Design and development of self generating ceramic heater

Design and development of self generating ceramic heater

In severe cold winter, heating products are favored by people. Heating products from hot water bag to electric heating and chemical heating emerge in endlessly. With the increase of the types of heating products, people have higher and higher requirements for them. Whether they are energy-saving, environmental protection and easy to carry have also become the primary conditions for users to choose. Therefore, some portable hand warming treasures and hair heating stickers in the market have become hot heating products. Although these products meet the functionality and convenience of users' needs, most of them use chemical reaction to heat or use battery and charging to heat, while disposable products using chemical heating 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 conservation. At the same time, low temperature scald and other safety problems also make people flinch from it.

1、 Advantages of self generating heater

The heater in this design adopts passive power supply and uses energy collection device to convert kinetic energy in the environment into electric energy. Piezoelectric materials produce positive piezoelectric effect under the action of external force, so as to generate electric energy. This piezoelectric energy collector which uses piezoelectric vibration to generate electric energy has the characteristics of high power density and simple structure.

The heater also has two characteristics: first, it can convert the mechanical energy generated in people's daily life into electrical energy through the positive piezoelectric effect of piezoelectric ceramics. On this basis, it is equipped with a temperature control device for people who go out to work or travel. Second, when people are heating outdoors, the human body itself is a power source, 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 requirements of energy conservation and environmental protection.

2、 Overall scheme design of self generating heater

The overall structure design of the self heating controllable temperature heater based on piezoelectric ceramics is shown in Figure 1, which mainly includes various power modules such as piezoelectric ceramic self generating part, power stabilizing part, power collecting part, temperature control part and heating part. The heater takes the power supply generated by piezoelectric ceramics as the core, provides power for heating materials by collecting stable electric energy, and realizes the control of temperature range through temperature control device. It not only has the characteristics of no external power supply, but also caters to the concept of energy saving.

2.1 overall circuit principle design of heater

This product is a self generating controllable temperature 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 a key point to realize the function of the heater. Figure 2 is the overall structure principle circuit diagram of the realization of the function of the heater.

2.2 design of piezoelectric ceramic self generating part

The power generation part of this product mainly uses the properties of piezoelectric ceramic vibration power generation. It uses the positive piezoelectric effect of piezoelectric ceramics, which generates electric charge under the action of external force, so as to convert mechanical energy into electrical energy. The positive piezoelectric effect of piezoelectric ceramics is that when subjected to external force, it will produce mechanical deformation and generate electric charge, and when the external force is removed, it will return to the initial uncharged state. For example, when people walk, their feet exert pressure on the ground, and their feet leave the ground and return to the original state. The PZT piezoelectric ceramic system used in this product has very strong and stable piezoelectric properties. Because piezoelectric ceramics are hard and brittle, piezoelectric crystals and elastomers are connected to form piezoelectric oscillators. Because the vibration of piezoelectric oscillators produces large voltage and a small amount of charge, parallel piezoelectric stacking is adopted. The thickness telescopic piezoelectric stack can bear greater force than the length telescopic piezoelectric stack. When the piezoelectric stack can bear the maximum force with the same amount of piezoelectric vibrator, the thickness telescopic piezoelectric stack can produce greater current. After preliminary research, this product can generate heat while generating electricity. At 10cm × For example, 5cm warm baby paste is heated from normal temperature to 40 ℃, the specification of heating resistance wire carbon fiber is 3k, the resistance is 144 Ω / m, and the specific heat capacity of carbon fiber is 0.0008j / (g · K), which takes only 6.73s.

2.3 composition of power generation part of heater

A plurality of piezoelectric ceramics are connected in series with a switch. The piezoelectric ceramics generate electricity through the vibration of the body part. The switch controls the number of piezoelectric ceramics to control the amount of electric energy generated. Finally, the number of layers n, thickness D and bottom area a of piezoelectric stack are determined according to the required current and appropriate volume. As shown in Figure 3.

The self generating part of the heater adopts a cantilever beam structure with parallel electrodes and double piezoelectric sheets to form a piezoelectric ceramic sheet. The mass block in motion is used as the elastic material of the beam to receive the applied external force; The piezoelectric ceramic is adhered to the basic material with certain elasticity and attached to the free end of the cantilever beam to ensure that it can produce a sufficiently high vibration frequency when subjected to external force, so as to maximize the generated current. In order to make the power generation device have stronger power generation capacity in small excitation intensity and wide frequency range, multiple piezoelectric oscillators are used for power generation.

The connection mode adopts parallel connection with large output current. In this structure, the electrodes of the upper and lower ceramic sheets are connected together, shorted to each other, and then used as one electrode of the power generation device, and the other electrode is led out from the metal sheet.

2.4 overall arrangement of power generation part of heater

The most important function of piezoelectric vibrator is energy conversion. Because the external force determines the power generation capacity, it is used to improve the high-voltage electrical efficiency by increasing the external force. The product adopts the following structure to amplify the force to improve the piezoelectric efficiency, as shown in Figure 4.

2.5 steady current collection part of heater

Piezoelectric energy collection technology uses the piezoelectric effect of piezoelectric materials to generate electric energy. The structure of piezoelectric energy collection device is one of the research emphases of this product. The piezoelectric energy collection device of the product has the advantages of small volume, simple structure, no electromagnetic interference and easy processing. In order to realize the continuous power generation of the heater during use, the AC generated by piezoelectric ceramics needs to be treated. Firstly, the rectifier circuit is used to convert the AC generated by the vibration of piezoelectric ceramics into DC, but the waveform is not stable at this time and needs to be further filtered. Next, the voltage stabilizing device is used to stabilize the filtered easily abrupt voltage, and the processed current is finally sent to the storage circuit to realize stable current collection. The rectifier filter circuit is shown in Figure 5.

The voltage doubling rectifier circuit can store the voltage on their respective capacitors by using the rectification effect of lower AC voltage and higher withstand voltage, and then connect them in series according to the principle of polarity addition to output the high voltage higher than the input voltage. The DC voltage waveform output by the voltage doubling rectifier circuit is not good enough, so the filter circuit is needed to filter to reduce the ripple of the output voltage. In the design of this system, the quadruple voltage rectifier circuit is used, and the capacitance on the circuit also plays the role of filtering, so it has the role of both rectification and filtering.

For the DC boost circuit, me2111 voltage stabilizing chip is selected in the system design. It is a high-efficiency synchronous rectifier boost DC / DC converter, which only needs three peripheral devices (two capacitors and one inductance). Its starting voltage is low, it can work above 0.95v, and the efficiency can reach 94%.

After rectifying, filtering and boosting the current, the electric energy needs to be stored, that is, the energy storage module. This product uses hm4601 chip as the main control chip. Hm4601 adjusts the charging voltage and constant current charging current of lithium battery through constant voltage control ring and constant current control ring. At the same time, it also integrates temperature protection, maximum charging time limit and output short circuit functions.

2.6 temperature control part of heater

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 current of the power generation, stabilization and collection part acts on the heating layer to make it reach a certain temperature for people to warm, but the temperature at this time is not the most comfortable temperature for the human body. Because the temperature beyond the controllable range will also cause harm to human body, such as low-temperature scald, etc., in order to solve this kind of problem, the product is designed with a built-in temperature control device to control the upper and lower temperature by adjusting the temperature controller. When the temperature at any point on the surface of heating material reaches the upper limit temperature of 60 ℃, the temperature probe senses the signal and feeds it back to the temperature controller, The temperature controller reduces the output current to reduce the temperature; When the temperature drops to the lower limit temperature of 40 ℃, the temperature probe feeds back a signal to the temperature controller to increase the current, so as to increase the temperature. The temperature control is realized by adjusting the output current through this signal feedback.

Because the human body will be scalded at low temperature if it is exposed to a temperature higher than the body temperature for a long time, the heat-resistant layer resin is used to wrap the wire core of the heating layer. In the outermost layer of the portable heater, flannelette will also be used to separate the skin and the heating part to avoid low-temperature scald.

epilogue

In this paper, the positive piezoelectric effect of piezoelectric ceramics is used to apply external force to realize piezoelectric power generation. A self generating heater is designed, and the relevant theories are designed and analyzed. The power generation part of the heater adopts a cantilever structure to put pressure on the piezoelectric ceramics and generate a large amount of charge efficiently. Then, the rectifier filter circuit and energy storage device are used to convert the collected charge into current and store it in the battery for the use of the heating layer. The built-in temperature control device controls the temperature within the comfortable temperature range of human body, which can avoid the safety problem of low-temperature scald. The heater uses piezoelectric ceramics, a clean energy, to realize passive power supply, green environmental protection, convenient use, in line with the concept of energy conservation and environmental protection, and also meets the requirements of national low-carbon environmental protection.