Microwave apparatus to study the mechanical behavior of solid samples subjected to external stresses

We present a differential microwave apparatus to investigate the mechanical behavior of samples subjected to any stress which produces a change in the sample length. The device measurements small displacements through the measurement of the resonance frequency variation of a microwave resonator and corresponds to about 7 X 10-8 in the height of the resonator, having such dimension as to resonant in the TE011 mode in the X band. This means that changes in the sample length of some nanometers can be measured, whatever is the value of the sample length. The resolution of the device of some nanometers 'single shot' looks high enough, however the good stability of the apparatus along long periods allows that periodic stresses and averaging may be applied, in this way the resolution becomes some picometers. The extended measurement range is another interesting feature of the apparatus, indeed, if the DC coupling is used, with the resolution limit less than one ten of nanometers, a displacement up to 100 micrometers can be recorded. The frequency response ranges from DC to some Hz.