We report on the development and application of an aqueous sensor network (ASN). Designed for operation in lakes or drinking water reservoirs, the immersed ASN nodes are secured in place at a controlled depth by use of anchors with a node to node separation distance of ≤ 20 m. The individual nodes are integrated with various types of sensors enabling measurement of both physical and chemical analyte parameters. Node operation is overseen by programmable microcontrollers; the software on the microcontrollers is structured in a modular format so it can adapt to different types of sensors without extensive reprogramming. Node-to-node communication is achieved using timed bursts to avoid interference from unwanted signal reflections arising from the impedance mismatch at the water-air and water-land interface. We report on the application of the ASN for monitoring temperature and pH throughout a small pool. As desired the individual nodes of the ASN can be integrated with suitable chemical/biological sensors to detect down stream effluents from a source, or to ensure water reservoir quality.
Magnetoelastic sensors, made of amorphous metallic glass ribbons or wires, have been used to measure various environmental parameters such as temperature, humidity, viscosity, and chemical concentration including pH, carbon dioxide, and ammonia. The parameter of interest is determined by remote detection of the shift in the resonant frequency of the magnetoelastic sensors, which is dependent upon several factors including stress, pressure, temperature, and magnetic field. This paper describes the operating principles of the magnetoelastic sensors and presents several proven applications, as well as methods for optimizing the sensor performance.
The inductor-capacitor (LC) sensor, comprised of a thick- film printed LC resonant circuit the resonant frequency of which can be remotely detected with a loop antenna, has been used for the monitoring of temperature, humidity, atmospheric pressure, salt concentration, and complex permittivity, as well as the detection of bacteria in a liquid medium based upon changes in the complex permittivity due to the bacteria growth. Due to its low unit cost and wireless detection, the LC sensor is potentially suitable for commercial scale monitoring of food quality. This paper includes the operational principles and design criteria of the LC sensor, and illustrates the monitoring of bacteria growth in milk, meat, and beer.
This paper begins with an overview of nanostructured magnetoelastic materials, namely the amorphous ferromagnetic alloys, detailing how the material structure gives rise to unique magnetic and physical properties suitable for sensor applications, such as a high magnetostriction coefficient, high magnetoelastic coupling, as well as low coercive force and anisotropy field. With the correlation between the material structure and the magnetic and physical properties established, we then show how these unique properties are utilized for measuring multiple physical parameters such as stress/strain, liquid density and viscosity, fluid flow velocity, coating elasticity, ambient temperature, and chemical analyte concentrations including glucose, pH, carbon dioxide, and ammonia.
Although acoustic wave sensors that use piezoelectricity have many advantages, all of them need electrical connections to excite the piezoelectric crystals with an alternating voltage. This paper presents a new type of continuously operating, in-situ, and remotely monitored sensor that doesn't require electrical connections. The new sensor is comprised of a magnetoelastic metallic glass ribbon. Its sensing principle is similar to acoustic wave sensors. An externally applied alternating current (ac) magnetic field is used to excite magnetoelastic waves inside the magnetoelastic thin ribbon. Frequency responses are monitored with a pickup coil located outside the test area and the resonant frequencies are measured. The sensor responds to mass loading as a microbalance by decreasing its resonant frequency. When immersed in liquid, its resonant frequency is correlated with the square root of the product of liquid viscosity and density. We studied the relationship between the frequency shift and the square root of the product of viscosity and density of a starch solution. We found that the frequency shift was linearly proportional to the starch concentration. After bonding a poly-hydroxyethyl acrylate (poly-HEA) membrane to the magnetoelastic ribbon, the sensitivity of the sensor to water loading was greatly increased. The new sensor has also been used to monitor polymer curing. After bonding the ribbon with a pH sensing membrane, it was used to monitor pH. Because the sensor does not require electrical connections, it can remotely monitor concentrations in situ in a sealed container.
Magnetoelastic thin film sensors can be considered the magnetic analog of surface acoustic wave sensors, with the characteristic resonant frequency of the magnetoeleastic sensor changing in response to different environmental parameters. We report on the application of the magnetoeleastic sensors for remote query measurement of pressure, temperature, liquid viscosity and, in combination with a glucose- responding mass-changing polymer, glucose concentrations. The advantage of using magnetoelastic sensors is that no physical connections, such as wires or cables are required to obtain sensor information allowing the sensor to be monitored from inside sealed containers. Furthermore since it is the frequency response of the sensor that is monitored, rather than the amplitude, the relative orientation of the sensor with respect to the query field is unimportant.