Our long-term goal is to develop multi-functional materials for challenging applications involving combined acoustic, mechanical, and thermal functions. As the first step towards this goal, we are developing a new class of heat sinks based on periodic porous materials that are able to dissipate heat, absorb noise, as well as have high mechanical strength. This work is done in collaboration with Prof. Shankar Krishnan, IIT Bombay.
Thermal management in many systems involve fan-mounted heat sinks which results in in fan-generated noise as an undesired by-product . Further, as fan speed increases, thermal resistance decreases but noise level increases (panel (A) in the figure above). Many of these applications require noise reduction and attempt to reduce noise using separate devices. However, space for separate heat sinking and noise-reducing functionalities may be limited in complex systems such as consumer electronics cooling, motors, automotive, aviation, and data center thermal and acoustics management.
To address this challenge, we are developing new type of porous materials that can perform both heat sinking and noise reduction in the same functional volume. We also include mechanical strength functionality for some applications.
Designed periodic unit cells are repeated in a controlled form to generate three-dimensional materials that can perform multiple functions. Examples of two unit cells are shown in panel (C). A heat sink of simple block-shape, where a selected unit cell is repeated uniformly in all three directions, and attached to a base plate, is shown in panel (B). The principles involved in multi-functional performance, and the methods involved in designing these unit cells, design of the macro-scale shape, and their resulting multi-functional performances are discussed in the publications listed below. Computational, analytical, and experimental methods are adopted in this development. Improving the multi-functional materials is an ongoing effort in our lab.
Using unit-cell approach, we designed periodic foams, predicted and experimentally benchmarked their acoustic absorption and mechanical strength.
We showed how to select periodic cellular structures for multifunctional applications directly based on their geometry, reducing the effort from typical lengthy computational modeling. Three geometric parameters of the unit cell, viz., porosity, wet surface area, and angular orientation of the struts, are shown to be sufficient to predict the functional performance for acoustic absorption coefficient, thermal conductivity, and mechanical Young's modulus. Using a material property index defined as a weighted sum of the normalized functional quantities, it is possible to evaluate the multifunctional performance of the unit cell candidates directly based on geometry.
Selected Journal publications relevant to this work:
Ramamoorthy, S. and Krishnan, S., "Towards thermal-acoustic co-design of noise reducing heat sinks, IEEE Transactions on Components, Packaging, and Manufacturing Technology, 8(8), pages 1411-1419, 2018.
Deshmukh, S., Ronge, H., Ramamoorthy, S., "Design of periodic foam structures for acoustic applications: concept, parametric study, and experimental validation", Materials & Design, 175, p. 107830, 2019.
Choudhary, R., Sachan, S., Krishnan, S., and Ramamoorthy, S., “Design and parametric study of macro-structure of foams for combined high absorption and low pressure drop.”. Applied Acoustics, 166, 107358, 2020.
S. Deshmukh, S. Kumar, A. Wagh, S. Krishnan, and S. Ramamoorthy, "Selection of periodic cellular structures for multifunctional applications directly based on their unit cell geometry", International Journal of Mechanical Sciences, 107133, 2022
H. Ronge, S. Upalkar, A. Wagh, R. Choudhary, S. Krishnan, S. Ramamoorthy, "A model for sound propagation through corrugated structures with mean flow", Journal of Vibrations and Acoustics, 145(2), 021007, 2023.
A. Wagh, S. Deshmukh, S. Ramamoorthy, S. Krishnan, "Effect of material distribution in the unit cell on effective thermal conductivity and Young's modulus of cellular structure", Journal of Applied Mechanics, 90(1), 011008, 2023
H. Ronge, S. Upalkar, A. Wagh, S. Krishnan, S. Ramamoorthy, "Evaluations of corrugated macro-structure porous heat sinks for the combined heat dissipation and noise reduction performance", International Journal of Thermal Sciences, 187, 108157, 2023
S. Sachan and S. Ramamoorthy, "Microstructure-based modeling to characterize low pore density open-cell foams and its experimental validation," Journal of the Acoustical Society of America, 155, pages 188-205, 2024.
A Wagh, S Krishnan, S Ramamoorthy, "Tonal and Broadband Noise-Reducing Heat Sinks Using Long-Neck Helmholtz Resonator Arrays and Corrugated Periodic Cellular Materials", Journal of Electronic Packaging, 148 (1), 011002, 2026
Active Noise Control
We are integrating active feedback control in some applications involving these multifunctional materials using DSPACE. Our prior work on active feedback noise cancellation, unrelated to multifunctional materials, can be seen in the 'Past work' tab.
Active noise control inside a small acoustic cavity
A small cuboidal cavity with porous material is attached with two speakers, one acting as a "noise" source and the other as a control speaker. A microphone is also integrated as a sensor to demonstrate active noise cancellation in a simple system. The closed-loop sensitivity (pressure at the microphone with active control vs. without active control) in dB is shown in the right.
Active feedback control to increase low-frequency absorption in foams
Journal publications relevant to this work:
P Nayak, SB Noronha, S Ramamoorthy, "Enhancement of acoustic absorption coefficient of foams using active feedback control", The Journal of the Acoustical Society of America, 158 (4), 3400-3411, 2025.
Deafness is the most prevalent sensory disability across nations. The sense of hearing has been least understood owing to the challenge in accessing the inner ear deeply positioned inside the head. In addition to the challenging physiological environment, experiments in the live mammalian cochlea continue to demand better methods and innovative sensors. Our long term goal is to develop better understanding and effective diagnosis of hearing loss by developing novel instrumentation geared towards live intra-cochlear measurements, as well as to develop better understanding of the active vibro-acoustics in the inner ear using computational modeling.
Sound entering the outer ear vibrates the middle ear bones and launches vibroacoustic waves inside the inner ear organ, cochlea. Complex processing of sound inside the cochlea eventually leads to signals that provide input to the auditory nerve.
In our 2007 JASA paper, titled "A mechano-electrical-acoustic model of the cochlea: response to acoustic excitation", we developed a multi-scale model of the cochlea integrating mechanical, electrical, and acoustic domains. This 'MEA' model is able to predict the data obtained from several physiological experiments in live guinea pig cochlea. A description of the MEA model can be seen in the "Past work" tab.
In our recent publication in 2020, we showed that there is a fine balance between the local electromechanical and vibroacoustic properties of the cochlea, and that this balance is important for the active feedback amplification of low level sounds processed by our ear. The relevant journal publication is:
N. Agarwal and S. Ramamoorthy, “Balance in the feedback loop components of the mammalian cochlear amplifier.”, Journal of Applied Physics, 128(3), 034701, 2020.
The nonlinear mechanics of the cochlea is integrated into the MEA model and combining it with a model for the middle and outer ear to predict otoacoustic emissions in human subjects, as shown in this article:
N. Agarwal and S. Ramamoorthy, S. A nonlinear mechano-electro-acoustic model of the human cochlea. In AIP Conference Proceedings (Vol. 3062, No. 1, p. 040008). AIP Publishing LLC, 2024.
Nonlinear mechanical-electrical-acoustic “MEA” model of the human cochlea (custom finite element codes)
Using optical coherence tomography (OCT), we have developed a sensor for simultaneous measurement of the velocity of a vibrating structure and the fluid pressure in the vicinity of the structure. Spectral-domain OCT can simultaneously measure the vibrations of multi-layered structures in the axial direction. By inserting a designed miniature vibroacoustic sensor whose diaphragm is placed in the vicinity of the vibrating diaphragm of interest and measuring the vibrations of both diaphragms simultaneously using spectral-domain OCT, the proposed method is demonstrated. This method could be used inside any micro-channel, including the mammalian cochlea as illustrated in the panel.
The sensor is described in the following journal publication:
Ramdas, R., Agarwal, N., Atpadikar, M., and Ramamoorthy, S., “Simultaneous measurement of vibration and pressure in vibroacoustic microchannels.” Applied Acoustics, 169, 107489, 2020.
This sensor could be used to measure the acoustic impedance of human subjects, shown in this article on an ear-simulator:
R. Ramdas, N. Agarwal, M. Atpadikar, and S. Ramamoorthy, "OCT-based method for the combined measurement of structural vibration and fluid pressure.", In AIP Conference Proceedings (Vol. 3062, No. 1, p. 020007). AIP Publishing LLC. 2024.
Our broad objective is to combine computational modeling with non-invasive auditory measurements such as otoacoustic emissions to help understand nuances of human hearing.
Distortion product otoacoustic emissions (DPOAE) in a normal hearing human subject and suppression tuning of cubic DPOAE by a third tone are shown here.