ARL-TR-7880 ● NOV 2016

US Army Research Laboratory

US Army Research Laboratory (ARL) Standard 

for Characterization of Electric-Field Sensors,

10 Hz to 10 kHz

by Sean M Heintzelman

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ARL-TR-7880 ● NOV 2016

US Army Research Laboratory

US Army Research Laboratory (ARL) Standard 

for Characterization of Electric-Field Sensors,

10 Hz to 10 kHz

by Sean M Heintzelman

Sensors Electron and Devices Directorate, ARL

Approved for public release; distribution unlimited.
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November 2016

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03/2012–09/2016

4. TITLE AND SUBTITLE

US Army Research Laboratory (ARL) Standard for Characterization of 

Electric-Field Sensors, 10 Hz to 10 kHz

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6. AUTHOR(S)

Sean M Heintzelman

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US Army Research Laboratory

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2800 Powder Mill Road

Adelphi, MD 20783-1138

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ARL-TR-7880

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13. SUPPLEMENTARY NOTES

14. ABSTRACT

The US Army Research Laboratory (ARL) has designed and build a one-of-a-kind electric-field sensor characterization 

facility. The unique facility features a large parallel plate capacitor with guard rings to control fringing fields, controlled by a 

custom LabVIEW program and several pieces of test hardware with less than 0.6% combined measurement error. ARL’s 

electric-field characterization facility creates an approximately 1-m3 region with better than 1.5% electric-field uniformity in a 

smaller physical system than that described in the Institute of Electrical and Electronics Engineers Standard 1308-1994. The 

custom-developed LabVIEW code thoroughly tests the frequency response, linearity, total harmonic distortion, and noise 

across a 60-dB frequency range of an electric-field sensor in less than 10 min. The instrumentation, calibration, and 

characterization methods are detailed.

15. SUBJECT TERMS

electric field, sensors, characterization, LabVIEW, sensor testing

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Sean M Heintzelman

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Contents

List of Figures iv

1. Introduction 1

2. Hardware Used for Autonomous Operation 4

2.1 Data Acquisition Chassis 4

2.2 Analog-to-Digital Converter (ADC) 5

2.3 Arbitrary Waveform (Function) Generator 5

2.4 Serial/Ethernet Port and Current Preamplifier (Optional 

Components) 5

3. Characterizing Capabilities for Electric-field Sensors 6

3.1 Frequency Response 6

3.2 Phase Response 8

3.3 Noise Spectral Density 9

3.4 Linearity 11

3.5 Total Harmonic Distortion (THD) 13

4. Conclusions and Future Work 14

5. References 15

Appendix A. Results and Analysis of Various Electric-field Sensors 17

Appendix B. Operation of the Electric-field Cage 27

Appendix C. LabVIEW Electric-field Cage Control 35

List of Symbols, Abbreviations, and Acronyms 43

Distribution List 44
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List of Figures

Fig. 1 IEEE Std 1308-1994 recommended configuration for calibrating 

electric-field sensors ..............................................................................2

Fig. 2 (Left) ARL electric-field cage model showing the percent error in 

electric-field accuracy at all points within 5% of the electric-field 

magnitude and within 0.5° of the field direction. (Right) Computeraided design model of the ARL electric-field cage with insulated 

mounting. ...............................................................................................3

Fig. 3 (Left) The error in electric-field intensity of conducting spheres placed 

at the center of different electric-field cage designs. The field intensity 

is evaluated at the 2 outer points of the sphere closest to the endplates, 

and the error is derived by comparison to the sphere modeled in free 

space (right). ..........................................................................................3

Fig. 4 Four ARL electric-field cage hardware configurations for sensor 

calibration with no guard tubes drawn. (A) Electrically floating sensor

in a bipolar field. (B) Large GRS in a unipolar field. (C) Testing small 

electrically floating sensors in a high-strength bipolar field. A 

conducting fabric is connected to the guard tube and creates a 

temporary endplate within the IEEE-recommended s/2 spacing. (D) 

Testing small GRS in a higher-strength unipolar field. .........................4

Fig. 5 Setup and wiring for autonomous characterization of sensors with the 

electric-field cage...................................................................................6

Fig. 6 Frequency response of our 31 × 5 test matrix used for standard sensor 

characterization......................................................................................7

Fig. 7 The ARL characterization system error as a function of frequency. The 

error remains under 0.6% over an 80-dB bandwidth.............................8

Fig. 8 Phase response of our 31 × 5 test matrix used for standard sensor 

characterization......................................................................................9

Fig. 9 The voltage NSD of the ARL characterization system, where the 

endplates are connected in parallel to the ADC to account for cage 

impedances...........................................................................................10

Fig. 10 The EFNSD of the ARL characterization system................................10

Fig. 11 Linearity of the ARL sensor characterization system over an 80-dB 

range of field strengths.........................................................................12

Fig. 12 The ARL characterization system linearity as a function of electricfield strength remains within ±0.3% at each order of magnitude in our 

80-dB bandwidth..................................................................................12

Fig. 13 The 0.05% THD of the ARL system is shown. The results provide 

validation that sensor THD can be characterized with better than 0.1% 

accuracy. ..............................................................................................13

Fig. A-1 PS25102 sensors’ frequency and phase responses...............................18
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Fig. A-2 PS25102 sensors’ deviation from the 316-Hz sensitivity value and 

linearity ................................................................................................19

Fig. A-3 PS25102 sensors’ measurements for THD and ERNSD .....................20

Fig. A-4 QUASAR sensors’ frequency and phase responses.............................21

Fig. A-5 QUASAR sensors’ deviation from the 316-Hz sensitivity value and 

linearity ................................................................................................22

Fig. A-6 QUASAR sensors’ measurements for THD and ERNSD ...................23

Fig. A-7 D-dot sensor’s frequency and phase responses....................................24

Fig. A-8 D-dot sensor’s deviation from the 316-Hz sensitivity value and 

linearity ................................................................................................25

Fig. A-9 D-dot sensor’s measurements for THD and ERNSD ..........................26

Fig. B-1 Front panel diagram of the autonomous characterization scheme used 

for sensor characterization at the US Army Research Laboratory ......29

Fig. C-1 The test sequences of 3 executable options .........................................36

Fig. C-2 Reading and loading input values for the characterization test ...........37

Fig. C-3 Processing input parameters to select and load proper values into the 

test sequence ........................................................................................37

Fig. C-4 Function generator output values established and a 1-s measurement is 

performed.............................................................................................38

Fig. C-5 Postmeasurement processing and data capture of the frequency 

response................................................................................................39

Fig. C-6 Performing 1-s THD measurement......................................................40

Fig. C-7 Post-measurement processing and data capture of the THD ...............40

Fig. C-8 NSD measurement performed by LabVIEW code ..............................41
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vi

INTENTIONALLY LEFT BLANK.
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1. Introduction 

Electric-field sensors use a conductor of known size and conductivity to collect 

charge on their transducers, followed by analog circuitry and signal processing to 

output a voltage proportional to the electric field at the sensor interface.

Electric-field sensors generally fall into 3 categories. Electric-field mills use a 

shutter to repeatedly expose and shield a conductor to measure it in a charged and 

uncharged state, respectively, and are suited to static and subkilohertz fields.1 A

second sensor approach is to measure ΔV between 2 conductors at a fixed separation 

d, in a configuration the US Army Research Laboratory (ARL) has named a 

“potential gradiometer”.2 A third method of sensing quasi-static fields is to use 

ground reference sensors (GRSs), where 2 conductors are connected through a 

transimpedance amplifier to measure dE/dt as a function of dq/dt on the source 

conductor relative to the sink conductor.3 Sensors using the second and third 

methods have been characterized at ARL, with results documented in Appendix A 

of this report.

The electric field E created by an point charge with arbitrary magnitude Q(t)in free 

space is given from Coulomb’s law:

EE(tt) = QQ(tt)

4ππεε0

rr�

|rr�⃑|2 , (1)

where r is a vector representing the field coordinates relative to the source charge 

and ε0 is the permittivity of free space. If instead the electric potential V is known 

for 2 sides of a parallel plate capacitor, then the electric-field magnitude can easily 

be approximated as

EE(tt) = ∆VV(tt)

dd , (2)

where ΔV is the potential difference between the 2 plates and d is the distance 

between them. Equations 1 and 2 provide the basis of electric-field sensing in the 

“near zone” of electric-field sources, meaning they can be used to calculate both 

static and quasi-static electric fields. 

The Institute of Electrical and Electronics Engineers (IEEE) Standard (Std) 1308-

19944 provides a method for generating uniform electric fields that allow testing of 

electric-field sensors, shown on the Fig. 1. A voltage generator connected to a 

center-tapped transformer is used to differentially drive 2 parallel square 

conductors (called “endplates”), separated up to half the distance of the side length. 

The configuration also requires that any conductor placed in the geometric center 
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of the plates is small, so the uniformity of the field remains within 1%. The sensor 

should not exceed 0.23 m in its largest diagonal direction for a 1.5 × 1.5 m endplate 

configuration,

5 with no ground planes within 0.5 m of the endplates. 

Fig. 1 IEEE Std 1308-19944 recommended configuration for calibrating electric-field

sensors

At ARL, we have interest in characterizing sensors up to 1 m in the largest diagonal 

direction, meaning IEEE Std 1308-20064 suggests the endplates must be about 

6.5 × 6.5 m with 3.25-m separation. With the additional 0.5-m separation from 

ground planes or a Faraday cage, one needs a 7.5 × 7.5 × 4.5 m laboratory just to 

hold the testing system. Conversely, if we take a more reasonable laboratory size 

of 3 × 3 m, the IEEE standard restricts the system to 2 × 2 × 1 m size and therefore 

the sensor size to 0.31 m in the largest diagonal direction. This complication 

presents a need to design an electric-field sensor characterization facility with a 

larger uniform area in a smaller system size.

To overcome these problems, a conductive shield is used with a linear potential 

gradient along its length from the endplate potentials +V to –V (Fig. 2). This 

reduces capacitance between the endplates and external conductors while also 

lowering capacitance between the shield and the endplates, both of which mitigate 

noise in sensor measurements. The ARL electric-field cage (Fig. 2) was designed 

on this principle by using “guard tubes” connected by resistors to reinforce a linear 

potential along the length of the electric-field cage.

6
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Fig. 2 (Left) ARL electric-field cage model showing the percent error in electric-field 

accuracy at all points within 5% of the electric-field magnitude and within 0.5° of the field 

direction. (Right) Computer-aided design model of the ARL electric-field cage with insulated 

mounting.

Modeling using ARL method of moments (MoM) software shows the center of the 

cage provides an approximately 1-m3 volume (greater than 1.2-m largest diagonal 

distance), where a known electric field is generated with less than 1.5% error.

6 To 

verify the performance of our cage with sensor-like objects inside, we use ARL 

MoM software to show the distortion in electric-field intensity of various-sized 

conducting spheres. This distortion is compared to the distortion of the spheres in 

a uniform electric field, the IEEE-standard calibration system, and the QUASAR 

Federal System’s calibration system based of the IEEE standard.

7 The results of the 

3 cages relative to the free space model are shown in Fig. 3. 

Fig. 3 (Left) The error in electric-field intensity of conducting spheres placed at the center 

of different electric-field cage designs. The field intensity is evaluated at the 2 outer points of 

the sphere closest to the endplates, and the error is derived by comparison to the sphere 

modeled in free space (right).
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All 3 sensing modalities can be characterized easily in the ARL electric-field cage 

due to an access door on one of the endplates (GRS modality) and a nonconductive 

mount in the center (potential gradiometer and field mill modalities). Four unique 

testing configurations with the ARL electric-field cage are pictured in Fig. 4.

Fig. 4 Four ARL electric-field cage hardware configurations for sensor calibration with no 

guard tubes drawn. (A) Electrically floating sensor in a bipolar field. (B) Large GRS in a 

unipolar field. (C) Testing small electrically floating sensors in a high-strength bipolar field. 

A conducting fabric is connected to the guard tube and creates a temporary endplate within 

the IEEE-recommended s/2 spacing. (D) Testing small GRS in a higher-strength unipolar 

field.

Figure 4 shows the high-level hardware and software components used in electricfield sensor characterization, including structural modification to test within IEEE 

Std 1308 guidelines. Additionally, ARL is interested in automating characterization 

(calibration) routines for our sensors to reduce test times and human error. Various 

hardware was purchased and LabVIEW software was custom-developed to create 

a rigorous and autonomous characterization system. 

2. Hardware Used for Autonomous Operation

2.1 Data Acquisition Chassis

Data acquisition and basic signal processing during a characterization test is 

handled by a Peripheral Component Interconnect Extensions for Instrumentation 
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(PXIe) 1062Q is an 8-channel LabVIEW express chassis. The rear panel provides 

connectors (Ethernet, Bayonet Neill–Concelman [BNC], etc.) that can be used for 

communication with external hardware devices (i.e., function generators). One PXI 

card used with the PXIe 1062Q in our experiment is the PXIe8101 with an Intel 

2-GHz embedded controller. The LabVIEW software code runs on this Intel 

processor, and the controller PXI card provides connections for communication/

data transfer.

2.2 Analog-to-Digital Converter (ADC)

To measure the reference signal (dotted black line) in Fig. 4a–d and up to 3 analog 

sensor outputs during characterization tests, a PXI4462 4-channel 24-bit analog-todigital converter (ADC) is used. An NI9239 4-channel ADC is also used in parallel 

to provide 8 total channels for measurements. Of the sensors presented in 

Appendix A, none required more than one ADC for characterization. These 2 ADCs 

can be used interchangeably due to their similarities dynamic range and noise 

floors, and the sensors have been characterized with both ADCs. 

2.3 Arbitrary Waveform (Function) Generator

The waveform generator is used to create necessary electric potential at the ARL 

electric-field cage endplates. The function generator creates single-ended or 

differential (180° out of phase) sinusoidal voltages on the 2 output channels, as well

as provides an in-phase transistor–transistor logic (TTL) trigger output referenced 

to the first channel. To reduce time-domain phase shifts from this trigger for our 

sub-100-kHz frequencies, we use a 2-m BNC cable. We also use an Agilent 33522A 

function generator.

2.4 Serial/Ethernet Port and Current Preamplifier (Optional 

Components)

Data need to be transferred between the hardware pieces and the LabVIEW chassis, 

and each hardware piece can have different serial speeds. The SR 2016 is a 16-port 

gigabit switch device that allows serial interfacing the chassis and multiple-speed 

hardware devices, which interfaces the hardware devices to the LabVIEW software.

In most of our experiments, it is used to interface between the PXIe 1062Q and the 

waveform generator only.

A current to voltage amplifier is needed for sensors with true current outputs, such 

as an SR 570 amplifier. A current preamplifier allows us to add low-pass filtering 

and variable gain levels to the sensor output to better suit the PXI4462’s voltage 

input requirements. The current amplifier settings should be tracked by the user 
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since the device is manually controlled (not by LabVIEW code) and these settings 

are necessary during postexperiment data processing.

Figure 5 shows the physical connections between all hardware components listed 

in this section. Details of the custom software code developed in LabVIEW are 

provided in Appendixes B and C. 

Fig. 5 Setup and wiring for autonomous characterization of sensors with the electric-field 

cage

3. Characterizing Capabilities for Electric-field Sensors

This section details the performance of the ARL electric-field cage connected in 

parallel to the ADC, with the function generator as the source signal. This 

characterizes the operational accuracy of the electric-field cage excitations used for 

sensor measurements and serves as a corollary to documented measurements6 of 

electric-field accuracy over the cage volume. 

3.1 Frequency Response

While electric-field sensors directly measure an electric field, their outputs are read 

as voltages. Data sheets typically provide a sensitivity value, the voltage output per 

unit of field over a specific frequency band, for sensors. The frequency response of 

a sensor describes how sensor output voltage changes in response to electric field 

as the frequency varies and is an important factor in our voltage to electric-field

mapping. Frequency responses are typically measured with phase-locked loops 
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(PLLs) or fast Fourier transform (FFT) measurements at the appropriate frequency 

bin, and while ARL can perform both measurements types, ARL predominantly 

uses the FFT-based method. 

For most sensor characterization tests, we use a standard matrix of 5 magnitudes 

spaced approximately an order of magnitude (20 dB) apart and 31 frequency points 

spaced equally on a logarithmic scale (fn+1 = 1.259fn ). The exact values of the 

matrix are presented as points in Fig. 6.

Fig. 6 Frequency response of our 31 × 5 test matrix used for standard sensor 

characterization

The frequency response allows us to calculate the sensitivity of each sensor at 

different frequency values. The sensitivity provides an estimate on the maximum 

electric field the sensor can reliably measure. An ideal sensor will have a single 

value that can be applied throughout the entire frequency band and rated dynamic 

range of the sensor, although circuitry and device physics usually cause deviations 

near the edges of this range.

The sensitivity value, derived from frequency response, can also be used to reliably 

approximate the upper end of the sensor’s dynamic range. The sensor’s maximum 

output voltage can be divided by a sensor’s sensitivity value, giving the maximum 

electric-field magnitude our sensor can reliably measure.

The sensitivity can be considered for the ARL electric-field cage itself. We apply 

19.6 V across the endplates to produce a 4.67-V/m field, meaning the sensitivity χχ

is 4.2 V/(V/m) or 4.2 m; the separation distance of our cage endplates. Real sensors 

will have a less trivial and nonlinear sensitivity dependence due to effects from 

transducers, amplifiers, and so on. 

 10 100 1k 10k

1u 

10u

.1m

 1m

.01

 .1

 1

 10

Freq (Hz)

Sensor Output (V)

System Frequency Response

 10 100 1k 10k

1u 

10u

.1m

 1m

.01

 .1

 1

 10

0.000476 V/m

0.00473 V/m

0.0471 V/m

0.469 V/m

4.667 V/m
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The error in the applied electric-field strength also must be characterized for the 

system, which gives us the maximum error in sensor sensitivity calculations.

Results from Fig. 7 are used for sensor characterization within the 0%–0.55% error 

values reflected in the graph. The values are used to create correction factors at 

each test point in the frequency response matrix, allowing postmeasurement 

processing to reduce system errors to under 0.1%. 

Fig. 7 The ARL characterization system error as a function of frequency. The error 

remains under 0.6% over an 80-dB bandwidth.

For sensor characterization tests where only 1% accuracy is desired, however, an 

averaged value from Fig. 7 can be used for the “calibration of measurement system”

variable described in Appendix B.

3.2 Phase Response 

The phase response measures how much an electric-field sensor output lags behind 

the electric-field cage endplate excitation potential. The phase response is a 

function of the sensor transducer, filters, gain circuitry, nonlinearity, and so on. 

This measurement is simply the phase portion of the FFT taken during the 

frequency response. For our system phase response, we measure the phase of the 

second endplate referenced to the endplate in phase with the function generator’s 

TTL signal. The results are presented in Fig. 8. 

 10 100 1k 10k

 -1%

 

 

 

-.2%

 0%

 .2%

 

 

 

 1%

Freq (Hz)

Deviation

System Frequency Response Linearity

 10 100 1k 10k

 -1%

 

 

 

-.2%

 0%

 .2%

 

 

 

 1%

0.000476 V/m

0.00473 V/m

0.0471 V/m

0.469 V/m

4.667 V/m
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Fig. 8 Phase response of our 31 × 5 test matrix used for standard sensor characterization

As can be seen in Appendix A, our system has a more linear phase response than 

many commercial off-the-shelf and Government off-the-shelf sensors. The system 

phase response results show the ARL characterization system is within with 0.6° of 

ideal linearity up to 10 kHz. The results from Fig. 8, much like the results from 

Fig. 7, are used to derive correction factors for sub-1% accuracy sensor 

characterizations.

3.3 Noise Spectral Density

We measure the voltage noise floor or noise spectral density (NSD) of these sensors 

as a function of frequency to determine the lower limit of the sensor’s dynamic 

range. In laboratory environments, one is often limited by electric-field noise that 

exists in the measurement equipment and especially at power harmonics. To limit 

these environmental noise effects, we de-energize all noncritical lab equipment 

during testing. The resulting system NSD is shown in Fig. 9.
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Fig. 9 The voltage NSD of the ARL characterization system, where the endplates are 

connected in parallel to the ADC to account for cage impedances

The NSD measurement must first be normalized into volts per root hertz, or 

V/√(Hz), if the FFT bin size is not exactly 1 Hz already. For example, a 10-s FFT 

measurement requires the 10 FFT bins, which represent the equivalent single-hertz 

bin width (e.g., 0.5–1.4 Hz bins representing a 1-Hz bin) to be summed together. 

The NSD is then divided at each frequency bin by the sensor’s sensitivity value to 

determine the electric-field-referred noise spectral density (EFNSD) of the sensor, 

shown in Fig. 10.

Fig. 10 The EFNSD of the ARL characterization system

 10 100 1k 10k

-160dB

-120dB

-80dB

-40dB

0dB

Freq (Hz)

Amplitude (Vrms/sqtr(Hz))

Noise Spectral Density for System

Zero V/m Field

Grounded ADC

 10 100 1k 10k

-160dB

-120dB

-80dB

-40dB

0dB

 10 100 1k 10k

-160dB

-120dB

-80dB

-40dB

0dB

Freq (Hz)

Amplitude ( |Erms| / sqrt(Hz))

Field-referred Noise Spectral Density for System

Zero V/m Field

Grounded ADC

 10 100 1k 10k

-160dB

-120dB

-80dB

-40dB

0dB
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We have performed an EFNSD measurement on our system as shown in Fig. 10 by 

dividing each bin in the NSD measurement by the sensitivity value of the system, 

4.2. For this report, all EFNSD graphs are reported in electric-field magnitude per 

root hertz, or |E|/√(Hz), since this is similar to the common V/√(Hz) representation 

in sensor literature. 

With both the maximum and minimal detectable electric-field values being 

determined from the frequency response and EFNSD graphs, the frequencydependent dynamic range of a sensor can then be calculated:

DDDDDDDDDDDDDD RR RRRR �dddd VV

mm� = 20 ∗ llll �

VVMMMM

χ � − 20 ∗ llll {EEmmmmmm} , (3)

where VMO is the maximum output voltage of the sensor and Emin corresponds to a 

selected frequency value from the EFNSD measurement. This dynamic range value 

would ideally be constant, but environmental effects and circuit nonlinearity create 

a frequency dependence of the dynamic range value. 

From the frequency response and EFNSD measurements, our system is found to 

have approximately 140 dB of dynamic range at the 316-Hz midband frequency 

and at least 130-dB dynamic range throughout the entire testing bandwidth. 

Therefore, sensors with dynamic ranges over these values are limited by the ARL 

characterization system. 

3.4 Linearity

Sensor linearity for our sensor characterization system refers to ability to maintain 

a voltage output directly proportional to the electric-field strength when held at a 

single frequency. An ideal sensor produces a consistent χχ value for any selected 

frequency within its rated bandwidth. The data acquired during the frequency 

response also provide the data needed to characterize the linearity of the ARL 

system and are presented in Fig. 11. 
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Fig. 11 Linearity of the ARL sensor characterization system over an 80-dB range of field 

strengths

To calculate percent linearity for our sensor across the measurement bandwidth, we 

select the sensitivity value at the logarithmic midpoint of the frequency bandwidth 

(316 Hz at 4.667 V/m) and find its ratio with the sensitivity at other frequencies. 

The results are shown in Fig. 12. 

Fig. 12 The ARL characterization system linearity as a function of electric-field strength 

remains within ±0.3% at each order of magnitude in our 80-dB bandwidth

If a sensor is perfectly linear (i.e., χχ316 Hz /χχf is exactly 1), the deviation from 

linearity is precisely 0%. This calculation of linearity for this report is defined as

1m .01 0.1 1 10 1m 

1u 

10u

.1m

 1m

.01

 .1

 1

 10

Field Strength (V/m)

Sensor Output (V)

System Linearity with Frequency

10 Hz

100 Hz

1000 Hz

10000 Hz

1m .01 0.1 1 10 1m 

1u 

10u

.1m

 1m

.01

 .1

 1

 10

.1m 1m .01 0.1 1 10 

 -1%

 

 

 

-.2%

 0%

 .2%

 

 

 

 1%

Field Strength (V/m)

Deviation

System Deviation from Ideal Linearity

10Hz

100Hz

1000Hz

10000Hz

.1m 1m .01 0.1 1 10 

 -1%

 

 

 

-.2%

 0%

 .2%

 

 

 

 1%
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SSSSSSSS SS LLLLLL LL LL = mm �∑ �1 − χ316 HHHH

χff

� ∗ 100% ff=10000

ff=10 � , (4) 

where f denotes any of the 31 test frequencies from the frequency response. 

3.5 Total Harmonic Distortion (THD)

When in the presence of a monotone sinusoidal electric field, an ideal electric-field 

sensor output will be a proportional monotone sinusoid. The ratio of energy in the

sensed harmonic tones relative to the energy at the fundamental frequency is known 

as total harmonic distortion (THD), which can be calculated as

TT = � ∑ VVnn

VV1

=∞

=2 � ∗ 100% , (5)

where V1 is the FFT amplitude of the sensor output at the fundamental frequency 

and Vn is the FFT amplitude at the nth harmonic. 

To avoid power harmonics for the first 15 harmonics and complement the NSD 

bandwidth, a 93-Hz fundamental frequency is selected and measured with a 1-s 

FFT to calculate the sensor THD. For this report, we truncate the THD calculation 

at the 20th harmonic since the results show a signal-to-noise ratio value near 1 

starting near 2 kHz. The ARL characterization system THD has been measured 

with the endplates connected in parallel to the ADC, with results shown in Fig. 13. 

Fig. 13 The 0.05% THD of the ARL system is shown. The results provide validation that 

sensor THD can be characterized with better than 0.1% accuracy.

 10 100 1k 10

-140dB

-120dB

-100dB

-80dB

-60dB

-40dB

-20dB

0dB

20dB

System THD Measurement @ 93Hz

Freq (Hz)

Amplitude (V)

 10 100 1k 10

-140dB

-120dB

-100dB

-80dB

-60dB

-40dB

-20dB

0dB

20dB
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4. Conclusions and Future Work

This report has presented the theory, design, and performance of the ARL electricfield cage and how it is used to characterize electric-field sensors. Electrical 

measurements have demonstrated the uncalibrated hardware system to have less 

than 0.6% error in magnitude and less than 0.6° error in phase, therefore providing 

a reliable environment for electric-field sensor characterization. Improvements are 

currently being made to the testing facility to allow greater electric-field strengths 

to be generated while maintaining 1% linearity over a 100-kHz bandwidth. 
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15

5. References

1. About electric field mill operation. Tuscon (AZ): Mission Instruments; 2006

[accessed 2016]. http://www.missioninstruments.com/pages/learning/

about_fm.html.

2. Hull D, Heintzelman S. Characterization and analysis of electric-field sensors.

2015 IEEE. Industry Applications Society Annual Meeting; 2015 Oct 18–22; 

Dallas, TX. doi: 10.1109/IAS.2015.7356747.

3. Heintzelman S. Self-adjusting quasi-static electric-field sensor. Electrostatic 

Society of America; 2016 [accessed 2016]. http://www.electrostatics.org/

images/O1.pdf.

4. IEEE recommended practice for instrumentation: specifications for magnetic 

flux density and electric field strength meters - 10 Hz to 3 kHz. Piscataway 

(NJ): IEEE Power Engineering Society; 1995 (reaffirmed 2001, 2010). Report 

No.: 1308-1994. doi: 10.1109/IEEESTD.1995.79525.

5. Takuma T, Kawamoto T, Sunaga Y. Analysis of calibration arrangements for 

AC field strength meters. IEEE Trans Power Apparatus and Systems. 1985; 

PER-5(2):489–496. doi: 10.1109/TPAS.1985.319065.

6. Hull D. ARL electric-field cage modeling, design, and fabrication. Military 

Sensing Symposium; 2005 Aug 23–25; Baltimore, MD.

7. QUASAR Federal Systems homepage. San Diego (CA): QUASAR Federal 

Systems; 2016 [accessed 2016]. http://www.quasarfs.com/.
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Appendix A. Results and Analysis of Various Electric-field 

Sensors 
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A-1 Plessey EPIC

Figures A-1 through A-3 show 2 PS25102 sensors1 spaced 60 mm apart with

differential output.

Fig. A-1 PS25102 sensors’ frequency and phase responses

 1 Plessey Semiconductors homepage. Devon (UK): Plessey Semiconductors; n.d. [accessed 2016]. 

http://www.plesseysemiconductors.com/epic-plessey-semiconductors.php.

 10 100 1k 10k

1u 

10u

.1m

 1m

.01

 .1

 1

 10

Freq (Hz)

Sensor Output (V)

Plessey Frequency Response

 10 100 1k 10k

1u 

10u

.1m

 1m

.01

 .1

 1

 10

0.000476 V/m

0.00473 V/m

0.0471 V/m

0.469 V/m

4.667 V/m
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Fig. A-2 PS25102 sensors’ deviation from the 316-Hz sensitivity value and linearity
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Fig. A-3 PS25102 sensors’ measurements for THD and ERNSD

Note: Total harmonic distortion (THD) = 0.8%, dynamic range (316 Hz) = 100 dB,

and sensitivity (316 Hz) = 130 mV/(V/m).

 10 100 1k 10k

-140dB

-120dB

-100dB

-80dB

-60dB

-40dB

-20dB

0dB

20dB

Plessey THD Measurement @ 93Hz

Freq (Hz)

Amplitude (V)

 10 100 1k 10k

-140dB

-120dB

-100dB

-80dB

-60dB

-40dB

-20dB

0dB

20dB

 10 100 1k 10k

-160dB

-120dB

-80dB

-40dB

0dB

Freq (Hz)

Amplitude ( |Erms| / sqrt(Hz))

Field-referred Noise Spectral Density for Plessey

Powered Sensor

Grounded Sensor

Grounded ADC

 10 100 1k 10k

-160dB

-120dB

-80dB

-40dB

0dB
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A-2 QUASAR RVS

Figures A-4 through A-6 show 2 voltage detection sensors (QUASAR2) spaced 

60 mm apart with differential output.

Fig. A-4 QUASAR sensors’ frequency and phase responses

 2 QUASAR Federal Systems homepage. San Diego (CA): QUASAR Federal Systems; 2016 [accessed 

2016]. http://www.quasarfs.com/.

 10 100 1k 10k

1u 

10u

.1m

 1m

.01

 .1

 1

 10

Freq (Hz)

Sensor Output (V)

QUASAR Frequency Response

 10 100 1k 10k

1u 

10u

.1m

 1m

.01

 .1

 1

 10

0.000476 V/m

0.00473 V/m

0.0471 V/m

0.469 V/m

4.667 V/m

 10 100 1k 10k

-150

-100

-50

0

50

100

150

Freq (Hz)

Output Phase (Degrees)

QUASAR Phase Response

 10 100 1k 10k

-150

-100

-50

0

50

100

150 0.000476 V/m

0.00473 V/m

0.0471 V/m

0.469 V/m

4.667 V/m
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Fig. A-5 QUASAR sensors’ deviation from the 316-Hz sensitivity value and linearity

 10 100 1k 10k

-20%

 

 

 -5%

 0%

 5%

 

 

 20%

Freq (Hz)

Deviation

QUASAR Frequency Response Linearity

 10 100 1k 10k

-20%

 

 

 -5%

 0%

 5%

 

 

 20%

0.000476 V/m

0.00473 V/m

0.0471 V/m

0.469 V/m

4.667 V/m

.1m 1m .01 0.1 1 10 

-20%

 

 

 -5%

 0%

 5%

 

 

 20%

Field Strength (V/m)

Deviation

QUASAR Deviation from Ideal Linearity

10Hz

100Hz

1000Hz

10000Hz

.1m 1m .01 0.1 1 10 

-20%

 

 

 -5%

 0%

 5%

 

 

 20%
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Fig. A-6 QUASAR sensors’ measurements for THD and ERNSD

Note: THD = 2.6%, dynamic range (316 Hz) = 110dB, and sensitivity (316 Hz) = 

870 μV/(V/m) 

 10 100 1k 10k

-160dB

-120dB

-80dB

-40dB

0dB

Freq (Hz)

Amplitude ( |Erms| / sqrt(Hz))

Field-referred Noise Spectral Density for QUASAR

Powered Sensor

Grounded Sensor

Grounded ADC

 10 100 1k 10k

-160dB

-120dB

-80dB

-40dB

0dB
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A-3 ARL Smart D-dot

Figures A-7 through A-9 show one d-dot sensor3 tested in the cage configuration 

pictured in Fig. 4d in the report.

Fig. A-7 D-dot sensor’s frequency and phase responses

 3 Heintzelman S. Self-adjusting quasi-static electric-field sensor. Electrostatic Society of America; 2016 

[accessed 2016]. http://www.electrostatics.org/images/O1.pdf.

 10 100 1k 10k

-150

-100

-50

0

50

100

150

Freq (Hz)

Output Phase (Degrees)

Smart Ddot Phase Response

 10 100 1k 10k

-150

-100

-50

0

50

100

150 0.002365 V/m

0.0235 V/m

0.2335 V/m

2.3335 V/m

23.335 V/m
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Fig. A-8 D-dot sensor’s deviation from the 316-Hz sensitivity value and linearity

 10 100 1k 10k

-20%

 

 

 -5%

 0%

 5%

 

 

 20%

Freq (Hz)

Deviation

Smart Ddot Frequency Response Linearity

 10 100 1k 10k

-20%

 

 

 -5%

 0%

 5%

 

 

 20%

0.002365 V/m

0.0235 V/m

0.2335 V/m

2.3335 V/m

23.335 V/m

1m .01 0.1 1 10 100

-20%

 

 

 -5%

 0%

 5%

 

 

 20%

Field Strength (V/m)

Deviation

Smart Ddot Deviation from Ideal Linearity

10Hz

100Hz

1000Hz

10000Hz

1m .01 0.1 1 10 100

-20%

 

 

 -5%

 0%

 5%

 

 

 20%
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26

Fig. A-9 D-dot sensor’s measurements for THD and ERNSD

Note: THD = 2.8%, dynamic range (316 Hz) = 120dB, and sensitivity (316 Hz) = 

6.9 mV/(V/m). 

 10 100 1k 10k

-140dB

-120dB

-100dB

-80dB

-60dB

-40dB

-20dB

0dB

20dB

Smart Ddot THD Measurement @ 93Hz

Freq (Hz)

Amplitude (V)

 10 100 1k 10k

-140dB

-120dB

-100dB

-80dB

-60dB

-40dB

-20dB

0dB

20dB

 10 100 1k 10k

-160dB

-120dB

-80dB

-40dB

0dB

Freq (Hz)

Amplitude ( |Erms| / sqrt(Hz))

Field-referred Noise Spectral Density for Smart Ddot

Powered Sensor

Grounded Sensor

Grounded ADC

 10 100 1k 10k

-160dB

-120dB

-80dB

-40dB

0dB
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Appendix B. Operation of the Electric-field Cage
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28

B-1 Checklist for testing

1. Mount the desired sensor according to Fig. 4 in the report and connect 

necessary wires for powering and measuring the device output (battery, 

Bayonet Neill-Concelman [BNC], Ethernet, etc.).

2. Connect all power outlets on the function generator, Peripheral Component 

Interconnect Extensions for Instrumentation (PXIe) 1062Q, current 

preamplifier, and/or Ethernet switch to a battery or isolated power outlet.

3. Use BNC cables to connect the 2 outputs of the Agilent 33522A signal 

generator to each electric-field cage endplate. Set the output the impedance 

to 50 ohm.

4. Insert the analog-to-digital converter (ADC) and Intel controller cards into 

available slots on the PXI1062Q chassis. The choice of slots is up to the 

user since LabVIEW software should automatically recognize and map the 

ports/connections on each PXI card to correct names in the main LabVIEW 

code. Connect the NI9239 ADC to a USB port on the computer, if desired. 

5. Use a BNC cable to connect the function generator trigger output to an 

analog input on the ADC. Any channel can be used for the trigger/reference 

signal; however, the software program defaults to Ai0 (analog input 0) and 

should be changed to reflect otherwise.

6. Connect the “active link” port on the PXIe8101 to one of the SR 2016’s 

communication channels with Ethernet cable. Connect a second Ethernet 

cable between SR 2016 and the local area network port on the Agilent 

33522A.

7. Use VGA to USB cable/adaptor between the PXIe8101 port and a computer 

display.

8. If sensor outputs are current outputs, configure the SR570 to appropriate 

filter and gain settings. Take manual note of these setting for postprocessing 

of the characterization data.

9. Connect sensor outputs to available ports on PXI4462 and/or the NI9239 

ADC(s). 

10. Ensure LabVIEW DAQmx software, appropriate drivers, and needed 

updates have been downloaded from the National Instruments website

(http://www.ni.com/en-us.html).
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29

11. Use LabVIEW “Measurement and Automation Explorer” to confirm proper 

hardware connections and communication capabilities. All devices should 

have a green check mark to the left of their name, and settings can be 

configured appropriately for the device under test.

12. Load the “Efield Testing” LabVIEW project on monitor and load the “SH 

Standardized Characterization” virtual instrument (VI). The program 

should load all sub-VIs and the front panel appears when complete. 

B-2 Front Panel Navigation

The front panel of SH Simple Data Collection Sweep.vi is shown in Fig. B-1.

Fig. B-1 Front panel diagram of the autonomous characterization scheme used for sensor 

characterization at the US Army Research Laboratory

The left side of the front panel contains inputs for the VI, while the right side will 

display measurements while the program is running. Each component labeled is 

explained as follows: 
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30

(A) Measurement Summary File Path. This contains the file hierarchy and file 

name, which will record the summary data for the measurement. To change 

the name or path of the file, select the folder icon next to this box. Navigate 

to the proper folder on the hard drive and create a .txt file if one is not 

already created. Copy the file path and filename, then paste into the text 

area of this control on the front panel.

(B) Log Raw Data? This Boolean control displays bright green when true and 

a forest green when false. A “true” setting logs the raw samples collected 

by the PXI4462 as a .csv file for every trigger channel and physical 

channel(s) during the entire test duration. The data should match the “Total 

Measurements” front panel waveform when plotted in Excel or MATLAB.

(C) THD Test? This Boolean when selected will run a total harmonic distortion 

test for the sensor and capture the measurement as a .csv file. A 1- or 10-s 

sample will be taken to compute the fast Fourier transform (FFT) based on 

block-diagram settings. 

(D) Noise Measurement? A “true” setting on this Boolean collects 1 s of 

continuous samples of all PXI4462 channels at 50 kS/s and performs a 

software FFT on the data, and the measurement length can be increased in 

software as desired. The FFT results are saved as a .csv file for simple 

plotting in MATLAB or Excel, and should match the “Noise Test Results”

front panel waveform. 

(E) E-field Generator. The arrow along the right side of this control is used to 

select the electric-field cage being used for the measurement. The choice 

for most tests is “ALC 202 3G085 Cage Big.lvlclass” (Fig. 4a or b 

configurations) or “ALC 202 3G085 Cage Small.lvlclass” (Fig. 4c or d 

configurations). When the play button is selected and the test begins to run, 

the appropriate values for the selected cage configuration with populate the 

“Number of Guard Tubes”, “Plate Separation”, and “Cage Load (Ohms)”

indicators. The values are logged in one of the posttest data files, and plate 

separation is used to calculate the electric-field strength for logging in the 

data files. 

(F) Amplitude Sweep Settings. This LabVIEW custom datatype has 4 individual 

controls for the user. “Sweep Points” is an integer for the number of voltage 

amplitudes to sweep through for the frequency response measurement.

“Sweep Start” is a 3-decimal float for the lowest voltage to apply to the 

electric-field cage endplates. “Sweep Stop” is a 3-decimal float for the 

highest voltage to apply to the endplates. “Sweep Type” selects linear or 
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31

logarithmic spacing between the amplitude points when the “Sweep Points”

control is greater than 2.

(G) Frequency Sweep Settings. This LabVIEW custom datatype has 4

individual controls for the user. “Sweep Points” is an integer for the number 

of frequency amplitudes to sweep through for the measurement. “Sweep 

Start” is a 3-decimal float for the lowest frequency at the electric-field cage 

endplates. “Sweep Stop” is a 3-decimal float for the highest frequency to 

the endplates. “Sweep Type” selects linear or logarithmic spacing between 

the frequency points when “Sweep Points” has a value greater than 2.

(H) Acquisition Settings. A custom datatype is used to control the ADCs 

connected to the LabVIEW chassis. “Sample Rate” refers to the acquisition 

speed of the ADC, and should be kept at least 2.4 times higher than the 

maximum test frequency to safely meet Nyquist criteria. “Block Size 

(samples/ch)” controls the number of captured samples to be used with the 

optional phase-locked loop (PLL) measurement algorithm. “Min Value”

and “Max Value” icons determine the voltage range that will be accepted 

by the ADC measurements and should be just greater than the “Sweep Stop”

value of the “Amplitude Sweep Settings” datatype. “Trigger Channels” and 

“Physical Channels” select the ports on the PXI4462 to use as the phase

reference and signal channels, respectively. “AI Coupling” selects whether 

to use AC or DC coupling on the ADC analog inputs during

characterization.

(I) AC Drive Units. This control contains a list of 8 enumerated settings used 

to correlate the amplitudes in the “Amplitude Sweep Settings” to function 

generator voltage outputs. The true Agilent 33522A outputs determines the 

“V” used to calculate the applied electric field (E=V/d, d is the “Plate 

Separation” value) logged in the measurement summary file.

(J) Magnitude Cal. This value is a correction factor based on small hardware 

errors in the testing system. To calculate the appropriate value, see 

Section B-3.

(K) Drive AC Gnd. This button control is used to initiate tests with the ground 

reference sensors (GRSs). One endplate will have the applied voltage 

determined by the “Amplitude Sweep Settings” while the other endplate is 

kept at ground.

(L) Averaged THD. This button initiates only the FFT portion of the sensor 

characterization test, but repeats the FFT measurement 100 times by default 

to create an averaged THD measurement. 
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32

(M) Drive AC Diff. This button control is used to initiate tests where a fully

differential electric field is desired for the measurement. Each endplate will 

have the applied voltage determined by the “Amplitude Sweep Settings”

and will be 180° out of phase with one another. This maximizes the electricfield strength compared to the single-ended configuration.

(N) Stop. This button will cancel the current measurement at any point during 

the sweep. Can cause issues with saving/opening the generated data files, 

use only when necessary.

(O) Current Lockin Sample. This waveform graph displays the data sample 

captured by the PXI4462 during the current sweep setting. The time 

difference between points and total number of points are determined by the 

sample rate and measured samples per ADC channel. The “mag” and “Theta 

Relative” numbers to the right of this graph populate with the measured 

sensor magnitude and phase, respectively.

(P) THD Measurement. This waveform graph displays the result of the most 

recent THD measurement. The “FundMag” and “% THD” blocks reflect the 

strength of the fundamental tone in volts and the THD value for the first 5 

harmonics, respectively.

(Q) Noise Test Results. This waveform graph displays the results for current 

portion of the sensor noise measurement in volts per hertz. MATLAB 

postprocessing gets the data from this graph into a more readable form. 

B-3 Calibration of Measurement System

To normalize any voltage gain/attenuation caused by all characterization system 

hardware, we perform a basic calibration of the system. The calibration scalar can 

be determined using the function generator:

1. Connect one output from the function generator to any ADC analog input.

This might require disconnecting on of the sensor’s outputs temporarily.

2. Set the “Physical Channel” under acquisition settings on the LabVIEW 

front panel to the channel selected in step 1. 

3. Select a single voltage amplitude of 1 V and a single frequency between 

10–10000 Hz by modifying the “Amplitude Sweep Settings” and 

“Frequency Sweep Settings” appropriately. 

4. Ensure “Magnitude Cal” on the front panel is set to 1. 
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33

5. Press the play then “Drive AC Diff” buttons. The experiment will run for 

less than 10 s before finishing. 

6. The 3-decimal float populating the “R” indicator on the front panel should 

be populated. Calculating 1/R gives the calibration constant; the scalar 

multiple difference between the actual input voltage and measured voltage.

7. The calculated calibration constant should be entered in the “Magnitude 

Cal” block of the front panel. Sensor outputs during characterization will be 

multiplied by this constant to negate the sensor effects due to this small error 

in the test hardware. 

B-4 Making a Sensor Characterization Measurement

After following the methods of Sections B-1 to B-3, a sensor characterization is 

ready to be completed:

1. Note the ADC inputs which the Agilent 33522A transistor–transistor logic

(TTL) signal and sensor output(s) are connected. These should reflect the 

values in the “Acquisition Settings” “Trigger Channels” and “Physical 

Channels” blocks. For correct syntax, use LabVIEW standards.

1

2. Input the desired sweep settings in the “Amplitude Sweep Settings”, 

“Frequency Sweep Settings”, and “AC Drive Units” for the 

characterization.

3. Select appropriate Boolean values for recording the raw data collected by 

the ADC, the THD measurement, and/or the noise tests. 

4. Press the play button on the front panel diagram. The button should darken 

in color.

5. Press either the “Drive AC Gnd” or “Drive AC Diff” button to begin the 

measurement sequence. The play button on the front panel will release or 

turn lighter in color when the test is complete, or if “Stop” button is pressed 

during a measurement.

6. View summary files to ensure the data was updated with the newest 

characterization test results. Copy and rename the .txt summary file as a .csv 

file to be saved/exported when data processing begins.

 1 What is the syntax for physical channel strings in DAQmx? Austin (TX): National Instruments; 2014 

[accessed 2016]. http://digital.ni.com/ public.nsf/allkb/9A2AF5E10E0C893386256FE8006807DF.
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Appendix C. LabVIEW Electric-field Cage Control
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36

The flow diagram (Fig. C-1) represents 3 different test sequences corresponding to 

the 3 different executables that can be selected on the LabVIEW front panel. The 

“Drive AC Diff” and “Drive AC Gnd” executables follow similar paths, with the 

only difference being whether one of the endplates is held at ground (unipolar field) 

or tracking 180° out of phase (bipolar field). This Appendix details how inputs from 

the LabVIEW front panel are used in the test sequence of the first 2 columns 

pictured in Fig. C-1, while the “Averaged THD” column will not be described due 

to its straightforwardness. 

Fig. C-1 The test sequences of 3 executable options

C-1 Configuration

The US Army Research Laboratory (ARL) electric-field cage “object” (Fig. C-2) 

is loaded (1) with its associated properties: plate separation, number of guard tubes, 

and cage load in ohms. The communication with the function generator is verified

(2). All other front panel inputs are passed into the main graphical user interface 

loop to determine proper automation sequencing.
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Fig. C-2 Reading and loading input values for the characterization test

C-2 FR, Linearity, and PR Measurement

The frequency sweep settings and amplitude sweep settings (Fig. C-3) are passed 

into sub-virtual instruments (VIs) (2) and (3), which create 2 arrays of voltage and 

frequency values of size M and N, respectively, and thereby our M×N test matrix 

for the frequency response. An Excel spreadsheet is also created (4) with 

appropriate header labels (5) to track the frequency response. The “plate 

separation” parameter is extracted (1) from the electric-field cage object, and the 

acquisition setting parameters are separated (6) for individual use later in the 

program.

Fig. C-3 Processing input parameters to select and load proper values into the test sequence
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38

As shown in Fig. C-4, arrays (1) must be initialized to store values between 

iterations of the nested for loops; the outer loop (2) corresponds to each point in the 

“amplitude sweep settings” array while the inner loop (3) repeats for each point in 

the “frequency sweep settings” array. A custom VI (5) performs a 1-s fast Fourier 

transform (FFT) measurement and extracts the sensor output and phase values in 

the FFT corresponding to the tested frequency, as well as preserving the timedomain waveform captured during the 1-s FFT.

Fig. C-4 Function generator output values established and a 1-s measurement is performed

The current voltage amplitude, frequency, DC offset, plate separation, and cage 

impedance parameters are then passed into another custom VI (4) to create and set 

the function generator to appropriate output settings. This VI uses the cage 

impedance parameter to set the function generator output to either a high or low

impedance setting. The amplitude value and plate separation are normalized to a 

standard electric-field unit of Vpp per meter and the Vpp value is set on the function 

generator, which later will be mathematically converted to Vrms per meter. 

The results from the measurement are plotted in the time domain (1) on the front 

panel of Fig. C-5. The extracted phase value of every sensor output is combined 

into an array and the trigger-channel waveform phase is used to convert into a 

relative phase for each sensor output (2) and (3). The measured sensor output is 

multiplied by the calibration constant (5) to create the calibrated sensor response 

described earlier. 
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Fig. C-5 Postmeasurement processing and data capture of the frequency response

The time-domain trigger signal and sensor output are converted into arrays (4) and 

stored between passes of the M×N test matrix (8), which will be stored into an 

Excel file if the “Log Raw Data” Boolean of the front panel is set to true. The 

relative phases and test frequency are converted into strings (6), as well as the 

calibrated sensor magnitude (7). The strings from (6) and (7) are organized and 

inserted into an Excel file, which by the final loop pass will contain all electricfield magnitudes, electric-field frequencies, calibrated sensor magnitudes, and 

relative phase measurements made during the M×N test matrix. 

C-3 Total Harmonic Distortion (THD)

The function generator (Fig. C-6) is set to a sinusoidal 93-Hz signal for the total 

harmonic distortion (THD) measurement (1). The ADC measurement units (2), 

sample rate (3), and sample length (4) are set for a 1-s measurement. An FFT of the 

measurement is taken (5) and plotted (6) on the front panel. 
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40

Fig. C-6 Performing 1-s THD measurement

The sensor output to the first 5 tone harmonics are extracted from the sensor output 

FFT (1) then used for calculation (3) (4) of an estimated sensor THD value (5). An 

Excel file is created (2) to store the FFT data after conversion to a string (6), which 

is used to create more versatile graphs in Excel or MATLAB software. 

Fig. C-7 Post-measurement processing and data capture of the THD

C-4 Noise Spectral Density (NSD)

The electric-cage endplates are grounded and a 1-s measurement is taken (1), as 

shown in Fig. 8. The user is then prompted to short-circuit the sensor frontend 
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41

transducer and hit OK (2), then a second measurement is taken. The user is finally 

asked to disconnect the sensor and ground all ADC inputs (3), for a final 1-s FFT 

to measure the noise of the hardware. The data from the 3 nose measurements are 

converted into strings and stored in 3 different Excel files (4) (5) (6), which are then 

saved and closed (7) (8) (9) to end the test sequence.

Fig. C-8 NSD measurement performed by LabVIEW code
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List of Symbols, Abbreviations, and Acronyms

AC alternating current

ADC analog-to-digital converter 

ARL US Army Research Laboratory 

BNC Bayonet Neill–Concelman

DC direct current

EFNSD electric-field-referred noise spectral density 

FFT fast Fourier transform 

GRS ground reference sensor 

IEEE Institute of Electrical and Electronics Engineers 

MoM method of moments

NSD noise spectral density 

PLL phase-locked loop

PXIe Peripheral Component Interconnect Extensions for Instrumentation

Std Standard 

THD total harmonic distortion 

TTL transistor–transistor logic 

USB universal serial bus

VI virtual instrument
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44

1 DEFENSE TECH INFO CTR

(PDF) DTIC OCA

2 US ARMY RSRCH LAB

(PDF) IMAL HRA MAIL & RECORDS MGMT

RDRL CIO L TECHL LIB

1 GOVT PRNTG OFC

(PDF) A MALHOTRA

1 US ARMY RSRCH LAB

(PDF) RDRL-SES P S HEINTZELMAN