A microwave sensor and a system for detection of microplastics in liquids

Abstract

ABSTRACT A microwave sensor and a system for detection of microplastics in liquids A resonator (100) design utilizing a microwave system is employed to assess the concentration of microplastics in liquid environments. The sensitivity of this system is influenced by the dielectric properties of the materials involved. Variations in the dielectric characteristics of the sample lead to changes in both the resonant frequency and the amplitude level. The shift in frequency serves as a key metric for sensitivity. Experimental validation is conducted by applying different concentrations of microplastics samples to the sensor, revealing observable amplitude changes corresponding to the varying microplastics concentrations. FIG.

Specification

Description:FIELD OF THE INVENTION
The present invention relates to the detection of microplastics in liquids, such as contaminated water, wastewater effluent streams and the like.

BACKGROUND OF THE INVENTION
Plastic production had exponential growth, and over the past half-century, it skyrocketed to 311 megatonnes in 2014 from merely 15 megatonnes in 1964. This trend is anticipated to continue doubling over the next twenty-year period as the use of plastic is expanding in many applications. [Agenda, World Economic Forum 2016] As one of the greatest threats to humanity, plastic pollution is now pervasive and found in the air, on land, and in the ocean. Most plastic debris eventually find its way into the sea through lakes and rivers, where it can linger for years. [RM Blair et al. 2019].

Microplastics in water behave differently based on their density. Dense microplastics sink and cluster near the source, while lighter microplastics float and get carried away. However, the net buoyancy can be impacted by a few processes (such as biofilms, gas bubbles, and aging), causing microplastics to settle in the sediments [Sagawa et al. 2018]. The efficient identification and quantification of microplastic pollution is a scientific hurdle since it gets harder to distinguish and identify smaller particles. Most of the research focuses on the in situ detection of microplastics in the air, while only a few focus on the challenging water environment, due to constraints like light absorption and scattering. Many techniques are explored and investigated for microplastic detection. But, currently, there are hardly a few quick, standardized, and straightforward analytical techniques that can reliably identify microplastics in actual water in various environmental matrices outside of laboratories. Given these antecedents, the goal of this research is the identification of microplastics in a liquid medium using an RF sensor.

There is no one standard solution to identify microplastics, and visual inspection is almost always the most common method for identifying and quantifying microplastics, even if tracked by chemical analysis. In visual inspection, particles are categorized as plastic based on physical characteristics, either directly observed or observed under a stereoscope or microscope. In these methods, microplastics must be isolated and treated individually from samples such as water, sediment, or organisms. Thus, the identification phase requires a time-consuming measure of highly competent researchers. (Prata et al., 2019). According to the literature, spectroscopic methods like Fourier transforms infrared (FTIR) (Cabernard et al., 2018, Kaeppler et al., 2018, Kai Yin et al., 2021, X Chen et al., 2021) and Raman spectroscopy (Cabernard et al., 2018, Saeed et al. 2020) are used most frequently to identify microplastics. These techniques are fast and reliable for identifying and distinguishing various microplastic types. While non-destructive, the sample preparation involving microplastic extraction from the environment may be potentially detrimental to the sample due to the physical detachment from the backdrop.

Thus, there is need to develop a system to detect a microplastics in liquids.

OBJECTS OF THE INVENTION
It is an object of the present invention is an economical RF resonator designed for the detection of microplastics in liquids.
Another objective of the current invention is to establish a system for detecting microplastics in liquids.

SUMMARY OF THE INVENTION
The present invention disclosed a microwave resonator (100) is specifically engineered for the detection of microplastics in liquid media, incorporating a multilayer structure for enhanced functionality. It features a patch that includes a top layer (101), a metal resonator (102) fabricated from copper positioned atop this layer, and a dielectric material layer (103) composed of Arlon dielectric situated on the resonator. Encircling the dielectric is a thin metal ring (104), while an integrated input (105) and output (106) facilitate the transmission and reception of RF signals from a Vector Network Analyzer (VNA). This configuration, utilizing an FR-4 substrate for the top layer, is optimally designed to resonate at a frequency of 6 GHz, ensuring precise evaluation and analysis of microplastic presence. The FR-4 substrate is composed of glass-reinforced epoxy laminate.

The Present invention also provides system for detecting microplastics in liquids comprises a microplastic detection sensor and a liquid sample containing dispersed microplastics within a solution. Central to this system is a Vector Network Analyzer (VNA), which is adeptly configured to emit RF signals into the liquid sample. Upon interaction with the resonant sensor, the VNA subsequently receives and analyses the output signals, thereby determining the presence of microplastics. Furthermore, this system enhances its analytical capabilities, as the VNA applies RF signals through an electric connection to the detection sensor and captures the reflected wave. It is also proficient in identifying the type of microplastics by calculating the dielectric properties based on constant and loss tangent values derived from the input reflection coefficient.

BRIEF DESCRIPTION OF THE FIGURES
FIG. 1 illustrates a microwave resonator (100) designed for the detection of microplastics in liquid environments.
FIG. 2 illustrates the identification of microplastics in liquids through an innovative system that employs Vector Network Analyzer technology.
FIG. 3 presents a schematic representation of an RF resonator in accordance with an embodiment of the current invention.
FIG. 4 presents a photocopy of the constructed RF resonator as an embodiment of the present invention.
FIG. 5 illustrates the microplastic detection system and measurement configuration according to an embodiment of the current invention.
FIG. 6 illustrates the correlation between frequency and reflection coefficient in the assessment of PS microplastics within the present study.

DETAILED DESCRIPTION OF THE INVENTION
The increasing prevalence of microplastics in the environment has prompted significant technological advancements aimed at their detection and analysis. The present invention, a specialized microwave resonator (100), addresses this challenge through its intricate multilayer design, optimizing functionality for detecting microplastics in liquid media.

Referring to FIG.1, Microwave Resonator (100) for Microplastic Detection in Liquid Media. Central to this device is a patch that comprises a meticulously structured top layer (101) built from FR-4 substrate. This foundational layer supports a metal resonator (102) crafted from copper, which is strategically positioned atop it. The choice of copper is paramount due to its excellent conductivity, enhancing the resonator's efficiency. Above the metal resonator lies a layer of dielectric material (103), specifically composed of Arlon dielectric, renowned for its favorable dielectric properties that facilitate effective microwave signal propagation.

The innovative design further incorporates a thin metal ring (104) that encircles the dielectric, significantly contributing to the electromagnetic characteristics of the resonator. This ring aids in confining the microwave fields, thus improving sensitivity and selectivity in detecting microplastics. To streamline the communication of signals, the resonator is equipped with integrated input (105) and output (106) components that facilitate the seamless transmission and reception of radio frequency (RF) signals, in conjunction with a Vector Network Analyzer (VNA).

Tuning the resonator to resonate at a frequency of 6 GHz allows for heightened precision in evaluating the presence of microplastics within various liquid media. This frequency is optimal for distinguishing microplastic signatures from other potential interfering substances, thereby enhancing the reliability of the analysis.

This microwave resonator (100) represents a significant advancement in the field of environmental monitoring. Its multilayer structure, strategic material selection, and precise frequency tuning collectively facilitate the efficient detection of microplastics, underscoring its pivotal role in addressing a pressing environmental concern.

The issue of microplastics contamination in aquatic environments has garnered significant attention in recent years due to its detrimental effects on ecosystems and human health. In response to this pressing problem, the present invention offers a sophisticated system for the detection of microplastics within liquid samples.
Referring to FIG.2, detection of Microplastics in aquatic environments: A Novel System Utilizing Vector Network Analyzer Technology.

This system comprises a microplastic detection sensor(100) and a liquid sample that contains dispersed microplastic within a solution.

At the core of this innovative detection system is a Vector Network Analyzer (VNA), a highly versatile instrument known for its ability to measure the frequency response of various electronic components. The VNA is meticulously configured to emit radio frequency (RF) signals into the liquid sample. Upon interaction with the resonant sensor, the VNA receives and analyzes the output signals, which enables the determination of the presence of microplastics within the sample.

The analytical proficiency of this system is further enhanced through the VNA's capability to apply RF signals via an electrical connection to the detection sensor. By capturing the reflected wave resulting from the interaction of RF signals with the microplastics, the system can derive critical data. Notably, the VNA excels in identifying the types of microplastics present by calculating the dielectric properties based on constant and loss tangent values obtained from the input reflection coefficient.

The system of the present invention represents a significant advancement in the detection of microplastics in liquids. By leveraging the advanced capabilities of a Vector Network Analyzer, it not only identifies the presence of microplastics but also provides insights into their specific types. This dual functionality positions the system as a valuable tool for researchers and environmental monitors seeking to address the pervasive challenge of microplastic pollution.

Figures 3 and 4 illustrate a schematic diagram of an RF resonator as per an embodiment of the present invention. The RF microwave sensor is constructed on an FR4 substrate, which has a dielectric constant of 4.3 and a thickness of 1.6 mm. This structure resonates at a frequency of 6 GHz, and the analysis of dielectric parameters related to microplastics has validated the sensing component. The dimensions of the RF microwave sensor structure are detailed in the table below.

Table-1: dimensions of the RF microwave sensor structure

Parameters Size (mm)
P 17 mm
L 13 mm
R1 10.49
R2 8.54
w 1
l 1
h1 1.6
h2 0.035
t1 0.035
t2 1
t3 0.1

Figure 5 depicts the microplastic detection system and measurement setup as per an embodiment of the present invention.
This measurement setup comprises an Agilent technologies N9917A Vector Network Analyzer(VNA), a coaxial cable, a fabricated RF-resoantor, and a microplastics sample(polystyrene). A simulation and measurement of the reflection coefficient for a microplastic sample up to 50 mg/dL are shown in the Figurer. Each 5mg/dL microplastic sample was taken into the vial with dissolved water. And the resonator sensor setup was placed in top of the 50 ml beaker. Six different microplastic sample concentrations ranging from 5 to 50 mg/dL were obtained for this investigation. Using micro pipette, one drop of sample each containing roughly 5 mg/dL was applied to the sensing area at a time.
The designed structure's resonant frequency has been validated at 6.2 GHz through both simulation and measurement. The resonance is influenced by the dielectric characteristics of the analyte being tested. A resonance frequency of 6.16 GHz suggests the detection of a deionized water sample within the holder. Additionally, a resonance at 6.12 GHz signifies the presence of polystyrene microplastics in the water. Changes in amplitude levels are noted as the concentration of the polystyrene microplastics sample is varied. The characteristics of the resonator for PS microplastics are presented in Table 2.
Table-2: Resonator Characteristics for polystyrene (PS) Microplastics.
S.NO Characteristics Resonance (GHz) Return Loss (dB)
1 f1 (Resonator only) 6.2 -22.872
2 f2 (With sample holder) 6.13 -22.848
3 f3 (with water) 6.16 -22.228
4 f4 (with PS 5) 6.16 -22.797
5 f5 (with PS15) 6.12 -22.622
6 f6 (with PS 20) 6.12 -23.644
7 f7 (with PS 30) 6.12 -25.424
8 f8 (with PS 40) 6.12 -25.313
9 f9 (with PS 50) 6.12 -23.549

Figure 6 presents an illustrative graph depicting the relationship between frequency and reflection coefficient for the measurement of PS microplastics in the current investigation.
The sensitivity is influenced by the dielectric properties of the material. Variations in the dielectric characteristics of the incident sample will result in changes to both the resonant frequency and the amplitude level. The shift in frequency serves as the metric for sensitivity. Experimental validation is conducted by applying different concentrations of polystyrene (PS) samples to the sensor, revealing observable amplitude variations as the concentration of polystyrene (PS) changes.
 
, Claims:WE Claim,

1. A microwave resonator (100) for detection of the microplastics presence in liquid media, comprising:
a) a patch with the addition of a top layer (101);
b) a metal resonator (102) positioned atop the layer (101);
c) a dielectric material layer (103) situated on the metal resonator (102);
d) a thin metal ring (104) encircling the dielectric material (103); and an input (105) and output (106) for a vector analyzer, facilitating subsequent evaluation and analysis;
wherein the input (105) & output (106) are designed to transmit an RF signal to the resonator (100) from the Vector Network Analyzer (VNA) and to receive the output signal for relaying back to the analyzer for additional evaluation and analysis.

2. The RF resonator (100) as claimed in claim 1, wherein the top layer consists of an FR-4 substrate.

3. The microwave resonator (100) as claimed in claim 1, wherein FR-4 substrate is composed of glass-reinforced epoxy laminate.

4. The microwave resonator (100) as claimed in claim 1, wherein the metal resonator (101) fabricated from copper metal.

5. The microwave resonator (100) as claimed in claim 1, wherein the dielectric material (103) consists of Arlon dielectric material.

6. The microwave resonator (100) as claimed in claim 1, where the resonator (100) is designed to resonate at 6GHz.

7. A system for detecting the presence of micro plastic in liquids, the system including:
a microplastic detection sensor (100) of claim 1;
a liquid sample which contains microplastic dispersed within a solution,
a vector network analyzer (VNA),
wherein the VNA is configured to emit RF signals to the liquid sample, subsequently receiving and analyzing the output signals generated by the resonant sensor to determine the presence of microplastics in the liquid.

8. The system for detecting the presence of micro plastic in liquids as claimed in claim 1, wherein the vector network analyzer (VNA) configured to apply RF signals to the microplastic detection sensor (100) through electric connection and receive a reflected wave as output signal.

9. The system for detecting the presence of micro plastic in liquids as claimed in claim 1, where in the vector network analyzer (VNA)is configured to calculate the type of the microplastics by calculating a dielectric depending on the type of constant and loss tangent value based on the input reflection co-efficient.

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