Abstract
Measurements of the dimensionless figure of merit of different thermoelectric devices are presented and discussed, as obtained with a prototype zT meter which is based on the porcupine method. The instrument’s architecture and operation are discussed to support claims made on the accuracy of results. Different types of thermoelectric devices were tested, focusing on the size of the porcupine’s snout for each. The latter is probably the major source of uncertainty in Harman methods, but is well measurable with the porcupine method, which therefore allows definition of the correction needed to obtain accurate evaluation of zT. Accuracies much better than 1% in the determination of the dimensionless figure of merit and series resistance are possible in this way. A survey of various devices is reported, and results are shown to indicate that corrections up to the 10% level and more are needed, depending on the configuration.
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Abbreviations
- f :
-
Frequency (Hz)
- I 0 :
-
Electric current of the generator (A)
- j:
-
Imaginary unit
- K TE/2:
-
Total DC thermal conductance of the thermoelectric elements (W K−1)
- R :
-
Series electric resistance of the module in DC (Ω)
- R B :
-
Electrical resistance defined in Fig. 1 (Ω)
- R C :
-
Electrical resistance of the center of the porcupine body’s circle (Ω)
- R I :
-
Instrument’s reference resistance, R I = V 0/I 0 (Ω)
- R x :
-
Variable resistance in the optimization process of Eq. 4 (Ω)
- R ε :
-
Equivalent resistance of the Seebeck effect (Ω)
- T :
-
Temperature (K)
- V 0 :
-
Electric voltage of the generator (V)
- V Ω :
-
Ohmic voltage drop (V)
- y T :
-
Total complex thermal admittance (W K−1)
- z el :
-
Complex electrical impedance (Ω)
- zT :
-
True dimensionless figure of merit of the module
- β, γ :
-
Phase angles defined in Fig. 1
- δ :
-
Relative circularity error of the porcupine body discussed in Ref. 4
- Δ:
-
Quantity to be minimized in the optimization process of Eq. 4
- M:
-
Value at the operating point where γ is maximum
- *:
-
Quantity referred to the porcupine body’s approximation circle (lumped approach)
References
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De Marchi, A., Giaretto, V., Caron, S. et al. A Novel zT Meter Based on the Porcupine Method and a Survey on the Size of the Snout Correction Needed for Various Thermoelectric Devices. J. Electron. Mater. 42, 2067–2072 (2013). https://doi.org/10.1007/s11664-013-2530-2
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DOI: https://doi.org/10.1007/s11664-013-2530-2