Biomedical Engineering Reference
In-Depth Information
Figure 12.30 Photograph showing substrate with fabricated traces and land pattern (below) and with sensor
attached (above).
process. The sensor as embedded was demonstrated to work successfully. The 1-Wire protocol was
implemented in an SX48-based microcontroller that serves as the 1-Wire master. The total network
length (master to device) was about 20 cm for this proof-of-principle work.
Any sensor with a temperature-dependent output may require control or calibration of
thermal effects. Repetitive reads of the DS18B20X were observed to cause a temperature increase
as a result of self-heating effects in the IC. The observed temperature rise after 5 min is shown in Figure
12.31 as a function of the reading rate. Obviously, the heat capacity and thermal conduction coeffi-
cients of the particular sample determine the dynamic and ultimate steady-state temperature increase.
A 10 by 10 array of the same sensors was also fabricated on similar FR4 circuit board material.
After verification of the operation of the 10 by 10 array it was embedded in an aramid fiber (Kevlar)
reinforced composite panel. The panel is 15 cm by 15 cm square, and is about 2.5 mm thick. It was
formed from 16 layers of aramid fabric under vacuum-assisted resin transfer molding. A two-part
epoxy resin was pulled through the fabric by the vacuum action to provide complete wetting of the
fibers. In this case, the fabric was draped over the sensors and substrate. This panel is shown in
Figure 12.32.
12.2.4.6
Sensors for Structural Health Monitoring
Continued research is necessary to successfully develop a sensor integration technology within a
braided fiber component of a composite. It will be necessary to measure the mechanical properties
1.6
1.4
1.2
1
0.8
0.6
0.4
0.2
0
0
1
2
3
4
5
6
7
Reading rate (1/sec)
Figure 12.31
Observed temperature increase (over 5 min) of the DS18B20X as a function of reading rate.
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