We demonstrate improved terahertz (THz) modulation using thermally crystallized telluride (GeTe) GeTe is a that exhibits a nonvolatile, amorphous to crystalline at approximately 200 °C, as well as six orders of magnitude decreased In this study, amorphous GeTe were on substrates and then tested using THz time-domain The test samples, heated while collecting measurements, exhibited a gradual absorbance increase, an abrupt nonvolatile reduction at the transition temperature, followed by another gradual increase in absorbance. The transition temperature was verified by conducting similar thermal tests while monitoring THz transmittance modulation data were investigated between 10 and 110 cm−1 (0.3–3.3 THz). A peak modulation of approximately 99% was achieved at 2.3 THz with a 100 nm GeTe on a substrate. After isolating the and the crystalline GeTe (GeTe) absorbance contributions, the results showed THz modulations ranging from 88.5% to 91.5% that were attributed solely to the single layer of transitioned GeTe. These results strongly motivate using GeTe or other in THz filters, and metamaterial applications.
The measurments in this paper were collected with a TeraView THz-TDS
spectroscopy system equipped with a variable temperature sample holder.
Tuesday, 28 July 2015
Tuesday, 14 July 2015
Piezoelectric transducers are widely utilized in Structural Health Monitoring (SHM). They are used both in guided wave-based and electromechanical impedance-based methods. Transducer debonding or unevenly distributed glue underneath the transducer reduce the performance and reliability of the SHM system. Therefore, quality assessment methods for glue layer need to be developed. In this paper, the authors present results obtained from two methods that allow the quality assessment of adhesive bonds of piezoelectric transducers. The electromechanical impedance method is utilized to analyze transducer adhesive bonding. An improperly prepared bonding layer is a source for changes in the electromechanical impedance characteristics in comparison to a perfectly bonded transducer. In the resistance characteristics of the properly bonded transducer the resonance peaks of the structure were clearly visible. In the case when adhesive layer is not equally distributed under sensor, the amplitudes of structural resonance peaks are reduced. In the case of completely detached transducer, the structural resonance peaks disappear and only resonance peaks of the transducer itself are visible. These peaks (peaks of free transducer hanging on wires) are significantly larger than the resonance peaks of the investigated structure in the considered frequency interval. The bonding layer shape is also analyzed using time-domain terahertz spectroscopy in reflection mode. This method allows to visualize the adhesive layer distribution based on C-scan analysis. C-scans of signals or envelope-detected signals can be used to estimate the area of proper adhesion between bonding agent and transducer and hence provides a more quantitative approach towards transducer inspection.
Teraview's TPS Spectra 3000 was used the investigate the materials used in the paper.
Monday, 13 July 2015
SPIE Photonics West OPTO 2016 Terahertz, RF, Millimeter, and Submillimeter-Wave Technology and Applications IX conference
Abstracts are accepted now through 3 August 2015
For more information go to http://spie.org/PWO/conferencedetails/thz-rf-mm-submm-wave-technology
Wednesday, 8 July 2015
In this work, ten carbon black (CB) loaded elastic acrylonitrile butadiene rubber (NBR) nano-composites have been prepared to be used in microwave shielding applications. The DC electric properties of these CB loaded NBR composites have been studied. The evolution of DC conductivity of CB loaded NBR composites with loading level revealed S-shapes curve in accordance with the percolation theory. The current (I)-voltage (V) relations have been studied for these samples at room temperature. All CB loaded NBR composite samples showed Ohmic behavior with the exception of two samples namely CB30 and CB40 in which space charge limited conduction is obvious. Microwave shielding has been calculated from the transmittance data measured using terahertz time domain spectroscopy (THz-TDS) technique. The analysis of microwave shielding data revealed that the sample CB70 has the highest shielding effectiveness. The results of the microwave shielding effectiveness of CB loaded NBR composites were correlated to their DC electric conductivities. Results showed that there is a strong relationship between the DC electric conductivity of the samples and their activity regarding microwave shielding effectiveness. The current investigation of microwave shielding properties of CB loaded NBR composites magnifies the importance of DC electric conduction losses as a major mechanism for microwave shielding.
TPS Spectra 3000, (TeraView, UK) was used for measuring transmittance of the samples in the frequency range 10-1000 GHz
Thursday, 2 July 2015
In this paper result of detection and localization of artificially initiated delaminations in small carbon fibre reinforced polymer CFRP and glass fibre reinforced polymers GFRP samples were presented. The first method was electromechanical impedance method (EMI). This method utilizes electromechanical coupling of piezoelectric transducer with host structure. Due to this coupling mechanical resonances of structure can be seen in electrical impedance characteristic of piezoelectric transducer. Instead of electrical impedance other parameters such as resistance, conductance, admittance or susceptance are very often utilized. In the research real part of electrical impedance (resistance) was measured. Delamination in CFRP sample caused frequency shift of certain resonance frequencies visible in resistance characteristic. The second method was a laser vibrometry. It is a noncontact technique that allows to measure vibration of structure excited by piezoelectric transducer. During research standing waves (vibration–based method) and propagating waves (guided waves–based method) were registered for CFRP sample. In the vibration–based method, the frequency shifts of certain resonance frequencies were analyzed. In guided waves-based technique, the interaction of elastic waves with delamination can be seen in the RMS energy map. The third method is Terahertz spectroscopy. The device uses an electromagnetic radiation in the terahertz range (0.1–3 THz). The spectrometer is equipped with moving table that allows for XY scanning of large objects. During research the scanning heads working in reflection mode were utilized and the measurements were taken for GFRP sample with delamination. During research time signals as well as sets of signals creating B–scans and C–scans were analysed. The obtained results showed that the THz spectroscopy technique can detect and visualize delamination between the GFRP layers.
Teraview's TPS Spectra 3000 was used in these investigations