The research activity in the field of condensed matter physics mainly concerns the problems related to the behaviour of disordered systems: glasses, amorphous ionic conductors, glass forming liquids. Various techniques, from structural to dynamical ones have been used.

Ultrasounds : *kHz-MHz*

Ultrasonic techniques are largely used in physics and engineering for non-destructive testing (NDT). The pulse-echo method, for instance, is often applied to test solids, liquids and soft materials. The equipment is based on a Matec TB1000 and a MATEC 6000 pulser – receiver, for measurements in the kHz-MHz frequency range.

The measurement method employs a pulse or wave packed emitted from a transducer that is bonded to one end of the sample. After traveling through the sample the waves are detected by a receiver and analyzed with suitable equipment. Ultrasonic waves at MHz frequencies are usually produced by piezo-electric effect on applying a voltage to a transducer (a quartz crystal). After propagation through the sample the signal can be collected by the same transducer or by another receiver, then is displayed using an oscilloscope and analyzed. The measurement can also be run automatically at lower frequencies down to some kHz using a TB1000 board (MATEC).

The study of mechanical relaxations between 100 kHz and 300 MHz at temperatures between 450 K and 4.2 K allows to obtain useful insight on the dynamical properties of different materials (polymers, composites, ceramics, ferroelectrics, organic and inorganic liquids).  Moreover, from the measured values of the sound velocity is possible to obtain the elastic constants of the materials investigated.

Dielectric spectroscopy 

Broadband measurement system  10^-3 Hz – 2 GHz

This home-made experimental setup allows to measure the real part,  ε'(ω), and the imaginary part, ε"(ω), of the complex permittivity of a given material (solid, liquid) in a very large frequency range  10^-3 Hz -2∙10⁹ Hz  at temperatures between 450 K and 3 K using a single sample. The sample is placed in a shielded condenser cell which is part of a coaxial transmission line. The complex transmission coefficient is measured by a network analyzer and the complex dielectric permittivity is then calculated using a suitable software.

Wave guides: 8.2 GHz – 40 GHz

Measurements of the complex permittivity at microwave frequencies using waveguide transmission lines between room temperature and 10K are performed using samples inserted in a section of the waveguide. We use a transmission line made of rectangular waveguides. The line is connected to the ports of a vector network analyzer through some suitable mode-converters (adapters) and coaxial cables. The complex scattering parameters S_ij (reflection and transmission) of the transmission line are measured and then the real and the imaginary part of the complex permittivity are calculated using a suitable software.

At microwave frequencies (GHz) dielectric measurements can be also performed down to low temperatures using cylindrical cavity resonators, characterized by a big quality factor Q. Although many resonating frequencies are possible for a single cavity, the lowest resonant frequency, corresponding to the so-called fundamental mode, is normally chosen for the experiments.

Combining the advantages of the different measurement techniques available we can investigate the mechanical and dielectric properties and the dynamical processes originating at a microscopic level, in liquids, polymers, ionic glasses, biomaterials, etc.