Clamped dielectric constant

This table lists the permittivity e, frequently called the dielectric constant, of a number of inorganic solids. When the material is not isotropic, the individual components of the permittivity are given. A superscript S indicates a measurement made under constant strain ( clamped dielectric constant). If the constraint is removed, the measurement yields e, the undamped or free dielectric constant. 

Fig. 4.5-6 Gd2(Mo04)3. kJ, and tcf versus T. kJ is the free dielectric constant Kc measured at 1 kHz, and Kc is the clamped dielectric constant Kc measured at 19 MHz...

One of the early dielectric constant detectors was that designed by Grant [10] but the detector cell had a volume of 2-3 ml. Poppe and Kunysten (11) described a dielectric constant detector which included a reference cell for temperature compensation. The cell consisted of two stainless steel plates 2 cm x i cm X 1 mm separated by a gasket 50 pm thick. The two cells were identical and clamped back to back, sharing a common electrode. 

LATdlNHftUHi Oe H2O) Family LiNH 0,H 06 H2O (LAT) (LB Number 68A-I). Ferroelectric activity appears along the b axis below 106 K (Fig. 4.5-92). The dielectric constant of the clamped... 

Phenomena associated with "dielectric relaxation" are often observed in polymers. In polyethylene, for example, if the fiber is pulled and then clamped at constant strain, the birefringence will increase and become asymptotic to a constant value which depends upon the strain at which it was clamped and the temperature. The evolution of birefringence looks like the graph in Fig. 4. The birefringence in tests of this kind is always measured in places where the specimen is deforming homogeneously. 

The boundary conditions for these piezoelectric equations are important (a) The condition mechanically free stipulates specifically that boundaries of a piezoelectric sample (e.g., a piezoelectric vibrator) can move, i.e., the vibrator vibrates with a variable strain and zero (or constant) stress. Under this condition, the coefficients in these equations carry a superscript T e.g., is the dielectric constant at constant stress, (b) The condition mechanically clamped stipulates specifically that the boundaries of a vibrator cannot move. This condition means that, when the frequency of the applied voltage is much higher than the resonance frequency of the vibrator, the strain is constant (or zero), while the stress varies. In this case, the coefficients in these equations carry a superscript S e.g., is the dielectric constant at constant strain, (c) The condition of electrical short circuit implies specifically that the electric field = 0 (or a constant), while the electric displacement D 0 inside the vibrator. This is the case when the two electrodes on the surface of the crystal sample are electrically connected (or the electric potential on the entire surface of the sample is constant). Under this condition, the coefficients in these equations carry a superscript E e.g., sfj (or c ) is the elastic compliance (or stiffness) coefficient at constant electric field, (d) The condition of electrical open circuit corresponds to the case when aU the free charges are kept on the electrodes of the sample (electrically insulated) and the internal electric field / 0, while = 0 in the sample, hi this case, the coefficients in these equations carry a superscript D e.g., sjj (or c ) is the elastic compliance (or stiffness) coefficient at constant polarization. 

---