Educational Applets

Properties of Materials Applets

The traditional, lecturer-driven classroom is giving way to a new more active environment, where students have access to a variety of multimedia course materials.  In collaboration with Prof. Madhyastha in Computer Engineering Department at UCSC, we created several Java applets for the electrical engineering course Properties of Materials.  These applets help describe concepts related to electron and hole motion in metals and semiconductors.  They address ideas which are often difficult for students to visualize and yet important for students to intuitively understand.

Electron movement in metals is a key concept that describes many physical properties such as electrical and thermal conduction.  Our simulation illustrates the random motion of electrons, as well as how that motion is affected by changes in temperature and an applied bias.  The simulations are interactive: students can change parameters and see how the electron motion is affected.  Figure below is a screen shot of the Electrons in Metal Simulation.  The sliders on the right and buttons on the bottom of the screen allow students to change the temperature, field strength, addition of impurities, and the valence of the metal.  In addition, students can use counters, electron traces, and speed variations to see the effects of their changes.  Electron movement in a semiconductor is similar, but there are some key differences (including the existence of holes) which our simulations illustrate.  Second figure is a screen shot of the Electrons in Extrinsic Semiconductor Simulation.  In addition to the simulations, we created a tutorial which operates like a slide-show.  All applets are available online at the Collage Website (http://www.collage.soe.ucsc.edu/available_applets.htm).

We deployed these applets in a class of roughly 140 students at San Jose State University, and a smaller class of roughly 20 students at the University of California at Santa Cruz.  The results of our experiments showed that one form of presentation is not enough, and students benefited from having additional resources to use outside of class.  The simulations helped clear up difficult concepts, and made students think about these ideas outside of class.

 

Boltzmann Transport Flash Applet

One can treat electrical and thermal conduction and the thermoelectric effects in semiconductors in a unified approach using the concept of “differential conductivity” (i.e. conductivity of electrons with a given energy inside the solid). The traditional derivation based on the Boltzmann transport equation and relaxation time approximation is calculation intensive and it is not appropriate for undergraduate education. It is also difficult to gain insight about the underlying physics. Here we created a user-friendly interface using Macromedia Flash Technology for the Boltzmann transport equation. The key functions such as density-of-states, Fermi-Dirac distribution function and differential conductivity are plotted versus electron energy. Electron mobility, electrical conductivity and Seebeck coefficient are accurately calculated based on the transport model described below. One can change the material properties (such as electron effective mass and mean-free-time between collisions) or the ambient temperature and see how these graphs are modified and what is the effect in the overall conductivity and Seebeck coefficient. These applets are used as educational tools in a class on Properties of Materials. They are cross platform compatible; they can be run on any PC or Mac. Figure below shows an example of the Flash applets. These applets are available online at http://www.collage.soe.ucsc.edu/applets/

 

 

Online Fiber Optic Communication Lab

With the support of Agilent Technologies and the NSF, the Online Fiber Optic Communications Lab’s mission is to make high-end fiber optic test equipment accessible to engineering students via the Internet.  The fiber optic communications lab is centered on a Windows 2000 PC running LabView software.  The LabView software controls the experiment and acts as the laboratory’s Internet interface at the same time.  Bit patterns are generated by an Agilent 86130A, 3.5Gbit/sec Bit Error Rate Tester and sent as electrical signals to a 1.5mm distributed feedback laser where they are converted to light wave signals.   The light wave signal is then sent to the other end of a 132.5km long fiber optic cable, where it is received by a pin detector and Agilent 86100B Infiniium DCA Wide-Bandwidth Oscilloscope and the Bit Error Rate Tester.  The Bit Error Rate Tester compares the received signal with the signal that it sent out to quantify the error in the channel, known as the Bit Error Rate.  Meanwhile the Infiniium DCA Wide-Bandwidth Oscilloscope generates “eye-diagrams,” graphs that show every possible logic transition and allow students to actually see the distortion in the signal as it is received.   The Fiber Optic Communications Lab allows students to study the relationships between bit rate, laser power and signal amplitude in long distance fiber optic communication.