Overview of Radio Fuze Failure Mechanism Researches under Energy Type Interference*

XIONG Jiuliang，WU Zhancheng

(Institute of Electrostatic and Electromagnetic Protection，Ordnance Engineering College，Shijiazhuang 050003，China)

1 Introduction

Radio fuze is a kind of proximity fuze，which uses the electromagnetic waves to obtain target information.So，its normal performance is closely related to the electromagnetic environment.The use of all kinds of frequency equipment leads to the electromagnetic signals distributed in time－domain，frequency－domain，space－domain and energy－domain which have huge scales，complex modes，dense overlapping and dynamic folding.This complex electromagnetic environment would seriously affect the normal performance of radio fuze[1－3].

In comparison with information type interference，the power density and energy of the energy type interference source are higher.Without tracking the fuze’s working frequency and choosing the interference signal and time[4]，it can affect the normal function of radio fuze in the whole life cycle.The electromagnetic energy can couple from antenna，cable，aperture and so on.It can generate several kV of peak voltage or tens of kA peak current into the fuze system，resulting in the failure of fuze.

In order to improve the ability to resist the energy type interference，the coupling mechanism，the energy transmission characteristic，the fuze’s sensitive devices or the failure mode should be understood thoroughly.However，the fuze has the characteristics of small volume，high dynamic，high overload and short－ range work，resulting in the complexity and difficult observability of the fuze’s failure factors.In addition，different fuze has different circuit structure，and different sensitive device has different electromagnetic effect，leading to the dissimilarity and the uncertainty of failure mode.Moreover，the fuze antenna，slot and cable cause the diversity of electromagnetic signal coupling approaches.The problems above increase the difficulty in studying the failure mechanism of radio fuze under the energy type electromagnetic interference.

2 Classification and Characteristics Analysis of Energy Type Interference Signals

The radiation source composing the energy type interference signals is very plentiful.It contains not only the natural interference source，like lightning and electrostatic，but also the artificial interference sources，such as radar，communication，and directed energy EMP weapon[5].The frequency band of the equipment includes almost the entire range of the electromagnetic spectrum，and it can impose on radio fuze，resulting in interference effect，damage effect or destruction effect.Especially the strong electromagnetic pulse(EMP)，which has high peak field strength，wide range of radiation，quickly changes of rising edge strength and wide spectrum，affects the normal function of radio fuze seriously.

2.1 ESD EMP Signal

Electrostatic discharge(ESD)[6]is the universal electromagnetic radiation source in the natural environment.It is characterized by high electronic potential，strong electric field and short－ time discharge current.The current waveform rise time may be less than 1 ns.The frequency band is wide 0～3 GHz and often causes damages of the sensitive components in electronic systems.

2.2 LEMP Signal

Lightning is the most intense transient electromagnetic radiation in nature.Lightning electromagnetic pulse(LEMP)is characterized by big surge current，short－ time duration，big current change gradient and so on[7].According to AD － 722675 report of American，the integrated circuit(IC)will be invalid when the field exceeds 0.07 Gs，while perpetual destroy when it exceeds 2.4 Gs.

2.3 NEMP Signal

Nuclear electromagnetic pulse(NEMP)[8－9]is characterized by intensity energy，high peak field intensity，wide spectral range and long coverage radius.It has a strong transient electromagnetic field，and the electromagnetic energy can destroy a lot of electronic equipment and electronic systems instantly through radiation，coupling or conduction.From the destruction mechanism，NEMP can produce electrical effects，disease effects and thermal effects，not only destroying the communication，command，control，computer and intelligence systems，but also killing humans and animals.

2.4 UWB EMP Signal

Generally，the signal that has a percentage bandwidth Bp≥25% is referred to ultra－wideband(UWB)[5].The peak power of UWB has reached 100 GW，and the pulse repetition frequency is about 1 MHz.The pulse width is very narrow，less than 10 ns，and the rising edge is less than 1 ns.The spectrum is extremely rich，stretching from tens of MHz to several GHz and even tens of GHz.The electromagnetic energy generated by UWB is dispersed in a very wide frequency band，covering the response frequency of the target system and generating a strong destruction.

2.5 HPM Signal

High power microwave(HPM)[5，10－11]refers to the frequency from 300 MHz to 300 GHz，the peak power is greater than 100 MW.It is characterized by high frequency，short pulses(tens of nanoseconds)，high power and so on.HPM can produce multiple oper-ating frequencies simultaneously and radiate over GW microwave.The output power of HPM is 20 to 30 dB higher than the electronic jammer’s.Travelling at the speed of light，HPM is not sensitive to the weather.It can destroy the electronic equipment in a second of time，even the equipment is closed.HPM can couple with the electronic equipment through antenna system，cable connectors and aperture，leading to the electronic components temporary failure or permanent damage.Therefore，HPM is an important factor to affect radio fuze’s normal work.

3 Researches at Home and Abroad

3.1 Foreign Researches

Due to the highly confidential characteristic of radio fuze technology，few of references about fuze failure mechanism can be found.However，from the related reports of the EMP weapons development，EMP effect and standard making，we can believe that foreign countries research the failure mechanism deeply.

In the development of strong EMP weapons，Russia and America are the representatives.Russia exhibited a HPM weapon，named Ranets－E，in 2001.It uses X band，500 MW EMP source，to generate 10 ～ 20 ns EMP.The peak power is 0.1 ～1 GW，average output power is 2.5 ～5 kW.According to the report，the fatal blow distance of the precision guided weapon system is about 32 km.The electricity institute of Russia established a UWB experimental device，named SEF303，which is consisted of tesla transformer，gas switch，blumlein cable，matched load and a control system.It can generate UWB pulse with several few hundred kV and several ns.The power radiation efficiency is up to 70%by using transverse electromagnetic(TEM)antenna or antenna array.America also put great attention into the research and the development of strong EMP weapons.In 1996，the national laboratory of America developed a suitcase－sized high－energy EMP weapon.The research of UWB pulse source in America is at the forefront of the world.The Philips Laboratory(PL)，Lawrence Livermore National Laboratory(LLNL)，Los Alamos National Laboratory(LNAL)，Sandia，Power Spectra Inc.and PI have been carrying out the research of UWB technology.The Air Force Research Laboratory of America started to develop H(Hindenburg)series of UWB pulse source in 1990，which has evolved from H1 to H6[4].At present，the foreign EMP weapons radiation spectrum can cover 30 MHz～ 100 GHz，and the transient radiation EMP peak field is up to hundreds of kV/m.

In the research of damage mechanism，since 1950s，America has started the HERO(Hazards of E-lectromagnetic Radiation to Ordnance)work.Since 80＇s in last century，the basic problems of EMP damage and protective mechanism of weapon system have begun.The book "EMP Radiation and Protective Techniques"，written by L.W.Ricktts，was published in 1976.The book introduced the effects of the discrete semiconductor components under the NEMP experiments[12].In October 1977，America carried out the apparatus damage research work of transient induction EMP[13].In 1984，America carried out the work of EMP vulnerability assessment methods[14].In 1986，A-merica actualized the"LANCE Vulnerability and Hardening"test plan.The damage mechanisms of the most sensitive parts in high transient voltage，such as diode，transistor，silicon controlled rectifier(SCR)and IC，were deeply researched.In the plan，the triangle wave was injected directly into the device under test(DUT)，and the damage state was observed by scanning electron microscope.50 kinds of 1800 semiconductor components were tested，and the damage thresholds were ascertained[15－16].In 2003，IEEE Spectrum published an article on"EMP bomb"，which introduced the semiconductor device’s damage mechanism.Russia has completed the experimental study on mechanism of microelectronic circuit in the EMP bomb environment at the end of last century.In 2004，IEEE Electromagnetic Compatibility Transactions published a special issue on"intentional electromagnetic interference"，which introduced the latest research progress of UWB EMP damage effects in Germany，Great Britain，Sweden and A-merica.

In strong EMP weapon protection，Russia had completed the irradiation effect experimental study on the electronic components and circuits in strong EMP environment，and large EMP simulators were established.A-merica researchers have researched the weapons’electromagnetic hazard for many years.Lots of EMP effects experiments，from small electronic components to large weapons and equipments，were done，and the database of EMP effect was established.As early as 2003，America clearly put forward the fuze’s safety requirements of the electromagnetic interference and EMP.

America leads the research of the fuze electromagnetic environmentaladaptability teststandard.In 1960s，America military standard MIL － STD －1385 clearly proposed the RF hazards of armaments.MIL －STD－331A standard promulgated in 1976 did not specify the scope of electromagnetic environment.In March 1997，the military standard MIL－STD －464 proposed the general requirements for electromagnetic environment effect of the whole life cycle process of weapon system，and for the first time put forward the consideration of electromagnetic environmental effects of the weapon system，including fuze.At present，America has formed a relatively complete fuze electromagnetic environment military standards and test methods.

After decades of study，America，Russia and other developed countries have been basically formed the basis theory of the failure mechanism and protective system of the complex electromagnetic environment on the weapon system，including fuze.The coupling channel，effect rule and failure mechanism of fuze are all validated.The key technology has been conquered，and the results play an important role in the combat system.

3.2 Domestic Researches

At present，the fuze in the developed countries has entered the network era，while our fuze just enters the microelectronics technology era by the electronic technology era.From the technical level of radio fuze，we can see that there is a big gap on the radio fuze research between China and the developed countries.

Chinese researchers have made some achievements in the development of high power pulse source and high power pulse weapons.China Academy of Engineering Physics successfully developed a 1 GW UWB EMP source[17].And the academy already has the basic experimental research platform.Shenyang Institute of Technology designed a UWB high power EMP antenna and relevantperformance experiments had been done[18].The results show that the energy efficiency of the antenna can reach 90%，getting 120～250 MHz electromagnetic radiation power.The repetition frequency is 50 ～ 100 Hz，and the output power instability is less than ±10%.As can be seen，the advantage of the UWB device is that the antenna radiation efficiency is very high，reaching 90%，while the disadvantage is that the radiation signal bandwidth is narrow.National University of Defense Technology made a large number of research results in the UWB EMP source.Reference[19]developed a broadband EMP generator，with adjustable center frequency from 270 MHz to 380 MHz，a percentage bandwidth of less than 11%and a adjustable output power from 2.9 MW to 5.2 MW.Mechanical Engineering College[8]established the high power EMP field simulation system，using gigahertz transverse electromagnetic cell(GTEM)as the field transmission device.At the same time，the college[4，6，8，20－21]established a continuous wave simulator system，a LEMP simulator system，and a NEMP simulator system，which lay a good foundation for the research of all kinds of energy signal interference effects.

In terms of the radio fuze failure mechanism and protection theory，the domestic scholars have studied a lot.The radio fuze effect experiments under all kinds of energy type interference，such as the continuous wave，the UWB EMP，the LEMP，the NEMP and the HPM，were carried out，getting the following conclusions[4，20－21，34－40]:

(1)High－power electromagnetic signals interference belongs to energy type interference;

(2)Energy type interference can not only lead to hard injury，but also have potential damage.The technical indicators，like ignition sensitivity and working current，appear different degree of change，and the damage has cumulative effect，until the formation of hard injury;

(3)Different signal has different coupling channels and different effect mechanism.There are two types of energy coupling，"front door"coupling and"back door"coupling.Continuous wave signals and low frequency pulse signals mainly couple through the"front door"channel，while high frequency EMP signals mainly couple through the"back door"channel;

(4)Different fuze has different failure mechanism under the same interference sources，because the failure mechanism is affected by many factors;

(5)the execution circuit is the sensitive circuit under energy type interference.

High power EMP can affect directly on the fuze’s executive circuit(for example，SCR)，and lead to bomb without the normal gate triggering signal.In addition，the references[4，37，41－44]researched the radio fuze protection theory，and proposed the following protection and reinforcement measures:

濱660塊設計沙四段為直井長縫開發(fā)。該區(qū)塊屬于濱南沙四灘壩沙儲層，測井解釋滲透率（5～15）×10-3μm2，為低滲-特低滲儲層，從油層應力剖面看出，濱660塊沙四段油藏呈多層發(fā)育，層間地層應力差異較大，隔層應力較高，壓裂易產(chǎn)生多裂縫。油層與隔層應力差為2～5MPa，大型壓裂裂縫形態(tài)復雜。

(1)Take appropriate measures，such as shielding and overlapping，cut off the EMP energy coupling transmission channel;

(2)For sensitive circuits and components，using a variety of high frequency transient interference measures;

(3)Use circuit optimization design and insensitive components to improve anti－interference ability of the circuit.

4 Existing Problems and Corresponding Countermeasures

4.1 Existi ng Problems in Present Research

As can be seen from the analysis of the open reports，there is a big gap between the domestic research and the foreign research in the radio fuze’s research.The domestic researches still exist the following problems:

(1)The studies are mainly in experimental and theoretical analysis are not deep enough.From the studies，almost all of the researches are analyzed through the circuit and validated by experiment，lacking of theory analysis.In addition，the failure mechanism of fuze is determined to the device currently.The abnormal working characteristics of the vulnerable components and devices are not further researched;

(2)The fuze type in experiment is limited，and the conclusion is lack of generality.As can be seen from the relevant references，most types of the present experimental fuze are continuous wave doppler fuze，lacking of other types.The research conclusions are only established for the single source and single kind of fuze，even the specified experimental condition.For different source，different type of fuze and even different experimental condition，the failure mechanism can not be accurately predicted;

(3)Lacking of systemic research，and basic research should be urgently solved.From the contrast，we can find that there is still a big gap in EMP weapon development，experimental equipment performance and standard making in China.All of these severely restrict the further study on the failure mechanism of radio fuze.

4.2 Corresponding Countermeasures

According to the existing problems in present research，we can make a breakthrough in the following aspects:

(1)Broaden the fuze types，and carry out the effect experiment.To carry out the energy type interference effect experiments of all kinds of fuze as much as possible，in order to realize the failure mechanism of different fuze in different environment;

(2)Research the abnormal working characteristics of the vulnerable components and devices.Use the semiconductor theory and the circuit modeling method to analyze the energy coupling characteristic and failure mechanism of the fuze deeply;

(3)Fuze system energy coupling model.On one hand，we can establish the theoretical model by electromagnetic topology theory.On the other hand，we can use the system identification theory to establish the fuze system model.Through the coupling model，the failure mechanism of different fuze and different source can be predicted;

(4)Focus on the basic research of the fuze.Speed up the development of higher performance test equipment，standard making and so on，in order to improve fuze’s research foundation.

5 Conclusion

Radio fuze failure mechanism under energy type interference has becoming a hot topic at home and abroad.This paper analyzes the classification and characteristics of the energy type interference signals.Then，it compares the research results in China with the research results in foreign countries.It is clear that there is a biggish difference between China researches and the foreign researches.Three existing problems in the present research are analyzed，and four corresponding countermeasures are proposed in this paper.

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