Physics and design methods of FGTM
L.I. Anatychuk, L.N. Vikhor
FGTM (functionally graded thermoelectric material) is considered as one of the promising methods improving the efficiency of thermoelectric energy conversion. Physical meaning of FGTM lies in using for the operation of thermoelectric generators and coolers not only contact, but also bulk effects. Maximum opportunities of using these effects are achieved when creating materials with programmable inhomogeneity. Magnetic or force fields affecting material can be also optimally inhomogeneous. The search for optimal inhomogeneity functions of both material itself and the fields affecting it is the main physical problem in the design and creation of FGTM technologies.
The method for computer design of FGTM for single-and multi-stage generators and coolers based on the use of mathematical optimal control theory is presented. The temperature dependencies of thermoelectric material properties and optimal electric and thermal matching of stages are taken into account. The area of permissible changes in kinetic material properties as a function of current carrier concentration is selected with regard for real band structure of material, energy spectra of phonons and current carriers, their scattering mechanisms. The advantage of suggested method of seeking for FGTM over known ones is demonstrated.
The results of development of the method of seeking for two optimal inhomogeneity functions simultaneously: of material and magnetic field affecting it for low-temperature thermoelectric coolers are given. The efficiency of using FGTM in thermoelectric energy converters is confirmed.