Enhanced sensitivity in magnetoelectric current-sensing devices with frequency up-conversion mechanism by modulating the magnetostrictive strainJitao Zhang, Ping Li, Yumei Wen, Wei He, Jin Yang, Aichao Yang, Caijiang Lu, and Wenli Li

Citation: Journal of Applied Physics 115, 17E505 (2014); doi: 10.1063/1.4862081 View online: http://dx.doi.org/10.1063/1.4862081 View Table of Contents: http://scitation.aip.org/content/aip/journal/jap/115/17?ver=pdfcov Published by the AIP Publishing Articles you may be interested in Dynamic magnetostrictive properties of magnetization-graded ferromagnetic material and application inmagnetoelectric composite J. Appl. Phys. 115, 17C726 (2014); 10.1063/1.4866089 Enhanced magneto-impedance in Fe73.5Cu1Nb3Si13.5B9 ribbons from laminating with magnetostrictiveterfenol-D alloy plate Appl. Phys. Lett. 101, 251914 (2012); 10.1063/1.4773237 High-resolution current sensor utilizing nanocrystalline alloy and magnetoelectric laminate composite Rev. Sci. Instrum. 83, 115001 (2012); 10.1063/1.4763570 Highly zero-biased magnetoelectric response in magnetostrictive/piezoelectric composite J. Appl. Phys. 112, 024504 (2012); 10.1063/1.4737404 The magnetostrictive material effects on magnetic field sensitivity for magnetoelectric sensor J. Appl. Phys. 111, 07E503 (2012); 10.1063/1.3670607

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Enhanced sensitivity in magnetoelectric current-sensing devices withfrequency up-conversion mechanism by modulating themagnetostrictive strain

Jitao Zhang, Ping Li,a) Yumei Wen, Wei He, Jin Yang, Aichao Yang, Caijiang Lu,and Wenli LiResearch Center of Sensors and Instruments, College of Optoelectronic Engineering, Chongqing University,Chongqing 400044, China

(Presented 5 November 2013; received 22 September 2013; accepted 17 October 2013; published

online 22 January 2014)

A frequency-tunable current sensor consisting of Terfenol-D/PZT/Terfenol-D magnetoelectric (ME)

laminate and Fe73.5Cu1Nb3Si13.5B9 nanocrystalline alloy has been developed. Almost all ME

current-sensing devices have higher outputs at resonance conditions, but this advantage is useful only

for narrow bandwidth. For the purpose of broadband current sensing, a frequency up-conversion

mechanism is introduced by means of nonlinearity of the field-dependence magnetostriction k(H).

Current sensitivity enhancement is realized by modulating the low-frequency dynamic

magnetostrictive strain to its resonance conditions. This solution provides the possibility to achieve

resonance-enhanced sensitivity at the power-line frequency of 50 Hz, and the capability to immune

the noise floor. Experimental results show that the modulated sensitivity is increased from 48.6 mV/A

to 178.4 mV/A at 50 Hz, and a small current step change of 3 mA can be clearly distinguished

by amplitude or phase of the output signals. These results provide possibilities to accurately

detect weak currents in the noise ambient at low frequencies. VC 2014 AIP Publishing LLC.

[http://dx.doi.org/10.1063/1.4862081]

Current sensor is an economical and reliable device with

great potential applications such as pump load monitoring,

converter controlling, and over current protecting.1,2 In the

last decades, the current-sensing techniques have attracted

an ever-increasing focus and provoked many research activ-

ities. Most approaches for current measurement can be di-

vided into two types: contact measurement and non-contact

measurement. The contact current-sensing technique, repre-

sented by shunt resistor, is used as a proportional measure of

dc or low-frequency (<100 Hz) ac current flow by monitor-

ing the output voltage drops.3 There are a lot of non-contact

current-sensing techniques such as current transformer (CT),

Hall device, and giant magnetoresistance (GMR) sensor. For

the protection purpose, saturation is a major concern of the

CT, once the CT saturates, secondary signals become dis-

torted and may cause relay maloperation.4 To avoid distor-

tion, air-core-framed Rogowski coils are used to measure ac

or pulsed currents, their limited dynamic range abilities and

the weak outputs for small currents severely hinder their

practical applications.5 Hall current sensor with wide fre-

quency bandwidth is more accurate than CT and Rogowski

coil, but this active device must be supplied by an external

power, and the extra power energy is consumed.6 The GMR

sensors are widely used in vehicles, military weapons, and

electric equipments, but the 1/f noises induced by thermal

fluctuations of domain walls limit the improvement of its

sensitivity.7–9 Recently, an upsurge in the fields of non-

contact current-sensing techniques research by utilizing mag-

netoelectric (ME) composites and smart materials

appeared.10–14 A ring-type current sensor composed of

Terfenol-D short fiber and PZT piezoelectric ceramic with

sensitivity of 157 mV/A at electromechanical resonance

(EMR) frequency of 62 kHz is presented by Zhang et al.11

The ME current sensors have higher sensitivities relative to

the conventional Hall (or GMR) current sensors. However,

this advantage is useful only at their EMR frequencies with

narrow bandwidth. Once the size of the ME composite is

determined, the EMR frequency is fixed correspondingly. In

a word, some key issues including the low sensitivity for low

frequencies of conventional current-sensing techniques and

the narrow bandwidth of ME current-sensing solutions still

exist in the previously reported methods.

In this study, we introduce a frequency up-conversion

mechanism to our proposed current-sensing device by means

of the magnetostrictive strain modulation. Consequently, the

modulated sidebands can be shifted to the electromechanical

resonance frequency and the output sideband signal contains

all the information about the measured low-frequency signal.

Compared with the previously proposed current-sensing

architectures, several advantages are provided: (i) frequency-

tunable capability for weak ac current detecting with the

higher sensitivity by modulating the magnetostrictive strain,

this technique allows the sensor to operate in up-conversion

frequency mode with enhanced sensitivity for its frequency-

tumble bandwidth; (ii) a maximum enhancement of current-

voltage sensitivity in the proposed sensor is obtained over a

wide modulating frequency band; and (iii) an ac current step

change as small as 3 mA can be accurately distinguished by

amplitude or phase.

The schematic diagram and photograph of the proposed

current sensor are illustrated in Fig. 1. As the key sensitive

element, Terfenol-D/PZT/Terfenol-D trilayer laminate isa)Electronic mail: liping@cqu.edu.cn.

0021-8979/2014/115(17)/17E505/3/$30.00 VC 2014 AIP Publishing LLC115, 17E505-1

JOURNAL OF APPLIED PHYSICS 115, 17E505 (2014)

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fabricated by using epoxy adhesive with curing temperature

of 80 �C. The magnetostrictive Terfenol-D plate, with large

magnetostrictive coefficient (k� 1600 ppm), is commercially

supplied (Gansu Tianxing Rare Earth Functional Materials

Co., Ltd., China) with dimensions of 12� 6� 1 mm3 and the

magnetostrictive crystallographic axis [110] oriented along

longitudinal direction. Piezoelectric ceramic PZT plate

(Electronics Technology Group Corporation 26th Research

Institute, China) is selected as the output element with its

dimensions of 12� 6� 0.8 mm3. An open-loop magnetic

concentrator of nanocrystalline alloy Fe73.5Cu1Nb3Si13.5B9,

with an air slit for the use of concentrating the vortex mag-

netic field, and the ME laminate is placed at the air slit of the

concentrator. More details about fabrication and measure-

ment can be found in our previously reported literature.12

As a function of frequency, the ME voltage coefficient

(aME) of the Terfenol-D/PZT/Terfenol-D ME laminate is

measured at an ac driving magnetic field Hac of 1 Oe. The

resonance aME of 1.495 V/Oe is obtained at the peak fre-

quency of 102.9 kHz, which is approximately 37 times larger

than that at the off-resonance frequency at 1 kHz. Therefore,

a frequency up-conversion mechanism is introduced into the

proposed sensor to obtain higher sensitivity at low frequen-

cies. According to the theory of magnetostrictive strain

modulation, the operating frequency can be shifted by in-

corporating the nonlinear response of magnetostrictive

strain.15,16 This technique offers the possibility to achieve a

resonance-enhanced output at the low frequency which is far

from the resonance frequency. The magnetostrictive strain

k(H) is a nonlinear function of the magnetic field H.

Therefore, it can be written in a Taylor expansion series as17

kðHÞ ¼ a0 þ a1H þ a2H2 þ � � � ; (1)

where ai (i¼ 0, 1, 2…) is the Taylor expansion coefficient of

ith order. When the laminate is excited by H0�cos[(2pf0)t]with a superimposed modulating field Hm�cos[(2pfm)t],then we can obtain a 2nd order crossing term H0Hmcos

[2p(fm 6 f0)t] by substituting the superimposed signal into the

expression of magnetostrictive strain k(H). The nonlinearity

of the magnetostriction results in a crossing term of ac fields

with sum and difference frequencies. The piezoelectric plate

can also be used to receive the magnetostrictive-modulated

strain into electrical signal. The sideband frequencies fm 6 f0describe the process of nonlinear modulating of ac magnetic

fields, and the output sideband signal contains all the informa-

tion about the measured low-frequency signal H0�cos(2pf0)t.This technique allows the proposed current sensor to operate

in resonance mode with high sensitivity within its

frequency-tunable bandwidth if the modulated sideband fre-

quencies fm 6 f0 are equal to the electromechanical resonance

frequency fr.An experimental verification of the field modulation

approach is performed by using our proposed current sensor.

The measured signal of the ac vortex magnetic field is gener-

ated by the input ac current, with power-line frequency of

50 Hz and amplitude of approximately 20 mA (�0.0004 Oe)

along with a modulating field, with a frequency of

102.85 kHz and amplitude of approximately 0.00135 Oe. The

modulating signal is imposed on the sensor by using the

square coil. The output voltage waveforms captured by an os-

cilloscope connected directly to the electrodes of the piezo-

electric layer are demonstrated in Fig. 2. Obviously, the

amplitude of the input sinusoidal current signal with standard

time period of 20 ms has been modulated to the carrying field,

and the frequency of the sidebands signal is shifted to the res-

onance frequency. By means of the magnetostrictive strain

modulation technique, the frequency of input measured cur-

rent signal can be shifted to a higher frequency approaching

the resonance conditions. Consequently, this technique offers

the possibility to achieve resonance-enhanced sensitivities

within a tunable-frequency bandwidth of 1 Hz� 100 kHz.

We use a square coil with 100 turns surrounding the ME

transducer to generate a modulation field of 0.00135 Oe, and

the modulation frequency is chosen as 102.85 kHz so that

modulated single sideband frequency 102.85 kHzþ 50 Hz is

equal to the resonance frequency of 102.9 kHz. The sideband

signal with frequency 102.85 kHzþ 50 Hz contains the in-

formation about the measured field at the power-line

FIG. 1. Cross-sectional view and photograph of the proposed current sensor.FIG. 2. Output waveforms of the proposed sensor driven by a 0.00135 Oe

modulation field at 102.85 kHz respond to an input current signal of 20 mA

at 50 Hz.

FIG. 3. Comparison of the direct signal (circles) and the modulated signal

(squares) from our proposed sensor as a function of input current at the

power-line frequency of 50 Hz.

17E505-2 Zhang et al. J. Appl. Phys. 115, 17E505 (2014)

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frequency. Meanwhile, the corresponding output sensitivity

curve at 102.9 kHz is recorded by using the lock-in amplifier.

The experimental data are shown in Fig. 3, the induced ME

voltage has an excellent linear relationship with the input

current of a nonlinearity error less than 0.00023%FS in the

dynamic range from 3 mA to 150 A, its current sensitivity is

178.4 mV/A. Signal drift occurs in the region of the input

current less than 3 mA, the magnetic/electrical fluctuations

induced noise and the pyroelectric noises from piezoelectric

plate lead to the sensitivity drift. A noise floor of 1.38

lV/�Hz is measured at approximately EMR conditions with

a corresponding SNR (signal-to-niose) ratio of 20 dB, hence,

the measured sensitivity for the input current less than 3 mA

is submerged in the noise floor. In comparison, the direct

output sensitivity without modulation at 50 Hz is presented

in the dynamic range from 10 mA to 150 A, which shows a

similar relationship for current sensitivity of 48.6 mV/A.

Therefore, the modulated current sensor exhibits a �2.6

times higher sensitivity than of the sensor without

modulating.

Figure 4 shows the resolution of our proposed sensor to

small ac current variations under the power-line frequency of

50 Hz. The modulated output signal goes through a step

change by adjusting the amplitude of input current within

about 250 s. It is clear that the input signal changes (DI) as

small as 3 mA can be clearly distinguished by the voltage or

phase above the noise floor in time-domain capture mode, as

illustrated in Fig. 4(a). In comparison, the resolution of the

sensor without modulation is 10 mA, shown in Fig. 4(b),

which means the resolution improvement in a factor of

approximately 0.3 can be reached by using of the modulation

technique. From Fig. 4(a), we can see that the output voltage

and phase fluctuations are less than 2.6 lV and 0.13�, respec-

tively. However, there is weak output fluctuation of the cur-

rent sensor without modulation illustrated in Fig. 4(b)

whether voltage or phase, it means that this solution is to

improve the current resolution at the expense of enhancing

the time stabilities.

The proposed ME current sensor with up-frequency

mechanism is of technological importance for its frequency-

tunable capabilities, but almost all previously reported solu-

tions for current detection are not able to tune the operating

frequencies. By integrating the frequency up-conversion

mechanism, significant technical resonance-enhanced sensi-

tivity with broadband performances can be realized. Although

the conventional magnetic sensors represented by Hall devi-

ces have wide bandwidth with low temperature drifts, the

low-frequency sensitivity is still necessary for improvement.

By contrast, the proposed electric ME current sensor based on

modulation technique do not suffer from these problems, and

the passive device integrated with frequency-modulation solu-

tion by utilizing nonlinear magnetostriction allows realization

of a self-powered and frequency-tunable magnetic sensor

with broadband performance.

In summary, a broadband current sensor with frequency

up-conversion mechanism is proposed. According to the

nonlinear characteristic of the magnetostrictive plate, low-

frequency enhancement of the current sensitivity is realized

by modulating the dynamic magnetostrictive strain to its res-

onance conditions. This technique offers the possibility to

achieve resonance-enhanced sensitivities at the power-line

frequency far from the resonance frequency. Consequently,

the power-line frequency 50 Hz of the proposed device can

be modulated to the higher-frequency sidebands. This solu-

tion is effective for the working frequencies in the range of

1 Hz� 100 kHz below its resonance frequency, thus enabling

a more useful design solution over conventional methods.

The experimental results demonstrate that an electric current

step change as small as 3 mA can be accurately distinguished

by amplitude or phase. The proposed sensor integrated with

frequency up-conversion mechanism exhibits great poten-

tials for the capabilities of frequency-tunable and weak ac

current detection in practical applications.

This research was supported by the National High

Technology Research and Development Program of China

(863 Program) (No. 2012AA040602) and the National

Natural Science Foundation of China (Grant Nos. 61374217

and 61071042).

1S. Ziegler et al., IEEE Sens. J. 9, 354 (2009).2A. Patel and M. Ferdowsi, IEEE Trans. Veh. Technol. 58, 4108 (2009).3F. Pan et al., Measurement 45, 597 (2012).4J. Salach et al., IEEE Trans. Magn. 48, 1493 (2012).5Y. Liu et al., IEEE Sens. J. 11, 123 (2011).6A. Ajbl et al., IEEE Sens. J. 13, 2271 (2013).7A. Ozbay et al., Appl. Phys. Lett. 94, 202506 (2009).8S. Ingvarsson et al., Phys. Rev. Lett. 85, 3289 (2000).9M. D. Cubells-Beltr�an et al., IEEE Sens. J. 9, 1756 (2009).

10S. X. Dong et al., Appl. Phys. Lett. 85, 2307 (2004).11S. Y. Zhang et al., J. Appl. Phys. 113, 17C733 (2013).12J. T. Zhang et al., Rev. Sci. Instrum. 83, 115001 (2012).13E. S. Leland et al., J. Micromech. Microeng. 19, 094018 (2009).14Y. C. Chen et al., IEEE Sens. J. 12, 2129 (2012).15A. Pantinakis and D. A. Jackson, J. Appl. Phys. 65, 2872 (1989).16S. M. Gillette et al., IEEE Magn. Lett. 2, 2500104 (2011).17D. A. Burdin et al., J. Appl. Phys. 113, 033902 (2013).

FIG. 4. Current resolution of the output voltage and phase respond to small

current step changes as a function of time for (a) the proposed sensor with

modulation and (b) the sensor without modulation.

17E505-3 Zhang et al. J. Appl. Phys. 115, 17E505 (2014)

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