08-05-2014, 11:32 AM
smart sensors
smart sensors.docx (Size: 183.5 KB / Downloads: 10)
Introduction:
The advent of integrated circuits, which became possible because of the tremendous progress in semiconductor technology, resulted in the low cost microprocessor. Thus if it is possible to design a low cost sensor which is silicon based then the overall cost of the control system can be reduced .We can have integrated sensors which has electronics and the transduction element together on one silicon chip. This complete system can be called as system-on-chip .The main aim of integrating the electronics and the sensor is to make an intelligent sensor, which can be called as smart sensor. Smart sensors then have the ability to make some decision. Physically a smart sensor consists of transduction element, signal conditioning electronic and controller/processor that support some intelligence in a single package. In this report the usefulness of silicon technology as a smart sensor, physical phenomena of conversion to electrical output using silicon sensors, characteristics of smart sensors. A general architecture of smart sensor is presented.
Definition:
Smart sensors are sensors with integrated electronics that can perform one or more of the following function logic functions, two-way communication, make decisions.
Usefulness of Silicon Technology in Smart Sensor:
There are very convincing advantages of using silicon technology in the construction of smart sensor. All integrated circuits employ silicon technology. A smart sensor is made with the same technology as integrated circuits. A smart sensor utilizes the transduction properties of one class of materials and electronic properties of silicon (GaAs). A transduction element either includes thin metal films, zinc oxide and polymeric films. Integrating electronics circuits on the sensor chip makes it possible to have single chip solution. Integrated sensors provide significant advantages in terms of overall size and the ability to use small signals from the transduction element. The IC industry will get involved in smart sensor if a very large market can be captured and the production of smart sensor does not require non-standard processing steps.
Signal conversion effects:
We know that silicon shows a suitable physical signal conversion effect. Many of the physical effects of silicon can be used in making sensors. Based on these effects, different types of sensors can be constructed which can be used for measuring different physical and chemical measured.
Table1 below shows how different non electrical signal in which we can classify different measured and Table 2 shows the physical effects for sensors in silicon.
Thermal Signal Domain:
We know that all electron devices in silicon show temperature dependence, this property of silicon can be used for the measurement of temperature. This can be achieved by using two bipolar transistors with a constant ratio of emitter current. Another way of measuring temperature is to integrate thermocouples consisting of evaporated aluminium films and diffused p-type and n-type layers. This is possible because See beck in silicon is very large.
Magnetic Signal Domain:
Silicon is a non –magnetic material but it can be used for the construction of Hall plates and transistor structures that are sensitive to magnetic fields. These sensors are constructed by depositing a thin magnetic Ni-Fe film on top of silicon chip that also contains electronic circuits.
Importance and Adoption of Smart Sensor:
The presence of controller/processor in smart sensor has led to corrections for different undesirable sensor characteristics which include input offset and span variation, non-linearity and cross-sensitivity. As these are carried in software, no additional hardware is required and thus calibration becomes an electronic process. Thus it is possible to calibrate the batches of sensor during production without the need to remove the sensor from its current environment or test fixture.
Conclusions:
In conclusion, silicon is very suitable material for fabrication of smart sensors. But still a lot of research is required to get benefits of the smart sensor, but from the experience of already existing devices, we can expect that in the coming decade a large number of successful smart sensors will emerge.