# Non-Destructive Detection of Golden Passion Fruit Quality Based on Dielectric Characteristics
## 2 Materials and Methods
### Measurement Equipment and Methods  
2.2.1. Dielectric Parameter Measurement  
The passion fruit dielectric properties acquisition system, as shown in Figure 2, primarily consists of an LCR digital electric bridge tester (TH2830 type, Tonghui electronics equipment company, Changzhou, China), a fruit electrical parameter testing platform (self-made) and a computer. The measurement method involves the placement of the sample between two parallel plates in direct contact with them to assess the sample's dielectric properties, which encompass \(\varepsilon^{\prime}\) and \(\varepsilon^{\prime\prime}\). The entire system is housed within a sealed shielded enclosure to safeguard against external interference.  
The LCR tester has a frequency range of 0.05-100 kHz and a measurement accuracy of 0.05%. Two measurement probes of the LCR tester are connected to the parallel plate capacitor formed by the upper and lower brass plates. Consistency in applying external force during different experimental processes is ensured through a pressure sensor. When the force reaches 1 N, the motor stops running and the dielectric parameters are measured. Data are acquired using the testing system software (TH2832 LCR 2.2.21). Samples are  
Figure 1: Passion fruit sample pictures; these samples become more mature from left to right.  
Figure 2: Electrical characteristics testing platform. Among them are 1. Electrical machinery, 2. Support stand, 3. Force sensor, 4. Lead screw, 5. Sample, 6. Electrodes, 7. Shielding box, 8. Force display, 9. Motor drive module, 10. Microcontroller, 11. LCR tester.  
placed horizontally along the longitudinal axis, and data are collected every 120\({}^{\circ}\) rotation along the longitudinal axis. The obtained dielectric parameters from three measurements are averaged to represent the dielectric characteristics of the sample.  
After placing the test sample between the parallel plates, the equivalent circuit consists of a parallel combination of capacitance \(Cp\) and conductance \(G\). The capacitance value \(Cp\) and conductance value \(G\) at the characteristic frequency are measured using an LCR tester. According to Formula (1), the real and imaginary parts of the dielectric constant are calculated as the relative permittivity \(\epsilon^{\prime}\) and the dielectric loss factor \(\epsilon^{\prime\prime}\)[23; 24], as shown in Formula (2).  
\[Z=G+j\omega C_{p}=j\omega C_{0}\bigg{(}\frac{C_{p}}{C_{0}}-j\frac{G}{\omega C _{0}}\bigg{)} \tag{1}\]  
\[\begin{cases}\epsilon t=\frac{C_{p}d}{\epsilon_{0}S}\\ \epsilon^{\prime\prime}=\frac{G}{\omega C_{0}}\end{cases} \tag{2}\]  
where \(Z\) is the complex impedance, \(\Omega\); \(C_{p}\) is the parallel capacitance of the golden passion fruit, F; \(d\) is the distance between plates during the test, m; \(C_{0}\) is the vacuum capacitance when the dielectric is air, F; \(\epsilon_{0}\) is the dielectric constant of free space, taken as 8.85 \(\times\) 10\({}^{-12}\) F/m; \(S\) is the area of the plates, m\({}^{2}\); \(G\) is the conductance value, \(S\); and \(\omega\) = 2\(\pi\)f; \(f\) is the test frequency, Hz.