Sensitivity Enhancement in Magnetic Sensors Based on Ferroelectric-Bimorphs and Multiferroic Composites

Abstract

Multiferroic composites with ferromagnetic and ferroelectric phases have been studied in recent years for use as sensors of AC and DC magnetic fields. Their operation is based on magneto-electric (ME) coupling between the electric and magnetic subsystems and is mediated by mechanical strain. Such sensors for AC magnetic fields require a bias magnetic field to achieve pT-sensitivity. Novel magnetic sensors with a permanent magnet proof mass, either on a ferroelectric bimorph or a ferromagnetic-ferroelectric composite, are discussed. In both types, the interaction between the applied AC magnetic field and remnant magnetization of the magnet results in a mechanical strain and a voltage response in the ferroelectric. Our studies have been performed on sensors with a Nd-Fe-B permanent magnet proof mass on (i) a bimorph of oppositely-poled lead zirconate titanate (PZT) platelets and (ii) a layered multiferroic composite of PZT-Metglas-Ni. The sensors have been characterized in terms of sensitivity and equivalent magnetic noise N. Noise N in both type of sensors is on the order of 200 pT/√Hz at 1 Hz, a factor of 10 improvement compared to multiferroic sensors without a proof mass. When the AC magnetic field is applied at the bending resonance for the bimorph, the measured N ≈ 700 pT/√Hz. We discuss models based on magneto-electro-mechanical coupling at low frequency and bending resonance in the sensors and theoretical estimates of ME voltage coefficients are in very good agreement with the data.

Enhanced Energy Conversion Performance of a Magneto–Mechano–Electric Generator Using a Laminate Composite Made of Piezoelectric Polymer and Metallic Glass

“…The magnetic proof mass was attached to the beam‐end for tuning the resonance frequency of the MME generator, maximizing magnetoelectric coupling by optimum DC magnetic bias, and introducing the magnetic torque to MME generator under AC magnetic field. [ 7c,d,15b ] The energy conversion performance of MME generator depends on the magnetic torque to the generator, [ 18 ] the device structure, [ 8c ] and the selecting substrate composition. [ 19 ] The Figure 4b shows a photographic image of the cantilever structured MME generator with an actual size of 4 × 2 cm 2 .…”

“…The maximum α ME of the MME generator was approximated to be ≈910.14 V cm −1 Oe −1 at 38.2 Hz, which is higher than those of previously reported inorganic and polymeric components‐based MME generators under only AC magnetic field. [ 7c,8c,9,10,12,15 ] To calculate the effective power of the MME generator, peak load voltage was measured as a function of circuit load resistance ranging from 1 kΩ to 100 MΩ (Figure 5d). Load voltage was gradually built up and saturated at around 12.1 V as the resistance was increased.…”

“…These phenomena are apparently due to the insufficient bending moment of the magnetostrictive substrate induced by an increased flexural rigidity of the multilayer substrate. [ 15b ] In addition, the resonance frequency of each model increased depending upon the number of laminated Metglas sheet layers. The resonance frequency (ω 0 ) can be expressed as (where YI is the flexural rigidity, L is the length of the cantilever, m is mass per unit length, and M t is tip mass) and have the proportional relationship with flexural rigidity; as a result, the ω 0 shifted to high frequency by increasing the thickness of metallic substrates.…”

“…Moreover, this device showed a high α ME of 910.14 V cm −1 Oe −1 , which is considered as an improved result compared to the previously reported inorganic piezoelectric components‐based MME generators. [ 7c,8c,9,10,12,15 ] In addition, finite element analysis (FEA) is conducted using multiphysics simulation to theoretically explore the output performance produced from the fabricated MME generator. The introduced simple, practical, and economic MME generator fabrication technique is a breakthrough in developing mechanically stable/flexible and bio‐eco‐friendly magnetoelectric energy harvesting technology.…”

Review of Magnetoelectric Sensors

“…Compared with singlephase ME material, ME heterostructures and ME laminates perform greatly enhanced coupling capability, which is generally characterized by ME coefficient α ME [7][8][9]. After a development of nearly half a century, tremendous progress regarding ME composites and related device applications has been reported [1][2][3]6,[10][11][12][13][14][15][16][17][18][19].…”