Known and unknown phenomena of nonlinear behaviors in the power harvesting mat and the transverse wave speaker

Known and unknown behaviors of three nonlinear systems are described in this paper. The power harvesting project is mentioned where the power generation mat using piezoelectric elements was experimented and demonstrated in Tokyo station of Japan Railways east (JR-east) company in 2006 and 2008 respectively. The commuters and passengers generate electric power by passing the power generation mats through SUICA (RFID) gates which can provide enough electric power for operating the RFID gate system. The system is composed of the power generation circuit and the super capacitor circuit to store the generated electric power. Thermoelectric power generation project is also proposed in this paper where peltier elements are used for generating the continuous power harvesting. Unknown phenomena of the transverse acoustic waves from a new speaker are depicted in this paper. The new speaker under development is useful in railways stations and trains where we can hear the transverse acoustic sound clearly in noisy places. The transverse wave speaker does not generate reverberant sound and the sound attenuation in distance is much smaller than 6dB. 1. History of power harvesting mat in JR-east In 2003, one of my undergraduate students (Mr. Kohei Hayamizu) for senior project developed a power generation circuit using human voices where a piezoelectric element was used [1]. In 2003, then, I have proposed a new power harvesting project to Mr. Mutsutake Ohtsuka at the JR-east party who was the president of JR-east railway company [2]. Instead of using human voices, my idea is that a variety of vibrational energy in railways can be converted to electronic power. Because JR-east railway company in Tokyo is infamous for trains jampacked with commuters, vibrational energy by commuters walking or foot steps can be utilized for electric power generation. In July 2006, we have experimented the first power generation mat in the headquarter building of JR-east railway company in Shinjuku [3]. Based on the result of the first experiment in Shinjuku, from October to December 2006 for two months, we have tested the second power generation mat in Tokyo station at the north gate of Marunouchi where the mat was laid down at the automatic IC card SUICA ticket gate [2]. The durability of the power generation mat and the performance and deterioration of the piezoelectric elements were evaluated through the experiment. The third experiment was performed again in Tokyo station in January 2008 where the total of 90 m power generation mat were laid down in the stairs, in front of the convenience store, and the SUICA ticket gate [4]. In the second power generation mat, the conventional piezoelectric elements (speaker elements) were used while the third power generation mat uses piezoelectric elements which are specially tailored and dedicated for generating electric power. The new piezoelectric device should be able to generate electric power 10 times better than that of the second generation mat. Since it is a single-layered piezoelectric element, it is expected to generate more electric power by multiple-layered piezoelectric element. The size, thickness, and shape of the piezoelectric elements are keys for better performance. The durability is also considered in our project. 2. Principle of power generation mat Piezoelectric effect was discovered by Jacques and Pierre Curie in 1880 when a mechanical force was given to certain crystalline minerals, the crystals became electrically polarized. The converse effect was mathematically deduced by Gabriel Lippmann in 1881. “Piezo” is a Greek word which means pressure. Best known piezoelectric application is a barbeque or cigarette lighter that uses a piezoelectric element to create a spark to ignite a gas. Best known converse application is a piezoelectric speaker used in mobile phones or laptop computers to create acoustic sound. Piezoelectric ceramic element is widely used in our society and called PZT. The piezoelectric element is the mixed solid solution of lead zirconate (PbZrO3) of ferroelectric and lead titanate (PbTiO3) of anti-ferroelectric. The piezoelectric element is a bidirectional energy transformation transducer: mechanical energy to electrical energy and electrical energy to mechanical energy. Fig. 1 (a) (b) (c) depict current piezoelectric power generation models respectively: (a) neutralized ions in unpoled ferroelectric ceramic, (b) unbalanced ions in poled ferroelectric ceramic when compressed, and (c) unbalanced ions in poled ferroelectric ceramic when expanded. Electrical dipoles in Fig. 1 (a) tend to be aligned in regions called Weiss domains. The Weiss domains are randomly oriented. When the piezoelectric ceramic material is pressed by our steps, positive electric charges are generated on top while negative electric charges are on bottom. When releasing our steps from the piezoelectric ceramic material, negative electric charges are generated on top while positive electric charges are on bottom. We don’t know how to construct the best Weiss domains for power generation. (a) neutralized ions (b) unbalanced ions (compressed) (c) unbalanced ions(expanded) Fig. 1 Unpoled and poled ferroelectric ceramic 3. Power generation mat circuits Our power generation mat uses piezoelectric elements in parallel. There are two types of circuits to store the generated electric power: one using the full as shown in Fig. 2 and another using the pump circuit as shown in Fig. 3. Fig.2 Bridge circuit with a super capacitor -bridge circuit Fig. 3 Pump circuit with a super capacitor 4. Computation of generated electric power Generated electric energy is given by the following equation: Energy = CV (joule) where V is the voltage of the C capacitor (Farad). In other words, one joule is equivalent to one For example, when 1 F capacitor is charged and the voltage becomes 4V, the energy is 8 Watt·second. Fig. 4 and Fig.5 show JR-east p 2006 respectively. Based on our experiment, a 47uF capacitor is charged to 7.8 Volt by ten times stepping a single piezoelectric element. This means that one step to a piezoelectric element generates 0.14 m Conventional piezoelectric speakers were used in the power generation mat. Fig. 4 Power generation mat in 2006 Fig. 5 Power generation mat at Marunouchi North gate of Tokyo station in 2006 Watt·second. ower generation mat in