THz Science and Technology

Terahertz technologies utilize electromagnetic radiation in the frequency range between 300 GHz and 10 THz. Potential applications for terahertz technology in biology, chemistry, medicine, astronomy and security are wide ranging. THz wavelengths have several properties that could promote their use as sensing and imaging tool. There is no ionization hazard for biological tissue and Rayleigh scattering of electromagnetic radiation is many orders of magnitude less for THz wavelengths than for the neighboring infrared and optical regions of the spectrum. THz radiation can also penetrate non-metallic materials such as fabric, leather, plastic which makes it useful in security screening for concealed weapons.

TheTHz frequencies correspond to energy levels of molecular rotations and vibrations of DNA and proteins, as well as explosives, and these may provide characteristic fingerprints to differentiate biological tissues in a region of the spectrum not previously explored for medical use or detect and identify trace amount of explosives. THz wavelengths are particularly sensitive to water and exhibit absorption peaks which makes the technique very sensitive to hydration state and can indicate tissue condition. THz radiation has also been used in the characterization of semiconductor materials, and in testing and failure analysis of VLSI circuits. Recently, THz techniques allowed art historians to see murals hidden beneath coats of plaster or paint in centuries-old building, without harming the artwork.

Power Skin: Integarted Nanostructures for Energy Harvesting and Storage

“Power skin” consists of 1D nano devices for energy harvesting and storage. The unique advantage of this technology is the ability of energy harvesting in currently untapped FIR and THz spectral range as well as visible spectral range. The final goal is to create a robust large scale manufacturing technique to fabricate these devices from a variety of materials on different substrates and experimentally prove their energy conversion and storage capabilities by taking advantage of emerging ‘top down’ and ‘bottom up’ manufacturing techniques.

Well established and understood vapor-liquid-solid (VLS) growth mechanism and deep reactive ion etching (DRIE) techniques along with standard nanofabrication processes are being used to fabricate the nanorod based energy conversion and storage structures. These structures include photovoltaic conversion elements for visible range energy conversion, nanorod based rectenna (combination of a rectifier and an antenna)

elements consisting of coaxial metal-insulator-metal (MIM)diodes andmonolithically integrated nanorod antenna structures for FIR and THz range energy conversion and nanowire based energy storage elements; all as separate layers which can be stacked vertically or horizontally virtually on any substrate by a polymer assisted transfer technique. In this transfer technique, a large array of elements can be fabricated on a mother substrate and transferred onto a host substrate maintaining the structural integrity.

Integarted Biosensors

THz plasmonic devices can be used for sensing and detection of biological and chemical substances in different modalities. The THz frequencies correspond to energy levels of molecular rotations and vibrations of many molecules including DNA and proteins and these provide characteristic spectral fingerprints for such molecules. Frequency tunable THz plasmonic detectors can measure the absorption spectra of the substance of interest illuminated by a broadband radiation source without requiring complex and bulky

frequency selection optics. Measured spectral absorption characteristics are compared to the database of spectral fingerprints to identify and quantify the substance. THz plasmonic detectors with integrated microfluidic channels can substantially improve the disease detection capabilities.

Surface functionalization is commonly used method for sensing and detection of a variety of biological and chemical compounds such as DNA and prostate specific antigen (PSA) which can also be used with plasmonic THz detectors. Depending on the target molecule to be sensed, a probe molecule (an antibody) is anchored on the surface of the sensing device using chemical compounds such as thiol groups.Specific binding affinity between the probe and target molecules allow to capture only the target molecule causing changes in the surface potential as well as dielectric properties of the surrounding medium. Both changes should change the response of the proposed plasmonic THz detectors allowing the sensing, detection and quantification of the biological molecules such as thiol-modified DNA strands and antibodies.

Free Space Optical Communication

Mobile ad-hoc networks, meshed wireless networks, sensor networks, vehicular networks, disruption-tolerant networks and peer-to-peer networks are examples of highly dynamic networks, where the graph structure, node availability or link weights change rapidly. An important realization of recent research is that such dynamic networks benefit from efficient node localization (or embedding in a Euclidean coordinate plane), since it enables stateless geographic routing within the network. Efficient localization has therefore been studied both in wireless and overlay/peer-to-peer contexts, and some techniques can be used in both contexts. The most important aspect of the localization algorithm is scalability, especially for applications with thousands of geographically dispersed nodes.

Also, very-low-cost dynamic networks benefit from localization schemes that work with few or no anchor nodes; that can accommodate low density deployment of the nodes in the network; and with minimally centralized infrastructure. In this project, we leverage directionality of FSO communications in a cross-layer manner, to construct a virtual coordinate system, despite sparse interconnectivity of the network. FSO has several advantages over conventional RF communication technology. It is license-free (FCC does not regulate above 300 GHz) and offers huge potential spectrum. FSO does not suffer from lower interference issues (unlike RF which is prone to interference). Due to the high directionality and small dispersion of optics (compared to RF), it offers enormous potential for spatial reuse and security. Within the optical spectrum band, wavelength division multiplexing is also possible for additional gain in bit rate.