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1. Effect of External Source Impedance on the Input Impedance of Digital Impedance Circuits

   https://doi.org/10.1109/ISCAS45731.2020.9180570  

   Hecht, Kristy A.; Daniel, Christopher G.; Weldon, Thomas P. (October 2020, 2020 IEEE International Symposium on Circuits and Systems (ISCAS))

   The input impedance of recently-introduced digital impedance circuits has been discovered to be dependent on the impedance of the external signal source. To address this problem, the theory for the dependence of digital impedance on external source resistance is presented. These digital impedance circuits provide an important digitally-controlled digitally-tunable alternative approach to difficult design problems, such as design of negative capacitances for stable wideband non-Foster antennas and metamaterials. Unfortunately, undesired source-dependent variation of the digital impedance can arise in scenarios where off-the-shelf high-speed analog-to-digital and digital-to-analog converters commonly have 50 ohm impedance. Further complicating matters, the sensitivity of digital impedance on source resistance appears to also depend on other design parameters of the digital circuit. Therefore, theory and simulation results are presented to show the dependence of digital impedance on the external source resistance. Lastly, measured results for a prototype of a digital non-Foster negative capacitance confirm the theoretical results. 

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2. Mechanical Impedance

   French, Mark (April 2019, American lutherie)

   We all know what “impedance” is, right? It’s that stuff... the force that... well, what is it really? Turns out it’s something like pushing a kid on a swing at the wrong time. And it has a lot to do with the resonances of acoustic instruments, which has a lot to do with how they sound. Anyway, Professor Mark gives us the scoop. 

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3. Mechanical Impedance

   French, Mark (January 2019, American lutherie)

   We all know what “impedance” is, right? It’s that stuff... the force that... well, what is it really? Turns out it’s something like pushing a kid on a swing at the wrong time. And it has a lot to do with the resonances of acoustic instruments, which has a lot to do with how they sound. Anyway, Professor Mark gives us the scoop. 

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4. Tunable Impedance-Matching Filters

   https://doi.org/10.1109/LMWC.2021.3083184  

   Estrada, Jose Antonio; Johannes, Seth; Psychogiou, Dimitra; Popovic, Zoya (August 2021, IEEE Microwave and Wireless Components Letters)

   null (Ed.)
5. Simulation of Localized Surface Plasmon Resonances in Two Dimensions via Impedance-Impedance Operators

   https://doi.org/10.1137/20M133066X  

   Nicholls, David P.; Tong, Xin (January 2021, SIAM Journal on Applied Mathematics)

   null (Ed.)