Heather Broadbent

A miniature, low cost CTD system for coastal salinity measurements

In this work we describe a small, low cost conductivity, temperature and depth (CTD) system for measurements of salinity in coastal waters. The system incorporates three low cost expendable sensors, a novel planar four-electrode conductivity cell, a planar resistive temperature device and a piezoelectric pressure sensor. The conductivity cell and the resistive temperature device were fabricated using novel printed circuit board (PCB) microelectromechanical (MEMS) techniques combined with a new thin-film material, liquid crystal polymer (LCP). Printed circuit board techniques allow for mass production of the sensors, thereby lowering the cost of the system. The three sensors are packaged so that they are independent of one another and can be quickly replaced if bio-fouled or damaged. Deployments in Bayboro Harbor, St Petersburg, FL demonstrate that the novel CTD systems are capable of obtaining highly resolved in situ salinity measurements comparable to measurements obtained using commercially available instruments. The estimated accuracies for the conductivity, temperature and pressure sensors are ±1.47%, ±0.546 °C and ±0.02 bar, respectively. This work indicates that a small, low cost CTD system with expendable/replaceable sensors can be used to provide accurate, precise and highly resolved conductivity, temperature and pressure measurements in a coastal environment.

Fabrication of a LCP-based conductivity cell and resistive temperature device via PCB MEMS technology

Printed circuit board microelectromechanical systems are a set of fabrication techniques that use traditional inexpensive printed circuit board processes to construct microsensors. These techniques keep gaining popularity and are utilized herein. The design, fabrication and construction of a miniature, low-cost conductivity cell and resistive temperature device transducers are presented. The transducers utilize a liquid crystal polymer (LCP), a thin-film material, which exhibits moisture resistant properties that makes it suitable for aquatic applications. Novel processing techniques that are reported here include the use of a direct-write photolithography tool eliminating the use of photomasks and chemical catalytic metallization of LCP material. The rapid fabrication of these devices and the repeatability of the fabrication are demonstrated by comparing the calibration of multiple devices. The sensors sensitivities are found to be 1082.40 ± 144.18 mS cm−1 per siemens and 5.910 ± 0.765 °C per ohm for the conductivity and temperature transducers, respectively.

A miniature rigid/flex salinity measurement device fabricated using printed circuit processing techniques

The design, fabrication and initial performance of a single substrate, miniature, low-cost conductivity, temperature, depth (CTD) sensor board with interconnects are presented. In combination these sensors measure ocean salinity. The miniature CTD device board was designed and fabricated as the main component of a 50 mm × 25 mm × 25 mm animal-attached biologger. The board was fabricated using printed circuit processes and consists of two distinct regions on a continuous single liquid crystal polymer substrate: an 18 mm × 28 mm rigid multi-metal sensor section and a 72 mm long flexible interconnect section. The 95% confidence intervals for the conductivity, temperature and pressure sensors were demonstrated to be ±0.083 mS cm−1, 0.01 °C, and ±0.135 dbar, respectively.

Distributed Enviromental Sensor Network: Design and Experiments

Algorithms for sensor deployment and adaptive sampling form the basis for multisensor fusion of spatio-temporal data from a wireless environmental network of deployed sensors. Derivation of sampling algorithms based on parametric methods are described. These algorithms form the basis for deployment of an array of wireless CTD (conductivity, temperature, depth) sensors to observe basic oceanographic data in Tampa Bay, Florida, USA. This distributed sensor network communicates using RF wireless 802.11b systems, and provides data in real-time to a shore observation station. In the experiments described here, five CTD sensors recorded reliable data over 25 hours. These data have been analyzed using multisensor fusion algorithms to characterize the temporal and spatial patterns. The resulting data analysis is available for integration with other observations made during these experiments, including biological and chemical variables. The approach demonstrates the ability to design and deploy a distributed sensor network that monitors real-time spatio-temporal oceanographic data, and supports further deployments that will incorporate mobile nodes capable of adaptive reconfiguration

Direct Write Patterning of Microchannels

Microchannel-based master molds or final devices are typically produced using a series of resist deposition, exposure, development and etching steps. These steps can then be repeated to create multi-layer fluidic structures. Traditional fabrication of these devices requires the use of a physical mask for the photolithographic exposure process. In the research and development environment, where designs are constantly undergoing changes, or in rapid-time-to-device applications, this can be a costly and time-consuming practice. We have employed a novel, micron-scale resolution maskless photoimaging/patterning tool that permits the creation of small, arbitrary features. This microdevice printer is useful for constructing fluidic channels, devices, structures and packages utilizing any photoimageable or photoreactive material that can be applied towards fabrication of integrated microfluidic-based systems. The fabrication technology can provide features down to 20 microns simultaneously over a 2×2 cm2 field of view. Additionally, manual stitching techniques can yield unlimited field-of-view for large area fluidic patterns with high-resolution elements. The instrument relies on the use of microoptics and spatial light modulation to create the required 2D aerial image for photoimprinting. The instrument creates mask-free designs on planar and curved surfaces and has been applied to a variety of materials, including metals, ceramics, organic polymers and semiconductors. We have demonstrated the utility of the instrument for creating mechanical, optical, fluidic and electronic components and combinations that would form the basis of integrated microfluidic systems, microanalytical systems and micrototal analysis systems (uTAS). We have also created fluidic channels having structures integrated within the channel geometry. The technology has widespread applications in the MEMS, bioMEMS, microcooling technologies and sensor markets. A further extension of the technology is the application of the direct printer to rapid prototyping of microchannels and minichannels for fuel cells, microrefrigerators, heat exchangers, and biomedical devices.© 2003 ASME

A low-cost, miniature CTD for animal-borne ocean measurements

The study of fine-scale linkages between animal behavior and the physical microstructure of the marine habitat is essential for understanding the ecology of many marine animals. Animal-borne salinity data has the potential to define the importance of physical water mass features to the ecology of marine animals. Recently CTD (conductivity, temperature and depth) data loggers mounted on large marine mammals (pinnipeds and cetaceans) have been able to capture direct qualitative information on the physical microstructure of the foraging environment and microhabitat. In order to understand the physical environment of smaller marine animals (penguins, fish and reptiles) a miniature, inexpensive CTD biologger is being developed. The biologger circuit boards are of a modular design so that several prototypes for different marine species can be developed. Currently two designs (A and B) have been fabricated and they measure 50 × 25 × 25 mm and 85 × 25 × 15 mm (unpotted), respectively. The biologger has additional internal sensors that are managed by a low-power microcontroller. The complete multisensor system measures conductivity, temperature, pressure, light, three-axis acceleration, three-axis magnetic fields, wet/dry and GPS. CTD measurements are used to calculate salinity and must be in close proximity to one another and the seawater. Therefore a novel CTD board was fabricated. The conductivity sensor was fabricated using printed circuit board (PCB) techniques and integrated with MEMS (micromechanoelectrical system) sensors, a thermistor and piezoresitive pressure module, on a liquid crystal polymer substrate (LCP). A four-electrode conductivity circuit that measures electrical resistance was designed. In this paper the biologger initial design is presented along with the conductivity cell circuit and preliminary CTD characterization data.

Micro Ion-Optical Systems Technology [MIST] for Mass Spectrometry Using PCBMEMS

Within the traditional mass spec instrumentation field there is ongoing interest in new atmospheric ion source designs for more effective and versatile ion generation. The objective of the present study is to apply organic MEMS microfabrication technologies to generation of atmospheric pressure ion optical devices. We have devised novel materials, processes, and designs for micro ion optical systems for control of ions within sources, and across apertures and conductance arrays. PCBMEMS using LCP have been used in the construction of the devices. Vacuum compatibility of the polymeric material has been found to be similar to glass in performance characteristics. Processes for shaping the polymer dielectric for fluid flow control and the metallization for electrical field control have been devised. Different geometries, both tubular and planar, combined with electrical field shaping circuitry and fluidic flow control networks are part of the effort.

PCB-MEMS Environmental Sensors in the Field

Sensor networks for in-water measurements using Organic MEMS are progressing in our research effort. PCBMEMS enabled systems, primarily in Liquid Crystal Polymer material (LCP) have emerged from the laboratory and are operational in the field. The latest progress in sensor development has yielded PCBMEMS sensors operating in the field for extended periods. In addition, we have developed the multisensor system that measures conductivity, temperature, and pressure, and combined it with a 3D system-in-package wireless module based on the 802.11b protocol to create a salinity network node and an environmental network system. The power consumption, reliability and fouling of the fieldable sensors have been evaluated. Our results indicate that biofouling has become the limiting factor for sustained performance of the multisensor system within the environment.