Engineering Resonance Modes for Enhanced Magnetoelectric Coupling in Bilayer Laminate Composites for Energy Harvesting Applications

The magnetoelectric (ME) effect in composites, a strain-mediated coupling phenomenon between piezoelectric and magnetostrictive phases, has a wide range of technological applications. Here, ME coupling phenomena are explored in $\mathrm{Pb}$-free piezoelectric, $0.5\mathrm{Ba}({\mathrm{Zr}}_{0.2}{\mathrm{Ti}}_{0.8}){\mathrm{O}}_3\text{−}0.5({\mathrm{Ba}}_{0.7}{\mathrm{Ca}}_{0.3}){\mathrm{Ti}\mathrm{O}}_3$ and piezomagnetic ${\mathrm{Ni}\mathrm{Fe}}_2{\mathrm{O}}_4$ bilayer laminate composites. The direct and converse ME coupling strengths are found to be enhanced at the electromechanical resonance modes, rather than at the off-resonance frequencies. Here, it is proposed to further enhance the ME coupling strength at electromechanical resonance modes by the in-phase superimposition of the radial and second bending modes via varying the bilayer thickness, which, in turn, varies the volume fraction of the bilayer. The proposed enhanced ME coupling is experimentally demonstrated at a theoretically envisaged bilayer thickness of about 1.8 mm. This results in a large direct ME coupling coefficient of $22.5\mathrm{V}\mathrm{c}{\mathrm{m}}^{-1}\mathrm{O}{\mathrm{e}}^{-1}$, which is around 100% more than the values observed at individual resonance modes. The results are further validated by calculations from theoretical models. The method adopted in this work gives a roadmap to the significant enhancement of the ME effect in laminate composites.

Figure 1

XRD patterns for (a) BZT-BCT and (b) NFO samples.

Figure 2

Impedance and phase versus frequency plots for the 0.4BZT-BCT/NFO laminate composite.

Figure 3

(a) Schematic representation of radial and bending modes of the bilayer laminate structure. (b) Change in positions of radial and bending modes caused by variation in R and/or b. (c) Out-of-phase superimposition and (d) in-phase superimposition of the modes.

Figure 4

Impedance and phase as a function of frequency for $t^p=0.4$, 0.6, 0.8, and 1.0 mm in the BZT-BCT/NFO laminate structure. Insets show enlarged versions of the impedance plots near the region where the modes are merging.

Figure 5

Variation of (a) ${\alpha }_{\mathrm{DME}}$ and (b) ${\alpha }_{\mathrm{CME}}$ as a function of dc magnetic field for laminate composites with $t^p=0.4$, 0.6, 0.8, and 1.0 mm. Inset in (a) shows maximum values of ${\alpha }_{\mathrm{DME}}$ and ${\alpha }_{\mathrm{CME}}$ as a function of BZT-BCT volume fraction, V. (c) Plot of dM²/dH_dc with respect to external H_dc; inset shows the M-H curve of the NFO sample. Calculated ${\alpha }_{\mathrm{DME}}$ value for $t^p=0.6\mathrm{mm}$ is plotted along with measured ${\alpha }_{\mathrm{DME}}$ values.

Figure 6

${\alpha }_{\mathrm{DME}}$ and ${\alpha }_{\mathrm{CME}}$ plots as a function of frequencies under self-bias and bias conditions, along with impedance, for $t^p=0.4\mathrm{mm}$ laminate composites.

Figure 7

(a) Phase of vibration, (b) ${\alpha }_{\mathrm{DME}}$ at bias field, and (c) ${\alpha }_{\mathrm{CME}}$ at bias field for BZT-BCT/NFO bilayer laminate composites with various $t^p$ at acoustic modes of the f_R and f_B2 frequency range.

Figure 8

Observed and calculated (a) electromechanical resonance frequencies and (b) ${\alpha }_{\mathrm{DME}}$ of different bilayers samples plotted as a function of volume fraction, V.

Figure 9

Recorded output ac voltage from DME measurements at (a) zero bias and (b) 145 Oe bias field for $t^p=0.8\mathrm{mm}$ bilayer laminate composite. (c) Schematic diagram of the bridge rectifier used to convert output ac voltage into dc voltage. Demonstration of magnetic energy harvesting: (d) observed dc voltage and its current obtained after rectification and (e) calculated power with respect to different resistors. Inset shows an energy harvesting experiment by lighting a series of LEDs powered by the obtained output voltage from the ME laminate composite at a bias field of 145 Oe.