www.lesswrong.com/posts/TzwMfRArgsNscHocX/the-incredible-fentanyl-detecting-mach...
1 correction found
you need electrodes to be touching the sample.
That is too absolute. Standard electrical impedance tomography often uses contact electrodes, but contactless impedance and dielectric spectroscopy methods also exist using capacitive coupling.
Full reasoning
This statement overstates the limitation. Many common impedance techniques do use direct-contact electrodes, but impedance spectroscopy is not inherently limited to touching electrodes.
Credible published work describes capacitively coupled, contactless impedance/dielectric spectroscopy methods:
- A Scientific Reports paper explicitly says conventional EIT usually uses direct-contact electrodes, then presents "a contactless method" based on capacitive coupling for dielectric spectroscopy imaging.
- A Sensors paper says impedance spectra can be obtained "even when the measuring electrodes are capacitively coupled with the object".
So the more accurate claim would be that the most familiar medical impedance methods use contact electrodes, not that impedance spectroscopy as such requires electrode contact.
2 sources
- Capacitively Coupled Phase-based Dielectric Spectroscopy Tomography
Most common form of impedance imaging is electrical impedance tomography (EIT), which requires direct contact with the medium via electrodes. In this work we present a novel impedance imaging using capacitive coupling which provides a contactless method...
- Capacitive-Coupling Impedance Spectroscopy Using a Non-Sinusoidal Oscillator and Discrete-Time Fourier Transform: An Introductory Study
A frequency spectrum of complex impedance for the measured object can be obtained even when the measuring electrodes are capacitively coupled with the object...