Benjamin B. Yang

A High-Q Terahertz Resonator for the Measurement of Electronic Properties of Conductors and Low-Loss Dielectrics

The successful engineering of sources and components in the terahertz (THz) regime benefits from good characterization of materials properties. Previous research reports have shown that calculations of material parameters that are valid at radio frequencies are no longer accurate at THz frequencies. A high-quality-factor quasi-optical hemispherical resonator operating between 300 GHz-1 THz has been designed and implemented for the measurement of electronic properties of conductors as well as low-loss dielectrics. This apparatus is the first quasi-optical resonator to achieve Q≈ 4×105 at frequencies greater than 400 GHz in the THz regime. It is also the first open resonator designed to measure effective conductivity at these frequencies. This paper discusses the techniques that enabled high-Q operation in the THz regime. It also includes measurements of silicon with different doping densities and conductors of various surface roughness values with comparison to theoretical predictions.

Study of the effect of surface roughness and skin depth on the conductivity of metals at 650 GHz

A high-quality-factor quasi-optical resonator operating at 650 GHz is used to measure the conductivity of mechanically roughened metal surfaces. The results explore the effective conductivity of metals in the terahertz regime when the surface roughness is on the order of the skin depth.

Generation of Terahertz Regime Radiation by Microfabricated Folded Waveguide Traveling Wave Tubes

The fabrication of a terahertz regime folded waveguide traveling wave tube (FWTWT) using MEMS microfabrication techniques is currently underway. Recent developments in the design, fabrication method, and measured data are presented

Atmospheric Attenuation of 400 GHz Radiation Due to Water Vapor

We present an experimental study of electromagnetic losses resulting from atmospheric attenuation due to water vapor on 400 GHz radiation. A hermetically sealed, high quality factor quasi-optical resonator system permits the precise control of the atmospheric water vapor content, and allows for measurement of electromagnetic losses. The empirically determined losses are compared with predictions by various different electromagnetic attenuation models. Close agreement is demonstrated with four of the models, while another differs by more than an order of magnitude at higher values of water content.

Investigation of the attenuating effects of atmospheric water content at 400 GHz

We present an experimental study of electromagnetic losses resulting from atmospheric absorption and scattering on terahertz (THz) radiation. A sealed, high-Q quasi-optical resonator system permits the control of the atmospheric water content and allows for measurement of electromagnetic losses.

Examination of electromagnetic attenuation induced by atmospheric water content on terahertz radiation

Many proposed applications of terahertz (THz) regime radiation involve atmospheric propagation which is subject to significant attenuation due to absorption. Accurate prediction of signal attenuation enables system designs tailored to the anticipated operating environment. In this presentation we report detailed measurements of electromagnetic wave attenuation at 400 GHz in atmospheric pressure air for relative humidity (RH) continuously varying between 0.4 – 64%.

Electromagnetic attenuation due to water vapor measured at 400 GHz

We present experimentally measured electromagnetic attenuation losses due to water vapor at 400 GHz. The measurements are made using a hermetically sealed high-Q quasi-optical resonator system, which allows for control of water vapor levels. We compare our measurements to attenuation predictions from two versions of the Millimeter-wave Propagation Model. We find that one model has predictions in close agreement with the data while the other model differs significantly.

Terahertz conductivity of rough metallic surfaces

Summary form only given. The terahertz (THz) regime, commonly designated as the frequency region between 300 GHz and 3 THz, is relatively underutilized compared to other areas of the electromagnetic spectrum. However, THz radiation has many potential applications in molecular spectroscopy, communications, medical imaging, and security imaging1.

Measurement of surface roughness effects on conductivity in the terahertz regime with a high-Q quasioptical resonator

A high-Q quasi-optical resonator is used to experimentally measure metal samples with controlled nano-scale textures at 400 GHz and 650 GHz. The results explore the effect of surface roughness on effective conductivity in the terahertz regime.

Measurement of surface roughness effects on conductivity in the terahertz regime with a high-Q quasi optical resonator

Summary form only given. Successful design and engineering of sources and components in the terahertz (THz) regime benefits from good characterization of material properties. Previous research reports have shown that calculations of material parameters that are valid at radio frequencies are no longer accurate at THz frequencies. A high quality factor (Q ~ 4.2>; ; 4χ105 at near-THz frequencies greater than 400 GHz. It is also the first open resonator designed to determine effective conductivity at these frequencies. The measurements of metallic samples with controlled, nano-scale textures will provide insight into how surface roughness alters effective conductivity when the topographical features are on the order of the skin depth. Preliminary results with mechanically polished samples indicate a roughly linear relationship between average roughness, and effective conductivity. The smoothest sample, with an average roughness of 5.5 nanometers, or 4.5% of the skin depth at 400 GHz, has an effective conductivity that is 28% lower than the DC value. In addition to mechanically lapped specimens, additional samples with controlled, microfabricated grating-like structures will be examined with the resonator apparatus. These samples provide geometries that can be modeled with theoretical calculations for comparison purposes. This paper will discuss the techniques that enabled high-Q operation at 400 GHz and 650 GHz. It will also compare the measured relationship between surface roughness and effective conductivity with theoretical predictions.