SENSOR TECHNOLOGIES
Abstract:
Recent advances of sensor technologies have been powered by high-speed and low-cost
electronic circuits, novelsignal processing methods, and advanced manufacturing technologies. The
synergetic interaction of new developments inthese fields provides promising technical solutions
increasing thequality, reliability, and economic efficiency of technical products.With selected
examples, we will give an overview about the significant developments of methods, structures,
manufacturing technologies, and signal processing characterizing today’s sensors andseI.
INTRODUCTION:
The Competition in markets requires the permanentenhancement of quality and reliability of
products. Therising demand for automation, security, and comfort leads to completely new
applications for sensor systems. The number ofsensor systems required and the diversity in most
applicationsare permanently increasing. To keep up with the new requirements, the design of
sensor systems is required to provide novelapproaches and solutions profiting from recent
developments inscience and technology.Sensors and sensor systems achieve their function
through aninterlocked interaction of sensor structure, manufacturing technology, and signal
processing algorithms.The developments in sensor technology are consequentlybased on the
permanent technical progress in these fields. Particularly, in the last years, a significant upturn is
observed in these fields involving a great potential for completelynovel approaches of sensors and
sensor systems. Using newtechnologies and signal processing methods, even
well-knownmeasurement principles could be used, leading to considerablyimproved sensor
features.
SENSOR STRUCTURE:
In the kernel of a sensor system is the sensor element,which changes its output depending on the
measured quantity.In a preprocessing unit, the sensor signal is transformed in an adequate
amplified and filtered signal using analog signalprocessing techniques. Using digital signal
processing, themeasured quantity can be calculated under consideration ofmanufacturing
variance, influence factors, and aging processesnsor systems. Predominantly observed
development trends in thefuture are discussed.
By means of low-cost analog-to-digital converters, signal processing is increasingly shifted from the
higher system level in the sensor level. The diverse facilities in digital signal processing involve new
approaches for the improvement of sensor properties. Calibration and consideration of several
effects,such as manufacturing variance or cross sensitivity, become a simple task.Embedding other
functions, such as online self-test or selfcalibration, is today winning a special importance,
improvingthe system reliability, and reducing installation and maintenance costs.The structure of a
sensor with self-monitoring differs from the standard structure in particular through the
consideration of supplementary knowledge to the actual measurement information.Generally,
specific relationships are required about the sensor behavior and the expected confidence limits of
sensor properties .The state of the sensor system can be inspected by a comparison of the real
output to the expected value due to the previously known relationships . For instance, acceleration
sensors with a closed-loop structure compensate the inertial force acting on the mass through an
electrically generated restoring force . Through the application of restoringforces with well-known
values, self-tests can be carried out.
TECHNOLOGY SENSOR:
Many recent advances in the sensor technology become mainly possible by means of micro
technologies. These new technologies offer high-volume manufacturable systems with small
dimensions, lower power consumption, and higher reliability. Thereby, realized microsystems
integrate sensors, actuators, mechanical, and electronic units. They provide low-cost solutions that
were not realizable with microelectronic systems. Their development involves special challenges
for device modeling, microfabrication, material, and packaging technologies. Micromachined
systems are today already inherent components in automotives, color printers, mobile phones,
and medical systems. The most popular micromachined sensors are pressure, angular rate , and
acceleration sensors. They allowed the widespread implementation of low-cost airbag systems and
catalytic converters. Silicon micromachining is one of the most significant micro technologies for
sensor systems . The eminent properties of the silicon material, such as the freedom of hysteresis
errors, and the earlier advances in the field of microelectronics have permitted this important
technical evolution.In case of bulk micromachining, the substrate is structuredby means of wet and
dry etching processes. The high etchingselectivity and reliability are the advantages of the bulk
micromachining . In an isotropic process, the etching speed is independent from the direction in
the substrate. In this case, theobtainable device configurations are limited and the silicon material
may not be efficiently utilized. In an anisotropic process, the etching speed is orientation
dependent. The manufactured structures in bulk micromachining have from the beginning a high
aspect ratio. This means that the structure height is high relative to the minimal lateral dimension
of the whole structure.This property involves considerable advantages for sensor performance,
such as higher sensitivity, displacement, mechanical robustness, and reduced noise.In case of
surface micromachining, three-dimensional mechanical structures are developed by a sequential
deposition and selectively removing of sacrificial layers (e.g., SiO ) separating the individual layers
in the structure. Recently, the use of reactive ion etching (RIE) allowed a cost-effective realization
of structures
FUTURE TRENDS IN SENSOR TECHNOLOGY:
The development trends in sensor technology result frommarket-economical aspects, general
customer requests, andspecific requirements of the target applications.Costs reductions and more
improvement in accuracy and speed will be achieved in the future using measurement methods
with higher performance, new manufacturing technologies, and sophisticated signal processing
methods. The greater demand for environmental protection demands the development of highly
reliable sensors. Maintenance-free sensors with long life expectancy and low electric power
consumption will, thereby, be the focus of interests. The main development trends in sensor
technology are, ingeneral, toward miniaturization and an increasing use of multisensor and
wireless systems .
Microsystem Technology Miniaturization: is an outstanding strategy of success in modern
technologies. A reduction of characteristic dimensions usually results in shorter response times so
that a correspondingly higher speed is achievable in signal generation and processing. In many
cases, it reduces costs because of the higher integration rate, lower power consumption, and
higher reliability. Miniaturization is generally gaining importance in all fields of applications, where
smaller structures and greater precision are becoming decisive to the market acceptance of
individual products. The development trend to miniaturization goes on within nanotechnologies,
which will open up access to still smaller dimensions . For instance, for the monitoring of vital
parameters of human beings, health care devices can be used so that an emergency call could be
released automatically in case of unconsciousness ofthe observed person. For acceptance by users,
the device should be light and provide unhindered mobility. The user should be able to ignore it
and to live normally without being obliged to take it off in any situation during the whole day.The
concept of the MIT-ring, as a highly miniaturized solution, fulfills the requirements for this special
application. A light-emitting diode in the ring continuously emits lightinto the finger of the
observed person. By an evaluation of thereflected light, the ring can measure the pulse rate, the
potential l cardiac condition, and possibly blood pressure. By means f an embedded antenna,
signals can be transmitted to a signal receiver nearby.
Trend in use of sensor :
The use of multisensor systems is becoming more important in widespread applications. Their
applications reach from the monitoring and automation of manufacturing processes to robotics,
automotive applications, smart home. Future trends in sensor technology.MIT-ring for healthcare,
process control, environmental engineering, biotechnology, and life sciences. Multisensor systems
provide the advantage that economical sensors can be used even for the achievement of a high
level of precision and reliability. Thereby, a big amount of availableinformation is managed using
sophisticated signal processing techniques so that the system achieves a better
performance.Multisensor data fusion is in effect intrinsically performed by animals and human
beings to achieve a more accurate assessment of the surrounding environment. A directly related
example is the electronic nose, which consists of an array of different sensors that have been
shown to respond to definite organic and inorganic compounds with low concentrations. In order
to reach a high resolution at low concentrations, the response of a sensor array is used like in the
real human nose. The applications of the electronic nose are widespread in the chemical analysis,
environment monitoring, food and wine inspection, emission control, and narcotic detection.The
development trends of multisensor systems are in the development of modular systems, which are
easily extendible with new units without disturbing the already available functions.
Trend in Wireless Systems:
With the large amount of components, which are indispensable for the achievement of the
required functionality, the electric wiring of spatially distributed systems becomes complex and
causes difficulties in the system’s handling. The use of wireless systems implies a better
convenience and leads to a considerable cost reduction. Wireless sensor systems have the
advantage that they can be placed anywhere, and can,therefore, record the measured quantity
closely to its occurrence, independent of potential harsh circumstances.
Wireless sensors can communicate over ultrasonic or infraredsignals. For instance, surface acoustic
wave devices(SAW transponders) can be used for object identificationand for the measurement of
physical, chemical, and biological uantities such as temperature, pressure, torque, acceleration, or
humidity.nergy-autonomous sensors will gain a particular importance mong wireless sensors [13]
because, in this case, wires are no onger necessary, even for electricity supply. This kind of sensor s
necessary for many applications in which long distances are o be bridged, or a large number of
distributed components are necessary