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Evaluating Characteristics of Electrostatic Discharge (ESD) Events in Wearable
Medical Devices: Comparison With the IEC 61000-4-2 Standard
Article in IEEE Transactions on Electromagnetic Compatibility · November 2017
DOI: 10.1109/TEMC.2017.2773271
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Evaluating Characteristics of Electrostatic
Discharge (ESD) Events in
Wearable Medical Devices:
Comparison with IEC 61000-4-2 Standard
Mehdi Kohani, Aniket Bhandare, Li Guan, David Pommerenke, Fellow, IEEE,
and Michael G. Pecht, Fellow, IEEE
Abstract— Electrostatic discharge (ESD) malfunctions in
wearable medical devices have resulted in injuries and deaths. The
U.S. Food and Drug Administration (FDA) recommends medical
device manufacturers to qualify the electromagnetic compatibility
of their products according to the IEC 60601-1-2 collateral
standard, within which the IEC 61000-4-2 standard is the
recommended ESD immunity test method. This paper shows that
the IEC 61000-4-2 standard does not provide adequate immunity
for wearable medical devices, due to the differences between the
test setup and the real usage. The peak and maximum time
derivative of the ESD current and transient magnetic fields were
measured during realistic discharge scenarios, where a metal
piece, in lieu of a wearable device, was worn around human hand
or waist. At five voltage levels from 2kV to 10kV, the peak currents
and their maximum time derivatives for realistic discharge
scenarios were larger than the most severe discharges obtained
from the IEC 61000-4-2 test configuration. This discrepancy
between the current results from the IEC 61000-4-2 standard
setup and the realistic discharge scenarios indicates that the ESD
immunity standard for wearable devices needs to be changed with
realistic test configurations, to prevent device malfunctions that
can subsequently jeopardize patient safety.
Index Terms— Medical device, Electrostatic discharge,
Wearable device, Discharge current, Transient magnetic field
I. INTRODUCTION
W
HEN a charged human body and a grounded object (e.g.,
a door frame) come in close enough proximity, the
medium between them electrically breaks down and an
electrostatic discharge (ESD) occurs. The resulting discharge
current can cause permanent damage to electronics if the
charges flow directly into the component. ESD can also
indirectly cause disturbances in electronic equipment when the
discharge current produces transient electromagnetic fields that
induce abnormal currents in the circuitry. The severity of an
ESD event can be characterized by the peak value and
maximum time derivative of the discharge current, and the
transient electromagnetic fields [1], [2].
M. Kohani and M. G. Pecht are with the Center for Advanced Life Cycle
Engineering (CALCE), University of Maryland, College Park, MD, 20742 USA (email:
mkohani@umd.edu, pecht@umd.edu) Corresponding Author: Michael. G. Pecht
A. Bhandare, L. Guan and D. Pommerenke are with the Department of Electrical
and Computer Engineering, Missouri University of Science and Technology, Rolla, MO
65409-0001 USA (email: anbwx7@mst.edu, lg3yf@mst.edu, davidjp@mst.edu)
In a hospital environment, many routine activities result in
accumulation of electrostatic charge on a human body and other
equipment such as beds and carts. For instance, walking on a
carpet, sliding a patient with transfer boards, sitting or laying
down on a hospital bed result in charge buildup. ESD events
due to electrostatic charging of the human body have resulted
in medical device malfunctions such as data corruption and
changes in the settings of cochlear implants [3], changes in the
baseline sensor reading of intracranial pressure monitors [4], or
controller reset in a ventricular assist device that resulted in two
deaths and four injuries [5], [6].
The U.S. Food and Drug Administration (FDA) recognizes
the IEC 60601-1-2 collateral standard for electromagnetic
safety of medical electronic equipment. This standard
recommends the IEC 61000-4-2 test method for ESD immunity,
which simulates an ESD event caused by a charged person
holding a metal piece (e.g., a key or a tool) in hand and
approaching the device under test (DUT). The standard claims
that “… this metal discharge situation is sufficiently severe to
represent all human discharges in the field” [7].
To evaluate the ESD robustness of electronic equipment
according to the IEC 61000-4-2 test method, the performance
of the electronic equipment is monitored when an ESD gun
injects an ESD pulse into the equipment placed on a tabletop.
However, in the real scenario, the discharge mostly occurs
when the wearable device is worn around the patient’s body
parts (e.g., waist, hand, chest), and the patient touches a
grounded conductive object such as a doorknob. The source of
charge in the real scenario is the human body, while in the
standard setup, an ESD gun is the source. The differences
between the test configuration in the standard setup and the real
usage can result in dissimilar severity of ESD events in the two
situations, leading to insufficient immunity for field use. This
could result in ESD malfunctions, which, in the case of lifesupporting devices such infusion pumps, may result in patient
injury or death.
Some researchers have measured the ESD from body-worn
metal objects, in lieu of wearable devices, and compared the
results with discharges caused by an ESD gun calibrated
according to the IEC 61000-4-2 standard [8]–[10]. The
discharge current during ESD testing of wearable devices is
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most likely lower than the current during calibration of the ESD
gun, as the calibration is performed by injecting an ESD pulse
into a grounded metal sheet. Thus, the current from the
calibration becomes an upper bound for the discharge current.
If the real discharge current is even larger than the upper bound,
then it is clearly likely that the differences between the
geometry of the usage scenario and the standard testing lead to
insufficient ESD robustness.
Ishida et al. [8] measured the discharge current waveform for
ESDs from a 1kV charged human subject discharging to a
ground plane via a hand-held metal bar or a semi-sphere metal
piece attached to the subject’s head, arm or waist. The peak
current via the waist-worn metal piece was the largest compared
to other body parts, and it was about 4 times larger than the
results of calibration of an ESD gun charged at the same body
voltage. Ishida et al.’s study [8], had limitations as it only
considered 1kV for the body voltage, while much larger
voltages (as high as 20 kV) may accumulate on a human body
in hospital environments [11], [12]. Moreover, the only
parameter that was analyzed in this study was the peak
discharge current. Other parameters that reflect the severity of
ESD events such as current derivative with respect to time and
maximum transient electromagnetic field and their derivatives,
were not analyzed.
Pommerenke and Aidam [10] investigated the differences
between discharge current and transient electromagnetic field
waveform during ESD events from a human hand (while
holding metal objects), and ESD generators. It was found that
ESD from a charged human resulted in discharge currents up to
10 A/kV, while the ESD simulators calibrated by the IEC 8012 standard (an earlier version the IEC 61000-4-2) resulted in a
much lower value of 3.75 A/kV. Similar to Ishida et al.’s study
[8], they only considered body voltage at 5kV.
In a recent study, Zhou et al., [13] developed an ESD
demonstrator board to measure the transient electromagnetic
fields when a subject charged at 1kV and 8kV discharged to a
vertical ground plane via a waist-worn metal piece (i.e., socalled brush-by scenario) or a hand-held metal bar. Using
statistical distribution of the electromagnetic fields, they
showed that the peak values of the transient fields during a
brush-by ESD scenario were larger than discharges from a
hand-held metal bar. This study, however, was limited to the
peak electromagnetic fields and did not investigate the
discharge currents and its maximum derivatives during the ESD
events.
In this paper, we measured the discharge current and
magnetic (H-) field parameters including peak values and the
maximum time derivatives during discharge scenarios that
could occur in a hospital environment and affect patients with
wearable medical devices. The results of distributions of ESD
events over a range of body voltages from 2kV to 10kV are
compared with the results of ESD gun calibration according to
the IEC 61000-4-2 standard. This comparison between realistic
discharge events and the upper bound of the ESD obtained
during calibration shows whether the standard provides
sufficient ESD immunity for wearable medical devices.
2
II. METHODS
The IEC 61000-4-2 test setup treats wearable electronic
devices as if they are used as tabletop equipment, such as a
laptop. However, in reality, the device is worn around a body
part, such as an infusion pump, which is worn around a patient’s
waist. To investigate the differences between realistic
discharges and the standard setup, and analyze the
consequences, two test setups have been created. The ESD
current and H-fields were measured from a charged human with
a metal piece worn on his body in the first setup, and from an
ESD gun discharging to a standard current target in the second
setup.
A. Discharge scenarios for human body ESD tests
To define a discharge scenario in which an ESD event affects
a wearable device, the location of the device on the body and
the body point at which discharge from the body to the ground
occurs need to be selected. Wearable medical devices can be
worn on different parts of the body such as wrist [14], arm [15],
waist [16], chest [17], or head [18]. In this study, the options for
the device location on the body were limited since a subject had
to hold an H-field sensor close to that location to measure the
transient H-field of the ESD. Only two device locations were
selected: device on the chest and on the waist. In fact, these two
locations are more likely to touch a grounded object, for
instance, when a patient touches the metal frame of a hospital
bed or a doorframe with his hand or waist. In lieu of an actual
wearable medical device, a small metal piece with a
hemispherical tip was worn on the discharge location (i.e., hand
or waist), as shown in Figure 1.
Figure 1. Small metal piece worn on the subject's body in lieu of an
actual wearable device
At each discharge location, two scenarios were considered to
initiate an ESD event, thus, four discharge scenarios were
defined. Figure 2 shows the placement of the field sensors and
the body-worn metal piece on the subject’s body in the four
discharge scenarios (DS1 to DS4). In DS1 and DS2, the bodyworn metal piece mounted on the subject’s waist (DS1) or hand
(DS2), directly discharged the accumulated charge to the
ground. In these two scenarios, the charged subject was holding
the H-field sensor in his hand, relatively close to the discharge
location (i.e., 10cm). In DS3 and DS4 scenarios, discharge to
ground occurred via the subject’s waist such as a belt (DS3) or
via his hand such as a key (DS4), while the body-worn metal
piece was worn on his chest, at about 40cm distance from the
discharge location. The H-field sensor in these scenarios was
held in subject’s arm (close to his chest) as shown in Figure 2.
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It is assumed that in these two scenarios, the discharge current
does not directly affect the device, but it creates transient
electromagnetic fields that can couple into the circuitry of the
chest-worn device.
The subject was initially charged to a high voltage (2kV, 4kV,
6kV, 8kV, and 10kV), using a power supply. Figure 3 shows
3
the setup used for charging the subject (height: 175cm,
weight:70kg) while laying down the bed. To reduce the current
flowing to the subject’s body, a 1GΩ resistance was added to
the wire from the power supply. A voltage measurement system
was designed to record the body voltage at the moment of
discharge. The subject was holding a metal probe, connected to
Figure 2. Schematic representation of four ESD scenarios affecting a wearable medical device worn by a patient
lying on a bed
a surface DC voltmeter in his right hand, and a wire with 1GΩ
resistance from the power supply in his left hand.
After applying the high voltage via a power supply, the
subject’s body voltage increased exponentially, due to the body
capacitance. A second subject monitored the first subject’s
body voltage to ensure the voltage has reached a constant level
equal to the applied voltage. At this moment, the second subject
approached a grounded metal rod (air-discharge tip of an ESD
gun) to the hemispherical tip of the body-worn metal piece
mounted on the first subject’s body who was laying down on
the bed.
field sensor, body voltage meter and the oscilloscope inside a
shielded metallic enclosure. The discharge tests at each body
voltage and discharge scenario were repeated four times.
Therefore, a total of 80 data points were collected from the four
discharge scenarios, at 5 body voltages (from 2kV to 10kV) and
4 discharges at each level. The room temperature and the
relative humidity during the experiments were relatively
constant at 22°C and 20%, respectively.
Figure 3. Human body charging setup
Figure 4 shows the setup for discharge current measurement.
A current clamp was placed around the grounded metal rod to
measure the discharge current through a shielded coaxial cable
connected to an oscilloscope. A deconvolution method was
implemented to compensate for the frequency response in the
range of 10 Hz to 1GHz [19]. A 40dB pulse attenuator and an
ESD protection diode were used to protect the oscilloscope
from the resulting ESD current.
Figure 5 shows a schematic of the ESD measurement setup
including the discharge current measurement equipment, H-
Figure 4. Current measurement setup
The four discharge scenarios involved generation of a spark
in the air gap between the body-worn metal piece and the
grounded metal rod. To ensure consistency between the
discharge events, and to obtain similar spark lengths, the
discharge tests were performed with a relatively constant speed
of approach. However, in many cases, the current and magnetic
field results of one, or sometimes two of the discharge event
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4
Figure 5. ESD measurement setup including the oscilloscope, H-field sensor,
current clamp and body voltage measurement system
were remarkedly lower than the remaining discharges. These
low values of current or H-field were potentially related to the
generation of partial sparks between the metal rod and flat part
of the body-worn metal piece that resulted in an incomplete
discharge. These outliers were removed from the analysis.
B. ESD gun tests according to the IEC 61000-4-2 standard
In the discharge scenarios of body-worn devices, similar to
all real ESD events, the discharge occurred via a spark (known
as air-mode discharge). On the contrary, ESD tests during
product qualification according to the IEC 61000-4-2 standard,
mostly use contact mode discharges, where the tip of the gun
makes contact with the DUT, without generating any sparks.
For plastic surfaces on the DUT, the IEC 61000-4-2 standard
requires air-mode discharges initiated by approaching the ESD
gun towards the DUT. However, the peak current of contact
mode ESD is usually larger than the air-mode discharges with
the ESD gun, given the same charging voltage, due to the
resistance of the air gap.
In most cases, the discharge current during the ESD testing
of a wearable device in a tabletop configuration, cannot exceed
the current during calibration of an ESD gun, given the same
voltage. In the calibration setup, an ESD gun directly injects a
pulse into a current target that has about 2 Ω impedance. This
lower discharge current during DUT testing can be attributed to
the smaller size of the DUT compared to the calibration plane
from an ESD gun are shown in Figure 6. Two situations were
examined: when the magnetic field sensor is 10cm, and 40 cm
away from the discharge location. These two scenarios were
selected to compare their results with the human body tests
described in the previous section. The results of the calibration
experiments where the H-field sensor is 10 cm away from the
discharge location are compared with the results of DS1 and
DS2, and for 40 cm distance, the results are compared with that
of DS3 and DS4.
In each discharge scenario (10 cm and 40 cm away from the
discharge location), five ESD voltage levels, 2kV, 4kV, 6kV,
8kV and 10kV were applied to the ESD target in the middle of
a vertical coupling plane (VCP), as shown in Figure 6. The
and the limited capacitance of the DUT relative to the ground.
During ESD testing, the DUT is placed on a 0.5mm thick
insulator above a metal plate that is only grounded via 470 Ω
resistance. Therefore, the discharge currents obtained from the
contact-mode calibration of an ESD gun are the maximum
currents that could be measured from the IEC 61000-4-2
standard setup. This worst-case discharge scenario from the
calibration setup was studied in this research.
Figure 6. IEC 61000-4-2 setup for ESD gun calibration (H-field sensor
is 10cm away from the target in the picture)
The calibration setup and measurement equipment used to
obtain ESD current and the resulting transient magnetic field
current target was connected to a shielded coaxial cable via an
SMA adapter. The other end of the coaxial cable was connected
to an oscilloscope with 2 GHz bandwidth.
C. Data processing: finding parameters of the current and
field waveform
For every discharge scenario and body voltage, four
parameters for the current and the transient magnetic field
waveform were extracted including the peak, and the maximum
𝑑𝑖
derivative with respect to time (i.e., 𝐼𝑚𝑎𝑥 , 𝑚𝑎𝑥 ( ), 𝐻𝑚𝑎𝑥 ,
𝑑𝐻
𝑑𝑡
𝑚𝑎𝑥 ( ) ). Figure 7 shows an example of a current waveform
𝑑𝑡
obtained during calibration testing of an ESD gun and its peak
and maximum time derivative.
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III. RESULTS AND DISCUSSIONS
Our hypothesis is that the real ESD events for a charged
human with a body-worn device are more severe than the worst
case ESD testing according to the IEC 61000-4-2 standard. This
hypothesis, if confirmed, shows that the ESD immunity
standard does not provide adequate immunity for wearable
medical devices, and therefore, device malfunction and patient
complication might occur. This section discusses the
comparison between the current and H-field results of ESD in
realistic human body discharges and the ESD gun calibration.
5
to a charged subject laying down on a bed. Moreover, in this
study, a distribution of the data was obtained as opposed to
single data points reported in previous studies.
The maximum derivatives of the current waveform for the
two discharge scenarios are also compared with the ESD gun
calibration experiments (Figure 9). The distributions of the two
discharge scenarios overlap, however, the median maximum
current derivative of discharges to waist, before 8kV, is on
average, 1.8 times larger than those obtained by an ESD gun.
At all voltage levels, the current derivative of the ESD gun is
close to the lowest whiskers (i.e., 25th percentile) of the two
distributions. Figure 9 also shows an increasing trend in the
results of both distributions over ESD voltage, however, a slight
decrease occurs at 10 kV.
Figure 8. Comparison of the maximum peak current for discharge to
waist, discharge to hand and ESD gun
Figure 7. Example of peak current and maximum time derivative
extracted from an ESD current waveform (above picture shows the
waveform and the bottom one shows a zoomed in view containing peak
and maximum slope)
A. Discharge current results
Discharge current waveform depends on the input voltage
and the impedance of the object subjected to the ESD relative
to ground (i.e., subject’s body or ESD target on a VCP). In this
analysis, the four discharge scenarios were divided into two
categories based on the body impedance seen from the point of
discharge: “discharge to waist” including DS1 and DS3, and
“discharge to hand including DS2 and DS4. Since each
experiment was repeated four times, 8 data points were
obtained in each category. For the ESD-gun, the resulting
discharge current was analyzed in only one category since all
experiments have the same target impedance.
Figure 8 shows the distribution of the maximum peak
currents for discharge to waist, discharge to hand and the ESD
gun via boxplots. The median peak current for discharge to the
waist in all the five voltage levels shows higher peaks than both
discharge to hand and the ESD gun. The median current of
discharges to waist at body voltages of 2kV to 10kV was, on
average, about 1.5 times larger than discharges to hand, and
ESD gun results. The results cannot be compared with the
previous related literature [9], [10] mainly due to the
differences between our test setup where the discharge occurs
The results shown in Figure 8 and Figure 9 confirm our
hypothesis about realistic discharges from body-worn objects
compared to the ESD immunity standard. These results indicate
that in many voltage levels, the maximum peak and maximum
derivatives of the ESD current for realistic discharges, exceed
the levels obtained by the most severe discharges from an ESD
gun using the IEC 61000-4-2 standard test setup. Therefore, the
realistic ESD events analyzed in this study are more severe than
even the upper bound of the discharges from an ESD gun.
Therefore, the ESD robustness of wearable medical devices
should not be qualified by the IEC 61000-4-2 standard.
It is to be noted that the variations in the distribution of the
peak current and maximum current derivative of the human
discharge scenarios are potentially due to the variation in the
spark lengths. Previous literature has also found that spark
length is a critical factor that affects the current waveform in
air-mode discharges [1], [2], [20].
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6
(10cm in DS1 and DS2, 40 cm in DS3 and DS4). Ampere’s law
assumes that the discharge current flows in a cable with infinite
length. This assumption, although not correct in this
experiment, can be used as a reasonable approximation to
validate the results.
1) Max H-field vs. ESD voltage
Figure 9. Maximum current derivative comparison for discharge to
waist, discharge to hand, and ESD gun
B. H-field Results
Analysis of the H-field results is more complicated than the
current waveform due to the complex geometry of the discharge
location. In this section, two parameters related to H-field
including the maximum H-field intensity and the maximum
time derivative of the H-field waveform obtained for the
discharge scenarios and the ESD gun are analyzed.
Three different analyses were performed on the H-field
results including “maximum H-field vs. ESD voltage”,
“maximum H-field vs. peak current”, and “maximum H-field
derivative vs. maximum current derivative”.
The H-field waveform depends on the discharge current and
the distance between the sensor and the discharge location. In
each of the three analyses for H-field, two categories are
considered for comparison: “discharge to waist” (DS1 and
DS3) and “discharge to hand” (DS2 and DS4). Each category
has the same body impedance (discharge current path) is the,
however, different distances between the H-field sensor and the
discharge location. The H-field intensity for the scenario with a
shorter distance to the discharge location is likely larger than
the other one. Therefore, DS1 and DS2 are expected to have
greater H-field intensity than DS3 and DS4, respectively. To
evaluate this assumption, the effect of sensor position in each
category are compared between the two discharge scenarios:
DS1 vs. DS3, in “discharge to waist category”, and DS2 vs.
DS4 in “discharge to hand category”.
In each analysis, the results of the discharge scenarios are
compared with the H-field data obtained from the ESD gun at
two distances from the discharge point: “10cm distance to the
sensor”, and “40cm distance to the sensor”.
In the second and third analysis, where the peak ESD current
or its maximum derivative is the independent variable, the
Ampere’s law estimation is plotted as a function of the
discharge current or its derivative. The Ampere’s law
estimation for the H-field as a function of the peak current is
expressed in equation (1):
𝐼
𝐻=
(1)
2𝜋𝑟
Equation (2) describes the relation between the maximum
derivative of the H-field and the derivative of the current
waveform with respect to time:
𝑑𝐻
𝑑𝑡
=
𝑑𝑖
𝑑𝑡
( )
2𝜋𝑟
(2)
In these two equations, 𝐼 is the peak current, and r is the
distance between the discharge location and the H-field sensor
Figure 10 shows the maximum H-field intensity as a function
of the applied voltage (i.e., subject’s body voltage for discharge
to waist (DS1 and DS3) and discharge to hand (DS2 and DS4)),
compared with the results of the ESD gun. Based on the
distance between the discharge location and the H-field sensor,
results of DS1, and DS2 are expected to be close to the result of
the ESD gun at 10 cm, and both are expected to be larger than
the results of the ESD gun at 40 cm, as well as DS3 and DS4.
The results of Figure 10 shows that DS3 and DS4 data are
close to the ESD gun results at 40 cm as expected, however,
slightly lower. This result could be attributed to the resistance
of the air gap in the DS3 and DS4 scenarios compared to the
sparkless discharges in the ESD gun calibration tests.
In most ESD voltages, DS1 and DS2 results are slightly
greater than DS3, and DS4 respectively, as well as the ESD gun
results at 40cm. However, DS1 and DS2 results are much lower
than the ESD gun results at 10 cm. The results show a clear
discrepancy between the ESD gun results at 40cm compared to
10cm. However, for the human body tests, this difference
between the two distances is not as large as the ESD gun. This
result implies that the H-field at the vicinity of the discharge
location on the human body (DS1 or DS2) is lower than our
expectation, possibly due to geometry factors.
It is to be noted that the lower maximum H-field results from
human body discharges compared to the worst-case discharges
from the calibration setup, does not necessarily mean that the
realistic discharges are less severe than ESD testing of actual
wearable devices according to the IEC 61000-4-2 standard
Only if the realistic discharges are even more severe than the
ESD gun calibration results, a meaningful conclusion can be
drawn about the effectiveness of the standard setup for ESD
immunity during usage.
Fluctuations in the results of DS1 to DS4 can be attributed to
different spark lengths that leads to variations in the discharge
current and therefore, the H-field results. However, the results
of the contact-mode calibration of the ESD gun at both 10cm
and 40cm fit well with linear relationships. Previous literature
[21], [22] have argued that the transient H-field intensity in
contact mode ESD, have a reciprocal relationship with the
distance from the current target, as expressed in equation 3:
1
𝐻∝( )
(3)
𝑟
where r is the distance. Thus, in our case, the ratio of the Hfield results at 10 cm to 40 cm, is expected to be around 4,
assuming the same discharge current in both scenarios due to
similar body impedance (i.e., discharge path). To investigate
this relationship, two linear fits were found on the ESD gun
results as shown in Figure 10 The ratio between the slopes of
7.76
the two lines is
= 3.99, which is very close to the expected
1.99
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7
Figure 11. Max H-field as a function of ESD voltage for DS1, DS3 (a) and DS2, DS4 (b)
Figure 10. Max H-field as a function of maximum peak current for DS1, DS3 (a) and DS2, DS4 (b)
Figure 12. Max H-field derivative as a function of current derivative for DS1, DS3 (a), and DS2, DS4 (b), compared to the ESD gun and the
Ampere's law estimation
result of 4.
2) Max H-field vs. max ESD current
Figure 11 shows the transient H-field peak values as a
function of the peak ESD current for the four discharge
scenarios compared with the ESD gun. Results. The Ampere’s
law estimations are also shown at 10cm (red line) and 40cm
(blue line) away from the discharge point. DS1 and DS2 data
are far from both the ESD gun results and the Ampere’s law
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8
estimation at 10 cm. At 40 cm, however, the H-field results of
DS3 and DS4 are close to both the Ampere’s law estimation and
the ESD gun results. DS1 results are also close to the results at
40 cm, however, the majority of DS2 data points are between
the Ampere’s law estimation at 10cm and the ESD gun results
at 40 cm, and do not fit well with either of the two lines.
The data obtained for the maximum H-field of ESD gun at
10 cm is above all the other results and the ratio of the slope of
2.28
its fitted line to that of the ESD gun at 40cm is
= 3.93,
0.58
which is close to the expected result of 4. As the discharge
current increases, the gap between the ESD gun results and the
Ampere’s law increases, however, the ESD gun at 10 cm
deviates faster than at 40 cm. These deviations could be due to
the effects of nonlinearities of the spark and complex geometry
near the discharge location.
the maximum transient H-field intensity at 40cm away from the
discharge location for the discharge scenarios. The derivative
of the Ampere’s law also provided acceptable estimations
3) Max H-field derivative vs. current
[2]
Figure 12 shows the maximum H-field derivative results as a
function of the maximum current derivative. Similar to previous
plots, the ESD gun results at 10 cm show the largest values
among all. However, in contrast to previous results, DS1 results
are well correlated with the Ampere’s law assumption at 10 cm,
even at high levels of the current derivative.
DS3 results are between ESD gun results at 40cm and
Ampere’s law estimation at the same distance. DS4 data points
correlate well with the Ampere’s law estimation at 40m, except
a few points between 13A to 20A, where the data fit better with
the ESD gun results at 40 cm. The ratio of the slopes of ESD
3.79
gun results at 40 cm to 10 cm is
= 3.05. Thus, the
1.24
maximum derivatives of the H-field do not follow a
𝑑𝐻
REFERENCES
[1]
[3]
[4]
[5]
[6]
1
( ) relationship, similar to H-field intensity.
𝑟
IV. CONCLUSIONS
Immunity of wearable medical devices against ESD events
during usage is critical as any malfunction may jeopardize
patient health. The FDA recommends manufacturers of
wearable medical devices to qualify their products using the
IEC 61000-4-2 standard test method for ESD immunity. When
qualifying a DUT using the IEC 61000-4-2 standard, the
currents will most likely be smaller than the current during
calibration. Thus, observing currents in real discharge scenarios
that are even larger than the calibration current, indicates that
the test setup used for body-worn medical equipment (tabletop
setup according to IEC 61000-4-2) cannot provide sufficient
ESD immunity for wearable medical devices. The results of our
study confirm this hypothesis as the peak and the maximum
derivative of the discharge current obtained from realistic
discharge scenarios were larger than the most severe ESDs
obtained from the calibration setup of an ESD gun.
Analyzing the transient H-field results revealed that the
maximum intensity and derivative of the H-field from an ESD
gun at 10cm away from the discharge location are greater than
realistic discharge scenarios investigated in this study.
Ampere’s law was found to be reasonably accurate to predict
𝑑𝑖
for 𝑚𝑎𝑥 as a function of 𝑚𝑎𝑥 , at 10cm distance from the
𝑑𝑡
𝑑𝑡
discharge location.
Future work includes analyzing electric field waveforms,
performing experiments on actual wearable devices, and
developing computer simulations to predict the current and
electromagnetic fields at more discharge locations and wearable
device positions on a subject’s body.
[7]
[8]
[9]
[10]
[11]
[12]
[13]
[14]
[15]
R. Chundru, D. Pommerenke, K. Wang, T. Van Doren, F. P.
Centola, and J. S. Huang, “Characterization of human metal ESD
reference discharge event and correlation of generator parameters to
failure levels- Part I: reference event,” IEEE Trans. Electromagn.
Compat., vol. 46, no. 4, pp. 498–504, Nov. 2004.
K. Wang, D. Pommerenke, R. Chundru, T. Van Doren, F. P.
Centola, and J. S. Huang, “Characterization of human metal ESD
reference discharge event and correlation of generator parameters to
failure levels-part II: correlation of generator parameters to failure
levels,” IEEE Trans. Electromagn. Compat., vol. 46, no. 4, pp. 505–
511, Nov. 2004.
M. D. McGinnis, “An ESD-Control Program for Children with
Cochlear Implants,” J. Educ. Audiol., vol. 10, pp. 57–64, 2002.
M. Andresen, M. Juhler, and O. C. Thomsen, “Electrostatic
discharges and their effect on the validity of registered values in
intracranial pressure monitors.,” J. Neurosurg., vol. 119, no. 5, pp.
1119–24, Nov. 2013.
M. O’Riordan, “FDA Issues Formal Rebuke to HeartWare,”
Medscape, 2014. [Online]. Available:
http://www.medscape.com/viewarticle/828007. [Accessed: 15-Dec2016].
S. Lawrence, “Heartware Issues Recall Again for Implantable Heart
Pumps Due to Risk of Death,” FierceBiotech, 2015. [Online].
Available: http://www.fiercemedicaldevices.com/story/heartwareissues-recall-again-implantable-heart-pumps-due-risk-death/201502-23. [Accessed: 10-May-2016].
IEC 61000-4-2, “Electromagnetic compatibility (EMC)- Part 4-2:
Testing and measurement techniques - Electrostatic discharge
immunity test.” International Electrotechnical Commission, Genova.
T. Ishida, F. Xiao, Y. Kami, O. Fujiwara, and S. Nitta,
“Characteristics of Discharge Currents Measured through BodyAttached Metal for Modeling ESD from Wearable Electronic
Devices,” IEICE Trans. Commun., vol. E99–B, no. 1, pp. 186–191,
Jan. 2016.
T. Ishida, S. Nitta, F. Xiao, Y. Kami, and O. Fujiwara, “An
Experimental Study of Electrostatic Discharge Immunity Testing for
Wearable Devices,” in IEEE International Symposium on
Electromagnetic Compatibility (EMC), 2015, pp. 839–842.
D. Pommerenke and M. Aidam, “To what extent do contact-mode
and indirect ESD test methods reproduce reality?,” in Electrical
Overstress/Electrostatic Discharge Symposium Proceedings, 1995,
pp. 101–109.
P. Holdstock and N. Wilson, “The effect of static charge generated
on hospital bedding,” in Proceedings Electrical
Overstress/Electrostatic Discharge Symposium, pp. 356–364.
T. Viheriakoski, M. Kokkonen, P. Tamminen, E. Karja, J. Hillberg,
and J. Smallwood, “Electrostatic threats in hospital environment,”
2014, pp. 1–9.
J. Zhou et al., “An ESD demonstrator system for evaluating the
ESD risks of wearable devices,” in ESD/EOS Association
Symposium, 2017.
C.-S. Chu et al., “A finger-free wrist-worn pulse oximeter for the
monitoring of chronic obstructive pulmonary disease,” 2016, p.
96981C.
W. D. Lynn, O. J. Escalona, and D. J. McEneaney, “ECG
monitoring techniques using advanced signal recovery and arm
worn sensors,” in 2014 IEEE International Conference on
Bioinformatics and Biomedicine (BIBM), 2014, pp. 51–55.
IEEE TRANSACTIONS ON ELECTROMAGNETIC COMPATIBILITY
[16]
[17]
[18]
[19]
[20]
[21]
[22]
N. Bidargaddi et al., “Wavelet based approach for posture transition
estimation using a waist worn accelerometer,” in 2007 29th Annual
International Conference of the IEEE Engineering in Medicine and
Biology Society, 2007, pp. 1884–1887.
J. H. Zhang, D. J. Macfarlane, and T. Sobko, “Feasibility of a Chestworn accelerometer for physical activity measurement,” J. Sci. Med.
Sport, vol. 19, no. 12, pp. 1015–1019, Dec. 2016.
K. Williams, K. Moffatt, D. McCall, and L. Findlater, “Designing
Conversation Cues on a Head-Mounted Display to Support Persons
with Aphasia,” in Proceedings of the 33rd Annual ACM Conference
on Human Factors in Computing Systems - CHI ’15, 2015, pp. 231–
240.
S. Yang, J. Zhou, D. Pommerenke, and D. Liu, “A simple frequency
response compensation method for current probe measurement of
ESD current,” in IEEE International Symposium on
Electromagnetic Compatibility, 2017.
R. Jobava et al., “Computer simulation of ESD from voluminous
objects compared to transient fields of humans,” IEEE Trans.
Electromagn. Compat., vol. 42, no. 1, pp. 54–65, 2000.
D. Pommerenke, “ESD: transient fields, arc simulation and rise time
limit,” J. Electrostat., vol. 36, no. 1, pp. 31–54, Nov. 1995.
G. P. Fotis, I. F. Gonos, and I. A. Stathopulos, “Measurement of the
magnetic field radiating by electrostatic discharges using
commercial ESD generators,” Measurement, vol. 39, no. 2, pp. 137–
146, Feb. 2006.
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