Analysis of Corona Discharge Interferenceon Antennas on Composite Airplanes Huan-Zhan Fu, Yong-Jun Xie, and Jun Zhang, Member, IEEE Abstract—Static electrification of the airframe can of
Trang 1Analysis of Corona Discharge Interference
on Antennas on Composite Airplanes
Huan-Zhan Fu, Yong-Jun Xie, and Jun Zhang, Member, IEEE
Abstract—Static electrification of the airframe can often cause
electromagnetic interference on aircraft radios Triboelectric
charging, occurring when an aircraft is operated in precipitation,
raises the aircraft potential until corona discharges occur from
points of high dc field on the aircraft These corona discharges
generate noise that is coupled into antenna systems installed on
the aircraft The characteristics of electrostatic accumulation on
the surface of carbon fiber composite airplanes are studied in this
paper The differences in electrostatic accumulation between
car-bon fiber composite airplanes and metal airplanes are also
demon-strated Based on the E fields radiated by an electrostatic discharge
(ESD) current, a model of ESD in composite airplanes is
estab-lished As is shown, the induced currents excited by the ESD can
successfully predict the interference to the airborne antennas in the
frequency and time domains, providing a reference for composite
airplane design.
Index Terms—Antenna, composite airplane, corona discharge,
electrostatic discharge (ESD), interference.
I INTRODUCTION
UNDER all-weather conditions, electrostatic accumulation
happens on the surface of an airplane when in flight As a
result, electrostatic discharge (ESD), breaking the raised
poten-tial, occurs on the tip of the airplane where the electric field is
intense, such as the end of an airfoil, the end of an empennage,
and so on
It is shown in [1]–[3] that these discharges can produce serious
interference in airplane and receiving antennas, and disable
com-munication and navigation systems The discharge form,
accom-panied by a series of short pulses, generates considerable RF
en-ergy, and produces serious interference at low frequencies (LF)
and high frequencies (HF) due to the energy of the ESD Since
the hazard of ESD on airplanes and the interference in antennas
are clear, it is worthwhile paying attention to these problems
A variety of early work [4]–[8] studied the generation of ESD
interference and its elimination in aircraft Some researchers
studied the characteristics of ESD and devised techniques for
the elimination of electrostatic interference in aircraft [9] The
noise generated by corona discharge [3], as well as its
interfer-ence to airborne antennas [10], has also been studied in some
early work Alternately, some researchers used the geometrical
theory of diffraction (GTD) to compute the surface current and
Manuscript received December 27, 2007 Current version published
November 20, 2008 This work was supported by the University of Ministry
of Education, China, under Grant NECT-04-0950 to the Program for the New
Century Excellent Talents.
The authors are with the National Laboratory of Antennas and Microwave
Technology, Xidian University, 710071 Xi’an, China (e-mail: laycko@tom.com;
yjxie@xidian.edu.cn; zhangjun1982@163.com).
Color versions of one or more of the figures in this paper are available online
at http://ieeexplore.ieee.org.
Digital Object Identifier 10.1109/TEMC.2008.2004598
charge density induced on aircraft [11] The form of the dis-charge current pulse, numerical models, and the fields radiated
by ESD were studied in [12]–[14] As early as 1966, Yee first presented the equivalent electric dipole model [13], and in 1991, Wilson introduced a relatively simple dipole model of corona discharge to predict radiation fields [14] Preceding studies show that these electrostatic discharges occur on metal aircraft With the wide application of composite materials in aviation, ESD should also be considered under composite conditions
In this paper, corona discharge interference to antennas
on carbon fiber composite airplanes is discussed The corona discharge current waveform produced by corona discharge
in a composite airplane is given in Section II In Section III, the model of ESD in a composite airplane is established to analyze the characteristics of corona discharge and its effects
on antennas In Section IV, the induced current density on the surface of a carbon fiber composite airplane and the radiation patterns of corona discharge are studied Based on the electric fields radiated by an electrostatic corona discharge current, the interference to the airborne antennas is analyzed both in the frequency and time domains, and the induced currents excited by the corona discharge can predict the influence on the equipment of receiving antennas in composite aircraft Finally,
in Section V, conclusions are drawn on the various results of this study
II CORONADISCHARGEDIFFERENCESBETWEEN
COMPOSITE ANDMETALAIRCRAFTS
A General
Triboelectric charging associated with impinging precipita-tion particles during low-altitude flight of composite airplanes generally charges the airplanes to a high potential As charge accumulates on a composite aircraft, the potential will increase until a threshold is reached above which corona discharge break-down occurs in regions of high electric field at the aircraft ex-tremities This breakdown occurs as a series of discrete pulses of short duration and rapid rise time, and therefore, produces noise over a broad spectrum The pulses can be very adequately ap-proximated by a decaying exponential with zero rise time The time-varying corona discharge current pulses generated during the discharge cycle are double exponential in nature and can be represented by the following equation [12]:
I (0, t) = KI p
e −αt − e −β t
, t ≥ 0
where K = 1, α = 4 × 10 6.8 , β = 4.76 × 10 7.6 , I p = 0.05.
For composites, the corona discharge occurs as a series of discrete impulses, but much different from corona discharge 0018-9375/$25.00 © 2008 IEEE
Trang 2for metals The following section discusses a single corona
discharge current pulse produced by a corona discharge at an
airfoil terminal
B Corona Differences Between Composite and Metal Airplane
The electrostatic distribution on a composite airplane is
asym-metric Similar to the metal material case, it mostly concentrates
on the positions where the curvature is large, such as the nose of
the fuselage, the airfoil tips, or points inboard of the dischargers
on the wing
The most common charging mechanism on the surface of
an airplane is triboelectric charging This mechanism involves
electron or ion transfer upon contact, due to the frictional
local-ized heating of microscopic contact areas on solid surfaces The
localized microscopic regions of material are melted, allowing
increased charge mobility Distinctions among various levels of
material resistivity are based on surface and volume resistance
Categories with corresponding ranges of surface and volume
resistivity are given in Table I [15] The electrostatic mobility of
a material gets stronger as the surface or volume resistance trails
off The electrostatic charge that can be developed on an airplane
is a function of its relative position in the triboelectric series,
and of its resistivity Those materials in the series that also have
a higher resistivity can accumulate significant charge because a
longer time is required for charge to bleed off such materials
However, under certain circumstances, even conductive
mate-rials, such as metals, can be charged Compared with metal,
electrostatic accumulation capacity on composite airplanes is
much larger In addition, the attenuation time of an electrostatic
discharge is longer, so it is impossible to totally discharge
Sim-ilar to metal materials, the accumulated electrostatic charge on
a composite airplane is allowed to transfer to positions where
brushes are located, and to be bled off with corona discharge
The time-domain representation of the positive corona
dis-charge current pulses produced on a composite airplane is shown
in Fig 1 Fig 2 shows the corona discharge current pulses in the
frequency domain This breakdown occurs as a series of discrete
impulses of short duration
Compared with metal, as a primary interference source, the
rise time of positive corona discharge current pulses on a
com-posite aircraft is longer (100 ns at sea level), and the loss time
is longer, with a time of 2000 ns Besides, I P reaches a peak
of about 19 mA, which is larger than on a metal aircraft From
Fig 2, we note that the frequency spectrum is less than 30 MHz
and the spectrum energy mostly centralizes around 1 MHz
Dif-ferent series of corona discharge current pulses have the same
spectrum range
Fig 1 Corona discharge current pulses in the time domain.
Fig 2 Corona discharge current pulses in the frequency domain.
III SIMULATIONMODEL The composite airplane here is a certain type of unmanned airplane made of carbon fiber composite material The relative
permittivity is ε r = 439.81 − j227.19 and the relative
perme-ability is µ r = 1.0 Fig 3 shows the model of the composite
air-plane The belly and tail-cap antennas are monopoles that have center frequencies of 150 MHz and 1 GHz, respectively The lengths of the belly and tail-cap antennas are 0.5 and 0.075 m, and the wingspan of the composite airplane is 10 m In the HF range, the size of the airplane wingspan is about ten times longer than the radiation wavelength, so we use the method of multi-level fast multipole algorithm (MLFMA) to simulate the corona discharge radiation field But, in the LF range, the method of moment is used to calculate the interference on antennas Electrostatic charge accumulates at the tip of the airplane because the curvature of the tip is large, and the accumulated electrostatic charge is of high density The E fields radiated
by an ESD current are given by E = σ/S As is shown, with
the increase of electric potential at the surface of a composite
Trang 3Fig 3 Model of the composite airplane.
airplane, the air molecules around are easier to ionize and corona
discharges occur at the tip of the airfoil According to the theory
of corona discharge, dischargers can be installed on an aircraft
to permit current to be discharged
In an airplane, the corona discharge model could be equivalent
to an electric dipole [13] So, the effect of corona discharge to
the belly and tail-cap antennas can be computed as the effect
generated by an electric dipole model At the tip of the left and
right composite airfoil, the electric dipole models can be located
to simulate the excitation of an ESD current, as shown in Fig 3
Further, corona discharge characteristics and its interference to
antennas are illustrated
IV CORONADISCHARGECHARACTERISTICS AND
ITSEFFECTS INCOMPOSITEAIRCRAFT
A Corona Discharge Characteristics in Composite Aircraft
1) Induced Current Density: Surface current density can be
induced on the airframe surface owing to corona discharge to
the aircraft Sampling the frequencies between 0.1 and 200 MHz
and computing the electric fields radiated by an ESD current,
the current density that is induced on the surface of the airframe
is shown
Fig 4(a) illustrates the induced current density on the back
surface of a composite airplane and (b) shows it on the belly
The more bright the color is, the greater the induced current
density As is shown in Fig 4, the induced current density was
mainly concentrated at the nose of the airplane, the edge of
the airfoil, and the tail of the composite airplane Besides, the
maximum current destiny distribution positions induced on the
edge of airfoil are quite repetitive and predicable It should be
noted that sensitive instruments should not be installed at these
positions
2) Corona Discharge Far-Field Radiation Pattern: At
dif-ferent frequencies, for example, 30, 60, and 100 MHz, the corona
discharge far-field radiation pattern is different, as is shown in
Fig 5 It is shown that the far radiation field remains largely
symmetric, and the electric fields radiated by corona discharge
are concentrated mostly at the nose and the tail of the airplane
at 30 MHz The directions with strong radiation increase with
the increase of the frequency The higher the frequency is, the
more complex the corona discharge far-field radiation pattern
Fig 4 Distribution of the induced current density on the surface of the airplane.
Fig 5 Corona discharge far-field radiation patterns (a) 30 MHz (b) 60 MHz (c) 100 MHz.
Trang 4Fig 6 Electric noise field at the belly antenna location in the frequency
domain.
B Corona Discharge Interferences on Antennas
To investigate the interference generated by the discharging
of corona produced on the airplane, an airplane model (antennas
were mounted as indicated in Fig 3) was established to predict
the noise generated in aircraft antennas The airborne antennas
were installed at the belly and the tail-cap of the composite
airplane When corona discharges happen at the tip of the airfoil,
the electric radiation fields could have effects on the antennas
According to the results in the time domain for the corona
discharge current pulses that were shown in Fig 1, we can get the
counterpart in the frequency domain by Fourier transformation,
as shown in Fig 2 By setting up the equivalent excitation source,
we can simulate the electric noise field at the belly and tail-cap
locations, and the currents induced in the antennas
1) Electric Noise Field E: The electric noise field at the
belly antenna location in the time domain and the frequency
do-main are shown in Figs 6 and 7, respectively In Fig 6, E is
in-tense when the frequency is under 10 MHz When the frequency
is higher than 10 MHz, the electric noise field decreases
gradu-ally From Fig 7, we can draw the conclusion that the E field has
a change from 113 to 86 V/m The E field in the time domain at
the belly antenna location changes slowly At about 3× 10 −6s,
the value of the E field increases to a maximum of 113 V/m
and it falls to the minimum of 86 V/m at 7× 10 −6s Figs 8
and 9 show the electric noise field at the tail-cap antenna location
in the frequency and time domains Compared with [3] and [9],
the value of the frequency domain E fields at the belly and
tail-cap locations in the composite airplane are much higher than that
in the KC-135(707) aircraft As shown in Figs 6 and 8, the form
of time-domain E field is similar to the ESD form at the high
electric potential in [14] But, the value of the maximum noise
field in that paper is higher than that shown in Figs 6 and 8
2) Induced Noise Current I: By computing the induced
cur-rents at the belly and tail-cap antennas and using an inverse
Fig 7 Electric noise field at the belly antenna location in the time domain.
Fig 8 Electric noise field at the tail-cap-antenna location in the frequency domain.
Fig 9 Electric noise field at the tail-cap antenna location in the time domain.
Trang 5Fig 10 Belly antenna noise current in the time domain.
Fig 11 Tail-cap antenna noise current in the time domain.
Fourier transformation, the time-domain current induced in the
antennas can be illustrated in Figs 10 and 11 Figs 12 and 13
show the noise currents in the frequency domain In the
com-posite condition, the induced current is concentrated within
10 MHz The induced currents on the belly and tail-cap
an-tennas are lower than the ESD current generated at the tip of
the airfoil With the increase of frequency, the induced currents
become lower and appear oscillatory from 10 to 300 MHz In
the time domain, the currents at the belly and tail-cap antennas
induced by corona discharge generated at the tip of airfoil reach
to the maximum of 59 and 1.7 µA, respectively, at the time of
20 ns, and become lower quickly as time passes Compared
with [3], the value of induced current on the belly antenna in the
composite airplane is ten times the current on the belly antenna
in 431-1 aircraft The value of tail-cap antenna noise current is
smaller than that induced at the tail-cap of the 353-1 aircraft and
the 431-1 aircraft
Fig 12 Belly antenna noise current in the frequency domain.
Fig 13 Tail-cap antenna noise current in the frequency domain.
V CONCLUSION The aforesaid study has indicated that the characteristics of corona discharge in composite aircraft are different from the characteristics that occur in metal aircraft For a composite air-plane, an electric dipole model was used to simulate the charac-teristics of corona discharge at the tip of the airfoil The induced current density and the radiation pattern of corona discharge were illustrated in this paper Besides, the electric noise fields at belly and tail-cap antenna locations have been analyzed Corona interference on antennas in the frequency and time domains has been predicted The results shown can predict the interference
on the airborne antennas, thus decreasing the risk of corona dis-charge and providing reference for composite airplane design and the distribution of interior airborne equipments
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Yong-Jun Xie received the B.S., M.S., and Ph.D.
degrees in electronic engineering from Xidian Uni-versity, Xi’an, China, in 1990, 1993, and 1996, respectively.
From 1998 to 1999, he was with the University of Texas at Dallas, Dallas, as a Postdoctoral Research Associate From 1999 to 2001, he was with Duke University as a Postdoctoral Research Associate In
2004, he was supported by the Program for the New Century Excellent Talents in the University of Ministry of Education, China Currently he is a Pro-fessor at Xidian University His research interests include electromagnetic the-ory, microwave technology, and mobile telecommunication.
Jun Zhang (M’02) received the Bachelor’s degree in
electronic engineering in 2005 from Xidian Univer-sity, Xi’an, China, where, since 2006, she has been working toward the Master’s degree.
She has been focusing on the electromagnetic in-terference on composite aircraft Her current research interests include the area of techniques for the elim-ination of corona on aircraft.