Current sensor based on an atomic magnetometer
for DC application
Guozhu Li (李国祝)
1
, Qing Xin (辛 青)
1,
*, Xuxing Geng (耿旭兴)
2
, Zhi Liang (梁 植)
2
,
Shangqing Liang (梁尚清)
1
, Guangming Huang (黄光明)
2
, Gaoxiang Li (李高翔)
2
,
and Guoqing Yang (杨国卿)
1,
**
1
College of Electronics and Information, Hangzhou Dianzi University, Hangzhou 310018, China
2
College of Physics, Huazhong Normal University, Wuhan 430079, China
*Corresponding author: xinqing@hdu.edu.cn; **corresponding author: gqyang@hdu.edu.cn
Received November 2, 2019; accepted November 28, 2019; posted online February 21, 2020
A DC current sensor based on an optically pumped atomic magnetometer is proposed. It has a high linearity in a
wide operation range, since the magnetometer measures the absolute magnitude of the magnetic field produced
by the current to be measured. The current sensor exhibits a high accuracy with a non-moment solenoid and
magnetic shielding to suppress the influence from the environment. The absolute error of the measured current is
below 0.08 mA when the range is from 7.5 mA to 750 mA. The relative error is 5.54 × 10
−5
at 750 mA.
Keywords: current sensor; atomic magnetometer; high accuracy.
doi: 10.3788/COL202018.031202.
Precision DC current sensing techniques are required by
scientific studies and industrial applications. Current
measurements with high accuracy are usually applied to
current sources in fundamental research. Currents were
controlled with feedback systems to produce stable mag-
netic fields in the Watt balance experiment, whose pur-
pose was to realize the electronic kilogram
[1]
. Accurate
DC current measurement can be used to evaluate current
generators at the picoampere level for the calibration of
other electrical instruments
[2]
. Precise current measure-
ment can be applied to keep the magnetic fields in the
large hadron collider consistent
[3]
. DC current measure-
ment is also very importa nt and widely used in the appli-
cations for power management, industrial control, and
conditions monitoring. The DC current component in
power grids induced by geomagnetic activities is moni-
tored to prevent the saturatio n of transformers
[4]
. Sensors
capable of measuring DC current up to a kiloampere are
desirable for electrowinning industries
[5]
. Besides accuracy
and stability, linearity is an important parameter in auto-
motive applicatio ns
[6]
. However, it is difficult to maintain
high accuracy in a wide operating range. Thermal drift
and nonlinearity of the material in a high field are the
main reasons to degrade the linearity of current sensors.
Current sensing techniques with magnetic field sensors
have attracted wide attention, with emphasis on the study
of high accuracy and linearity. Several compensation
methods have been proposed. Thermal drift can be com-
pensated with temperature monitoring in a magneto-
resistive current sensor
[7]
. Differential structure has been
used to protect current sensors from external magnetic
fields for high accuracy
[8,9]
. The closed-loop configuration
with a magnetic core and a feedback winding in a fluxgate
current sensor can improve the sensitivity and eliminate
the offset and drift related to temperature
[10]
. Another ef-
fective approach is utilizing magnetometers that have a
low thermal drift and nonlinearity and are suitable for
a highly accurate current sensor. Atom ensembles can be
used to produce a chip-scale high accuracy sensor
[11,12]
.
Current sensors with atomic magnetometers have been
articulated for a broad range of in situ calibration pur-
poses
[13]
. The strength of the magnetic field B produced
by the current to be measured is related to the Larmor
precession frequency f
L
by the atomic g-factor
[14]
. Since
most g-factors can be traceable to about 10
−7
[15]
, an atomic
magnetometer can be used to accurately define a magnetic
field
[16]
. It is expected to have uncertainties in the range of
parts in 10
6
. The magnetic resonance spectrum for mag-
netometers can work in a wide magnetic field range and
exhibit a sharp peak when it is in resonance
[17,18]
. Atomic
magnetometers can be used for current sensors with high
accuracy and linearity.
In this Letter, we propose a new current sensor based on
an optically pumped atomic magnetometer. The current
sensor has high linearity in a wide range because the
atomic magnetometer is a kind of absolute magnetometer
using the fixed atomic g-factor. To achieve high accuracy,
we design a non-moment solenoid to produce a magnetic
field that has a stable relationship with the current to be
measured. Finally, we experimentally demonstrate a DC
current sensor with a high accuracy and linearity.
A schematic diagram of the proposed current sensor is
shown in Fig.
1. The M
Z
type optically pumped atomic
magnetometer is applied in the current sensor
[18]
.An
895 nm laser diode is used as a light source that is locked
to the cesium D
1
line F
g
¼ 4toF
e
¼ 3 transition with sa-
turated absorption spectroscopy. The light from the laser
diode is collimated and conve rted to circular polarization
with a lens and a quarter-wave plate (not drawn in Fig.
1).
The resonant light and a resonant radio frequency (RF)
field excite the cesium atoms in the magnetic field, which
causes magnetic resonance. The signal is detected by a
COL 18(3), 031202(2020) CHINESE OPTICS LETTERS March 2020
1671-7694/2020/031202(4) 031202-1 © 2020 Chinese Optics Letters