---
tags:
  - science/physics
  - electromagnetic-radiation
  - infrared
  - sensors
created: 2026-05-16
breadcrumb: "Physics > Electromagnetic radiation > Infrared"
---

# Infrared

> **Mechanism:** Thermal & near-IR photon detection

## Items

- **Thermopile** — Many thermocouples in series; IR heats a hot junction, voltage measures the temperature difference. The detector inside non-contact thermometers.
- **Pyroelectric (PIR)** — Polarisation in a crystal shifts with temperature change; AC-coupled output. The motion sensor in burglar alarms.
- **Bolometer** — Temperature-dependent resistor; absorbs IR, resistance changes. The original thermal-imaging primitive.
- **InGaAs photodiode** — Short-wave-IR (0.9–1.7 µm) semiconductor; standard for fibre-optic links and SWIR cameras.
- **Microbolometer array** — Uncooled thermal-imaging chip; each pixel is a tiny bolometer. The detector behind every modern thermal camera.

## Related

- [[visible-light]]
- [[ultraviolet]]