MICROSENSORS AND MICROACTUATORS. MICROELECTROMECHANICAL SYSTEMS(MEMS)

MICROSENSORS

1. Topic : Sensor and Actuator Interface Design .

2. Objectives Sensors, actuators and their operating principle. Micro fabrication techniques for designing and developing sensors (Several applications from Electronics to Biomedical ). Interfacing of sensors and signal conditioning circuits to establish any control system or monitoring system. Knowledge about simulation and characterization of different sensors & understanding on characteristic parameters to evaluate sensor performance. Micro technology and its use to fabricate sensors and systems , exposure & importance in the real world understanding on modern day.

3. Any tool and component that is within the machine that is responsible for the physical movement of the other parts or for actuating it is that an actuator . Sensor is when it senses the physical parameters converts into a human-readable display For example , let us talk about temperature if you can measure the temperature it is a temperature sensor Sensor and actuator there is a fundamental difference in the way both the components are defined , when you talk about actuator you can take an example of a valve. So, let us also focus on micro and nano for designing a sensor or actuators ,which are micro in dimensions and the nano material to fabricate or realize the sensors. Lot of sensors are there some sensors come with electronics embedded , some sensors that does not come with electronics.

4. So, when we talk about micro means 1 millionth . So, we talk about human hair it is about 80 to 100 microns . Now, we are talking about 1 micron. 1 micron would be about 10 to the power minus 6 . So, from meter we had 1 meter, then you say 10 centimeters and you have 1 centimeter, 1 millimeter, 100 microns, 10 microns, 1 micron, then you have angstroms then go to 1 nanometer. So, what we will be talking about is in this particular range from micro to nano all to design sensors which are of micro dimensions and same way for the actuators as well. American National Standards Institute definition is a device which provides usable output in response to a specific measurand . So, a sensor is a measurand & omnipresnt supports IoT systems, drones, and robotics they can provide information about motion, speed, direction, and range. 

5. Now, let us see physical principles and need for sensors . When talk about physical principles there are several laws that need to understand . First law is Ampere’s law , where a current carrying conductor in a magnetic field experiences a force , for example, galvanometer. While when we talk about Curie Weiss law then there is a transition temperature at which ferromagnetic materials exhibit paramagnetic behavior there is a Curie Weiss law Faraday’s law of induction most of us should know it is a coil resist a change in magnetic field by generating an voltage or current. For example, transformer are several types we know there is a step-up transformer, step down transformer and then each of them has its own core. Faraday’s law of induction works for transformer, then we talk about photoconductivity effect.

6. So, photoconductivity effect is when the light strikes the certain semi-conductor materials , the resistance of the material decreases for example, a photo resistor. So, most of the sensor they operate on certain principle either can be Amperes law, it can be Curie Weiss law, it can be Faraday’s law, it can be photoconductivity effect so on. Now, when you talk about need for sensors; what is the need? So, the need for sensors is sensors are omnipresent . The embedded in our bodies automobiles, airplanes, cellular telephones, radios, chemical plants, industry plants and countless other application. Getting knowledge of fabrication of micro sensors and actuators will help you to design a technology that can be used in healthcare domain as well as in different applications.

7. How the physical principles of sensing and sensor types are related. Studying from charges and application was from Seebeck to Peltier effects tools, understanding the conversion of thermal energy into electrical energy  Now, when we talk about sensors, sensors are fabricated using a material called silicon. So, substrate is any material on which we are going to fabricate a sensor or an actuator.

8. This is very easy definition of a substrate a material on which we are going to fabricate our device that becomes a substrate . Now, this material can be glass . So, glass can be used as substrate , this can be silicon, this can be germanium, this can be an insulating material . This can be a metal or polymer as well. So, substrates when we define it can be a material made up of polymer; semiconductor polymer will be an insulator or a conductor on which we are going to fabricate a sensor. Now, in this particular space 90 percent of the sensors are fabricated on silicon on silicon. Silicon is fabricated using sand, then what is sand? Sand is nothing, but silicon dioxide SiO2. There are two processes; one is Czochralski technique and one is Float-zone technique through which the silicon dioxide is processed . Purity of the silicon wafer that we are looking at from the silicon dioxide which is 99.9 percent pure.

9. Silicon boule is there from which the wafers are sliced and the boules are nothing, but the large logs of silicon and then this log are sliced to form the uniform silicon wafers . So, how and where would these silicon boules would be fabricated or where the silicon wafers would be sliced and fabricated. The room is much more cleaner and less of the impurities are present, because even one small single impurity of 0.5 micron will kill your entire chip. if there is a 0.5-micron particle that sits on the wafer, it will kill thousands of transistors at the same time. So, to avoid that we require to have a clean room facility.

10. Ler we discuss about fabrication of the silicon wafer , starts with the crystal growth and seed crystal (used in chemistry and materials science to create pure, well-structured crystals s inserted into the silicon melt and these are polysilicon ( is a highly pure form of silicon that is used in solar panels and electronic s) Which are heated at a high temperature, so that it becomes a melt and then this rod is inserted and it is pulled out slowly in a uniform fashion such that you start forming the single crystal silicon. Second thing is that there is a silicon melt . As you have seen there is a crucible susceptor and then there is a heater. Susceptor is a material that absorbs electromagnetic energy, like radiofrequency or microwave radiation, and converts it into heat.  Susceptors are used in industrial heating and cooking processes. It can be used in sensors to transfer heat to a target material .

11. Now, finally have to cover this with a thermal shield covering the entire system and when you pull out the silicon seed slowly, this is at lower temperature forming the single crystal silicon . Then the seed crystal is pulled out and then there is a c rystal pulling and formation of the silicon boule . The process of pulling and forming a silicon boule is called the  Czochralski process, or crystal pulling . 

12. Understanding basics about micro fabrication and technology, sensor design technology can help you to fabricate several sensors and actuators for medical domain. The same sensors and actuators can be used for other applications as well.

13. Here sensor is right in the center of this particular device that is why it is micro sensor. Contact to the micro sensor we have used some zigzag pattern not like straight lines the reason is that, now it will have a less stress when the material is flexed . Thus the contact will not get broken, it will not get damaged. Using this understand the weight of a fly . Now this is a micro fluff this a micro sensor which is capable of measuring the weight of a Housefly, itself has a lot of sensors. But are not interested in understanding the anatomy of this particular insect, we fabricate a micro sensor that is able to measure the weight of a housefly. silicon substrate that can measure the weight of a housefly.

14. The limit detection range (500×500 mm) is used as an object that can be considered as easily detectable. As a rule of thumb, the limit detection range of the sensor is 25 to 50% larger than the operating detection range. The limit detection range is viewed as the maximum reachable distance. Ultrasonic sensors : Can detect objects up to 2.5 meters away.  Infrared sensors : Typically cover short to medium ranges.  Laser, radar, and LiDAR sensors : Designed for longer distances.  Inductive proximity sensors : Have a narrow range, typically from fractions of millimeters to 60 mm.  Capacitive proximity sensors : Usually have a longer range than inductive sensors, typically between 3 and 60 millimeters.  Flame sensors : Can detect the presence and quality of fire.  Contrast sensors : Detect printed or control marks on packaging or printing machines.  Luminescence sensors : Detect visible and non-visible marks that illuminate when using ultraviolet (UV) light. 

15. Fabrication of sensors involves the design, materials selection, and processes required to create devices capable of detecting and measuring specific physical, chemical, or biological parameters. Here's an overview of the process: 1. Understanding the Sensor Requirements Type of Measurement : Identify what needs to be measured (e.g., temperature, pressure, light, gas concentration, etc.). Sensitivity and Range : Define the precision and range required. Environment : Consider operating conditions (e.g., temperature, humidity, chemical exposure, etc.). Form Factor : Size, shape, and portability requirements. 2. Materials Selection Sensing Material : The material that reacts to the parameter being measured. Examples : Polymers (chemical or gas sensors). Semiconductors (optical, temperature, or gas sensors). Metals or metal oxides (temperature or gas sensors). Piezoelectric materials (pressure or vibration sensors).

16. Substrate Material : Supports the sensor structure. Examples : Silicon, glass, flexible polymers. Electrodes : Materials for electrical signal transduction. Examples : Gold, silver, platinum, ITO (Indium Tin Oxide). 3. Fabrication Techniques Sensor fabrication depends on the sensor type and its application. Common techniques include: a) Microfabrication (MEMS Technology): Used for small-scale sensors (e.g., accelerometers, pressure sensors). Involves processes like: Photolithography : Patterning materials on the substrate. Etching : Removing material selectively (chemical or plasma etching). Deposition : Adding thin films (CVD, PVD, or sputtering). Doping : Altering electrical properties (ion implantation or diffusion).

17. c) Chemical Fabrication: For sensors detecting chemical or biological analytes . Methods: Self-assembly : Functional molecules forming layers. Electrochemical deposition : Coating electrode surfaces. Spin Coating : Uniform films for optical sensors 4. Integration Transducer Integration : Converts the sensed parameter into a measurable signal (electrical, optical, etc.). Circuitry : Amplification, filtering, and signal processing circuits. Packaging : Protection against environmental factors while allowing interaction with the target parameter. 5. Testing and Calibration Verify sensor sensitivity, accuracy, repeatability, and response time. .

18. Actuator is very important it is a mechanism which that converts some type of energy into motion in order to work. Remotely operated vehicle is called ROV and the 3 common types of energy used in ROV work are electrical, hydraulic pressure or pneumatic pressure. While the most common actuator is used in ROVs are motors solenoid valves as well as pneumatic or hydraulic and or hydraulics. So, this is the application of the actuators.

19. The common MEMS ( Microelectromechanical Systems ) phase actuators are piezoelectric actuators, thermal actuators and magnetic actuators. Examples of piezo actuators or piezoelectric actuators , as piezo resistive is different when you apply a force a change in resistance is piezo register ,a change in the voltage . So, what are the actuator materials or piezoelectric materials? The first one is PVDF which is Polyvinylidene fluoride   (used in a variety of applications, including laser scanners, touch displays, and solar trackers) Second one is zinc oxide which is ZnO (create optically switchable electrical channels) Third one is Lead zirconate titanate which is PZT(convert electrical energy into mechanical energy) and Fourth one is PMNT ( Used in piezoelectric stack actuators. PMNT actuators can be used in high-performance devices because they have high coercive fields and phase transition temperatures) So, the most commonly used piezoelectric material when you want to fabricate a micro actuator

20. In case of thermal actuators it uses the thermal expansion for actuating very effective and high force output per unit area. The actual translates in this direction for example, the actuator will move in this particular direction depending on how the cold and hot arm are changing it is temperature. So, when we apply a current input pad then there is a displacement which causes the change in the, there is a heating in the actuator which consists the change in the displacement or translates into a directional point of view.

21. The processing unit is a microelectronic circuit. Now the way is to pass the data to microelectronics. First is constantly gather data from environment, Second is pass data to microelectronics for processing and Third one is that it can measure and monitor mechanical thermal biological This is the role of the micro-sensors for monitoring several data from the environment. The micro-actuators acts as a trigger to activate external device microelectronics will tell microactuators to when to activate. So, first this sensor the data goes from the microsensors to microelectronics So, microelectronics will send the data to the microactuator to actuate . Finally, have a microstructures this microstructures are extremely small structures built onto surface of chip and built right into silicon of MEMs.

22. DESE the Department of Electronic Systems Engineering in IISC Bangalore have a class 10000 clean room. It may be around 20,000 particles of size greater than 5 microns should be limited for the given cubic meter area in cleanroom has been classified based on the particle size it is count in the given area. This is a class 10000 cleanroom and there is a certain protocol that needs to be followed

23. As an Example how to interface Sensors and Actuators with Arduino . Arduino board . It is a microcontroller that can be used to interface our sensors as well as control our actuators. An Arduino board is nothing, but a microcontroller that can be programmed; It is a development board basically. Arduino IDE where we will be doing the programming. The programming language over here is based on embedded C. The IR sensor working the white one is the transmitter and the black one is the IR receiver. So, that the light undergoes refraction right. So, when the transmitter sends IR signals, if an object is there to reflect it, it will come back to the receiver. So, based on this reflection, the receiver will get this IR light back. We have 16 PWM pins among these digital pins which can be utilized to control the speed of the motor and the other things. operating voltage is 9 to 12volt, Arduino mega board has 54 digital input-output pins.

24. In Serial communication once this function is being called, serial data will be sent from Arduino to the PC and we can use it for multiple purposes. connecting the LED to the 7 th pin as output. Since an LED is an Output, also similarly pin mode A0, connected to a potentiometer as input. Actually, we need not define A0 as input, because by default the analog pins are input only. In the void loop we take the value from the potentiometer and control it, and use it to control the brightness of the LED. This PWM signal can be used to control the brightness of LEDs; as simple as that to even just controlling the speed of motors and other devices Will be interfacing Arduino with different Sensors and also some actuators and there also you will be using these functions.

25. The design of sensor and actuator interfaces is critical in systems where physical measurements and control are required, such as in Embedded systems, Robotics, and IoT devices. Below are the main considerations and steps involved in designing a robust and efficient interface for sensors and actuators: Understand the Requirements Application Needs: Define the purpose of the system and its performance requirements, such as speed, accuracy, and precision. Sensor and Actuator Selection: Identify the sensors (e.g., temperature, pressure, proximity) and actuators (e.g., motors, valves, LEDs) needed for your application. Understand System Requirements Application Objective: Define what the system needs to measure and control (e.g., temperature, motion, light intensity). Performance Criteria: Determine resolution, accuracy, response time, and environmental conditions.

26. Select Sensors and Actuators Sensor Types: Based on input variables (e.g., temperature, pressure, humidity, light, or motion). Actuator Types: Based on required output actions (e.g., motor movement, valve operation, light, or sound). Consider compatibility with the controller in terms of: Signal type (analog or digital) Voltage and current requirements Communication protocols Signal Conditioning for Sensors Amplification: Match the signal level to the ADC input range of the controller. Filtering: Remove noise using low-pass, high-pass, or band-pass filters. Linearization: Adjust non-linear sensor outputs to create linear mappings. Level Shifting: Adapt signal levels to match the microcontroller's input specifications.

27. Communication Protocols Sensors and actuators communicate with the controller using standard protocols: Analog Interfaces: Voltage signals (e.g., 0–5V, 4–20mA current loop) Digital Interfaces: Serial Communication: I2C, SPI, UART Pulse-Based Signals: PWM, PPM Wireless Protocols: Bluetooth, Zigbee , Wi-Fi for remote sensors/actuators Power Management Ensure appropriate power supply for both sensors and actuators. Use voltage regulators and isolation (e.g., optocouplers ) if necessary. Protect against overcurrent and voltage spikes using diodes or fuses. Software Design Sensor Interface Code: Handle signal processing, calibration, and data acquisition. Actuator Control Code: Implement logic for actuation, feedback control, and safety mechanisms. Error Handling: Include fault detection and fallback mechanisms.

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