In most industrial operations and applications, object manipulation is highly dependent on non-contact object detection. This has led to the development of numerous sensing devices including capacitive and inductive sensors. However, currently available sensors use sophisticated and costly sensing devices.
In a recent paper published in Microelectronics Journal, Professor Mikio Deguchi from the National Institute of Technology (KOSEN), Niihama College, Japan proposed a simple and cost-effective object detection method. The method was based on effective permittivity changes and did not require sophisticated sensing devices as the circuit used comprised of general-purpose semiconductors. The design consisted of an electric wire acting as a sensor and an electronic circuit for detecting the propagation delay time of the signal through the wire.
Generally, the presence of an object near electric wire results in a larger effective permittivity within the object and wire surrounding attributed to the larger material permittivity than air. This consequently results in an increase in the propagation delay time due to a decrease in the velocity of the propagating signal in the wire. The difference in permittivity was detected by observing the propagation delay time. To vary the effective permittivity around the sensing line, plastic plates were stacked on the sensing line surface. As the number of plates increased, the output voltage increased and the voltage changes was used to detect both the presence of an object and the number of objects. It was advantageous to keep the length of the sensing line desirably longer to enhance its sensibility.
The object detection method was validated using three application examples: detection of metals, vital sign sensing, and water level measurements. The presence of a metal near a sensing wire increased the effective permittivity around the wire allowing its detection. Even though water has relatively low permittivity as compared to metals, it is considerably large and can be easily detected. The relationship between the amount of water and output change was observed to effectively monitor the water level. Additionally, effective permittivity changes with the movement of a human body, and thus the proposed method could be effectively used for vital sign detection.
In a nutshell, the study presented a simple and low-cost object detection method based on effective permittivity changes. The difference in effective permittivity is detected based on changes in the propagation delay time of the sensing signal with respect to the velocity of the signal through the wire. The principle of the sensing method demonstrated great potential for a wide range of applications. For instance, it was successfully used to monitor water level, detect metal objects, and vital signs. In a statement to Advances in Engineering, Professor Deguchi mentioned his method can be applied to various fields and is highly promising for the development of proximity sensors as well as the detection of other phenomena involving permittivity changes, a crucial aspect of practical and industrial applications.
Deguchi, M. (2020). Simple and low-cost object detection method based on observation of effective permittivity change. Microelectronics Journal, 95, 104678.
Deguchi, M. (2020). A simple method for detecting very small changes in capacitance or inductance. Microelectronics Journal, 101, 104802.