Low-frequency magnetic sensing by magnetoelectric metglas/bidomain LiNbO₃long bars

Abstract

We present an investigation into the magnetic sensing performance of magnetoelectric bilayered metglas / bidomain LiNbO 3 long thin bars operating in a cantilever or free vibrating regime and under quasi-static and low-frequency resonant conditions. Bidomain single crystals of Y+128 o-cut LiNbO 3 were engineered by an improved diffusion annealing technique with a polarization macrodomain structure of the "head-to-head" and "tail-to-tail" type. Long composite bars with lengths of 30, 40 and 45 mm, as well as with and without attached small tip proof masses, were studied. ME coefficients as large as 550 V/cm•Oe, corresponding to a conversion ratio of 27.5 V/Oe, were obtained under resonance conditions at frequencies of the order of 100 Hz in magnetic bias fields as low as 2 Oe. Equivalent magnetic noise spectral densities down to 120 pT/Hz 1/2 at 10 Hz and to 68 pT/Hz 1/2 at a resonance frequency as low as 81 Hz were obtained for the 45 mm long cantilever bar with a tip proof mass of 1.2 g. In the same composite without any added mass the magnetic noise was shown to be as low as 37 pT/Hz 1/2 at a resonance frequency of 244 Hz and 1.2 pT/Hz 1/2 at 1335 Hz in a fixed cantilever and free vibrating regimes, respectively. A simple unidimensional dynamic model predicted the possibility to drop the low-frequency magnetic noise by more than one order of magnitude in case all the extrinsic noise sources are suppressed, especially those related to external vibrations, and the thickness ratio of the magnetic-to-piezoelectric phases is optimized. Thus, we have shown that such systems might find use in simple and sensitive room-temperature low-frequency magnetic sensors, e.g., for biomedical applications.

Magnetoelectric metglas/bidomain y + 140°-cut lithium niobate composite for sensing fT magnetic fields

“…The measured impedance spectra of the thin-bar ME metglas / bidomain y+140º-cut LNC composite and of the PE bidomain y+140 o -cut LNC crystal alone operating in a free vibrating regime are shown in Figure 3(a). Superimposed are the calculated results obtained using a simple unidimensional ME model [18,19]. The resonance and antiresonance peaks are associated with lowfrequency bending electromechanical modes (EMR).…”

“…Despite their outstanding PE characteristics, these materials have a number of drawbacks, such as a low Curie temperature, considerable mechanoelectric hysteresis, creep (time delay and saturation between mechanical deformation and electric signal), nonlinear behavior, strong dependence of the properties on the temperature, as well as large dielectric losses. One possible approach to improve these parameters is to use lead-free PE single crystals such as lithium a) Correspondence should be addressed to a.turutin@misis.ru niobate with high voltage piezoelectric coefficients (g), low permittivity and very low mechanical and dielectric losses [16][17][18][19][20][21]. Furthermore, asymmetric bi-layered systems with bimorph PEs, containing two oppositely poled layers along the thickness direction, are able to generate large voltages under a low-frequency bending deformation and partially cancel both extrinsic vibrational and thermal noises [8,22].…”

“…Furthermore, some new promising techniques have been developed to directly engineer two ferroelectric domains with antiparallel spontaneous polarization vectors in a single crystal plate (bidomain) [23,24]. In a previous studies we proposed the use of square or long bar metglas / PE bi-layered composites with y+128°-cut LNC single-crystal "head-to-head" (H-H) and "tail-to-tail" (T-T) bidomains in sensitive magnetic field sensors [18,19].…”

“…Figure 4(a) shows the result of the quasi-static measurement of the transversal ME coefficient as a function of the applied in-plane bias field. Using a low-frequency model [18,19], the maximum expected quasi-static ME coefficient of |α E31 | = 5.4 V•(cm•Oe) -1 was calculated. The maximum measured quasi-static ME coefficient was as large as |α E31 | = 1.9 V•(cm•Oe) -1 .…”

“…Furthermore, a reference 100 pF capacitor was measured in order to show the voltage noise density floor of the detection circuit. The calculated curve was obtained taking into account the impedance thermal Jonhson-Nyquist noise (4•k b •T• ′ ) 1/2 of the sensor while operating at room temperature [18,19]. The calculated e n values are shown to be as low as 63 nV/Hz 1/2 at the resonance frequency of 6862 Hz.…”