Decoupling of Temperature and Strain Effects on Optical Fiber-Based Measurements of Thermomechanical Loaded Printed Circuit Board Assemblies

This study investigated the use of distributed optical fiber sensing to measure temperature and strain during thermomechanical processes in printed circuit board (PCB) manufacturing. An optical fiber (OF) was bonded to a PCB for simultaneous measurement of temperature and strain. Optical frequency-domain reflectometry was used to interrogate the fiber optic sensor. As the optical fiber is sensitive to both temperature and strain, a demodulation technique is required to separate both effects. Several demodulation techniques were compared to find the best one, highlighting their main limitations. The importance of good estimations of the temperature sensitivity coefficient of the OF and the coefficient of thermal expansion of the PCB was highlighted for accurate results. Furthermore, the temperature sensitivity of the bonded OF should not be neglected for accurate estimations of strains. The two-sensor combination model provided the best results, with a 2.3% error of temperature values and expected strain values. Based on this decoupling model, a methodology for measuring strain and temperature variations in PCB thermomechanical processes using a single and simple OF was developed and tested, and then applied to a trial in an industrial environment using a dynamic oven with similar characteristics to those of a reflow oven. This approach allows the measurement of the temperature profile on the PCB during oven travel and its strain state (warpage).

Determining the Thermal Properties of Buckypapers Used in Photothermal Desorption

Volatile organic compounds (VOCs) pose an occupational exposure risk due to their commonplace usage across industrial and vocational sectors. With millions of workers annually exposed, monitoring personal VOC exposures becomes an important task. As such, there is a need to improve current monitoring techniques by increasing sensitivity and reducing analysis costs. Recently, our lab developed a novel, preanalytical technique known as photothermal desorption (PTD). PTD uses pulses of high-energy, visible light to thermally desorb analytes from carbonaceous sorbents, with single-walled carbon nanotube buckypapers (BPs) having the best overall performance. To apply this new technology most effectively for chemical analysis, a better understanding of the theoretical framework of the thermal phenomena behind PTD must be gained. The objectives of the present work were 3-fold: measure the thermal response of BPs during irradiation with light; determine the best method for conducting such measurements; and determine the thermal conductivity of BPs. BPs were exposed to four energy densities, produced by light pulses, ranging from 0.28 to 1.33 J/cm2, produced by a xenon flash lamp. The resulting temperature measurements were obtained via fast response thermocouple (T/C) mounted to BPs by three techniques (pressing, adhering, and embedding). Temperature increase measured by T/C using the adhering and pressing techniques resulted in similar values, 29.2 ± 0.8 to 56 ± 3 °C and 29.1 ± 0.9 to 50 ± 5 °C, respectively, while temperature increase measured by embedding the T/C into the BP showed statistically larger increases ranging from 35.2 ± 0.9 to 76 ± 4 °C. Peak BP temperatures for each mounting technique were also compared with the temperatures generated by the light source, which resulted in embedded BPs demonstrating the most temperature conversion among the techniques (74-86%). Based on these results, embedding T/Cs into the BP was concluded to be the best way to measure BP thermal response during PTD. Additionally, the present work modeled BP thermal conductivity using a steady-state comparative technique and found the material's conductivity to be 10.6 ± 0.6 W/m2. The present work's findings will help pave the way for future developments of the PTD method by allowing calculation of the energy density necessary to attain a desired sorbent temperature and providing a means for comparing BP fabrication techniques and evaluating BP suitability for PTD before conducting PTD trials with analytes of interest. Sorbents with greater thermal conductivity are expected to desorb more evenly and withstand higher energy density exposures.

Thermopneumatic Soft Micro Bellows Actuator for Standalone Operation

Typical pneumatic soft micro actuators can be manufactured without using heavy driving components such as pumps and power supplies by adopting an independent battery-powered mechanism. In this study, a thermopneumatically operated soft micro bellows actuator was manufactured, and the standalone operation of the actuator was experimentally validated. Thermopneumatic actuation is based on heating a sealed cavity inside the elastomer of the actuator to raise the pressure, leading to deflection of the elastomer. The bellows actuator was fabricated by casting polydimethylsiloxane (PDMS) using the 3D-printed soluble mold technique to prevent leakage, which is inherent in conventional soft lithography due to the bonding of individual layers. The heater, manufactured separately using winding copper wire, was inserted into the cavity of the bellows actuator, which together formed the thermopneumatic actuator. The 3D coil heater and bellows allowed immediate heat transfer and free movement in the intended direction, which is unachievable for conventional microfabrication. The fabricated actuator produced a stroke of 2184 μm, equivalent to 62% of the body, and exerted a force of 90.2 mN at a voltage of 0.55 V. A system in which the thermopneumatic actuator was driven by alkaline batteries and a control circuit also demonstrated a repetitive standalone operation.

Comparison of two skin temperature assessment methods after the application of topical revulsive products: Conductive iButton data logger system vs contact-free infrared thermometry

Background

Skin temperature assessments comprise conductive and contact‐free techniques. Comparison between conductive data loggers and contact‐free thermometry after the application of revulsive products is scarce. This study aimed to compare iButton data loggers with an infrared thermometer after the application of two revulsive products. Secondly, the relation between skin temperature kinetics with skin's perfusion of microcirculation was investigated.

Materials and methods

Healthy females (n = 25) were randomly allocated to two groups, representing the products A and B. Skin temperature was measured with “iButtons” and an infrared pistol at baseline and up to 1 hour after application. Skin's perfusion of microcirculation was monitored with a laser speckle contrast imager.

Results

Baseline “iButton” temperature values were significantly lower compared with infrared pistol values in both groups. After application of the products, skin temperature decreased as recorded with both devices followed by an increase to baseline values when measured with the pistol. The results obtained by the “iButtons” reached values above baseline in both products towards the end of the follow‐up period. A moderate correlation was found between infrared pistol and “iButton” system in product A, with a weak negative correlation between skin's perfusion of microcirculation and temperature devices. For product B, the correlation between the devices was moderate and between skin's perfusion and temperature devices weak and positive.

Conclusion

Both devices produced similar kinetics, except at baseline, where they may differ as metallic loggers have been insufficiently adapted to skin temperature. Skin's perfusion of microcirculation could not explain skin temperature changes.

Effect of Diode Laser (810 nm) Irradiation on Marginal Microleakage of Multi-mode Adhesive Resins in Class V Composite Restorations

Introduction: Some studies have shown that laser irradiation on unpolymerized adhesives can improve composite-dentin adhesion. The aim of the present study was to evaluate the effect of the diode laser (810 nm) on the microleakage of multi-mode adhesive systems at enamel and dentin margins of composite restorations. Methods: Classic class V boxes were prepared on 48 sound premolar teeth and randomly divided into 6 groups (n=16). In the control groups, Scotchbond Universal (SBC), G-Premio (GBC), and Ambar U (AMC) were used by a self-etch mode. In the test groups (SBL, GBL, ABL), the 810 nm diode laser was irradiated (1 W) for 10 seconds before the polymerization of the adhesive. The boxes were restored by the resin composite. After finishing and polishing, the samples were thermocycled (5°C to 55°C) for 1000 cycles and then immersed in 0.1% methylene blue dye (48 hours). Dye penetration through the gingival and occlusal margins was measured by Stereomicroscope. The data were analyzed at the 5% significance level using Kruskal-Wallis and Mann-Whitney U tests. Results: Significant differences were found between the control and test groups (P < 0.05). The occlusal margins of the SBL and GBL groups and the cervical margin of the SBL group exhibited the lowest microleakage (P < 0.05). The AM control group showed maximum microleakage at cervical and occlusal margins. Conclusion: The irradiation of the 810 nm diode laser on the unpolymerized universal adhesive systems in a self-etch mode caused a significant reduction in enamel and dentin marginal microleakage of composite restorations.

Estimating uncertainty of temperature measurements for studies of flow boiling heat transfer in minichannels

This paper presents the method of estimating the uncertainty of temperature measurements conducted using K-type thermocouples in the study of flow boiling heat transfer in minichannels. During heat transfer experiments. the fluid temperature at the inlet and outlet of the minichannel is measured with thermocouples connected to a DaqLab 2005 data acquisition station. The major part of the experimental setup for calibration of temperature measurement included a calibrator of thermocouples. The thermocouples were manufactured by Czaki Thermo-Product. Poland. The temperatures recorded with the thermocouples were compared statistically while measuring the temperature of demineralised water at several characteristic points at liquid phase change or using the reference temperature known from the calibrator. The experimental error of the temperature measurement method was determined according to the principles of statistical analysis. Estimates of the mean value and the experimental standard deviation of the experimental error as well as the confidence interval for a single experimental error and the measurement accuracy were presented. The uncertainty of the difference in temperature was also calculated