What each component does
Open a component to see what it does. In short: the power supply provides the energy, the function generator sets the timing, and the MOSFET switches the current on and off.
DC power supply Provides the heating energy
One supply powers the sample circuit. Set it to about 1.5–2 V, which gives roughly 0.7–1 A through the sample while the switch is on. Never exceed 2 A; typical tests run near 1 A. If your supply has a current limit, set it before turning the output on.
Function generator (Analog Discovery 3) Sets when heating happens
Controlled from a laptop running WaveForms, it sends a 0–5 V square wave to the MOSFET gate. Frequency sets how many heating cycles happen each second, and duty cycle sets the fraction of each cycle spent heating. A 180° phase offset keeps the output at 0 V when it’s disabled. The generator only sends the command; the heating current comes from the power supply.
MOSFET (IRLZ44NPBF) The electronic switch
The gate (G) receives the command, the drain (D) connects to the sample side of the circuit, and the source (S) connects to the common return. About 5 V between gate and source turns it on so current flows; 0 V turns it off. Switching off stops the heating, and the sample then cools on its own.
Liquid-metal coating and PDES strip Turn heating into motion
Current through the liquid-metal coating produces heat (P = I²R). The heat warms the PDES, which contracts and lifts the hanging mass. When the current stops, the sample cools and stretches back out. How evenly the coating covers the sample, and how well it contacts the clips, both affect the resistance and how repeatable the results are.
Copper clips, thin wire and hanging masses Hold, connect and load the sample
The copper clips hold the sample and make the electrical contact. The thin wire attaches to one of the hanging weights, completing the circuit while letting the sample move freely. The wire has its own resistance (about 1 Ω), so it also produces some heat outside the sample. When you record the hanging mass, include everything that hangs from the sample.
Multimeter Checks the connections
Used to measure the thin wire’s resistance on its own (about 1 Ω), then the total series resistance once the sample is mounted (target 1.9–2.1 Ω). Subtracting the two gives the liquid-metal connection resistance. Switch it to voltage mode or disconnect it before running the test.
LED and 6 kΩ resistor Show the command on video
The LED and its resistor form a separate branch from the generator output to the common return; the resistor limits the LED’s current. The LED lights whenever the command is high, which is how the analysis finds the frame where actuation starts. It can light even if the sample is disconnected, so it confirms the command, not the heating current.
Oscilloscope (optional) Checks the switching
The protocol doesn’t require one, but it helps with troubleshooting. Channel 1 on the gate shows the 0–5 V command. Channel 2 on the drain drops close to 0 V while the MOSFET is on and rises toward the supply voltage while it’s off. Neither trace measures strain or temperature.
Camera, ruler and MATLAB analysis Measure the movement
The camera records the clips, ruler and LED at 60 fps. The ruler, mounted in the same plane as the sample, converts pixels to millimeters. The MATLAB code tracks the distance between the clips frame by frame and calculates the contraction strain from it.