## 5 Output Voltage and Feasibility  
[PERSON] [91] notes that vibration-based energy harvesters strongly depend on the alignment of their resonance frequency with surrounding vibration frequencies. Although using flexible materials and multi-mode structures can substantially improve energy output, these systems often remain confined to specific frequency ranges, limiting their use in places with low or inconsistent vibrations. Additionally, optimizing multiple parameters at once becomes challenging for large-scale applications. In [PERSON] et al. [5], a maximum voltage of 6.06 V was achieved after 20 s of continuous pressure by a 60 kg individual. While this output is enough to power low-power devices (e.g., LED streetlights or small electronics), significantly more scaling would be requiredfor larger energy needs. Combining solar PV with piezoelectric transducers helps maintain a steady power supply--even when weather changes--because the piezoelectric part can supplement energy production in high-foot-traffic periods [16]. In [17], each step generated between 1 V and 14 V, depending on the user's weight. On average, 9600 steps were needed to charge a 12 V battery. This approach suits powering low-power streetlights in busy areas. Likewise, Ref. [15] reported an average output of 9.46 V and 126.6 mA under test conditions, peaking at 9.59 V and 134.1 mA (with a 70 kg individual walking over piezoelectric tiles). This voltage can run small electronic devices such as sensors or mobile chargers. The hybrid system proposed in [15] is suitable for low-power operations, especially where both kinetic and solar energy are accessible. By using two energy sources, the system remains consistent even when solar is unavailable. [PERSON] et al. [4] employ a Spatially Varying (SV) electric field model for piezoelectric energy-harvesting gyroscopes. At optimum load resistance (\(10^{3}\)\(\Omega\) to \(10^{8}\)\(\Omega\)), the system achieves 1.3 mV in open-circuit and 2.1 mV in closed-circuit near 65 kHz (energies-16-02000-v2). Though these are low-power outputs (millivolt scale), they can still power small MEMS sensors. The SV model is also more accurate than constant-field models when predicting performance across different loads. [PERSON] et al. [3] recorded an open-circuit voltage as high as 33.7 V. However, when powering a single LED, the output dropped to 2.4 V, and two LEDs in series produced 4.8 V. Nonetheless, it is enough for low-power applications such as LEDs or other small devices. Installing 30 tiles at the entrance of a building could generate an estimated 60 Wh over 8 h--enough to power a security camera for around 11 h. [PERSON] et al. [6] propose a hybrid system that is well-suited for large-scale setups, combining the continuous foot traffic during football matches with available solar power; this hybrid system ensures a reliable output even when one source is limited. [PERSON] et al. [26] report each mat module can deliver a peak open-circuit voltage of 192 V, a short-circuit current of 69.10 mA, and a maximum power of 100 mW--156% more voltage and 212% more power than equivalent hybrid shoe designs. The mat can also store 6.88 V in 10 s under steady 120 BPM stepping by a 60 kg individual, enough for short-term power. In a later design, [PERSON] et al. [27] confirm the same peak performance figures (192 V, 69.10 mA, 100 mW), again highlighting a 6.88 V storage level in 10 s of continuous stepping at 120 BPM by a 60 kg person. Although [PERSON] and [PERSON] [62] show promise, they do not provide detailed power results. By contrast, [PERSON] et al. [26; 27] report the largest increase in energy output: a 156% surge in voltage and a 212% improvement in peak power over prior systems, thanks in part to a portable, modular configuration. Still, their tri-hybrid generators were mainly tested in controlled environments. [PERSON] et al. [99] explored biomechanical energy from walking, but they offered fewer specifics on power output than [PERSON] et al. [26; 27]. [PERSON] et al.