NovDec_AMP_Digital

irect write technology is an innovative and economi-

cal materials deposition process that integrates con-

ductive traces, antennas, circuits, and sensors onto

components or embeds them within structures. The tech-

nology was initially developed under the Defense Ad-

vanced Research Projects Agency’s (DARPA) Mesoscopic

Integrated Conformal Electronics (MICE) program by

Stony Brook University, N.Y., and its partners. The process

has been in development since 2002 for use in aerospace,

military, and energy markets.

Direct write technology basics

The direct write process uses a

small torch and aperture system to

fabricate patterned material traces and

coatings onto complex surfaces. The

print head generates a highly colli-

mated, well defined particle stream

capable of fabricating low profile, fine

feature conductor patterns and ce-

ramic dielectrics onto critical compo-

nents, as shown in Fig. 1.

Patterns are printed with typical

feature sizes ranging from 250 µm to

3 mm wide and roughly 50 µm thick

(thinner and thicker deposits are pos-

sible). A7-axis robotic system ensures

pattern placement accuracy and man-

ufacturing consistency afforded by 20 µm tool path repeata-

bility. The process enables a wide range of materials to be

deposited including ceramic dielectrics, high quality copper

and precious metal conductors, sensor alloys, and functional

ceramic oxides. The process is also compatible with most

substrate/component materials including polymer laminates,

fiber-filled composites, and metallic structures.

Advantages include the ability to conformably print

onto 3D geometries, operation in standard atmosphere (no

vacuum or inert atmosphere required), and robust deposits

that withstand high temperatures (>1000°C) and are both

erosion resistant and strain tolerant. Direct write printing is

used to construct aerospace components by enabling em-

bedded circuitry, and in high temperature propulsion sys-

tems by incorporating diagnostic sensors (temperature and

heat flux) for structural health monitoring. The technology

has also been used to integrate UHF/VHF/L-Band antennas

into air and space vehicle components for advanced com-

munications and signals intelligence.

Printed thermocouple sensors

Many types of thermocouple systems can be fabricated

to provide integrated sensing for operational components.

A variety of NIST standard alloys

including types T, E, K, and N as

well as precious metals can be

used to achieve the requisite performance and durability.

The latter have been tested in oxidizing environments at

1000°C for 8000 hours, exhibiting >4% drift. Thermocou-

ple sensors (TCs) are printed directly and conformally onto

structures and embedded within protective coatings if nec-

essary. Leads are routed to convenient locations for signal

acquisition. TCs have been printed onto a range of materi-

als including polymers, fiber composites, metals, and

ceramic matrix composites (Fig. 2). Temperature measure-

ments provide information relative to the materials re-

sponse in specific thermal environments and offer a means

of monitoring the component via closed-loop control.

Through interactions with OEM partners, sensors were

successfully used in gas turbine engines at full load as well

as in hypersonic scramjet engine tests.

Benefits of using printed thermocouples to measure

temperature include:

• Direct printing onto 3D components or polymer

laminates for composite integration

• Low profile design, generally 50 µm thick

• Repeatable installation using robotics

• Embedding within thermal barrier coatings or other

protective surface treatments

• Creation of “smart” components for health

monitoring and assessment

• Accuracy improvement of prognostic models by

measuring part temperature

Printed heat flux sensors

Heat flux sensors were developed based on multilay-

ered thermopile architectures to supplement temperature

measurements in monitoring engine transients for ad-

vanced hypersonic scramjet control systems. Extensive

testing was performed at the Air Force Research Lab

(AFRL) under an SBIR Phase II contract, within the com-

bustor at simulated Mach 5 flight conditions, where gas

temperatures often exceed 1900°C.

ADVANCED MATERIALS & PROCESSES •

NOVEMBER-DECEMBER 2014

Smart Deposition Process Integrates

Sensors and Heaters into Coatings

Jeff Brogan

MesoScribe Technologies Inc.

Setauket, N.Y.

Fig. 1 —

Sensor

application using direct

write technology.

Fig. 2 —

Thermocouples created

with direct write. Instrumented

compressor blade (above), TC array

onto a metallic structure (above

right), TC array onto cylindrical

component (right).