（8）

So, PZT element compressive strain can not increase further increase stress situation. It is unlikely to appear in an instant, whenever, as long as the discharge and wear, acoustic shock waves from the PZT element face into. Machine speed is about 4 mm * us - 1, as a result, the deformation in a few microseconds only is complete (depending on the length of the PZT element). In this case, transferred to the PZT element on additional the mechanical energy can be converted into additional electricity Wea 

       (9)

In fact, Wea values will be mainly depends on PZT element assembly method and the method of pressure, Wwa has great effect on the total energy of electric spark, can increase the effective ignition circuit Wea. 

     （10）       

By type, you can see that on the maximum effective ignition energy equivalent capacitance C and Vb voltage electric field can be.
Corresponding energy density Wkd = Wtd/B, namely 

 （11）

For a given formula of PZT, d33, C are measurable, as the constant value, so the Wkd as the function of mechanical stress F3. Figure 2 draw several materials of Wkd and F3. 

Figure 2 in PZT4 PZT41, per unit volume of total energy is the function of stress F3. The 1, 3 for the maximum static stress points; 2 for the maximum dynamic stress points. In a static system, if a cycle n spark producing, so the total energy should be equal to: 

    （12）

Type V = n * Vb is under open circuit state in peak voltage. Discussed so far, almost all of the information principle is more ideal piezoelectric materials, these materials are ideally applied stress. So, in the actual application and improvement of the performance is limited by some, so for these limitations must be considered. A. if the PZT element is usually the same as pressure in the middle of the steel cylinder, due to its low coefficient of smooth, will change on the additional horizontal clamping, therefore, PZT element will become A barrel rather than uniform deformation, this will lead to give g33 of RMS is reduced, the output voltage is reduced, however, from our test, this has little effect, just A slightly different voltage waveform. Figure 3 reflects this kind of situation.
B. after just put the electricity, voltage is not zero at the ends of the element, and is equal to the flameout of discharge gap voltage Va, therefore effective ignition energy should be As can be seen from the output voltage waveform, Va < < Vb, so its impact is small.

C. as shown in equation (1), the open system of compressive stress produces a polarization voltage and polarity of the same voltage, this will not lead to polarization. But one point, the voltage will change into extinction voltage less than it, any residual mechanical stress can cause depolarization. Using PZT materials, therefore, should be able to meet the strict requirements of depolarization, especially when under quasi static stress. 

(a) ceramic and shell assembly 

(b) ceramics and shell assembly can be made 

D. after sparking discharge, when is still in the closed state, even if very low values of F3 is enough to cause nonlinear effect, therefore, the creation of charge more than linear piezoelectric effect he expected. Painted figures 4 and 5 out of the piezoelectric ceramic formula for PZT4, PZT4I, PZT2, PZT2I electric displacement is the function of mechanical stress (in short circuit conditions), in both diagrams, the curve for mechanical stress increases gradually, while the following curve for PZT element through put some stress after falling (reset). These nonlinear effects can make the reversible and irreversible. As long as the curve of the ups and downs, we will enlarge the reversible effect around to deal with. Under high stress, the curves of bullying will no longer be consistent, the thought that this material has been partially depolarization. So, for the application of multiple times ignition, maximum stress choice in keep depolarization in appropriate limits is very important. 

According to these characteristics, designed for those that according to the principle of the quasi static stress of various ignition device, the formula selection for "hard" ceramic PZT materials, namely in the PZT makings,added Such as metal oxides. The following characteristics: 

(1) high mechanical quality factor;
(2) the relative dielectric constant and low dielectric loss;
(3) strong field correction;
(4) plane electromechanical coupling coefficient k is low;
(5) Good thermal stability, high Curie point to namely;
(6).Good durability 
According to these requirements and figure 4 can be seen in figure 5, PZT4 and PZT4I two materials is the most suitable material. PZT8, PLS etc also can be used as a quasi static ignition PZT element.
E. due to the electric loss of PZT materials, PZT materials and pressure device both inelastic deformation, leakage resistance, parasitic capacitance, etc., therefore, in the discharge power and not all power effectively. 

2.2 dynamic stress (shock ignition)
In the so-called shock ignition system, with a spring loaded hammer device for PZT element, dynamic stress is applied when the hammer under the effect of elastic impact, to produce pressure microwave in the hammer and PZT elements, on the PZT element formed by mechanical stress, and the resulting voltage depends on the acoustic characteristics of the ignition device used components.
The simplest case is the area of A
Of the hammer and the area of Ac PZT element between the freedom of the impact, colleague, assuming that the difference between Aa and Ac is not big, so its biggest mechanical stress can use the following formula to calculate very close

     (13)

Type, U is hammer impact velocity, V is the compression wave propagation velocity in the hammer hammer Y is the elastic modulus of materials used, useful is hammer all materials acoustic impedance, Z is the acoustic impedance of PZT open circuit condition.
This formula is only roughly said to actual device of the mechanical stress, commonly used in the preliminary calculation when product design, while the actual mechanical ability easily derived by the output voltage waveform. 
If the breakdown voltage of PZT elements with Vb, peak open-circuit voltage V on the discharge mechanism, the spark of effective energy W as follows:

  (14)

Real effective can depends on the size of the sparks to keep the voltage level, and therefore depends on the spark impedance. Caused by nonlinear effect of the electric displacement distribution, to a large extent depends on the duration of the mechanical stress cycle. If the pulse is a for a few milliseconds or longer, PZT element stress distribution has the quasi static properties, the electric displacement is nonlinear. But, if the pulse duration is close to 1 us, this time, shorter than relaxation time of ferroelectric domain, because all the nonlinear effect. At this time of the electric displacement is equal to the linear piezoelectric effect, the electric displacement is proportional to mechanical stress. For intermediate pulse width, nonlinear effect as the pulse width is reduced and the lower base. This means that if the pulse period, can impose higher stress and won't appear depolarization. 

Due to the stress caused by depolarization is not so strict, therefore, has a high energy output of the PZT material can be used again under the dynamics. Specifically:
1. High d33, C is high, and > 10;
2. E is high. e1500
3. The high value of Kp
4. Qm value lower
Compared with quasi-static PZT materials, the dynamic loads using PZT materials, the formula is more, technology is relatively mature, however, there are some problems: "soft" material of high output voltage, spark energy is high, the single durability is poorer; "Hard" materials, on the other hand, the durability is better, but the low output voltage, in a timely manner about 15 kv, but because of the capacitance is small, small spark energy, light rate is low. According to these conditions, we use the "soft" material and "hard" developed by mixing materials is a kind of ideal material for PSS, as follows: the main indicators.
Other materials such as PZT2 PZT2I PZT4I, PBS, PLS also can be used in the shock ignition.

The structure of the ignitor
Due to the fragile piezoelectric ceramic materials, therefore, when subjected to high stress, some protective measures must be taken. Protection of PZT elements of the most common way is to load it in a plastic shell, plastic or bonding method makes its positioning. In this way, the bearing surface in PZT more even, also facilitate acoustic matching between the parts and good insulation. The structure of the igniter as shown in figure 6.

3.1 the PZT components
Most piezoelectric ignitor is placed two reverse polarity of PZT elements, the system of metal end piece of ground, high pressure at the center electrode lead, two PZT elements on the mechanical is connected in series, and the circuit is in parallel, the advantages of this design is that discharge energy twice for a PZT element, is conducive to the ignition, and insulation problem is limited to high voltage side.
In fact, for some special applications, by a PZT element can get enough energy. Just in this case, can also be designed to accommodate a PZT element of ignition (as shown in figure 6 (b)), and of course the occasion of PZT elements should be used according to the size of the design.
A static and dynamic output, igniter depends not only on PZT material properties, element also depends on its size and its stress state. And the effective life of PZT elements depends on mechanical stress causes depolarization of chengdu, mechanical strength, surface condition, etc. Thus PZT element of two end face must be parallel to each other and perpendicular to the axis, and as smooth as possible, without any traces of concave and convex. 
3.2 the center electrode
Between two PZT elements, insert a thin metal electrode to form a center, also known as power. Contact piece are connected to the high voltage wires using methods such as viscosity, welding, bonding method commonly used at present. The adhesive must have the following interface features:
1) have good interfacial properties
2) strong cohesive force
3) have good insulation
4) easy to operate, and the economy.
Contact materials commonly used aluminum, copper, nickel and iron alloy sheet stamping, plastic, can, for prevention of corrosion for the surface roughness of Re value of 0.2. 
3.3 high voltage wire
High voltage wire connected the center electrode to put electric acupuncture. According to the igniter use state, this kind of lead must meet the following requirements:
1. Must be suitable for the methods of bonding, welding connected;
2. Must adopt multi-strand wire, because the impact of load vibration, that cause metal fatigue. The fatigue can lead to single core wire fracture and click somewhere out;
3. Lead the breakdown voltage shall be the igniter in the condition of using the highest peak voltage twice;
4. The lead should be capable of high temperature;
5. Lead and discharge gap capacitance should be its decline of PZT elements;
6. Lead and time constant of discharge gap voltage pulse rise time of the heavy rain, which leads the leakage resistance must be high enough.
High voltage wire capacitance and leakage resistance, both of which depends on the wire length and the quality of the insulating material used. Therefore, fuses must as far as possible. Do is suitable for high voltage wire insulation is chloroprene rubber, silicone rubber and ptfe, these materials can be in up to 1100 degrees, 225 degrees and 300 degrees Fahrenheit. In order to avoid high voltage wire and metal parts contact with a sharp edges and corners, in the actual hard to fix lead. 
3.4 the metal end piece
If you want to make the PZT components to withstand higher mechanical stress, then these must be in the cylinder face evenly, so as to ensure the longest trial in life. In the face of PZT elements add a metal end piece can do this. As the material of the metal end piece meet the following two conditions; 
1. Close to the acoustic impedance of PZT materials, which can obtain good acoustic matching;
2. Has good elasticity, in force from time to tome deformation but not deformation.
Generally use copper and steel as the material of the metal end piece, the experiment proved that using 45 # steel is most appropriate. The surface of the metal end piece for PZT element must be flat and smooth, the roughness shall not be greater than Re value is 0.2, generally should be approved by grinding flat grinding machine.
3.5 the shell
All kinds of prefabricated components can be loaded in the shell, can be after the components are assembled, the surrounding injection into the shell. The latter has the following disadvantages compared to the former. 
1. Injection before the various components must be assembled into a whole, complex operation;
2. Easy to cause depolarization PZT materials;
3. Due to the plastic shrinkage, in the process of cold to take off the PZT element is too tight, and absorb a part of mechanical energy, when the sound waves through and thus reduce the output;
4. Before the injection, PZT cylinder must be painted.
The shell must meet the following requirements:
1. The breakdown voltage at least shall be the ignition device of double peak voltage;
2. Should be impervious
3. The ability of a certain high temperature.
Shell commonly used materials: PE, pp, nylon, ABS resin and other materials. Polyethylene is suitable for injection molding shell, and the other is suitable for prefabricated housing. 
3.6 internal insulation
If the PZT insulation level is not enough, the surfaces along the cylinder body wall of arcing discharge is inevitable, thus substantially reducing the output energy or no output. Therefore, PZT element must be fully clean before assembly, the procedure is: water, alcohol, gasoline. After cleaning the walls painted with a layer of insulation materials, commonly used material is gauge fat, silicone oil, paint, etc. 
1. Squeeze the igniter and shock ignition
4.1 squeeze the igniter (static stress)
Extrusion type igniter is based on the quasi-static stress produces high pressure principle, the basic mechanism is to use a lever will force applied to one or two PZT cylinder, figure 7 is the diagram of the machinery. 

A major feature of the ignition device is applied mechanical load when the ignition is duration is longer, load lasts about half a second, of course, this also varies from person to person. In last period, piezoelectric lines loaded first, and then reset and cause fire several times, the number of fire depends on the length of the discharge gap. To increase the rate of fire, fire several times has great advantages, namely if a fire without burning combustible gas and air mixture, then the next fire could be lit.
Static ignition system fault is voltage rise for a long time, every time the fire energy is low, easy to leakage and cause energy loss, and leakage resistance to ignition device, should be at least 1010 Ω, high voltage fuses should be short. Compression ignition of the screws is a line, so applying the hardness, mechanical parts to play, at least above HRC55.
4.2 shock ignition (dynamic)
Automatic ignition stoves and lighter with the dynamic load to the PZT cylinder ignition system, the ignition system is through a hammer with a spring clip device to exert dynamic load (see figure 8). The largest institutions stress and the resulting voltage is a function of impact velocity and the area of the hammer. For hammer and end pieces of contact area when protruding, and even when compared to the former the rise time of a mechanical stress wave and voltage peaks more, should be considered in the design of this. 

Figure 9 waveform diagram shows the design good shock ignition voltage pulse, on the light rate and the effective life of PZT cylinder, smooth pulse graph with satisfactory results.

Shock ignition than extrusion igniter has the following advantages:
1. Due to voltage pulse time is short, the leakage resistance of the whole system's enough 1 m Ω;
2. Because the duration of the load short, PZT cylinder can bear greater load without depolarization;
3. The link igniter in gas valve, can accurate determination of the gas valve and a spark between the cost of time.
Which impact the application scope of igniter is greatly exceeded the compression ignition. 

1. The rate of light
Suitable ignition device structure can speak leakage resistance and parasitic capacitance for light rate of adverse effects to the smallest degree. And therefore have relatively low discharge gap impedance was the only way that spark cannot consume all available energy. Although this is inevitable as a result, a single supply the energy of the discharge gap, still often enough to burn combustible gas, the light rate is very high.
Spark discharge in the form of rapid fire for many times. If ignition device is small, low energy, then a flame energy might be too low, so that can guarantee enough fire rate, that is, it should be many fine flame as a combined discharge energy, increase energy, to increase the rate of fire.
Solution to the problem is in the load as far as possible near the discharge gap inserted a resistance value is 20 ~ 40 k Ω conforms to the resistor, to increase the time constant of the system. Results we found that spark, at the same time the volt-ampere characteristics of ups and downs are suppressed, light rate increased by 20%, further solution is an inductance connected high voltage wire, single is not economic to do so. 
Light rate also depends on the following features:
1. The flow velocity of the gas
2. The combination of gas and air
3. The components of the gas
4. Open the gas valve and spark a time lag
5. The location of the spark
6. Click on the distance 
These parameters and the rate has a lot to do, so the best conditions should be determined according to the experiment. 
From currently on the market to meet all kinds of piezoelectric igniter, and in the information feedback from users, for the most part we found that the failure of piezoelectric igniter and not the durability can not meet the requirements or depolarization and so on, but the PZT cylinder is break, while imports especially for Japanese goods, under the same condition, thirty thousand impact test, broken little PZT cylinder.
Japan's technical conditions, the requirement of mechanical strength is static pressure &production) is less than 5 t * CM - 2. We are the factory and several other manufacturers of ceramics on the material testing machine for the contrast test of a linear relationship with basic static strength, for a nonlinear relationship with dynamic igniter.
We made some improvements on the box parts assembly, the increase mechanical strength of ceramics under shock condition experience has the following points: 
6.1 the processing of raw materials
Should pay attention to material handling the process, because the granularity of raw materials directly affect the performance of the piezoelectric ceramics and intensity. Due to coarse granularity, contact between each other decreases, and make solid instead should speed slow down, even incomplete reaction, free oxide and did not react, causing uneven composition of the piezoelectric element, the internal stress will occur, causing low mechanical strength, easy to broken, so, on the particle size of raw materials, hardness and surface should be measured, according to the results of determination of the technological conditions of each raw material processing, to which great hardness, particle coarse material, should be appropriately increased time of ball mill, such as ZrO2, SnO2, etc. Ensure all the raw materials of grinding granularity, all through 120 mesh sieve. 
6.2 the sintering temperature and holding time
Sintering emperor on the high side, heat preservation time is too long, cause the crystal secondary recrystallization, form a larger grain size, porcelain body after sintering density is too high, reached 7.8 ~ 7.9 g * com - 3 this ceramics is very fragile, poor resistance to impact strength. So should be used as the lower temperature during sintering. The most fundamental way is to improve the synthetic material fineness, after the fine powder, the faster the reaction rate, the lower the sintering temperature. 
6.3 the molding pressure
Appropriately raise the molding pressure. After forming a density is higher, the easier the sintering, low sintering temperature, the more uniform, dense structure, porosity in the microstructure after sintering is less, the higher the strength of ceramic machinery.
The current molding process, mostly adopt the method of double pressure, can satisfy the basic requirement of forming. But the molding pressure, said most of the data should not be more than 2. OT CM 2,, this statement is not accurate. Root show us a lot of experiments, within a certain range, the molding pressure, the greater the piezoelectric ceramic mechanical strength is higher (figure 10). But the molding pressure, the product, prone to delamination, crack forming grinding tool wear is bigger, so should improve the abrasive surface hardness and roughness. Comprehensive consideration, we think that the pressure of 3.5 tc m - 2, abrasive surface hardness is HRC60-62, roughness Ra value of 0.1 is relatively appropriate. 

6.4 pressure speed
Polarization speed pressurized shoulds not be too fast, the voltage should not be too high. Due to the cylindrical ceramic length is longer, when polarization, due to the pressure too fast, voltage too high or other product breakdown voltage mutation, causing excessive internal stress and make the central cylinder of tensile, some polarization was not broken, but put the transverse fracture after period of time, smooth section as a whole, such as poor resistance to impact strength was not broken products.
Of course, mechanical strength and the whole structure of ignition system. Igniter with card and so on also has a lot to do, these can only be used from the actual test. 
The development of the 7 testing output voltage standard equipment
Due to the output voltage is the main performance index of the igniter, therefore, we have developed piezoelectric ceramic igniter colleagues, began the research of test equipment.
We query a lot of relevant standards, although there is no national standard. But Japan, Hong Kong companies are using matsushita electric company in 1965 in a technical report method, with a 11.8 g steel ball from 500 mm height of free fall, impact on the igniter, use memory oscilloscope record output voltage waveform, measure the peak voltage.
We import prototype made in accordance with the above standards and a dedicated equipment, but the effect is not ideal, the reason is:
1) steel ball free land on igniter, without using special positioning device, test results deviation is very big;
(2) memory oscillograph is expensive, with 100% of its measurement is not very economic, it is not easy to promotion and popularization.
In order to overcome the above two defects, we develop a design together with university of electronic science and technology first three positioning, automatic the release of the ball falling ball, and digital display peak pulse voltage tester, marry only 20% of the original equipment, and test precision from + 1000 v to + 1000 v. Now has been widely used in China with, ready to rise to national standards, the national rail voltage electric ceramic professional mechanical and electrical department (working group in 1991 issued by "piezoelectric ceramic ignition test standard stipulated in the" use this instrument. 
8 the conclusion
Above is part of the work we do, weakening is over the past few years we will have a piezoelectric ceramic ignitor production, scientific research briefly discussed, compared with foreign advanced level, there are certain gap, we would like to work with domestic counterparts all work together to catch up.
In the process of product research and paper writing, get guo-liang pan Shanghai silicate institute senior engineer, associate professor of xi 'an university of electronic science and technology chang-xing pei, lanzhou, deputy director of kitchen equipment factory MiaoJianGuo Yang Jilin engineer and our factory engineers such as comrade guidance and assistance, in this thank you. 
reference
1. Ren Guiguang, piezoelectric ceramic element's manufacturing
2. Japan NTX company, piezoelectric lines ignition technology conditions
3. Guo-liang pan, piezoelectric ceramic ignition detonated in proceedings of the application of functional ceramics, 1990
4. Matsusa Eleccric panasonic (samples), Electric Compomenta, 1973
5. Japan patent, zhao 49-32788, 50-6931, 50-32788 zhongguo kuangye daxue zhongguo kuangye daxue zhongguo kuangye daxue ploidy - 7318-7318-7318-16462. Zhongguo kuangye daxue zhongguo kuangye daxue - 28849-28849