01. Working Principles of Microsensors

Electrochemical sensors work on the principle that certain biological substances, such as glucose in human blood, can release certain elements by chemical reaction. These elements can alter the electricity flow pattern in the sensor, which can be readily detected.

Biosensors work on the principle that biomolecules can react in specific ways with certain analytes. The main use of such sensors is in detecting the presence of certain biomolecules in a biological specimen, such as enzymes and proteins.

BioMEMS consist of biosensors, bioinstruments, and surgery tools, and are systems for biotesting and analysis for quick, accurate, and low-cost testing of biological substances.

Biomedical sensors are used to measure biological substances as well as for medical diagnosis purposes. They can analyze biological samples in quick and accurate ways.

Biomedical sensors require a minute amount of samples and can perform analyses much faster with negligible dead volume.

The principle application of an acoustic wave sensor is to measure chemical composition in a gas.

Acoustic wave sensors generate acoustic waves by converting mechanical energy to electrical energy.

Acoustic wave devices are used to actuate fluid flow in a microsystem.

Acoustic Wave Sensors are used as band pass filters in telecommunications, with approximately 3 billion units produced per year.

Acoustic Wave Sensors are used for tire pressure monitoring in the automotive industry.

Acoustic Wave Sensors can sense vapor, humidity, temperature, and mass.

A MEMS (Micro-electromechanical system) contains components of sizes ranging from 1 micrometer to 1 mm and is constructed to achieve a certain engineering function by electromechanical or electrochemical means.

Optical Sensors work on the principle of interaction between light and the electrons in the solids that receive the light.

Biomedical Sensors are used to detect biological substances.

Chemical sensors are similar to biosensors except that the species to be detected are chemical compounds, normally gases like carbon monoxide, ammonia, nitrogen, etc. They operate on the principle that polymers embedded in metal inserts change the electric conductivity or capacitance of the metal when exposed to particular gases, causing a change in the output current.

A microsystem is an engineering system that mostly contains MEMS components designed to perform engineering functions.

Photodiodes and Phototransistors are devices that capitalize on the properties of light for optical sensing.

Optical Sensors are capable of converting optical signals into electronic output such as in television.

A Microsensor consists of a Transduction unit and a Sensing Unit. It is built to sense the existence and intensity of certain physical, chemical, or biological quantities such as temperature, pressure, force, sound, light, magnetic flux, and chemical compositions.

A Biosensor is any measuring device that contains a biological element, such as antibodies or enzymes, which interact with analytes to be detected.

A chemiresistor sensor uses organic polymers with embedded metal inserts to detect chemical compounds by changing their electric resistance.

Photolithography principles are based on optical sensing and relevant reaction mechanisms.

Semiconductors such as gallium arsenide, p- or n- crystalline silicon, and metals such as lithium, sodium, potassium, rubidium, cesium are often used as sensing materials in Optical Sensors.

Transduction is the action or process of converting something such as energy or a message into another form.

The principal function of a microsensor is to detect.

Pressure Sensors work on the principle of mechanical deformation and stresses of thin diaphragms induced by the measurand pressure.

A chemicapacitor sensor uses polymers as the dielectric material in a capacitor to detect chemical compounds by changing their capacitance.

Photovoltaic sensors generate an electric potential when light shines on them.

The principal function of a microactuator is to move.

A Sensor is a device that converts one form of energy into another and provides the user with a usable energy output in response to a specific measurable input.

Photoconductive materials respond to light by a measurable change in its electrical resistance.

The essential components of a microsystem include a transduction/signal processing unit, a sensing unit, and an actuating unit.

Stresses and deformation in Pressure Sensors are converted into electrical signal output through several means of transduction.

A chemimechanical sensor uses polymers that change shape when exposed to chemicals to detect the presence of those chemicals.

Microsensors are the most widely used MEM device.

The two types of Pressure Sensors are Absolute and Gage Pressure sensors.

Metal oxide gas sensors use several semiconducting metals that change their electric resistance after absorbing certain gases.

Acoustic Wave Sensors detect the alterations of propagating waves through a medium that encounters changes in properties such as mass and viscoelasticity.

Acoustic waves are more related to stress or deformation of the media in which they propagate.

Actuation energy is required to generate acoustic waves in Acoustic Wave Sensors.

The Seebeck coefficient for a Type E thermocouple (Chromel/Constantan) at 0°C is 58.70 μV/°C.

The temperature range for a Type J thermocouple (Iron/Constantan) is -210 to 1200°C.

The two principal mechanisms that provide actuation energy for Acoustic Wave Sensors are Piezoelectric and Magnetostrictive mechanisms.

Piezoelectric crystals are capable of transducing mechanical energy to electrical energy and vice versa.

A Type K thermocouple is made of Chromel and Alumel.

Back side pressurization is a method of applying pressure where there is no interference with the signal transducer.

An example of a piezoelectric material used in Acoustic Wave Sensors is Lead-Zirconium-Titanate (PZT).

The Seebeck coefficient for a Type R thermocouple (Platinum (10%)-Rh/Pt) at 600°C is 10.19 μV/°C.

Front side pressurization is a method of applying pressure where the pressurizing medium interferes with the signal transducer.

Some ferromagnetic materials change their shape or dimensions when subjected to a magnetic field. These magnetostrictive materials can convert magnetic energy into kinetic energy, or vice versa.

The voltage range for a Type T thermocouple (Copper/Constantan) is -6.26 to 20.87 mV.

Factors that affect the performance of pressure sensors include the sensed pressure range, sensitivity of the diaphragm material, and the shape and thickness of the sensing die.

A thermopile is made of connecting a series of thermocouples in parallel. The induced voltage (ΔV) by the temperature change (ΔT) at the hot junction is given by ΔV = N β ΔT, where N is the number of thermocouple pairs in the thermopile.

Thermal sensors work on the principle of electromotive force (emf) produced at the open ends of two dissimilar metallic wires when the junction of the wires (called the bead) is heated.

The Seebeck Effect is the phenomenon where a temperature rise at the junction of two dissimilar metallic wires produces an electromotive force (emf) or voltage.

The sensitivity of a thermal sensor is largely dependent on the material pair used in the sensor.

The generated voltage (V) by a temperature rise at the bead (ΔT) is calculated using the formula V = β ΔT, where β is the Seebeck coefficient.