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Publications

Publications by António Valente

2011

Glucose monitoring system based on osmotic pressure measurements

Authors
Leal, A; Valente, A; Ferreira, A; Soares, S; Ribeiro, V; Krushinitskaya, O; Johannessen, EA;

Publication
Sensors and Transducers

Abstract
This paper presents the design and development of a prototype sensor unit for implementation in a long-term glucose monitoring system suitable for estimating glucose levels in people suffering from diabetes mellitus. The system utilizes osmotic pressure as the sensing mechanism and consists of a sensor prototype that is integrated together with a pre-amplifier and data acquisition unit for both data recording and processing. The sensor prototype is based on an embedded silicon absolute pressure transducer and a semipermeable nanoporous membrane that is enclosed in the sensor housing. The glucose monitoring system facilitates the integration of a low power microcontroller that is combined with a wireless inductive powered communication link. Experimental verification have proven that the system is capable of tracking osmotic pressure changes using albumin as a model compound, and thereby show a proof of concept for novel long term tracking of blood glucose from remote sensor nodes. © 2011 IFSA.

2001

On-chip integrated silicon bulk-micromachined soil moisture sensor based on the DPHP method

Authors
Valente, A; Couto, C; Correia, JH;

Publication
TRANSDUCERS '01: EUROSENSORS XV, DIGEST OF TECHNICAL PAPERS, VOLS 1 AND 2

Abstract
This paper reports the design, modelling, fabrication and assembly of a silicon bulk-micromachined soil moisture microsensor using the Dual-Probe Heat-Pulse (DPHP) method. Soil humidity measurement is essential to study soil preservation and control the development of plants, namely in closed ecosystem. The DPHP method uses a heater (Peltier effect) and a temperature probe (Seebeck effect) to determine the volumetric heat capacity of the soil and hence water content (theta (v)). This is the first time that the DPHP method is implemented in a microdevice and the first integrated sensor for soil moisture. This microdevice is more suited to measure at different soil depths in a non-destructive and automated manner.

2000

On-chip integrated silicon bulk-micromachined soil moisture sensor with electronics and bus interface

Authors
Valente, A; Couto, C; Correia, JH;

Publication
PROCEEDINGS OF THE 2000 IEEE INTERNATIONAL SYMPOSIUM ON INDUSTRIAL ELECTRONICS, VOL 1 AND 2

Abstract
This paper presents an on-chip silicon bulk-micromachined Soil Moisture Sensor (SMS) for irrigation control in greenhouses. The system-on-a-chip includes the SMS, readout electronics, self-test, calibration facilities and a digital bus interface for external data transmission. Moreover, this low-cost device can be applied in several locations (e. g. per each plant root), and networked together with the 1-wire bus. The heat-pulse technique is used (for measuring the maximum temperature on a distant point) to determine the volumetric heat capacity and hence the water content of a porous media, such as soil. In order to validate this method, experimental results were achieved with a macrosensor based on the heat-pulse and capacitance methods. The capacitance method relates the volumetric water content with the capacitance change (dielectric properties) of a probe, inserted in the soil. Several tests were performed for different type of soils and water contents. These results are compared with the measurements achieved using the conventional thermogravimetric method.

1998

Integrated management irrigation system

Authors
Valente, A; Cunha, JB; Couto, C;

Publication
COMPUTERS IN AGRICULTURE, 1998

Abstract
Soil water content has a direct influence on the cooling and growth mechanisms of the plants. Crop evapotranspiration is majoring influenced by solar radiation and the air temperature, humidity and movement. An efficient irrigation system must supply and maintain, at soil root zone of the plants, the adequate amount of water that best regulate the physiological mechanisms of the plant. For this purpose, an intelligent real-time greenhouse irrigation system was implemented which uses accurate sensors for measuring soil moisture, as well to determinate the crop evapotranspiration. To avoid loss of control, it was provided fault-detection capabilities to the soil moisture sensor and used a knowledge-based approach to estimate replacement values for the faulty sensors. A model-based controller was implemented to regulate the water content at the root zone of the plants. These tasks are very complex and difficult to meet, unless microcontroller and microprocessor systems are employed, such as in the integrated management irrigation system. The system comprises four modules: Sensor/Actuation, Acquisition and Data Validation, Data Correction, Model Based Controller, and Control Signals Generation. All the modules are linked and supervised by a higher-level supervision module to achieve an intelligent irrigation.

2012

Automatic detection of bunches of grapes in natural environment from color images

Authors
Reis, MJCS; Morais, R; Peres, E; Pereira, C; Contente, O; Soares, S; Valente, A; Baptista, J; Ferreira, PJSG; Bulas Cruz, JB;

Publication
JOURNAL OF APPLIED LOGIC

Abstract
Despite the benefits of precision agriculture and precision viticulture production systems, its rate of adoption in the Portuguese Douro Demarcated Region remains low. We believe that one way to raise it is to address challenging real-world problems whose solution offers a clear benefit to the viticulturist. For example, one of the most demanding tasks in wine making is harvesting. Even for humans, the environment makes grape detection difficult, especially when the grapes and leaves have a similar color, which is generally the case for white grapes. In this paper, we propose a system for the detection and location, in the natural environment, of bunches of grapes in color images. This system is able to distinguish between white and red grapes, and at the same time, it calculates the location of the bunch stem. The system achieved 97% and 91% correct classifications for red and white grapes, respectively.

2011

Internet-based collaborative E-exercisebook system for primary math teaching

Authors
Reis, MJCS; Bacelar, M; Reis, MGAD; Meira, D; Bessa, M; Peres, E; Morais, R; Valente, A; Soares, S; Bulas Cruz, J;

Publication
2011 2nd National Conference on Telecommunications, CONATEL 2011 - Proceedings

Abstract
The academic performance and social competence of a child in school is positively associated with the involvement of their parents. However, the researches about educational learning models often ignore the parents' part. Internet opens a new paradigm: education and communication approach is more complex than ever. Here, we would like to present an Internet based system to support students' homework. We believe that one of the major advantages of our system is time saving, particularly from the teacher's point of view. Also, this system gathers statistical data concerning different groups of students selected by the teacher. From these data on, the teacher can easily see where the students are having problems and decide what to do next. From the student (or parent) point of view, the prompt feedback about the exercises correctness, added to the training with different exercises sets about the same subject, besides the utilization of video, color, sound, etc., that positively reinforce child's senses, are elected as the main advantages. © 2011 IEEE.

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