Radiofrequency dielectric

Parts from PVDF can be machined, sawed, coined, metallized, and fusion bonded more easily than most other thermoplastics. Fusion bonding usually yields a weld line that is as strong as the part. Adhesive bonding of PVDF parts can be done epoxy resins produce good bonds [31]. Because of a high dielectric constant and loss factor, PVDF can be readily melted by radiofrequency and dielectric heating. This is the basis for some fabrication and joining techniques [32]. 

Convection of heat via blood depends primarily on the local blood flow in the tissue and the vascular morphology of the tissue. Thermal diffusion is determined by thermal conductivity in the steady state, and thermal diffusivity in the unsteady state. In addition to these transport parameters, we need to know the volumes and geometry of normal tissues and tumor. In general, tumor volume changes as a function of time more rapidly than normal tissue volume. In special applications, such as hyperthermia induced by electromagnetic waves or radiofrequency currents, we need electromagnetic properties of tissues—the electrical conductivity and the relative dielectric constant. In the case of ultrasonic heating, we need to specify the acoustic properties of the tissue—velocity of sound and attenuation (or absorption) coefficient. 

A typical dielectric welding tool consists of two platens that are electrically connected to a generator that imposes an alternating electric field. The platens are used both as electrodes and apply pressure to the joint area. Various parameters will affect the quality of the dielectric weld. These include the type of fibre in the fabric, its propensity to heat in a dielectric field (called the material s dielectric loss), the thickness of the fabric, and the melt temperature of the fabric. Time, pressure, and field frequency (directly related to temperamre) will also affect the quality of the joint. The frequency of the field being generated can be from the radiofrequency range (13—100 MHz) up to microwave frequency (2—20 GHz). 

Heat generation within the material by dielectric, radiofrequency, or microwave heating. 

Application of the model to clay-solution aggregates showed that the radiofrequency dispersions of these systems at 10-50 MHz are fairly well described by the model. These dispersions were found to depend on the clay type (kaolinite, illite, montmorillonite), degree of consolidation, and soil fabric these properties are reflected in the values of the geometrical parameters and of the dielectric constant of the solid which fit the dispersion curves best. 

Moreover, the same model with identical geometrical parameters also gives a fair quantitative prediction of plug potentials (i.e. electrical potential differences between two calomel electrodes in NaCl-solutions of different concentrations separated by the plug) and of the variation of the apparent dielectric constant and the conductivity of the heterogeneous columns at radiofrequencies, as discussed in the following. 

Another low-fe dielectric system is the nanoporous SiOCH dielectric thin films prepared by radiofrequency inductively coupled plasma chemical vapor deposition of bistrimethylsi-lylmethane (BTMSM) precursor and oxygen gas at various flow rate ratios followed by annealing at 25, 200, 300, or 400 °... 

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