The Seebeck effect is a fundamental phenomenon in thermoelectricity, where a voltage (electromotive force, EMF) is generated across two dissimilar conductors or semiconductors when their junctions are maintained at different temperatures. This effect is the basis of thermocouples, widely used for temperature measurement and power generation. Discovered by Thomas Johann Seebeck in 1821.
Table of Contents
Physical Principle
When two different materials, say metal A and metal B, form a closed loop, and the two junctions are maintained at temperatures \(T_1\) and \(T_2\) (\(T_1 \neq T_2\)), a thermoelectric voltage develops.
Mathematically, the Seebeck voltage \(V\) is given by:
\[
V = \int_{T_1}^{T_2} (S_B – S_A) \, dT
\]
Where:
- \(S_A\) and \(S_B\) are the Seebeck coefficients of materials A and B (V/K)
- \(T_1\) and \(T_2\) are the temperatures of the cold and hot junctions
If the temperature difference \(\Delta T = T_2 – T_1\) is small:
\[
V \approx (S_B – S_A) \, \Delta T
\]
Seebeck Coefficient
The Seebeck coefficient \(S\) (thermopower) is defined as:
\[
S = \frac{dV}{dT}
\]
Material properties:
- Metals: small \(S \sim 10 \mu V/K\)
- Semiconductors: higher \(S \sim 100–1000 \mu V/K\)
- Sign of \(S\): positive for p-type, negative for n-type semiconductors
Applications
- Thermocouples for temperature measurement: measures wide temperature range, industrial use
- Thermoelectric generators (TEG): converts waste heat into electrical energy, used in spacecraft, remote generation, automotive
- Power generation in sensors and wearables: converts body or environmental heat into small electricity
Advantages
- No moving parts (solid-state)
- Operates in harsh environments
- Direct conversion of heat to electricity
Limitations
- Low conversion efficiency (<10%) for practical power generation
- Requires materials with high Seebeck coefficient, low thermal conductivity, and high electrical conductivity
Summary
The Seebeck effect allows direct conversion of temperature differences into voltage. Fundamental equation:
\[
V = \int (S_B – S_A) \, dT
\]
It is crucial in thermocouples and thermoelectric power generation. Understanding it is essential for GATE-level questions in Engineering Physics, Electrical Engineering, and Instrumentation.