Electronic Sensors

Electronic sensors are elements used to measure and record a host of quantities of importance to engineering systems. These include sensors to measure force, torque, acceleration, pressure, strain, temperature, humidity, etc. In addition to wire resistance strain gages used to measure static strains, the piezoelectric effect is used to measure d5mamic strains. 

Valentini et al. [49] demonstrated that the three-dimensional hairlike CNFs can be used as resistive gas sensors for NO2 detection as well. A vertically aligned film with individual CNFs heavily entangled with each other is deposited between two Pt interdigital electrodes by PECVD. Because of the large diameter and abundant defects of these CNFs, the dopant effect due to the charge transfer between CNF and the NO2 adsorbates should be small. The adsorbed NO2 molecules may intercalate between the contact points of neighboring CNFs to contribute to the resistance change. 

The success of FET-based CNT gas sensors quickly attracted interest for use in biosensing applications, particularly since biomolecules such as DNA and proteins are heavily charged under normal conditions. SWCNT FETs are expected to be more sensitive than chemisorbed gas molecules to the binding of such charged species. However, the wet chemical environment with the presence of various ions and other biomolecules makes it much more complicated than gas environments. Studies demonstrated that proteins in the solution tend to adsorb irreversibly onto the bare CNT surface and induce significant change in FET characteristics [67,68]. Thus, extensive efforts have been made to passivate CNT with various polymers, such as PEI, poly(ethylene glycol) (PEG), Nafion, or Tween 20 [67,69,70]. It is conunonly accepted that a polymer or surfactant 

Besides semiconducting SWCNTs, properly doped diamonds can also be nsed as the channel material for fabricating FETs for biosensing as demonstrated by Song et al. [75]. DNA probes are immobilized directly on the aminated snr-face of a p-type polycrystalline diamond film which serves as the conduction channel between the source and drain electrodes. Since a diamond surface is chemically stable and presents a wide potential window, it permits direct contact of biomolecules with the channel surface, eliminating the needs of a polymer coating (in CNT FETs) or dielectric encapsulation (in Si-FETs). As a result, diamond FET is potentially a much more sensitive and faster biosensor, which can operate in solution. Hybridization with complementary and 3-mer mismatched DNA targets in 10 pM can be discriminated in cyclically repeated hybridization and denatnre experiments. 

Whatever system may be developed, the basic objective is the same. Different technologies may be employed, but the reason for the system is always to locate and identify explosive molecules in air, water or soil, or on a surface, in order to pinpoint the source of these molecules. Ideally, the source is located before it can be actuated in a harmful way. Consequently, every system developed for this purpose will have some characteristics in common with any other developed for the same purpose. Therefore, it is valuable to consider those common elements in a general way. 

We are faced with locating molecules that are sparse within the environment, hence the term trace. There are several basic steps that are necessary, independent of the design of the specific system or the technology being incorporated. Table 1.1 lists those steps and correlates them with more common electronic instrumentation nomenclature. Some of the actions will involve 

TABLE 1.1 Common Processes in Locating and Identifying Explosive Molecules within the Environment 

Sample Introduce a quantity of explosive-bearing medium into the system Receiver or transducer 

Separate Pass the sample through some process that preferentially selects the explosive molecules Tuner 

---

Minimization of pollutants from the combustion chamber. This approach consists of designing the engine with improved fuel-air distribution systems, ignition timing, fuel-air ratios, coolant and mixture temperatures, and engine speeds for minimum emissions. The majority of automobiles sold in the United States now use an electronic sensor/control system to adjust these variables for maximum engine performance with minimum pollutant emissions. 

Another tool the interstates use to maintain their pipelines is a device known as an intelligent pig. Propelled through the pipeline with the gas stream, these devices, taking thousands of measurements with electronic sensors that can be analyzed later by computers, can inspect pipeline interior walls for corrosion or other defects and remove accumulated debris from a section of pipeline. Pipelines also use state-of-the-art coating and cathodic protection to battle corrosion. 

Richard L. Rowe is retired chief executive officer of MCMS, Inc., a 550 million electronics contract manufacturing company. His experience includes sensor technologies applied to aviation security, and his expertise includes new technologies in optics and radio frequency, electronic sensors, and switch products. He has more than 20 years of experience in the electronic sensors and switch products in-... 

Pressure loss coefficient, 13 261 Pressure measurement, 11 783 20 644-665. See also Vacuum measurement electronic sensors, 20 651-657 mechanical gauges, 20 646-651 smart pressure transmitters, 20 663-665 terms related to, 20 644-646 Pressure measurement devices. See also Pressure meters Pressure sensors location of, 20 682 types of, 20 681-682 Pressure meters, 20 651 Pressure microfiltration/ultrafiltration,... 

The model immunoassay is the enzyme-linked immunosorbent assay (ELISA) in which a non-specific capture antibody is bound to a surface, such as a multi-well plate or small tube [13]. In the basic form of ELISA, a second antibody tagged with an enzyme interacts specifically with the analyte. The enzyme assay produces a colored product that is read with a spectrophotometer. There are many variations on the basic immunoassay format that serve to increase sensitivity, specificity, linear range, and speed. Many commercial instruments have been developed to take advantage of various technologies for reporter molecules. The immunoassay may be coupled to an electronic sensor and transducer, such as a surface acoustical wave (SAW) sensor. Electrochemiluminescence (ECL) is a method in which the detector antibody is tagged with a ruthenium-containing chelate [13-15]. When the tag is... 

Initially, in the time immediately after the sample is introduced to the flowing mobile phase and before any mixture component elutes (time 1 in Figure 11.15), the electronic sensor sees only the flowing mobile... 

FIGURE 11.15 An illustration of the tracing of an instrumental chromatogram as separated mixture components elute from the column and pass through an electronic sensor. 

It is obvious that the flow rate must be precisely controlled. The pressure from the compressed gas cylinder of carrier gas, while sufficient to force the gas through a packed column, does not provide the needed flow control. Thus a flow controller valve is built into the system. The flow rate of the carrier gas, as well as other gases used by some detectors, must be able to be carefully measured so that one can know what these flow rates are and be able to optimize them. Flow meters are commercially available. However, a simple soap bubble flow meter is often used and can be constructed easily from an old measuring pipet, a piece of glass tubing, and a pipet bulb. See Figure 12.10. With this apparatus, a stopwatch is used to measure the time it takes a soap bubble squeezed from the bulb to move between two graduation lines, such as the 0- and 10-mL lines. The commercial version uses an electronic sensor to measure the flow rate based on the bubble movement. See Workplace Scene 12.3. 

The interface gauging probe incorporates a measuring tape on a reel, connected to an electronic sensor head. The sensor head contains a float-ball and magnetic relay switch assembly that distinguishes between air and fluids also contained in... 

Electrical and electronics Sensor and logic controller Displays Motors Fleaters Power supply Electrical cord 25.00 25.002 ... 

The exploitation of ambient fuels is attractive in situations where power needs for small electronic devices are distributed, disconnected, and long-term. This might be true for electronic sensor systems for monitoring of plant health, air quality, weather, or the presence of biohazards. In principle, the fuel can be derived from carbohydrates contained in plants or from effluent of human or animal processes. 

An ideal sensor recognizes analytes in a sensitive, selective, and reversible manner. This recognition is in turn reported as a clear response. In recent years, conducting polymers have emerged as practical and viable transducers for translating analyte-receptor and nonspecific interactions into observable signals. Transduction schemes include electronic sensors using conductometric and potentiometric methods and optical sensors based on colorimetric and fluorescence methods [1]. 

In each of these situations, sensing the aroma, which, for the purposes of this book, we will consider to consist of a specific molecule or suite of molecules that is uniquely produced by its source, provides the means of identification and/or location of the source. In each of these examples the user would gain significant advantage if a very sensitive and specifically tuned electronic sensor, which could accurately and reliably identify the characteristic aroma for that application, were available. 

REST need not necessarily involve any animals at all. If electronic sensors of adequate sensitivity are developed, they can replace the animals. Certainly, the history of electronic instrument development shows that the earlier generations of any device are more suited for laboratory than field use, and that laboratory units can normally be expected to show better performance than portable ones. Calibration of an electronic instrument, which corresponds to training of a mammal, should become more precise and dependable than that training. 

U.S. Army Night Vision and Electronic Sensors Directorate, Ft. Belvoir, Virginia. 

Editor Has there been an occasion in your experience where some electronic sensor has achieved an LOD comparable to those of the animals with which you have worked ... 

Northrop Grumman Systems Corporation Electronic Sensors and Systems PO Box 17319/MS A-255 Baltimore, MD, 21203 Ph 410.993.6848 321.726.7526 (Jim Stratford) www.es.northropgrumman.com Automatic Mine Detection System, AN/AQS-14 Post Mission Analysis System and Airborne Laser Mine Detection System (ALMDS). 

U.S. Army) Night Vision Electronic Sensors Division... 

Chapter 7, Explosive Detection Using Ultrasensitive Electronic Vapor Sensors Field Experience, applies some of the concepts of the preceding chapters by describing system development work in field conditions. It describes some surprising head-to-head comparisons between dogs and electronic sensors. 

On the horizon are two new methods that are at the margin between the microelectronics industry and biotechnology One is the ability to visualize the results of a molecular test using electronic sensors the other is the capacity to alter molecular hybridization conditions through the use of electric fields. Each of these is likely to cause a stir among molecular diagnosticians. 

The critical technology development areas are advanced materials, manufacturing techniques, and other advancements that will lower costs, increase durability, and improve reliability and performance for all fuel cell systems and applications. These activities need to address not only core fuel cell stack issues but also balance of plant (BOP) subsystems such as fuel processors hydrogen production, delivery, and storage power electronics sensors and controls air handling equipment and heat exchangers. Research and development areas include ... 

Over the last decade, interest in release and delivery of VOCs has been steadily growing, with a particular focus on food, environmental and medical applications [186-190]. Consequently, considerable effort was invested to develop analytical methods capable of capturing such dynamic VOC release processes (Fig. 15.14) [179, 191]. This led to improvements in electronic sensor methods (often termed electronic noses ) [192]. 

Shaw, P.E., Rouseff, R.L., Goodner, K.L., Bazemore, R., Nordby, H.E. Widmer, W.W. (2000) Comparison of headspace GC and electronic sensor techniques for classification of processed orange juices. Lebensm.-Wiss. Technol. 33 331-334. 

---