>>11821918A number of searches for Dyson Spheres have been made in the past. A few candidates have been identified but discounted for various reasons.
For below the fold items click links for Slysh, Others, Fermilab
Sagan and Walker carried out an early analysis of the possibility of detecting a Dyson Sphere. They showed that a search out to 1000 pc was feasible even with sixties technology but that the possible confusion with natural signatures could require searches for other artifacts of intelligence such as radio signals associated with a candidate source.
Jugaku and colleagues have carried out a series of searches for partial Dyson Spheres. Typically they used the 2.2 ?m K band as an indicator of the photospheric radiation of a star hosting a partial Dyson Sphere and then looked for an infrared excess in the IRAS infrared satellite 12 ?m band. A 1 magnitude difference would arise if the Dyson Sphere covered 1% of the host star. The measured differences were characteristically less than 0.3 magnitude which is consistent with measurement errors. They selected a set of 1774 stars from the Woolley catalog nearer than 25 pc and found 458 with matches in the 12 ?m IRAS band. They looked at 384 of these stars for infrared excesses. With the exception of a few cases discussed in their 1990 article they found no sources with excesses suggestive of a partial Dyson Sphere covering as much as 1% of the host star.
https://home.fnal.gov/~carrigan/infrared_astronomy/Other_searches.htm 
