Six Sensor Principles

Ⅰ. What is a sensor?

The element or device that converts the received data into a signal that can be processed by the device is referred to as a sensor.

Humans will behave based on information obtained through sight, hearing, smell, and touch, while equipment will regulate or process information obtained from the sensor, 

Temperature, light, color, air pressure, magnetism, speed, acceleration, and other signals (physical quantities) are among the signals (physical quantities) collected and transformed by the sensor  .

There are other biosensors that use biological components such as enzymes and bacteria, in addition to these changes in materials that use semiconductors.

IoT and sensors

The Internet of Things  (IoT) is a concept in which all objects are linked to the Internet.

Medical equipment, wearable gadgets, automobiles, natural habitats, infrastructure, and other items can all be connected to the Internet to share information, resulting in a more convenient, secure, and safer society.

The "sensor" that detects the state is required for these to be realized.

[Definition of terms related to  IoT ]

The Internet of Things  (IoT) is a situation in which sensor  s are embedded in surrounding items and connected to one another, allowing objects and people to communicate with one another.

Industry 4.0 in Germany: It is a German government-proposed concept for improving industrial intelligence, as well as a national project supported by business, government, and academia. Introducing a new concept in the manufacturing that uses the Internet of Things  to create new value.

Machine to Machine (M2M) refers to direct communication between items via networking without the use of a human as a middleman. P2M stands for "People to Machine Communication," while M2P is for "Machine to People Communication."

GE's industrial  IoT strategy is referred to as the "Industrial Internet" (Generel Electric Company).

Ⅱ. Geomagnetic  sensor 

The magnetic force of the magnetic field surrounds the earth, which is known as geomagnetism.

The geomagnetic sensor.  sometimes known as a "electronic compass," is a sensor  that senses the earth's magnetism.

By detecting geomagnetism, the geomagnetic sensor  can determine the direction.

[Geomagnetism around the earth]

The geomagnetic sensor  monitors the magnetic force value in all directions and has two axes (X and Y) and three axes (with Z).

Only the X and Y axis data are used if tilts such as simple compasses are not taken into account. When considering tilt, the 3-axis value of the geomagnetic  sensor must be combined with the acceleration sensor to adjust it to the proper direction.

When the geomagnetic sensor spins horizontally, the distribution of X and Y readings is shown in the diagram below.

Under ideal conditions, the center of the output distribution graph becomes zero when the geomagnetic sensor rotates horizontally without being impacted by the surrounding magnetic field.

However, because the center of the circle moves owing to the impact of the external magnetic field, adjustment is required to bring the circle's center to zero.

The magnetic north pole is the north pole determined by a geomagnetic sensor (slightly deviated from the north pole). The direction can be easily determined by using the above equation to get the angle of the magnetic north.

Magnetic sensors come in a variety of shapes and sizes.

A magnetic sensor is a device that measures the strength and direction of magnetic fields.

There are many different types of sensors for various applications; the following is a list of common sensors.

Hall sensor

A sensor that uses the Hall effect to assess magnetic flux density and outputs a voltage proportional to the flux density.

It's simple to operate and is primarily used for non-contact switch applications, such as detecting the opening and closing of doors and computers.

Sensor for magnetic resonance imaging

The MR (Magneto Resistance) sensor.  also known as a magnetoresistance effect sensor.  measures the amount of geomagnetism by measuring the change in object resistance caused by a magnetic field.

Because of its better sensitivity and lower power consumption than the Hall sensor.  it is a more extensively used magnetic  sensor ,  It's also utilized for motor rotation and position sensing, in addition to geomagnetic detecting applications like electronic compasses.

MI sensor

The MI (Magneto Impedance) sensor is a next-generation magnetic sensor that employs the magneto-impedance effect and requires a specific amorphous wire.

It has a sensitivity more than 10,000 times that of the Hall sensor, and it can accurately assess minor changes in geomagnetism.

It can be used for ultra-low-current location detection (electronic compass) as well as applications with high sensitivity features, such as indoor positioning and metal foreign body identification.

Ⅲ. Pulse sensor

The pulse wave is the volume change waveform of a blood artery formed when the heart transmits blood, and a pulse sensor  is the detector that measures the volume change.

For starters, electrocardiography, photoelectric pulse wave method, blood pressure measurement method, and phonocardiography are the four ways for monitoring heart rate.

The photoelectric pulse wave method is a pulse sensor-based measurement method.

The pulse sensor of the photoelectric pulse wave technology has two types: transmission and reflection, due to the different measuring methodologies.

By irradiating infrared or red light to the body surface and measuring the pulse wave as the amount of change in light transmitted through the body, the transmissive type analyzes the change in blood flow that changes with the heart's pulse.

This procedure can only be used on regions of the body that are easily pierced,

Reflective pulse sensor 

The reflecting pulse sensor irradiates a living body with infrared, red, and green light with wavelengths of around 550 nm, and measures the light reflected by the live body using a photodiode or phototransistor. In arterial blood, oxygenated hemoglobin exists, and it has the ability to absorb incident light. As a result, it detects the blood flow (change in blood vessel volume) that fluctuates over time and with the heartbeat to determine the pulse signal.

Furthermore, unlike transmission measurements, there is no need to limit the measuring location with reflected light measurements.

[Principle of reflective pulse sensor  ]

When the infrared or red light is used to detect the pulse wave, it is impacted by the infrared rays found in outside sunshine, making it impossible to obtain a stable pulse wave measurement. As a result, it is only suggested for indoor or semi-indoor applications.

The rate of hemoglobin absorption in the blood is high in outdoor applications such as sports watches. We utilize a green LED as the illuminating light since green light is less impacted by ambient light.

Pulse sensor application

In general, the following two points can be used to determine arterial oxygen saturation (SpO2). Examine the heart rate (pulse rate) using the waveform acquired by the pulse sensor's fluctuation period; observe the pulsation (variation) using two wavelengths of infrared and red light.

Furthermore, with high-speed sampling and high-precision measurement, it is predicted to acquire various vital indicators such as HRV analysis (pressure level), blood vessel age, and so on as a pulse sensor application.

Ⅳ. Barometric pressure sensor 

A sensor that senses atmospheric pressure is known as an air pressure sensor, 

The pressure sensor has sensors of various materials and methods depending on the pressure value to be measured, as indicated below.

The sensor that measures atmospheric pressure (used for air pressure detection) is commonly referred to as an air pressure sensor, 

[Materials used-Pressure sensors classified by method]

A piezoresistive air pressure sensor made of silicon (Si) semiconductors is a common variety.

ROHM's air pressure sensor is a piezoresistive air pressure sensor as well.

Piezoresistive air  pressure sensor  

The piezoresistive air pressure sensor uses a Si single crystal plate as a diaphragm (pressure receiving element), forms a resistance bridge circuit by diffusing impurities on its surface, and calculates the pressure (air pressure) by using the deformation caused by pressure as the resistance value change.

[Piezoresistive air pressure sensor]

The piezoresistive effect is a phenomenon in which the resistivity (conductivity) of resistance varies as a result of pressure applied to it. ROHM's air pressure sensor  IC incorporates piezoresistive pressure-receiving elements (diaphragm structure and piezoresistance are integrated*MEMS), as well as integrated circuits (*ASIC) such as temperature correction processing and control circuits, into a single package that can be easily installed. Obtain high-resolution air pressure data.

MEMS (Micro Electro Mechanical System) is an acronym for Micro Electro Mechanical System (Micro Electro Mechanical System)

On a circuit board, a device that incorporates mechanical components, sensors, and actuators (drive components).

Use Specific Integrated Circuit (ASIC) is a type of integrated circuit that is designed for a specific application (application-specific integrated circuit)

It's a type of integrated circuit that combines several circuit functions into a single device.

Ⅴ. Accelerometer

The IC that monitors acceleration is known as an acceleration sensor ,  Acceleration refers to the speed generated per unit time.

The tilt and vibration of the object can be measured by measuring its acceleration.

m/s2 (International System of Units SI) is the unit of acceleration.

Furthermore, the unit G represents an acceleration value based on gravity (1 G = 9.806 65m/s2).

There is also a unit *Gal (CGS unit system) that is used to identify earthquake vibration acceleration.

SI (International System of Units) (Système international d'unités) (French: Système international d'unités) (French: Système international d'unités) (F

A combination of length m, weight kg, and time s makes up the international unit (MKS units).

a normal gravity

The acceleration of an object is due to gravity's influence. When the object is in free fall, the object's speed per unit time (9.806 65m/s2) is calculated.

※ Gal

The CGS (length cm, weight g, time s) unit system's acceleration unit. It's 1/100 of the SI unit system (1Gal=0.01 m/s2).

As illustrated in the diagram below, acceleration sensors are classified into two categories: low G acceleration sensors and high G acceleration sensors.

Capacitive acceleration sensor

The Rohm Group acceleration sensor is a MEMS-based capacitive acceleration sensor, 

A fixed electrode made of Si, a moveable electrode, and a spring makes up the sensor element. The distance between the fixed electrode and the movable electrode is the same when no acceleration is applied. The movable electrode is shifted when acceleration is applied. As a result, the inter-electrode capacity changes as well as the positional relationship with the fixed electrode. The  ASIC  converts the change in capacity into voltage and calculates the acceleration.【Capacitive principle】

※ ASIA

ASIC (application-specific integrated circuit) is an integrated circuit that combines numerous circuit functions for a given purpose.

Ⅵ. Current sensor

What is a current sensor?

The current sensor refers to a sensor that detects the value of current flowing in a circuit.

Current detection method

Methods for detecting flowing current can be loosely classified into resistance detection type and magnetic field detection type.

[Current detection methods and characteristics]

The voltage drop induced by the shunt resistance is converted into current by the resistance detecting type. The installation is straightforward and inexpensive, and the operation is straightforward, however, the power loss on the resistor generates a significant quantity of heat.

Magnetic field detection type <With iron core>

The current flowing in the current line is used to determine the amount of the magnetic field generated in the iron core, as well as the current value. This approach does not require contact, and the power loss is minimal, but the iron core is larger, and a large mounting area is an issue.＜No iron core＞

The Hall effect is used to quantify the current value by converting the magnetic field generated surrounding the flowing current into a voltage (Hall voltage). The IC is made up of a Hall element and an amplifier circuit due to the low voltage created by the Hall effect. Power loss will occur due to the necessity to introduce current into the IC.

M1 current sensor

ROHM has developed a magnetic field detection type non-contact current sensor employing MI (Magneto Impedance) elements to address the above-mentioned drawbacks of the magnetic field detection type in terms of installation difficulty (with iron core) and power loss (without iron core).

The MI sensor is a new generation sensor that uses the magneto-impedance effect of a particular amorphous wire. It is distinguished by its capacity to detect magnetic fields with ultra-high sensitivity.

Sensitivity greatly exceeds that of the Hall element, allowing for the precise detection of minor changes in magnetism. As a result, high-accuracy non-contact current monitoring (magnetic detection) is feasible without injecting current into the package.

[Structure comparison of current sensors (Rohm survey)]

In summary, the MI current sensor can perform non-contact current measurement with less power loss and further reduce the mounting area.

Ⅶ. Color sensor

A color sensor is one that detects the three primary hues of R (red), G (green), and B (blue) in a light sensor (light sensor).

The color sensor determines the RGB value by receiving ambient light through the photodiode.

Color sensor principle

The object is irradiated with light that has RGB components, and the color component of the reflected light changes with the color of the object.

A red object's reflected light component, for example, is red, while a yellow object's reflected light component is red and green. The colors red, green, and blue are all present in white.

[Schematic diagram of the reflected light color of the object]

The color of an object is determined by the ratio of the light color (R, G, B) components reflected by the object, as can be seen.

The reflected light component is used by the human eye to determine an object's color.

In the dim light, you can't see anything! This is because there is no irradiated light and no naturally reflected light, therefore it appears absolutely dark.

The color sensor.  like the human eye, receives light through a photodiode and distinguishes color by computing the ratio of R, G, and B received.

The structure of the color sensor  IC

The color sensor  IC's construction is depicted in the diagram below. A color filter (Color filter) and an infrared cut filter are installed on the inside (Ir cut filter).

[Brief structure of ROHM's representative color sensor]

The following compares the spectral characteristics of the sensor with or without these filters.

[Schematic diagram of RGB spectral characteristics]

By equipping the internal sensor with filters of various colors of R, G, and B, as well as an infrared cut filter with infrared removal characteristics, the color sensor  IC has high RGB spectroscopy characteristics and can distinguish colors with high precision.