A short note on stability of linear time delay systems

Our research on stability criteria for linear systems with time delay in a frequency domain has brought in a new stability criterion that belongs to the group of graph-analytical stability criteria. Via the theory of functions with a complex variable, this criterion is based upon Cauchy's theorem of argument and condition that for frequency omega varying from -infinity to +infinity the argument of function f*(j omega,e(j omega iota)) has positive change. In solution, as a graphic interpretation in the f* - plane, a spiral curve is obtained, which possesses some characteristics crucial for the stability of a system with time delay. Through given examples, simplicity and facility of criteria application to different cases of systems are shown.