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Packaged angle-sensing device with magnetoelectric laminate composite and magnetic circuit
Sensors and Actuators A 273 (2018) 232–239
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Sensors and Actuators A: Physical journal homepage: www.elsevier.com/locate/sna
Packaged angle-sensing device with magnetoelectric laminate composite and magnetic circuit Zhiyi Wu a,∗ , Leixiang Bian b , Sheng Chen a a Engineering Research Center for Mechanical Testing Technology and Equipment of Ministry of Education, Chongqing University of Technology, Chongqing, 400054, China b School of Mechanical Engineering, Nanjing University of Science and Technology, Nanjing City, 210094, China
a r t i c l e
i n f o
Article history: Received 30 November 2017 Received in revised form 23 February 2018 Accepted 25 February 2018 Available online 27 February 2018 Keywords: Angle sensor Magnetoelectric effect Magnetic circuit Piezoelectric transformer
a b s t r a c t A packaged angle sensor consisting of four PZT/FeGa/PZT magnetoelectric (ME) laminate composites, four magnetic accumulation arcs, a magnetic accumulation (MA) ring, a multi-polar magnetic ring (MPMR), a shaft, and necessary shells is fabricated and characterized. The ME laminate composite with a slim shape is placed between the MA arc and the MA ring. The MPMR fixed on the shaft is used to apply a magnetic field associated with angle information to the ME laminate composites. Under the role the MA parts, the magnetic field applied to the ME laminate composites can be enhanced about 7 times. With the increasing of the rotational speed, the frequency of the sensor’s output signal is increased linearity, which can be used to measure the rotational speed. The amplitude of the output signal is increased as well and finally reached a stable value of 45.3 Vpp. In order to realize static test without the participation of an excitation coil, one of the ME laminate composites has been used as a piezoelectric transformer. In experimental, a resolution of 0.2◦ and a favorable stability with a standard deviation in population of ∼40 Vpp are achieved from this sensor. These characteristics show that the packaged sensor can be successfully used in rotational parameters testing and has the potential to establish self-powered wireless angle-sensing devices. © 2018 Elsevier B.V. All rights reserved.
1. Introduction Nowadays, many kinds of angle sensors based on optical, electric, and magnetic principles have been developed to monitor the operating performance and using security of rotational devices in people’s life and production. An optical grating encoder, famous for its high accuracy and resolution [1,2], has been widely used in many machine tools for precision manufacturing. But it is very strict to the working environment. Based on the concept of optical grating, according to the knowledge of magnetism and electricity, magnetic grating encoders and capacitive grating transducers have been developed and successfully replaced the optical grating encoder in some area [3–5]. Compared with the optical grating encoder, the magnetic encoder with a simple construction has a good resistance to humid and dirty environments [3]. However, the grating structure is a double-edged sword. These encoders are usually larger and more expensive if higher accuracy in angular measurement is necessary [2,6]. Synchros and resolvers as angular
∗ Corresponding author. E-mail address: wuzhiyi [email protected] (Z. Wu). https://doi.org/10.1016/j.sna.2018.02.042 0924-4247/© 2018 Elsevier B.V. All rights reserved.
sensors are widely spread in industrial applications. Although they have robustness and stable accuracy in unfriendly environments [7–10], the problem of large volume also could not be avoided. With the progress of technology and the development of multifunction in fusion, the characters of angular sensors such as small size, low power, and easy integration are playing an increasingly important role. Researchers have designed some magnetic angular sensors consisted of Hall sensors placed around a small radial magnetized ring or diametrically magnetized cylindrical or annular magnet [11–13]. The magnetoelectric (ME) effect is a polarization response to an applied magnetic field, or conversely a magnetization response to an applied electric field [14]. The ME effect has been successfully demonstrated in the potential application of magnetic sensors [15–19] and energy harvesters [20–23]. The reported sensitivity is up to 10.12 V/Oe of a FeCuNbSiB/Ni/PZT composite, which is much higher than that of Hall sensors [15]. So, for investigating the role of the ME effect in rotational parameters detection, an ME rotational parameter sensor consisting of a magnetostrictive/piezoelectric laminate composite (MPLC) and a multi-polar magnetic ring (MPMR) has been proposed [24]. Based on this sensor, the rotational speed can be measured by determining the
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Fig. 1. Schematic view of the packaged sensor. (a) Explosion view of the proposed sensor. (b) Assembly diagram of the proposed sensor.
frequency of the output signal and the rotational position can be detected by the phase discrimination. In this sensor, the ME effect is used to detect the AC magnetic field produced by the magnetic ring, so it is suitable only for dynamics testing. For realize dynamics and static testing by the ME effect, a modulation coil winded around the MPLC is used to pro-apply an AC magnetic field to the MPLC which works in the resonance state [25]. However, the existence of the coil leads to the increasing of the sensor’s volume and the requirements for assembly. Moreover, the piezoelectric transformer laminated with the magnetostrictive layer has been used to sensing the magnetic field [26], which offers significances for removing the coil. In addition, for improving the performance of the sensor, necessary encapsulation and magnetic circuit design should be considered. In this paper, a packaged angle sensor consisting of four PZT/FeGa/PZT ME laminate composites, four magnetic accumulation (MA) arcs, a MA ring, a MPMR, a shaft, and necessary shells is fabricated and characterized. The effect of the magnetic circuit made up of MA parts in enhancing the magnetic field has been discussed. The relationship between the proposed sensor’s output signal and the rotational parameters has been analyzed. The methods of measure rotational speed and position are given and discussed. This paper also probes into the angle-sensing performance of the PZT/FeGa/PZT ME laminate composite used as a composite piezoelectric transformer. 2. Analysis and design of the sensor 2.1. Sensor design A schematic diagram of the proposed packaged angle sensor is shown in Fig. 1. It contains four ME laminate composites, four MA arcs, a MA ring, a MPMR, a shaft, two bearings, a pedestal, and a lid, as shown in Fig. 1(a). The ME laminate composite with a slim shape for decreasing the demagnetic field [27,28] is placed between the MA arc and the MA ring. The magnetostrictive (M) layer is embedded into the U-shaped slots of the MA parts to reduce the magnetic flux leakage [29]. Four MA arcs, four M layers, and the MA ring compose a closed magnetic circuit. The MPMR fixed on the shaft is used to apply a magnetic field associated with angle information to the ME laminates. The two bearings are fixed on the two sides of the shaft to connected with the pedestal and the lid. These details are plotted in Fig. 1(b).
2.2. Working principle When the shaft is rotating, with the role of the magnetic circuit, the MPMR applies an enhanced alternating magnetic field to the MPLC. The MPLC undergoes the magnetic field variations, and the alternating magnetic field causes the M layer to generate stress. Then the stress is transmitted to piezoelectric (P) layer, which generates electrical signal. The alternating magnetic field is related with the rotational parameters such as rotational speed and position. Thus, through detecting and analyzing the output signal of the MPLC, the rotational parameters can be measured.
2.2.1. Analysis of the magnetic circuit The role of the magnetic circuit is analyzed through the simulation results of Maxwell 16.0. Without the help of the magnetic circuit, no matter what is the relationship between the M layer and the MPMR, only a little magnetic force lines pass through the M layers along their length direction, as shown in Fig. 2. The magnetic force lines distribution of the proposed sensor with magnetic circuit are described in Fig. 3. Fig. 3(a) shows that when the M layers opposite the interface of two poles, the magnetic force lines only converge in the MA arcs. In Fig. 3(b), When the M layers opposite the N or S pole, almost all the magnetic force lines are pass through the M layers along their length direction. The magnetic field applied to the four M layers have the same amplitude. The numerical results of the effect of the magnetic circuit are shown in Fig. 4. From it, under the role of the magnetic circuit, the average magnetic field along the longitudinal direction (Hal ) in the M layer is enhanced about 7 times. The relationship between Hal and the rotational angle () can be regarded as a triangle wave. Considering the frequency-doubling effect of the magnetostrictive materials, the mathematical expression of Hal in a cycle can be approximately expressed as
⎧ H A ⎪ 0≤≤ ⎨ 4 /4 Hal = HA T = ⎪ ⎩ 2HA − HA ≤ ≤ /4
4
(1)
2
Where HA is the amplitude of the Hal , which is about 70 Oe in this situation.
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Fig. 2. Magnetic force lines distribution of the proposed sensor without the magnetic circuit. (a) M layers opposite the interface of two poles. (b) M layers opposite the N or S pole.
Fig. 3. Magnetic force lines distribution of the proposed sensor with the magnetic circuit. (a) M layers opposite the interface of two poles. (b) M layers opposite the N or S pole.
Fig. 5. Schematic diagram of the PMP laminate composite.
(L-T) mode, based on the equivalent circuit method [30], the ME coefficient ␣V of the MPLC can be given as
Fig. 4. The average magnetic field along the longitudinal direction in the M layer vs. the rotational angle.
2.2.2. Output performance of the MPLC As shown in Fig. 5, the M and P layers are oriented parallel and perpendicular to the chief vibration direction, respectively. So, the PMP laminate composite works in the longitudinal-transverse
˛V =
n (1 − n) td31,p d33,m ∂V
E = 2 H ∂H εT33 n 1 − k31p s11 + (1 − n) s33
(2)
E , sH are the elastic compliance coefficients at conwhere, s11 33 stant electric field strength and constant magnetic field strength; d31p and d33m are the piezoelectric and piezomagnetic coefficients; εT33 is the dielectric permittivity at constant stress; k31 is the electromechanical coupling coefficient of piezoelectric material; n is
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Fig. 6. Photographs of the proposed sensor. (a) Sensor parts. (b) Semi-manufactured sensor. (c) Finished sensor.
the thickness ratio of the magnetostrictive layers; and t is the thickness of the piezoelectric material, respectively. According to Eqs. (1) and (2), the output voltage (Vout ) can be expressed as
In there, with the determine of materials’ parameters, device sizes, fixed form, driving conditions, etc., the transformer ration K is a function of the rotational angle.
Vout = ˛V Hal
3. Sensor fabrication and experimental setup
n (1 − n) td31,p d33,m
=
εT33
n
2 1 − k31p
E s11
H + (1 − n) s33
n (1 − n) td31,p d33,m
=
2 E + H εT33 n 1 − k31p s11 (1 − n) s33
· HA T
3.1. Processing and assembling (3)
· HA T (NStr )
where, N is the number of magnetic poles, S is the rotational speed, and tr is the rotational time. According to Eq. (3), the frequency (f) of Vout can be written as f =
N S 2
(4)
Then, S can be got as S=
2f N
(5)
There is a linear relationship between f and S. At the same time, the rotational position is equal to the phase of Vout . Hence, these relationships provide some insight into the measurement principle about the variations of rotational speed and position. However, the value of Vout is attributed to the rotational of MPMR. So, the rotational position only can be dynamic tested by Vout . 2.2.3. Output performance of the composite piezoelectric transformer According to the PMP laminate composite shown in Fig. 5, it can be used as a composite piezoelectric transformer (CPT), that is the two P layers used as the drive and generate parts, respectively. When applying an alternative voltage (VTd ) to the drive part, according to the direct and converse piezoelectric effects, the generate part can export a lower voltage (VTg ). For enhancing the output performance of CPT, the frequency of VTd is specified to equal the resonance frequency of CPT. As the existence of the M layer, with the change of Hal , it can adjust the working conditions of CPT. So, the relationship between VTg and VTd can be simply wrote as
VTg = K (Hal ) VTd = K VTd
(6)
The proposed sensor is fabricated as shown in Fig. 6. Fig. 6(a) exhibits the sensor parts. The lid, pedestal, and shaft are made up of aluminum by lathe and machining center. The MA parts are fabricated by wire electrical discharge machining with permalloy. The MPMR is four poles bonded NdFeB permanent magnet with dimensions of D30-26 × 5 mm3 , and the maximum value of the magnetic induction intensity on MPMR’s surface is 152.03 mT. The MPLC is consisted of PZT8 and FeGa. PZT8 is commercially supplied (China Electronics Technology Group Corporation No. 26 Research Institute) to have dimensions of 7 × 1.6 × 0.6 mm3 , electrodes are distributed in the two largest surfaces. The FeGa plate (University of Science & Technology Beijing, China) is used as the M layer with dimensions of 10 × 1.6 × 0.8 mm3 . To fabricate the sample, it is bonded together with PZT8 and FeGa by epoxy adhesive. The sample is cured at 80 ◦ for 4 h under load to provide a strong bond between layers. The resonance frequency of the MPLC is about 264 kHz. The semi-manufactured sensor is shown in Fig. 6(b). The M layers are connected with the ground and embedded into the Ushaped slots of the MA parts which are attached on the pedestal. So, the shell of the proposed sensor also is connected with the ground. The finished sensor is shown in Fig. 6(c). The diameter and the height of the proposed sensor are 60 mm and 21 mm, respectively. The volume of the proposed sensor is about 59.35 cm3 . 3.2. Experimental setup The experimental setup used to measure the characterization of the proposed sensor is shown in Fig. 7. As shown in the subgraph of Fig. 7, the proposed sensor is rigid coupled with a 750 W servo motor. A clamping mechanism mounted on the fixed plate is used to grip the shell of the proposed sensor. The control system of the motor takes PLC as the control nucleus, touch screen as humancomputer interface, it makes the system friendly watched, easily operated and handled. A function signal generator is used to apply
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Fig. 7. Photograph of the experimental setup.
Fig. 8. Output voltages of Vout 1 + and Vout 1 - under S = 120 rpm.
Fig. 9. Output voltages of Vout1 + , Vout2 + , Vout3 + , and Vout4 + under S = 120 rpm.
a sinusoidal signal with 264 kHz and 20 Vpp to the drive part of CPT. The output signal of the proposed sensor is monitored by an oscilloscope. In addition, the output signal auto detecting system made of a NI-DAQ card, virtual instrument software, and a computer is established. 4. Results and discussion 4.1. Test of the MPLC Taking a MPLC as an example, the output voltages of Vout 1+ and Vout 1 - (shown in Fig. 5) under the rotational speed equals 120 rpm are described in Fig. 8. The amplitudes of Vout 1+ and Vout 1 - are mostly equal, but phase of them are inversed. And when the MPMR rotates a circle, the output voltages have four periods. Then associating with Fig. 4, these results confirmed the frequency-doubling effect of the M layer. The magnetic field applied to the four M layers have the same amplitude. So, with the rotation of MPMR, the four MPLCs have the same output. This has been demonstrated in Fig. 9. The difference among the four output voltages’ amplitude are ascribed to the size difference of the PZT plates which are cut by manual.
Fig. 10. Output voltages of Vout+ , Vout - , and Vout+ - Vout - under S = 120 rpm.
In Fig. 10, Vout+ describes the parallel result of Vout1+ , Vout 2+ , Vout3+ , and Vout4+ , so does Vout - . The differential output result of Vout+ and Vout - is recorded as Vout+ - Vout - . In this situation, the peakto-peak value of Vout+ - Vout - is up to 29.3 Vpp. With the change of S,
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Fig. 11. The peak-to-peak values of Vout+ , Vout - , and Vout+ - Vout - under different rotational speed.
237
Fig. 13. The output waveforms of the input and output signals with angle increase () equals 5◦ at f = 264 kHz.
Fig. 14. The resolution of the proposed sensor. Fig. 12. The frequency of the output signal and the measurement speed (Sm ) under different rotational speed.
4.2. Test of the composite piezoelectric transformer
the relationships between the peak-to-peak values of Vout+ , Vout - , and Vout+ - Vout - and S are tested in Fig. 11, respectively. When the MPLC is connected with the oscilloscope in the experimental, the capacitance of the PZT plates and the input impedance of the oscilloscope can be RC high-pass filter. [31] So, with the increasing of S, the peak-to-peak values of Vout+ , Vout - , and Vout+ - Vout increase firstly, and then reach stable values, which are 23.6 Vpp, 22.0 Vpp, and 45.3 Vpp, respectively. Compared with other sensors reported previously, the proposed sensor has the largest output voltage which demonstrates the potential to establish self-powered wireless angle-sensing devices. In addition, even when the rotational speed is 1200 rpm, the frequency of these output waveforms is only 80 Hz. So, these waveforms are consistent the low frequency characteristics of the ME effect. And then, if the rotational speed can fast enough to let the ME laminates worked in their resonance state, the output voltages of the proposed sensor at least can enhance hundreds of times. In the following, the role of the proposed sensor in measuring the rotational speed has been studied. Fig. 12 describes the frequency of the output signal is directly proportional to the rotational speed. According to Eq. (5), the measurement speed (Sm ) with different rotational speed can be calculated as shown in Fig. 12. The Sm is linear directly proportional to the rotational speed. The slope of the line is about 0.9975, that is to say, the error of Sm is about 0.25%.
For realize static testing by the proposed sensor, a MPLC is used as a CPT. When an excitation signal with f = 264 kHz specified to equal the resonance frequency of the MPLC is applied to the drive part, the output waveforms of the CPT under different angle are described in Fig. 13. The details of the output waveforms shown in the subgraph expresses that the amplitude and phase of the output waveform are changed with the angle. Taking the amplitude as an example, with the angle changes 5◦ , the variation of the output waveform (VTg ) can up to about 200 mVpp. And then, the resolution of the proposed sensor has been tested and shown in Fig. 14. The peak-to-peak value of VTg goes through a step-change by adjusting the motor. It is clear that as small as 0.2◦ can be distinguished with VTg nearly equals 6 mV. The value of VTg is smaller than 40 mV reported in Ref. [25], but it can be increased by enhancing VTd . And due to the poor signal-to-noise ratio of VTg , the noise caused by the motor is exhibited in this waveform. In addition, under the role of the magnetic force, the shaft tends to rotate to the balance places where have the largest magnetic force (shown in Fig. 3). When the shaft is fixed firmly, due to the clamping mechanism (shown in Fig. 7) couldn’t ensure the shell of the proposed sensor can have a tight junction with the fixed plate, the shell may also rotate to the balance place. So, the output values exist upside moving. To avoid this situation, the connectivity style of shaft and the fixed mode of the shell in the commercial rotational sensor are worth to draw lessons from. Such as optical encoders usually use a rigid metal support to fix the shell on tested elements by screws.
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about 0.9975. A resolution of 0.2◦ at a rotational speed of 120 rpm is achieved from this sensor, so a small step-change rotational angle of 0.2◦ can be clearly distinguished. And the stabilities of the packaged sensor are evaluated by long time measurement of 1 h, and the subsequent analysis is performed by using a mathematical statistics method. Results of the evaluation indicate that the sensor has favorable stability with only a slight standard deviation in population. These characteristics show that the proposed packaged angle sensor can be a promising candidate device for rotational applications, such as robots, motors, revolving stage, etc. And it has the potential to establish self-powered wireless angle-sensing devices. Acknowledgments This work was supported by the National Natural Science Foundation of China (Grant No. 61503051), the Scientific and Technological Research Program of Chongqing Municipal Education Commission (Grant No. KJ1600904), the Natural Science Foundation of Chongqing (Grant No. cstc2017jcyjAX0124), and the Program for Innovation Team Building at Institutions of Higher Education in Chongqing (Grant No. CXTDX201601029). References
Fig. 15. Stability test results. (a) Original data of the sensor output over a period of 1 h. (b) Histogram of the output voltage distribution.
To evaluate the stability of the packaged angle sensor, a continuous test over a period of time is completed. Fig. 15(a) plots the original data of the sensor output within 1 h. A tiny fluctuation can be observed in the magnitude of the V level. These data have been analyzed by using mathematical statistics method, and the corresponding histogram is shown in Fig. 15(b). Obviously, the experimental data obey standard normal distribution. Therefore, the confidence level can reach 99.99% in the confidence interval of [4.034 730 913 Vpp, 4.034 733 776 Vpp] for the normal distribution, and its standard deviation in population is only ∼40 Vpp. 5. Conclusion In this work, a packaged angle sensor based on ME effect and magnetic circuit has been designed, fabricated, and functionally characterized. The angle sensor is composed of four PZT/FeGa/PZT ME laminate composites, four MA arcs, a MA ring, a MPMR, a shaft, and necessary shells. For decreasing the demagnetic field, the M layers are specified with a slim shape. The M layers are embedded into the U-shaped slots of the MA parts. The design of U-shaped slot is aim to reduce the magnetic flux leakage. The closed magnetic circuit consisted with the M layers and MA parts can enhance the magnetic field applied to the M layers about 7 times. With the rotation of the shaft, the two P layers of the MPLC have the same amplitude but the opposite phase. And the four P layers in the same side of the MPLCs have the same output waveforms. So, connecting the four output waveforms in parallel and then subtract the parallel results of other four P layers, the output signal of the proposed sensor can be got. With the increasing of the rotational speed, it increases firstly and finally reaches a stable value of 45.3 Vpp. In addition, the varying frequency of the output signal has a linear relationship with the rotational speed, the slope of which is
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Biographies Zhiyi Wu was born in Chongqing, China. He received the B.E. degree in electronic science and technology and the Ph.D. degrees in instrumentation science and technology from Chongqing University, Chongqing, China, in 2008, and 20013, respectively. He is currently a Research Associate with the Engineering Research Center for Mechanical Testing Technology and Equipment of Ministry of Education, Chongqing University of Technology. His research interests include sensing technology, energy harvesting and nanoenergy. Leixiang Bian was born in Jiangsu, China. He received the B.E. degree in electronic science and technology and the Ph.D. degrees in instrumentation science and technology from Chongqing University, Chongqing, China, in 2004, and 2009, respectively. He is currently an associate Professor with the College of energy and power, Nanjing University of Science and Technology. His research interests include sensing technology, energy harvesting and vibration control. Sheng Chen received the B.E. degree in mechanical engineering from Chongqing university of arts and sciences, Chongqing, China, in 2015. He is currently pursuing the M.E. degree at Chongqing University of Technology, Chongqing, China. His research interest is focused on sensing technology.
Contents lists available at ScienceDirect
Sensors and Actuators A: Physical journal homepage: www.elsevier.com/locate/sna
Packaged angle-sensing device with magnetoelectric laminate composite and magnetic circuit Zhiyi Wu a,∗ , Leixiang Bian b , Sheng Chen a a Engineering Research Center for Mechanical Testing Technology and Equipment of Ministry of Education, Chongqing University of Technology, Chongqing, 400054, China b School of Mechanical Engineering, Nanjing University of Science and Technology, Nanjing City, 210094, China
a r t i c l e
i n f o
Article history: Received 30 November 2017 Received in revised form 23 February 2018 Accepted 25 February 2018 Available online 27 February 2018 Keywords: Angle sensor Magnetoelectric effect Magnetic circuit Piezoelectric transformer
a b s t r a c t A packaged angle sensor consisting of four PZT/FeGa/PZT magnetoelectric (ME) laminate composites, four magnetic accumulation arcs, a magnetic accumulation (MA) ring, a multi-polar magnetic ring (MPMR), a shaft, and necessary shells is fabricated and characterized. The ME laminate composite with a slim shape is placed between the MA arc and the MA ring. The MPMR fixed on the shaft is used to apply a magnetic field associated with angle information to the ME laminate composites. Under the role the MA parts, the magnetic field applied to the ME laminate composites can be enhanced about 7 times. With the increasing of the rotational speed, the frequency of the sensor’s output signal is increased linearity, which can be used to measure the rotational speed. The amplitude of the output signal is increased as well and finally reached a stable value of 45.3 Vpp. In order to realize static test without the participation of an excitation coil, one of the ME laminate composites has been used as a piezoelectric transformer. In experimental, a resolution of 0.2◦ and a favorable stability with a standard deviation in population of ∼40 Vpp are achieved from this sensor. These characteristics show that the packaged sensor can be successfully used in rotational parameters testing and has the potential to establish self-powered wireless angle-sensing devices. © 2018 Elsevier B.V. All rights reserved.
1. Introduction Nowadays, many kinds of angle sensors based on optical, electric, and magnetic principles have been developed to monitor the operating performance and using security of rotational devices in people’s life and production. An optical grating encoder, famous for its high accuracy and resolution [1,2], has been widely used in many machine tools for precision manufacturing. But it is very strict to the working environment. Based on the concept of optical grating, according to the knowledge of magnetism and electricity, magnetic grating encoders and capacitive grating transducers have been developed and successfully replaced the optical grating encoder in some area [3–5]. Compared with the optical grating encoder, the magnetic encoder with a simple construction has a good resistance to humid and dirty environments [3]. However, the grating structure is a double-edged sword. These encoders are usually larger and more expensive if higher accuracy in angular measurement is necessary [2,6]. Synchros and resolvers as angular
∗ Corresponding author. E-mail address: wuzhiyi [email protected] (Z. Wu). https://doi.org/10.1016/j.sna.2018.02.042 0924-4247/© 2018 Elsevier B.V. All rights reserved.
sensors are widely spread in industrial applications. Although they have robustness and stable accuracy in unfriendly environments [7–10], the problem of large volume also could not be avoided. With the progress of technology and the development of multifunction in fusion, the characters of angular sensors such as small size, low power, and easy integration are playing an increasingly important role. Researchers have designed some magnetic angular sensors consisted of Hall sensors placed around a small radial magnetized ring or diametrically magnetized cylindrical or annular magnet [11–13]. The magnetoelectric (ME) effect is a polarization response to an applied magnetic field, or conversely a magnetization response to an applied electric field [14]. The ME effect has been successfully demonstrated in the potential application of magnetic sensors [15–19] and energy harvesters [20–23]. The reported sensitivity is up to 10.12 V/Oe of a FeCuNbSiB/Ni/PZT composite, which is much higher than that of Hall sensors [15]. So, for investigating the role of the ME effect in rotational parameters detection, an ME rotational parameter sensor consisting of a magnetostrictive/piezoelectric laminate composite (MPLC) and a multi-polar magnetic ring (MPMR) has been proposed [24]. Based on this sensor, the rotational speed can be measured by determining the
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Fig. 1. Schematic view of the packaged sensor. (a) Explosion view of the proposed sensor. (b) Assembly diagram of the proposed sensor.
frequency of the output signal and the rotational position can be detected by the phase discrimination. In this sensor, the ME effect is used to detect the AC magnetic field produced by the magnetic ring, so it is suitable only for dynamics testing. For realize dynamics and static testing by the ME effect, a modulation coil winded around the MPLC is used to pro-apply an AC magnetic field to the MPLC which works in the resonance state [25]. However, the existence of the coil leads to the increasing of the sensor’s volume and the requirements for assembly. Moreover, the piezoelectric transformer laminated with the magnetostrictive layer has been used to sensing the magnetic field [26], which offers significances for removing the coil. In addition, for improving the performance of the sensor, necessary encapsulation and magnetic circuit design should be considered. In this paper, a packaged angle sensor consisting of four PZT/FeGa/PZT ME laminate composites, four magnetic accumulation (MA) arcs, a MA ring, a MPMR, a shaft, and necessary shells is fabricated and characterized. The effect of the magnetic circuit made up of MA parts in enhancing the magnetic field has been discussed. The relationship between the proposed sensor’s output signal and the rotational parameters has been analyzed. The methods of measure rotational speed and position are given and discussed. This paper also probes into the angle-sensing performance of the PZT/FeGa/PZT ME laminate composite used as a composite piezoelectric transformer. 2. Analysis and design of the sensor 2.1. Sensor design A schematic diagram of the proposed packaged angle sensor is shown in Fig. 1. It contains four ME laminate composites, four MA arcs, a MA ring, a MPMR, a shaft, two bearings, a pedestal, and a lid, as shown in Fig. 1(a). The ME laminate composite with a slim shape for decreasing the demagnetic field [27,28] is placed between the MA arc and the MA ring. The magnetostrictive (M) layer is embedded into the U-shaped slots of the MA parts to reduce the magnetic flux leakage [29]. Four MA arcs, four M layers, and the MA ring compose a closed magnetic circuit. The MPMR fixed on the shaft is used to apply a magnetic field associated with angle information to the ME laminates. The two bearings are fixed on the two sides of the shaft to connected with the pedestal and the lid. These details are plotted in Fig. 1(b).
2.2. Working principle When the shaft is rotating, with the role of the magnetic circuit, the MPMR applies an enhanced alternating magnetic field to the MPLC. The MPLC undergoes the magnetic field variations, and the alternating magnetic field causes the M layer to generate stress. Then the stress is transmitted to piezoelectric (P) layer, which generates electrical signal. The alternating magnetic field is related with the rotational parameters such as rotational speed and position. Thus, through detecting and analyzing the output signal of the MPLC, the rotational parameters can be measured.
2.2.1. Analysis of the magnetic circuit The role of the magnetic circuit is analyzed through the simulation results of Maxwell 16.0. Without the help of the magnetic circuit, no matter what is the relationship between the M layer and the MPMR, only a little magnetic force lines pass through the M layers along their length direction, as shown in Fig. 2. The magnetic force lines distribution of the proposed sensor with magnetic circuit are described in Fig. 3. Fig. 3(a) shows that when the M layers opposite the interface of two poles, the magnetic force lines only converge in the MA arcs. In Fig. 3(b), When the M layers opposite the N or S pole, almost all the magnetic force lines are pass through the M layers along their length direction. The magnetic field applied to the four M layers have the same amplitude. The numerical results of the effect of the magnetic circuit are shown in Fig. 4. From it, under the role of the magnetic circuit, the average magnetic field along the longitudinal direction (Hal ) in the M layer is enhanced about 7 times. The relationship between Hal and the rotational angle () can be regarded as a triangle wave. Considering the frequency-doubling effect of the magnetostrictive materials, the mathematical expression of Hal in a cycle can be approximately expressed as
⎧ H A ⎪ 0≤≤ ⎨ 4 /4 Hal = HA T = ⎪ ⎩ 2HA − HA ≤ ≤ /4
4
(1)
2
Where HA is the amplitude of the Hal , which is about 70 Oe in this situation.
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Fig. 2. Magnetic force lines distribution of the proposed sensor without the magnetic circuit. (a) M layers opposite the interface of two poles. (b) M layers opposite the N or S pole.
Fig. 3. Magnetic force lines distribution of the proposed sensor with the magnetic circuit. (a) M layers opposite the interface of two poles. (b) M layers opposite the N or S pole.
Fig. 5. Schematic diagram of the PMP laminate composite.
(L-T) mode, based on the equivalent circuit method [30], the ME coefficient ␣V of the MPLC can be given as
Fig. 4. The average magnetic field along the longitudinal direction in the M layer vs. the rotational angle.
2.2.2. Output performance of the MPLC As shown in Fig. 5, the M and P layers are oriented parallel and perpendicular to the chief vibration direction, respectively. So, the PMP laminate composite works in the longitudinal-transverse
˛V =
n (1 − n) td31,p d33,m ∂V
E = 2 H ∂H εT33 n 1 − k31p s11 + (1 − n) s33
(2)
E , sH are the elastic compliance coefficients at conwhere, s11 33 stant electric field strength and constant magnetic field strength; d31p and d33m are the piezoelectric and piezomagnetic coefficients; εT33 is the dielectric permittivity at constant stress; k31 is the electromechanical coupling coefficient of piezoelectric material; n is
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Fig. 6. Photographs of the proposed sensor. (a) Sensor parts. (b) Semi-manufactured sensor. (c) Finished sensor.
the thickness ratio of the magnetostrictive layers; and t is the thickness of the piezoelectric material, respectively. According to Eqs. (1) and (2), the output voltage (Vout ) can be expressed as
In there, with the determine of materials’ parameters, device sizes, fixed form, driving conditions, etc., the transformer ration K is a function of the rotational angle.
Vout = ˛V Hal
3. Sensor fabrication and experimental setup
n (1 − n) td31,p d33,m
=
εT33
n
2 1 − k31p
E s11
H + (1 − n) s33
n (1 − n) td31,p d33,m
=
2 E + H εT33 n 1 − k31p s11 (1 − n) s33
· HA T
3.1. Processing and assembling (3)
· HA T (NStr )
where, N is the number of magnetic poles, S is the rotational speed, and tr is the rotational time. According to Eq. (3), the frequency (f) of Vout can be written as f =
N S 2
(4)
Then, S can be got as S=
2f N
(5)
There is a linear relationship between f and S. At the same time, the rotational position is equal to the phase of Vout . Hence, these relationships provide some insight into the measurement principle about the variations of rotational speed and position. However, the value of Vout is attributed to the rotational of MPMR. So, the rotational position only can be dynamic tested by Vout . 2.2.3. Output performance of the composite piezoelectric transformer According to the PMP laminate composite shown in Fig. 5, it can be used as a composite piezoelectric transformer (CPT), that is the two P layers used as the drive and generate parts, respectively. When applying an alternative voltage (VTd ) to the drive part, according to the direct and converse piezoelectric effects, the generate part can export a lower voltage (VTg ). For enhancing the output performance of CPT, the frequency of VTd is specified to equal the resonance frequency of CPT. As the existence of the M layer, with the change of Hal , it can adjust the working conditions of CPT. So, the relationship between VTg and VTd can be simply wrote as
VTg = K (Hal ) VTd = K VTd
(6)
The proposed sensor is fabricated as shown in Fig. 6. Fig. 6(a) exhibits the sensor parts. The lid, pedestal, and shaft are made up of aluminum by lathe and machining center. The MA parts are fabricated by wire electrical discharge machining with permalloy. The MPMR is four poles bonded NdFeB permanent magnet with dimensions of D30-26 × 5 mm3 , and the maximum value of the magnetic induction intensity on MPMR’s surface is 152.03 mT. The MPLC is consisted of PZT8 and FeGa. PZT8 is commercially supplied (China Electronics Technology Group Corporation No. 26 Research Institute) to have dimensions of 7 × 1.6 × 0.6 mm3 , electrodes are distributed in the two largest surfaces. The FeGa plate (University of Science & Technology Beijing, China) is used as the M layer with dimensions of 10 × 1.6 × 0.8 mm3 . To fabricate the sample, it is bonded together with PZT8 and FeGa by epoxy adhesive. The sample is cured at 80 ◦ for 4 h under load to provide a strong bond between layers. The resonance frequency of the MPLC is about 264 kHz. The semi-manufactured sensor is shown in Fig. 6(b). The M layers are connected with the ground and embedded into the Ushaped slots of the MA parts which are attached on the pedestal. So, the shell of the proposed sensor also is connected with the ground. The finished sensor is shown in Fig. 6(c). The diameter and the height of the proposed sensor are 60 mm and 21 mm, respectively. The volume of the proposed sensor is about 59.35 cm3 . 3.2. Experimental setup The experimental setup used to measure the characterization of the proposed sensor is shown in Fig. 7. As shown in the subgraph of Fig. 7, the proposed sensor is rigid coupled with a 750 W servo motor. A clamping mechanism mounted on the fixed plate is used to grip the shell of the proposed sensor. The control system of the motor takes PLC as the control nucleus, touch screen as humancomputer interface, it makes the system friendly watched, easily operated and handled. A function signal generator is used to apply
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Fig. 7. Photograph of the experimental setup.
Fig. 8. Output voltages of Vout 1 + and Vout 1 - under S = 120 rpm.
Fig. 9. Output voltages of Vout1 + , Vout2 + , Vout3 + , and Vout4 + under S = 120 rpm.
a sinusoidal signal with 264 kHz and 20 Vpp to the drive part of CPT. The output signal of the proposed sensor is monitored by an oscilloscope. In addition, the output signal auto detecting system made of a NI-DAQ card, virtual instrument software, and a computer is established. 4. Results and discussion 4.1. Test of the MPLC Taking a MPLC as an example, the output voltages of Vout 1+ and Vout 1 - (shown in Fig. 5) under the rotational speed equals 120 rpm are described in Fig. 8. The amplitudes of Vout 1+ and Vout 1 - are mostly equal, but phase of them are inversed. And when the MPMR rotates a circle, the output voltages have four periods. Then associating with Fig. 4, these results confirmed the frequency-doubling effect of the M layer. The magnetic field applied to the four M layers have the same amplitude. So, with the rotation of MPMR, the four MPLCs have the same output. This has been demonstrated in Fig. 9. The difference among the four output voltages’ amplitude are ascribed to the size difference of the PZT plates which are cut by manual.
Fig. 10. Output voltages of Vout+ , Vout - , and Vout+ - Vout - under S = 120 rpm.
In Fig. 10, Vout+ describes the parallel result of Vout1+ , Vout 2+ , Vout3+ , and Vout4+ , so does Vout - . The differential output result of Vout+ and Vout - is recorded as Vout+ - Vout - . In this situation, the peakto-peak value of Vout+ - Vout - is up to 29.3 Vpp. With the change of S,
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Fig. 11. The peak-to-peak values of Vout+ , Vout - , and Vout+ - Vout - under different rotational speed.
237
Fig. 13. The output waveforms of the input and output signals with angle increase () equals 5◦ at f = 264 kHz.
Fig. 14. The resolution of the proposed sensor. Fig. 12. The frequency of the output signal and the measurement speed (Sm ) under different rotational speed.
4.2. Test of the composite piezoelectric transformer
the relationships between the peak-to-peak values of Vout+ , Vout - , and Vout+ - Vout - and S are tested in Fig. 11, respectively. When the MPLC is connected with the oscilloscope in the experimental, the capacitance of the PZT plates and the input impedance of the oscilloscope can be RC high-pass filter. [31] So, with the increasing of S, the peak-to-peak values of Vout+ , Vout - , and Vout+ - Vout increase firstly, and then reach stable values, which are 23.6 Vpp, 22.0 Vpp, and 45.3 Vpp, respectively. Compared with other sensors reported previously, the proposed sensor has the largest output voltage which demonstrates the potential to establish self-powered wireless angle-sensing devices. In addition, even when the rotational speed is 1200 rpm, the frequency of these output waveforms is only 80 Hz. So, these waveforms are consistent the low frequency characteristics of the ME effect. And then, if the rotational speed can fast enough to let the ME laminates worked in their resonance state, the output voltages of the proposed sensor at least can enhance hundreds of times. In the following, the role of the proposed sensor in measuring the rotational speed has been studied. Fig. 12 describes the frequency of the output signal is directly proportional to the rotational speed. According to Eq. (5), the measurement speed (Sm ) with different rotational speed can be calculated as shown in Fig. 12. The Sm is linear directly proportional to the rotational speed. The slope of the line is about 0.9975, that is to say, the error of Sm is about 0.25%.
For realize static testing by the proposed sensor, a MPLC is used as a CPT. When an excitation signal with f = 264 kHz specified to equal the resonance frequency of the MPLC is applied to the drive part, the output waveforms of the CPT under different angle are described in Fig. 13. The details of the output waveforms shown in the subgraph expresses that the amplitude and phase of the output waveform are changed with the angle. Taking the amplitude as an example, with the angle changes 5◦ , the variation of the output waveform (VTg ) can up to about 200 mVpp. And then, the resolution of the proposed sensor has been tested and shown in Fig. 14. The peak-to-peak value of VTg goes through a step-change by adjusting the motor. It is clear that as small as 0.2◦ can be distinguished with VTg nearly equals 6 mV. The value of VTg is smaller than 40 mV reported in Ref. [25], but it can be increased by enhancing VTd . And due to the poor signal-to-noise ratio of VTg , the noise caused by the motor is exhibited in this waveform. In addition, under the role of the magnetic force, the shaft tends to rotate to the balance places where have the largest magnetic force (shown in Fig. 3). When the shaft is fixed firmly, due to the clamping mechanism (shown in Fig. 7) couldn’t ensure the shell of the proposed sensor can have a tight junction with the fixed plate, the shell may also rotate to the balance place. So, the output values exist upside moving. To avoid this situation, the connectivity style of shaft and the fixed mode of the shell in the commercial rotational sensor are worth to draw lessons from. Such as optical encoders usually use a rigid metal support to fix the shell on tested elements by screws.
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about 0.9975. A resolution of 0.2◦ at a rotational speed of 120 rpm is achieved from this sensor, so a small step-change rotational angle of 0.2◦ can be clearly distinguished. And the stabilities of the packaged sensor are evaluated by long time measurement of 1 h, and the subsequent analysis is performed by using a mathematical statistics method. Results of the evaluation indicate that the sensor has favorable stability with only a slight standard deviation in population. These characteristics show that the proposed packaged angle sensor can be a promising candidate device for rotational applications, such as robots, motors, revolving stage, etc. And it has the potential to establish self-powered wireless angle-sensing devices. Acknowledgments This work was supported by the National Natural Science Foundation of China (Grant No. 61503051), the Scientific and Technological Research Program of Chongqing Municipal Education Commission (Grant No. KJ1600904), the Natural Science Foundation of Chongqing (Grant No. cstc2017jcyjAX0124), and the Program for Innovation Team Building at Institutions of Higher Education in Chongqing (Grant No. CXTDX201601029). References
Fig. 15. Stability test results. (a) Original data of the sensor output over a period of 1 h. (b) Histogram of the output voltage distribution.
To evaluate the stability of the packaged angle sensor, a continuous test over a period of time is completed. Fig. 15(a) plots the original data of the sensor output within 1 h. A tiny fluctuation can be observed in the magnitude of the V level. These data have been analyzed by using mathematical statistics method, and the corresponding histogram is shown in Fig. 15(b). Obviously, the experimental data obey standard normal distribution. Therefore, the confidence level can reach 99.99% in the confidence interval of [4.034 730 913 Vpp, 4.034 733 776 Vpp] for the normal distribution, and its standard deviation in population is only ∼40 Vpp. 5. Conclusion In this work, a packaged angle sensor based on ME effect and magnetic circuit has been designed, fabricated, and functionally characterized. The angle sensor is composed of four PZT/FeGa/PZT ME laminate composites, four MA arcs, a MA ring, a MPMR, a shaft, and necessary shells. For decreasing the demagnetic field, the M layers are specified with a slim shape. The M layers are embedded into the U-shaped slots of the MA parts. The design of U-shaped slot is aim to reduce the magnetic flux leakage. The closed magnetic circuit consisted with the M layers and MA parts can enhance the magnetic field applied to the M layers about 7 times. With the rotation of the shaft, the two P layers of the MPLC have the same amplitude but the opposite phase. And the four P layers in the same side of the MPLCs have the same output waveforms. So, connecting the four output waveforms in parallel and then subtract the parallel results of other four P layers, the output signal of the proposed sensor can be got. With the increasing of the rotational speed, it increases firstly and finally reaches a stable value of 45.3 Vpp. In addition, the varying frequency of the output signal has a linear relationship with the rotational speed, the slope of which is
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Biographies Zhiyi Wu was born in Chongqing, China. He received the B.E. degree in electronic science and technology and the Ph.D. degrees in instrumentation science and technology from Chongqing University, Chongqing, China, in 2008, and 20013, respectively. He is currently a Research Associate with the Engineering Research Center for Mechanical Testing Technology and Equipment of Ministry of Education, Chongqing University of Technology. His research interests include sensing technology, energy harvesting and nanoenergy. Leixiang Bian was born in Jiangsu, China. He received the B.E. degree in electronic science and technology and the Ph.D. degrees in instrumentation science and technology from Chongqing University, Chongqing, China, in 2004, and 2009, respectively. He is currently an associate Professor with the College of energy and power, Nanjing University of Science and Technology. His research interests include sensing technology, energy harvesting and vibration control. Sheng Chen received the B.E. degree in mechanical engineering from Chongqing university of arts and sciences, Chongqing, China, in 2015. He is currently pursuing the M.E. degree at Chongqing University of Technology, Chongqing, China. His research interest is focused on sensing technology.