•An innovative analysis procedure, complementing the standard TRT analysis.•A novel temperature profile is presented as an additional measurement during the TRT.•Estimate thermal conductivity profile ...of geothermal layers crossed by perforation.•Implemented by fitting 3D FEM simulation results with experimental data.•Allowed the detection of a highly conductive layer in an experimental BHE installation.
Ground thermal conductivity and borehole thermal resistance are key parameters for the design of closed Ground-Source Heat Pump (GSHP) systems. The standard method to determine these parameters is the Thermal Response Test (TRT). This test analyses the ground thermal response to a constant heat power injection or extraction by measuring inlet and outlet temperatures of the fluid at the top of the borehole heat exchanger. These data are commonly evaluated by models considering the ground being homogeneous and isotropic. This approach estimates an effective ground thermal conductivity representing an average of the thermal conductivity of the different layers crossed by perforation. In order to obtain a thermal conductivity profile of the ground as a function of depth, two additional inputs are needed; first, a measurement of the borehole temperature profile and, second, an analysis procedure taking into account ground is not homogeneous. This work presents an analysis procedure, complementing the standard TRT analysis, estimating the thermal conductivity profile from a temperature profile along the borehole during the test. The analysis procedure is implemented by a 3D Finite Element Model (FEM) in which depth depending thermal conductivity of the subsoil is estimated by fitting simulation results with experimental data. The methodology is evaluated by the recorded temperature profiles throughout a TRT in a BHE (Borehole Heat Exchanger) monitored facility, which allowed the detection of a highly conductive layer at 25 meters depth.
This contribution describes an accurate approach implementing a Time-to-Digital Converter using a Field-Programmable Gate Array (FPGA) device. Time differences with a FWHM better than 100 ps for 24 ...pairs of channels working simultaneously have been achieved. This was possible through the proper management of FPGA internal resources and by an accurate device calibration process minimizing the effect of temperature and voltage fluctuations. The system calibration results and the time differences between multiple channels are presented. The current approach suggests the possibility of carrying out precise Time of Flight (TOF) measurements with, for instance, Positron Emission Tomography (PET) systems.
This contribution describes the optimization of a multichannel high resolution Time-to-Digital Converter (TDC) in a Field-Programmable Gate Array (FPGA) initially capable of obtaining time ...resolutions below 100ps for multiple channels. Due to its fast propagation capability it has taken advantage of the FPGA internal carry logic for accurate time measurements. Furthermore, the implementation of the TDC has been performed in different clock regions and tested with different frequencies as well, achieving improvements of up to 50% for a pair of channels. Moreover, since the TDC is potentially going to be used in a trigger system for Positron Emission Tomography (PET), the algorithm for coincidence identification has been subjected to tests in order to estimate the impact on occupied resources and the execution time. This time has been optimized, resulting in speed improvements of up to 20% while preserving occupied resources.
Due to the lateral inscription process, photo-induced birefringence is present in fiber Bragg gratings (FBGs) written into photosensitive single mode fiber. The birefringence value is generally too ...small to be perceived in the grating spectral response but it can lead to significant polarization dependent loss (PDL) and differential group delay (DGD) evolutions. In this paper, we first theoretically analyze the evolution with wavelength of PDL and DGD as a function of the grating parameters and the birefringence value. We demonstrate that the PDL and DGD evolutions with wavelength can be strongly enhanced by a modification of the grating parameters. Simulations carried out using the coupled mode theory and the Jones formalism are then confirmed by experiments conducted on FBGs written into photosensitive single mode fiber. Our work brings a complete characterization of polarization related phenomena in FBGs and presents a great interest for the evaluation of system performances and the design of gratings for specific applications, either for telecommunications or sensing purposes. In addition, based on the comparison between experimental and simulated evolutions, we are able to verify that the birefringence value is strongly dependent on the fluence of the laser used for the grating inscription.
Birefringence in fiber Bragg gratings (FBGs) leads to polarization-dependent properties such as polarization-dependent loss (PDL). Although this property is not desired for telecommunications ...applications, we demonstrate that the PDL generated by uniform FBGs written into standard single-mode fiber can be advantageously used for transverse strain measurements, which is not directly possible through amplitude spectral measurements.
Silicon photomultipliers (SiPMs) have become an alternative to traditional tubes due to several features. However, their implementation to form large arrays is still a challenge especially due to ...their relatively high intrinsic noise, depending on the chosen readout. In this contribution, two modules composed of 12 ×12 SiPMs with an area of roughly 50 mm×50 mm are used in coincidence. Coincidence resolving time (CRT) results with a field-programmable gate array, in combination with a time to digital converter, are shown as a function of both the sensor bias voltage and the digitizer threshold. The dependence of the CRT on the sensor matrix temperature, the amount of SiPM active area and the crystal type is also analyzed. Measurements carried out with a crystal array of 2 mm pixel size and 10 mm height have shown time resolutions for the entire 288 SiPM two-detector set-up as good as 800 ps full width at half maximum (FWHM).
In this paper, we completely study the wavelength dependency of differential group delay (DGD) in uniform fiber Bragg gratings (FBG) exhibiting birefringence. An analytical expression of DGD is ...established. We analyze the impact of grating parameters (physical length, index modulation and apodization profile) on the wavelength dependency of DGD. Experimental results complete the paper. A very good agreement between theory and experience is reported.
In this paper the design, fabrication and experimental characterization of an spectral amplitude coded (SAC) optical label swapper monolithically integrated on Indium Phosphide (InP) is presented. ...The device has a footprint of 4.8x1.5 mm2 and is able to perform label swapping operations required in SAC at a speed of 155 Mbps. The device was manufactured in InP using a multiple purpose generic integration scheme. Compared to previous SAC label swapper demonstrations, using discrete component assembly, this label swapper chip operates two order of magnitudes faster.
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