One power source.
One controlled switch.
A MOSFET-controlled circuit sends periodic current through the liquid-metal coating, so the PDES sample heats and cools in repeated cycles. The DC supply provides the energy, and the function generator decides when the MOSFET lets it through.
Live circuit
Click any componentFunction generator
Circuit values
Readouts
Current = V1 ÷ (R1 + R2 + MOSFET on-resistance ≈ 0.025 Ω). Values are calculated, not measured.
Simulated oscilloscope
Source schematic. Figure 1, PDES Joule Heating Circuit: MOSFET-switched resistive heating with optical synchronization. Source: Anthony Honeine, HAND_Anthony.pptx, slide 5; test-point labels added for measurement reference.
Open the schematic PDF ↗Trace each path through the circuit.
The circuit has three paths that meet at one shared reference. Pick a path to highlight it on the live schematic above.
What every part does.
Each card summarizes the protocol’s description of that component. Use “Show on schematic” to jump to it in the live circuit.
Fast switching, slow response.
The electrical switching happens almost instantly, but heating, cooling and the resulting movement take much longer. Repeating the two intervals below produces cyclic actuation.
High: heating
Current flows from the supply’s positive terminal through the coated sample, through the thin wire and through the conducting MOSFET to the negative terminal. Resistive heating raises the sample’s temperature and drives the contraction.
Low: cooling
The MOSFET interrupts the current and electrical heating stops. The sample cools passively and stretches back out under the hanging load, more slowly than the switch turned off.
At 0.5 Hz and 50% duty, each 2 s cycle has 1 s of heating followed by 1 s of cooling. The playhead follows the live circuit above.
Rules for working on the circuit.
Make every wiring change and every resistance measurement with the DC supply output and the function generator both disabled. Disconnect power before switching the multimeter to resistance mode, and never leave it in resistance mode while the circuit is energized.
Run the actuator at a target current of 0.7–1.0 A and never exceed 2 A. Set the supply’s current limit before enabling its output.
The generator return, the MOSFET source and the supply negative terminal must all connect to the common return. Verify every connection before mounting the sample.
Bring-up checklist
Thin-wire resistance · power disconnected
- Measure the resistance between the thin wire’s end connections.
- For a new wire, scrape the insulating coating off the connection points first.Without this the wire won’t make electrical contact.
- Move the wire gently while watching the reading. It should vary by no more than 0.1 Ω.
- Record the wire resistance (about 1 Ω in the original setup).
Function generator
- Set a square wave alternating between 0 and 5 V.
- Choose the fixed frequency or frequency sweep, and record the frequency, duty cycle and test duration.
- Apply a 180° phase offset (original WaveForms setup) and check that the output stays at 0 V while disabled.
- With no sample connected, enable the generator briefly and confirm the LED follows the signal. Then disable it.
DC supply
- Set the current limit according to the operating requirements.
- Set an initial voltage between 1.5 and 2.0 V.You’ll fine-tune it during operation to reach 0.7–1.0 A.
- With the sample disconnected and the gate signal disabled, enable the output briefly and check the current reads about zero.
- Disable the output before mounting the sample.
After mounting · power disconnected
- Measure the combined resistance of the thin wire and the coated-sample connection.
- Adjust the coating and contacts until the reading is stable and within 1.9–2.1 Ω.
- Record the total, then calculate Rconnection = Rseries − Rwire.This includes the liquid-metal coating and its contact resistance.
- Disconnect the multimeter, or switch it to voltage mode, before enabling the supply.
Start of the run
- Enable the DC supply with the function generator still disabled, and confirm the sample current stays near zero.
- Start recording, wait about 5 s, then enable the generator.
- Confirm cycling from the LED and the sample’s motion, and check the current stays in range.
- Afterwards, let the sample cool and, with power disconnected, measure the connection resistance again.
What the supply display can and can’t tell you.
The power supply’s display is an operating check. Its update rate and internal averaging mean it can’t follow the current waveform during fast switching, so the value it shows can be distorted.
The original protocol runs a separate 0.1 Hz cycle before higher-frequency tests to get the on-state current. Record it as a reference measurement, note the frequency it was taken at, and don’t report it as the current waveform of the faster experiment.
For a time-resolved current measurement, use a suitable current probe, or measure the voltage across a calibrated series resistance with appropriate differential instrumentation. A sustained drop in current during a run means the total circuit resistance has changed, and the conductive path should be inspected.
Optional: oscilloscope check
Oscilloscope measurements supplement the original procedure. If you use one, record the probe configuration and acquisition settings with the experiment.
| Channel | Probe tip | Ground clip | What you see |
|---|---|---|---|
| CH1 | TP1 · gate | Common return | The applied 0–5 V control waveform |
| CH2 | TP2 · drain | Common return | Falls during conduction; rises toward the supply voltage when the MOSFET turns off |
Never put a grounded probe clip on the drain or the supply positive; that can short part of the circuit through the oscilloscope. Check your instrument’s grounding configuration first.
Why a rising coating resistance can increase heating.
Changes in coating or contact resistance change both the current and how the heating is shared around the circuit. At a fixed supply voltage, the power in the coating is:
Coating power vs. coating resistance
V = 2.00 VRremaining is everything else in series: mainly the thin wire, plus the MOSFET and leads. Coating power rises with coating resistance while Rcoating is below Rremaining, peaks when they’re equal, and falls as Rcoating keeps rising.
The orange dot is the R1 value set in the live circuit. Record resistance changes and use measured electrical values when interpreting actuator performance.