Calculated Results
Results appear here after calculation and stay above the input form.
Responsivity vs Frequency Graph
Calculator Inputs
This tool uses a linear small-signal bolometer model and calculates thermal response, readout sensitivity, NEP, detectivity, SNR, and minimum detectable power.
Example Data Table
| Parameter | Example Value | Notes |
|---|---|---|
| Incident power | 2.0 × 10-6 W | Low-level optical test signal. |
| Absorptivity | 0.90 | High absorption coating assumed. |
| Modulation frequency | 30 Hz | Typical chopped measurement case. |
| Heat capacity | 3.0 × 10-8 J/K | Small thermal mass sensor. |
| Thermal conductance | 8.0 × 10-7 W/K | Moderate thermal isolation. |
| Resistance | 12,000 Ω | Nominal bolometer resistance. |
| Temperature coefficient α | 0.015 1/K | Linearized around operating point. |
| Current-bias responsivity | ≈ 9.93 × 102 V/W | Using the sample values above. |
| Voltage-bias responsivity | ≈ 1.88 × 103 V/W | Readout depends on divider conditions. |
| Thermal time constant | ≈ 3.75 × 10-2 s | Sets speed and roll-off. |
Formula Used
The calculator applies a compact thermal-detector model and a linear resistance-temperature approximation around the operating point.
How to Use This Calculator
- Enter the incident power and absorptivity to define absorbed optical heating.
- Provide thermal conductance, heat capacity, and modulation frequency.
- Enter bolometer resistance and its temperature coefficient.
- Fill in current-bias and voltage-divider readout values.
- Enter RMS output noise, detector area, and measurement bandwidth.
- Click Calculate Sensitivity to display results above the form.
- Review the graph to see how responsivity rolls off with frequency.
- Use the CSV or PDF export buttons to save your report.
Frequently Asked Questions
1) What does this calculator call bolometer sensitivity?
It treats sensitivity as electrical responsivity, meaning output voltage per watt of incident power. It also reports NEP, detectivity, SNR, and minimum detectable power for a fuller performance picture.
2) Why are there current-bias and voltage-bias results?
Bolometers are often read with different circuits. A current-biased readout scales with I × ΔR, while a divider readout depends on supply voltage, detector resistance, and load resistance.
3) What does absorptivity change in the result?
Absorptivity changes how much of the incident optical power becomes heat. A lower value reduces temperature rise, resistance shift, signal voltage, and responsivity.
4) Why does sensitivity fall at higher frequency?
The thermal system behaves like a low-pass response. As modulation frequency increases, the detector has less time to heat, so temperature change and electrical output decrease.
5) What is NEP used for?
NEP estimates the input power needed to produce a signal equal to the RMS noise. Lower NEP means the detector can resolve weaker signals.
6) Why does the calculator ask for detector area?
Detector area is needed for specific detectivity, D*. That metric normalizes performance against both active area and bandwidth so different detectors can be compared more fairly.
7) Can I use a negative temperature coefficient?
Yes. Some bolometer materials show decreasing resistance with temperature. Enter the signed coefficient that matches your device, and the tool will carry that behavior into the readout estimate.
8) Is this calculator a full electrothermal simulator?
No. It is a fast design and estimation tool. It does not model full nonlinear electrothermal feedback, packaging parasitics, or detailed material physics.