5.8 Wireless communication for biomedical applications 139 (a) 10 5 (b) 10 0 Frequency, THz 0.1 1 1 10 10 4 cm -1 10 3 10 2 Absorption Transmission 10 -1 × 10 10 1 10 0 10 -1 1 cm 1 mm 100 m 10 m 1 m 10 -2 10 -3 1 cm 1 mm 100 m 10 m 1 m Wavelength Wavelength FIGURE 5.10 Absorption (a) and transmission (b) spectra of THz and IR radiation in water [11] radiation efficiency will be diminished by the square of the ratio of antenna length to wavelength, as it was discussed in Section 5.4: