Sec. 5-1] RADIATION TRANSDUCERS 279 



469 (1956); a theoretical study primarily concerning the frequency character- 

 istic of bolometers exposed to radiation of a periodically fluctuating intensity 

 is due to J. N. Shive, J. Appl. Physics, 18, 389 (1947). 



Dielectric materials, instead of metals, can be used for the con- 

 struction of bolometers. The first dielectric bolometer, using cello- 

 phane or pliofilm (in an a-c bridge), is described by Moon and 

 Steinhard. 1 A theoretical study by Ewles 2 reveals that the sensi- 

 tivities of radiation thermoelements and metallic radiation bolom- 

 eters are almost alike, while that of dielectric bolometers can be 

 considerably higher (see, however, below). 



The resistance-temperature coefficient of semiconductors can be 

 much higher than that of metals (by a factor of about 10), and a 

 number of authors have used semiconductors for the construction 

 of bolometers. Bauer 3 has investigated bolometers made from 

 cuprous oxide; Brattain, 4 Dodd, 5 and Wormser 6 have employed 

 thermistors. Gilliam 7 has built a bolometer from semiconducting 

 antimony which has a high resistance (18 MQ). Ward 8 described a 

 bolometerforhighradiationintensities, 1.4cal/(cm 2 )(min), containing 

 one thermistor exposed to radiation and another measuring environ- 

 mental temperature. The indication of this system is almost 

 independent of the environmental temperature in the range between 

 -19 and +0.5 o C. 



The resistivity of electronic conductors becomes zero at very low 

 temperatures (superconduction). In the transition zone from normal 

 conduction to superconduction the resistance-temperature coeffi- 

 cient attains very high values (of the order of several thousand per 

 cent per degree), so that bolometers operated in the transition range 

 are very sensitive. The operation at low temperature also offers 

 other advantages, such as the reduction of noise and of thermal 

 reradiation. Superconducting bolometers were first built with tan- 

 talum wires operated between 3.22 and 3.23°K. 9 Later construc- 

 tions used columbium nitride operated at 15°K. 10 Superconducting 



1 P. Moon and L. R. Steinhard, J. Opt. Soc. Am., 28, 148 (1938). 



2 J. Ewles, J. Set. Instr., 24, 57 (1947). 



3 G. Bauer, Phys. Z., 44, 53 (1943). 



4 W. H. Brattain, J. Opt. Soc. Am., 36, 354 (1946). 



5 R. E. Dodd, J. Sci. Instr., 28, 12 (1951). 



6 E. M. Wormser, ./. Opt. Soc. Am., 43, 15 (1953). 



7 E. J. Gilham, loc. cit. 



8 W. H. Ward, J. Sci. Instr., 34, 317 (1957). 



9 D. H. Andrews et al., Rev. Sci. Instr., 13, 281 (1942). 



10 D. H. Andrews, R. M. Milton, and W. DeSorbo, J. Opt. Soc. Am., 36, 353 

 (1946), and N. Fuson, J. Opt. Soc. Am., 38, 845 (1948). 



