EEWeb Pulse - Issue 52, 2012

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Beth CooperNASA GlennResearch Center

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TABLE OF CONTENTS

Beth CooperNASA GLENN RESEARCH CENTER

The Development of NASA Auditory

Demonstrations Laboratory for Testing

of Hearing Protection DevicesBY JEFF SCHMITT, BETH COOPER AND DAVID NELSON

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Interview with Beth Cooper - NASA Internal Agency Hearing Conservation Consultant

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INTERVIEW

Co perBeth

NASA Glenn ResearchInternal Agency HearingConservation Consultant

How did you get intoengineering and when didyou start?

I became involved in engineering

through acousticsthe science of

sound. When I was a child, I guess

you could say that I had some

musical talent. I was able to pick out

melodies on the piano at a young

age, and I taught myself to play

several musical instruments. As I

got older, I would write harmoniesfor tunes that I learned in school

or camp. This interest propelled

me into an involvement in music,

and that was how I spent most of

my time in high school. The focus

of many school projects was the

science of music studying how

it was produced and why people

perceived music the way they did.

I was especially interested in the

relationships between sounds,

which is one aspect of the disciplineof music theory.

When I started to apply to colleges I

very nearly became a music theory

major. It wasnt until the very last

minute that I realized that there was

a name for what I really liked, which

was the physics of musicintervals,

tones, and those kinds of things. Thetechnical field that encompasses

all of that is acoustics. So, to find

a college, I did what, today, would

be an Internet searchI went to

the libraryand found that there

were four schools in the country that

offered undergraduate programs

in acoustics, one of them being the

University of Hartford. The program

there was a Bachelor of Science in

Engineering (B.S.E.) program inAcoustics and Music. Students in

this program took most of the same

coursework as a music performance

major at the conservatory, Hartt

College of Music, as well as the

core coursework of an engineering

major. It sounded like the perfect

program for me, so thats what I did.

For the first two years of my college

education I was a double major in

music and acoustics.

I eventually switched my major

to mechanical engineering, only

because the B.S.E. program at

that time was not accredited, and

I didnt want to have any concerns

about the validity of my degree

while job hunting later. But I still

took all the same courses over and

above what was required for myB.S.M.E. degree, so I also earned

the equivalent of a B.S.E. in Music

and Acoustics.

From there I went on to Penn

State because it had the most

acclaimed program in the country

that awarded graduate degrees in

acoustics. The program was very

broad: it covered everything from

underwater acoustics to speech

science and audiology. I hadhoped to study musical acoustics,

but I needed to focus on an area

where there was ample funding

for assistantships. I modified my

academic approach to emphasize

speech science and speech

processing, which was probably

about as close as I could get to

musical acoustics. The connection

is really human perception, which

links speech and hearing sciencesto musical acoustics. So its not hard

to imagine the link between that and

being a hearing conservationist,

which is what I am now.

Where did you frst go to workafter you graduated?

I worked in private industry for about



INTERVIEW

four years, but it wasnt what I really

wanted to do, since my ambition was

always to work for the government

in a research capacity. It took a

while to get an acoustics position at

NASA, but as soon as I heard there

was an opening at Glenn Research

Center in Cleveland, thats where I

went. Ive worked here for nearly my

entire professional careerabout

25 years.

Can you tell us about whatyou do at NASA?

Since Ive been at NASA Ive had

four major assignments, each

lasting from about five to seven

years. My first assignment was

on a team doing research on the

noise produced by jet nozzles

from aircraft exhaust engines. The

program included both analytical

and experimental research; the

work I was doing specifically

involved testing scale models of

exhaust nozzles in wind tunnels and

other laboratories.

As a typical researcher in a wind

tunnel, you have a fairly cyclic work

routine. You take data, analyze the

data, then write a paper and go to

a conference to present your work.

But because I had a slightly different

interest area than most of the other

people in my group, I was asked if

I would take a look at a community

noise problem that had developed

with one of our test facilities, where

researchers were doing aircraft

engine component testing in an

open parking lot. Obviously, it was

generating a lot of noise, and since

the testing was being done during

third shift to save money on power,

some residents of the nearby

communities had begun to regularly

call and complain. It had become a

pretty significant community noise

issue that was threatening the

success of the research program,

and so my boss said, We know that

human perception of sound is one

of your interests, so will you take a

look at what we can do to solve this

problem? One thing led to another,

Over the span of mycareer, I have cometo be acknowledged

as NASAs noiseperson, and now

my responsibility isto advise our senior

environmentalhealth officer and theoccupational health

personnel at our fieldcenters about noise

exposure issues,particularly relatedto noise control and

hearing conservation

program policies.

and we ended up building a

geodesic-dome-shaped enclosure

that severely reduced the noise that

could be heard in the surrounding

community. The facility also has an

anechoic interior lining that keeps

the noise from reverberating inside

the dome; this allows the space

to be used for noise emission

measurements on various aircraft

components.

After leading the acoustical design

and managing the construction

of this facility, I realized that I

didnt want to go back to being a

researcher. I really enjoyed facility

design and noise control, and I

had, at that point, developed a bit

of a reputation as a noise control

person, leading me to take on

other smaller noise control-related

tasks. Eventually, I knew I wanted tocontinue working on noise control

projects, which inspired me to find

my next home in the Health and

Safety organization.

During my interview for that

position, the person interviewing

mewho would eventually become

my bosssaid, We would love to

have you work on noise control,

but its really just one element of

a hearing conservation programand needs to be approached that

way. Would you like to manage the

hearing conservation program?

So I did that from about 1994 to

1999, establishing the hearing

conservation program here at NASA

Glenn Research Center. It ended up

being a very high-quality program,

and I think that is partly because

there was a significant emphasis

on noise control, which typicallygets neglected in the context of

a classical program. As part of

that assignment, I implemented

an aggressive campaign of noise

control solutions for our test facilities

and infrastructure buildings. I

also developed a number of novel

programs that NASA has since



INTERVIEW

adopted on an agency-wide basis.

By 1999 the Glenn hearing

conservation program was

mature and had developed a lot

of momentum, so I started lookingfor a new challenge. Just like in my

previous assignment, I realized that

one capability we needed, but didnt

have, was an anechoic chamber

dedicated to performing small-

scale testing of equipment destined

for the International Space Station.

All flight hardware is required to

go through a series of qualification

tests. One of those tests verifies

that the equipment doesnt maketoo much noise, with the goal of

preventing hearing loss as well as

ensuring a comfortable working

environment for the astronauts.

Payload developers here at NASA

Glenn were always looking for quiet

places where they could take the

required noise measurements on

their science payloads to get them

qualified for flight. It was pretty

clear that we needed a proper test

facility to do that, so I proposed to

the engineering organization that I

come and work for them and help

build one.

It took about a year to find funding to

build the chamber, but another year

later, we opened a commercially

viable state-of-the-art anechoic test

laboratory that was specifically

designed to accommodate a

couple of major projects that were

planned for the International Space

Station. I led the facility design and

managed the construction project

and then became the manager ofthe lab. The lab provided acoustic

emissions testing services, but we

also developed and provided other

related services, like low-noise

design consulting and education

for payload developers on how to

design low-noise flight hardware.

This acoustic emissions testing

laboratory later earned accreditation

by the National Voluntary Laboratory

Accreditation Program for the tests

we performed; we also became the

only laboratory accredited for the

specific test required for acoustic

emissions verification of large flight

racks for the International Space

Station.

Over the span of my career, I

have come to be acknowledged

as NASAs noise person, and

now my responsibility is to advise

our senior environmental health

officer and the occupational health

personnel at our field centers about

noise exposure issues, particularlyrelated to noise control and hearing

conservation program policies. My

fourth major assignmentthe work

that Im primarily involved in right

nowis focused on developing

programs and resources for

helping employees identify and

purchase equipment that is

inherently quiet. This approach

also has a component that requires

our in-house designers to design

equipment and systems that are

quiet. It makes good economic

sense to avoid being in a situation

where you are spending money

to fix pre-existing noise problems

while purchasing and building

new equipment that may produce

the very same problems. Noise

emissions should be considered

along with other criteria when

youre purchasing or designing

equipment. This is the essence of aBuy-Quiet program, and NASAs is

leading the way in the United States.

Do you have any tips forelectronics hardwaredesigners regarding noise?

Electronic components dont usually

contribute much noise themselves.



INTERVIEW

But if you have to provide cooling or

ventilation for a piece of equipment

youre designing, you should

think about those requirements at

the earliest possible stage of the

design process to avoid creating

unnecessary noise that then

requires the addition of noise control

treatments that will consume space

and may create other problems for

your design. Often, the worst noise

problems are the result of airflow

issues. Anything that restricts airflow

or causes very sharp turns or bends

in the airflow path is going to cause

noise. This noise is very hard to get

rid of after the fact, but it can belargely prevented if the challenge

is addressed early enough in the

design.

Another piece of advice for designers

is to be very explicit and intentional

in demanding low-noise-emission

products from manufacturers. NASA

has developed a tool for Buy Quiet

Purchasing called the Buy Quiet

Roadmap. Basically, the Roadmap

is an online process that helps end

users identify an appropriate noise

emission criterion for a particular

item to be purchased and then to

evaluate the total long-term cost of

different manufacturers products

that may differ in both cost and noise

emission. The heart of the Roadmap

is a calculation that quantifies the

total long-term cost of occupational

exposure to various noise levels.

Its the only tool of its kind, and

it has been commended by the

Occupational Safety and Health

Administration (OSHA) and the

National Institute for Occupational

Safety and Health (NIOSH) as

well as international regulatory

agencies, and it has been adopted

by a number of organizations in

the private sector. The Roadmap,

as well as a number of other free

and publicly available NASAresources that support hearing loss

prevention, can be accessed here.

I am a strong advocate of Buy

Quiet Purchasing, and I encourage

people to use this resource.

What are some of the toolsand approaches that youuse when diagnosing noiseproblems?

Its important to look at the boththe frequency spectrum and the

temporal characteristics of the

sound, not just the volume (how loud

the sound is), because the quality

of the sound is very important to

human perception, especially

when it comes to providing a work

environment that will be comfortable

and foster productivity. NASAs noise

emission and noise exposure limits

are based on volume, but even if we

satisfy those requirements, there

can still be tones, hissing, rumbling

or intermittent events that attract

attention and cause discomfort and

annoyance. A piece of equipment

can produce an acceptable

volume of sound, but if the

spectrum has a significant high or

low frequency component or one or

more tones, it will likely be perceived

as annoying or distracting. For

this reason, you have to look at theentire spectrum as well as how it

varies with time. This approach,

which considers the sound quality,

is more comprehensive and

considers human factors that are

not accommodated by the classical

approach that addresses only the

volume of the noise emission.

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The Development of NASAAuditory Demonstrations

Laboratory for Testing ofHearing Protection Devices

Editors Note: The following article is a synthesis of

two separate papers written by members of the ADL

development team and arranged by an EEWeb editor

[1] [2]. Each paper can be accessed in the References

section.

This article will outline the design of NASAs Auditory

Demonstration Laboratory (ADL) for performing

Real Ear Attenuation at Threshold (REAT) measurements

to meet industry standards for the Noise Reduction

Rating (NRR) of personal hearing protective devices.

The calculation of an NRR implies highly specific testrequirements for the conditions in the room in which the

test is conducted, the signal generation equipment and

the processing of normal hearing subjects. This article

will also profile the development of NASAs REATMaster

software as well as its key features that will aid in signal

generation and data acquisition for all REAT testing

facilities in which the system is employed.

Development of REAT Facility

The development of the REAT test facility began in the fall

of 2007. The primary goals of this project were to design

Figure 1: NASA GRC Auditory Demonstration Laboratory controlroom with NASA REATMaster and Stimulus Presentation SoundSystem Rack (left) and Auditory Demonstrations Rack (right).



PROJECT

an acoustic test chamber and signal generation systemfor REAT testing in accordance with industry standards.

In order that the human test subject receive accurate data

from signal generations, the laboratory needed to have

very low background noise levels to accommodate the

hearing of a normal hearing subject. At the same time,

it needed to be equipped with a sound system capable

of generating spacecraft launch-level sound fields to test

the performance of the hearing protection technology.

The site for the ADL was chosen in the basement of a

building with ideal conditions for conducting low-noise

acoustic measurementsconcrete walls, a roof cap and

heavy steel doors. A pre-fabricated ETS-Lindgren steel

reverberant test chamber was installed in the basement

laboratory to ensure a diffuse sound field environment.

Both the test chamber and isolation within the basement

provided optimal sound isolation levels at relevant test

frequencies with the addition of several massive silencer

units to reduce external effects on the testing.

With the establishment of an isolated and secure ADL

chamber came the need for the proper sound system to

perform the signal generation tests. The sound system

would need to create diffuse field sound pressure levels

to allow REAT testing and provide stable gain and high

slew rate output throughout. With these specifications,it would also need to operate quietly when operated at

full gain while at the same time attenuating any system-

generated noises. For the ADL, we implemented a three-

channel system, utilizing ElectroVoiceT251 horn loaded

loudspeakers that are driven by a Bryston 6BSST power

amplifier. This amplifier delivers 300 watts per channel,

more than 110 dB of signal to noise ratio and has a fixed

gain input setting that facilitates system calibration. This

system also employs a high-power 30 dB L-pad load box

attenuator that achieves the desired low background

noise levels needed for testing. If very high sound levels

are needed, the L-pad attenuator can be removed.

For the signal generation and data acquisition technology

in the ADL, we selected the National Instruments PXI

platform. We used two NI PXI-4461 dual-input, dual-

output, 24-bit digital dynamic signal acquisition (DSA)

and generation modules, which provided three channels

of signal generation and uncorrelated outputs needed to

drive the sound system, and one to four input channels for

sound pressure level monitoring and measurement. For

detection of subject response, via a variety of response

switch options, we used a National Instruments PXI-6220 digital I/O board with a custom response switch

interface.

NASA REATMaster Software

The NASA REATMaster software was developed by

Nelson Acoustics to provide the ADL with a software

application that would conduct calibrated real ear

attenuation at threshold (REAT) measurements using the

Figure 2: Interior View of NASA GRC Auditory DemonstrationsLaboratory REAT Test chamber, showing diffusing panel, intercom

speaker system and subject instruction video display.

Figure 3: The fabric panels in the ADL test chamber are removedfrom the test chamber when it is used for REAT testing. The fabricpanels add the absorption needed to make the chamber convertiblefor use in presenting auditory demonstrations using the secondaryaudio sound system.



PROJECT

National Instruments hardware. National Instruments

LabView is the programming language used in the

signal generation, user interface, system calibration and

test automation software. REATMaster allows flexible

configuration of system hardware for one to four channels

of signal generation and provides system calibration

tools that allow for both level and frequency calibration

of each channel. It has a manual operating mode that

supports system function verification, calibration and

subject training, yet also has an automated threshold-

seeking feature. All of the audio files produced by signal

generations are in WAV format, and all of the threshold

data can be exported to Microsoft Excel spreadsheets

for post-process analysis.

On completion of the test chamber and equipment

installation and software development phases of theproject, the entire system was calibrated and qualified

per the requirements outlined in ANSI S12.6. Using a

GRAS 40AQ random incidence microphone and the

analog inputs on the National Instruments Digital Signal

Analysis boards, the Nelson Acoustics Trident acoustic

measurement application was used to conduct the level

calibration and frequency equalization of the sound

system.

The diffuse sound field properties of the chamber

were evaluated for sound pressure level uniformity and

directionality at the location of the subjects head. ANSIS12.6 outlines a measurement procedure and criteria

for these parameters, with the intent being the creation

of a very uniform and highly omni-directional sound

field in the region surrounding the subjects head so as

to minimize the measurement uncertainty associated

with the hearing protector attenuation as a result of

uncertainties in the measurement presented to the

subject.

The NASA GRC ADL REAT and hearing protector testsystems have been successfully designed, installed, and

qualified to the ANSI S12.6 test method for measuring

the real-ear attenuation of hearing protectors. The NASA

REATMaster software development project resulted in

a software tool that the ADL and other qualified hearing

protection laboratories can employ using industry

standard computer-based digital signal generation

and data acquisition hardware. The system is currently

being used at NASA GRC, the National Institute for

Occupational Safety and Health (NIOSH), the U.S.

Army Aeromedical Research Laboratory, and severalcommercial hearing protector evaluation laboratories in

the US and internationally.

References

[1] Jeff Schmitt, Beth Cooper and David Nelson. The

Development of NASA Auditory Demonstrations

Laboratory for Measurement of Real Ear Attenuation

of Hearing Protection Devices. NOISE-CON 2010, 19-

21/04/2010.

[2] Jeff Schmitt. NASA Auditory Demonstration

Laboratory Uses LabVIEW and PXI to Test Hearing

Protection Devices. . National Instruments, n.d. Web.

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TECHNICAL ARTICLE

These are interesting times for

the engineering profession.

On the surface, there are signs

of a real engineering Renaissance.Technological magic seems to generate

ever-more impressive gadgets, our cars

are achieving near miraculous efficiency

at affordable prices for the consumer,

and modern engineering disciplines

like biomedical engineering are

offering new hope to countless people

who would have been functionally

marginalized in decades past. So why

are engineering educators so grumpy

these days?

Tom LeeChief Education Officer

WhyCant

JohnnyDesign?Part 1: Challenges in Modern

Engineering Education



TECHNICAL ARTICLE

No, there is no scientific study that

has tracked a grumpiness index

among our professors, but in recent

years, there definitely seems to be

some sense of angst among the

academic community. Recently, at

a conference of Innovation Centers

for Engineering Education (ICEE)

on Jeju Island in Korea, Korean

professors gathered as part of

a regular sequence of meetings

among a network of 60 Korean

engineering universities. These

universities were charged by the

national government to close the

gap that exists between Korean

engineering programs and the

needs of Korean industry. Today,

it is widely believed that Korean

industry can legitimately claim the

hard-fought title of the next Japan.

Certainly on the consumer side, the

products of the Korean electronics

and automotive industries like

Samsung and Hyundai, by any

measure, command brand respect

approaching, if not equaling,

legendary Japanese brands such as

Sony and Toyota.

The Korean ICEE initiative is

significant in that it is a focused, well-funded initiative by an engineering

community that is targeting the

future driven by engineering

creativity and innovation rather

than manufacturing quality and

aggressive labor costs. The

sessions at this conference focused

not so much on graduating more

engineers to meet increasing

demands; it tackled the more

challenging, big-picture, questions

on what qualities the engineers

of tomorrow should embody and

how the academic community can

deliver the appropriate training.

ICEE is currently concluding its first

five-year mandate from the national

government of Korea indicating

that funding will be renewed, if not

increased.

Grand Challenges of

Modern Engineering

The Korean ICEE experience

is a case study in a regional

response to the larger issue of

the readiness of engineering

Figure 1: Engineering deans gather in Beijing to explore avenues to transform the undergraduate curriculum



TECHNICAL ARTICLE

graduates. The most ambitious

statement of the significance of

engineering requirements of the

future is best articulated by the

so-called Grand Challenges for

Engineering. In 2008, the National

Academy of Engineering in the

United States presented fourteen

major technological issues that

vex humankind and encouraged

the global engineering community

to use these as a framework for

assessing education, research,

policy, and industrial strategies.

The grand challenges are: make

solar energy economical, provide

energy from fusion, develop carbonsequestration methods, manage

the nitrogen cycle, provide access

to clean water, restore and improve

urban infrastructure, advance

health informatics, engineer better

medicines, reverse-engineer the

brain, prevent nuclear terror, secure

cyberspace, enhance virtual reality,

advance personalized learning,

and engineer the tools of scientific

discovery.

For many in the academic

community, these challenges

have precisely articulated the

significance of the work of modern

engineers but unfortunately, it also

highlights how difficult it will be to

prepare our students to tackle these

immense challenges.

The current engineering

curriculum, delivered by the greatmajority of institutions worldwide,

had its genesis in the mid-twentieth

century. Largely motivated by then

urgent requirements of the so-called

Space Race and its darker flipside,

the Cold War, a large number of

engineers had to be trained to

meet the needs. The response

from the academic community

was a curriculum that one might

consider to be linear start

with mathematical and scientific

foundations in the early years,

progress to application courses

in the middle years, then cap it

off with a rigorous thesis or senior

project. Additionally, the tradition

of separating students into well-

defined engineering disciplines

(electrical, mechanical, chemical,

civil, etc.) became entrenched.

Although one cannot deny that this

approach was effective in that the

needs of society were largely met,

it left this generation with lingeringmemories of being completely lost

for four or more years and eventually

seeing the light once they began

experiencing the real world.

The mismatch for the modern

context often sites two very

significant issues. First, as anyone

that graduated from engineering

programs during this period, is the

simple reality of keeping students

motivated through the very intensive

and often abstract, theory-heavy

gauntlet of the first years of the

undergraduate program. Many of

us asked, What is the significance

of this calculus theorem proof in

the real world? as we struggled

through the process. In some

sense, this is the easier problem

as many successful techniques

have emerged within the past

few decades that have attemptedto introduce more applications,

hands-on labs and case studies to

help soften the blow.

The trickier issue is the latter

the disconnect between

the traditional structure of the

engineering disciplines and the

emerging complexities of modern

engineering systems. With the pace

of innovation and the increasing

sophistication of products and

infrastructure, many consider

the techniques represented by

the traditional curriculum out-of-

date. Modern engineering teams

are typically cross-functional

with contributions from a variety

of specializations. This included

technical and non-technical

specializations, including business

and human factors. The shortening

project time-lines also demand

greater project parallelization and

cross-functional tasks that simply donot map cleanly to the disciplines.

Simply put, engineers need to know

more and do more, all with less time

and resources.

Technologically, such pressures

have triggered highly innovative

techniques often facilitated by

modern information and digital

technology. A clear testament to

this trend is the academic migration

of the traditional departments of

Electrical Engineering (EE) to

the more contemporary hybrid

departments of Electrical and

Computer Engineering (ECE).

In another important corner of

the engineering world, many

departments of Mechanical

Engineering (ME) are starting to

express themselves as Mechanical

and Mechatronic Engineering

(MME). This sort of trend is oneof the modern responses of the

academic community; creating new

departments to accommodate new

techniques. Is this sufficient?

The reality is: this will generate a

relatively small specialized group

of engineers skilled in even more



TECHNICAL ARTICLE

specialized and narrow fields. It

also leaves the vast majority of

our students in the framework of

the traditional disciplines. A very

practical example of the deficiency

in this approach becomes clear in a

very familiar context: modern cars.

A Practical Example:

The Green Car

Virtually all consumer vehicles

produced today are electronically

fuel-injected. More precisely, they

are typically computer-controlled,

deploying the same semiconductor

technology we use in our general

purpose computers. The electroniccontrol unit (ECU) manages the fuel

injection and ignition timing and

other key parameters that influence

the burning and energy release

of the engine. For many cars,

there will also be some computer

control through the drivetrain (e.g.

traction control). Within the rapid

development cycles of todays

auto industry, it becomes essential

for the engineering team to workwith the system in its totality. In the

case of the engine, you will need

to consider mechanical, chemical,

and electrical characteristics as

a minimum. You will also need

computing knowledge, as the

engines are computer-controlled.

From a workflow perspective, new

techniques such as hardware in

the loop testing (HIL), offer a rapid,

highly accurate and cost-effectiveway of testing the performance

of control systems for engines or

any other computer-controlled

subsytem. This is a way of testing

key components without having

to physically prototype the entire

system only to find a critical design

flaw. This type of sophisticated

simulation and control systems

design will demand a system-level

approach that blends techniques

and knowledge from many of

the specialized disciplines.

Extrapolating further to green

vehicle design, the same problems

become greatly amplified for

hybrid electric vehicles (HEV), fully

electric (EV), and fuel-cell powered

vehicles. For these applications,

chemical engineering knowledge

becomes increasingly important as

battery design and alternative fuels

become the big variables.

The Renaissance Engineer

The professors at the Korean

conference expressed keen

interest in techniques that

introduce such multidisciplinary

and system-level approaches to

an engineering education. It may

seem simple enough to begin

merging select techniques from

other disciplines into programs,

but the actual implementation is

substantially more difficult. Thecurriculum legacy is entangled

within a large complex system of

organizations and suborganizations

with bureaucratic structures and

decision-making processes that

ensures academic freedom but

hinders coordinated transformation.

Furthermore, the recent focus

on the research function of the

engineering university also needs

to be tempered to allow greatercreativity and energy to revitalize

the teaching function.

The Korean context was used to

highlight the level of commitment

and vision required to educate the

modern Renaissance engineer.

This particular group would be the

first to admit that they have only

taken a baby step. But that first

step is literally a doozy. Korea is

a nation of fifty million people for

whom the engineering community

has literally lifted the population out

of mass poverty within a generation.

For this country, the revitalization

of the engineering community

is an issue of national priority

and government, industry, and

academic institutions seem to be

in-sync to implement the changes.

They are not alone, however. At

another recent conference in Asia,

approximately three hundred

deans of engineering and other

senior engineering educationadministrators met in Beijing at

the 2011 Global Engineering

Deans Conference presented by

the International Federation of

Engineering Education (IFEES).

In the audience were significant

contingents from North American

institutions who are also anxious

to learn from their global peers

and trigger positive action in their

respective juristictions.

Throughout North America and

elsewhere, a generation of children

have embraced robotics as a hobby

and even an obsession. These same

children also lose sleep at night

wondering whether their world will

provide sufficient food, clean water,

and livable environments when

they take the helm. In many ways,

the scene is fundamentally different

from the concerns of Westernnations on whether we are training

enough engineers to compete

against emerging economic

superpowers. The demands on

the engineering community are

becoming deeply personal and we

witness an empowered generation

ready to take on the challenges



TECHNICAL ARTICLE

but they can only succeed if our

generation can structure our

institutions and methods to guide

them wisely.

Part two of this article will explorespecific techniques and case

studies on education innovation

and key trends that are aimed at

the revitalization of the engineering

curriculum.

About the Author

Dr. Lee has been an active contributor

in the global engineering and control

systems community for over twenty

years. As Chief Education Officer atQuanser, a leader in realtime control

and mechatronics solutions for

education, research, and industry,

Dr. Lee develops and implements

the companys strategy for enriching

and increasing the educational

effectiveness of technology in the

modern engineering education

context. Prior to his appointment at

Quanser, Dr. Lee was Vice President

of Applications Engineering

at Maplesoft, creators of the

renowned Maple mathematical

software system. In that capacity,

he helped the company transform

the mathematical technology to a

complete engineering modeling

and simulation solution. He also

serves as an Adjunct Professor of

Systems Design Engineering at

the University of Waterloo, noted

for its leadership in engineering,

computer science, and

mathematics. Dr. Lee earned his

Ph.D. in Mechanical Engineering

at the University of Waterloo, andhis M.A.Sc. and B.A.Sc. in Systems

Design Engineering at the University

of Waterloo. He has published

numerous papers and is a frequent

invited speaker in the areas of

engineering education, engineering

modeling and simulation, and

engineering computation.

Join Today


Electrical Engineering Community

EEWeb


19/29

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SEE Hardness

- SEL and SEB LETTH . . . . . . . . . . . . . . . . . . 86.4MeV/mg/cm2

- SEFI LETTH. . . . . . . . . . . . . . . . . . . . . . . . . . . . 43MeV/mg/cm2

- SET LETTH . . . . . . . . . . . . . . . . . . . . . . . . . . 86.4MeV/mg/cm2

70

75

80

85

90

EFFICIENCY(%)

LOAD CURRENT (A)

0 1 2 3 4 5 6 7 8 9

FIGURE 1. EFFICIENCY 5V INPUT TO 2.5V OUTPUT, TA = +25C

10 11 12

CH4 SYNC

CH3 VOUT x 10

CH2 SLAVE LX + 15V

CH1 MASTER LX + 20V

-6 -4 -2 0 2 4 6 8 10 12 14

TIME (s)

AMPLITUDE

(V)

25

20

15

10

5

0

FIGURE 2. 2-PHASE SET PERFORMANCE at 86.4MeV/mg/cm2

April 5, 2012FN8264.1

Intersil (and design) is a registered trademark of Intersil Americas Inc. Copyright Intersil Americas Inc. 2012All Rights Reserved. All other trademarks mentioned are the property of their respective owners.

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TECHNICAL ARTICLE

TDR:Reading the Tea Leaves

MichaelSteinberger

LeadArchitect,SerialChannelProducts

Time domain reflectometry (TDR) is an essential

microwave measurement technique and also anessential technique for analyzing measured S

parameters. However, extracting as much information as

possible from a TDR trace can resemble the work of a

fortune teller. There is a lot of information that escapes

the casual observer but is readily apparent if one knows

what to look for. This article reviews the basic techniques

for interpreting TDRs and then adds a couple of simple

techniques that are not as well known.

What Happens Where

The goal of time domain reflectometry (TDR) is tocorrelate the electrical behavior of a transmission line

circuit with its physical features. Once one understands

which physical features have the most significant effect

on electrical behavior, its a lot easier to improve the

design.

TDR is almost always associated with measured data-

either the TDR data is measured directly or else its

computed from measured S parameters. Either way, the

goal is to determine the magnitude and location of the

transmission line discontinuities that are in the actualcircuit, independent of what any model might predict.

TDR data can also be generated for models, and thats

useful for comparison to measured data.

Figure 1 and Figure 2 are examples of TDR data

computed from measured S parameters. Each figure

shows a time domain waveform which approximates the

reflection coefficient as a function of time (and therefore

distance). The two figures show TDR data looking from

opposite ends of the same interconnect network. As will

be explained in the following sections, the individual

elements such as vias, traces, and connectors areclearly visible in the TDR trace. Some of these features

are labeled in the figures.

How TDR Data is Measured

Time domain reflectometry measures the voltage step

response at the input to the device under test. The source

impedance is typically a standard reference impedance

such as 50 ohms single ended or 100 ohms differential.


21/29



TECHNICAL ARTICLE

Nonetheless, these approximations are good enough to

obtain some useful information.

If one assumes that the three simplifying approximations

are valid, then for a transmission path with varying

impedance , the reflection coefficient for a short length

--- of that path is:

Taking the limit as and applying the

approximation of constant impedance,

Applying the second and third approximations (low loss

and constant velocity) to the calculation of the impulse

response at the driving end, and assuming that the

propagation velocity is y,

One can then get the step response (that which is actually

measured) by integrating with respect to time. The result

is:

In other words, the amplitude of the step response at

a particular time is approximately proportional to the

impedance at some corresponding distance along the

transmission path. This is the desired result.

As each of the approximations breaks down, however,

the step response exhibits additional artifacts.

1. Impedance Variations

a. As the impedance variations become more and more

extreme, the impedance scale in the TDR waveform

becomes distorted. For example, an open circuit

(essentially infinite impedance) does not result in an

infinite step response amplitude; it results in a doubling

of the step response amplitude.

Therefore the amplitude scale of a TDR waveform is

really incident wave plus a reflection coefficient

between 0 and 2 rather than a linear impedance scale.

b. If there are multiple discontinuities in the transmission

path, then the step response edge reflected by a

disontinuity which is further from the measurement point

will be reflected by the nearer discontinuities and then

reflected again by the further discontinuity, resulting in

multiple reflections arriving at the measurement point.

2. Transmission Loss

As the step response edge propagates along the

transmission path, it encounters loss, especially at

higher frequencies. This loss smooths out the edge that

is incident on discontinuities which are further from the

measurement point. The step response edge that is

reflected also gets smoothed out on its way back to the

measurement point. Therefore features which are further

from the measurement point become less distinct.

For example, the features on the right hand side of Figure

1 and Figure 2 are much less distinct than those on the

left hand side, even though the features on the left hand

side of one figure are exactly those of the right hand sidein the other figure.

3. Propagation Velocity Variations

If the propagation velocity changes, for example because

the transmission medium changes from PC board to

cable, then the translation from time to distance will be

distorted accordingly.

Interpreting the TDR Trace

Figure 4 shows a view of the example TDR in Figure 1 that

has been plotted on an impedance scale and expandedto show some detail at the beginning of the TDR trace.

Measurement/calculation setup

The first two nanoseconds of the TDR trace show some

details about how the TDR was calculated, or how the

equivalent trace would be measured in the lab.

Since the original S parameter data was supplied to

Figure 3: Time domain reflectometry measurement of interconnect

network

InterconnectNetwork

Z0

Z0

Z0

StepStimulus Measure Step

Response

+

+


23/29



TECHNICAL ARTICLE

impedance. That is,

For example, the via in Figure 4 increases the conductance

of the transmission line from 1/52.5 Semens to 1/49.6Semens, for an increase of 0.00114 Semens. One half of

the round trip delay of 72pS in the TDR trace is 36pS, so

the excess capacitance of the via is approximately 41fF.

Steady State Values

It is often observed that the steady state value of a TDR

trace is higher than the initial stimulus amplitude. This

is apparent in Figure 1 and Figure 2, and is illustratedagain using an impedance scale in Figure 5.

This feature of the TDR trace is not a numerical artiface;

its a fundamental behavior of the interconnect network

and a useful piece of information. Consider that when

the TDR trace (as a step response) settles to a long term

value, the equivalent circuit is

Figure 5: Example TDR with series resistance shown

Figure 6: Steady state measurement of interconnect network

Therefore from Figure 5, the series resistance of that

particular interconnect network is approximately 3.

For another view of the measurement of interconnect

network behavior at low frequencies, see [2].

References

[1] Matthei, Young and Jones, Microwave Filters,

Impedance Matching Networks, and Coupling

Structures, section 5.02, equation 5.02-5, page 164,

McGraw-Hill, copyright 1964.

[2]h t tp : / / rea lt imewi th .com/pages/ r twvprof i le .

cgi?rtwvcatid=13&rtwvid=1691

About the Author

Michael Steinberger, Ph.D., is responsible for leading

SiSofts ongoing tool development effort for the design

and analysis of serial links in the 5-30 Gbps range. Dr.

Steinberger has over 30 years experience in the design

and analysis of very high speed electronic circuits.

Dr. Steinberger began his career at Hughes Aircraft

designing microwave circuits. He then moved to Bell

Labs, where he designed microwave systems that

helped AT&T move from analog to digital long-distance

transmission. He was instrumental in the development of

high speed digital backplanes used throughout Lucents

transmission product line. Prior to joining SiSoft, Dr.Steinberger led a group of over 20 design engineers at

Cray Inc. responsible for SerDes design, high speed

channel analysis, PCB design and custom RAM design.

That is, at steady state, the only relevant circuit elements

are the resistances in the circuit. For most interconnect

networks (those with negligible DC leakage), the

resistances are the source resistance, the load resistance,

and the series resistance of the interconnect network.

Time (ns)

0.0

70.0

65.0

60.0

55.0

50.0

45.0

40.0

2.0

Ohms

4.0 6.0 8.0 10.0 12.0 14.0

y1: (50.0)y2: (53.010)dy: 3.012

Interconnect

Network

Z0

Z0

StepStimulus Measure Step

Response

R

+

+



TECHNICAL ARTICLE


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TECHNICAL ARTICLE

Introduction

In digital circuit design, a clock signal is one that

oscillates between a high and a low state and directs a

circuits performance. Logic may toggle on the rising

edge, falling edge or both edges in an application.

With thousands of instances running off of a given clock

domain, it is necessary to insert a tree of buffering to

adequately drive the logic. Clock trees often have delay,

skew, minimum power, and signal integrity requirements

that the layout engineer must meet.

Arguably clock descriptions and diagrams are the most

critical information that must be communicated when

a circuit is transferred from a front-end designer to the

back-end layout engineer. Hours, days, and even weeks

of design work has been lost over the years due to

miscommunications, misunderstandings, and needs for

complete re-synthesis involving clock trees.

Before layout, ideal clocks are used for synthesis and

timing constraints. Clock definition constraints may

appear on top-level pads or pins of a block; on the

output of a macro such as a delay-locked loop (DLL) or

phase-locked loop (PLL); or as a generated clock on a

dividing register. These clock definitions may or may not

be where the layout engineer needs to define clock roots

to attain optimal latencies, balancing and skew across

various modes of operation. A high level of information

exchange between the front end and layout along with anunderstanding of what layout will do with that information

will greatly improve the CTS process of the physical

design flow.

Design Tips for Successful CTS

Some of the following tips have been circling around the

industry for quite a while, but based on experience over

the last few years, they are worth repeating.

Billie JohnsonPhysical Design Engineer

YourClocks,My Layout



TECHNICAL ARTICLE

Establish a naming convention for clock muxes or

instances that you know will be a start point for a clock

tree. This provides a nice sanity check for layout because

it is easy to search and count in a layout database based

on strings.

Use medium- to high-strength drivers for clock root

instances. This allows the clock tree to get off to the right

start. Do not use the highest drive strength available in

your library, however, because it is useful to be able to

upsize later in the design if issues are uncovered with

signal integrity (SI) analysis or on-chip variation (OCV)

analysis.

Make certain that clock divide registers and their sync

registers are purposely driven by muxing logic if they are

to run in a separate test mode. This allows the capability

to add delay on the input side of the mux for a test mode

without pushing out all of the other registers clocked by

the generated clock in functional mode.

Figure 1 shows two register clock divide registers.

Without additional muxing logic, a functional clock

will most likely not work for a test mode. The divide-by

registers wont be balanced with any of the registers

downstream. The fewer registers in the green domain

would likely lead to a much faster clock than in that of the

purple domain.

Figure 2 illustrates a muxing scheme that would allow for

each clump of downstream registers and the divide-bys

to have a minimized clock through one input of a mux

AND a balanced one through the other.

Insert a reset-specific driver if necessary. Sometimes a

couple of registers will be used to synchronize a reset. It

may not be necessary for those registers to be balanced

to all of the other ones also driven by that clock. In Figure

3, without a focused strategy, software will try to balance

the blue registers after the gating logic with each of the

pink registers contained in the reset synchronizing logic.

This scenario can be easily handled in the layout if they

are split from the rest of the registers with their own

exclusive driver.

Figure 4 demonstrates how a place-holder or excluding

buffer can be inserted and easily identified in the hand-

off communication so the layout engineer knows where

balancing attempts can diverge.

Figure 1

Figure 4

Figure 3

Figure 2

50

810SQ

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11

10SQ

11

10S

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11

Clock

Root

Rst_out

ClockRoot #2

excludedfrom

CTS of#1

Rst_out

k#1

500

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11



TECHNICAL ARTICLE

clock root insertion points, latency, skew and transition

targets, and specifics for gating logic, through-registers,

and cross-domain relationships can be ported directly

into the CTS tool. The layout engineer will then use their

discretion concerning buffer types to use, optimization

iterations and requirements for the router like spacing,

shielding, and metal layers.

Before clock trees are inserted, a trace can be performed

to ensure endpoints that are intended to be balanced

will be. Gating logic, excluded legs off of a clock root,

IO endpoints, and reconvergent instances can also be

revealed and assessed.

Clock trees can consist of buffering cells only or series

of inverters. Most technologies today have special clock

buffering and clock inverting cells that have a balanced

rise and fall time to help ensure an uncompromised duty

cycle. Other requirements like levels in a tree or max

fanout of each clock cell can also be incorporated.

Conclusion

In addition to everything discussed so far, the layout

engineer will likely experiment with clock-gate-aware

placements, clock routing guides and floorplan tweaks.

Iterations of CTS will often be run with minor modifications

for the skew, latency, and transition targets. Trial and

error helps achieve the perfect blend. If the front end

understands how CTS works, and communicates the

clock structure at the onset, then the layout engineer can

embark upon the task more proficiently. Time for CTS

in the schedule can be spent tuning and improving your

clocks rather than simply trying to insert them into my

layout.

About the Author

Billie Johnson is a Physical Design Engineer at ON

Semiconductor. Her work experience spans test, design,

technical marketing and layout, and she holds a B.S. in

Engineering and an MBA from Idaho State University inPocatello, Idaho. She has participated in numerous K-12

math and engineering outreach programs throughout her

career including MATHCOUNTS ,FIRSTLEGO

League (FLL) , Wind for Schools and Introduce a Girl

to Engineering Day.

Provide a better-than-you-think-you-need clock diagram

and extensive written description. When front end

design is ready to deliver the netlist to layout, they

are already widely familiar with the design and clock

requirementsor at least they should be. Sometimes

initial CTS efforts will uncover that the ideal values

used in pre-layout timing constraints are not physically

achievable. Problems leading to this can be revealed

sooner rather than later if an accurate clock diagram is

provided with the netlist handoff along with information

about the clocking scheme.

An overall diagram or diagrams representing all of the

designs clocks including gating logic is ideal. This could

be software-generated either with a drawing program or

a schematic capture tool. It can even be drawn by hand

and saved in a PDF or faxed to the layout engineer. Thispicture could be worth a thousand words spread over

dozens of phone calls and e-mails trying to get the clock

formats straight.

Since diagrams can get complicated and messy,

accompanying written descriptions are needed. This

includes explanations of generated clocks, details of

any clock gating or muxing patterns, and requirements

for skew balancing and latencies. These particulars are

necessary for each mode of operation because each

mode must be addressed during clock tree insertion.

Registers may wind up balanced beautifully for functionalmode but miserably unbalanced for test modes if we are

not careful.

If the clocks utilize a DLL or another macro or if it

passes through gating logic, these details are necessary.

Macros purposes must be explained. It is possible to

synthesize and balance through those types of macros

if that is what is desired. As for gating logic, if a scenario

exists in which one pin is accessed in one mode, but

another pin of the same cell is accessed in another mode

the trace tool will identify this as a Reconvergent Clock.

Although layout tools can resolve these cases, it may be

better to force the tool to look through one pin instead of

the other during the clock insertion.

CTS Within Industry Tools

Industry software facilitates clock tree synthesis with

powerful tools driven by designers specifications and

guidelines. Information from the front end pertaining to


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EEWeb Pulse - Issue 52, 2012

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