A near-field scanning microwave microscope for measurement of the permittivity and loss of high-loss materials

Measurement of the permittivity and loss of high-loss materials using a Near-Field Scanning Microwave Microscope

“…This is connected to the piezo-controller (PI E-710), which has built-in closed-loop control circuits that can be used to maintain contact mode. In previously-reported work [23] a tuning fork was used for detecting shear force, however a method based on optical beam deflection [5] [20] has been found to be easier to set up. In the present design the cavity inner conductor (a brass rod 10Ø  50 mm) has saw cuts (0.3 mm width) to create a tuning fork structure (Fig.…”

“…3). This has a higher mechanical Qfactor (≈400) than a cantilever-based design [23] and much less dependence on aspects such as how tightly components in the system are bolted down. The wire probe was attached to the brass rod with conducting paint.…”

“…The window material used was ultrathin glass 3 . This has a high quality surface finish 4 , and is thinner and stiffer than the PEEK window used in previously reported work [23] (which had a tendency to creep during measurements). Using a Linear Variable Differential Transformer (LVDT) system and gauge blocks, the thickness was measured as 0.031 mm with a population standard deviation of 0.001 mm (for pieces from the same batch).…”

“…In this text the subscript W is used for the properties of the window. Measurements on dimethyl sulphoxide (DMSO) contained in a cell with PEEK window were previously reported [23], but this liquid is found to be unsuitable for measurement with an ultrathin glass window.…”

Traceable measurement and imaging of the complex permittivity of a multiphase mineral specimen at micron scales using a microwave microscope

“…The optical beam-deflection method enables the length of the wire probe that protrudes beyond the cavity to be short (<1 mm), which improves sensitivity and reduces error caused by stray field effects. This is a significant advantage compared to an alternative method of obtaining contact mode based on a tuning fork [25]. A measurement of the response of the output voltage of the lock-in amplifier as a function of the Z-axis setting of the piezo stage is shown in Fig.…”