Table 1.

Characteristics of various sources for energy harvesting.

Reference	Energy source	Power density	Efficiency (%)	Advantage	Bottleneck
[30,31]	Perovskite solar cells	35.0 $\mathsf{\mu }$W/cm${}^2$	25.2	Flexible and lightweight; suitable for wearable applications	Require light
[32,33,34,35]	Thermoelectric	Human: 100 $\mathsf{\mu }$W/cm${}^3$ Industrial: 100 mW/cm${}^3$	10–15	Cost-effective technology; does not require body motion or light	Low power source
[36,37]	Acoustic	1.436 mW/cm${}^2$ at 123 dB	0.012	Require minimum maintenance; suitable to be used in remote or inaccessible locations	Hard to capture energy from the sounds wave source
[35,38,39,40]	Pyroelectric	3.5 $\mathsf{\mu }$W/cm${}^3$ at the temperature rate of 85 °C/s $@0.11$ Hz	1–3.5	Cost-effective technology; ubiquitous and serves as a low-grade waste	Low output power
[41,42,43]	Piezoelectric	29.2 $\mathsf{\mu }$W/mm${}^3$	83.3	Does not require RF waves or light	low power source; require body activity
[44,45,46]	Biofuel cells	3.7 mW cm${}^{-2}$	86	The integration of the power module and sensing module results in better compactness; does not require RF waves, body activity, or light	The analyte concentration influences the power density
[47,48]	Triboelectric	2.5 W/m${}^2$	——	Simple fabrication process and low cost	low power source; require body activity
[38]	RFEH	GSM: 0.1 $\mathsf{\mu }$W/cm${}^2$ WiFi: 0.01 $\mathsf{\mu }$W/cm${}^3$	50–70	Does not require light or body motion and is continuously available	Low output power; distant dependent