Carlos Medina Rodriguez

Scopus Publications

Jet Grouting for Excavation Support, Underpinning, and Groundwater Control for the Construction of Sewage Treatment Plant Tanks
Russell W. Preuss, Daniel V. Cacciola, Carlos Medina
Geotechnical Special Publication, 2019
The Bay Park Sewage Treatment Plant improvement project involved the replacement of three detritus-type grit tanks with three vortex grit tanks within an existing treatment building. The proposed tanks extend 20 ft below grade, 12 ft below existing foundations, and 6 ft below groundwater. Complex site issues included: high groundwater table, pervious soils, space constraints, utility constraints, existing foundation concerns, and a construction staging plan which required one tank remain operational during construction. Traditional underpinning was not possible since dewatering would cause excessive foundation settlements. An innovative solution utilizing jet grouting was implemented to provide support of excavation, underpinning, and control groundwater infiltration during construction. The installation and performance of jet grouting operations was verified and monitored by rig instrumentation and column coring. Near real-time displacement monitoring was utilized to monitor the structure. This paper presents details of the jet grouting design, construction, monitoring and verification results, and lessons learned.
Selective processing of auditory evoked responses with iterative-randomized stimulation and averaging: A strategy for evaluating the time-invariant assumption
Joaquin T. Valderrama, Angel de la Torre, Carlos Medina, Jose C. Segura, A. Roger D. Thornton
Hearing Research, 2016
Ultrasound indoor positioning system based on a low-power wireless sensor network providing sub-centimeter accuracy
Carlos Medina, José Segura, Ángel De la Torre
Sensors Switzerland, 2013
This paper describes the TELIAMADE system, a new indoor positioning system based on time-of-flight (TOF) of ultrasonic signal to estimate the distance between a receiver node and a transmitter node. TELIAMADE system consists of a set of wireless nodes equipped with a radio module for communication and a module for the transmission and reception of ultrasound. The access to the ultrasonic channel is managed by applying a synchronization algorithm based on a time-division multiplexing (TDMA) scheme. The ultrasonic signal is transmitted using a carrier frequency of 40 kHz and the TOF measurement is estimated by applying a quadrature detector to the signal obtained at the A/D converter output. Low sampling frequencies of 17.78 kHz or even 12.31 kHz are possible using quadrature sampling in order to optimize memory requirements and to reduce the computational cost in signal processing. The distance is calculated from the TOF taking into account the speed of sound. An excellent accuracy in the estimation of the TOF is achieved using parabolic interpolation to detect of maximum of the signal envelope at the matched filter output. The signal phase information is also used for enhancing the TOF measurement accuracy. Experimental results show a root mean square error (rmse) less than 2 mm and a standard deviation less than 0.3 mm for pseudorange measurements in the range of distances between 2 and 6 m. The system location accuracy is also evaluated by applying multilateration. A sub-centimeter location accuracy is achieved with an average rmse of 9.6 mm.
Accurate time synchronization of ultrasonic TOF measurements in IEEE 802.15.4 based wireless sensor networks
C. Medina, J.C. Segura, A. de la Torre
Ad Hoc Networks, 2013
A synchronous TDMA ultrasonic TOF measurement system for low-power wireless sensor networks
Carlos Medina, José C. Segura, Ángel de la Torre
IEEE Transactions on Instrumentation and Measurement, 2013
This paper presents the design and evaluation of an ultrasonic time-of-flight (TOF) measurement system in the context of a smart sensor wireless network. In particular, the ZigBee protocol is used for data transmission and synchronization purposes. Low-cost and low-power restrictions are taken into account in the design. A synchronous measurement scheduling approach is used to minimize the network traffic and, therefore, the power consumption, while avoiding the need of wired connections between the nodes or the use of specific radio link to provide synchronization. A theoretical model that describes the accuracy of the proposed system is derived. This model takes into account both clock drift effects and finite clock resolution of the network nodes. According to the model, the estimation of the TOF is biased due to the clock drifts, and a solution is proposed to compensate this bias. The compensation is based on an accurate estimation that each node performs for its own clock drift. An error analysis of this estimation procedure is also developed, and its effects on the TOF accuracy are presented. A theoretical model of the system that predicts the system performance in terms of TOF accuracies is proposed. An implementation of the TOF measurement system is presented, from which experimental results that validate the theoretical derivations and the effect of the clock drift compensation are obtained. Experimental evaluation of the system also demonstrates that TOF accuracies better than 2 μs are achievable, which will be more than adequate for achieving subcentimetric or even submillimetric precisions in ultrasound-TOF-based distance measurement systems. Even though a particular approach for TOF estimation is considered in this work, most of the derived results are also applicable to other systems involving time synchronous measurements.
Temperature dependent dynamic properties of oily clay
C. I. Medina, M. Pervizpour, S. Pamukcu, M. A. Mentzer
Geotechnical Special Publication, 2012
An ongoing study is investigating the measurement of dynamic impact strains within a body of clay using embedded fiber optic sensors. A finite element model of this impact process is developed through ABAQUS Explicit to aid in quantification and calibration of these strains. The required dynamic properties of the material (oil-based clay) as used for ballistic impact studies are determined through resonant column tests. The lack of moisture in this type of oilbased clay allows consistent and repeatable determination of the material properties. The dynamic characteristics of the material are determined in: undisturbed (as is clay bricks), remolded (compacted cylinders), and heat conditioned (to ballistic test requirements) states. The frequency dependent shear modulus and damping characteristics of the clay are obtained for a range of confining pressures and temperatures. Resonant column tests are conducted for strain ranges of 10-6 to 10-3 yielding shear modulus values of 4 to 57 MPa, and damping ratios of 4 to 14%. The strain and frequency dependency of the results as presented in the paper are best approximated through hyperbolic models. The frequency dependent damping response is used to determine the Rayleigh damping coefficients for proportional damping representation as required by the finite element model.
TELIAMADE ultrasonic indoor location system: Application as a teaching tool
C. Medina, I. Alvarez, J.C. Segura, A. de la Torre, C. Benitez
ICASSP IEEE International Conference on Acoustics Speech and Signal Processing Proceedings, 2012
This paper proposes TELIAMADE (an indoor location system based on ultrasonic and radiofrequency signals) to be used as a teaching tool in the context of Telecommunication Engineering. Due to its simple design, the versatility of its configuration and the characteristics of the involved signals, TELIAMADE is an appropriate tool for teaching basic aspects in location systems, digital communication systems, encoded signalling, microcontroller programming, radio protocols or advanced signal processing techniques. The TELIAMADE design allows students to sample, store and analyze signals at different points of the circuits by using conventional oscilloscopes. Furthermore, some parameters can be configured, allowing students to assess the advantages and inconveniences of each specific configuration with respect to features such as bit-rate, range, robustness against noise or updating period. Our system presents advantages in the field of teaching for understanding commercial systems for location (like GPS) or communication (like wireless digital communication systems).
Feasibility of ultrasound positioning based on signal strength
C. Medina, J.C. Segura, S. Holm
2012 International Conference on Indoor Positioning and Indoor Navigation Ipin 2012 Conference Proceedings, 2012
The objective of this paper is to analyze the performance of an indoor positioning system based on the ultrasound level, usually called RSSI (received signal strength indicator). This paper builds on past experiences where RSSI values from beams sent in different directions were compared [1]. There relative values of RSSI were measured but herein we go one step further and perform localization based on absolute values of RSSI. The use of RSSI could potentially mean a simplification of the traditional positioning systems design in relation to other methods such as TOF (time-of-flight), being an alternative and interesting method for positioning. The distance between nodes (transmitter and receiver) is estimated from RSSI values using a signal propagation model in which the power losses due to the spherical divergence and atmospheric absorption are considered. However, in real conditions, other factors related to the characteristics of the nodes have their impact on RSSI measurements. One of them has to do with the beamwidth of the transducers. The signal strength will be conditioned by the angle of incidence of the transducers when these have a narrow beamwidth. On the other hand, the common use of wireless nodes in the deployment of these systems leads to the RSSI measurement to be affected by the battery level in the nodes. These effects introduce significant errors in the distance estimation and therefore on the localization precision. Herein we propose a mechanism for modeling the power loss due to the orientation of the ultrasonic transducers, as well as an algorithm to compensate for the effect of the variations in the battery level on RSSI measurements. Some experimental results have been obtained with 5 nodes (4 transmitters and 1 receiver) to show the quality of our compensation using a real positioning system. Location errors smaller than 10 cm for each coordinate are obtained in contrast to errors of several meters which are normally attained in this kind of systems based on RF (radio frequency) RSSI-values.
Subsurface geo-event monitoring using wireless sensor networks
Ehsan Ghazanfari, Suk-Un Yoon, Yi Dong, Xu (Eric) Li, Carlos I. Medina, Donald Seserko, Liang Cheng, Tae Sup Yun, Sibel Pamukcu
Geotechnical Special Publication, 2011
Wireless Sensor Networks (WSN) can be useful in subsurface geo-event monitoring. Hazard monitoring and effective in-situ characterization are some key issues that can be addressed by use of WSN in the subsurface. In this study a new concept of WSN application for subsurface geo-event monitoring was investigated. The new concept of functional signal takes advantage of the variations of signal strength of radios transmitted between the distributed sensor nodes of a WSN to monitor and characterize the sensed area. Experiments demonstrated that calibrated wireless signal strength variations can be used as indicators to sense changes in the subsurface. Based on the experimental results the new approach can be exploited further to provide a sensing methodology to identify and monitor subsurface hazards through the evolution of select physical conditions in the subsurface. These subsurface hazards can range from intrusion of a chemical plume to the onset of a slide which could change markedly the physical properties of the host soil, hence the functional signal transmitted with an embedded WSN.