Improving Sensors

While much of this chapter is focused on extreme Islamist terrorism, it should be emphasized that only a tiny fraction of the world s 1.44 billion Muslims support terrorism. Terrorism is a mindset and a tactic of extremes, either right or left, ethno nationalist, or religious. There has been much progress in the war on terrorism, but as demonstrated by recent attacks, we must remain vigilant for many reasons including  

1 Some of the most skilled and resolute terrorists remain at large including Osama Bin Laden, his deputy Ayman al-Zawahiri and Abu Musab al-Zarqawi, 

2 A1 Qaeda is resilient and has morphed from a more hierarchical group into a distributed organization, which will be even more difficult to defend against, 

3 The war in Iraq has energized al Qaeda affiliates and other Islamic fundamentalist groups to fight the United States and other members of the coalition, 

4 Regional organizations have also been impacted by the war on terrorism, but remain serious threats, 

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Improved sensors allow computer monitoring of the system for safety and protection of the equipment from damage. Sensors include lubrication-flow monitors and alarms, bearing-temperature sensors, belt scales, rotation sensors, and proximity sensors to detect ore level under the crusher. The latter prevent jamming of the output with too high an ore level, and protect the conveyor from impact of lumps with too low an ore level. Motion detectors assure that the conveyor is moving. Control applied to crusher systems including conveyors can facilitate use of mobile crushers in quarries and mines, since these can be controlled remotely by computer with reduced labor. 

Household appliances make up one of the largest markets for electrotechnical and electronic products. While comparatively simple versions of sensors and microsystem products, such as temperature sensors or level sensors, have long been used in household appliances, new and improved sensors conquer the market at a breathtaking rate. The way modern sensors with intelligent control systems are used is one of the main distinguishing features between the various products and companies. 

Improved sensors will be used in many other household appliances, such as... 

Examples of small appliance features due to new or improved sensors include ... 

Some of these functions could be monitored with improved sensors, instruments and microsystems, like microspectrometers and color sensors, thermopiles, artificial noses, etc. Also some dosing and mixing functions (e. g. of herbs and spices) could be controlled by microfluidic systems. 

The need for improved sensor performance has led to the emergence of micro and nanofluidics. These fields seek to develop miniaturized analysis systems that combine the desired attributes in a compact and cost-effective setting. These platforms are commonly labeled as labs-on-chip or micro total analysis systems (pTAS)2, often using optical methods to realize a desired functionality. The preeminent role that optics play has recently led to the notion of optofluidics as an independent field that deals with devices and methods in which optics and fluidics enable each other3. Most of the initial lab-on-chip advances, however, occurred in the area of fluidics, while the optical components continued to consist largely of bulk components such as polarizers, filters, lenses, and objectives. 

During the last years, so-called microhotplates (pHP) have been developed in order to shrink the overall dimensions and to reduce the thermal mass of metal-oxide gas sensors [7,9,15]. Microhotplates consist of a thermally isolated stage with a heater structure, a temperature sensor and a set of contact electrodes for the sensitive layer. By using such microstructures, high operation temperatures can be reached at comparably low power consumption (< 100 mW). Moreover, small time constants on the order of 10 ms enable applying temperature modulation techniques with the aim to improve sensor selectivity and sensitivity. 

I. Simon, N. Barsan, M. Bauer, and U. Weimar. Micromachined metal oxide gas sensors opportunities to improve sensor performance . Sensors and Actuators B73 (2001), 1-26. 

Artificial neural networks arose from efforts to model the functioning of the mammalian brain. The most popular ANN — the feedforward ANN — has deeper roots in statistics than in neurobiology, though. A form of ANN (a Probability Neural Network) has been used within a QPA context to improve sensor data reliability, but not as an on-line quality model [57]. The best way to represent a feedforward ANN as an on-line quality model for SHMPC is... 

Sensors or analyzers exist for some of the priority analytes, such as 09, pH, and N03 . The challenge in these cases is to improve sensor stability, response rates, or lifetime. However, for most of the priority analytes, there is no existing sensor or analyzer system that will operate for long time periods without operator intervention. The development of sensors for most of these analytes, such as chlorofluorocarbons or dissolved iron, must circumvent the difficulties posed by low analyte concentrations or interference from other dissolved material. Development of specific sensing chemistry is the ultimate means of circumventing these problems. 

A similar approach has been used to solve more complicated cases of two enzymes in one layer (Schulmeister and Scheller, 1985, p. Ill) and the multi-layer/multienzyme model (Schulmeister, 1987, p. 223). It is important to note that oxidases are one of the largest group of enzymes and therefore the improved sensors for substrates other than glucose can and have been developed according to this scheme. 

Before any discussion of potential targets or coping strategies to improve sensor performance, the foreign body reaction as understood by the scientific community must be reviewed. In this chapter, the foreign body reaction will be categorized into two broad segments minutes to days and days to months. 

Our belief is that vascularizing compounds can increase vessel growth within the encapsulation tissue surrounding a foreign body and probably improve sensor function modestly. Nonetheless, they have not been found to overcome the relentless process of collagen deposition and capsule formation caused by the foreign body reaction, which eventually blocks sensor function. In addition, they could have several major side effects. 

Polyurethanes have also been employed as outer sensor membranes. Yu et al. evaluated the biocompatibility and analytical performance of a subcutaneous glucose sensor with an epoxy-enhanced polyurethane outer membrane.15 The membrane was mechanically durable and the resulting sensors were functional for up to 56 days when implanted in the subcutaneous tissue of rats. Despite the improved sensor lifetime, all of the polyurethane-coated sensors were surrounded by a fibrous capsule, indicating an enduring inflammatory response that is undesirable due to the aforementioned effects on analytical sensor performance. To date, the clinical success of most passive approaches has been rather limited. It is doubtful that one passive material alone will be capable of imparting long-term (i.e., weeks to months) biocompatibility for in vivo use due to the extremely dynamic nature of the wound environment. 

The line shifts of f-f transitions discussed in sect. 4.2, offer an interesting possibility to establish high pressure gauges. As mentioned in sect. 2, ruby is still the most widely used gauge for pressure determination. However, some deficiencies caused a continuous search for improved sensor materials. Especially the temperature induced broadening and quenching limits the application of ruby to below 500 °C. 

During recent years there has been an increasing demand for better operation of wastewater treatment plants in order to guarantee satisfactory effluent quality at minimal cost. The renewed interest in instrumentation and control comes after a period of huge investments in sewer networks and treatment plants. Several factors have contributed to the potential for better operation and control, such as cheap computing power, improving sensors and better knowledge of process dynamics and control. 

Alternative ways to improve sensor sensitivity and stability of the bienzyme system reported use of redox polymers for bienzyme systems, specifically to interact with HRP instead of with oxidoreductases. 

Subsequently, Schuhmann reported GOx entrapment by ferrocene derivatives attached to the enzyme outer surfrce via long flexible polyethylene spacer chains within polyp5Trole films [126]. However, this system still did not significantly improve sensor sensitivity and the author pointed out that modifications are needed to increase the concentration of redox relays to enhance the sensor efficiency. 

Compared with sensing based on intrinsic analyte properties (e.g., spectroscopic, dielectric, paramagnetic), sensing that utilizes a responsive sensing material1-8 dramatically expands the range of detected species, improves sensor performance (for example,... 

It can be seen from the above discussion that the use of nanoionic materials for gas sensors is a natural extension to the findings already reported. Nanosized materials offer advantages in terms of improved sensor response due to the much higher surface areas available. However, the definition of a nano ionic sensor material can be very broad the nanoionic component of the sensor material might refer to the bulk majority phase, but alternatively it could refer to a dispersed catalytic or dopant phase, or even a combination of both. 

Nickel oxide has also been used as the electrode material for NO sensors [264—274]. One of the advantages of NiO electrodes is the improved sensor response at high temperatures. Figure 13.23 shows the sensitivities of XO, sensors with WO3 [254—259, 262] or NiO [264—269] electrodes. As shown above for CO sensors, the responses of sensors vhth WO3 electrodes decrease as the temperature is increased above 600 °C. The responses of sensors with NiO electrodes, however, remain high up to operating temperatures of900 °C. The response of NiO electrodes can be increased even further with the addition of ruthenium [268]. 

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