Researchers from the University of Colima (UdeC), alongside other scientists from several universities in Mexico, have discovered that papaya and lemon skin can absorb microwave frequencies (ranging from 8 to 10.5 GHz) generated by electronic devices. 

According to a note from UdeC's Press Office, large quantities of these fruits' peels are discarded in Mexico and the state of Colima.

In statements collected by the university, José Luis Álvarez Flores, a professor from the Faculty of Mechanical and Electrical Engineering (FIME) at UdeC, explained that the large amounts of organic waste could be used as microwaves absorbers, instead of being discarded. 

He mentioned that the current microwave absorbers are made of polyurethane, a highly polluting material derived from petroleum. Some uses include military applications: shielding or casing for printed circuit boards (PCBs), antenna covers, and test boxes, to reduce electromagnetic interference (EMI).

Álvarez Flores noted that frequency absorbers "are recommended in areas with high frequencies due to the increasing demand for communication."

Flores explained that the theory forecasts that all materials with high carbon content can absorb microwave frequencies, which is why they undertook measurements using a WR90 waveguide, operating from 6-8 GHz up to 20 GHz.

Specific Absorption Rate (SAR) in microwaves refers to the measurement of energy absorbed by the human body. This rate is measured in watts per kilogram (W/kg), and it is recommended that, for example, the SAR of a cell phone should not exceed 2 W/kg.

For the research, the professors placed pineapple, papaya, melon, watermelon, banana, and coconut inside a microwave to take samples. 

The research was published in the online library Wiley, titled “Evaluation of the Microwave Absorption Properties of Solid Dehydrated and Powdered Agricultural Waste at X-Band Frequencies.”

The article is open to the public, and it shows that lemon and papaya peels have the highest frequency absorption (68.32% at 9 GHz and 63.46% at 10 GHz, respectively) and the widest bandwidth.

Multidisciplinary Work

The research also involved professionals from the Universidad Autónoma de Zacatecas, the National Technological Institute of Mexico Campus San Luis Potosí, and the Universidad Autónoma de San Luis Potosí.

The academics involved are Jorge Flores Troncoso, Ricardo Gómez Rodríguez, Jorge Simón, Gustavo Vera Reveles, Marco Cárdenas, Emmanuel Hernández, and Juvenal Villanueva Maldonado.

From the Faculty of Mechanical and Electrical Engineering, the team included Leonel Soriano Equihua, Marcelo Maciel Barbosa, Pablo Armando Alcaraz Valencia, Hugo Castillo Topete, and José Luis Álvarez.