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Alic Chen, Ph.D.
Alic Chen is a Post-doctoral Researcher in the Department of Mechanical Engineering at University of California, Berkeley. His research is focused on two fronts: (1) Methods to improve LED efficiency through cooling with low-noise piezoelectric fans and (2) design and synthesis of extremely low-cost composite thermoelectric materials for waste heat energy generation. Alic is also the Research & Development Manager of Health Care at the Center for Information Technology Research in the Interest of Society (CITRIS) and works on developing large multi-institutional and multi-disciplinary health care research projects. Alic's CITRIS Health Care Bio can be found here:
Prior to his current work, Alic's research focused on thermal energy harvesting with thermoelectrics for self-powered sensors, with applications to implantable medical devices, body sensor networks and aging in place. During his Ph.D. research, Alic developed new methods for fabricating high-aspect ratio and high density array thermoelectric devices using printed manufacturing methods. His previous experiences include research on human thermometry at the National Institutes of Health (NIH), biomedical devices for uremia detection at the Industrial Technology Research Institute (ITRI), lab-on-chip BioMEMS systems for disease detection and piezoelectric acoustic sensors for blood pressure monitoring at Johns Hopkins University. His current research interests include mobile healthcare technologies, wireless sensor systems for medical and industrial applications and clean energy technologies.
Alic received his PhD and M.S. in Mechanical Engineering from University of California, Berkeley in 2011 and 2009, respectively, and his B.S. in Mechanical Engineering from Johns Hopkins University in 2007.
Thermal Energy Harvesting with Thermoelectrics for Self-powered Sensors: With Applications to Implantable Medical Devices, Body Sensor Networks and Aging in Place
Alic's Ph.D. research examined the feasibility of using thermoelectric generators as power sources for implantable medical applications. His work focused on thermoelectric design principles, manufacturing methods and novel materials.
Rapid advancements in the field of biomedical engineering has led to the vast number of implantable medical devices developed within the last few decades. As implantable medical devices provide more functionality, sufficient energy storage while maintaining compactness becomes challenging. The lifetime of implanted medical devices will often be much shorter than the expected lifespan of patients, adding risks and costs to the patient in the form of additional surgical procedures. A perpetual power source that extends the longevity of implantable devices still remains elusive. This presents opportunities for solid-state thermal energy harvesting with thermoelectric energy generators (TEGs) that scavenge waste heat, the most abundant source of energy from the body.
Thermoelectric energy generators (TEGs) provide solid-state energy by converting temperature differences into usable electricity. Since the fat in the human body provides thermal insulation, the largest temperature differences (typically 1-5 K) are found in the highest fat regions of the body. Bioheat transfer modeling shows that the optimal placement of TEGs for energy generation is in the abdomen under high convective conditions. Based on average 100 µW (at 1 V) input power requirements of implantable medical devices, thermoelectric and heat transfer design theories suggest a need for high aspect ratio thermoelectric elements in high density arrays to take advantage of the low temperature differences in the fat layer.1
In order to maximize power output, traditional thermoelectric device designs must be abandoned and a planar TEG device design is proposed as an effective and scalable method for implantable medical applications. Dispenser printing has been shown as a scalable and repeatable manufacturing method for depositing thick-film thermoelectric materials in the fabrication of planar TEGs.2 The use of printed fabrication methods led to the development and synthesis of novel printable composite thermoelectric materials. Current materials development have yielded a maximum dimensionless figure of merit (ZT) at 302K for an n-type Bi2Te3-epoxy composite at 0.18 when cured at 250°C, and a ZT of 0.34 for a p-type Sb2Te3-epoxy composite when cured at 350°C.3,4 A 50-couple TEG prototype with 5 mm x 640 µm x 90 µm printed element dimensions was fabricated on a polyimide substrate with evaporated metal contacts. The prototype device produced a power output of 10.5 µW at 61.3 µA and 171.6 mV for a temperature difference of 20K resulting in a device areal power density of 75 µW/cm2,4.
The results of the work are promising and novel efforts to improve the performance of future devices are ongoing.5,6 While the initial focus of Alic's work was specific to the field of biomedical devices, the technologies that have been developed are applicable to other fields involving energy harvesting. The prospective impact of this work ultimately paves the path towards the advanced healthcare system of the future based on integrated autonomous wireless systems for the needs of "aging in place" or "aging at home" technologies.
LED Cooling using Low-noise Piezoelectric Fans
With the increasing global demand for more efficient lighting solutions, light emitting diodes (LED's) have gained widespread adoption in both consumer and industrial lighting markets. While LED's have proven efficiency and longevity, such performance enhancements are highly correlated to their operating temperatures. While LED's do not produce infrared (IR) radiation, more than 60% of the input power is lost as heat. In order to maximize LED brightness (lumen output) and lifetime, it is essential to reduce the junction temperature through effective thermal management. Typical thermal management methods include passive heat-sinking and conventional fan cooling. While passive heat-sinks provide a noise-less solution to excess heat, natural convection does not provide sufficient cooling for higher powered LED systems. Fan cooling provides forced convection for effective cooling while taking advantage of well-established heat-sink design guidelines developed by the electronic industry. However, the improvement from fan cooling comes at a trade-off between acoustic noise and fan speed.
Piezoelectric fans can potentially provide low-noise and long-term cooling solutions for modern LED systems. A piezoelectric fan consists of a piezoelectric cantilever beam with a longer mylar blade attached below the beam. When an AC voltage is applied at the beam's resonant frequency (typically 115V at 60 Hz), the tip of the fan experiences a large displacement, resulting in air movement. The vortices flowing from the tip of the blade provide unique airflow patterns for LED cooling applications. Since the frequency of the piezoelectric beams are typically on the lower end of the audible range, acoustic noise from piezoelectric fans are not noticeable. Current research is focused on the design of heat-sinks for cooling LED's with piezoelectric fans to take advantage of their unique flow patterns. This research is focused on (1) experimental heat transfer analysis, (2) computational design and analysis using COMSOL multi-physics and (3) flow visualization of piezoelectric fans to optimize heat-sink designs.
- Chen, A., P.K. Wright (2012). "Medical Applications of Thermoelectrics" in Thermoelectrics and Its Energy Harvesting, Edited by D.M. Rowe (Boca Raton, CRC Press). [Link] [PDF]
- Wright, P., D.A. Dornfeld, A. Chen, C.C. Ho, J.W. Evans (2010). "Dispenser Printing for Prototyping Microscale Devices" Transactions of NAMRI/SME, Vol. 38, pp. 555-561. [PDF]
- Madan, D., A. Chen, P.K. Wright, J.W. Evans (2011). "Dispenser Printed Composite Thermoelectric Thick Films for Thermoelectric Generator Applications" Journal of Applied Physics, Vol. 108, 034904. [Link] [PDF]
- Chen, A., D. Madan, P.K. Wright, J.W. Evans (2011). "Dispenser-printed Planar Thick-film Thermoelectric Generators" Journal of Micromech. & Microeng., Vol. 21 (10), 104006. [Link] [PDF]
- Madan, D., A. Chen, R.C. Juang, P.K. Wright, J.W. Evans (2012). "Printed Se doped M.A. n-type Bi2Te3 Thick Film Thermoelectric Generators" Journal of Electronic Materials, DOI: 10.1007/s11664-011-1885-5. [Link] [PDF]
- Wang, Z., A. Chen, R. Winslow, D. Madan, R.C. Juang, M. Nill, J.W. Evans, P.K. Wright (2012). "Integration of dispenser-printed ultra-low-voltage thermoelectric and energy storage devices" Journal of Micromech. & Microeng., Vol. 22 (9), 094001. [Link] [PDF]