A novel impedance sensor based on a microfluidic chip is presented. The sensor consists of two single-layer coils and a straight micro-channel, and can detect, not only ferromagnetic and non-ferromagnetic particles in oil as an inductive sensor, but also, water droplets and air bubbles in oil as a capacitive sensor. The experiments are carried out at different excitation frequencies, number of coil turns and particle sizes. For the inductance detection, the inductance signals are found to increase with the excitation frequency and the noise is constant; both the inductance signals and the noise increase with the number of coil turns, but because the noise increases at a faster rate than the signal, the signal-to-noise ratio decreases with the number of coil turns. We demonstrate the successful detection of 40 μm iron particles and 110 μm copper particles using the coil with 20 turns at the excitation frequency of 2 MHz. For the capacitance detection, capacitance signals decrease with the excitation frequency and the noise is constant; the capacitance signals decrease with the number of coil turns, while the noise increases, thus, the signal-to-noise ratio decreases with the number of coil turns. We can detect 100 μm water droplets and 180 μm bubbles successfully using the coil with 20 turns at the excitation frequency of 0.3 MHz.

https://www.mdpi.com/2072-666X/8/8/249/pdf/1

A Novel On-Chip Impedance Sensor for the Detection of Particle Contamination in Hydraulic Oil.

This paper focuses on the output characteristic of the microfluidic inductive sensor. First the coil-metal particle system model is established from Maxwell’s equations. Then series solution is achieved by solving partial differential equation. Finally the numerical simulations and physical experiments are compared on particle feature, particle size, excitation frequency, coil turns, and coil density. The experiments coincide well with the simulations.

https://downloads.hindawi.com/journals/jnm/2014/725246.pdf

Research on the Output Characteristics of Microfluidic Inductive Sensor

Based on the microfluidic technology, we designed a high-throughput sensor to detect the hydraulic oil contamination. The sensor has two working modes: inductance detection and capacitance detection. The inductance detection mode can detect ferromagnetic and non-ferromagnetic metal particles in the hydraulic oil. By changing the coil connection to switch to the capacitance detection mode, it can detect water droplets and air bubbles in the hydraulic oil. An annular microchannel is designed to increase the detection flow and to shorten the detection time. A pair of silicon steel sheets are built into the annular microchannel to collect the dispersed magnetic field in the detection area, which improves the accuracy in detecting ferromagnetic and non-ferromagnetic particles. Our experiments showed that the detection sensor is more stable when the plane coils have 20 turns. The magnetic field effect of the silicon steel sheet can improve the detection accuracy in inductance detection. Without the silicon steel sheet, the sensor can detect iron particles as small as 60–70 $\mu \text{m}$ with a signal-to-noise ratio (SNR) of 1.55 and copper particles as small as 150– $160~\mu \text{m}$ with an SNR of 1.35. With the silicon steel sheet, the sensor can detect iron particles as small as 60– $70~\mu \text{m}$ with an SNR of 3.42 and copper particles as small as 150– $160~\mu \text{m}$ with an SNR of 3.10. Capacitance detection can detect the water droplets of size 190– $200~\mu \text{m}$ and air bubbles of size 260– $270~\mu \text{m}$ .

High-Throughput Sensor to Detect Hydraulic Oil Contamination Based on Microfluidics

A multi-parameter sensor based on microfluidic chip is presented. The sensor consists of a planar coil and a metal wire inserted into the center hole of coil. It can be used as an inductive sensor or capacitive sensor, so multiple parameters can be detected on one sensor. The vertical channel effectively prevents the clogging of the microchannel, reducing the detection error and improving the service life of the detection chip. The related experiments were carried out on the built detection system, which proved the annular microchannel can force that the metal particles pass through the most sensitive region, therefore the sensitivity of inductance detection is enhanced. And the cross-sectional area of the microchannel increases, so the throughput is higher. For the inductance detection, the signal-to-noise ratio initially increases with the coil turns, but then it has a tendency to decrease. For the capacitance detection, the signal-to-noise ratio decreases with the coil layers. We used the coil with 40 turns, which can ensure the detection sensitivity of the inductance detection and the capacitance detection, to explore the floor level of chip. We successfully detected 40 μm iron particles, 125 μm copper particles, 60 μm water droplets and 120 μm air bubbles.

A multi-parameter on-chip impedance sensor for the detection of particle contamination in hydraulic oil

Wear is one of the common faults in the mechanical transmission system. Detection of wear particles in lubricating oil can detect and evaluate the wear degree of mechanical equipment. The electromagnetic sensor for metal wear particle detection can be connected in series with the oil circuit, which has the advantages of full liquid flow, simple structure, distinguishing metal properties, and not being influenced by bubbles and vibration. In view of the shortcomings of the existing electromagnetic sensor for wear particle detection, the detection principle and the induction electromotive force model were studied, and the magnetic field change of the metal particles through three coil differential solenoids was analysed. The optimisation design method was proposed here, which was about the related parameters, such as the wire diameter, the coil turns, the coil widths and so on. The experimental analysis of the sensor was carried out based on detection hardware system that could provide the phase-locked amplification function. The 10-mm inner diameter sensor could detect the minimum 100-μm ferromagnetic metal abrasive particles after optimisation. The developed sensor could provide data information for the abrasive particle detection, fault diagnosis and early warning of wear degree of mechanical equipment.

https://ietresearch.onlinelibrary.wiley.com/doi/pdf/10.1049/joe.2018.9080

Design of electromagnetic sensor for metal wear particle detection in oil

This paper introduced a microfluidic lab-on-chip device,which could be applied to detect the metal wear debris in the oil.Driven by the syringe pump,the sample oil in the inlet well of the PDMS microfluidic lab-on-chip passed through the capacitance detection zone which has two 25 μm-diameter copper wires acting as electrodes of a 3D capacitive sensor.Due to the different permittivity between the metal debris and the oil,each debris generated a capacitive pulse signal when passing through the capacitive sensor.The amplitude of this signal reflects the size of the grains,and the number of pulses is the quantity of the particles.With this device,the detection and counting debris of 8μm diameter are achieved.The device described is simple and in-expensive without losing high accuracy and sensitivity,which can be applied to develop a portable device for off-line oil analysis onboard ships.

LI Meng-q

Papers

Microfluidic capacitance sensor for detecting metal wear debris in lubrication oil