nic properties of semiconductors are exploited in the presence of optical fields. Based on the principle of photoconductivity in the semiconductor materials, these sources are created. In the source, over the semiconductor material, a voltage-based antenna is printed. The ultrashort femtosecond laser pulse is used for excitation and photocarrier generation in the material. Based on optical excitation, the terahertz sources are divided into continuous-wave THz sources and pulsed THz sources. 12.5.1 SPINTRONICS MATERIALS There are three generations of spintronic devices as follows: based on spin transport and the spin dynamics employing electric field, based of spin-orbit effects and electro- magnetic coupling, and using three-dimensional structures and quantum engineering. The ferromagnetic metal layer sandwiched between two non-magnetic metal layers is used as a THz source where the spin current in the magnetic layer leads to THz gener- ation. Later, the generated THz waves is diffused through the non-magnetic part of the device using a super-diffusive process. The advantages of spintronic emitters are that they are easy-to-use, robust, efficient, and don't require any electrical connections. These types of spintronic materials can be fabricated through lithographic techniques. 12.5.2 PHOTO MIXERS Terahertz generation from photo mixers can be obtained using two CW lasers having frequencies very close to each other. The schematic of the photo mixer to generate the terahertz wave is represented in Figure 12.1. Two single mode lasers, with Terahertz Antenna in Future Healthcare Informatics Laser beam with W1 and B1 Radiated THz wave with o=W1-W2 Laser beam with W2 and B2 FIGURE 12.1 Schematic diagram of terahertz photo mixer. frequencies of w , and W2 and phases of B and B2 respectively, are merged using a beam combiner and propagate collinearly. The resulting beam is targeted on the DC- biased THz photo mixer antenna to generate THz radiation of W0 frequency (where, (see Figure 12.2). The optical frequencies of the