A Corrugated Planar-Goubau-Line Termination for Terahertz Waves

The planar Goubau line is a promising low-loss metal waveguide for terahertz applications. To enable advanced circuits and multi-port measurements based on planar Goubau lines, there is a strong need for broadband impedance-matched loads, which can be used to absorb the energy and minimize standing waves in a system. In this work, we propose a termination for planar Goubau lines based on an exponentially-tapered corrugated line, gradually increasing conductor losses while maintaining small reflections. The corrugation density is high enough to increase conductor losses without requiring an auxiliary low-conductivity material. A 400-\ub5m long planar Goubau line load was fabricated on a 10-\ub5m thick silicon substrate suspended in the air. Simulations of the load show excellent agreement with calibrated reflection measurements in the frequency range 0.5 THz – 1.1 THz. Above the cut-off frequency of around 580 GHz, the measured reflections are less than -19 dB, below the noise floor of the characterization setup

Transmission Loss in Coplanar Waveguide and Planar Goubau Line between 0.75 THz and 1.1 THz

In many cases, metallic planar waveguides are required in the design of integrated circuits. However, at terahertz frequencies, metallic planar waveguides present high losses, which make necessary the use more efficient waveguides to avoid power limitations. In this work, the attenuation constant of two popular planar waveguides for terahertz frequencies, Coplanar Waveguide (CPW) and Planar Goubau Line (PGL), are compared between 0.75 THz and 1.1 THz. To measure the PGL, its transition is deembeded using a multiline Thru-Reflect-Line calibration standard. Measurement results show a lower attenuation constant across the band for a PGL (0.13 mm-1 < α < 0.39 mm-1) than for a CPW (0.68 mm-1 < α < 0.99 mm-1) when an ultra-thin substrate is used suspended in air, which greatly reduces the substrate mode coupling from the PGL. These results put the PGL as a less lossy metallic planar waveguide for terahertz applications

On-Chip Characterization of High-Loss Liquids Between 750 and 1100 GHz

Terahertz spectroscopy is a promising tool for analyzing the picosecond dynamics of biomolecules, which is influenced by surrounding water molecules. However, water causes extreme losses to terahertz signals, preventing sensitive measurements at this frequency range. Here, we present sensitive on-chip terahertz spectroscopy of highly lossy aqueous solutions using a vector network analyzer, contact probes, and a coplanar waveguide with a 0.1 mm wide microfluidic channel. The complex permittivities of various deionized water/isopropyl alcohol concentration are extracted from a known reference measurement across the frequency range 750–1100 GHz and agrees well with literature data. The results prove the presented method as a highsensitive approach for on-chip terahertz spectroscopy of high-loss liquids, capable of resolving the permittivity of water

Terahertz Planar Goubau Line Components on Thin Suspended Silicon Substrate

The planar Goubau line is a low-loss planar single-conductor waveguide that holds promise for terahertz applications,\ua0where power efficiency is crucial. We present three circuit elements for planar Goubau line: a stopband filter, a matching\ua0load, and a power divider, which have been fabricated in a high-resistivity silicon membrane. Simulation results are presented for\ua0the matching load and the power divider. The filter’s performance is validated by comparing measurement results with simulations,\ua0showing good agreement

Capacitively-coupled resonators for terahertz planar-Goubau-line filters

Low-loss planar Goubau lines show promising potential for terahertz applications. However, a single-wire waveguide exhibits less design freedom than standard multi-conductor lines, which is a significant constraint for realizing standard components. Existing filters for planar Goubau line lack clear design procedures preventing the synthesis of an arbitrary filter response. In this work, we present a design for a bandpass/bandstop filter for planar Goubau line by periodically loading the line with capacitively-coupled \u1d706∕2 resonators, which can be easily tuned by changing their electrical length. The filter’s working principle is explained by a proposed transmission-line model. We designed and fabricated a passband filter centered at 0.9 THz on a 10-\u1d707m silicon-membrane substrate and compared measurement results between 0.5 THz and 1.1 THz to electromagnetic simulations, showing excellent agreement in both \u1d44611 and \u1d44621. The measured passband has an insertion loss of 7 dB and a 3-dB bandwidth of 31%. Overall, the proposed filter design has good performance while having a simple design procedure

A Capacitive-Gap Coupled Terahertz Planar-Goubau-Line Power Divider

The planar Goubau line is a single-conductor waveguide with a low attenuation constant at terahertz frequencies compared to other planar waveguides. However, its single-conductor nature complicates the design of circuit elements compared to multi-conductor waveguides, especially when impedance transformation is needed, like in the case of power dividers. In this paper, we present a power divider for a planar Goubau line based on capacitive-gap coupled lines, providing a matched input port. A 900-GHz equal power divider was fabricated on a suspended silicon membrane and was characterized with a Vector Network Analyzer and terahertz probes between 0.5 THz and 1.1 THz. Simulations and measurements are in good agreement, the measured input return loss is lower than 15dB at the design frequency, and the average coupler loss is estimated to be lower than 1 dB when de-embedding the feeding lines

Terahertz Frequency Domain Sensing for Fast Porosity Measurement of Pharmaceutical Tablets

Porosity is an important property of pharmaceutical tablets since it may affect tablet disintegration, dissolution, and bio-availability. It is, therefore, essential to establish non-destructive, fast, and compact techniques to assess porosity, in-situ, during the manufacturing process. In this paper, the terahertz frequency-domain (THz-FD) technique was explored as a fast, non-destructive, and sensitive technique for porosity measurement of pharmaceutical tablets. We studied a sample set of 69 tablets with different design factors, such as particle size of the active pharmaceutical ingredient (API), Ibuprofen, particle size of the filler, Mannitol, API concentration, and compaction force. The signal transmitted through each tablet was measured across the frequency range 500-750 GHz using a vector network analyzer combined with a quasi-optical set-up consisting of four off-axis parabolic mirrors to guide and focus the beam. We first extracted the effective refractive index of each tablet from the measured complex transmission coefficients and then translated it to porosity, using an empirical linear relation between effective refractive index and tablet density. The results show that the THz-FD technique was highly sensitive to the variations of the design factors, showing that filler particle size and compaction force had a significant impact on the effective refractive index of the tablets and, consequently, porosity. Moreover, the fragmentation behavior of particles was observed by THz porosity measurements and was verified with scanning electron microscopy of the cross-section of tablets. In conclusion, the THz-FD technique, based on electronic solutions, allows for fast, sensitive, and non-destructive porosity measurement that opens for compact instrument systems capable of in-situ sensing in tablet manufacturing

Monte Carlo study of the noise performance of isolated-gate InAs/AlSb HEMTs

In this work, the extrinsic dynamic behaviour and noise performance of a 225 nm isolated-gate InAs/AlSb HEMT have been studied by means of Monte Carlo simulations. A very good agreement with experimental results has been achieved for fT. Discrepancies between experimental and simulated fmax have been observed and attributed to the experimental frequency dispersion of gd and Cds. The simulations of the intrinsic and extrinsic noise parameters indicate an excellent performance for this device (Fmin=0.3 dB@10 GHz) even if we confirm that the presence of the native oxide under the gate induces an significant decrease in fT and fmax of around 20%, together with an increase of noise figure and noise resistance.ROOTHz (FP7-243845

Millimetre-wave dielectric spectroscopy for cell analysis

A millimeter-wave sensor based on a CPW line has been designed and fabricated as a first prototype for impedance spectroscopy to be combined with a multifunctional micropipette for cell and membrane analysis. The first mm-wave measurement results show the sensitivity of the layout by distinguishing the cells from the media and monitoring the attachment process of the cells to the sensor surface. Measurements were performed on umbilical cord stem cells and cartilage thumb cells

Dynamic Monte Carlo study of isolated-gate InAs/AlSb HEMTs

In this work, by means of Monte Carlo simulations, the static and dynamic behavior of isolated-gate InAs/AlSb high electron mobility transistors (Sb-HEMTs) has been studied and compared with experimental results. The influence of the existence of a native oxide under the gate, the value of the surface charges in the gate recess and the possible variation of electron sheet carrier density, ns, has been studied. A decrease in the gate-source capacitance, transconductance and intrinsic cut-off frequency is observed because of the presence of the native oxide, while changes in the value of the surface charges in the recess only introduce a threshold voltage shift. The increase of ns shifts the maximum of the transconductance and intrinsic cut-off frequency to higher values of drain current and improves the agreement with the experimental results.ROOTHz (FP7-243845