A Novel Sustainable and Cost-Effective Triboelectric Nanogenerator Connected to the Internet of Things for Communication with Deaf–Mute People

Abstract

Low-cost and sustainable technological systems are required to improve communication between deaf–mute and non-deaf–mute people. Herein, we report a novel low-cost and eco-friendly triboelectric nanogenerator (TENG) composed of recycled and waste components. This TENG can be connected to a smartphone using the internet of things (IoT), which allows the transmission of information from deaf–mute to non-deaf–mute people. The proposed TENG can harness kinetic energy to convert it into electrical energy with advantages such as a compact portable design, a light weight, cost-effective fabrication, good voltage stability, and easy signal processing. In addition, this nanogenerator uses recycled and waste materials composed of radish leaf, polyimide tape, and a polyethylene terephthalate (PET) sheet. This TENG reaches an output power density of 340.3 µWm⁻² using a load resistance of 20.5 MΩ at 23 Hz, respectively. This nanogenerator achieves a stable performance even after 41,400 working cycles. Also, this device can power a digital calculator and chronometer, as well as light 116 ultra-bright blue commercial LEDs. This TENG can convert the movements of the fingers of a deaf–mute person into electrical signals that are transmitted as text messages to a smartphone. Thus, the proposed TENG can be used as a low-cost wireless communication device for deaf–mute people, contributing to an inclusive society.

1. Introduction

Human communication is required for daily interactions and access to public services, as well as for achieving a better quality of life. However, this form of communication is a significant challenge for deaf–mute people [1,2,3]. Recently, the World Federation of the Deaf (WFD) has estimated that there are 70 million deaf–mute people in the world [4,5]. Generally, transmission of information from deaf–mute to non-deaf–mute people can be achieved through lip reading and sign language interpreters [6]. However, lip-reading is useless when people need to wear masks, limiting the application of this communication approach. On the other hand, the WFD has reported that there are more than 200 sign languages worldwide [7]. In addition, sign language interpreters are scarce and expensive, restricting their global use. Also, for many people, it is difficult to learn sign language and it requires professional training. Thus, novel technological systems are necessary to solve this communication problem between deaf–mute and non-deaf–mute people.

Recently, technological systems integrated with triboelectric nanogenerators (TENGs) have allowed the creation of self-powered devices and smart systems [8,9,10,11,12]. TENGs offer advantages such as an easy working principle, high performance, stable output voltage, low-cost fabrication, and simple signal processing [13,14,15]. These TENGs can be connected to the Internet of Things (IoT) for applications in smart cities, healthcare systems, textile industry, agriculture, transportation infrastructure, and environmental monitoring [16,17,18,19,20,21]. The technology of triboelectric nanogenerators can harness environmental energy, transforming it into electricity. Thus, this technology can be used to develop smart devices that improve the transmission of information from deaf–mute to non-deaf–mute people. The operational principle of TENG resolves around contact-based triboelectrification and electrostatic induction between materials with triboelectric properties [22,23,24]. Consequently, the performance of a triboelectric nanogenerator can be influenced by several factors, including the thickness, contact area, surface charge density, and distance from the triboelectric layers [25,26,27]. Furthermore, the working frequency and the pressure applied to the triboelectric layers affect the performance of the nanogenerators [28,29]. In recent years, various researchers have designed triboelectric nanogenerators that contain triboelectric materials formed by natural and synthetic polymers [30,31,32,33,34,35]. These nanogenerators offer eco-friendly materials and cost-effective fabrication processes, supporting the circular economy and decreasing manufacturing costs. Thus, these TENGs allow for the promising technological development of self-powered smart systems and harvesting the environment’s renewable energy.

Babu et al. [36] developed a green TENG composed of extracted leaf powder of the Rumex vesicarius plant and polyethylene terephthalate (PET). However, the triboelectric layers and electrodes of this nanogenerator used two cardboard sheets as the support frame, which could be easily damaged by high environmental humidity and temperature. Investigations related to the wear of the triboelectric components and performance stability of this nanogenerator are required. Luo et al. [37] designed a living plant leaf-based triboelectric nanogenerator with potential applications for smart agriculture. However, the living leaves of this nanogenerator can be damaged under extreme weather conditions, such as strong winds and a high temperature.

Herein, we propose a sustainable and eco-friendly triboelectric nanogenerator connected to the IoT, which can be used as a low-cost wireless communication device between deaf–mute to non-deaf–mute people. This triboelectric nanogenerator can harvest the kinetic energy of finger movements of a person and convert it into electrical energy. This TENG uses an Arduino UNO board to process its electrical signals and transform them into text messages that can be transmitted to a connected Android mobile phone via the Bluetooth module. For this, we designed an application for mobile phones, which can receive and display these messages. This nanogenerator has advantages such as the use of recycled and waste materials, a compact and portable structure, a light weight, low-cost fabrication, voltage stability, and easy signal processing. The nanogenerator has a first triboelectric layer formed by a fresh radish leaf (Raphanus sativus) that is glued to copper electrode layer. This radish leaf is a biodegradable waste material with a large surface area and a flexible ability to adhere to different substrate types, which offers advantages with respect to other types of triboelectric materials such as wool felt, paper, silk, or fish scales [38,39,40,41]. The second triboelectric layer of the nanogenerator consists of a polyimide layer bonded to another copper electrode layer. These triboelectric parts employ a PET sheet as the supported frame, allowing their contact–separation transduction. The polyimide and PET are recycled materials whose use in the nanogenerator can support the circular economy. This TENG achieves an output power density of 340.3 µWm⁻² using a load resistance of 20.51 MΩ at 23 Hz, respectively. The nanogenerator has a stable voltage behavior and can be used to power small electronic devices.

2. Materials and Methods

2.1. Materials

The triboelectric nanogenerator (TENG) incorporated a radish leaf and a polyamide layer as the triboelectric materials. Both materials were fixed to two copper-coated bakelite plates (52.2 mm × 52.2 mm). The radish leaf (402 μm thick) was recycled from a local supermarket, and the polyamide layer (50 mm wide and 60 μm thick) was obtained from the Steren brand [42].

2.2. Working Mechanism

The triboelectric nanogenerator (TENG) used the contact–separation transduction mode, as depicted in Figure 1. This transduction mode combined electrostatic induction and contact electrification. For the initial resting step (Figure 1a), there was not potential difference between the electrode layers. Applying pressure on the outer surface of the TENG caused the top part (copper-coated bakelite/polyamide layer) of the nanogenerator to come into contact with its bottom plate (radish leaf and copper-coated bakelite). As these triboelectric layers physically touched each other, electrostatic charges accumulated in the connection area due to contact electrification, as shown in Figure 1b. Thus, the polyimide and radish leaf were negatively and positively charged, respectively. Subsequently, the pressure was withdrawn, and charges with the opposite polarity to those of the triboelectric layers were produced in the bottom and top electrodes, as depicted in Figure 1c. As result, electrical potential difference was generated between both electrodes, which caused a current flow when a load resistor was connected. This current ceased when the two plates achieved the maximum gap, as illustrated in Figure 1d. By reapplying the pressure on the top plate of the nanogenerator, the gap was decreased. This change in the separation distance generated a voltage between both electrodes, reinstating the current (Figure 1e). Finally, periodic contact–separation transduction of the TENG generated an alternating current (AC) output signal (Figure 1f).

2.3. TENG Manufacturing and Setup

For the manufacturing of the triboelectric nanogenerator, a copper electrode (62.2 mm × 52.2 mm × 66 μm) was glued to the top area of a first bakelite plate (52.2 mm × 52.2 mm × 1.5 mm), as shown in Figure 2a. This copper tape (electrode) extended beyond the bakelite plate, measuring 10.2 mm in length. The excess length of the copper tape was fixed to the thickness and underside of the bakelite plate, resulting in 8.5 mm of copper film on the underside. Subsequently, a polyamide film was adhered to the copper electrode of the plate, as illustrated in Figure 2b. After, a tinned copper wire with a diameter of 644 μm was soldered to the underside of the plate, as shown in Figure 2c. Figure 2d depicts a second copper tape-coated bakelite plate (52.2 mm × 52.2 mm × 1.5 mm) of the TENG. Additionally, the radish leaf (Figure 2e) was cut to obtain a surface area of 52.2 mm × 52.2 mm, which was glued to the copper electrode of the second plate. For this, white glue was used on the second plate, employing a spin-coating equipment at 1550 rpm for 15 s to attach it to the radish leaf. The radish leaf was distributed over the glue-coated area on the second bakelite plate (Figure 2f). After, the radish leaf was left to dry at room temperature for 24 h. Later, we welded a tin copper wire to the electrode of the second plate. Next, the bakelite plates were glued to a recycled PET sheet (Figure 2g). Finally, Figure 2h shows the main components of the radish leaf-based nanogenerator. For the proposed TENG, the polyamide layer served as the electronegative triboelectric material and the radish leaf functioned as the electropositive triboelectric layer.

The experimental setup to assess the performance of the radish leaf-based triboelectric nanogenerator is illustrated in Figure 3. This setup included a controlled vibration shaker. Vibration generation was achieved through a combination of a function generator (Agilent 33500B series, Santa Clara, CA, USA), a direct current source (B&K Precision 9129B, Yorba Linda, CA, USA), and a signal amplifier (Texas Instruments TPA3118, Dallas, TX, USA). To quantify the vibration acceleration, a vibrometer (LUTRON VB-8213, Lutron, Coopersburg, PA, USA) was used. Moreover, a digital oscilloscope (TEKTRONIX TBS 1052C, Beaverton, OR, USA) was connected to both copper electrodes of the radish leaf-based device. This setup assessed the performance of the device relative to vibration accelerations and frequencies.

3. Results and Discussion

We hereby report the measurements of a sample of the radish leaf using Fourier transform infrared spectroscopy (FTIR), scanning electron microscopy (SEM), and atomic force microscopy (AFM). Furthermore, experimental results regarding the performance, humidity influence, and use of the radish leaf-based triboelectric nanogenerator are presented.

3.1. Fourier Transform Infrared Spectroscopy (FTIR)

FTIR analysis was used to identify the chemical structure of a sample of radish leaf. Figure 4 depicts the attenuated total reflection (ATR)–Fourier transform infrared spectroscopy (FTIR) spectra acquired from a sample of radish leaf. The IR spectrum of the radish leaf was recorded using an FTIR spectrometer (Agilent 600 FTIR). The data obtained from the FTIR spectra of the radish leaf showed different transmittance peaks ascribed to the different groups in the leaf (Figure 4). Plant biomass (e.g., leaves, flowers, bark, and pods contain lignin, cellulose, and hemicellulose) are rich sources of bioactive compounds such as ascorbic acid, flavonoids, actinoids, and phenolic compounds. For untreated cellulose, specific peaks at 3315 cm⁻¹ and 2898 cm⁻¹ are ascribed to the characteristic peaks of O-H and C-H stretching vibration, respectively, and hemicellulose, derived principally from fatty acids. These results are presented in

Table 1. Functional groups of a radish leaf.

No	Peak Vales	Functional Group
1	3262.95	O-H
2	2917.76	O-CH3
3	2848.33	C-H in aldehydes and acids
4	1596.76	N-H
5	1411.63	CH2
6	1027.87	P-O
7	593.96	N=C=S

.

3.2. Scanning Electron Microscopy (SEM)

The surface morphology of a radish leaf sample was obtained using SEM images. Figure 5a–d depict protrusions, roughness, and porosities of the radish leaf, which may affect the performance of the radish leaf-based triboelectric nanogenerator. In addition, Figure 5a illustrates the uniform surface of the radish leaf. Figure 5c,d depict the cellulose fiber of the radish leaf. Also, particular features of the radish leaf are observed, such as cellulose fiber, lignin, and characteristic veins. Finally, Figure S1 of the Supplementary Materials depicts the elemental composition recorded by EDS of the radish leaf used in the nanogenerator.

3.3. Atomic Force Microscopy (AFM)

The roughness of a radish leaf fiber was characterized using AFM equipment (dimension edge Bruker, Santa Barbara, CA, USA). Figure 6 shows the roughness of a section of the sample of radish leaf. We can observe valleys and peaks on the sample’s surface. This topography can increase the contact surface of the radish leaf sample with the polyimide film of the TENG.

3.4. Output Performance of the TENG

To study the triboelectric influence of the radish leaf in a nanogenerator under finger actuation, we measured the peak-to-peak open-circuit voltage of two TENGs. The first TENG incorporated a triboelectric layer of radish leaf and another triboelectric layer of polyimide. The second TENG did not include the radish leaf and only considered the triboelectric layer of polyimide and a glue coating on the copper electrode, which was deposited employing a spin-coating method at 1550 rpm for 15 s. We connected both nanogenerators in parallel to an oscilloscope, as shown in Figure S2 of the Supplementary Information. The external force was manually applied to the top plate of each device using finger actuation. We used finger actuation to simulate the use of the TENG by a person. The open-circuit voltages of the nanogenerators were recorded with the assistance of an oscilloscope, including an impedance probe of 100 MΩ. Figure S2b,c of the Supplementary Materials display the peak-to-peak open-circuit voltage results for both nanogenerators. The TENG with the radish leaf produced a higher peak-to-peak open-circuit voltage (V_p-p) compared to the nanogenerator without the radish leaf. Thus, the TENG with the radish leaf and a polyimide layer achieved a maximum V_p-p close to 52 V, while the TENG with only the polyimide layer generated a maximum V_p-p of less than 20 V. This demonstrated that the radish leaf coupled with the polyimide layer could enhance the performance of the proposed device. For a visual representation of the output performance of the nanogenerators, please refer to Video S1 of the Supplementary Information.

Figure 7a shows the V_p-p of the radish leaf-based TENG under different vibration frequencies. In most of the frequencies, the V_p-p of the nanogenerator improves when the frequency increases. Only under the vibration frequency of 15 Hz did the V_p-p of the nanogenerator decrease in comparison to the frequency of 13 Hz. This reduction in the V_p-p could have been caused by variations in the environmental humidity. For all the frequencies, the maximum V_p-p of the device was achieved at a frequency of 23 Hz. On the other hand, we assessed the output performance of the radish leaf-based device using several vibration accelerations, from 0.5 g to 6.0 g, maintaining a constant frequency of 23 Hz. Figure 7b depicts the V_p-p of the nanogenerator under different vibration accelerations. The V_p-p of the nanogenerator increased when the vibration acceleration increased until achieving the value of 5 g. After 5 g, the V_p-p of the nanogenerator had a low decrement. Furthermore, we measured the output voltage and current of the TENG with respect to the load resistor. The voltage increased when the load resistance (R_L) changed from 1.5 MΩ to 180 MΩ, while the current reduced when the load resistance increased, as shown in Figure 7c. However, the V_p-p of the device decreased when the load resistor achieved a value of 151 MΩ. Also, we measured the output power density of the device in relation to the load resistance, as illustrated in Figure 7d. We used load resistors ranging from 1.5 MΩ to 180 MΩ between the two electrodes of the nanogenerator at a vibration frequency of 23 Hz. The maximum output power density reached 340.3 µWm⁻² with a load resistor of 20.5 MΩ, as demonstrated in Video S2 of the Supplementary Information. The maximum power density was achieved under matching load conditions when the load resistance equaled the output resistance of the TENG. Finally, we assessed the V_p-p stability of the nanogenerator under a vibration acceleration of 1.8 g with a frequency of 23 Hz over 41,400 operating cycles (Figure 7e). The results indicated an output voltage stability of the device with a gradually increasing trend, which could have been caused by the contact electrification influence between its triboelectric layers. After 41,400 working cycles, the triboelectric layer based on the radish leaf showed minimum wear. Moreover, the compact design of the proposed TENG allows for the simple replacement of its triboelectric layers.

To assess the influence of environmental humidity on the open-circuit voltage of the proposed nanogenerator, we measured its response under three different relative humidity values (40%, 50%, and 60%). We used the setup depicted in Figure 8, including a dehumidifier 3 L of Steren, a x-y mechanism, a linear actuator, a tilting vise, a DC source, and an oscilloscope with a 100 MΩ impedance probe. This mechanism allowed the control of the position and velocity. The first plate of the TENG formed by the polyimide layer was attached to the end of the linear actuator. On the other hand, the second plate of the TENG composed of a radish leaf was adhered to a vertical wooden plate whose angle was controlled by a tilting vise. For these measurements, we used a maximum separation distance between both triboelectric layers of 22.2 mm and a minimum gap of 1 mm. This minimum separation distance was employed to avoid the wear of the radish leaf layer, which could affect the response of the TENG.

Table 2. Measurements of the open-circuit voltage of the radish leaf-based triboelectric nanogenerator at 10 Hz frequency and 40% relative humidity.

Operating Cycles	Vp-p (V)	Vmax (V)	Vmin (V)	Temperature (°C)
1	5.4	2.0	−3.4	19.3
3000	5.2	2.1	−3.8	19.4
6000	7.5	2.8	−4.7	19.6
9000	8.4	3.0	−5.4	19.6
12,000	7.8	2.9	−4.9	19.6
15,000	7.8	2.9	−4.9	19.6
18,000	8.1	3.0	−5.1	19.6
21,000	8.3	3.1	−5.2	19.6
24,000	8.9	3.4	−5.5	19.6
27,000	8.9	3.4	−5.5	19.6
30,000	8.8	3.4	−5.4	19.6
33,000	8.2	3.1	−5.1	19.6
36,000	8.2	3.1	−5.1	19.6

,

Table 3. Measurements of the open-circuit voltage of the radish leaf-based triboelectric nanogenerator at 10 Hz frequency and 50% relative humidity.

Operating Cycles	Vp-p (V)	Vmax (V)	Vmin (V)	Temperature (°C)
1	2.8	1.0	−1.8	19.9
3000	4.1	1.4	−2.7	20.0
6000	4.2	1.5	−2.7	20.0
9000	4.5	1.6	−2.9	20.0
12,000	5.3	1.9	−3.4	19.9
15,000	6.0	2.2	−3.8	20.2
18,000	5.6	2.0	−3.6	20.3
21,000	5.6	2.0	−3.6	20.3
24,000	6.1	2.2	−3.9	20.2
27,000	6.0	2.1	−3.9	20.2
30,000	5.9	2.1	−3.8	20.1
33,000	5.9	2.0	−3.9	20.1
36,000	5.8	2.1	−3.7	20.2

and

Table 4. Measurements of the open-circuit voltage of the radish leaf-based triboelectric nanogenerator at 10 Hz frequency and 60% relative humidity.

Operating Cycles	Vp-p (V)	Vmax (V)	Vmin (V)	Temperature (°C)
1	1.4	0.6	−0.8	22.0
3000	2.5	1.1	−1.4	22.0
6000	3.0	1.3	−1.7	22.0
9000	3.0	1.3	−1.7	22.0
12,000	3.2	1.4	−1.8	22.0
15,000	2.8	1.2	−1.6	22.0
18,000	2.8	1.2	−1.6	22.0
21,000	2.3	1.0	−1.3	22.0
24,000	2.4	1.0	−1.4	22.0
27,000	2.4	1.1	−1.3	22.0
30,000	3.1	1.3	−1.8	22.1
33,000	2.6	1.1	−1.5	22.1
36,000	2.5	1.1	−1.4	22.1

show the measurements of the open-circuit voltage of the device after 41,400 working cycles at 10 Hz with a relative humidity (RH) of 40%, 50%, and 60%, respectively. The magnitudes of the minimum open-circuit voltage (V_min), maximum open-circuit voltage (V_max), and V_p-p of the device significantly decreased when the relative humidity increased. The maximum V_p-p of the device with an RH of 40% decreased up to 31.5% and 64.0% compared to the TENG at RH of 50% and 60%, respectively. Thus, the increment in the environmental relative humidity decreased the output voltage of the proposed device.

3.5. Applications

The radish leaf-based triboelectric nanogenerator produced an AC signal. This signal was rectified using a diode bridge and stored in capacitors, as shown in Figure 9a. After, the TENG was placed on a shaker oscillating at 1.8 g acceleration and 23 Hz frequency. The rectified signal of the TENG was employed to charge five different capacitors (0.22 μF, 1 μF, 10 μF, 33 μF, and 47 μF). The charging performance of these capacitors is depicted in Figure 9b.

Furthermore, we powered small electronic devices using the radish leaf-based TENG. Figure 9c depicts the charging voltage of a 33 μF capacitor for 480 s at 3.6 g acceleration and 23 Hz frequency. Figure 9d illustrates the voltage stored in the 33 μF capacitor, reaching 2.06 V. This capacitor had a discharge voltage close to 0.80 V when a digital chronometer was powered. Videos S3 and S4 of the Supplementary Information depict a digital chronometer and digital calculator that were powered by the nanogenerator. In addition, Figure 9e,f show the charging and discharging results of a 33 μF capacitor, reaching 2 V and dropping to 0.62 V when a digital calculator was turned on. The Supplementary Information, including Video S5 and Video S6, shows the application of the nanogenerator, lighting various commercial green and blue LEDs. The proposed TENG generated electrical energy through finger actuation to illuminate these LEDs. Video S6 exhibits the nanogenerator lighting 116 blue LEDs.

The proposed system can transform and record the mechanical energy applied with the hand on the nanogenerator into an electrical energy signal. For this, the system uses the Arduino Uno board, which is responsible for detecting a variation in the signal produced by the nanogenerator when it is pressed (Figure 10). This variation in the signal is interpreted by the Arduino microcontroller as a pulse. When a significant change in the signal reading is detected, a timer is started to measure the duration of the pulse. If the pulse signal reaches the predefined threshold, then it is considered a valid pulse, is counted, and a digital counter is incremented. Each time the sensor detects a new peak in the signal, the counter is updated, thus recording the total number of pulses.

Once the first pulse has been recorded, the system reads for three seconds to see if there are more pulses. With the number of keystrokes recorded, the program proceeds to assign a word to each number of keystrokes (1 = hello, 2 = yes, 3 = no, 4 = goodbye, and 5 = help). In addition, if five keystrokes are registered, the system activates a light-emitting diode (LED) and a buzzer to emit the distress signal in Morse code (SOS). The duration of the light and sound signal varies according to whether it corresponds to a dot or a line in Morse code. In this way, the user can request help or assistance in a possible emergency. Also, the system includes the ability to send the number of times the nanogenerator was pressed to a mobile device via a Bluetooth module. To achieve this, a serial communication library is used to transmit the data to the Bluetooth module. Video S7 of the Supplementary Information shows the performance of a low-cost wireless communication device in a conversation from deaf–mute to non-deaf–mute people.

Table 5. Performance parameters of different triboelectric nanogenerators fabricated with recycled materials.

Triboelectric Materials	Triboelectric Layer Area	Open-Circuit Voltage	Power Density	Advantages	Drawbacks	Ref.
Rumex vesicarius and poly(ethylene terephthalate) (PET)/polytetrafluoro	50 × 50 mm2	3.86 V	1.894 mWm−2 at RL of 20 MΩ	Easy design, cost-effective fabrication, and voltage stability	Fragile support frame	[36]
Coffee grounds and polyimide	52.2 × 52.2 mm2	90.7 V	75.48 mWm−2 at RL of 39.97 MΩ	Portable configuration, low-cost eco-friendly materials, and easy processing signal	Wear of triboelectric layers and humidity affects its performance	[8]
Nopal powder and polyimide	52.2 × 52.2 mm2	16.4 V	0.556 mWm−2 at RL of 76.89 MΩ	Compact design, simple operating principle, and low-cost manufacturing	Wear of triboelectric layers	[43]
Hosta plantaginea leaf and PMMA	80 × 80 mm2	230 V	45 mWm−2 with RL of 10 MΩ	Eco-friendly materials	Limited service time	[44]
Rice paper and PVC	30 × 30 mm2	244 V	376.4 mWm−2 with RL of 70 MΩ	Low-cost recycled materials and stable performance	Wear of triboelectric layers	[45]
Radish leaf and polyimide	52.2 × 52.2 mm2	26 V	0.340 mWm−2 at RL of 20.51 MΩ	Eco-friendly materials, portable design, cost-effective fabrication, voltage stability, and easy signal processing	Humidity affects its performance	This work

shows the comparison of the main performance parameters, advantages, and drawbacks of several triboelectric nanogenerators composed of recycled materials. Our nanogenerator has a simple design that allows its cost-effective fabrication using recycled and waste materials. In addition, the proposed TENG presents a portable structure, a light weight, and easy signal processing, which are advantages for its application as a novel communication device with social impact for deaf–mute people. However, when the relative humidity increases, the open-circuit output voltage of nanogenerator decreases. To lessen this negative effect, coatings with hydrophobic surfaces could be applied on the triboelectric materials to decrease the influence of the relative humidity.

Furthermore, the utilization of recycled and waste materials can support the circular economy, reducing the fabrication costs of triboelectric nanogenerators. By employing a glue coating, radish leaves can be glued to various surfaces of recycled materials, facilitating the development of sustainable and cost-effective TENGs.

4. Conclusions

A novel low-cost wireless communication device from deaf–mute to non-deaf–mute people was developed. This communication device was designed using recycled and waste materials with advantages such as a compact portable structure, a light weight, a simple fabrication process, good voltage stability, and easy signal processing. The operating principle of the proposed device used a triboelectric nanogenerator with a contact–separation transduction mode. This TENG harvested the kinetic energy of the movements of the fingers of a person to convert it into electrical signals. Thus, these signals were transmitted as text messages to a smartphone. The proposed nanogenerator reached a maximum output power density of 340.3 µWm⁻² using R_L of 20.5 MΩ at 23 Hz, respectively. Furthermore, the effect of the relative humidity on the output voltage of the triboelectric nanogenerator was measured. Also, this nanogenerator was employed to power various devices, including LEDs, chronometers, and calculators. Also, the array of radish leaf-based TENGs offers a promising technology for clean energy generation sources with applications in smart sensors, electronic devices, alarm systems, and communication systems. The integration of IoT with recycled and waste-based TENGs can allow the development of communication systems for deaf–mute people, contributing to a more inclusive and sustainable society.

Future research directions will incorporate polymer coatings to generate hydrophobic surfaces on the triboelectric layers of the TENG to improve its performance under high relative humidity. Furthermore, we will measure the service time of the triboelectric layer based on the radish leaf material.