Nordson Testing Wearable Electronics Application Note

Testing Wearable Electronics

Application Note

The Importance of Testing
Mechanical and Electrical
Performance Simultaneously

Introduction

Wearable electronics present exciting new opportunities for
technology such as health monitoring, fashion and sports
performance evaluation. Sensors, antennae and batteries
can all be incorporated into textiles, making clothing an
integrated circuit that is capable of tirelessly monitoring vital
human body functions, and the environment of the wearer.

One of the main challenges in developing this technology
into consumer products is in understanding how they will
perform in dierent conditions and how they will deteriorate
through their intended life.

Conductive fabrics have been developed to provide
connections between electronic components distributed
around a garment, allowing an array of sensors to connect
back to a central processing unit.

The integrity of these connections is crucial if the end
product is to perform reliably. Even a small change

in voltage drop across a connection can result in
a corrupted signal.

Here we show how the integrity of conductive fiber
connections can be qualified over a range of
dierent conditions.

Figure 1. Metalized fibers form a conductive track through an electrically
voltage drop across fabric (purple); the metal wire transfers signal back to
the Prospector.

Testing Wearable Electronics

Application Note

Setting up the Test

A conductive fabric sample was tested using the DAGE
ProspectorTM Micro Materials Tester. The fabric was cyclically
stretched under displacement control and the voltage drop
was measured over the length of the fabric using a four­point resistivity measurement set-up shown in Figure 2.

The electrical measurements were taken using Prospector’s
accessory sensor box, and were automatically plotted

Trinocular camera,

recording video of

the test

against the force and displacement measurements in real
time. It is important that the voltage drop is constant,
independent of fabric stretching.

A change in voltage drop across the conductive track will be
presented to the processor as a change in the signal from
the sensor.

DAGE 5 kg capacity tweezer cartridge

Insulating fabric

Electrical connection to conductive fabric

Accessory sensor box

Figure 2. A strip of conductive fabric with 4-point voltage drop across wires attached. External sensor box can be seen in the background.

Standard vice workholder

Testing Wearable Electronics

Application Note

Test Findings

Figure 3 shows the force measured throughout a 30 second test cycle. The force versus time response is a consequence of the
position, time in the cycle and stress relaxation of the fabric.

Relaxation in load following initial peak

30

20

10

Force (gf)

0

0 5 10 15 20 25 30 35

Times (s)

Figure 3. Force versus time plot of several cycles of fabric stretching,
showing relaxation of load at constant displacement.

Fabric Connection 1_07 cycle30
Fabric Connection 1_07 cycle48
Fabric Connection 1_07 cycle64
Fabric Connection 1_07 cycle66