Hitachi intends to apply this sensor to various applications including next-generation oil and gas, and infrastructure monitoring

By Jean-Jacques
DeLisle, contributing writer



Japanese multinational conglomerate company Hitachi, Ltd.
announced it has developed
a new MEMS accelerometer
that can detect
vibrations up to three orders of magnitude smaller than previous designs that
target automotive applications. The new accelerometer mixes previous MEMS
technology with circuit-based technology, resulting in an achieved sensitivity
that compares to that of sensors used for oil and gas exploration, but at a
fraction of the power consumption. The high-sensitivity low-power MEMS
accelerometer can detect vibrations as low as 30 ng/√Hz and only consume 20 mW,
less than half the power usage of previous sensors. The challenge
Hitachi faced was creating a sensor that was powerful enough to detect low-frequency
vibrations without using a massive amount of power. Doing that is difficult
because the power required for sensors increases exponentially as the noise
floor is reduced.

Control IC,
detection IC and MEMS device in the accelerometer (left), moving mass inside
the MEMS device (right). Image source: Hitachi.

accelerometers consist of a specific mass mounted on a springboard. This mass
is free to move about, and has circuits in place that can both detect and
control its movements to keep its position balanced. As slight vibrations cause
the mass to move relative to its frame, that movement is transmitted or stored
for information analysis. Previous MEMS sensors were limited in their ability
to detect super-low signals because air molecules within them would collide
with the mass itself, slowing it down and altering its movement, which caused
readings to be slightly noisy. This tiny interference is negligible for most
applications, but for oil and gas exploration or for the detections of
artificial earthquakes, precision is of paramount importance.


managed to overcome that flaw in previous versions by using sophisticated
computers to model and redesign the aerodynamics of the mass within the sensor.
In the development of Hitachi’s sensor, unique perforations with different
entry/exit diameters based on fluid dynamics analysis were made on the moving
mass, which consists of an SOI substrate. The resulting shape halves the number
of air molecule collisions and yields sensors with far greater ability to
detect low-intensity sounds.


Soon, Hitachi
hopes to put its sensors to use not only in oil and gas exploration but also
for the detection of earthquakes. Other potential uses could be monitoring
infrastructure such as bridges and detecting small vibrations in the ground
that could be the sign of structural collapse in buildings. With the advantage
of consuming only half the power of competing sensors, we can be sure that
Hitachi will have its sensors in a multitude of places in the coming years.