Thermal management technologies are becoming more important as electronic equipment gets smaller. As consumer electronic devices continue to shrink, heat is dissipated into a smaller and smaller volume of air inside the case. At the same time, the reduction of the physical space is constraining the size of the cooling devices themselves.
Today’s designers are reaching the limitations of traditional technologies such as bulky dc fans. To meet these evolving requirements, Murata’s tiny Microblower will replace fans in compact electronic equipment. The piezoelectric cooling device, which is part of the company’s growing micro-mechatronics range (Fig. 1), measures 20 by 20 mm with a 1.85-mm profile (without nozzle).
The Microblower’s piezoelectric diaphragm vibrates up and down when a sine-wave voltage is applied, forcing air through a suction hole into the device and out again through a nozzle (Fig. 2) at its top. The diaphragm can produce airflow rates of up to 0.8 litres/minute and air pressure up to typically 1.5 kilopascal (kPa) (1 psi = 6.8948 kPa).
The blower can create high air pressures, so it can be used as an air pump. Its high flow rate means it suits the localized cooling and diffusion of heat from specific devices in “hot-spot” areas in a design. Multiple Microblowers could even be used in a consumer device to cool each different IC in the system. Since the piezoelectric diaphragm draws very little current, the Microblower requires little enough power to be used in multiple locations, even in battery-powered devices.
The Microblower can be applied to operate in two different modes (Fig. 3). If the nozzle of the device is pointed at the device or area that needs to be cooled, it can blow cool (ambient) air out of the nozzle toward the substrate. Or, the suction hole on the bottom side of the Microblower can be pointed toward the heat source to suck hot air away from the substrate and then direct it out of the case.
In blow mode, spot cooling is achieved by keeping the flow rate high. The whole system can be cooled with air from outside the device. The suck mode may be used where there is a particular hot spot on a board that needs intensive cooling. This mode can provide a ventilation effect if the volume of air is suitably small.
For example, we used this technology to cool a DRAM module. The module had the normal heatsinks attached, and the Microblower transported the dissipated heat away from the device. A small attachment with a profile of just 2.4 mm held the Microblower in place.
The total profile of the attachment and the Microblower itself was just 4.25 mm, so this is similar to how the device would be used in a confined space application (Fig. 4). The setup was held in the open air rather than in a confined case to facilitate the accurate measurement of temperatures with a thermal imaging camera.
Figure 5 illustrates the results of this experiment. The plot on the left is the thermal temperature of the surface of the DRAM heatsink with the Microblower switched off. The temperature measured at the surface of the heatsink at point (1) was 68.4°C. The right-hand plot is the same plot, measured when the Microblower was operational. The temperature measured at point (1) then decreased to 50°C.
Considering the margin of the measurement tool, a temperature difference of at least 17K on the surface of the heatsink was apparent. Knowing that the DRAM module dissipates 6.8 W, it was possible to calculate the difference in the thermal resistance of the heatsink with and without the aid of the Microblower. The thermal resistance of the heatsink alone was 6.3 Kelvin-metres per watt (K/W) compared to 3.8 K/W when the Microblower was switched on. This is a significant decrease of around 40%.
This demonstration proved that the piezoelectric Microblower can be used to provide forced-air cooling in confined spaces in consumer, industrial, and automotive electronics.
In consumer applications, the Microblower will be used to cool charge-coupled device (CCD) image sensors in compact equipment with cameras and to cool processing ICs such as GPUs and CPUs. In the industrial arena, in addition to spot-cooling ICs, the Microblower can be successfully used for power-supply cooling applications. Applications stretch from cooling LED headlamps in today’s vehicles to cooling LCD backlights in both consumer and industrial applications.
With the Microblower’s specifications enabled, it can be widely used and help create new applications. It can serve as an air pump, as an air supply for industrial machinery or batteries, or perhaps simply as a dust remover. Other applications range from aquarium air pumps to ionizing devices. Murata is also developing a liquid pump, the micro-pump, based on similar technology that will be used in fuel-cell applications.
Alex Schmoldt works in business development for micromechatronics and RFID products for Murata Europe. He has held positions at Swatch and Epson. He holds a master’s degree from the University of Munich.