Capacitors

Capacitors are extremely useful passive circuit elements that store charge to be used when a driving voltage source is not present. In this way, you can think of capacitors like “temporary batteries,” and they are used in countless electronic applications from your phone to cardiac pacemakers! Check out the introductory video below to learn more about capacitor function and how it can be used in such a diverse range of electronic devices!

Self-Assessment Questions:

Click here to test your understanding of Capacitors.

Discussion Questions:

1. Although parallel plate capacitors are the only capacitor type covered in this video, there are many other shapes capacitors can take to achieve slightly different functions. Research and find at least two other capacitor types and explain how they operate.
2. For each of the different capacitor types you found in question one, find an example of an electronic device that uses that type of capacitor. Explain how that specific capacitor type is best suited for the given application instead of a simple parallel plate capacitor.
3. Other than changing the capacitor shape, capacitors can also be made more effective by the use of doping to improve capacitor dielectrics. How do doping agents work to do this? How could the increased capacitance be helpful in different applications? Read this article by Homes et al. to help inform you on the benefits of doping.
4. What is the difference between powering a device with a battery versus a capacitor? Compare and contrast how the electrical energy is provided to the circuit in each case.
5. Compare and contrast capacitor usage in AC and DC circuits. How are capacitors used similarly and differently in each case?
6. Arguably the most important application of capacitors in human physiology is in understanding properties of the lipid bilayer. In what ways does the lipid bilayer mimic the function of a parallel plate capacitor? In what ways is it different? Use this article relating lipid bilayers to capacitors to help you answer this question.

Continue Reading:

• C. C. Homes and T. Vogt, “Colossal permittivity materials: Doping for superior dielectrics: Colossal permittivity materials,” Nat. Mater., vol. 12, no. 9, pp. 782–783, 2013. Read this resource here.
  • This article explains the operation principle of a new co-doped titanium oxide material used that prevents extreme dielectric loss while increasing the permittivity of the capacitor system. This allows for higher capacitance of capacitors and more possibilities for capacitors in electronics.
• J. Golowasch and F. Nadim, “Capacitance, Membrane,” in Encyclopedia of Computational Neuroscience, New York, NY: Springer New York, 2014, pp. 1–5. Read this resource here.
  • This article relates the biological features of the lipid bilayer to the electrical properties of capacitors. It explains how the lipid bilayer in cells is important for biological function.
• H. Li et al., “Fully bioabsorbable capacitor as an energy storage unit for implantable medical electronics,” Adv. Sci. (Weinh.), vol. 6, no. 6, p. 1801625, 2019. Read this resource here.
  • Many small, implantable medical devices such as pacemakers often run on batteries or capacitors that must be replaced, requiring the device to be removed after it is no longer operational. This article details a bioabsorbable capacitor technology that allows longer lasting devices in patients.
• A. E. Zadeh, “Nano-power switched-capacitor bandpass filters for medical implantable pacemakers and defibrillators,” in 2008 51st Midwest Symposium on Circuits and Systems, 2008, pp. 29–32. Read this resource here.
  • A major use for capacitors in medical devices such as pacemakers and defibrillators are for frequency filtering (see videos on high- and low-pass filters for details). This article explains the integration of a bandpass filter using capacitor technology that requires extremely small power delivery, thus increasing implantable device lifetime.

About the Creator:

This video was created by a student in the Rice Bioengineering Class of 2023 (used with permission).