Ionic polarization causes the ferroelectric effect as well as dipolar polarization. These forces originate from the attraction between permanent dipoles (dipolar molecules) and are temperature dependent. This is called dipole rotation, or dipolar polarisation. Often molecules contain dipolar groups, but have no overall dipole moment. Coupling is mediated by two processes, dipolar (through space) and isotropic (through bond). Dihydrolevoglucosenone is considered a candidate as a "green" aprotic dipolar solvent. Negative mass density is achieved with dipolar resonances of the gold sphere series. The dipolar term contributes to the plasmon oscillations, which leads to the enhancement. The dipolar coupling between two nuclei is inversely proportional to the cube of their distance. He then proposed a Frohlich condensate, a hypothetical coherent oscillation of dipolar molecules. Peak splittings due to J- or dipolar couplings between nuclei are also useful. These methods include monopolar, bipolar, dipolar, 360-degree, horn, waveguide, and line source. The wires and split rings create intrinsic electric dipolar and magnetic dipolar response. One technique for removing dipolar couplings, at least relatively weak ones, is magic angle spinning. This usually undesirable effect is commonly referred to as dipolar truncation.