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ROHM’s New Sensor Technology and Its Uses

  1. Introduction

The Internet of Things (IoT) is being adopted in an expanding number of fields to improve business operations, increase convenience, detect/prevent abnormalities, and enable automated operation by collecting, analyzing and using data from a variety of devices. In recent years, AI technology capable of automatically analyzing acquired data has taken center stage, but for IoT the most important aspect is how accurately data can be collected. In this case the sensor plays an essential role. A wide variety of sensors exist, from environmental types designed to detect the ambient temperature and humidity to sensors capable of detecting equipment vibrations and the movement/presence of people.

The ROHM Group develops a broad range of sensors utilizing 3 key technologies: 1) MEMS device technology (i.e. silicon deep etching), 2) Analog front end technology for processing weak signals output from sensor elements, and 3) Packaging technology, such as CSP (Chip Scale Packages). We are also advancing the development of sensor solutions that combine wireless communication with MCUs (Fig. 1).

ROHM Sensor Device Development Technologies
(Figure 1: ROHM Sensor Device Development Technologies)
  1. ROHM’s IoT-targeted sensor devices

Sensor devices developed at ROHM can be generally divided into 3 types: motion sensing, environment sensing, and interface devices. For motion sensing, in addition to geomagnetic and barometric pressure sensors, we also develop sensors that detect the movement of people and objects, such as accelerometers and gyroscopes utilizing ROHM Group company Kionix’s advanced MEMS technology. For environment sensing, we provide sensors capable of monitoring environmental conditions such as temperature, brightness, and color, while our interface lineup includes capacitive switches and resistive touch controllers (Fig. 2). We are also able to offer smaller packages by combining analog circuits for sensor control and leveraging one-chip and chip stack technologies.

ROHM Sensor Device Lineup
(Figure 2: ROHM Sensor Device Lineup)

ROHM Group provides a diverse range of sensors to meet a wide variety of market needs.

  1. Position detection using beacons

The following is an example of using sensors to solve problems with IoT beacons. A beacon is a device that transmits signals at certain intervals within a range of several meters to tens of meters, and are used to send coupons or other relevant information to terminals such as smartphones and tablets. They can send periodic one-way signals that allow smart devices such as smartwatches to receive data without the need for pairing with a tablet or phone. This convenience is believed to be largely responsible for its increased adoption in recent years.

Beacons are often used in locations such as offices and factories. Attaching beacons to people and devices makes it possible to improve operating efficiency by communicating location information with installed receivers. However, because this method estimates the location based on the strength of the signal delivered from the beacon to the receiver, problems such as a communication failure or positional error are common. For example, despite the presence of a person carrying a beacon in the room containing Receiver A, the person is incorrectly detected as being in the room containing Receiver B (Fig. 3). This is because when several receivers are installed inside a building, it is impossible to tell which receiver a beacon is closer when the wearer is situated halfway between two receivers.

Erroneous Location Detection
(Figure 3: Erroneous Location Detection)
  1. Developing beacons using ROHM sensor technologies

In order to solve problems related to erroneous detection, we developed a solution that uses motion data in addition to signal strength to estimate the location of a person or item. The configuration combines an accelerometer, barometric pressure sensor, geomagnetic sensor, microcontroller, and Bluetooth® Low Energy module from ROHM Group company LAPIS Semiconductor.

When the beacon transmits a periodic signal, this solution simultaneously sends data from individual sensors as well as processed data from all sensors. Utilizing the built-in accelerometer and algorithm in combination with the beacon’s signal strength results in increased location detection accuracy.

The following describes the sensors utilized in the beacon.

  • 3-Axis Accelerometer with Pedometer Algorithm (KX126-1063)

Kionix’s KX126-1063 is a 3-axis accelerometer that delivers high sensitivity, high accuracy, and low power consumption in a thin, compact 2.0mm x 2.0mm x 0.9mm form factor. Integrated motion detection algorithm makes it possible to detect gestures such as tapping along with free fall and device orientation. In addition, when analyzing vibration, component analysis can be performed using FFT or the like over a wide frequency band, and acceleration information can be output at a maximum data rate of 25.6kHz. A pedometer function is also included that reduces design load and enables immediate use by simply configuring the sensor, eliminating the need to run an algorithm on the microcontroller side after obtaining the acceleration value(Fig. 4).

  • Geomagnetic Sensor Utilizing a Magnetic Impedance Element (BM1422AGMV)

The BM1422AGMV from ROHM is a 3-axis geomagnetic sensor housed in a compact 2.0mm x 2.0mm x 1.0mm package.

Since 2013 we have worked with Aichi Steel to develop a special amorphous wire. The result is 10,000 times greater sensitivity over conventional Hall effect sensors along with lower noise and power consumption. In smartphones and wearable devices this enables indoor navigation and contributes to long-term use by increasing azimuth accuracy (Fig. 5).

  • Piezo-resistive Barometric Pressure Sensor (BM1383AGLV)

ROHM’s BM1383AGLV compact (2.5mm x 2.5mm x 0.95mm) barometric pressure sensor is equipped with a temperature correction algorithm that makes it unnecessary to carry out external temperature correction using a microcontroller, reducing computational load. This makes it ideal for applications such as relative altitude detection, floor detection, and calorie calculation (Fig. 6).

Kionix 3-Axis Accelerometer KX126-1063
(Figure 4: Kionix 3-Axis Accelerometer KX126-1063)
ROHM 3-Axis Geomagnetic Sensor BM1422AGMV
(Figure 5: ROHM 3-Axis Geomagnetic Sensor BM1422AGMV)
ROHM Barometric Pressure Sensor BM1383AGLV
(Figure 6: ROHM Barometric Pressure Sensor BM1383AGLV)
  1. Application examples of beacon using sensors

The use of beacons with sensors for high-accuracy location detection not only applies to the horizontal plane. As mentioned earlier, beacons are often used for monitor worker locations. In this area there is also a need to determine location in the vertical direction, such as at different heights. Previously, a barometric pressure sensor alone would be used to calculate the relative altitude. A commonly used method is to record the atmospheric pressure on the first floor of a building and set that value as the standard pressure, then move to the second floor and again record the atmospheric pressure, using the difference in values to confirm that a change in floors has occurred.

However, barometric pressure sensors are affected by ambient changes in atmospheric pressure. When weather conditions suddenly worsen, the sudden change in pressure results in the sensor erroneously detecting that the person has ascended/descended. Therefore, by combining readings from an accelerometer that can detect movement with the change in atmospheric pressure, altitude calculation can be achieved that takes into account fluctuations in ambient pressure. This allows ROHM’s beacons to monitor worker position not just horizontally, but vertically as well.

In addition, an accelerometer and geomagnetic sensor can be paired to create an electronic compass that can detect the direction a person or object is facing. Combining various sensors in different ways allows users to achieve a range of functions.

 Conclusion

Through innovative sensor development, ROHM has been able to deliver a wide lineup of sensor devices optimized for a variety of market needs. Furthermore, by developing modules that combine not just sensors but wireless technologies and proposing sensor fusion solutions that incorporate multiple sensors, we support improved energy savings and productivity in factories and the early adoption of sensors for IoT. And going forward, we will contribute to the realization of a smart society by developing products and solutions that meet the demands of not only the IoT market, but the automotive and industrial equipment sectors as well.

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