I've read that the exponential behavior predicted in e.g. RC circuits by taking the Laplace-domain impedance of capacitors to be 1/sC leads to a causality violation, and that after much testing of many capacitors some guys named Westerlund and Eklam determined that the true behavior is a probably a power law, which I guess means the dv/dt in I = C dv/dt would actually have to be some kind of fractional derivative. Can anyone elaborate on why this is so?
violation of causality by purely imaginary impedance functions
Started by ●March 25, 2023
Reply by ●March 25, 20232023-03-25
On Saturday, March 25, 2023 at 1:41:59 PM UTC-4, bitrex wrote:> I've read that the exponential behavior predicted in e.g. RC circuits by > taking the Laplace-domain impedance of capacitors to be 1/sC leads to a > causality violation, and that after much testing of many capacitors some > guys named Westerlund and Eklam determined that the true behavior is a > probably a power law, which I guess means the dv/dt in I = C dv/dt would > actually have to be some kind of fractional derivative. > > Can anyone elaborate on why this is so?Two morons over their head.
Reply by ●March 25, 20232023-03-25
On 2023-03-25 13:41, bitrex wrote:> I've read that the exponential behavior predicted in e.g. RC circuits by > taking the Laplace-domain impedance of capacitors to be 1/sC leads to a > causality violation, and that after much testing of many capacitors some > guys named Westerlund and Eklam determined that the true behavior is a > probably a power law, which I guess means the dv/dt in I = C dv/dt would > actually have to be some kind of fractional derivative. > > Can anyone elaborate on why this is so?'T'ain't so. Just another casualty of causality. (People, especially assistant professors, periodically announce causality violations due to mistaking group delay for true delay(*) or measuring logic transitions by output threshold crossings with a slowish input. Cheers Phil Hobbs (*) I did that myself once, in this very boutique. -- Dr Philip C D Hobbs Principal Consultant ElectroOptical Innovations LLC / Hobbs ElectroOptics Optics, Electro-optics, Photonics, Analog Electronics Briarcliff Manor NY 10510 http://electrooptical.net http://hobbs-eo.com
Reply by ●March 25, 20232023-03-25
On 3/25/2023 2:11 PM, Phil Hobbs wrote:> On 2023-03-25 13:41, bitrex wrote: >> I've read that the exponential behavior predicted in e.g. RC circuits >> by taking the Laplace-domain impedance of capacitors to be 1/sC leads >> to a causality violation, and that after much testing of many >> capacitors some guys named Westerlund and Eklam determined that the >> true behavior is a probably a power law, which I guess means the dv/dt >> in I = C dv/dt would actually have to be some kind of fractional >> derivative. >> >> Can anyone elaborate on why this is so? > > 'T'ain't so. Just another casualty of causality. > > (People, especially assistant professors, periodically announce > causality violations due to mistaking group delay for true delay(*) or > measuring logic transitions by output threshold crossings with a slowish > input. > > Cheers > > Phil Hobbs > > (*) I did that myself once, in this very boutique. >I guess this paper by Westerlund and Ekstam (not Eklam) might be what is being referred to: <https://ieeexplore.ieee.org/document/326654> There's also this more recent paper, ooh boy controversy! I bet it's a hot ticket <https://ieeexplore.ieee.org/document/8008998>
