The Efficient Energy Transfer Department (ηET) at Nokia Bell Labs in Ireland leads research in thermal management of electronics and photonics, energy harvesting and storage for wireless sensors and small cells.  The research from this group spans a broad range of application spaces such as:  

  • Wireless products, Fixed Access products and IP Routing and Transport applications
  • Cooling electronics and photonics operating at varying length scales, heat flux and temperature control levels, and thermal profiles
  • Single phase and two-phase cooling techniques, and 
  • Nano and macro scale cooling.

The Efficient Energy Transfer Department was created in Jan 2013, and is currently managed by Domhnaill Hernon.

Thermal Management Projects

Thermally Integrated Photonics Systems (TIPS)

Creating the thermal building blocks for future photonic packages

The TIPS project is focused on developing scalable and energy-efficient thermal solutions for terabit photonics packages. These packages are pluggable optical input/output (I/O) devices providing the optical-electrical signal conversion required to bring optical communications signals into telecommunications equipment. The extreme performance requirements of these terabit packages create large thermal and power densities that are demanding for designers.  

We approach thermal design holistically from the device (laser) to the system (rack) to enable massive scaling of data rate while reducing J/Bit. We select from an array of novel thermal building block technologies (µChannels, µTECs, µValves, mini pumps, nano spreaders, and novel heat exchangers) and new flow geometries for viscoelastic flows to promote microscale fluid mixing. This year we developed a full performance envelope for TIPS architecture showing the potential to reduce J/Bit in the transceiver by 70% while delivering terabit photonics capacity. We introduced new materials with 500X greater thermal conductivity around laser. We developed reliable, small, solid state (no moving parts) mini pumps. We demonstrated microscale mixing in microchannels via an elastic instability for enhanced localized heat transfer. Our continued thermal management efforts will be a key enabler of future optical interfaces and systems.




Photo of Ryan Enright
Ryan Enright
Dublin, Ireland
Photo of Shenghui Lei
Shenghui Lei
Dublin, Ireland
Photo of Kevin Nolan
Kevin Nolan
Dublin, Ireland


Fixed Access Thermal Research

Novel ways of cooling subterranean deployments

Innovative Bell Labs technology developed in Antwerp provides fiber-like speeds over copper wiring within a short range of the end user (typically at the end of domestic driveways). In order to reduce costs, traditional telecom deployments bury equipment directly in the soil or manholes; however as soil is a poor thermal conductor this presents a significant thermal challenge. We have developed novel thermal solutions to enable new deployment scenarios where the products are placed in hostile environments such as soil.


Bell Labs Garden



Concept to Product (C2P) Research

Rapidly converting concepts to product

This specialized sub-group of Efficient Energy Transfer focuses on bringing products from proof of concept to complete product demo in less than one year. We rely on strategic partnerships, patents and researcher expertise as well as parallel computational and experimental investigations to evaluate and optimize concepts.

Our group continually tests the limits on swiftly creating high-impact products for licensing or business unit transfers. We conceived and demonstrated biomimetic-inspired air moving devices for next generation reliable cooling solutions. We developed reliable, scalable solid-state (no moving parts) pumps. And we created high performing heat sinks to enable the deployment of next generation wireless devices.

Concept to Product



Photo of Akshat Agarwal
Akshat Agarwal
Dublin, Ireland
Photo of James Howard
James Howard
Dublin, Ireland
Photo of Nick Jeffers
Nick Jeffers
Dublin, Ireland

Acoustic Noise Research

Reducing noise with new designs and materials

Telecommunication devices today rely on air based cooling to maintain reliable hardware temperatures. Air-moving devices, such as rotating fans, are used to transfer equipment generated heat to the environment. As the telecom network grows, customers demand improved functionality within ever smaller product form factors, leading to even more heat generation per unit area/volume. We aim to improve cooling efficiency, reduce acoustic noise and alleviate dust deposition within air cooled equipment, adhere to standards set out by NEBS and ETSI, and ensure a safer (and quieter) working environment inside data centers.


Acoustic Beam Forming




Photo of Ian Davis
Ian Davis
Dublin, Ireland

Package to Rack Photonic Thermal Solutions

Novel solutions that keep equipment cool

We support Nokia's IP Routing and data center products with our Rack Photonic Thermal Solutions.  In typical installations, the network equipment resides in vast central offices or data centers, in the form of floor-to-ceiling cabinets loaded with densely populated circuit boards which consume large amounts of power. It is within these products that we find the highest chip power densities and the most temperature sensitive components. 

While these systems are typically cooled by standard air conditioning, we are developing thermal solutions for both high power devices and temperature sensitive components. We are working closely with IPR&T to develop cooling solutions that enable more functionality on every board.  We also aim to effectively cool temperature-sensitive components such as lasers that exist on the faceplate through better thermal interface design.  One solution involves liquid cooling within the cabinet. This allows for performance improvements, higher component densities, less fan noise and more reliable products.


Photo of Brian Donnelly
Brian Donnelly
Dublin, Ireland
Photo of Todd Salamon
Todd Salamon
Murray Hill, NJ, USA

Environmental Dust Corrosion Research

Tackling dust, humidity and temperature to improve hardware reliability

The global expansion of telecoms networks with equipment deployments across continents with increasingly harsh environments poses an increased risk to hardware reliability. Factors such as operating temperature, humidity, particle matter and corrosive agents (dust) constitute the main stressors of these aggressive environments. The latter three, particularly dust, is becoming a significant challenge as conditions can be highly diverse, both at local and regional levels. The deposition of dust on sensitive electronics can be exacerbated by air flow within the equipment. Our understanding of environmental conditions and upfront thermal management solutions allow us to keep ahead of these deployments. 

We approach dust mitigation with solutions that are alternatives or complimentary to conventional high-loss filters. We aim to develop environmental monitors so proactive and reactive design actions can be quickly implemented.  In this research we achieved an autonomous acquisition system for monitoring temperature, humidity, PM2.5 and PM10 which has more functionality, 60% smaller in size, and 20% of the cost of the best-in-class commercially available products.


Alternative Energy and Storage Projects

The Alternative Energy and Storage group develops technologies that improve deployment and operations of telecom systems.  We collaborate with CRANN, the nano-technology institute based in Trinity College Dublin, Ireland, to explore battery improvements -- such as improved capacity and lighter weights.


Alternative Energy Research

Novel solutions to power telecom equipment

The AES group is dedicated to developing technologies for powering off-grid telecom equipment.  We are researching power-autonomous equipment to reduce complexity and deployment times in both remote rural areas and dense urban environments. With the goal of providing high energy density and longer battery life, we plan to use small cells in future networks to address rapid data traffic growth.  We are researching ways to eliminate battery replacements in small cells and within wireless sensor nodes by employing energy harvesting and storage solutions. 

Energy Storage and Energy Harvesting Research

Cost-effective and efficient energy harvesting and storage systems

Ever increasing data traffic needs demand that we develop ways to increase network deployments with lower cost per bit solutions. We are exploring energy harvesting from vibrational, thermoelectric and photovoltaic power sources for wireless sensors and small cell products. We investigate ways to convert ambient vibrations into electrical energy to power wireless devices and ways to apply solar technology for indoor applications. Our research allows us to study new materials that will allow telecom operators to deploy lighter batteries with enahced capacity. We have projects to investigate material that is both cost-effective and efficient for photovoltaic panels.  




Photo of Ronan Frizzell
Ronan Frizzell
Dublin, Ireland
Photo of Paul King
Paul King
Dublin, Ireland
Photo of Diarmuid O'Connell
Diarmuid O'Connell
Dublin, Ireland

Advanced Prototype Lab

The Efficient Energy Transfer Department has a well-equipped machine lab that enables us to design and build advanced product prototypes. The Lab helps the ηET team design and test reliable air cooling devices for wireless products, Vibration Energy Harvesting (VEH) devices and next generation field trial cooling devices. Our lab can create unique environmental test chambers to help us test specific climatic effects on our products. We embrace leading edge technologies like high resolution (16µm) 3D printing to create micro channel cooling design models, micro-machining techniques for soft lithography and microscale liquid cooling, computer aided design and high precision geometry CNC machining to prototype RF resonators.

Our expert toolmakers, engineers and industrial designers work closely with researchers to convert early stage ideas into proof of concept prototypes, advanced prototypes and product designs. We show an example of a prototype evolution from research concept to final product design in the figure below.

Lab Lead

Photo of Ollie Burns
Ollie Burns
Dublin, Ireland



  • Mathews, I., Abdullaev,A., Lei, S., Enright,R.,  Wallace,M.J. and Donegan, J. F. 2015. Reducing thermal crosstalk in ten-channel tunable slotted-laser arrays. Opt. Express, vol. 23, no. 18, pp. 23380–23393, 
  • Donnelly, B. Meehan, R O’Reilly. Nolan, K. and Murray, DB. 2015, The dynamics of sliding air bubbles and the effects on surface heat transfer. International Journal of Heat and Mass Transfer. Vol. 91. Pp. 532-542.
  • Yang, X., Turan, A. and Lei, S. 2015, Thermoacoustic instability in a Rijke tube with a distributed heat source. Journal of Thermodynamics, in press.
  • Donnelly, B., Meehan, R. O., Nolan, K. & Murray, D. (2015), ‘The dynamics of sliding air bubbles and the effects on surface heat transfer’, International Journal of Heat and Mass Transfer 91, 532 – 542. 
  • Waddell, A., Punch, J., Stafford, J., and Jeffers, N., 2015, “On the hydrodynamic characterization of a passive shape memory alloy valve,” Appl. Therm Eng., Vol. 75, pp. 731-737.
  • O’Donoghue, D., Frizzell, R., Nolan, K., Kelly, G. & Punch, J. (2015), ‘The influence of mass configurations on velocity amplified vibrational energy harvesters’, Smart Materials and Structures, accepted. 
  • Mathews, I, King, P, Stafford, F, Frizzell, R. 2015, Wide-Bandgap III-V Solar Cells for Indoor Light Energy Harvesting , Accepted for publication in IEEE Journal of Photovoltaics 


  • Enright, R., Lei, S., Nolan, K., Mathews, I., Shen, A., Levaufre, G., Frizzell, R., Duan, G.- H. & Hernon, D. (2014), ‘A vision for thermally integrated photonics systems’, Bell Labs Technical Journal 19, 31–45. 
  • Raj, R., Adera, S., Enright, R., and Wang, E.N. 2014. High-resolution liquid patterns via three-dimensional droplet shape control.  Nat. Commun., vol. 5.
  • Enright, R., Sprittles, J.E., Nolan, K., Mitchell, R., and Wang, E.N., 2014. How coalescing droplets jump, ACS Nano. 
  • Preston, D.J., Miljkovic, N., Sack, J., Enright, R., Queeney, J., and Wang, E.N. 2014. Effect of hydrocarbon adsorption on the wettability of rare earth oxide ceramics,  Appl. Phys. Lett., vol. 105, no. 1, p. 011601.
  • Miljkovic, N., Preston, D.J., Enright, R., and Wang, E.N. 2014. Jumping-Droplet Electrostatic Energy Harvesting, Appl Phys Lett, vol. 105, no. 1, p. 013111. 
  • Lam, L.S., Melnick, C., Hodes, M., Ziskind, G., and Enright, R., 2014. Nusselt Numbers for Thermally Developing Couette Flow With Hydrodynamic and Thermal Slip,  J. Heat Transf., vol. 136, no. 5, p. 051703.
  • Enright, R., Miljkovic, N., Alvarado, J.L., Kim, K., and Rose, J.W. 2014. Dropwise Condensation on Micro- and Nanostructured Surfaces, Nanoscale Microscale Thermophys. Eng., vol. 18, no. 3, pp. 223–250.
  • Enright, R., Hodes, M., Salamon, T., and Muzychka, Y., 2014. Isoflux Nusselt number and slip length formulae for superhydrophobic microchannels, J. Heat Transf., vol. 136, no. 1, p. 012402, 2014.
  • Jeffers, N., Stafford, J., Nolan, K., Donnelly, B., Enright, R., Punch, J., Waddell, A., Ehrlich, L., O’Connor, J., Sexton, A., Blythman, R. & Hernon, D. (2014), Microfluidic cooling of photonic integrated circuits (PICS), in ‘4th European Conference on Microfluidics’. 


Bell Labs Efficient Energy Transfer

If you would like to learn more about the Efficient Energy Transfer team and our work, or if you would like to find out about internships or other opportunities, fill out the form here and we will reply.