Design and development of self-generating ceramic heater

In the severe cold winter, heating products are favored by people. From hot water bags to electric heating and chemical agent heating heating products emerge in endlessly. With the increase of heating product types, people have higher and higher requirements for them. Whether they are energy-saving, environmentally friendly, and portable It has also become the primary condition for user selection. Therefore, some hand warmers and heating stickers that are easy to carry on the market have become hot heating products. Although these products meet the functionality and convenience of user needs, most of them use chemical agents to generate heat or use batteries and charging. Heat generation, and disposable products that use chemical agents to generate heat will seriously pollute the environment and violate the concept of green environmental protection. Using electric energy to generate heat is a consumption of energy, which is contrary to the concept of energy saving. At the same time, safety issues such as low-temperature burns also make people discouraged.

1. Advantages of self-generating heaters

The heater designed this time uses passive power supply, and uses energy harvesting devices to convert kinetic energy in the environment into electrical energy. Piezoelectric materials produce positive piezoelectric effect under the action of external force, thereby generating electric energy, and the piezoelectric energy harvester that uses piezoelectric vibration to generate electric energy has the characteristics of high power density and simple structure.

This heater also has two features: one is that it can convert the mechanical energy generated in people's daily life into electric energy through the positive piezoelectric effect of piezoelectric ceramics, and on this basis, it is equipped with a temperature control device for the convenience of going out for work or travel. people carry. Second, when people are heating outdoors, the human body itself is a power source at this time, so there is no need to look for charging equipment; the temperature control device can not only improve people's comfort, but also improve the utilization rate of electric energy, which meets the current energy saving and environmental protection requirements .

2. The overall scheme design of the self-generating heater

The overall structural design of the self-heating and temperature-controllable heater based on piezoelectric ceramics is shown in Figure 1, which mainly includes piezoelectric ceramic self-generating parts, stabilizing parts, collecting parts, temperature controlling parts, and heating parts, etc. . The heater uses the self-generated power supply of piezoelectric ceramics as the core, provides power for heating materials by collecting stable electric energy, and realizes temperature range control through a temperature control device. It not only has the characteristics of no external power supply, but also caters to energy saving idea.

2.1 Design of overall circuit principle of heater

This product is a self-generating temperature-controllable portable heater based on piezoelectric ceramics. The design process includes the physical quantity conversion process in a series of devices such as power generation, power collection, power stabilization, and temperature control. Therefore, the circuit design is also the key to realize the heater function. A big point.

2.2 Design of piezoelectric ceramic self-generating part

The power generation part of this product mainly utilizes the nature of piezoelectric ceramic vibration power generation. It uses the positive piezoelectric effect of piezoelectric ceramics, and piezoelectric ceramics generate electric charges under the action of external force, thereby converting mechanical energy into electrical energy. The positive piezoelectric effect of piezoelectric ceramics is that when an external force is applied, it will produce mechanical deformation, thereby generating an electric charge, and when the external force is removed, it will return to the initial uncharged state. The ground returned to its original state. The PZT piezoelectric ceramic system used in this product has very strong and stable piezoelectric performance. Because the piezoelectric ceramic itself is hard and brittle, the piezoelectric crystal and the elastomer are connected to form a piezoelectric vibrator, and because the piezoelectric vibrator vibrates to generate a large voltage and a small amount of charge, a parallel piezoelectric stack is used. The piezoelectric vibrator stack with stretchable thickness can bear greater force than the piezoelectric stack with stretchable length. When the piezoelectric vibrator is equal and the piezoelectric stack can bear the maximum force, the piezoelectric stack with stretchable thickness can generate more force. large current. After preliminary research, this product can generate heat while generating electricity. Taking the 10CM×5CM warm baby paste as an example, it only takes 6.73s to heat from room temperature to 40°C, the specification of the heating resistance wire carbon fiber is 3k, the resistance is 144Ω/M, and the specific heat capacity of carbon fiber is 0.0008J/(g·k).

2.3 Composition of the power generation part of the heater

Multiple pieces of piezoelectric ceramics are connected in series with a switch. The piezoelectric ceramics generate electricity through the vibration of body parts. The switch controls the number of piezoelectric ceramics to control the amount of electricity generated. Finally, the number of layers n, thickness D, and bottom area A of the piezoelectric stack are determined according to the two conditions of the required current and the appropriate volume.

The self-generating part of the heater adopts a cantilever beam structure with parallel electrodes and double piezoelectric sheets, composed of piezoelectric ceramic sheets, and the mass block in motion is used as the elastic material of the beam to receive the applied external force; the piezoelectric ceramic It is glued to a basic material with certain elasticity and attached to the free end of the cantilever beam to ensure that it can generate a sufficiently high vibration frequency when subjected to an external force, thereby maximizing the generated current. In order to make the power generation device have stronger power generation capacity in a smaller excitation intensity and a wider frequency range, multiple piezoelectric vibrators are used to generate power.

The connection method adopts a parallel connection with a large output current. This structure is to connect the electrodes drawn from the upper and lower ceramic sheets together, short-circuit each other, and then serve as one electrode of the power generation device, and the other electrode is drawn from the metal sheet.

2.4 The overall layout of the power generation part of the heater

The main function of the piezoelectric vibrator is energy conversion, because the external force determines the power generation capacity, so the method of increasing the external force is used to improve the piezoelectric efficiency. This product adopts the following structure to amplify the force to improve the piezoelectric efficiency.

2.5 Heater stable electricity collection part

Piezoelectric energy harvesting technology uses the piezoelectric effect of piezoelectric materials to generate electrical energy. The structure of the piezoelectric energy harvesting device is one of the research focuses of this product. The piezoelectric energy harvesting device of this product has the advantages of small size, simple structure, no electromagnetic interference, and easy processing and production. In order to realize the continuous power generation of the heater during use, it is necessary to process the alternating current generated by piezoelectric ceramics. First, the rectifier circuit is used to convert the alternating current generated by piezoelectric ceramic vibration into direct current, but the waveform at this time is not stable, and further filtering is required. The current is finally sent to the storage circuit to realize stable power collection.

The voltage doubler rectifier circuit can use the rectification effect of lower AC power with higher withstand voltage, store the voltage on the respective capacitors, and then connect them in series according to the principle of polarity addition, and output a high voltage higher than the input voltage. The DC voltage waveform output by the voltage doubler rectifier circuit is not good enough, so a filter circuit is required for filtering to reduce the ripple of the output voltage. In the design of this system, a quadruple voltage rectifier circuit is used, and the capacitance on the circuit also acts as a filter, so it has both rectification and filter functions.

For the DC boost circuit, the ME2111 voltage regulator chip is selected in the system design. It is a high-efficiency synchronous rectification boost DC/DC converter and only needs three peripheral devices (two capacitors and one inductor). Its starting voltage is low, it can work above 0.95V, and its efficiency can reach 94%.

After the current is rectified, filtered, and boosted, the electric energy needs to be stored, which is the energy storage module. This product uses HM4601 chip as the main control chip. HM4601 adjusts the lithium battery charging voltage and constant current charging current through the constant voltage control loop and constant current control loop. It also integrates temperature protection, maximum charging time limit, and output short circuit functions.

2.6 Heater temperature control part

The temperature control device is a device for adjusting and controlling the heat generated by the heating layer, and it is also one of the key designs of this heater. The electric current of the electricity collecting part through power generation and stable electricity acts on the heating layer to make it reach a certain temperature for people to keep warm, but the temperature at this time is not the most comfortable temperature for the human body. Because the temperature that is not within the controllable range can also cause harm to the human body, such as low-temperature burns, etc., in order to solve such problems, this product is designed with a built-in temperature control device, and the upper and lower limit temperatures are controlled by adjusting the temperature controller. When the heating material When the temperature at any point on the surface reaches the upper limit temperature of 60°C, the temperature probe senses the signal and feeds it back to the thermostat, and the thermostat reduces the output current, thereby reducing the temperature; when the temperature drops to the lower limit temperature of 40°C, the temperature probe feedbacks The signal to the thermostat causes it to increase the current, thereby increasing the temperature. The temperature is controlled by adjusting the output current through this signal feedback.

Since the human body is exposed to temperatures higher than body temperature for a long time, it will cause low-temperature burns, so the heat-resistant layer resin is used to wrap the core of the heating layer. On the outermost layer of the portable heater, flannelette is also used to separate the skin and the heating part to avoid Low temperature burns.

epilogue

In this paper, the positive piezoelectric effect of piezoelectric ceramics is used to apply an external force to realize piezoelectric power generation. A self-generating heater is designed, and the design and analysis of related theories are carried out. The power generation part of this heater adopts a cantilever beam structure to press the piezoelectric ceramics to generate a large amount of charge efficiently, and then use the rectification filter circuit and energy storage device to convert the collected charge into current and store it in the battery. Used in heating layer. The built-in temperature control device controls the temperature within the comfortable temperature range of the human body, which can avoid the safety problem of low temperature burns. This heater utilizes the clean energy of piezoelectric ceramics to realize passive power supply, is green and environmentally friendly, easy to use, conforms to the concept of energy saving and environmental protection, and also meets the national low-carbon environmental protection requirements.

The above is the design scheme of the environmentally friendly and energy-saving heater based on piezoelectric ceramics introduced by Shenzhen Zuchuang Microelectronics Co., Ltd. for you. If you have program development needs for heaters, you can trust us. We represent a variety of single-chip microcomputers, voice chips, dual-mode Bluetooth ICs, and wifi chips. Brands include Songhan MCU, Yingguang MCU, Jerry Bluetooth, Ankai Bluetooth, Allwinner, and Realtek. Our technical services include: PCB design, MCU development, Bluetooth solution, software and hardware custom development, APP development, small program development, WeChat official account development, etc. It can also undertake the design of intelligent electronic products, the development of living appliances, the research and development of beauty equipment, the application of Internet of things platform, the smart home control system, the development of TWS earphones, Bluetooth earphone speakers, the development of children's educational toys, the design of electronic education products, etc.