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1. A Wearable CMOS Impedance to Frequency Sensing System for Non-Invasive Impedance Measurements

   https://doi.org/10.1109/TBCAS.2020.3025218  

   Hedayatipour, Ava; Aslanzadeh, Shaghayegh; Hesari, Shahram Hatefi; Haque, Mohammad Aminul; McFarlane, Nicole (October 2020, IEEE Transactions on Biomedical Circuits and Systems)

   null (Ed.)
2. 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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3. 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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4. 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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5. Evaluating impedance boundary conditions to model interfacial dynamics in acoustofluidics

   https://doi.org/10.1063/5.0225930  

   Kshetri, Khemraj Gautam; Nama, Nitesh (August 2024, Physics of Fluids)

   We present a numerical study to investigate the efficacy of impedance boundary conditions in capturing the interfacial dynamics of a particle subjected to an acoustic field and study the concomitant time-averaged acoustic streaming and radiation force fields. While impedance boundary conditions have been utilized to represent fluid–solid interface in acoustofluidics, such models assume the solid material to be locally reactive to the acoustic waves. However, there is a limited understanding of when this assumption holds true, raising concerns about the suitability of impedance boundary conditions. Here, we systematically investigate the applicability of impedance boundary conditions by comparing the predictions of an impedance boundary approach against a fully coupled fluid–solid model. We contrast the oscillation profiles of the fluid–solid interface predicted by the two models. We consider different scatterer materials to identify the extent to which the differences in interfacial dynamics impact the time-averaged fields and highlight the divergence within the predictions of the two models. Our findings indicate that, although impedance boundary conditions can yield qualitatively similar results to the full model in certain situations, the predictions from the two models generally differ both qualitatively and quantitatively. These results underscore the importance of exercising caution when applying these boundary conditions to model general acoustofluidic systems. 

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