Signal-carrying circuits

The alternating current field also causes additional current flow due to moving ions created by the frictional heating. This leads to poorer resistance to dielectric breakdown under A.C. fields. The effect of the energy absorbtion from the A.C. fields is on both the material and the electrical circuits. In the case of signal carrying circuits, the losses to the insulation can cause destructive loss of signal as well as increased noise due to the effect of heat on the materials. 

Dielectric constant/loss The value of the dielectric constant is important in the wire because of the effect that it has in coupling currents in one set of wires into another set of wires. The higher the dielectric constant, the higher the value capacitor that is formed between two wires. The capacitor thus formed is a signal carrying device at the frequencies used in communications and a signal can be capacitively coupled from one circuit to another. PE is the preferred choice for insulation of communication wire because of its low dielectric constant that minimizes the intercircuit coupling effect usually referred to as cross-talk. 

The American ThermalWorks company has developed a new carbon fibre composite printed circuit board and substrate material, STABLCOR, which comprises a high temperature resin incorporating carbon fibre sandwiched between two very thin layers of copper. The material has a Tg of 170 "C. However, the company is developing a version with a Tg of 240 C. The material is designed as a plane , or non-signal carrying layer in a ply stack with other dielectric layers to make a composite PCB or device substrate. The carbon composite material has a dielectric constant of approximately 13.4 which makes it electrically conductive. This material allows the user to tailor the coefficient of thermal expansion of a PCB down to 3 ppm/°C to match that of silicon. 

Figure 4.26 Possible electronic circuit for deriving one-dimensional position information from a position-sensitive detector with a resistive strip anode. The two charges Q, and Q2 on the ends of the anode are amplified, shaped and converted to a digital signal. The mathematical operations of Q = Qt + Q2 and Q2/Qj are performed electronically, and the result is stored in a histogramming memory from which it is read into the computer. Q2/Q carries the information first that an electron has been detected and second at which position this electron has hit the detector. From [Wac85].

---