Time-domain Reflection Measurements Research Articles

Geotechnical Deformation Distributed Measuring Technology Research Based on Parallel Spiral Sensing Line.

The precursors that appear when geological disasters occur are geotechnical deformations. This paper studies the TDR (Time Domain Reflection) measurement technology for the distributed measurement of geotechnical deformation using parallel spiral wire as a sensor, which is used for monitoring and early warning detection of geological disasters. Based on the mechanism of the electromagnetic field distribution parameters of the parallel spiral sensing wire, the relationship between the stretching amount of the parallel spiral wire and the change in its characteristic impedance is analyzed. When the parallel spiral wire is buried in the soil, the geotechnical deformation causes the parallel spiral wire to be stretched, and according to its characteristic impedance change, the stretching position and the stretching degree can be obtained, thus realizing the distributed measurement of geotechnical deformation. Based on this principle, the TDR measurement system is developed, and a local single-point stretching amount and stretching positioning experiment are designed for the parallel spiral sensing line to verify the effectiveness of the sensing technology and the usability of the measurement system.

Fiber Coupled Transceiver with 6.5 THz Bandwidth for Terahertz Time-Domain Spectroscopy in Reflection Geometry.

We present a fiber coupled transceiver head for terahertz (THz) time-domain reflection measurements. The monolithically integrated transceiver chip is based on iron (Fe) doped In0.53Ga0.47As (InGaAs:Fe) grown by molecular beam epitaxy. Due to its ultrashort electron lifetime and high mobility, InGaAs:Fe is very well suited as both THz emitter and receiver. A record THz bandwidth of 6.5 THz and a peak dynamic range of up to 75 dB are achieved. In addition, we present THz imaging in reflection geometry with a spatial resolution as good as 130 µm. Hence, this THz transceiver is a promising device for industrial THz sensing applications.

The use of THz time-domain reflection measurements to investigate solvent diffusion in polymers

Solvent diffusion into polymers is central to their performance, for example as controlled delivery pharmaceutical products. In this work, we present the novel application of terahertz (THz) time-domain reflectance spectroscopy to quantify the ingress of acetone into various polymer materials. Reflections from the top and bottom surfaces of the discs are temporally resolved, as is a reflection from the interface between acetone-wet polymer and dry polymer. These reflections enable both the polymer swelling and more importantly the position of the liquid diffusion front to be quantified as a function of time. Verification of these measurements is provided by equivalent magnetic resonance imaging (MRI) measurements, with which there is excellent agreement.

Terahertz wide aperture reflection tomography

We describe a powerful imaging modality for terahertz (THz) radiation, THz wide aperture reflection tomography (WART). Edge maps of an object's cross section are reconstructed from a series of time-domain reflection measurements at different viewing angles. Each measurement corresponds to a parallel line projection of the object's cross section. The filtered backprojection algorithm is applied to recover the image from the projection data. To our knowledge, this is the first demonstration of a reflection computed tomography technique using electromagnetic waves. We demonstrate the capabilities of THz WART by imaging the cross sections of two test objects.

Characterization and modeling of multiple coupled lines in an inhomogeneous medium from time-domain reflection measurements

A synthesis technique of an equivalent lossless (nondispersive) uniform multiconductor n-coupled lines (UMCLs) 2n-port system from the measured discrete time-domain reflection response is presented. This procedure is based on the decomposition of characteristic immittance matrix of UMCL in terms of partial mode immittance matrices. The decomposition scheme leads to the discrete transition matrix function of a UMCL an-port system. This, in turn, establishes a relationship between the normal-mode parameters of the UMCL and the measured impulse reflection and transmission response. Equivalence between the synthesis procedure presented in this paper and the solution of a special form of algebraic Riccati matrix equation whose solution can lead to the normal-mode parameters and including real termination network is illustrated. In order to exemplify the procedure, a typical microstrip structure with three lines is synthesized from the time-domain reflection (TDR) data.

Time domain reflectometry: Bilinear corrections and extending the range of analysis beyond the quarter and half wavelength conditions

Abstract The analysis for the determination of bilinear coefficients for time domain reflection measurements are presented here. The calculation of the coefficients is based on a short circuit and a standard liquid as calibration standards. The range of frequencies used in this anaylsis goes up to the frequency equivalent of the half wavelength condition for a coaxial transmission line terminated with a dielectric e•. The Newton-Raphson algorithm for the calculation of e• from e•tan(ωd/c)√e•)/(ωd/c)√e•) is also presented.