Solid electrolyte antiperovskite compositions for batteries, capacitors, and other electrochemical devices have chemical formula Li3OA, LiMx2OA, LiNx3OA, or LiCOXzY, wherein M and N are divalent and trivalent metals respectively and wherein A is a halide or mixture of halides, and X and Y are halides. The filler element is coupled to an ultrasonic testing device for accurately and consistently measuring the gap or hollow space. The plurality of wireless systems may include a WLAN system and a cellular system andor may be part of a small cell. The controller circuit also detects tachyarrhythmia using the secondary sensing circuit and also deems the tachyarrhythmia valid if the controller circuit detects the tachyarrhythmia using both the primary and secondary sensing circuit. Light having the predetermined mode is accepted into the first end of the fiber coil, and the filter accepts light of the input light beam having a corresponding mode.