Real area of contact & analog electronics

Contact Mechanics VIA Analog Electronics

Aim of this measurement

In this class, we will attempt to reproduce the `real area of contact' measurement of Bowden and Tabor using contact resistivity. The principle of the measurement is to use two conductive bodies of a known geometry and force them into contact while simultaneously monitoring the applied load and measuring (somehow) the junction resistance. As you might know, resistivity is a bulk property, and scales inversely with the size of the resistive junction. The junction resistance is inversely related to the area of contact under certain limits, and thus can be used to measure the real (as opposed to projected) area of contact.

In the spirit of this course, this module will rely extensively on analog electronic devices that we make in the lab. This will of course require us all to be on the same page with respect to analog electronics, which will be the focus of the first two meetings of this module. 

Analog Electronics

We will first learn a some of the basics about how analog electronics work. For us to work with this type of equipment in the lab, we will make extensive use of the DLL equipment on the bench. This includes a function generator, an oscilloscope, multimeters and a power supply, as well as the breadboard (and ultimately some of the functionality) of the National Instruments Elvis II + education board, which can replicate the functionality of most of the benchtop instrumentation to some extent.

In the spirit of the class, the lab exercises will be quite open ended - you'll find that the exercise doesn't necessarily have a unique solution, and leaves it up to you to come up with an approach that sufficiently addresses the exercise.

Lab exercises #1:

Videos, course notes & readings

day 1: Please refer to our Switch channel, located here. I request that you please review the introductory remarks video, the Wien bridge oscillator demo, the Hertz theory video, and finally the introduction to resistors and simple circuit laws video, from 8 a.m. until 10 a.m. tomorrow morning.

pdf notes 2020: Hertz theory and introduction to analog electronicsNotes 2019, Notes 2018, Reading (linked) The reading is from The Art of Electronics (AoE), chapter 1. These readings remain relevant for the entire module.

Manuals, datasheets and references

Oscilloscope manual

Function generator manual

Multimeter manual

Power supply manual

NI Elvis II + manual

Bowden and Tabor reference

Transistor datasheets: BP547 and 2N2905A

Instrumentation amplifiers

Current sources

LF 411 datasheet

LF 412 datasheet

INA 122 datasheet

Keithley low-level measurements handbook (see ch. 3 for low-voltage measurements)

AL6B load cell datasheet

LTSpice tutorial, spice files: bandpass filter, emitter amplifier