This Special Issue, “State-of-the-Art Sensor Technology in Japan 2015”, collected
papers on different kinds of sensing technology: fundamental technology for intelligent
sensors, information processing for monitoring humans, and information processing
for adaptive and survivable sensor systems. This series published former two issues
on state-of-the-art sensor technology in Japan in 2010 [1] and 2012 [2]. We selected
the same aim in the same direction as in the previous ones: the monitoring of humans
and the environment. However, the details of the topics have advanced from the former
two issues. This issue covered fundamental achievements for intelligent sensors, information
processing techniques for monitoring humans and children, and information processing
for adaptive and survivable sensor systems.
1. Deepening of Sensing Technologies: Sensors and Information Processing
Japan faces two critical issues as humans and environmental issues. This Special Issue
also selected the same topics as in the series of “State-of-the-Art Sensor Technology
in Japan” in 2010 and 2012. However, Japan’s demographics are still rapidly changing
as the population ages. The number of older people is growing, while the number of
children is decreasing due to the falling birthrate. A safe and secure society for
humans and children are required to solve these issues.
On the other hand, the environmental issues are also varied in Japan. Japan faced
earthquakes, the 2016 Kumamoto earthquakes, on 16 April in 2016. The Kumamoto earthquakes
also damaged more than 10 buildings of the Kumamoto Castle, which are nationally designated
as important cultural properties. Not only that, but the earthquakes also damaged
social infrastructures such as old bridges, roads, and mountains; therefore, they
should be monitored and repaired if necessary. Thus, sensing technology is a key for
a safe and secure society.
After the Greatest East Japan Earthquake on 11 March 2011, the resilience of information
systems has been an important issue. Various kinds of resilient systems have been
proposed and investigated extensively. Information and Communication Technology (ICT)
is a fundamental technology for resilient systems. Recently, the Internet of Things
(IoT) is also rapidly spreading and being used in society. Wearable devices are also
available (e.g., smart watches, computer glasses, and wearable health monitors). Image
sensors (cameras) are placed at roads and buildings anywhere, and they are operational.
Thus, various kinds of data can be collected from these sensors of this sort. The
next step is to construct survivable sensor systems that run even under even disaster
situations while gathering data. Information processing techniques would play major
roles in achieving the durable survivability of the resilient systems.
2. Fundamental Technology for Intelligent Sensors
Fundamental studies on sensors themselves are critical to develop intelligent sensors.
Studies on the different kinds of sensors have been reported in this Special Issue,
including X-ray sensors, infrared sensors, and biosensors. Furthermore, the development
process and cost also should be considered to spread the use of the new sensors. We
included the following five studies on fundamental research for the development of
the sensors.
Matsuura et al. [3] investigated low-cost X-ray detectors with gated silicon drift
detectors (GSDDSs). The X-ray detectors are required for on-site inspections of traces
of hazardous elements in food and soil. The thickness of GSDDs is a key parameter
for developing low-cost X-ray detectors. The study reported that the simulation results
showed improvement of GSDDs formed from Si wafers.
Takagawa et al. [4] investigated the detection wavelength control of uncooled infrared
sensors by using two-dimensional lattice plasmonic absorbers. Wavelength-selective
uncooled infrared (IR) sensors can be used for various kinds of applications such
as fire detection, gas analysis, and biomedical analysis. For uncooled IR sensors,
the study investigated the detailed effects of the lattice structures on the detection
wavelength. The authors compared the square lattice with the triangular one and reported
their design flexibility.
Yoshihara et al. [5] investigated new ratiometric molecular probes RP1 and RP2 for
sensing oxygen levels in cells. Molecular oxygen is critical in cell metabolism and
is also a key substrate in energy generation in aerobic organisms. The detection of
oxygen levels in living cells is of great importance not only in cell biology, but
also in other fields such as physiology and pathophysiology. The study reported that
the proposed radiometric oxygen sensors exhibited improved cellular uptake efficiencies,
and the radiometric images of living cells responded clearly to the oxygen concentration
of the cell incubator.
Harada et al. [6] developed a taste sensor using lipid-polymer membranes to evaluate
the taste of foods, beverages, and medicines. The response of the taste sensor, measured
as a change in the membrane potential caused by adsorption (CPA), corresponds to the
aftertaste felt by humans. The study investigated the relationship between the CPA
value and epigallocatechin gallate (EGCg). The results of this study would contribute
to the sensitivity of the taste sensors.
Camou [7] investigated a new technique for noninvasive and continuous monitoring of
blood glucose levels. Monitoring blood glucose levels (BGL) is important for human
health. BGL is a key quantity for monitoring human health because BGL is a critical
parameter related to diabetes. There are several sensors commercially available to
monitor BGL. The proposed technique is photoacoustic-based and noninvasive while commercial
sensors are invasive with finger-pricking. The author reported that the proposed technique
would reduce the patient’s burden for inspecting BGL.
3. Sensing Technology for Human Monitoring
Japan faces both human issues and environmental issues. For human issues, Japan’s
demographics are rapidly changing as the population ages. Further, the falling birthrate
also is quickly decreasing. Both issues (older people and the falling birthrate) are
urgent matters to solve. A safe and secure society is an important environment for
older people and children. Three studies are introduced in this Special Issue on monitoring
human and children.
Hashizaki et al. [8] studied weekly sleep pattern variations at home with a contactless
biomotion sensor. The sleep of people is restricted or disturbed by social obligations
such as work. Sleep plays a major role in maintaining a healthy lifestyle. The authors
recorded the sleep pattern of people using a contactless biomotion sensor with radiofrequency
waves. The study reported that sleep of younger people indicated sleep delays on both
weekdays and on the weekend due to social obligations.
Kaneko et al. [9,10] studied a measurement system for soft neurological signs (SNS)
using acceleration and angular velocity sensors. They applied the system and method
for children with Attention Deficit Hyperactivity Disorder (ADHD). Soft neurological
signs are evident in the motor performance of children and disappear as the child
grows up. The data observed by the proposed measurement system would quantify age-appropriate
developmental change SNS for children. Furthermore, the authors considered the data
of the motor performance of children with ADHD. The statistical analysis of the data
revealed that children with ADHD showed a lag of several years behind typically developing
children.
4. Intelligent Information Processing for Adaptive and Survivable Sensor Systems
The adaptiveness and resilience of sensor systems are still critical issues. The resilience
of sensor systems has been studied widely and extensively since the accident of the
Greatest East Japan Earthquake on 11 March 2011. However, Japan faced the similar
earthquakes, the Kumamoto earthquakes, on 16 April in 2016. The Kumamoto earthquakes
damaged the daily life of citizens, buildings, houses, and even important cultural
properties of Kumamoto Castle. Sensing technologies for saving humans and recovering
daily life are critical issues. Especially the resilience of the sensor systems is
a key technology for natural disasters.
Miyazaki et al. [11] proposed an adaptive algorithm for multiple human tracking using
binary infrared sensors. The proposed algorithm is able to estimate multiple human
movement paths in a room without a priori knowledge of the number of humans. Furthermore,
the proposed algorithm uses simple binary infrared sensors to construct the sensor
system. This point is valuable as an application in homes. The study finally reported
that the proposed algorithm showed adaptability, and it could handle the changes of
the number of humans in the room.
Tokumitsu et al. [12] proposed a framework for the resilient sensor networks. The
sensor systems are constructed by a huge amount of sensors and they communicate with
each other to exchange messages. The integration framework is necessary to build the
aggregate system of the sensors. The proposed framework involves resilience against
missing sensors. The data of the missing sensors are interpolated by spatiotemporal
interpolation with predefined profiles among sensors. The proposed framework would
help in the management of large-scale sensor networks since the missing sensors are
replaced with virtual sensors.
5. Toward the Next Generation of Sensing Technology
This Special Issue introduced various kinds of research on fundamental studies of
sensors and information processing techniques. Investigation of a sensor itself is
a critical issue. Further, the integration of the sensors is also an important issue
to construct adaptive and survivable sensor systems. The integration of the sensors
could detect the anomaly of the system itself or of monitoring targets. Information
processing creates higher-level sensors (virtual sensors) to replace faulty sensors
or expands the sensor system itself. The collective sensors [13] would produce valuable
information by communication and processing data. Intelligent information processing
and network technology are also key parts of sensing technologies. These three technologies,
sensors, intelligent information processing, and the network, would enhance safe and
secure society for humans and the environment.