Part A: Strain Gauges
Strain gauges are used to measure the strain or stress levels on the materials. Alternatively, pressure on the strain gauge causes a generated voltage and it can be used as an energy harvester. You will be given either the flapping or tapping type gauge. When you test the circle buzzer type gauge, you will lay it flat on the table and tap on it. If it is the long rectangle one, you will flap the piece to generate voltage.
1. Connect the oscilloscope probes to the strain gauge. Record the peak voltage values (positive and negative) by flipping/tapping the gauge with low and high pressure. Make sure to set the oscilloscope horizontal and vertical scales appropriately so you can read the values. DO NOT USE the measure tool of the oscilloscope. Adjust your oscilloscope so you can read the values from the screen. Fill out Table 1 and provide photos of the oscilloscope.
The minimum and maximum values with a soft and hard tap.
The photo above also works for this.
Part B: Half-Wave Rectifiers
2. Calculate the effective voltage of the input and output and compare the values with the measured ones by completing the following table. Effective (rms) values
3. Construct the following circuit and record the output voltage using both DMM and the oscilloscope.
The peak-to-peak and the root-mean-square values as measured by the oscilloscope and the digital multimeter when a 1-microfarad capacitor is used. Notice on the rightmost column the notes are actually switched, this was an error.
Part C: Energy Harvesters
1. Construct the half-wave rectifier circuit without the resistor but with the 1 μF capacitor. Instead of the function generator, use the strain gauge. Discharge the capacitor every time you start a new measurement. Flip/tap your strain gauge and observe the output voltage.
The maximum voltage we acquired with varying tap frequencies and duration of tapping.
2. Briefly explain your results.
3. If we do not use the diode in the circuit (i.e. using only strain gauge to charge the capacitor), what would you observe at the output? Why?
The gauge also creates a negative voltage after being pressed. The positive voltage spike, although large, happens for such a small amount of time, that the time that the voltage spends in the negative area can cancel it out. It would be like taking the integral of a sine wave over an entire period rather than over half of a period.