Sensors and Actuators MCQ Quiz - Objective Question with Answer for Sensors and Actuators - Download Free PDF

Explanation:

MEMS Foundries

Definition: MEMS (Micro-Electro-Mechanical Systems) foundries are specialized facilities where MEMS devices are fabricated. These devices combine electrical and mechanical components at a microscale, and they are used in a wide range of applications, from automotive sensors to medical devices.

Correct Option Analysis:

The correct option is:

Option 2: 1 and 3 only

This option correctly identifies two key aspects of MEMS foundries: the use of similar tools as IC (Integrated Circuit) fabrication and the typically three-dimensional nature of MEMS structures compared to the two-dimensional nature of ICs.

Explanation:

1. MEMS foundries use the same tools as IC fabrication:

MEMS foundries indeed utilize many of the same tools and techniques employed in the fabrication of integrated circuits. This includes photolithography, etching, deposition, and other processes that have been adapted from semiconductor manufacturing. The infrastructure and processes developed for IC fabrication are leveraged to produce the intricate and precise components required for MEMS devices. This commonality in tools is due to the similar scales at which both MEMS and ICs operate, often in the range of micrometers.

2. MEMS structures are typically 3D while ICs are 2D:

MEMS devices often require three-dimensional structures to perform their mechanical functions. For example, MEMS accelerometers and gyroscopes have moving parts that interact in three dimensions to sense motion and orientation. This three-dimensional complexity is a defining characteristic of MEMS technology. In contrast, ICs are generally planar, with components and interconnections laid out in two dimensions on the surface of the semiconductor wafer. While modern ICs may have multiple layers of circuitry, their fundamental design remains primarily two-dimensional.

Additional Information

To further understand the analysis, let’s evaluate the other options:

Option 1: 1 and 2 only

This option includes the statement that MEMS production is simpler and faster than IC fabrication, which is not entirely accurate. While MEMS and ICs share some fabrication processes, MEMS production can be more complex due to the additional mechanical structures and the need for precise alignment and assembly of these components. The integration of mechanical and electrical elements often requires more intricate and varied processing steps, which can complicate and extend the production timeline.

Option 3: 2 and 3 only

This option combines the incorrect statement about the simplicity and speed of MEMS production with the correct observation about the three-dimensional nature of MEMS structures. As previously mentioned, MEMS production is not necessarily simpler or faster than IC fabrication. The additional mechanical components and the complexity of integrating these with electrical circuits can make MEMS fabrication more challenging.

Option 4: 1, 2, and 3

This option includes all three statements, one of which (the simplicity and speed of MEMS production) is incorrect. While it is true that MEMS foundries use similar tools as IC fabrication and that MEMS structures are typically three-dimensional, the assertion that MEMS production is simpler and faster is misleading and not universally applicable.

Conclusion:

Understanding the nuances of MEMS fabrication is crucial for accurately assessing the similarities and differences between MEMS and IC production. MEMS foundries utilize many of the same tools as IC fabrication, and MEMS devices often have three-dimensional structures, distinguishing them from the typically two-dimensional nature of ICs. However, MEMS production involves additional complexities due to the integration of mechanical and electrical components, making it not necessarily simpler or faster than IC fabrication.

Explanation:

MEMS Gyroscopes

Definition: MEMS (Micro-Electro-Mechanical Systems) gyroscopes are devices that measure angular velocity, the rate of rotation around a particular axis. They are widely used in various applications, including automotive systems, consumer electronics, and navigation systems. MEMS gyroscopes utilize micro-scale mechanical structures to sense and measure angular motion.

Working Principle: MEMS gyroscopes operate based on the principles of vibrating structures. Unlike traditional gyroscopes that use a rotating mass to detect angular velocity, MEMS gyroscopes rely on the Coriolis effect. The Coriolis effect causes a vibrating structure to experience a force when it undergoes rotational motion, which can be measured to determine the angular velocity.

Structure and Mechanism: The core component of a MEMS gyroscope is a vibrating structure, typically made of silicon, which is driven to oscillate at a specific frequency. When the device rotates, the Coriolis force acts on the vibrating structure, causing a change in its motion. This change is detected by capacitive, piezoelectric, or piezoresistive sensors, which convert the mechanical motion into an electrical signal proportional to the angular velocity.

Advantages:

• Compact size and lightweight, making them suitable for integration into portable and handheld devices.
• Low power consumption, which is essential for battery-powered applications.
• High sensitivity and accuracy in measuring angular velocity.
• Cost-effective production due to the use of standard semiconductor manufacturing processes.

Disadvantages:

• Susceptibility to external vibrations and shocks, which can affect accuracy.
• Temperature sensitivity, requiring compensation mechanisms for stable performance.

Applications: MEMS gyroscopes are widely used in various applications, including:

• Navigation Systems: MEMS gyroscopes are used in Inertial Measurement Units (IMUs) for navigation and control in vehicles, aircraft, and drones. They provide critical information for maintaining orientation and stability.
• Consumer Electronics: They are integrated into smartphones, gaming controllers, and wearable devices for motion sensing and user interface control.
• Automotive Systems: MEMS gyroscopes are used in vehicle stability control, rollover detection, and adaptive cruise control systems.
• Industrial Applications: They are used in robotics, machinery monitoring, and precision instrumentation for measuring angular velocity and orientation.

Correct Option Analysis:

The correct option is:

Option 2: 2 and 3 only

This option correctly identifies the key aspects of MEMS gyroscopes. They use vibrating structures (statement 2) and are commonly used in navigation systems (statement 3).

Additional Information

To further understand the analysis, let’s evaluate the other options:

Option 1: 1 and 2 only

This option is incorrect because statement 1 is not true for MEMS gyroscopes. Traditional gyroscopes use rotating mass to detect angular velocity, but MEMS gyroscopes use vibrating structures instead.

Option 3: 1 and 3 only

This option is incorrect as well because statement 1 is not valid for MEMS gyroscopes. While they are used in navigation systems (statement 3), they do not use rotating mass (statement 1).

Option 4: 1, 2, and 3

This option is incorrect because it includes statement 1, which is not true for MEMS gyroscopes. MEMS gyroscopes use vibrating structures, not rotating mass, to detect angular velocity.

Conclusion:

Understanding the working principles and applications of MEMS gyroscopes is essential for distinguishing them from traditional gyroscopes. MEMS gyroscopes utilize vibrating structures to measure angular velocity and are widely used in various applications, including navigation systems. This technology offers several advantages, such as compact size, low power consumption, and high sensitivity, making it suitable for modern electronic devices and systems.

Explanation:

Piezoelectric Materials in MEMS

Definition: Piezoelectric materials are substances that generate an electric charge in response to applied mechanical stress. This property is widely used in Micro-Electro-Mechanical Systems (MEMS) for sensors and actuators.

Working Principle: When mechanical stress is applied to a piezoelectric material, it creates an electrical charge proportional to the force exerted. Conversely, applying an electrical voltage to a piezoelectric material induces mechanical deformation. This bidirectional property makes piezoelectric materials highly valuable in MEMS technology.

Explanation of the Correct Option:

The correct answer is:

Option 2: 2 and 3 only

This option correctly identifies the statements that are accurate regarding piezoelectric materials in MEMS. Here's a detailed explanation:

Statement 1: "Silicon is an ideal piezoelectric material."

This statement is incorrect. Silicon, while being a fundamental material in the semiconductor industry and crucial for MEMS fabrication, does not exhibit piezoelectric properties. Silicon is used extensively for its mechanical properties and compatibility with microfabrication processes, but it does not generate an electric charge when mechanically stressed.

Statement 2: "PVDF and ZnO are common piezoelectric materials."

This statement is correct. Polyvinylidene fluoride (PVDF) and Zinc Oxide (ZnO) are well-known piezoelectric materials used in MEMS. PVDF is a polymer that exhibits significant piezoelectric properties and is flexible, making it suitable for various sensor applications. ZnO is a ceramic material with excellent piezoelectric characteristics, often used in thin-film form in MEMS devices for sensing and actuation.

Statement 3: "Piezoelectric materials can act as actuators."

This statement is correct. Piezoelectric materials are used as actuators in MEMS devices. When an electric voltage is applied to a piezoelectric material, it undergoes mechanical deformation. This property allows piezoelectric materials to be used as precision actuators in applications requiring fine movement control, such as in micro-positioning systems, ultrasonic transducers, and inkjet printers.

Advantages of Piezoelectric Materials in MEMS:

• High sensitivity to mechanical stress, making them excellent for sensor applications.
• Ability to produce precise mechanical movements under electrical control, essential for actuators.
• Fast response times, suitable for high-frequency applications.
• Compatibility with microfabrication techniques, allowing integration into MEMS devices.

Applications of Piezoelectric Materials in MEMS:

• Sensors: Used in accelerometers, pressure sensors, and acoustic sensors due to their sensitivity to mechanical changes.
• Actuators: Employed in micro-positioning devices, inkjet printer heads, and micro-pumps, where precise control of movement is required.
• Energy Harvesting: Convert mechanical vibrations into electrical energy, useful in powering small MEMS devices.

Additional Information:

To further understand the analysis, let’s evaluate the other options:

Option 1: 1 and 2 only

This option is incorrect because Statement 1 is not true. Silicon is not a piezoelectric material, so combining it with Statement 2, which is correct, does not make the option valid.

Option 3: 1 and 3 only

This option is incorrect because, while Statement 3 is correct, Statement 1 is not. The combination of these statements does not accurately reflect the true nature of piezoelectric materials in MEMS.

Option 4: 1, 2, and 3

This option is incorrect because, although Statements 2 and 3 are correct, Statement 1 is not. Including an incorrect statement invalidates the entire option.

Conclusion:

Understanding the properties and applications of piezoelectric materials is crucial in MEMS technology. While silicon is a cornerstone material in microfabrication, it does not exhibit piezoelectric properties. PVDF and ZnO, on the other hand, are common piezoelectric materials used for their sensitivity and actuation capabilities. Piezoelectric materials' ability to act both as sensors and actuators opens up a wide range of applications in MEMS, making them indispensable in the development of advanced microdevices.

Explanation:

MEMS Pressure Sensors

Definition: MEMS (Micro-Electro-Mechanical Systems) pressure sensors are devices that measure pressure using microfabrication technology. They integrate mechanical and electrical components at a microscopic scale to detect changes in pressure and convert these changes into an electrical signal.

Working Principle: The fundamental principle behind MEMS pressure sensors involves the deflection of a thin membrane or diaphragm. When pressure is applied, the membrane deforms, causing a change in resistance, capacitance, or frequency, depending on the sensor design. This change is then converted into an electrical signal that can be measured and processed.

Correct Option Analysis:

The correct option is:

Option 3: They use a piezoresistive membrane and can be used in catheter-tip sensors.

This option correctly identifies two key characteristics of MEMS pressure sensors. Firstly, many MEMS pressure sensors use a piezoresistive membrane. A piezoresistive material changes its electrical resistance when subjected to mechanical stress. In MEMS pressure sensors, this property is utilized to detect pressure changes. Secondly, MEMS pressure sensors are used in catheter-tip sensors. Catheter-tip sensors require small, precise, and sensitive pressure measurement capabilities, which MEMS technology provides.

Piezoresistive Membrane:

A piezoresistive membrane is a thin diaphragm made of a material whose electrical resistance changes when subjected to mechanical stress. Silicon is a common material used for this purpose due to its excellent piezoresistive properties. When pressure is applied to the membrane, it deforms, causing a change in resistance that can be measured by an electrical circuit. This change in resistance is proportional to the applied pressure, allowing for accurate pressure measurement.

Catheter-Tip Sensors:

Catheter-tip sensors are used in medical applications to measure pressure within the body, such as blood pressure in arteries or pressure in the heart chambers. These sensors need to be very small, precise, and biocompatible, making MEMS pressure sensors an ideal choice. The small size of MEMS sensors allows them to be integrated into the tip of a catheter without significantly increasing its diameter, enabling minimally invasive pressure measurements.

Additional Information:

To further understand the analysis, let’s evaluate the other options:

Option 1: They use a piezoresistive membrane.

This option is partially correct as it identifies the use of a piezoresistive membrane in MEMS pressure sensors. However, it does not address the use of MEMS pressure sensors in catheter-tip sensors, which is crucial for the complete understanding of their applications.

Option 2: They are typically reusable and costly.

This option is misleading. While some MEMS pressure sensors can be reusable, many are designed for single-use applications, especially in medical settings where sterility is essential. Additionally, MEMS pressure sensors are generally not considered costly. The microfabrication processes used to produce them can achieve high volumes at relatively low costs, making them affordable for various applications.

Option 4: They use a piezoresistive membrane, are typically reusable and costly, and can be used in catheter-tip sensors.

This option combines the correct information about the piezoresistive membrane and the use in catheter-tip sensors with the misleading information about being typically reusable and costly. Therefore, it is not entirely accurate.

Conclusion:

Understanding the characteristics and applications of MEMS pressure sensors is essential for selecting the correct sensor for a given application. MEMS pressure sensors with piezoresistive membranes offer precise and reliable pressure measurements, making them suitable for critical applications such as catheter-tip sensors in medical settings. Their small size, sensitivity, and ability to be mass-produced at low costs contribute to their widespread use in various industries.

Explanation:

MEMS Gyroscopes and Their Structures

Definition: Micro-Electro-Mechanical Systems (MEMS) gyroscopes are miniature devices that measure angular velocity or the rate of rotation around a particular axis. They are widely used in various applications, including smartphones, gaming controllers, automotive systems, and aerospace technology, for their small size, low power consumption, and high precision.

Working Principle: MEMS gyroscopes typically operate on the principle of Coriolis acceleration. When a system undergoes rotational motion, the Coriolis force acts on the moving parts within the gyroscope, causing a measurable displacement. This displacement is then converted into an electrical signal that represents the angular velocity.

Correct Option Analysis:

The correct option is:

Option 2: Vibrating structure

MEMS gyroscopes typically use a vibrating structure due to the difficulty in micromachining rotating parts. The vibrating structure gyroscopes are based on the principle of vibrating objects' tendency to retain their plane of vibration when the base rotates. The most common types of vibrating structure gyroscopes include tuning fork gyroscopes, vibrating ring gyroscopes, and vibrating wheel gyroscopes.

In a typical vibrating structure gyroscope, a proof mass is driven to vibrate at a certain frequency. When the gyroscope experiences angular motion, the Coriolis force causes a secondary vibration perpendicular to the original vibration. This secondary vibration is detected by capacitive, piezoelectric, or other sensing mechanisms, and the angular velocity is calculated.

Advantages of Vibrating Structure Gyroscopes:

• High precision and accuracy in measuring angular velocity.
• Compact size, making them suitable for integration into small devices.
• Low power consumption, which is essential for battery-operated devices.
• Robustness and reliability due to the absence of rotating parts, which are more susceptible to wear and tear.

Applications:

Vibrating structure gyroscopes are used in various applications, including:

• Consumer electronics, such as smartphones and tablets, for screen orientation and image stabilization.
• Automotive systems, for stability control and navigation.
• Aerospace, for navigation and control systems in aircraft and spacecraft.
• Gaming controllers and virtual reality devices, for motion sensing and control.

Additional Information

To further understand the analysis, let’s evaluate the other options:

Option 1: Pendulum-based

Pendulum-based gyroscopes are not typically used in MEMS devices due to the challenges in miniaturizing pendulum structures. Pendulums are generally larger and more complex to integrate into small-scale MEMS technology.

Option 3: Magnetic field loop

Magnetic field loop gyroscopes, which utilize magnetic fields to measure angular velocity, are not commonly used in MEMS technology. The integration of magnetic field loops into MEMS devices is more complex and less practical compared to vibrating structures.

Option 4: Rotary gears

Rotary gears are mechanical components that involve rotating parts. The micromachining of such rotating parts at the MEMS scale is challenging due to issues related to friction, wear, and fabrication complexity. As a result, rotary gears are not typically used in MEMS gyroscopes.

Conclusion:

MEMS gyroscopes predominantly use vibrating structures due to their simplicity, precision, and reliability. The challenges associated with micromachining rotating parts make vibrating structures the preferred choice for these miniature devices. Understanding the principles and advantages of vibrating structure gyroscopes is essential for appreciating their widespread use in various modern technologies.

Example:

• "Proximity Sensor" includes all sensors that perform non-contact detection.
• A proximity sensor often emits an electromagnetic field or a beam of electromagnetic radiation (infrared, for instance), and looks for changes in the field or return signal.
• There are various types of Proximity Sensor. These are Inductive sensor, Capacitive sensor, Ultrasonic sensor, Photoelectric sensor, and Magnetic Sensor.
• Inductive sensors are used to detect only metal objects.
• Capacitive sensors are used to detect both metallic and non-metallic objects.
• Ultrasonic sensors can detect objects in solid, liquid, or granular as well.
• Magnetic proximity sensors are proximity devices used to detect magnetic objects through their large sensing ranges.
• Proximity sensors detect objects directly in front of them by detecting the sensor’s own transmitted light reflected back from an object’s surface.

Explanation:

Capacitive Sensors: 

• A capacitor consists of a pair of conductors, since no other materials are involved, capacitive sensors are very robust and stable and applicable at high temperatures and in harsh environments.
• The dimensions of capacitive sensors may vary from extremely small, up to very large (several metres).
• The theoretical relation between displacement and capacitance is governed by a simple expression, which in practice can be approximated with high accuracy, resulting in very high linearity.
• Using special constructions, the measurement range of capacitive sensors can be extended almost without limit while maintaining intrinsic accuracy. Moreover, because of the analogue nature of the capacitive principle, the sensors have excellent resolution.

Capacitive Sensors are used in the measurement of:

• Acceleration
• Force
• Torque
• Mass (Level control of Liquids)
• Angular position (Metrology application to measure shape errors)
• Pressure (Small vessel pump control)

Hence, it cannot be used in pollution detection

Concept:

The flow rate and stem movement of equal percentage plug is related as

Q= Q₀ e^βx

Where, Q₀ = minimum flow when stem movement x is zero, β = constant and x = stem movement

Calculation:

Given:

Q₀ = 2m³/s at x = 0 mm, Q_max = 24 m³/s at x = 30 mm

So,

Q= Q₀ e^βx

∴ 24= 2e^β(0.03)

\(\therefore \beta = \frac{{{\rm{ln}}\left( {\frac{{24}}{2}} \right)}}{{0.03}}\)

∴ β = 82.83

Now, at x = 10 mm

Q = 2e^{(82.83 × 0.01)}

Concept:

• Attenuation is the process of reducing the strength of signal of particular frequencies but not of removing signal of some frequencies.
• The term filtering is used to describe the process of removing a certain band of frequencies from a signal and permitting others to be transmitted.
• The wheat stone bridge can be used to convert a resistance change to a voltage change. 
• So both the statements are incorrect.

Explanation:

The capacitance of a tank is defined to be the change in the quantity of stored liquid necessary to cause a unity change in the potential (head). The potential (head) is the quantity that includes the energy level of the system.

\(Capacitance~ of ~Tank~=~\frac{Change~ in ~liquid~ stores~in~ m^3}{Change~in~Head~in~m}\)

• The capacitance of the Tank is measure in m² 
• Capacitance in nothing but cross-sectional of the tank.

The schematic diagram of the two tank liquid level system is shown below,

where q_i, q₁, q₂ = rates of flow of fluid, h₁, h₂ = heights of the fluid level, R₁, R₂ = Flow Resistance, A₁, A₂ = cross-sectional area of tank.

The correct answer is Multiplexer.

Key Points

• A multiplexer is a circuit that is able to have inputs of data from a number of sources and then, by selecting an input channel, give an output from just one of them.
• In applications where there is a need for measurements to be made at a number of different locations, rather than use a separate analog to digital converter (ADC) and microprocessor
• The multiplexer is essentially an electronic switching device that enables each of the inputs to be sampled in turn. 

Additional Information

• Analog inputs from the sensors are accessed through a multiplexer.
• A typical board might have 8 or 16 analog input channels.
• An analog to digital converter then converts the amplified sampled signal to a digital signal.
• The control element can be set up to control the multiplexer so that each of the inputs is sequentially sampled or perhaps samples are taken at regular intervals or perhaps just a single sensor signal is used.

Explanation:

Rotary actuator:

• A rotary actuator is based on the principle of a gear motor. Fluid enters at the top with high pressure, applying force on the gear faces resulting in rotation.
• The design and construction of a vane motor are similar to a vane pump.
• At the entry, a vane has high pressure on one side, whereas on the other side the pressure will be very low due to the high pressure of the fluid.
• This difference in the pressure exerted on the vane will produce a torque that would result in the rotation of the vanes.
• Therefore, rotary actuators are the hydraulic or pneumatic equivalent of electric motors which are used when twisting or turning motion is required and is proportional to the differential pressure.

Concept:

• A multiplexer is a circuit that is able to have inputs of data from a number of sources and then, by selecting an input channel, give an output from just one of them.
• In applications where there is a need for measurements to be made at a number of different locations, rather than use a separate analog to digital converter (ADC) and microprocessor
• The multiplexer is essentially an electronic switching device that enables each of the inputs to be sampled in turn. 

Working of Multiplexer:

• Analog inputs from the sensors are accessed through a multiplexer.
• A typical board might have 8 or 16 analog input channels.
• An analog to digital converter then converts the amplified sampled signal to a digital signal.
• The control element can be set up to control the multiplexer so that each of the inputs is sequentially sampled or perhaps samples are taken at regular intervals or perhaps just a single sensor signal is used.

From the above explanation, we can say that both statement (I) and statement (II) are individually true and statement (II) is the correct explanation of statement (I).

Explanation:

Settling time:

The settling time of a dynamic system is defined as the time required for the output to reach and steady within a given tolerance band. It is denoted as Ts. Settling time comprises propagation delay and time required to reach the region of its final value. It includes the time to recover the overload condition incorporated with slew and steady near to the tolerance band.

The tolerance band is a maximum allowable range in which the output can be settled. Generally, the tolerance bands are 2% or 5%.

For 1% settling time:

\(T_s=\frac{4.6}{ξ ω_n}\)

For 2% settling time:

​​\(T_s=\frac{4.6}{ξ ω_n}\)

where ξ = damping ratio, and ω_n = natural frequency.

Concept:

One form of capacitive proximity sensor consists of a single capacitor metallic and earthed figure.

As the object approaches so the 'plate separation' of the capacitor changes, becoming significant and detectable when the object is close to the probe.

Magnetic field proximity sensors are relatively simple and can be made using a permanent magnet. The magnet can be made a part of object being detected or can be part of the sensor device It can only be used for the detection of metal object and is best with ferrous metal.