Research On Transducing Characteristics Of Piezoelectric/Magnetostrictive Laminate Composites

Magnetoelectric (ME) material is widely used in sensors,transducers,memory and many other fields. Magnetoelectric composited material laminated by piezoelectric and magnetostrictive material is a hotspot in magnetoelectric material research fields recent years because of simple preparation and high efficiency in magnetoelectric conversion.The magnetic elastic loss of magnetostrictive materials is described comprehensively. By using the principle that the magneto-elastic loss in magnetostrictive materials could be changed by bias magnetic field (Hbias), a magnetoelectric laminated composite which could be used to measure the static magnetic field is presented. This magnetoelectric laminated composite is made of piezoelectric and magnetostrictive materials. It is a piezoelectric/magnetostrictive/ piezoelectric (PMP) three-layer structure similar to a sandwich. Magnetoelectric laminated composite works as a transformer: one piezoelectric layer in structure is used as a driving layer; the other is an output layer. When an AC voltage is applied to the driving layer, the corresponding output voltage can be obtained from the output layer. Because the output voltage amplitude changes with the static magnetic field, the static magnetic field can be detected. Vibration mode of the three-layer magnetoelectric laminated composite worked in transformer mode is analyzed. The magnetic-mechanical-electrical equivalent model which could reflect the relationship between input and output voltage is deduced. The equivalent model shows that output voltage amplitude is depend on mechanical quality factor and excitation voltage. The relationships between the output voltage amplitude and the excitation signal frequency,as well as the excitation voltage amplitude are detected. Static magnetic field detection sensitivities of the magnetoelectric laminated composite at different excitation voltage amplitudes are tested. By using PMPMP five-layer laminated composite as an example of multi-layer structure, the output voltages at different excitation methods and output connection ways are discussed. The experiment results show that: (i) when PMP structure vibrates on longitudinal mode, the output voltage is more sensitive at same static magnetic field. (ii) At an excitation voltage of 2Vpp, the static magnetic field sensitivity relative to the output voltage under longitudinal resonant mode is 22.6mV/Oe. (iii) The higher the input voltage amplitude, the greater the output voltage amplitude and the stronger the magnetic field sensitivity. According toΔE effect of magnetostrictive material, elastic modulus could be changed with stress state in the material. Based on theΔE effect, a method to control the resonance frequency of the magnetoelectric laminated composite is investigated. Based on the inverse piezoelectric effect, the pre-strain of laminated composite is adjusted by controlling the DC voltage of piezoelectric actuator layer in the PMP magnetoelectric laminated composite. Because the resonant frequency is related with the elastic modulus changed with the stress/strain (or DC bias voltage), the resonant frequency could be controlled by altering the DC voltage. The relationship between the DC voltage in piezoelectric actuator layer and the strain at laminated composite end point is analyzed. By using the constitutive equations of piezoelectric and magnetostrictive materials, the first order longitudinal resonant frequency and the ME voltage coefficient as a function of the elastic modulus are presented, respectively. By analyzing the stress effect on the elastic modulus,a formula which could prove the DC voltage's control action on resonant frequency is obtained.The magnetoelectric laminated composite transducer is set up and the test system is constructed. The results show that: (i) At a VDC magnitude of -170V~170V, the control range of resonance frequency is 1 KHz and the change of ME voltage coefficient could be neglected. (ii) There is a linear relationship between resonance frequency and VDC. (iii) The control range of resonance frequency doesn't vary with the bias magnetic field (Hbias) at 0Oe~225Oe.