Sensor passive

First, we may class sensors according to the activity required of the sensing system. Hence a system may be passive, active, or semiactive. Passive sensors... 

Bio)chemical sensors can be active or passive according to whether they use a sensing microzone to accommodate a chemical or biochemical reaction and/or a biochemical e.g. immunological) or physico-chemical separation e.g. sorption). It should be noted that passive sensors e.g. a fibre-optic tip immersed in an industrial process stream) do not meet one of the essential requirements included in the definition of sensors as regeirds composition... 

Probe (A) and flow-through (B) passive sensors. S sample. D ... 

Each mouse was placed in an acquainted home cage, and locomotor activity was measured for 3 h after the administration of METH, using an infrared-ray passive sensor system (SUPERMEX , Muromachi Kikai Co., Tokyo, Japan). 

Historically, the first SECM-type experiments were carried out to measure concentration profiles in the diffusion layer generated by a macroscopic substrate [3, 26]. This type of measurement represents substrate generation/tip collection (SG/TC) mode. When the tip is moved through the thick diffusion layer produced by the substrate, the changes in iT reflect local variations of concentrations of redox species (Fig. 3b). Ideally, the tip should not perturb the diffusion layer at the substrate. This is easier to achieve with a potentiometric tip, which is a passive sensor and does not change concentration profiles of electroactive species. 

Instrument Design for a Passive Sensor Based on Adaptive Speetral Imager with a Two-Dimensional Foeal Plane Array... 

Satellite information (images of visible and infrared ranges, time series from active and passive sensors onboard satellite platforms) is a necessary (in the absence of regular in situ measurements) and very effective means for monitoring the Aral Sea. 

Unlike the feedback mode of the SECM operation where the overall redox process is essentially confined to the thin layer between the tip and the substrate, in SG/TC experiments the tip travels within a thick diffusion layer produced by the large substrate. The theoretical treatment is easier when the tip is a potentiometric sensor. Such a passive sensor does not change the concentration profile of electroactive species generated (or consumed) chemically or electrochemically at the substrate. Still, a consistent theoretical treatment was proposed only for a steady-state situation when a small substrate (a microdisk or a spherical cap) generates stable species. The concentration of such species can be measured by an ion-selective microtip as a function of the tip position. The concentration at any point can be related to that at the source surface. For a microdisk substrate the dimensionless expression is (24,25)... 

It should be noted that GC mode experiments with amperometric tips may contain a feedback component to the current if the electrochemical process at the tip is reversible and the tip-to-specimen distance is less than about 5a. However, at greater distances or when employing a potentiometric tip, the tip acts approximately as a passive sensor, i.e., one that does not perturb the local concentration. This situation is quite distinct from feedback mode, where the product of the electrolysis at the tip is an essential reactant in the process at the specimen surface. This interdependence of tip and specimen reactions in feedback mode ensures that the biochemical process is confined to an area under the tip defined by the tip radius and diffusional spreading of the various reagents (20). In contrast, the biochemical process in GC mode is independent of the presence of the tip and may therefore occur simultaneously across the whole surface. In addition, the tip signal often does not directly provide information on the height of the tip above the surface methods to overcome this limitation are described in Sec. I.D. Finally, since the tip process and the biochemical reaction at the specimen are independent, a wide range of microsensors may be employed as the tip, e.g., ion-selective microelectrodes, which are not applicable in feedback experiments. 

After more than 25 years of development, prices are now at a low point for this mature product group. It is foreseen that passive sensors will be replaced by active ones because of their zero speed and rotational direction capabilities. 

The comparison of the housing geometry of active and passive sensors clearly shows the reduction of sensor dimension and weight reduction. The applied ASICs enable a large family of application-specific constructions because of their minimal packaging. Fig. 7.9.9 shows examples for further configurations. 

Table II (118) shows that the surface area, pore volume, and pore size of the deposited films vary consistently with the aging times. Thus the film structures may be tailored for such applications as surface passivation, sensors, membranes, or catalysts by a simple aging process prior to film deposition. In addition, multiple deposition schemes involving different compositions or structures or both allow the formation of complex layered architectures potentially useful for optics, electronics, or sensors.

Even though the ion-recognizing cap2d>llitles of the crown ethers and cryptands are well established, they are still "passive" sensors. The conversion of these "passive ionophores" into efficient fluorescent sensors depends on the choice of fluorogenic group and the way it is attached to these ionophores. 

Sensors can also be divided into passive and active sensors. Passive sensors achieve their output energy from an input signal such as a force or pressure active sensors achieve it from an internal source such as a chemical balance (Meijer 2008). 

The equipment to be used for the detection of anomalies will be a combination of active and passive sensors. Some of these can be described as standard for UXO-detection, others have their place in pipeline inspection or other fields of the oil- and gas-industry. The combination of these different modules is a major part of the uniqueness of this project ... 

Figure 8 presents a wider array of sensor types including active and passive sensors of different types. 

The Passive sensors acquire energy from an external source, e.g., the Sun, and for Active the energy is generated from within the sensor system, beamed ontward, and the fraction returned is measured. Other types of commonly deployed sensors in remote sensing studies are as follows ... 

The sensors employed in wearable body sensor network systems can be divided into active sensors and passive sensors. There is ambiguity in the classification, and many authors are using the other way around. In the biomedical measurement field, however, the definition of sensor type follows the convention of other electronic instrumentation fields the active sensors are those sensors that require an external power source to convert the input into a usable output signal, while passive sensors are those that intrinsically provide their own energy or derive energy from the phenomenon being... 

Most machine vision systems rely on data captured by hardware with fixed characteristics. These systems include passive sensing systems—such as video cameras—and active sensing systems—such as laser range finders. In an active vision system, the parameters and characteristics of data capture are dynamically controlled by the scene interpretation system. Active vision systems may employ either active or passive sensors. In an active vision system, however, the state parameters of the sensors, such as focus, aperature, vergence, and dlumination, are controlled to acquire data that will faciKtate scene interpretation. 

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