VTechWorks Repository :: Browsing by Author "Gao, Junqi"

Browsing by Author "Gao, Junqi"

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Comparison of noise floor and sensitivity for different magnetoelectric laminates
Gao, Junqi; Das, Jaydip; Xing, Zengping; Li, Jiefang; Viehland, Dwight D. (American Institute of Physics, 2010-10-15)
We present a comparison of the magnetoelectric (ME) response and magnetic-field sensitivities of engineered laminate sensors comprised of magnetostrictive and piezoelectric phases. The ME voltage coefficients for Metglas and single crystal fibers of Pb(Mg1/3Nb2/3) O-3-PbTiO3 (PMN-PT) or Pb(Zn1/3Nb2/3) O-3-PbTiO3 (PZN-PT) are about 2.8 times larger than those with Metglas-Pb(Zr, Ti)O-3 (PZT) ceramic ones. This results in a 1.7 times enhancement in the magnetic-field sensitivity for the structures with single crystals. Accordingly, the noise floors are about three to four times lower for composites with PMN-PT or PZN-PT fibers than those with PZT. (C) 2010 American Institute of Physics. [doi: 10.1063/1.3486483]
Dependence of magnetic field sensitivity of a magnetoelectric laminate sensor pair on separation distance: Effect of mutual inductance
Li, Menghui; Wang, Yaojin; Gao, Junqi; Gray, David; Li, Jiefang; Viehland, Dwight D. (American Institute of Physics, 2012-02-01)
The effect of mutual inductance on the performance of a pair of Metglas/Pb(Zr,Ti)O-3 laminate magnetoelectric (ME) sensors has been studied. The effective value of the ME coefficient (alpha(ME)) for the laminates was reduced when the distance between was < 40 mm. Separating the two laminates by distances of > 40 mm, the effect of mutual inductance was small. The laminates exhibited the maximum values of alpha(ME). The ME sensor unit with two laminates connected in parallel had higher magnetic field sensitivities. 2012 American Institute of Physics. [doi:10.1063/1.3684986]
Enhanced dc magnetic field sensitivity by improved flux concentration in magnetoelectric laminates
Gao, Junqi; Gray, David; Shen, Ying; Li, Jiefang; Viehland, Dwight D. (AIP Publishing, 2011-10-01)
In this letter, we present magnetostatic modeling results that show significant magnetic field concentration tunability through geometric modification of high-mu tnagnetostatic Metglas layers of laminate magnetoelectric (ME) sensors. Based on the modeling results, composite ME sensors were fabricated with longer Metglas foils and found to exhibit notably higher ME voltage coefficients at smaller DC magnetic biases in response to a 1 kHz driving signal. Such ME sensors have been used to detect DC magnetic field changes as small as 6 nT at 1 kHz, while maintaining a signal-to-noise ratio greater than 10. This represents an enhancement of similar to 250% relative to values previously reported for Metglas/Pb(Zr,Ti)O(3) laminates. (C) 2011 American Institute of Physics. [doi:10.1063/1.3650713]
Enhanced magnetoelectric effect in self-stressed multi-push-pull mode Metglas/Pb(Zr,Ti)O-3/Metglas laminates
Li, Menghui; Wang, Yaojin; Gao, Junqi; Li, Jiefang; Viehland, Dwight D. (AIP Publishing, 2012-07-01)
Two methods to effectively induce self-stress on Metglas/Pb(Zr,Ti)O-3/Metglas laminate are presented: (i) applying a dc magnetic field to the Metglas layers or (ii) applying a dc electric field to the core piezoelectric composites. An optimum self-stress enhances the magnetoelectric (ME) effect in the laminates. With a 20 Oe dc magnetic bias, the value of alpha(ME) for the self-stressed laminate was enhanced to 31.4 V/cm center dot Oe, which was by a factor of 1.24x compared to the laminate without self-stress. Furthermore, the equivalent magnetic noise floor was reduced by the self-stress at low frequencies. (C) 2012 American Institute of Physics. [http://dx.doi.org/10.1063/1.4737179]
Enhanced sensitivity to direct current magnetic field changes in Metglas/Pb(Mg(1/3)Nb(2/3))O(3)-PbTiO(3) laminates
Gao, Junqi; Shen, Liangguo; Wang, Yaojin; Gray, David; Li, Jiefang; Viehland, Dwight D. (American Institute of Physics, 2011-04-01)
We have developed Metglas/Pb(Mg(1/3)Nb(2/3))O(3)-PbTiO(3) magnetoelectric (ME) laminates that have notably larger ME coefficients, with maximum values of up to 45 V/cm Oe. Based on this giant ME effect, the dc magnetic field sensitivity for Metglas/PMN-PT laminate sensors was improved by a factor of > 3, relative to that for Metglas/Pb(Zr,Ti)O(3) (PZT)-based ones of the same geometry. Our new ME sensor can detect dc magnetic field changes as small as (i) 5 nT at 1 kHz and (ii) 1 nT near the resonant frequency in a shield chamber. (C) 2011 American Institute of Physics. [doi:10.1063/1.3569629]
Enhancement in magnetic field sensitivity and reduction in equivalent magnetic noise by magnetoelectric laminate stacks
Li, Menghui; Gao, Junqi; Wang, Yaojin; Gray, David; Li, Jiefang; Viehland, Dwight D. (American Institute of Physics, 2012-05-15)
We have investigated the equivalent magnetic noise and magnetic field sensitivity for a magnetoelectric (ME) sensor unit of N numbers of ME laminates stacked together. Our results show with increasing N that the modeled and measured equivalent magnetic noises decreased by a factor of root N and that the magnetic field sensitivities increased by root N. For Metglas/Pb(Mg-1/3,Nb-2/3) O-3-PbTiO3 laminates, the equivalent magnetic noise decreased and the magnetic field sensitivity increased by a factors of 2.1 and 2.3, respectively, for N = 4 relative to that for N = 1. (C) 2012 American Institute of Physics. [http://dx.doi.org/10.1063/1.4718441]
Flux distraction effect on magnetoelectric laminate sensors and gradiometer
Shen, Ying; Gao, Junqi; Wang, Yaojin; Hasanyan, Davresh J.; Finkel, Peter; Li, Jiefang; Viehland, Dwight D. (American Institute of Physics, 2013-10-07)
A magnetic flux distraction effect caused by a nearby metallic material was investigated for Metglas/Pb(Mg1/3Nb2/3)O-3-PbTiO3 laminated magnetoelectric ( ME) sensors. Using flux distraction, a ME sensor can perform an accurate search for metallic targets of different dimensions at various distances. Detection results and simulations were in good agreement. The findings demonstrate an effective means to employ stationary ME sensors and gradiometers for magnetic search applications. (C) 2013 AIP Publishing LLC.
Geometry-induced magnetoelectric effect enhancement and noise floor reduction in Metglas/piezofiber sensors
Wang, Yaojin; Li, Menghui; Hasanyan, Davresh J.; Gao, Junqi; Li, Jiefang; Viehland, Dwight D. (AIP Publishing, 2012-08-01)
The geometry-dependent magnetoelectric (ME) effect was theoretically and experimentally investigated for multi-push-pull mode Metglas/Pb(Zr,Ti)O-3 sandwich-like laminates. Such structures hold promise for passive sensor applications. A geometry-induced significant enhancement in the ME coefficient and an effective reduction in the equivalent magnetic noise was observed due to an increase in the Metglas width fraction. (C) 2012 American Institute of Physics. [http://dx.doi.org/10.1063/1.4737906]
Giant resonant magnetoelectric effect in bi-layered Metglas/Pb(Zr,Ti)O-3 composites
Gao, Junqi; Hasanyan, Davresh J.; Shen, Ying; Wang, Yaojin; Li, Jiefang; Viehland, Dwight D. (American Institute of Physics, 2012-11-15)
In this paper, giant resonant magnetoelectric (ME) effect in an unsymmetrical bi-layered Metglas/Pb(Zr,Ti)O-3 ME composites with multi-push pull configuration that can be significantly tuned was investigated experimentally and theoretically. The actual measured and predicted results present the similar resonant frequency shifting behaviors for such ME composites: The resonant frequency can be varied from 70 Hz to 220 Hz by tip mass loading, where the ME voltage coefficients were over 250 V/cm-Oe. Moreover, the giant frequency-tunable resonant effect allowed us to design a 60Hz magnetic field energy harvester to be capable of harvesting energy generated by electronic instruments working on a 60Hz ac power supply. (C) 2012 American Institute of Physics. [http://dx.doi.org/10.1063/1.4765724]
High non-linear magnetoelectric coefficient in Metglas/PMN-PT laminate composites under zero direct current magnetic bias
Shen, Ying; Gao, Junqi; Wang, Yaojin; Li, Jiefang; Viehland, Dwight D. (American Institute of Physics, 2014-03-07)
The non-linear magnetoelectric (ME) response of Metglas/PMN-PT based sandwiched ME laminate composites has been studied for various thicknesses of the magnetostrictive layer. A significant increase in the non-linear ME coefficient under zero direct current bias was observed with a decreased Metglas thickness ratio for a fixed number of Metglas layers of n = 2. The non-linear ME effect was further improved by driving the laminate at the electromagnetic resonant frequency. The approach offers the potential to modulate low frequency magnetic signals to higher frequencies, where the noise floor is much lower and the signal to noise ratio higher. (C) 2014 AIP Publishing LLC.
Magnetoelectric (ME) composites and functional devices based on ME effect
Gao, Junqi (Virginia Tech, 2013-06-03)
Magnetoelectric (ME) effect, a cross-coupling effect between magnetic and electric orders, has stimulated lots of investigations due to the potential for applications as multifunctional devices. In this thesis, I have investigated and optimized the ME effect in Metglas/piezo-fibers ME composites with a multi-push pull configuration. Moreover, I have also proposed several devices based on such composites. In this thesis, several methods for ME composites optimization have been investigated. (i) the ME coefficients can be enhanced greatly by using single crystal fibers with high piezoelectric properties; (ii) the influence of volume ratio between Metglas and piezo-fibers on ME coefficients has been studied both experimentally and theoretically. Modulating the volume ratio can increase the ME coefficient greatly; and (iii) the annealing process can change the properties of Metglas, which can enhance the ME response as well. Moreover, one differential structure for ME composites has been proposed, which can reject the external vibration noise by a factor of 10 to 20 dB. This differential structure may allow for practical applications of such sensors in real-world environments. Based on optimized ME composites, two types of AC magnetic sensor have been developed. The objective is to develop one alternative type of magnetic sensor with low noise, low cost and room-temperature operation; that makes the sensor competitive with the commercially available magnetic sensor, such as Fluxgate, GMR, SQUID, etc. Conventional passive sensors have been fully investigated, including the design of sensor working at specific frequency range, sensitivity, noise density characterization, etc. Furthermore, the extremely low frequency (< 10-3 Hz) magnetic sensor has undergone a redesign of the charge amplifier circuit. Additionally, the noise model has been established to simulate the noise density for this device which can predict the noise floor precisely. Based on theoretical noise analysis, the noise floor can be eliminated greatly. Moreover, another active magnetic senor based on nonlinear ME voltage coefficient is also developed. Such sensor is not required for external DC bias that can help the sensor for sensor arrays application. Inspired by the bio-behaviors in nature, the geomagnetic sensor is designed for sensing geomagnetic fields; it is also potentially used for positioning systems based on the geomagnetic field. In this section, some works for DC sensor optimization have been performed, including the different piezo-fibers, driving frequency and magnetic flux concentration. Meanwhile, the lock-in circuit is designed for the magnetic sensor to replace of the commercial instruments. Finally, the man-portable multi-axial geomagnetic sensor has been developed which has the highest resolution of 10 nT for DC magnetic field. Based on the geomagnetic sensor, some demonstrations have been finished, such as orientation monitor, magnetic field mapping, and geomagnetic sensing. Other devices have been also developed besides the magnetic sensor: (i) magnetic energy harvesters are developed under the resonant frequency condition. Especially, one 60 Hz magnetic harvester is designed which can harvester the magnetic energy source generated by instruments; and (ii) frequency multiplication tuned by geomagnetic field is investigated which potentially can be used for frequency multiplier or geomagnetic guidance devices.
Magnetoelectric nonlinearity in magnetoelectric laminate sensors
Shen, Liangguo; Li, Menghui; Gao, Junqi; Shen, Ying; Li, Jiefang; Viehland, Dwight D.; Zhuang, Xin; Sing, M. Lam Chok; Cordier, Christophe; Saez, Sebastien; Dolabdjian, Christophe (American Institute of Physics, 2011-12-01)
A nonlinearity in the magnetoelectric coefficient, alpha(Nonlin)(ME), of Metglas/Pb(Zr,Ti)O(3) (PZT) and Metglas/Pb(Mg(1/3),Nb(2/3))O(3)-PbTiO(3) (PMN-PT) laminate sensors has been observed. This nonlinearity was found to be dependent on the dc magnetic bias (H(dc)) and frequency of the ac drive field (H(ac)). The maximum value of alpha(Nonlin)(ME) for both types of composites was found near the electromechanical resonance. For Metglas/PZT laminates, the maximum occurred under a finite bias of H(dc) approximate to 5 Oe; whereas, for Metglas/PMN-PT, the maximum was found near zero dc bias. One application for alpha(Nonlin)(ME) is a cross-modulation scheme that can shift low frequency signals to higher frequency to achieve lower noise floor. For Metglas/PMN-PT, alpha(Nonlin)(ME) has another application: removal of the necessity of a dc bias, which helps to design high-sensitivity sensor arrays and gradiometers. (C) 2011 American Institute of Physics. [doi:10.1063/1.3665130]
Modeling of resonant magneto-electric effect in a magnetostrictive and piezoelectric laminate composite structure coupled by a bonding material
Hasanyan, Davresh J.; Wang, Yaojin; Gao, Junqi; Li, Menghui; Shen, Ying; Li, Jiefang; Viehland, Dwight D. (American Institute of Physics, 2012-09-15)
The harmonic magneto-electro-elastic vibration of a thin laminated composite was considered. A theoretical model, including shear lag and vibration effects was developed for predicting the magneto-electric (ME) effect in a laminate composite consisting of magnetostrictive and piezoelectric layers. To avoid bending, we assumed that the composite was geometrically symmetric. For finite length symmetrically fabricated laminates, we derived the dynamic strain-stress field and ME coefficients, including shear lag and vibration effects for several boundary conditions. Parametric studies are presented to evaluate the influences of material properties and geometries on the strain distribution and the ME coefficient. Analytical expressions indicate that the shear lag and the vibration frequency strongly influence the strain distribution in the laminates and these effects strongly influence the ME coefficients. (C) 2012 American Institute of Physics. [http://dx.doi.org/10.1063/1.4752271]
Nonlinear magnetoelectric response of a Metglas/piezofiber laminate to a high-frequency bipolar AC magnetic field
Wang, Yaojin; Shen, Ying; Gao, Junqi; Li, Menghui; Li, Jiefang; Viehland, Dwight D. (AIP Publishing, 2013-03-01)
A nonlinear magnetoelectric (ME) response has been investigated in a Metglas/piezofiber laminate by applying a bipolar AC magnetic field (H-ac) without a DC magnetic bias. The ME voltage (V-ME) was measured for various amplitudes of H-ac of up to 9 Oe over the frequency (f) range 0.1
Piezomagnetic strain-dependent non-linear magnetoelectric response enhancement by flux concentration effect
Shen, Ying; Gao, Junqi; Wang, Yaojin; Finkel, Peter; Li, Jiefang; Viehland, Dwight D. (AIP Publishing, 2013-04-01)
The non-linear magnetoelectric (ME) effect of Metglas/Pb(Mg1/3Nb2/3)O-3-PbTiO3 heterostructures has been studied. Such effect holds promise for modulation mode ME sensor applications that require no dc bias. The non-linear ME coefficient was found to be highly dependent on the derivative of the piezomagnetic strain coefficient, which could be increased by increasing the Metglas length due to magnetic flux concentration. The non-linear ME coefficient was equal to 9.5V/(cm - Oe(2)) at H-dc = -1 Oe and 7.5V/ (cm - Oe(2)) at H-dc = 0Oe for a structure with 10 cm long Metglas foils. (C) 2013 AIP Publishing LLC.
Stress reconfigurable tunable magnetoelectric resonators as magnetic sensors
Kiser, Jillian; Finkel, Peter; Gao, Junqi; Dolabdjian, Christophe; Li, Jiefang; Viehland, Dwight D. (AIP Publishing, 2013-01-01)
We report a magnetoelastic effect in doubly clamped ferromagnetic magnetostrictive Metglas resonators with electrically and magnetically reconfigurable frequency response. The field-induced resonance frequency shift is due to magnetostrictive strain, which is shown to have a strong dependence on uniaxial stress. Here, we demonstrate that this magnetic field induced behavior can be used as the basis for a simple, tunable, magnetoelectric magnetic field sensor. The effect of tension on the field dependent magnetostrictive constant and the sensor sensitivity is examined, and the equivalent magnetic noise floor of such a sensor is estimated. (C) 2013 American Institute of Physics. [http://dx.doi.org/10.1063/1.4789500]
Structural dependence of nonlinear magnetoelectric effect for magnetic field detection by frequency modulation
Li, Menghui; Wang, Yaojin; Shen, Ying; Gao, Junqi; Li, Jiefang; Viehland, Dwight D. (American Institute of Physics, 2013-10-14)
The structure differences of magnetoelectric (ME) laminates for passive and active mode sensors are discussed. The Fourier coefficient A(1) calculated from the data of alpha(ME)-H-dc indicates that N = 1 (where N is the number of Metglas layers) should be the optimum structure for the active mode. Experimental investigations of the magnetic field sensitivity agree well with this conjecture. For N = 1, the magnetic field sensitivity was 0.66 nT/Hz(0.5), which was 3.1 times larger than for N = 5. (C) 2013 AIP Publishing LLC.
Theoretical analysis of the intrinsic magnetic noise spectral density of magnetostrictive-piezoelectric laminated composites
Zhuang, Xin; Cordier, Christophe; Saez, Sebastien; Sing, M. Lam Chok; Dolabdjian, Christophe; Gao, Junqi; Li, Jiefang; Viehland, Dwight D. (American Institute of Physics, 2011-06-15)
The equivalent magnetic noise spectral density level for long type magnetostrictive-piezoelectric laminated composites has been investigated by using a 1D equivalent circuit model, and exemplified for a longitudinal-transverse mode. The theoretical developments explain well our experimental results. The findings show that similar ultimate magnetic noise spectral noise density can be expected whether using either charge or voltage amplifier detection methods. The findings show that a volume effect and the dielectric loss factor of the piezoelectric layer are the dominant sources of the noise floor. Our findings show that the noise scales as 1/root f. The lowest equivalent noise floor value that has been observed is 10/root f pT/root Hz for f << 10 kHz, with a white noise level of 100 fT/root Hz above 10 kHz. (C) 2011 American Institute of Physics. [doi:10.1063/1.3594714]
Theoretical and experimental investigation of magnetoelectric effect for bending-tension coupled modes in magnetostrictive-piezoelectric layered composites
Hasanyan, Davresh J.; Gao, Junqi; Wang, Yaojin; Viswan, Ravindranath; Li, Menghui; Shen, Ying; Li, Jiefang; Viehland, Dwight D. (American Institute of Physics, 2012-07-01)
In this paper, we discuss a theoretical model with experimental verification for the resonance enhancement of magnetoelectric (ME) interactions at frequencies corresponding to bending-tension oscillations. A dynamic theory of arbitrary laminated magneto-elasto-electric bars was constructed. The model included bending and longitudinal vibration effects for predicting ME coefficients in laminate bar composite structures consisting of magnetostrictive, piezoelectric, and pure elastic layers. The thickness dependence of stress, strain, and magnetic and electric fields within a sample are taken into account, as such the bending deformations should be considered in an applied magnetic or electric field. The frequency dependence of the ME voltage coefficients has obtained by solving electrostatic, magnetostatic, and elastodynamic equations. We consider boundary conditions corresponding to free vibrations at both ends. As a demonstration, our theory for multilayer ME composites was then applied to ferromagnetic-ferroelectric bilayers, specifically Metglas-PZT ones. A theoretical model is presented for static (low-frequency) ME effects in such bilayers. We also performed experiments for these Metglas-PZT bilayers and analyzed the influence of Metglas geometry (length and thickness) and Metglas/PZT volume fraction on the ME coefficient. The frequency dependence of the ME coefficient is also presented for different geometries (length, thickness) of Metglas. The theory shows good agreement with experimental data, even near the resonance frequency. (C) 2012 American Institute of Physics. [http://dx.doi.org/10.1063/1.4732130]
Theoretical model for geometry-dependent magnetoelectric effect in magnetostrictive/piezoelectric composites
Wang, Yaojin; Hasanyan, Davresh J.; Li, Menghui; Gao, Junqi; Li, Jiefang; Viehland, Dwight D.; Luo, Haosu (American Institute of Physics, 2012-06-15)
A quasistatic theoretical model including geometry effect is presented for predicting the magnetoelectric (ME) coefficients in a ME multilayer composite consisting of magnetostrictive and piezoelectric layers. The model is developed based on average-field method considering the geometry effect. The model characterizes the ME coefficient in terms of not only the parameters of two composite components and the thickness fraction but also the length and width fractions for the piezoelectric or magnetostrictive components. Analytical predictions indicate that the width and length fractions strongly influence the maximum ME coefficient and the corresponding thickness fraction also. Clearly, geometry effects cannot be ignored in predicting ME coefficient. Theoretical ME coefficients are also compared to experimental test data, demonstrating excellent agreement. (C) 2012 American Institute of Physics. [http://dx.doi.org/10.1063/1.4729832]

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