Looking for some data regarding thermocouple specs of platinum and gold, platinum and silver, and silver and gold, as end to end with joint. The ratio of resistivity seems to be about 1:3 . Thermopile would be all three in series. Tests were made long ago but with little data, in relation to transmitter frequencies applied over joints that had caused multiplication of frequencies harmonics and inharmonics as causing nodes interference. These metals were said to be the best for proper ratio.