticity,etc.The magnetoelectric coupling effect is derived from the coupling between the ordered parameters of ferroelectricity and ferromagnetism,and the materials with this effect are called magnetoelectric materials.Most single-phase magnetoelectric materials are difficult to be applied in practice because of their low working temperature and magnetoelectric conversion coefficient.The magnetoelectric composite materials composed of piezoelectric phase and magnetostrictive phase can show a large magnetoelectric coupling effect at room temperature,which is expected to develop new magnetoelectric sensors with superior performance.The layered magnetoelectric composite structure obtains the maximum magnetoelectric conversion coefficient because it overcomes the leakage current and other problems.The flexible polyvinylidene fluoride(PVDF)base magnetoelectric composite material not only has good magnetoelectric coupling performance,but also has excellent flexibility,which lays a foundation for the development of flexible magnetic field sensor.In this paper,polymer piezoelectric material PVDF and magnetostrictive materials(amorphous band(Metglas)and nickel(Ni))were used to prepare flexible layered magnetoelectric composites.And the magnetoelectric conversion performance(magnetoelectric output voltage,magnetoelectric conversion coefficient,resonance frequency,optimal bias field)and magnetic sensing characteristics(sensitivity,linearity,repetition,resolution and limit of detection)are studied.The specific work is as follows:(1)A magnetic field detection system was established to study the magnetic properties,piezoelectric properties and magnetoelectric conversion properties of PVDF/Metglas bilayer magnetoelectric composites.The experimental results show that the optimal bias field of the sample is 4.7 Oe,which is consistent with the magnetic field corresponding to the peak piezomagnetic coefficient of the magnetostrictive phase Metglas.The resonant frequency of the sample is 7.9 kHz in the bending resonance mode,and the corresponding magnetoelectric conversion coefficient is 146.623 V/cm Oe.In the plane vibration mode of the sample,the resonance frequency of the sample is 37.6 kHz,and the corresponding magnetoelectric conversion coefficient is 176.41 V/cm Oe.The above research results show that the composite which was prepared have good magneto-electric coupling properties.(2)In order to evaluate the practical application prospect of PVDF/Metglas bilayer magnetoelectric composites in magnetic field sensors,we investigated the magnetic sensing performance of the composite materials applied to AC/DC magnetic field sensors,plane vector sensors and flexible magnetic sensors,and measured and analyzed the sensitivity,linearity,repeatability and resolution of the samples.Firstly,the magnetic sensing characteristics of the sample in the AC/DC magnetic field were measured.The measurement results showed that the sensitivity of the sample to the AC/DC magnetic field was 892.96 mV/Oe and 157.6 mV/Oe,and the linearity was 0.99965 and 0.99444,respectively.The deviation and repeatability were both good.Secondly,the plane vector magnetic sensing characteristics of the sample were studied.The experimental results show that the output voltage of the sample presents a perfect sinusoidal function curve with the magnetic field Angle?,and the correlation coefficient r~2 between the output voltage and the magnetic field Angle?is 0.98741 and 0.98854 when the AC magnetic field intensity is0.3 Oe and 0.15 Oe,respectively.Finally,the influence of flexibility on the magneto-electric conversion performance and magnetic sensing characteristics of the sample was explored.It can be found from the measurement results that,with the increase of bending degree,the magnetoelectric conversion coefficient of the sample decreases gradually,and the resonance frequency increases gradually.In addition,we also found that the bending sample has a weak self-bias effect under the action of external force.According to the above studies,PVDF/Metglas bilayer magnetoelectric composite is a feasible candidate material for flexible in-plane vector resonance magnetic sensor.(3)In the second part of the investigation,we found that the external stress can make the bending sample produce self-bias effect,but the self-bias magneto-electric coupling effect is small.Firstly,we designed and fabricated arc Metglas/PVDF/Ni self-bias magnetoelectric composites.The self-bias effect of the samples was induced by the built-in stress,and the functional gradient effect between Metglas and Ni with different magnetic properties was used to further enhance the self-bias effect.Secondly,we study the magnetic sensing characteristics of the self-biased magnetoelectric composite when it is applied to the AC magnetic field sensor,realizing a wide frequency measurement range(5-25 kHz),which expands the application range of magnetoelectric composite.Finally,in order to realize the application of magnetoelectric composite in biomedical field,we studied the magnetic sensing characteristics of Metglas/PVDF/Ni self-biased magnetoelectric composites in low frequency magnetic field,mainly realizing that the effective detection limit of magnetoelectric composites on the intensity of AC magnetic field is 2 nT when the AC magnetic field is 40 Hz.The lower resolution is about 1 nT,which lays a foundation for the application of Metglas/PVDF/Ni self-biased magnetoelectric composites in biomedical field. |
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