A2.T1 Water currents measuring

Water current and direction can use ultrasonic waves in a micro device in CMOS fabrication with integration of in-system piezoelectric actuators. Recent application of this technology in domestic water-meters will allow the cost reduction of ultrasonic current meters to requirements in this project. As example, the Maxim MAX35101 is a low-cost time-to-digital converter with built-in amplifier and comparator targeted as a complete analog front-end (AFE) solution for the ultrasonic flow meter markets. Flow measurement is realized by different time-of-flight of acoustic signal in path in direct and opposite current directions.

However, salinity, turbidity and temperature variations could induce large error in measurements. The energy harvesting system from activity A3 can also be used for current measuring, since a micro turbine is expected.

Current direction will be measured with an integrated electronic compass.

A2.T2 Lab-on-chip biosensor for chlorophyll analysis

The Welschmeyer method is a new, simplified way to measure chlorophyll a without the need for acidification. Chlorophyll naturally absorbs blue light and emits red light. Fluorometers detect chlorophyll by transmitting an excitation beam of light in the 440nm (blue) range and by detecting the light emitted by the sample in the 680nm (red) range. Moreover, fluorometric measurements are not critically dependent on cuvette handling and matching, and a micro system can be  realized.

A microfluidic chip  can be developed, with a laser diode as an excitation light source, a photodiode detector and  a signal analysis circuit.  A photodetector pn-junction based on the n-well/p-substrate junction that collects more efficiently the red light can be designed and fabricated in CMOS technology. Micro-pumps and micro-valves will ensure proper and reliable operation in a real-time online system.

The microfluidic device will be fabricated using polymeric materials, due to its low-cost. Polystyrene or PDMS will be investigated depending on their hydrophobicity characteristics. If the choice sets on the PDMS, SU8 techniques will be used for the fabrication of the PDMS mold. The SU8 photosensitive resistor is chosen because it is an alternative material compared to the time-consuming and expensive technologies based on silicon and metal. The SU-8-based fabrication is a low cost process, biocompatible, UV lithography semiconductor compatible and does not require expensive masks. Moreover, SU-8-based processing enables the fabrication of deep microchannels with very low roughness that can be an added value. The SU-8 fabrication process is now implemented and characterized in the CMEMS laboratory and the team has a vast experience in fabricating devices using that [Minas, 2013] .

A2.T3 Electrochemical sensors

Indicator-based spectrophotometry pH methods are now proven and commonly used for analysis of ocean samples; however, few autonomous systems for long-term in situ applications has been developed based on this method, due to constrains inherent to the method (power, size, handling).

Ion sensitive field effect transistor (ISFET) technology will be tested in our pH sensors. The channel insulator and substrate comprising the solid-state FET are intrinsically insensitive to pressure. These characteristics (fast response time and high pressure tolerance) make the ISFET an excellent candidate for profiling applications on robotic floats/gliders, AUVs and  ROVs in addition to providing exciting new possibilities such as eddy correlation for quantifying the inorganic carbonflux across the sediment-water interface. The novel use of the Cl-ISE as a reference electrode has already led to a variety of pH measurements at high pressure from ROVs (Shitashimaet al. 2008). This would eliminate some potential problems with pressure and temperature-induced changes in liquid junction potentials that may exacerbate hysteresis during temperature cycles. As example, the Honeywell Durafet® pH sensor, a commercially available ISFET sensor exhibits stability of better than 0.005 pH over periods of weeks to months.

Salinity can be calculated from electrical conductivity typically obtained by electrochemical impedance spectrometry (at frequencies above 3kHz).

A2.T4 Turbidity, sediment accumulation,  and hidrodynamism

Turbidimeters operate based on the optical phenomena that occur when incident light through water body is scattered by the existence of foreign particles which are suspended within it. With advances in the development of photo detector sensors, later turbidimeter designs are able to detect very small changes (attenuation) of transmitted light intensity through a fixed volume sample. Here two main types of micro-turbidimeters will be tested:

Absorptiometers: which measure the absorption of a light intensity passing through the sample.

Nephelometers: which measure the portion of light scattered at angle 90° from the incident beam.

The use of piezoelectric transducers (using echo) and optical systems (using natural light as source) will be evaluated in the sediment accumulation measurement. An array (vertical shaped) of sensors will be placed in the anchor base, and the optical or acoustic influence of sediments in the array evaluated and correlated with sediment characteristics and accumulation over the array.

Micro-accelerometers and micro-barometers will be used to calculate hidrodynamism. The devices located near the surface will measure acceleration and pressure variations and these will be correlated with hydrodynamics of seawater. Barometer will also be used to calculate depth.

Research groups will be formed (for each technology to develop), supervised by activity coordinator and “Investigadror Auxiliar” contracted, to apply  the CMEMS research unit consolidated technologies in (optical, lab-on-chip, energy harvesting, CMOS design, networks and communications, sensors) in the marine application proposed.

A3.T1 Energy Harvesting and Management

Each device (or each rope) will have autonomy for 6 month monitoring. Moreover, an energy harvesting system will support longer operation, when other sources of energy area available. Since it’s intended to locate the devices completely submerged (deeper than 6m) to avoid vandalism, simple solar energy harvesting will be ineffective, since turbidity of coastal waters will absorb above 90% of available energy. Currents and turbulence will be used in electromagnetic induced micro-generators to provide extra power supply support. Energy management system will distribute available power trough the several functions of the device. When energy reaches minimum values (and when mean power consumption is reducing desired battery life) , sample rate will be reduced (and functions will be shut off) to support critical processes of device (ex. releasing as explained bellow), with available and harvested energy.

A3.T2 Underwater Communications Network

Each device (or each rope, if cost and energy requirements could not be fulfill)  includes an ultras-sonic transmitter, that can communicate with the boat in the surface. Devices are in a sleep mode to avoid energy consumption and in a programmable sampling interval, receiver are turned on to detect the presence of the boat and initiate half duplex communications. Carrier and modulation will be choose to balance energy consumption and baud-rate.

A3.T3 Sensors Integration and data management

In this task, all the sensors developed in activity A2 will be integrated with commercial sensors (temperature, pressure, accelerations) to develop the complete monitoring system, integrating also energy harvesting and management. Sampling times and data storage/management will be addressed here. Also in this task, the encapsulation of all electronic circuits and sensors will be developed. Moulded epoxy resins are a candidates for this function. Dummies and complete devices will be tested in task A8.

A3.T4  Biological colonization devices

The monitoring system will be also provided with biological colonization devices that can be released by command from the boat, allowing continuous sampling between discrete time periods. The sampling devices will be developed in order to assure the absence of contamination during the ascension to the surface (meaning the need to develop a system that can isolate the samplers from the surrounding water). A simpler release mechanism will be used to release monitoring devices from anchor when no longer needed, thus avoiding unnecessary dives and facilitating locating of devices in very turbid waters. The methodology to be developed can be applied in other situations than the coastal waters, namely in deep sea and lakes/reservoirs sampling.