THz Filters

Metamaterials have proven their ability to control the electromagnetic field propagation within the microwave region but there has been a growing interest in the last years to push their range of application toward THz and infrared regions up to the visible regime. Especially in the frequency range between 0.1 and 10 THz metamaterials seem to offer an invaluable means for filling the so called terahertz gap where nature does not provide materials with strong electric or magnetic response. In fact, the use of metamaterials has allowed achieving electric and magnetic response as well as negative refractive index providing the building blocks of a completely new class of devices with a great impact on a wide range of applications. Indeed, an ongoing effort is made to obtain the perfect lens, modulators as well as THz devices for imaging, absorbers, biochemical sensing and security screening.
The intrinsically resonance nature of the aforementioned metamaterials determines a narrow spectral range of activity for the related devices and poses a serious challenge to applications that require structures with a broadband behavior. A solution to overcome this drawback is represented by the multiresonance approach which solves the lack of a broadband response by resorting to two or more different single resonances. In [1] a broad transmission THz filter has been designed by exploiting a stochastic optimization procedure, namely the Genetic Algorithm (GA), in conjunction with a Periodic Method of Moments (PMM).