Subminiature panel (SMA-P) coaxial sensor for the determination of moisture content of mango cv. Chok Anan

The research describes the development of a simple, cheap and efficient open-ended coaxial sensor for the determination of moisture content of Chok Anan mango during fruit ripening from week 5 to week 17. The sensor was a modification of a standard subminiature panel (SMA-P). The finite element method was used to calculate the numerical values of the reflection coefficient. The reflection coefficient of the sensor was measured using a Microwave Network Analyzer in the frequency range from 1 to 4 GHz. The actual moisture content was obtained using standard oven drying method. A calibration equation was obtained to predict moisture content from the measured reflection coefficient at 1 GHz with accuracy within 1.5%. The results indicate that the amount of m.c. in Chok Anan mango can be determined with excellent accuracy using a SMA-P coaxial sensor as an OEC sensor

Microwave technique for moisture content and pH determination during pre-harvest of mango cv. Chok Anan

The maturity of mango is usually assessed by the determination of its moisture content (m.c.), soluble solid content (SSC) and pH. However, these techniques are either time consuming, tedious or destructive. In this research, we extend the application of the open-ended coaxial probe technique to determine m.c. and pH of Chok Anan mango from its dielectric properties from week 5 to week 17 after anthesis. The effects of frequency and m.c. on the values of the dielectric constant and loss factor were also investigated. The critical frequency separating the different polarizations was found to be inversely proportional to m.c. Also, in this research we proposed a new classification of fruit ripeness related to the number of weeks after anthesis. The actual dielectric properties, m.c., SSC and pH of Chok Anan mango were measured using standard methods. Relationships were established between the dielectric constant, loss factor, critical frequency, pH and m.c. The accuracy for the determination of m.c. and pH using the coaxial probe was within 1.7% and 3.0%, respectively

Open-ended coaxial sensor for determination of moisture content, soluble solid content, pH and dielectric properties of Chok Anan mango

The thesis presents the application of open-ended sub-miniature panel (SMA-P) coaxial sensor to determine moisture content, soluble solid content, pH and dielectric properties of Chok Anan mango during ripening from week 5 to week 17 based on reflection coefficient (|S11|) measurement in the frequency range between 1.0 GHz to 4.0 GHz. Measurements were conducted using Keysight FieldFox N9912A Network Analyzer. The mass (M), width (W), length (L), moisture content (m.c.), soluble solid content (SSC) and pH of Chok Anan mango were also measured. All the measured parameters were found to increase non-linearly from week 5 to week 17. This work focus on the internal properties of mango (m.c., pH and SSC) since the external properties (M, W, and L) may not truly represent its internal quality. The SSC and pH methods are only suitable for measurement at later stage of fruit ripeness, i.e. after week 16, which is too late to determine the ripening stage of mango fruits. In contrast, m.c. profiles was distinctively clear to distinguish all the stages of fruit ripeness for the whole 17 weeks of fruit development. Besides that, SSC and pH methods are laborious, difficult, time consuming and destructive whilst the m.c. can be determine fast, accurate and non-destructive using SMA-P coaxial sensor from calibration equations relating to the m.c. to the measured |S11|. The permittivity measurement for the different percentage of m.c. in mango is carried out using the Keysight 85070E dielectric probe kit, later the permittivity values obtained used as an input to calculate the |S11| using Finite Element Method (FEM). FEM was used to determine the accuracy of permittivity measurement by comparing the calculated values of |S11| using FEM with measurement results. Very closed agreements were obtained between measured and calculated |S11| where the mean errors were within 1.5% for all percentage of m.c.. Calibration equations were established to predict the m.c., dielectric constant (ε’) and loss factor (ε’’) from the measured |S11|, where the accuracies for the m.c. and ε’ were highest at 1.0 GHz within 1.5% and 1.6%, respectively, whilst ε’’ was 3.4% at 4.0 GHz. Also, calibration equation has been established to predict pH and SSC values from m.c. obtained from |S11| measurements. The accuracy of pH and SSC were within 3.0% and 5.2%, respectively when compared to standard techniques. The m.c. is the best parameter used to identify the quality of mango since it produced high accuracy based on |S11| measurements using SMA-P coaxial sensor. In conclusion, SMA-P coaxial sensor provides a simple, speedy, non-destructive, flexible and inexpensive approach for the determination of m.c., SSC, pH and permittivity in mango

Microcontroller-based moisture meter for ginger

This paper describes the development of a simple method to determine the permittivity and moisture content (m.c.) of ginger. The measurement system consists of a microwave sensor, directional coupler and a PIC microcontroller. The microwave sensor is a square flanged open-ended coaxial (OEC) sensor made from SMA stub contact panel with outer diameter (O.D) 4.10 mm. The microwave oven drying method was used to determine the actual m.c. of the ginger. All data acquisition, processing and display were accomplished using a PIC 16F690 microcontroller programmed using Flowcode software. The actual values of the permittivity of ginger were obtained by using the Agilent (now Keysight Technologies) 85070B dielectric probe along with a HP 8720B Vector Network Analyzer (VNA). The results showed good relationships between m.c., permittivity (dielectric constant (εʹ) and loss factor (ε̋)) and reflected voltage. The calibration equations between reflected voltage and m.c. have been established for the sensor. The measurement system provides a simple, fast and accurate technique to predict m.c., εʹ and ε̋ of ginger from reflected voltage measurements alone. The accuracy in determination of m.c., εʹ and ε̋ in ginger was within 2.9%, 2.7%, and 3.6%, respectively

Dielectric based measurement system for the determination of watermelon internal quality

A dielectric based measurement system was used in the determination of watermelon internal quality, focusing on maturity stage. This technique is based on microwave reflection measurement at watermelon surface using an open-ended coaxial probe with a microwave network analyzer operating in the frequency range from 1.0 to 8.5 GHz. The dielectric and physicochemical properties were measured during the fruit maturity stage from week 6 to 10. The effects of frequency and moisture content on the values of permittivity (dielectric constant, ɛ’ and dielectric loss, ɛ”) were investigated. Mass, volume and SSC values increased, while moisture content and density values decreased with maturity stage (time). Permittivity values decreased with maturity stage, in agreement with theory in which permittivity of moist materials is a function of moisture content, density and frequency. In addition, the dielectric constant at all maturity stages decreased with the increasing frequency suggesting watermelon ɛ’ followed the profile of water ɛ’. The dielectric loss decreased with frequency then increased slightly as frequency approached 8.5 GHz. The turning, known as critical frequency separates the bound and free water molecules. This technique showed potential to determine moisture content, then maturity stage from its dielectric properties