materials (given in Table 1) and the time honored method of trial and error.As shown in Figure 2, we have measured the reflection loss of all four samples in broad THz frequency region. To obtain the visual clarity and better interpretation, measured data points have been smoothened with five points. In general, all the samples show 10-20 dB reflection loss in lower and higher side of measurement spectrum, whereas very high reflection loss, i.e., 20-30 dB (more than 99% absorption of normal incident power) was observed between 1 and 2 THz, which is highly demanding feature in the development of any kind of absorbers for electromagnetic radiations.Very recently few groups [9, 10] have attempted the similar problem using metamaterials based approach, where special feature of tailoring of em response is possible due to resonant structures. These groups have reported very sharp absorption dips in narrow band, which is suitable for narrow band applications like bolometric detectors [11]. In our experiment, we have obtained 20-30 dB reflection loss in ultra broad frequency region, which is desired for stealthy applications in defence sector because 30 dB down in back scatter value is far beyond the detectable limits of existing uncooled or cooled THz detectors.
CONCLUSIONSWe have developed multilayer structures based on effective medium concept and shown that optimized combination of materials can reach absorptivities approaching unity in 1-2 THz fre-quency region. Because of broadband absorption of THz radiations, this approach would reduce the need of tailoring of em response of materials, which is normally done by metamaterials based techniques. 2. V.B. Bregar, A. Znidarsic, D. Lisjak, and M. Drofenik, Development and characterization of an electromagnetic absorberDual band terahertz metamaterial absorber: Design, fabrication and characterization, Appl Phys Lett 95 (2009), 241111:1-3. 11. D.H. Kim, D. Kim II, and C.M. Choi, A study on the design and fabrication of an electromagnetic wave absorber for the 94-GHz band,ABSTRACT: This letter assesses the performance transmission of 802.11g signals over a colorless bidirectional wavelength division multiplexed passive optical network employing a reflective semiconductor optical amplifier. Error-free operation is demonstrated, for a back-to-back configuration with at least 8 dB of optical margin.ABSTRACT: A novel low-profile broadband UHF RFID tag antenna with two parasitic patches is proposed. The tag antenna's bandwidth can be greatly enhanced by adding parasitic patches which are gap coupled to the driven patch for the excitation of additional resonant modes. The half-power bandwidth of the proposed antenna covers all the UHF RFID frequency bands, and the power reflection coefficient is lower than À7dB in the UHF RFID frequency bands (840-960 MHz). The proposed antenna can be easily fabricated at low cost by etching at a thin inexpensive FR4 substrate.