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                    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
                    asaresultofself-heatingeffectsintheIC.Theobservedtemperatureriseafter5minisshowninFigure
                    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
                               Temperature increase ( C)  0.8 1
                                1.4
                                1.2



                                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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