WO2012078024A1

WO2012078024A1 - Thermoelectric generator for soil sensor mote

Info

Publication number: WO2012078024A1
Application number: PCT/MY2011/000102
Authority: WO
Inventors: Wan Adil Wan Jamil; Amilia Ahmed Khozim; Gunawan Witjaksono; Airul Azha Abd Rahman; Aymen M Karim
Original assignee: Mimos Berhad
Priority date: 2010-12-10
Filing date: 2011-06-17
Publication date: 2012-06-14
Also published as: MY181773A

Abstract

The present invention provides a thermoelectric generator for soil sensor mote (20). In the ambient energy harvester, a lens (32) and heat trap compartment (36) provides light concentration (40) which increases the temperature gradient between the ground layers and ground surface (26) of the earth's soil which is detected by cold junction (22) and hot junction (24) respectively. A charge is developed and accumulated in the thermal element (40). The harvested power is then transformed to electrical potential. The micro thermal energy harvester in the soil sensor mote (20) device shall replace the usage of batteries, works even in rain and dry spells seasons, eliminate maintenance drawback and improve the deployment in locality where human assistance is remote.

Description

THERMOELECTRIC GENERATOR FOR SOIL SENSOR MOTE

The present invention relates to thermal gradient power generation, more particularly to thermal power generation for soil sensor mote wireless device to be used in remote monitoring systems.

BACKGROUND ART

Soil sensor device is used in remote monitoring systems mainly in farming activities. The parameter monitored is mainly soil moisture. The use of soil sensor has been expanded to monitor soil temperature and soil nutrient content. Due to the wide deployment and coverage of sensors required, wireless network is envisioned as the way forward for remote monitoring systems.

Present wireless sensor network rely on battery powered mechanism for power source. However, in term of lifespan, batteries are not sustainable source. For lush areas, the act of changing batteries of exhausted motes is just impractical. Therefore reliable and indefinite power source is required where the underlying lifeline requirement is a stable and zero downtime power management. Efforts are being made to develop a working prototype on non volatile energy source as a substitute for conventional batteries cells in soil monitoring system. Presently, there is a prior art of a battery-less soil sensor where the solution is based on mechanical vibration. This sensor includes a mechanical energy harvester. The sensor is configured to sense with the power supplied by the mechanical harvester where then non-volatile memory is configured to store output from the sensor. Another prior art listed a battery-less soil sensor device using RFID. This approach proposes a radio frequency electromagnetic waves energy harvester to run the wireless, battery-less sensor.

The above prior arts have unique specialty and limitation individually. The present invention is made in view of the need to provide energy without requiring routine maintenance by using the existing available resources. A simpler and minimal structure is proposed to achieve this aim while tapping power from an alternative source of power. SUMMARY OF INVENTION

The present invention proposes a thermoelectric generator for soil sensor mote device. Thermal power is harvested from temperature gradient between ground layer and surface of the earth's soil. Light is concentrated to achieve an enormous temperature gradient. The harvested energy provides energy even in rain and dry spell seasons without requiring routine maintenance. The thermal-powered soil sensor mote device is an autonomous device working with two section system mechanism: ambient energy harvester and electronic hardware. In the ambient energy harvester section, essential power is harvested from temperature gradient between ground layer and surface of the earth's soil which has shown to be enormous after light concentration. The harvested power is then transformed to electrical potential via the electronic section. The micro thermal energy harvester in the soil sensor device shall replace the usage of batteries, eliminate maintenance drawback and improve the deployment in locality where human assistance is remote.

BRIEF DESCRIPTION OF DRAWINGS

Fig. 1 is a sectional drawing of the thermal-powered soil sensor mote.

Fig. 2 is a sectional drawing of the light mechanism and heat trap compartment.

Fig. 3 is a diagram of the thermal element.

Fig. 4 is a block diagram of the thermal energy harvester architecture. DESCRIPTION OF EMBODIMENTS

Hereinafter, the present invention is described in detail.

The invention involves a thermal-powered soil sensor device as an autonomous device. The soil sensor mote [20] with the micro energy harvester is shown in Fig. 1 .

For the ambient energy harvester, both cold junction [22] and hot junction [24] are exposed at two different temperatures, where cold temperature is obtained in the underground level and the hot temperature is found on the ground surface [26]. The cold temperature underground can have a prevailing temperature of 28°C while the hot temperature of the ground surface after light concentration [28] is raised from nominal 33°C to 80°C. With this, the temperature gradient, At is approximately 50°C. Light concentration treatment starts with incident light [30] of the sun being concentrated by means of using lens [32] on top of the heat-trap compartment [34]. A heating plate [36] is housed at the bottom while a reflector [38] is used to preserve heat for an extended period of time. The reflector is a funnel shaped reflector. The pointing light heats up the micro thermal element [40], which by far has recorded a temperature up to 100°C. Likewise, nominal temperature 4 inches below the ground surface is 28°C with a typical variance most of the time of ±3°C. The light concentration mechanism and heat trap compartment [34] are shown in Fig. 2. A thermal element [40], as shown in Fig. 3, is sandwiched by hot junction [24] on top and cold junction [22] at the bottom to convert heat into electricity. The hot junction [24] is connected to the heat compartment while the cold junction [22] is coupled to a damper rod [42] which is buried underground. This damper rod [42] is to dissipate heat to the ground level.

Inside the thermal element, the temperature gradient develops a charge around the thermal sensitive plates. In the electronic hardware section, accumulated charge is captured by the highly-sensitive capacitor and the dc-converter converts the charge to voltage potential to a certain level that sufficient enough to run wireless sensor mote. Prior to output distribution, the voltage is stored in a storage reservoir such as super capacitor. The large reservoir ensures continuous current flows to the entire system without interruption. As a result a stable output voltage is achievable.

The main blocks of the electronic hardware can be divided into 4 main functions. They are micro thermal element [40], dc-dc converter, storage element and voltage stabilizer prior to stable output voltage. A stable accumulated dc output voltage is developed from thermal element [40] whereby both surface expose to two different temperature gradient, ground and soil surface. This gradient accumulates positive and negative charge electrically. Potential developed at both junctions approximately 10mV/At. This level is sufficient to drive step-up dc-to-dc converter to a satisfactory level to run wireless sensor network motes, transmitter and receiver efficiently.

A stable dc is uncompromised for reliable sensor motes. In securing uninterruptable power supply an efficient storage element is proposed. This could be fulfilled in the form of super-capacitor. As the element is capable to store large charge in a long period of time, continuous current supply to wireless sensor node is tenable. The expected current consumption by wireless sensor note is between 100 -200 mA/h, depending on load characteristics. The overall architecture of the thermal energy harvester is illustrated in detail in Fig. 4.

Accordingly, the invention disclosed a thermoelectric generator for soil sensor mote [20] device. The thermoelectric generator for soil sensor mote [20] device is an autonomous device working with a two section system mechanism, ambient energy harvester and electronic hardware. In the ambient energy harvester section, the heat trap compartment [36] provides light concentration [28] which increases the temperature gradient between the ground layers and ground surface [26] of the earth's soil which is detected by cold junction [22] and hot junction [24] respectively. A charge is developed and accumulated in the thermal element [40]. The harvested power is then transformed to electrical potential via electronic section. A gradient of 10mV/At is sufficient to drive step-up dc-to- dc converter to a satisfactory level to run wireless sensor network motes efficiently where the expected current consumption by wireless sensor note is between 100 -200 mA/h depending on load characteristics.

Claims

1. A thermoelectric generator [20] for soil sensor mote comprising:

a thermal element [40] to convert heat into electricity;

a hot junction element [24] at one end of thermal element [40];

a lens [32] to concentrate heat on hot junction;

a heat trap compartment [34] between lens and hot junction element;

a cold junction element [22] at the other end of thermal element [40]; and a damper rod [42] coupled to cold junction;

wherein hot junction element can receive concentrated and preserved heat while cold junction element can dissipate heat via damper rod to soil, thereby creating a temperature gradient over thermal element.

2. A generator according to claim 1 , further comprising a reflector [38] near hot junction.

3. A generator according to claim 1 , wherein the reflector [38] is a funnel shaped reflector.

4. A generator according to claim 1 , further comprising a heating plate [36] near hot junction to preserve heat.

5. A generator according to claim 1 , wherein the damper rod [42] is buried in the soil.