What is a sensor?
Sensor refers to the element or device that converts the collected information into a signal that can be processed by the device.
Humans will act based on the information obtained by sight, hearing, smell, and touch, and the equipment will also perform control or processing based on the information obtained by the sensor.
The signals (physical quantities) collected and converted by the sensor include temperature, light, color, air pressure, magnetism, speed, acceleration, etc.
In addition to these changes in materials that use semiconductors, there are also biosensors that use biological materials such as enzymes and microorganisms.
IoT and sensors
IoT (Internet of Things) where all objects are connected to the Internet.
Not only communication devices such as smartphones and personal computers, but also medical equipment, wearable devices, vehicles, natural environments, infrastructure, etc., all objects can be connected to the Internet to share information, thereby creating a more convenient, more secure, and safer society.
What is indispensable for realizing these is the "sensor" that detects the state.
[Definition of terms related to IoT]
IoT: Internet of Things (Internet of Things) refers to the state in which sensors are embedded in surrounding objects and connected to each other, so that objects and people can communicate with each other.
Germany·Industry 4.0: It is a concept proposed by the German government to improve the intelligent level of manufacturing, and it is also a national project jointly promoted by industry, government, and academia. Introducing a new concept aimed at creating new value through the Internet of Things in the factory.
M2M: Machine to Machine: Refers to direct communication through networking between objects without using human as the medium. P2M: People to Machine Communication, M2P: Machine to People Communication
Industrial Internet: The industrial IoT strategy advocated by GE (Generel Electric Company).
Geomagnetic sensor
The earth is surrounded by the magnetic force of the magnetic field, which is called geomagnetism.
The geomagnetic sensor is a sensor that detects the earth's magnetism and is also called an "electronic compass".
The geomagnetism sensor can detect the direction by detecting the geomagnetism.
[Geomagnetism around the earth]
The geomagnetic sensor has X and Y two-axis type and three-axis type with Z added, and measures the magnetic force value in all directions.
If tilts such as simple compasses are not considered, only the X and Y axis values are used. When considering tilt, it is necessary to combine the 3-axis value of the geomagnetic sensor with the acceleration sensor to correct it to the correct direction.
The figure below shows the distribution of X and Y values when the geomagnetic sensor rotates horizontally.
If the geomagnetic sensor rotates horizontally, the center of the output distribution graph becomes zero under ideal conditions without being affected by the surrounding magnetic field.
However, the center actually moves due to the influence of the environmental magnetic field, so adjustment is required to move the center of the circle to zero.
The north pole derived by the geomagnetic sensor is called the magnetic north (slightly deviated from the north pole). By calculating the angle of the magnetic north by the above equation, the direction can be easily known.
Hall sensor
A sensor that measures magnetic flux density based on the Hall effect, and outputs a voltage proportional to the magnetic flux density.
It is easy to use and is mainly used for non-contact switch applications, such as the opening and closing detection of objects such as doors and laptops.
MR sensor
MR (Magneto Resistance) sensor is also called magnetoresistance effect sensor, which uses the change of object resistance due to magnetic field to measure the magnitude of geomagnetism.
The sensitivity is higher than the Hall sensor, and the power consumption is lower, so it is a more widely used magnetic sensor. In addition to geomagnetic detection applications such as electronic compasses, it is also used for motor rotation and position detection applications.
MI sensor
The MI (Magneto Impedance) sensor is a next-generation magnetic sensor that uses a special amorphous wire and applies the magneto-impedance effect.
Its sensitivity is more than 10,000 times higher than that of the Hall sensor, and it can measure small changes in geomagnetism with high accuracy.
It can be applied to position detection with ultra-low current consumption (electronic compass), and can also be applied to applications with high sensitivity characteristics such as indoor positioning and metal foreign body detection.
Pulse sensor
The pulse wave is the volume change waveform of the blood vessel generated when the heart sends blood, and the detector that monitors the volume change is called a pulse sensor.
First of all, there are four methods for measuring heart rate, electrocardiogram, photoelectric pulse wave method, blood pressure measurement method, and phonocardiography.
The photoelectric pulse wave method is a method of measuring using a pulse sensor.
Due to the different measurement methods, the pulse sensor of the photoelectric pulse wave method has a transmission type and a reflection type.
The transmissive type measures the change in blood flow that changes with the pulse of the heart by irradiating infrared or red light to the body surface, and measures the pulse wave as the amount of change in light transmitted through the body.
This method is limited to parts that are easily penetrated, such as fingertips and earlobes.
Reflective pulse sensor
The reflective pulse sensor irradiates a living body with infrared light, red light, and green light with a wavelength of about 550 nm, and uses a photodiode or phototransistor to measure the light reflected by the living body. Oxygenated hemoglobin exists in arterial blood and has the property of absorbing incident light. Therefore, it measures the pulse signal by detecting the blood flow (change in blood vessel volume) that changes in time series and with the heart beat.
In addition, since it is a reflected light measurement, it is not necessary to limit the measurement location like the transmission type.
When infrared or red light is used to measure the pulse wave, it is affected by the infrared rays contained in the outdoor sunlight, and stable pulse wave measurement cannot be performed. Therefore, it is recommended to use it only for indoor or semi-indoor applications.
In outdoor applications such as sports watches, the absorption rate of hemoglobin in the blood is high. Since the green light source is less affected by the ambient light, we use the green LED as the illuminating light.
Pulse sensor application
Generally, arterial oxygen saturation (SpO2) can be measured by observing the following two points. Observe the heart rate (pulse rate) through the fluctuation period of the waveform obtained by the pulse sensor; observe the pulsation (variation) by using two wavelengths of infrared and red light.
In addition, as an application of pulse sensors, it is expected to obtain various vital signs such as HRV analysis (pressure level), blood vessel age, etc. through high-speed sampling and high-precision measurement.
Air pressure sensor
The air pressure sensor is a sensor that detects atmospheric pressure.
According to the pressure value to be measured, the pressure sensor has sensors of various materials and methods as shown below.
Among these pressure sensors, the sensor that detects atmospheric pressure (used for air pressure detection) is usually called an air pressure sensor.
A typical example of an air pressure sensor is a piezoresistive type using silicon (Si) semiconductors.
The air pressure sensor provided by ROHM is also a piezoresistive air pressure sensor.
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 generated when pressure is applied as the resistance value change.
The phenomenon that the resistivity (conductivity) changes due to the pressure applied to the resistance is called the piezoresistive effect. ROHM’s air pressure sensor IC uses piezoresistive pressure receiving elements (diaphragm structure and piezoresistance are integrated together*MEMS), and integrated circuits (*ASIC) such as temperature correction processing and control circuits are integrated in a single package, which can be easily Obtain high-precision air pressure information.
※ MEMS: Micro Electro Mechanical System (Micro Electro Mechanical System)
A device that integrates mechanical components, sensors, and actuators (drive components) on a circuit board.
※ ASIC: Application Specific Integrated Circuit (application specific integrated circuit)
It is an integrated circuit that combines multiple circuit functions into a specific application.
Accelerometer
Acceleration refers to the speed generated per unit time, and the IC that measures acceleration is called an acceleration sensor.
By measuring the acceleration, the tilt and vibration of the object can be measured.
The unit of acceleration is m/s2 (※International System of Units SI).
In addition, the unit G is an acceleration value based on ※standard gravity (1 G = 9.806 65m/s2).
There is also a unit *Gal (CGS unit system) used to detect the acceleration of earthquake vibration.
※ International System of Units SI (French: Système international d'unités)
The international unit is a combination of length m, weight kg, and time s (MKS units).
※ Standard gravity
The acceleration of an object under the action of gravity. When the object is in free fall, the speed value of the object per unit time (9.806 65m/s2).
※ Gal
The acceleration unit of the CGS (length cm, weight g, time s) unit system. It is defined as 1/100 of the SI unit system (1Gal=0.01 m/s2).
Capacitive acceleration sensor
The Rohm Group acceleration sensor is a capacitive acceleration sensor using MEMS technology.
The sensor element is composed of a fixed electrode made of Si, a movable electrode and a spring. When acceleration is not applied, the distance between the fixed electrode and the movable electrode is the same. When acceleration is applied, the movable electrode is displaced. As a result, the positional relationship with the fixed electrode changes, and the inter-electrode capacity changes. The change in capacity is converted into voltage by the ※ASIC, and the acceleration is calculated.
【Capacitive principle】
※ ASIC
Application Specific Integrated Circuit (application specific integrated circuit)
Refers to an integrated circuit that integrates multiple circuit functions for a specific purpose.
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 methods and characteristics]
The resistance detection type converts the voltage drop caused by the shunt resistance into current. The installation is simple and inexpensive, and the operation is simple, but the disadvantage is that the power loss on the resistor will generate a large amount of heat. Magnetic field detection type With iron core
The magnitude of the magnetic field generated in the iron core is measured according to the current flowing in the current line, and the current value is measured by this. This method does not require contact, the power loss is small, but the iron core is larger, and there is a problem of a large mounting area. ＜No iron core＞
The Hall effect is used to convert the magnetic field generated around the flowing current into a voltage (Hall voltage) for measurement, thereby measuring the current value. Because the voltage generated by the Hall effect is small, the IC is composed of a Hall element and an amplifier circuit. Because of the need to introduce current into the IC, power loss will occur.
M1 current sensor
In order to eliminate the above-mentioned shortcomings of the magnetic field detection type in terms of installation difficulty (with iron core) and power loss (without iron core), ROHM has developed a magnetic field detection type non-contact current sensor using MI (Magneto Impedance) elements.
The MI sensor is a new generation sensor that uses a special amorphous wire and utilizes its magneto-impedance effect. It is characterized by its ultra-high-sensitivity magnetic detection capability.
Sensitivity far exceeds Hall element, and can detect small changes in magnetism with high precision. Therefore, it is possible to perform non-contact current detection (magnetic detection) with high accuracy without introducing 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.
Color sensor
In the light sensor (light sensor), the one that detects the three primary colors of R (red), G (green), and B (blue) is called a color sensor. The color sensor receives ambient light through a photodiode and detects the RGB value.
Principle of color sensor
The light with RGB components is irradiated to the object, and the color component of the reflected light will change with the color of the object.
For example, the reflected light component of a red object is red, and a yellow object is red and green. White contains all the components of red, green, and blue.
The color of the object is determined by the ratio of the light color (R, G, B) components reflected by the object.
The human eye recognizes the color of an object by obtaining the reflected light component.
You can't see anything in the dark place! This is because there is no irradiated light, and the reflected light naturally does not exist, so it looks completely dark.
Like the human eye, the color sensor uses a photodiode to receive light and recognizes the color by calculating the ratio of the amount of R, G, and B received.
The structure of the color sensor IC
The color sensor IC is equipped with a color filter (Color filter) and an infrared cut filter (Ir cut filter).
The color sensor IC is equipped with R, G, and B color filters for the internal sensor, which has high RGB spectral characteristics, and through the infrared cut filter, it has infrared removal characteristics and can recognize colors with high precision.
