The physics of wave propagation, emergent from Maxwell's equations, impose fundamental bounds on the efficiency of power transfer over biological tissue. Theoretical analysis of these bounds yields insight on performance that can be achieved in specific powering configurations as well as new design concepts that may enhance efficiency. Our approach is inspired by the ideas underlying Shannon's information-theoretic channel capacity. Shannon first defined abstract source and channel models, and then sought to find the maximum information rate that can be reliably transmitted without regard for the details of implementation. By analogy, we adopt an analytically simple model for the channel, source, and receiver; and solve for the optimal source structure, and derive a global upper bound on the efficiency of power transfer. For powering deep-tissue devices, the optimal solution exhibits the properties of an immersion lens. To synthesize the optimal source, we propose and demonstrate the concept of a planar immersion lens based on metasurfaces. In this talk, I will describe the journey of solving this optimal-source problem in the past six years. I will also discuss engineering and experimental challenges to realizing such interfaces in animal models, including a pacemaker that is smaller than a grain of rice. These tiny devices can act as bioelectronic medicines, capable of precisely modulating local activity, that may be more effective treatments than drugs, which act globally throughout the body. I will conclude the talk with my thoughts on how information theory can play a role in realizing such bioelectronic medicines.
Ada was born and raised in Hong Kong. She received her B.Eng degree from the EEE department at the University of Hong Kong and her Ph.D. degree from the EECS department at the University of California at Berkeley. Her dissertation attempted to connect information theory with electromagnetic theory so as to better understand the fundamental limit of wireless channels. Upon graduation, she spent one year at Intel as a senior research scientist building reconfigurable baseband processors for flexible radios. Afterwards, she joined her advisor’s startup company, SiBeam Inc., architecting Gigabit wireless transceivers leveraging 60-GHz CMOS and MIMO antenna systems. After two years in industry, she returned to academic and joined the faculty of the ECE department at the University of Illinois, Urbana-Champaign. Since then, she has changed her research direction from wireless communications to integrated biomedical systems. In 2008, she moved back to California and joined the faculty of the Department of Electrical Engineering at Stanford University. She is a Terman Fellow at Stanford University. She received the Okawa Foundation Research Grant in 2010 and NSF CAREER Award in 2013.