Thermal analysis of piezoelectric actuators for active cooling of RF phased array radars
RF communications and radar systems present an extreme thermal management challenge. These systems are comprised of tightly packaged high wattage components requiring a controlled temperature to meet performance and reliability parameters. One approach being pursued to meet this thermal challenge is embedding piezoelectric actuators within the electronics to create synthetic air jet drives for localized cooling. U.S. Army AMRDEC is developing and testing actuator test beds to mature the concepts and develop practical solutions. This investigation attempts to model these actuators in a CFD thermal analysis program, verify the results of the models with the current test beds, and then insert the model in conceptual designs of phased array antennas. The goal of the investigation is to gain insight into the practical application of a maturing thermal management concept in a real world application. These cooling devices have achieved over 2.5 W/cm2 cooling capacity in a 1.3 cm3 package.
Active cooling substrates for thermal management of microelectronics
Heat removal in printed wiring boards (PWB) is primarily accomplished through conduction. This work presents a microelectromechanical system (MEMS) device comprised of an active cooling substrate (ACS) designed and fabricated to add fluidic cooling functionality to the PWB. Thermal management is enhanced through the additional heat convection mode. Synthetic jet technology makes the compact, but easily integrated, MEMS cooling device possible. The fluid control unit, a synthetic jet, has been implemented in an epoxy-glass printed wiring board by multilayer lamination. An air reservoir is drilled through the core of printed wiring board. A flexible polymeric diaphragm and a low profile electromagnetic driver create an active pumping system to produce vibrating air jets downstream of microfluidic channels which transports heat generated by hot microelectronic components. Test heater chips have been directly die attached to the substrate. The integrated packaging system has been characterized mechanically, electrically, and thermally. Peak jet velocities of 14 m/s and average jet velocities of approximately 3 m/s have been achieved at actuator powers of 60 mW. This integrated active cooling substrate has the potential for broad applications in thermal management at the system packaging level.
Pt Heater/Sensor Microarray for Distributed Fluidic Cooling Assessment

 This paper presents the design, fabrication, and characterization of a one-dimensional microscale heater array testbed that allows assessment of the spatial variation of temperature. Each pixel of the array acts as both a heater and a resistive temperature sensor simultaneously. The heater/sensor array is designed to mimic heat generation by line arrays of vertical-cavity surface emitting lasers (VCSELs), in order to assess microfluidic cooling schemes for these laser arrays. The array discussed in this paper is a linear micro array consisting of 100 heater elements, each of which has a 75μm pitch, and a nominal 20μmx20μm resistive heating area. Platinum is used for the heater as well as the resistive thermal sensor, since the resistance of platinum as a function of temperature shows extremely good linearity. A total of 101 probe pads are placed between the pixels to apply current for the heater function or to determine temperature for the sensor function. The array is fabricated on a silicon substrate and is diced to a size of 1.2mm × 8mm to match a typical VCSEL array size. Local heating and local cooling experiments (i.e., individual heater pixel or pixel groups) have been performed and demonstrate the versatility of the fabricated thermal testbed.