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Research on SAW Sensors in TPMS

Li tongbin Information Engineering School, Putian University, Fujian, China

E-mail: tobelee@126.com Zheng ning

Information Engineering School, Putian University, Fujian, China E-mail: zhen ning@ptu.edu.cn

Chen shien Information Engineering School, Putian University, Fujian, China E-mail: gracen_chen@ptu.edu.cn

Kang xin* School of Mechnical & Electronical Engineering,

Putian University, Fujian, China *E-mail: tokangxin@163.com

Abstract—In this paper, the performances of several tire temperature and pressure sensors in Tire Pressure Monitoring System (TPMS) were analyzed, and the corresponding IC and MEMS core technology in R&D of the active and passive sensors was studied. It is pointed out that the passive wireless sensor chips based on the surface acoustic wave (SAW) is the development direction in automotive safety products. In addition, this paper analyzed the principle, working process and the development of SAW sensors in recent two decades. As to the current international technical barriers, the patent technologies of the SAW sensor were presented, and the international competition and cooperation were discussed. Finally we draw the conclusions that in order to break the technical barriers of European and American automobile trade, it is quite necessary to develop the core technology of SAW sensors, together with the independence, resources integration, business risk control and the perfection of patent law, due to the huge economic benefits of the SAW sensors.

Keywords SAW; Passive sensor; RFID; TPMS; Smart Tire.

I. INTRODUCTION SAW (surface acoustic wave) is a kind of elastic wave

that propagates along the surface of object. The resonant frequency of SAW varies with the physical property changes of the measured objects. R&D on SAW sensor here means that a kind of SAW-sensitive passive material and physical structure is selected to sense tire temperature and pressure. The physical structure which has novel IC-SAW resonator can amplify the measured signals and then is read out by RFID (radio frequency identification) excitation. All of the functional modules and their peripheral circuits are integrated in one chip by MEMS technology (micro-electro-mechanical system). The chip based on resonant surface acoustic wave is a passive wireless SAW sensor for tire pressure and temperature detection. Since the advantages of no-power, light weight, small size, maintenance-free and low cost, SAW sensor chip is suitable to vehicle tires for multi-parameter detection such as temperature and pressure, and it can

update the currently widely used TPMS (tire pressure monitoring system). The passive wireless SAW sensors have become to the core technology of the new generation of TPMS research . The number of domestic TPMS R&D companies has reached more than 200. Their researches in the past mainly focused on the secondary development of active chips , as shown in Fig.1. The active chips are electronic sensor but not SAW sensor. Although there are many applications of the productive, it is not the master core technology, especially for the achievements of SAW sensor. Since China is turning from large to powerful nation in automotive filed, the automotive electronics needs a leap-forward development. Hence review and evaluation in SAW sensors research area will be of great significance.

II. BACKGROUND AND CURRENT SITUATION OF TIRE TEMPERATURE AND PRESSURE SENSOR

Before tire pressure and temperature sensor appeared, more than 30% of traffic accidents on the highway were caused by vehicle tire failure. In United States, the presentation was as high as 60% . To prevent the outburst of accidents, U.S and Europe had invested lots of funds to research the sensor, which would monitor tire’s pressure, temperature, dynamic balance and friction resistance. After a few MEMS sensors based on RF (Radio Frequency) and IC technology were invented and used widely in TPMS, traffic accident decreased greatly. In 2008, U.S forced vehicle to install the tire sensor as the third security products following seat belts and airbags, and EU did this in 2012.

The active MEMS sensor chip as shown in Fig.2 always belonged to technology monopoly by Germany's Infineon, American GE and Freescale . The product types are the SP30/37 series chip made by Infineon, the MPXY8300 series chip made by Free-scale, and the NPX2 series chip made by GE . Although the automotive electronics industry has huge demand for the sensor chip , but Chinese TPMS processing enterprises

2017 4th International Conference on Information Science and Control Engineering

DOI 10.1109/ICISCE.2017.348

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2017 4th International Conference on Information Science and Control Engineering

DOI 10.1109/ICISCE.2017.348

1668

2017 4th International Conference on Information Science and Control Engineering

DOI 10.1109/ICISCE.2017.348

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have to become third-rate companies for the lack of core technology. Many companies in China have been like foreign employee, meager profits, gradually eliminated .

These MEMS sensors used in China almost have same basic principle and similar technology solutions for TPMS. Due to the use of battery inside the tire, they have the following problems:

a. The wheel mass increased about 40g, the dynamic weight would increase more up 7000g in the high speed. This caused new dynamic balance security risks.

b. When the internal environment of tire exceeds the working conditions of battery, TPMS will do not work.

c. Due to the battery shortages such as small capacity, high replacement costs, the battery results sensor real-time monitoring, tire product identification and traceability, tire life free maintenance, tire networking applications in damage or loss. In particular, when TPMS intermittent work, the failure prediction probability for tire burst is present, just at that moment TPMS would not response of traffic accident.

d. The battery need add a few hardware and software functional modules for sensor, it resulted the program in longer running cycle, in lower efficiency and in lower reliability.

A SAW sensor does not have such problems and becomes the research focus of TPMS now. Table 1 shows the differences of all above sensors.

Table 1 Comparative analysis of the existing sensors and SAW sensor

Make Motorola Freescal

GE nova Infinoin SAW sensor

Typical model

MPXY83 00 NPX2 SP37

Working Capacitive Piezoresisti Piezoresistive, I i

resonanc A/D 10bit 12bit 8/16bit Quasi

di i lPressure ±2% ±6kP ±7kP ±5% Embedded MCU

Yes core with 8-bit, or 16-bit MCU No MCU RFIDRF

communic Yes

active Yes

active Yes active

acceleratio Yes Pow, Acq. and RF launch control No need voltage Yes battery efficiency and stability No need Package Type

20 pin OIC 16 pin SOP 14 pin SOP No PCB

Ov-temp cutting Y avoid battery failure, damage, explosion No need

standby 0.14μA 0.6μA 0.4μA 0 dynamic balancing

Affect more

Affect more Affect more Lesser

productio Expensive Expensive Expensive Cheaper

Based on its passive and cheapness, SAW sensor represents the development direction of TPMS. And it is feasible to study the SAW sensor over the active sensor technology and it is fit for the development strategy in China.

III. CHARACTERISTICS RESEARCH OF SAW SENSORS

According to SAW propagation theory, the SAW sensor can be divided into two types: delay linear and resonant .

Delay linear sensor uses a phase measurement method, so the sensor has higher precision and more information than the resonant. But the reflection intensity of the RFID signal is inversely proportional to the fourth power of the distance, the reflection modulation signal of the sensor is weak and the attenuation is fast. In detail, a radar equation shows the range of wireless sensor maximum transmission as following equation :

2 2 4

t t r

MAX 4

P G G1 R

S4 kTBF IL

(1)

Pr/t: received (or transmitted) RF signal power; Gr/t: receiver (or transmitter) effective antenna gain; R: distance between the transmitter and receiver;

: wavelength; F: receiver noise factor; T: antenna noise temperature; kT: standard input noise power density; B: noise bandwidth; S/N: required signal to noise ratio for detection circuit; IL: SAW resonator insertion loss.

When the distance between RFID and SAW sensor exceeds half a meter, it is difficult to read out the measurement result. Especially in the environment of tire high-speed rotation and motor vehicles motion closely to ground, delay linear sensor is difficult to achieve the passive function without battery. Only delay linear sensor used with battery as an active sensor, the performance of delay linear sensor is significantly better than the resonant ones, but is not good than the current sensors now.

Resonant SAW sensor has a higher Q value and its RFID distance is up to 2 meters even if no any power supply . It can meet the requirements to measure pressure and temperature, and can identify objects simply. The resonant type as wireless passive SAW sensor is just appropriate.

Fig.3 showed the schematic diagram of SAW sensor (hereinafter referred to as resonant type). Two IDTs (Inter Digital Transducers) form the transducers on the piezoelectric substrate. One emits RF and the other receives RF after connecting antenna with the impedance matching network. RF electromagnetic wave excites IDT stretching and contracting in the substrate surface. That is, piezoelectric effect produces SAW. SAW is reflected and added by a reflector (bars). The reflector is composed by discontinuous metal bars deposited on the piezoelectric substrate. When the excitation frequency of RF is equal to the natural frequency of SAW, SAW will resonate in the substrate and the resonant energy is much larger than excitation energy. The excited SAW energy is strong enough to reflect by emission transducer, and the reflected frequency is equal to the SAW resonant frequency. The reflected signal is read by the RFID.

The SAW’s resonant frequency and wavelength are generated by tangential, density and geometric parameters of piezoelectric substrate. Different tangential have

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different change rate for resonant frequency. The geometric parameters and density of substrate are determined by external pressure and temperature. In addition, the sensitivity and offset range of resonant frequency are related to the physical structure of SAW sensor.

IV. R&D RESULTS AND FOUND OF SAW SENSORS

In 2002, SAW sensor applied to TPMS experiment by M. Binhack who come from German Ilmenau Technical University, and changed previous relatively vague research . In 2006, B. Dixon and V. Kalinin proposed the idea of applying SAW sensors to a new generation of TPMS . In 2009, Bartin G., Kunze R. and Wall B. et al. designed the temperature and pressure sensor structures using dual SAW resonators . After that, the SAW sensor was to obtain some success and new discoveries, as follows:

A. SAW sensor and RFID match well in frequency range of 10MHz ~ 3GHz. When SAW sensor matches RFID, RFID can directly read the data out from SAW sensor which outputs quasi-digital without A/D converter. But it is difficult to reliably reach the RFID identification distance, because the reflection energy from SAW sensor is low. In order to solve the problem what the SAW reflection energy is low, one way is to develop high Q value, low SNR SAW resonator. The other way is the existing development what makes a power supply in the SAW substrate, the supply converts vibration energy of vehicle to SAW reflection energy by magnetostrictive or piezoelectric technique. And the energy is enough to meet communication distance requirement between SAW sensor and RFID.

B. For the energy converting from the vibration, SAW sensor communicates well with RFID. Tests found that the efficiency of the energy conversion mechanism (such as vibration arm) will gradually decline. When the wheel travels about 10,000 km, the power generation efficiency will attenuate, which may cause the SAW sensor failure. The SAW sensor would have a breakthrough if material fatigue can be solved .

C. Different piezoelectric materials were used as substrate of SAW. The material test results showed that the material tangential, elastic constant, piezoelectric constant, dielectric constant and thermal expansion coefficient have influence on SAW’s propagation speed, electromechanical coupling coefficient, propagation loss and temperature coefficient. It was also found that the velocity of SAW is mainly determined by the elastic modulus. The SAW frequency depends mainly on the material, tangential and density of piezoelectric substrate

. Experiments showed that quartz is a good substrate material for SAW sensor, and has advantages as: material stability, easy processing and reliable operating frequency. The disadvantage of quartz is that the value of Q is less than lithium niobate. But lithium niobate and other thin

film laminates material stability are difficult to meet the current requirements of the sensor.

D. SAW element quality was significantly improved with the IC process technology advances. Advanced IC technology is good for the design and production of high-performance IDT, such as the fingers and reflectors optimization of the number, gap, width, thickness, aperture and other parameters. SAW sensor chip now can have more the bandwidth, less the insertion loss, higher the RF signal to noise, than ever. In addition, an Al film can be used on a SAW substrate by magnetron sputtering or electron beam deposition techniques . The film is epitaxially grown on an alloy layer or a transition layer which can improve Al film properties. In other words, with the new technology of IC and MEMS, the SAW sensor chip which integrated antenna element and network impedance matching and auxiliary power supply, becomes more and more easy.

E. SAW sensor installation process needs in-depth discussion. One way is to secure the SAW sensor to the hub directly, which is high installation costs and still affect the dynamic load and dynamic balance of the wheel. The other way is to implant the SAW sensor into the tire to form intelligent tire, which has a small cost. But the sensor should overcome the deformation of the rubber at embedded position, and can endure the tire manufacturing process temperature (140~160 ) and pressure (215~3MPa) test .

V. R & D RISK OF SAW SENSORS

A. SAW sensor has a multi-disciplinary cross feature. The study of substrate materials is the combination of crystal piezoelectric and acoustic science. SAW component design and substrate material processing is integrated circuit technology. Measured is the application of radio communication disciplines RFID technology. Tire pressure temperature should rely on computer information processing. SAW sensor chip design requires MEMS technology support. The greater the number of unknowns, the greater the technical risk.

B. SAW sensor developing process is complex: From SAW sensor design piezoelectric substrate

material and cutting test base material processing technology design mask and microelectronics processing MEMS integrated package SAW die detection screening Tire vulcanization process embedded sensor performance testing and shipping.

No company has the ability to complete all the process, and SAW industry groups have not formed. So it needs to cooperate in different regions and companies. The semi-finished products of SAW device have a shorter timeliness, the coordination requirements are strict yet. So there is uncontrollable risk of technology management.

C. SAW sensors have intellectual property issues. Technology leaders use patent to set up a technical barrier against latecomers. Such as "Invention Patent Application

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No. 03810957.3, Publication No. CN1653321A" in China's Intellectual Property Office, seems to be applied by an ordinary foreigner through the Hong Kong patent agency. It is found that the patent lists 15 different mechanical structure of brochure that covers all the known pressure sensor mechanical structure in SAW industry. 14 rights requirements in patent blocked all the latecomers. But the corresponding patent in European and American countries (British patent application number: GB-2352814) only truthfully describes a mechanical structure used by its products. Visible, it can be seen that China's SAW sensor research and development hidden business and even legal risks, there must be a strong peep behind, ready to use our legal loopholes to kill us. Because independent intellectual property rights of SAW sensor can not only break the automobile trade technical and legal barriers, but also promote the domestic motor vehicle safety products and its legislative process, even the improvement of intellectual property law.

VI. CONCLUSIONS Cultivating a core technology industry, it generally

takes about 5 years to carry out academic research and 3-7 years of industrial incubation. Compared with China's SAW sensor research and development situation, the conclusion is that China's SAW sensor research has just entered the stage of product innovation. It is the period expanding money input for development and cooperation. SAW sensor R&D, if successful, and successfully enter the automotive electronics, automotive and tire manufacturing industry. Not only TPMS achieves the leapfrog development, tire has intelligent basis. Moreover, SAW sensor market capacity is equal to the number of tires on the earth. For the reference data that today's German Infineon SP30 series chip shipments have already exceeded 2 billion, SAW sensor output value estimated will exceed 200 billion yuan. And SAW sensor chip can support the TPMS industry whose output value is greater than 40 times of SAW sensor.

ACKNOWLEDGMENTS We acknowledge the financial support provided by

Fujian province key scientific research project and Putian Government’ funding (Nos: 2015H6018, 2015H0033 and 2014G18).

REFERENCES

[1] Zhibo Rui. China TPMS industry market analysis and development trend forecast report 2016-2021 [R]. Beijing Zhibo Rui Investment Consulting Co., Ltd. 2015

[2] LI junqing. Tire pressure monitor design base on SP30[D]. North China university, 2012-06-01.

[3] WANG weiji. Tire pressure monitor design base on MPXY8300A sensor [D]. south China university of technology, 2012-06-01.

[4] China Industry Research Network. 2017 Investigation on the Present Situation of China 's Automotive Electronics And market prospects analysis[R]. 2017

[5] Dong diannan. Research on automotive electronic market competition strategy for Freescale semiconductor[D]. Shandong university, 2012-10-15

[6] http://www.infineon.com [7] http://www.freescale.com [8] http://www.ge-mcs.com [9] Cinzia Caliendo. Theoretical Analysis of SAW Propagation in

3C-SiC/c-AlN[J]. Crystals. 2016(6-3):25 [10] Fabian Lurz, Stefan Lindner, Sarah Linz, Sebastian Mann, Robert

Weigel. High-Speed Resonant Surface Acoustic Wave Instrumentation Based on Instantaneous Frequency Measurement[J]. IEEE Transactions on Instrumentation and Measurement 2017:1-11.

[11] Liu Boquan, Zeng Yicheng, Tang Pinghua. A noise-robust method for passive wireless resonant SAWsensor[J]. Sensor Review, 2016(36-3):312-320

[12] S Klett, M Binhack, et al. Progress in Modeling of Sensor Function for Matched SAW Resonators[J]. IEEE Ultrasonics Symposium, 2002:471-474.

[13] B Dixon, V Kalinin, J Beckley, R Lohr. A Second Generation In-Car TPMS Based on Wireless Passive SAW sensors[C]. IEEE International FCS,2006:374-380.

[14] Martin G, Kunze R, Wall B. Temperature-stable double SAWRs[C]. IEEE Transactions UFFC,2009:199–207.

[15] Gnadinger Alfred P. Vibration analysis based on surface acoustic wave sensors[C]. MATEC Web of Conferences. 2015(24):2002

[16] Meriem, Omar, Sébastien, Laurent Bouvota, etl.. Magnetic field SAW sensors based on magnetostrictive-piezoelectric layered structures: FEM modeling and experimental validation[J]. Sensors and Actuators A: Physical, 2016(240):41-49

[17] Stoney R, Geraghty D, O'Donnell, G.E.. Characterization of Differentially Measured Strain Using Passive Wireless Surface Acoustic Wave (SAW) Strain Sensors [J]. Sensors, IEEE 2014(14-3):722-728

[18] Jeongho Eom, Hoyoung Lee, Bumkyoo Choi. A study on the tire deformation sensor for intelligent tires[J]. International Journal of Precision Engineering and Manufacturing, 2014(15-1):155-160

[19] Sensor technology company. a pressure monitor with SAW component [P]. application number in P.R.China’s SIPO:03810957.3, Open number:CN1653321A

[20] http://www.transense.co.uk [21]http://worldwide.espacenet.com/searchResults?compact=false&ST=

quick&sortField=ud&DB=EPODOC&page=2&locale=en_EP&asce nding=false&IA=transense

Fig. 1 A secondary R&D product in China

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Fig. 2 An active sensor chip

Fig. 3 Component of a resonant SAW sensor and the working principle

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