Proceedings etc2014 E-Book

The European Society of Telemetry

• Herausgeber: Books on Demand
• Kategorie: Fachliteratur
• Sprache: Englisch

Seitenzahl: 422

Veröffentlichungsjahr: 2014

Beschreibung

The European Telemetry and Test Conference etc2014 took place in Nuremberg in June 2nd-5th, 2014. Over 50 Technical Papers were presented in 10 Technical Sessions, highlighting the most recent innovations in methods, systems, and instrumentation from industry, researchers and laboratories all around the world. More than 50 companies attended the etc2014 exhibition and offered unique opportunities for technical discussions. Within the etc-Village, they presented numerous innovations, among others around new sensors and data acquisition architectures, Ethernet video solutions, C-band telemetry. This international success has been confirmed by the feedback of the participants: more than 85% were satisfied about the information offered in the Technical Sessions and the etc2014 Exhibition, the organisation and the location of the Conference. Organised for the first time in cooperation with SENSOR + TEST, the internationally leading trade fair for sensors, measuring, and testing technology, the new form of etc2014 opened the door to further 500+ exhibitors; potentially interesting for the daily and future applications of the telemetry professionals.

Leseprobe

Proceeding

etc2014 – 34. European Telemetry and Test Conference

Bei diesem Band handelt es sich um den Kongressband der etc2014 – European Telemetry and Test Conference.

Dieser Band beinhaltet die Manuskripte zu den jeweiligen Vorträgen.

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This volume covers the proceedings of the etc2014 – European Telemetry and Test Conference.

This volume comprises the manuscripts of the lectures.

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AMA Service GmbH accepts no responsibility for the correctness and completeness of the details and the consideration of private rights of third parties.

Herausgeber / Publisher:

The European Society of Telemetry

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Welcome to the 34th European Telemetry and Test Conference – etc2014

On behalf of the European Society of Telemetry, it gives me great pleasure to welcome you to the 2014 European Telemetry Conference etc2104. This year’s conference, the 34th European Telemetry Conference, is organised for the first time in cooperation with SENSOR+TEST, affording etc2014 participants access to the adjoining large exhibition area at the Nuremberg Convention Centrevenue.

The etc2014 Opening Ceremony will offer two breath-taking presentations. The leading-edge telemetry technology used for the Red Bull Stratos Project will be showcased by the company Riedel Communications. Airbus Helicopters will present the Optionally Piloted Vehicle flights, which took place at a European Air Force base in 2013.

The etc2014 technical programme includes a selection of contemporary papers from authors across Europe and beyond; with speakers from Brazil, India, China and the United States. Not only the quantity of technical papers will reach an all-time summit, but also the contents quality and up-to-dateness will be at optimum, as the referees will bring their presentation material directly to the conference, having included their latest results and ideas. Browsing the preliminary schedule it is apparent that the subjects of “new modulations” and “networking technology“ remain primary areas of interest and on-going R&D within thetelemetry community.

This year’s conference programme also features special technical sessions. The ICTS General Session (International Consortium for Telemetry Spectrum), the ETSC Open Meeting (European Telemetering Standardisation Committee) and the MDL User Meeting (Measurement Description Language) offer platforms for international information exchange and working groups on standards for telemetry.

As part of the goal of the European Society of Telemetry to support the technical growth and further formation in the field of telemetry, the conference dedicates two half daysthis year to short courses. Internationally recognised specialists will train or refresh on a wide range oftelemetry and test related technologies.

The ultimate success of the conference is of course entirely dependent upon your continued patronage. So thank you for supporting etc2014 and welcome to Nuremberg.

Renaud Urli

Vice-President and Chairman of the European Telemetry and Test Conference

Table of Contents

1. Sensors & Applications

Chairmen:

B. Koderer, Airbus Defence and Space, Manching (Germany)

1.1Wireless and Battery-less Sensor Using RF Energy Harvesting

C. Merz, G. Kupris, M. Niedernhuber, Deggendorf Institute of Technology, Deggendorf (Germany)

1.2An Introduction to achieving Industrial Applications of Wireless Passive SAW Sensors for Advanced Monitoring

G. Heider, SENSeOR SAS, Valbonne (France)

1.3Photovoltaic Cells for Optical Power and Data Transmission

Henning Helmers, Fraunhofer ISE, Freiburg (Germany)

1.4ELF Extended Low Frequency Sensor Designs

Kevin Westhora, Dytran Instruments Inc., Chatsworth, CA, U.S.A

1.6HAZARD2 project : airspeed and temperature measurements in jet engine blast

T.Boisson, Airbus Operations France, Lagardelle sur Leze (France)

2. Data Links

Chairmen:

C. Douglas, JDA Systems, Ihlow Riepe (Germany)

2.1Real-Time Channel Sounding for Channel-Adaptive Data Links

A. R. Ganis, C. Bluemm, C. Heller, Airbus Group, Munich (Germany); M. Loghi, University of Udine, Udine (Italy)

2.2A Modified OQPSK Detection for MIL-STD SOQPSK in the Satellite Communication

D. Xingwen, Beijing Research Institute of Telemetry, Beijing (China)

2.3A Low Cost Flying Telemetry Platform for Telemetry Tests

G. Mueller, Airbus Defence and Space, Manching (Germany)

2.4Characterisation of Channel Usage in ISM/SRD Bands

H. Lieske, F. Beer, J. Robert, A. Heuberger, Friedrich-Alexander-Universität Erlangen-Nürnberg (FAU), Information Technology (Communication Electronics), Erlangen (Germany); G. Kilian, Fraunhofer Institute for Integrated Circuits IIS, Erlangen (Germany)

2.5Smart Radio Control System (for Flight Test Centers)

J. Alvarez, Airbus Defence and Space, Flight Test, Getafe (Spain)

2.6A BRL-POMDP Based Cross-layer Optimization of Dynamic Spectrum Access

J. Tian, China Academy of Engineering Physics, YouXian, SiChuan (China)

3. Data Management

Chairmen:

D. Corry, Curtiss-Wright Avionics & Electronics, Dublin (Ireland)

3.1History and Evolution of Metadata Standards for the FTI Community

Alan Cooke, Principal Software Architect, Curtiss-Wright, Dublin (Ireland)

3.2Big Analog Data - Challenges of Managing Large Scale Data Capture and Analysis

I. Matthews, National Instruments, Nanterre (France)

3.3Advanced Monitoring Techniques

M. Gonzalez-Martin, P. Rubio-Alvarez, D. Roses-Sanchez, R. Lopez-Parra, G. Reillo-Morales, Airbus Defence and Space, Flight Test, Getafe (Spain)

4. Video

Chairmen:

S. Dettman, Airbus Operation SAS, Toulouse (France)

4.1Non-intrusive In-flight Propeller Blade Deformation Measurements by Means of a Rotating Camera

F. Boden, B. Stasicki, German Aerospace Center DLR, Göttingen (Germany)

4.2Video system for flight test facilities

P. Lamour, TDM, Mérignac (France)

4.3IR thermal imaging solutions for flight applications

M. Pfadt, MICRO-EPSILON MESSTECHNIK GmbH & Co. KG, Ortenburg (Germany)

4.4Track Targets Identification in Store Separation Tests using Digital Image Processing Techniques

A. Y. Kusumoto, L. E. Guarino de Vasconcelos, N. Leite, Instituto de Pesquisas e Ensaios em Voo (IPEV), São José dos Campos (Brazil); R. Pirk, Instituto Tecnológico de Aeronáutica (ITA), São José dos Campos (Brazil)

4.5A Dual Compression Ethernet Camera Solution for Airborne Applications

S. Willis, Curtiss-Wright Defense Solutions, Dublin (Ireland); B. Langer, Kappa Optronics GmbH, Gleichen (Germany)

5. C-Band & New Modulations

Chairmen:

G. Müller, Airbus Defence and Space, Manching (Germany)

5.1Academic experiences with an 802.15.4 based telemetry system for UAV applications

A. Rolando, C. Cardani, F. Rossi, Department of Aerospace Science and Technology Politecnico di Milano, Milano (Italy)

5.2COFDM – The Ultimate Modulation?

A. Wankerl, Artronics, Dachau (Germany)

5.3Standard Spacecraft Wireless Protocols

D. Parsy, M. Parsy, Beanair, Immeuble «Les Bureaux de Cergy», Cergy (France)

5.4C Band Telemetry Tests Results

F. Jimenez, Airbus Defence and Space, Sevilla (Spain)

5.5The Challenging Development and the Entry into Service of C-band Telemetry at Airbus Test Centre

L. Falga, Airbus Operations SAS, Toulouse (France)

5.6Chapter 10 Telemetry Downlink

M. Faber, Zodiac Data Systems, Bergisch Gladbach (Germany)

6. Methods & Standards

Chairmen:

G. Freaud, AIRBUS France, Toulouse (France)

6.1Ground Test Facilities and Integration Concepts for Combat Air Systems at Airbus Defence and Space

H. Plankl, Airbus Defence and Space Test Facilities, Manching (Germany)

6.2Overcoming Instrumentation Limitations in Spin Tests Using Flight Path Reconstruction Techniques

J. N. Dias, IPEV - Instituto de Pesquisas e Ensaios em Voo, São José dos Campos, São Paulo (Brazil)

6.3Air Speed Indication Calibration Measurement Position Error Correction - PEC

O. Freund, Airbus Helicopters (Germany)

7. Acquisition Systems 1

Chairmen:

C. Herbepin, Airbus Helicopters, Marignane (France)

7.1High-Speed Rolling Bearing Test Rigs with Contactless Signal Transmission for Measuring the Inner Ring Temperature

C. Brecher, M. Fey, A. Hassis, Werkzeugmaschinenlabor WZL der RWTH Aachen, Aachen, (Germany); S. Bonerz, OTT-JAKOB Spanntechnik GmbH, Lengenwang (Germany)

7.2Moving Data Analysis into the Acquisition Hardware

T. Fanzheng, China Flight Test Establishment (China); D. Buckley, Curtiss-Wright, Dublin (Ireland)

7.3Use of source coding techniques on Ariane 5 1553 data

D. Schott, AIRBUS Defense and Space, Les Mureaux Cedex (France)

7.4Challenges in Design and Development of Indigenous Flight Test Instrumentation System for a High Performance Fighter Aircraft

V. Madhusudana Rao, K. Singh Chowhan, V. Patel, N. Prasad, P. Subramanyam Aeronautical Development Agency(ADA), Bangalore (India)

7.5Use of FPGA Technology to Enable Custom Sensors and Communication for Future Test Systems

I. Matthews, National Instruments, Nanterre (France)

8. Networks & Acquisition Systems

Chairmen:

S. Penna, EMBRAER, Sao Jose dos Campos (Brazil)

8.1Next Generation Data Acquisition Networks

D. Lefevre & Ghislain Guerrero, ZODIAC DATA SYSTEMS, Courtaboeuf (France)

8.2ETHERNET PACKET FILTERING for FTI - PART1

Ø. Holmeide, J-F. Gauvin, OnTime Networks AS, Oslo (Norway)

8.3Interoperability Standards for Network Based Airborne Video Systems

M. Buckley, Telspan Data, Concord CA (USA)

8.4Addressing the Challenges Created by Large Networked Ethernet FTI Systems

P. Quinn, Curtiss-Wright Defense Solutions, Avionics & Electronics, Dublin (Ireland)

9. GNSS & Antennae

Chairmen:

W. Lange, Lange-Electronic GmbH, Gernlinden (Germany)

9.1Flying Boresight Source for Improved Testing and Calibration of Tracking Antennas and Advanced Flight Path Simulations

D. Haefner, A. Kimpe, L. Altenbuchner, P. Turner, DLR Mobile Rocket Base, Wessling (Germany)

9.2A new tool for simulation of geospecific multipath and obscuration of GPS / GNSS signals with relation to realistic 3-D city models

K. von Hünerbein LANGE-ELECTRONIC GmbH, Gernlinden (Germany); G. Moura, Oktal-SE, Vigoulet-Auzil (France)

9.3Future GNSS: Improved Signals and Constellations

G. Martínez Morán, Airbus Defense & Space, Getafe (Spain)

9.4A Compact Broadband Antenna for Wireless Terminals in Telemetry and Communication Systems

G. Kang, F. Wang, Y. Tian, Beijing Institute of Astronautical Systems Engineering, Beijing (China); Y. Ji, No.23 Research Institute, China Electronics Technology Group Corporation, Shanghai (China)

9.5SWAP with a consolidated PNT Modular Sensor

F. Silva, Spectracom, Les Ulis (France)

10. Acquisition Systems 2

Chairmen:

N. Leite, Instituto de Pesquisas e Ensaios em Voo (IPEV), Sao Jose dos Campos (Brazil)

10.1Magnetoelastic Sensors - Status, Commercial Readiness, and Outlook

J. Müller, NCTE AG, Unterhaching (Germany)

10.2Dynamic Load Acquisition on the Helicopter Rotor Blades by Sensor Telemetry

E. Manner, Manner Sensortelemetrie GmbH, Spaichingen (Germany)

10.3Miniaturized On Board Data Acquisition Unit

G. Solak, T. Çelebi, O. Yaşar, Aselsan Inc., Yenimahalle-Ankara (Turkey)

10.4Data Encryption Algorithm of Telemetry PCM System based on Chaotic Sequence

L. Qibin, Institute of Electronic Engineering, Mianyang, Sichuan (China)

Wireless and Battery-less Sensor Using RF Energy Harvesting

Christian Merz1, Gerald Kupris2, Maximilian Niedernhuber3

Deggendorf Institute of Technology, Edlmairstr. 6 + 8, 94469 Deggendorf, Germany

[email protected]

[email protected]

[email protected]

Abstract

The contribution introduces a RF energy harvesting circuit which can be used to power a wireless and battery-less sensor system. The sensor can be powered wirelessly over a distance of about two meters. The basic principles of RF energy harvesting are explained, it is shown how the system can be designed and special considerations are discussed. The proposed RF energy harvesting system operates at a frequency of 866.6 MHz, so that far field propagation is present. The system consists of an antenna, a matching circuit, a RF-to-DC conversion circuit and a power management module, including a storage capacitor, a comparator and a DC-to-DC converter. The harvester produces a pulsed output voltage of 1.8 V at an input power of at least -6 dBm.

Key words: RF Energy Harvesting, Wireless Power Transfer, Battery-less Sensor, RF-to-DC Conversion, Electromagnetic Far Field Propagation

Introduction

Energy harvesting is the process of capturing, conversion and storing of energy from the environment to supply low power devices or saving the energy for later use. There are many different types of energy harvesting sources, e.g. solar, vibration, temperature or electromagnetic waves. Of these sources, electromagnetic waves provide by far the least power density, which is indicated by table 1. [1]

Tab. 1: Different energy harvesting sources.

Source

Technology

Power Density

Solar

Photovoltaic Cell

100 mW/cm

2

Vibration

Piezoelectric Element

800 μW/cm

2

Temperature

Thermal Generator

60 μW/cm

2

Electromagnetic Waves

Antenna

< 1 μW/cm

2

Because of the fact that the power density of electromagnetic waves is very low, the energy feed-in and conversion has to be done very efficiently. The feed-in is performed by an antenna, which captures the incident electromagnetic waves and transfers the resulting AC voltage to the harvester circuit. Between the antenna and the energy conversion circuit there is the matching network. On the one hand, it has the task to ensure the maximum power delivery from the antenna to the remaining circuit and on the other hand it minimizes the signal reflections at the interface of the antenna and the matching circuit. The energy conversion circuit converts the RF power, which is delivered by the antenna, into DC voltage by using a cascaded Greinacher circuit. After the rectification, the resulting DC voltage is stored at a capacitor. The energy at this storage capacitor gets accumulated until an upper threshold voltage is reached. After exceeding this voltage, the storage capacitor discharges until a lower threshold voltage is reached. This charging and discharging of the capacitor is triggered by a comparator, which compares the voltage at the storage capacitor with an internal reference voltage and outputs a digital voltage indicating which one of the compared voltages is higher. The output of the comparator switches a DC-to-DC converter on and off, which increases the DC voltage level at the storage capacitor to another adjustable level, e.g. 1.8 V. Fig. 1 shows the components of the proposed RF energy harvesting system.

Fig. 1. Diagram of the proposed RF energy harvesting system.

Preconsiderations

The selection of the frequency band and the determination of the expected input power are very important aspects that must be dealt with before starting the design of the RF energy harvesting system. For energy harvesting purposes, four frequencies are mainly used in today’s industry for different applications. The frequencies have a major influence on the design and on the transmission behavior of the harvesting system. The frequencies are 125 kHz, 13.56 MHz, 868 MHz and 2.4 GHz. These frequencies are allowed by the ETSI to be used without permission. The different frequencies lead to various coupling mechanisms at distances of several meters. At the frequencies of 125 kHz and 13.56 MHz, mostly inductive coupling is used for power transmission. The frequencies of 868 MHz and 2.4 GHz typically are coupled electromagnetically. These coupling mechanisms depend on the field region at which the power transfer occurs. The two field regions are called near-field and far-field. The inductive coupling only occurs at the near-field region and the electromagnetic coupling only takes place at the far-field region. If the distance d of the sender and the receiver of the transmission is below λ/(2π), the near-field is present. Above this distance, the region is considered as the far-field. Within the near-field region, the magnetic field strength is dominant and decreases according to 1/d3. At the far-field, the magnetic and electric field are in phase and create an electromagnetic wave. The field strengths are decreasing within this region according to 1/d. Because of this, the use of far-field propagation is preferred to near-field propagation for long range applications. The frequency bands are divided into subbands, where different maximal field strengths or transmission powers are allowed. The 868 MHz band has for example the subband of 865.6 MHz – 867.6 MHz, where a transmission power of 2 Watt (ERP) is allowed without restrictions. Because of this, we use the frequency of 866.6 MHz for the power transfer, which is the middle of the subband. At the different frequencies, different antenna types are typically used to capture the energy. At 125 kHz and 13.56 MHz mostly antenna coils are used. At 868 MHz and 2.4 GHz mainly PCB-, chip-, patch- or monopole antennas are utilized depending on the application.

To calculate the incident power at the antenna at a certain distance R to the sender, the Friis transmission equation has to be used. It relates the received signal power (Pr) and the transmitted signal power (Pt) as

(1)

Gt and Gr are the antenna gains of the transmitting and the receiving antenna and λ is the wavelength of the transmitted signal. The Friis formula is only valid for the following four conditions.

First, the transmission has to take place in the far-field region at free space conditions. Second, the transmitting and receiving antenna must be correctly aligned and polarized. Third, the bandwidth of the transmission has to be so narrow that one value for the wavelength can be assumed. Four, the two antennas and their transmission lines are conjugate matched, so that no losses occur due to mismatching.

Antenna

The antenna has the task to harvest the incident electromagnetic waves that are propagated by a RF transmitter. On the one hand, the gain of the antenna should be as high as possible to increase the received power.

On the other hand, the antenna should be as isotropical as possible, so that the direction at which the electromagnetic waves are captured does not influence the harvesting very much. Because the two features cannot be achieved at the same time, a compromise has to be found. A quarter-wave monopole antenna is the best compromise, because it has a high gain of 2.15 dBi and an approximately isotropic antenna diagram, except at the antenna axis. The length of the quarter wave monopole at 866.6 MHz is 8.655 cm. The impedance of the antenna is 50 Ω, which is the same value typical RF measurement devices have.

Matching Circuit

The matching circuit is needed to ensure the maximum power delivery from the antenna to the remaining circuit and to minimize signal reflections. A T-match circuit is used to accomplish this task. It consists of two series inductors and one parallel variable capacitor.

The first step of the matching procedure is to determine the impedance of the harvesting circuit without the antenna and matching circuit. This can be performed by simulation or experimentally by using a network analyzer. In this work, the impedance has been determined experimentally. The impedance of the circuit does not only depend on the frequency, but also on the input power because of the diodes, which are nonlinear devices. The matching can be performed at one particular frequency and input power. The impedance of the circuit has been measured at a frequency at 866.6 MHz and an input power of -6 dBm, which is the lowest power at which the harvester begins to work. The measured impedance has the value of 97 Ω + j 96 Ω. This impedance has to be matched to the 50 Ω of the antenna.

Fig. 2. T-match circuit shown as two back-to-back L-networks with common virtual resistor R. [2]

(2)

The first serial reactance Xs1 can be computed with the following formula.

(3)

The first parallel reactance Xp1 calculated as follows.

(4)

For the L-network at the load end, the quality factor Q2 is defined by the virtual resistor R and the load resistor RL

(5)

With this value, the second parallel reactance Xp2 can be determined as follows.

(6)

The combined equivalent parallel reactance Xp can be calculated with eq. (7).

(7)

The second serial reactance Xs2 can be calculated using the following equation.

(8)

Finally, the values of the reactive elements L1L2 and Cvar can be calculated with the following three formulas.

(9)

(10)

(11)

For L1 and L2 the commercial available values 27 nH and 18 nH have been used.

C is a variable capacitor with the range of 1.4 pF to 3 pF so that device tolerances, measurement uncertainties and inductive and capacitive influences caused by the microstrip lines can be compensated. The matching with these components lead to a good match at -6 dBm. Fig. 3 depicts a smith chart that shows the measured impedance of the matched harvester circuit at the antenna input port from -8 dBm to 8 dBm.

Fig. 3. Impedance of the matched harvester in dependence on the input power.

Due to the matching, the voltage reflection coefficient decreases to approximately 2 % at an input power of -6 dBm. This means, that 98 % of the power which is captured by the antenna gets delivered to the rest of the harvester circuit. Fig. 4 shows the voltage coefficient in dependence to the input power from -8 dBm to 8 dBm.

Fig. 4. Voltage reflection coefficient over input power.

Rectifier Circuit

To convert the electromagnetic waves into DC voltage, a rectifier circuit is needed. Since the level of the collected power is very low, the rectifier circuit is based on a cascaded voltage multiplier circuit. To accomplish an effective rectification with an acceptable output DC voltage, a 7-stage cascaded Greinacher circuit is used. The circuit not only rectifies the incoming signal but also multiplies the peak amplitude. With increasing stages, the output DC voltage gets higher, but the losses also increase with each stage. Fig. 5 shows a single stage Greinacher circuit.

Fig. 5. Single stage Greinacher circuit.

Fig. 5 composes the elementary stage of the rectifier circuit where C1 (2.2 nF) and D1 form a negative clamp and C2 (2.2 nF) and D2 achieve peak rectification. C2 smoothes the output voltage and acts as a stage storage capacitor. The choice of the diodes is a very important aspect of the rectifier design and is critical for the overall performance of the harvester circuit. Because the harvester circuit operates at a frequency of 866.6 MHz and an input power of -6 dBm, the diodes should have a very fast switching time and a very low turn on voltage. These requirements can be achieved by using Schottky diodes, which use a metal-semiconductor junction instead of a semiconductor-semiconductor junction. This allows the junction to operate much faster and performs a very low forward voltage drop. The Schottky diodes HSMS-285P from Avago Technologies have been selected. They have a maximum forward voltage of 150 mV.

Energy Storage Capacitor

To cumulate the DC voltage, which is delivered by the rectifier, a storage capacitor is used. The value of the capacitor determines the amount of energy which can be stored. The leakage current of the capacitor should be as small as possible. Smaller capacitors charge more quickly, but lead to shorter operation cycles. Larger capacitors charge more slowly, but provide higher operation cycles. Because of this, the value of the storage capacitor depends on the application. The following equation can be utilized to estimate the necessary capacitor value.

(12)

Vout and Iout are the voltage and average current at the output of the DC-to-DC converter and ton is the on-time of Vout. For the proposed harvester, C has the value of 400 µF, which leads to an on-time of approximately 4 ms at an output voltage of 1.8 V and an average output current of 3.7 mA. These parameters are suitable to power a wireless low power sensor system consisting of a MCU and a sensor.

Comparator

A comparator is an electrical circuit that compares two different analog voltages and outputs a digital voltage that indicates which one of the compared voltages has the larger value. The comparator is needed to make sure that the energy which is stored at the storage capacitor cumulates until a certain voltage (Vcap, max) is reached. After exceeding this voltage, the comparator output switches to high which results in discharging the storage capacitor until a defined voltage (Vcap, min) is reached. This behavior is visualized by fig. 6.

Fig. 6. Output voltage of the comparator depending on the storage capacitor voltage.

DC-to-DC Converter

A DC-to-DC converter is an electronic circuit that is able to convert DC voltage from one level to another. For our harvester, we use the LTC3526L DC-to-DC converter from Linear Technology. He has the task to increase the voltage which is applied at the storage capacitor (940 mV – 1.27 V) to a DC voltage of 1.8 V during one operation cycle. The output voltage can be adjusted between 1.5 V and 5.25 V by an external resistor divider tap. The device has an input voltage range between 0.5 V to 5 V and is supplied by the storage capacitor. [5]

Complete RF Energy Harvesting System

The RF energy harvesting circuit proposed in this work has been designed with CadSoft EAGLE and fabricated using PCB technology. The maximum harvesting range of the system is approximately 2 m and the minimum necessary input power is -6 dBm. Fig. 7 shows the voltage at the output of the harvester (lower graph) and the voltage at the storage capacitor (upper graph) during one operation cycle. These voltages have been measured with an oscilloscope. It can be seen at the figure that the voltage at the storage capacitor decreases from 1.27 V to 940 mV which are the two threshold voltages determined by the comparator resistor dimensioning. During the discharge of the storage capacitor the DC-to-DC converter outputs a DC voltage of 1.8 V for a time of 4 ms. This is indicated by the two vertical lines at fig. 7. Within the on-time of the DC-to-DC output voltage, the load, which is typically a wireless sensor system, is powered and able to execute one operation cycle. Such cycle consists for example of the determination and transmission of temperature and humidity values. After operation, the sensor system waits on standby until the next operation cycle begins.

Fig. 7. Vcap and Vout over time during one cyle

Conclusion and Future Work

In this paper, a RF energy harvesting system for the 868 MHz band is presented. It can be used to energize low power devices, e.g. wireless sensor systems. The complete RF energy harvesting system can operate at input powers of at least -6 dBm and is optimized for a frequency of 866.6 MHz and has a maximum harvesting range of 2 m. It outputs an energy of up to 60 μJ during one operation cycle.

One future task of this work is the investigation of the behavior of the presented RF harvester circuit if it is integrated into several building and insulation materials, e.g. reinforced concrete or steel wool. Integrated into these materials, the RF energy harvesting circuit should be able to power a wireless sensor system, which measures and transmits the temperature and humidity values of these materials.

References

[1]K. Dembowski, Energy Harvesting fuer die Mikroelektronik, pp. 24 ff, 1st edition, VDE Verlag, Berlin, 2011.

[2]C. Bowick, J. Blyler, C. Ajluni, RF Circuit Design, page 71, Newnes, 2nd edition, 2007

[3]Maxim Integrated. (2005, Sep.) Application Note 3616: Adding Extra Hysteresis to Comparators. [Online]. Available: http://www.maximintegrated.com/appnotes/index.mvp/id/3616

[4]Maxim Integrated. (2014, Mar.) Ultra-Small, Low-Power Single Comparators in 4-Bump UCSP and 5-SOT23. [Online]. Available: www.maximintegrated.com/datasheet/index.mvp/id/5823

[5]Linear Technology Corporation. (2014, Mar.) LTC3526L/LTC3526LB. [Online]. Available: www.linear.com/product/LTC3526L

An Introduction to achieving Industrial Applications of Wireless Passive SAW Sensors for Advanced Monitoring

G. Heider1

1 SENSeOR SAS, Navigator B, 505 route des Lucioles, 06560 Valbonne, France contact [@] senseor.com

Abstract:

Surface Acoustic Waves (SAW) is a powerful technology enabling the design of innovative wireless passive sensors for temperature, strain or pressure measurements for instance. SAW technology exploits the piezoelectric properties of the sensors’ quartz substrate. Wireless SAW sensors are powered by the energy of radio waves emitted by the associated transceiver unit when remotely interrogating the sensors in real-time. Advanced interrogation methods implemented in the embedded firmware of the transceiver compute the frequency changes in the sensor response into measurements. SAW technology has been used since more than 30 years for frequency filters, like in mobile phones with high-volume production, but its use for measurement is a breakthrough and the development from “proof of concept” to industry-standard-compliant systems was a challenge. This article describes key developments to overcome these challenges, highlights SAW sensors’ features for industrial monitoring and provides examples of value-added applications.

Key words: Surface Acoustic Waves (SAW), sensor, wireless, passive, monitoring

Introduction

The need of additional remote monitoring solutions increases as industrial equipment and processes need to become more and more efficient and secure. For controlling critical parameters like temperature, on a real-time basis, even in the most remote locations or at the heart of the machinery, advanced innovative sensors like SAW sensors are essential. As their features become more widely known, the industrial applications expand. Being wireless, these sensors avoid the costs of cables and their installation. Most important, SAW sensors can often be installed right on the most critical parts of the equipment, even on rotating elements. The installation is also possible on existing equipment. Being totally passive, the sensors don’t require maintenance and operate in harsh environments - where active electronics or batteries, for example, could not survive. Once installed and commissioned, the sensors operate without maintenance, featuring infinite autonomy. Industrial usage of SAW technology though requires high robustness of the system, at each level of the measurement chain: sensitive element, packaging, antenna, electronic hardware and firmware, interrogation methods, Radio-Frequency link, among other criteria.

SAW Technology for Sensing

Besides the use of Surface Acoustic Waves for the widely known and used frequency filters, the same technology can be used for sensing any physical quantity.

Fig. 1. Operating principle

One way to use Surface Acoustic Waves for sensing is based on the interrogation of resonators, by a transceiver through a radio-frequency link (RADAR-like interrogation). The interrogation unit sends an un-modulated RF signal in order to load the SAW sensor resonator. The incoming RF wave is converted into a surface acoustic wave (SAW) on the sensor quartz substrate due to the piezoelectricity effect.

The velocity of a surface acoustic wave is very sensitive to the surface state. Under the effect of the physical parameter which is sensed, the velocity is modified and can be measured in the response transmitted back to the transceiver.

As the operation is based on the measurement of a frequency change on the interrogated substrate, this technology offers a wide array of possible applications: measurement of surface impact due to compression or expansion as is caused by temperature changes or physical impact - or measurement of frequency changes due to mass loading as used for chemical and biological sensing.

This technology brings major easily identified advantages like the absence of cable and the related cost reductions and easiness in commissioning, the absence of battery, avoiding maintenance visits and disposal of batteries, and the possibility to embed the sensors into material like concrete or rubber and interrogate them remotely, even in the most inaccessible places.

The wide spread availability of high volume production capacity for the SAW substrate (using the same processes as the production of SAW filters) offers high quality and maturity and allows to target low costs.

SAW sensors indicate the measurement value via frequency (in contrast to resistive or capacitive changes). Knowing that we can measure frequency changes with unparalleled high precision allows forecasting use of this technology for high precision applications. This is further supported by the characteristics of the base material - quartz - which is very stable over time.

Please Note that a SAW sensor can also be used in a wired configuration.

Wired Interrogation of SAW Sensors

The relative frequency stability S of a SAW-based oscillator is typically in the 10^{-9} range in a 1-10 s window, rising at longer integration times due to the temperature fluctuations of the resonator (see Fig. 2).

Assuming a temperature sensitivity T of the transducer in the tens of ppm/K, the temperature resolution based on such a short term stability is in the S/T=100 µK range. This performance opens important perspectives towards achieving resolutions beyond those achievable with today’s resistive sensor technologies.

Today’s accuracy is in the tens of mK range (simple demonstrator). AQP packaging and use of a stable reference clock is seen as a promise to achieve new and long-term accuracy performance limits. Ref [1]

Fig. 2. Allen Variance of a wired quartz resonator

Wireless Interrogation of SAW Sensors

Wireless temperature sensing through a 434 MHz SAW resonator using our “Fixed comb” interrogation strategy will typically achieve a 60Hz frequency identification resolution. Assuming a sensor design with a temperature sensitivity of 5 kHz/K, the resolution is in the 12 mK range.

The actual accuracy of the measurement is related to the calibration capability, long-term drift and the actual wireless communication channel (see also below). Assuming above sensor design we typically reach ± 1K accuracy at a temperature range of 180°C.

Different interrogation methods allow optimization of performances per application:

“Closed Loop“ approach combining higher refresh rate, improved accuracy with respect to the fixed comb approach, and improved interrogation range with respect to the 2-point (1-point) methods (350 Hz refresh rate @ 8 averages)

“FM 2 point” to achieve a 10-fold resolution improvement (down to 2 Hz demonstrated).

“1 point” – achieving very high refresh rate – 60 µs per resonance (17 kHz @ 1 average theoretical, 8 kHz @ 1 average practical)

“Radiomodem” – using high-volume off-the-shelf components to achieve very low power consumption, low prices and enable participation in wireless networks at the same time.

See also Ref [2]

Critical Success Factors for Wireless Interrogation of SAW Sensors

The big difference with ‘standard’ wireless communication is that here we have no ‘logic’ on the sensor – the communication is not encoded – we work directly with the ‘carrier’ (frequency, amplitude & phase)!

This is important to be understood. We had to develop a lot of very advanced capabilities in order to ensure dependable operation and quality of our systems in order to cover:

Frequency pulling – i.e. the signal is influenced by even minor changes in its environment.

Reflections – especially in metallic cavities.

RF Performance adaptation & tuning to different situations (distance, rotation, etc.).

Advanced filtering to allow operation in industrial environments and despite interferers.

Semi-automatic configuration and synchronization of multiple concurrent operations.

Calibration-free sensors for high volume applications.

RF Certification.

Use of differential sensors to achieve stable precision

If environmental conditions vary, antenna impedance will also vary and consequently resonant frequencies will also vary (this applies also to aging effects and other factors influencing calibration and performance).

Fig. 3. Differential measurement improvement

As you can see from the 3 illustrations above (Fig.3), comparing individual resonator stability in a simulated, realistic industrial environment, using a differential approach results in a 15-times reduction of the error influence.

Only differential sensors provide the basis to contain the frequency pulling effects.

Application of SAW Wireless Temperature Sensing on the crankshaft of naval Engines

The reference application for SAW sensing technology for almost a decade now is delivered by the Norwegian Ship Industry specialist Kongsberg Maritime. Over 4000 sensors per year are installed in the crankshaft bearings of the engines. Since installation they work failure-free – despite use in very harsh conditions.

These sensors provide predictive warning of crankshaft bearing problems – hence allow the engine to be stopped for maintenance before serious damage occurs. Comparative analysis show that this system is more effective than the legacy system based on oil-mist detection as it provides alarm indication well before the main bearing temperatures rises too much causing damages.

Fig. 4. Crank-shaft bearing temperature measurement

Application example of SAW Wireless Temperature Sensing in the Energy Sector

Another value-added application of temperature monitoring with SAW sensors gaining pace is electrical equipment surveillance. With increasing energy needs, systemic overload on the power grid due to the multiplying energy sources, the equipment is used to its limits, often in a run-to-fail approach. But in a smart grid, with energy efficiency improvements needed, remote continuous monitoring is a solution to enhanced performance reducing margins, while increasing safety. Temperature is a key parameter to monitor, as a temperature raise in electrical equipment is one of the key indicators of potential failure and abnormal operation. As SAW sensors are totally passive, and robust, they withstand high current and voltage, without any risk of arcing and without damage. For this, they need to be packaged in specifically designed housings, low-profile and RF-wise optimized. For instance, SENSeOR’s SAW sensors have been tested up to 545 kV and 4000 A. They thus enable to monitor the most critical hot points on transmission lines, in transformers, in AIS switchgears for instance (on circuit breaker, on busbars). The negative effect of metallic enclosure on RF link is overcome in these latest applications by the optimized design of antennas and robust, specific interrogation methods.

Like for diesel engines, SAW sensors can monitor inner temperature of generators and turbines for instance on bearings in cylinders, on piston head, on exhaust string. The benefits are clear in all these applications: stop the equipment proactively, only when necessary, but before it’s too late, enabling just-in-time preventive maintenance, enhanced performance and reduced life cycle-costs.

Application example of Wireless Temperature Sensing with SAW Sensors in Cookware

Interesting valued-added applications have also been identified in cookware and appliances. Indeed, the wireless and passive operation of the sensors enables to design wireless food probes for instance, both for application during cooking in high temperatures, and during freezing. Standard food probes are already used by professionals in ovens for instance, but the wire is always a limit for convenient use and cleaning. It often gets cut by the oven door for instance, leading to the replacement of the probe. Also, active wireless probes with battery overcome this limit, but are limited in operation to the temperatures withstood by the battery, restricted both in high and low temperature. SAW sensors ranging from -40°C (or even lower down to cryogenic applications) to 165°C cover the needed range for freezing to cooking, while getting rid of wires and batteries. This guarantees to monitor the goods temperature all over the cooking process, eliminating possible cold chain rupture and health risks due to under-cooking or over-frying for instance. Here again, the effects of metallic cavities like ovens or fridges on the radio-frequency link need to be compensated by optimized interrogation methods in transceiver firmware.

Conclusion

We have listed some of the many possible monitoring applications enabled by SAW sensors, thanks to their unique properties, and the challenges raised by their industrial use. The wireless interrogation for instance, is one of the key advantages, but requires optimized, robust interrogation methods and antennas to achieve the required fault-free operation in harsh industrial environments.

References

Ref[1]: B. Francois, G. Martin, P. Grosclaude, M. Lamothe, G. Goavec-Merou, S. Ballandras, J.-M Friedt, Fabrication and characterization of a SAW-oscillator-based sensing system including an integrated reciprocal counter and a wireless ZigBee transmission system Proc. Ultrasonics Symposium (IUS), 2010 IEEE (1290--1293)

Ref[2]: C. Droit, G. Martin, S. Ballandras, J.-M Friedt A frequency modulated wireless interrogation system exploiting narrowband acoustic resonator for remote physical quantity measurement Rev. Sci Instrum. Vol 81, Issue 5, 056103 (2010)

1.3

Photovoltaic Cells for Optical Power and Data Transmission

Henning Helmers, Fraunhofer ISE, Freiburg (Germany)

Abstract

The conventional setup of a data acquisition system consists of a sensor and a central unit. Data transmission is typically realized via optical fibers, whereas the power supply of the sensor is conducted via power transmission line. Conventional power transmission lines, however, can feature several application dependent challenges, such as electromagnetic interference, the risk of short circuits and sparks, the need for lighting protection, heavy weight for long distance cabling, or its susceptibility to corrosion and moisture.

By application of optical power transmission these challenges become obsolete. In addition, the power supply can be integrated into the same optical fiber that is used for data transmission. An optical power transmission system consists of a (monochromatic) light source at the central unit, typically a laser or a LED, the optical fiber, and a photovoltaic (PV) converter at the sensor that converts the light back into electricity. By modulation of the light, combined power and data transmission at the PV cell is feasible.

Manuscript was not available for printing.

ELF Extended Low Frequency Sensor Designs

Kevin Westhora

1 Dytran Instruments Inc., Chatsworth, CA, U.S.A

[email protected]

Abstract ELF Extended Low Frequency Sensor Designs:

Piezoelectric accelerometers are dynamic sensors with a usable frequency response that goes from fractions of one Hertz over 10 kHz. A piezoelectric sensor can de designed with a very low frequency response, called quasi-static, but it won't be a true static [DC] response.

DC type Accelerometers that can measure from static, zero Hertz; up to a few thousands Hertz, but not more.

The need for a single sensor package that can cover the complete frequency spectrum response from zero Hertz to more than 10 kHz convinced Dytran Instruments to develop the ELF which merges two sense elements combined into one output..

Key words: piezoelectric, vibration, accelerometers, MEMS, variable capacitance, Extended Low Frequency, DC, 10kHz, 15kHz.

Piezoelectric Accelerometers

Piezoelectric accelerometers are dynamic sensors. Their frequency response goes from fractions of one Hertz, up to the natural resonance frequency of the sensor element. Accelerometer users will utilize only the portion for the frequency response (in which the signal!) that it is proportional to the acceleration to be measured. Therefore, the usable frequency response, typically, will go from a few Hertz to about 1/3 of the natural frequency of the element, that usually goes to higher than 10 kHz. A piezoelectric sensor can de designed with a very low frequency response, called quasi-static, but it won't be a true static [DC] response. This fact of the dynamic behavior of all piezoelectric sensors is well known, and an accepted limitation by the users of this type of sensors..

DC-Type Accelerometers

Accelerometers that can measure static signals are called DC types. They can measure from static, zero Hertz; up to a few thousands Hertz. DC types sensors are using different technologies on the sensing element, some are MEMS, with a Silicon element in cantilever with a seismic mass of the same material, with variable capacitance sensing, servo [force balance], or strain gauges, also implemented in MEMS devices.

Using both types instead of choosing

Dytran instruments offers both types of sensors, piezoelectric accelerometers and DC MEMS accelerometers. In typical applications, a customer is only interested in a portion for the frequency response of the sensor, and more specifically only certain frequencies of interest. However, in occasions where a customer requires both types of signals, or a full frequency spectrum of the signals, they must use two different sensors, one DC MEMS type, with low frequency response, and a second one, piezoelectric type with high frequency response, then apply a low pass filter on the DC accelerometer with operating bandwidth from zero to a few hundred Hertz, and a high pass filter to the piezoelectric sensor that operates from just below 100 Hz up to its maximum operational bandwidth, usually 10 kHz. The data collected will be processed to obtain the full frequency spectrum of the vibration on the application.

Accelerometer Testing Challenges

There is a need for a single sensor package that can cover the complete frequency spectrum response from zero Hertz up to 10 kHz. In the past, users of the low frequency response, and other inertial devices, DC to 100 Hz, found that high frequency vibration signals in other orthogonal axes, than the axis of interest, result in a non vibrational displacement [sculling motion] within the operational bandwidth of the DC low frequency accelerometer. There are several well known algorithms used to compensate for sculling and pseudo sculling motions, but these add to the complexity of the data acquisition and analysis. Furthermore, they need the input of the secondary sensor measuring the magnitude of these high frequency vibrational signals to apply the proper compensation or correction values.

Dytran meets the Challenge

The need for such single sensor that can cover the full frequency response spectrum convinced Dytran Instruments of pursuing such endeavor. These are the characteristics and operational principles of the ELF accelerometer Dytran model 7705A [Extended Low Frequency accelerometer].

The main principle of operation of Dytran model 7705A is the instrumentation amplifier at the output buffer. The positive input is provided by the variable capacitance element and the negative input is provided by the piezoelectric element. Both variable capacitance element and piezoelectric element are filtered appropriately (low pass single pole and high pass single pole respectively) to provide the corner frequency of both filters precisely matched at approximately 30Hz. Both signals are also out of phase as they enter the instrumentation buffer

7705 Sensor options

Dytran model 7705A will be offered in sensitivities from 10, 50, and 100 mV/g, in one size, hermetically sealed, with dimensions as indicated on Figure 6.

Fig. 4. Model of sensor 7705A.

Fig. 1. Typical low frequency response of a piezoelectric accelerometer.

Fig. 2. Typical frequency response of a DC variable capacitance accelerometer.

The instrumentation amplifier performs a mathematical operation of subtraction on two input signals that are out of phase, and produces the continuous spectrum on the output:

Fig. 2. Typical frequency responses of the instrumentation buffer output.

Due to slight imperfections of the filter geometries and a minor mismatch in sensitivities from variable capacitance to piezoelectric element the overlap point between two elements is designated by the visible ripple in the signal spectrum

Frequency Response of Sensor

Fig. 5. Frequency response of the sensor 7705A..

Dimensions of Sensor

Fig. 5. Housing dimensions of model 7705A.

Conclusion

Requests from our customers have motivated Dytran to make sensors for measurement and monitoring for 34 years!

Dytran new series of accelerometers 7705A a.k.a ELF is a new generation of acceleration measurement instruments that combine two technologies which were used separately up to this moment. The accelerometer contains a piezoelectric and variable capacitance elements with respective filtering whose outputs are electrically superimposed over one another.

The result is an output from a single pin that provides one of the widest bandwidths from 0 Hz to 20 kHz with great resolution of 0.0008 gRMS.

This is one of the innovations which have led to creating the smallest, lightest and hottest and coolest sensors in the world!

The best innovations are yet to come!

HAZARD2 project : airspeed and temperature measurements in jet engine blast

[email protected]

Abstract : For ground airport operations, a dangerous area is defined behind the aircraft when engines are running. Measuring the temperature and airspeed in this area is needed to calibrate simulation models and adjust the danger area size to the real conditions. A heavy fixed on ground instrumentation was possible but an innovative solution has been chosen, based on Lidar technology for airspeed measurements and Bragg sensors on optical fibers for temperature measurements.

Key words: Jet engine blast, temperature, bragg sensors, optical fiber, Lidar

Airspeed and temperature measurements in jet engine blast :

A classical instrumentation is to fix in the ground an heavy metal structure to attach the sensors. This solution has many inconveniences including the need to build concrete foundations to attach the structure, which is difficult task in an airport area. This metal structure (3m height, 35m long) would have to sustain airspeed up to 150m/s. A huge number of sensor would be required with many wirings and acquisitions concerns. To obtain measurements in various distances from the aircraft, this one needs to be moved relatively to the sensor ramp :

To avoid this kind of instrumentation, a better solution has been put in place : an adapted Lidar was used to measure airspeed and an instrumented cable (140m long) was moved around the aircraft in the jet blast zone to perform a kind of temperature scanning.

Lidar solution for airspeed