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Transense Technologies has developed two distinct sensors, one measures torque and temperature the other pressure and temperature, and the requisite electronics to interrogate and read them.  These sensors utilise Surface Acoustic Wave (SAW) technology.

A SAW is an acoustic wave that travels along the surface of an elastic material. This kind of wave is commonly used in piezoelectric devices in electronic circuits. These piezoelectric devices will convert electrical pulses into mechanical vibrations and, conversely, mechanical vibrations into electrical pulses. A SAW resonant sensor is designed to resonate at a certain frequency, but if its piezoelectric substrate distorts through heat, mechanical stress or pressure, it will resonate at a different frequency. When a radio wave is directed at this device to interrogate its properties, it will, in the absence of any external forces, reflect (back scatter) a wave of the same frequency to the source. If, however, the device is subject to external force, e.g. heat or stress, the reflected wave will be of a different frequency and that change in frequency can be measured. The Company has developed a way of measuring the difference in frequency between these waves in a range of sensors, which can be used to accurately calculate torque, temperature and pressure. In order to read this change in frequency, the Company has developed associated interrogation electronics and software. These SAW devices are fabricated utilising common processes employed in the manufacture of silicon integrated circuits.



The Triple SAW Torque Device represents a breakthrough in quartz die technology, permitting temperature compensated strain measurement in 2 orthogonal directions for torque measurement in power steering and driveline applications





The Triple SAW Pressure Device is at the heart of Transense's TPMS technology, providing temperature compensated pressure measurement from a single quartz die operating in a simple bending mode




There are numerous automotive applications for our patented technology. Applications such as Tyre Pressure Monitoring Systems (TPMS), Electrical Power Assisted Steering (EPAS) and driveline management, we are now expanding into industrial markets. The diagram below shows how multiple SAW sensors can be incorporated into a single vehicle




Transense and KERS Technology

A Kinetic Energy Recovery System (KERS) is not a new idea.  Indeed the principle, often referred to as “regenerative braking”, by which kinetic energy of motion, normally lost when the brakes are applied, can be partially recovered, has been understood for more than 100 years:

On reaching the top of a long steep hill, if we do not want to coast, we convert the motors into dynamos, while running at full speed, and so change the kinetic energy of the descent into potential in our batteries. This twentieth century stage-coaching is one of the delights to which we are heirs, though horses are still used by those that prefer them.         
From: A Journey in Other Worlds, by John Jacob Astor IV, published 1894

The Swiss Gyrobus, designed and manufactured by Oerlikon in the 1940s relied on stored flywheel energy to power the bus. Electrical regenerative braking was employed to add energy back to the flywheel thereby extending the vehicle range.

The braking torque created by allowing the normally driven wheels of the vehicle to back-drive the electric motor to add charge to the battery, or to spin up a flywheel, can also be sufficient for most car braking purposes except emergency braking or slowing the vehicle to a stop. So, while a standard braking system is still required, it can be lighter and the friction surfaces should last many tens of thousands of miles.

The idea of adding torque from a stored electrical energy reserve (a battery or ultra capacitor) in order to boost acceleration has been introduced with parallel hybrid systems, where either an internal combustion engine or an electric motor or a combination of both provides motive power, such as in the Toyota Prius.

In 2009, F1 motor racing entered the hybrid car world with an FIA inspired optional addition of KERS to provide a “push to pass” acceleration boost option which could be derived from either mechanical (flywheel) or battery plus electric motor sources.  The concept had dual motives: to increase the excitement of F1 by increasing overtaking opportunities and to promote the green potential of energy saving technology by using the highly tuned and timely engineering skills of F1 teams and their suppliers.

However the FIA did not want a “free for all” approach which might result in significantly different performance from different designs leading to a lack of competitiveness, so it introduced strict rules:

Racecars can employ KERS to store up to 400kJ of energy per lap, to be reused via a 'boost' button which allows drivers to add up to 60 kW of power to their ic engine.

In practice, KERS (2009) enabled around 10% more power for almost 7 seconds per lap.

The specification reads quite simply, but in engineering terms it set some real measurement challenges:

Power is the product of KERS motor torque and speed (rpm).  Both must be precisely known at every moment so that the FIA limit is not exceeded – not trivial when it is realised that engine speed in a low rotary inertia F1 engine varies with every degree of crankshaft rotation.

Energy is the product of power and time.  So, when harvesting kinetic energy, KERS torque multiplied by rpm needs to be integrated over each lap time and must never exceed the FIA limit.

Systems in preparation during 2007–8 included both electrical and mechanical energy storage (flywheel) approaches.  However in the event, although very promising in principle, neither of the two flywheel systems appeared on the track in 2009.

A typical electric KERS F1 configuration locates the electric motor in front of the ic engine, connected via a small shaft spur-geared to the front of the crankshaft.  The shaft, turning at crankshaft speed, must be instrumented to measure torque, which can be in either sense: driving (positive) when the electric motor adds torque to the engine, and generating (negative) when the road wheels back-drive through the powertrain and engine to the electric motor which in turn creates a substantial braking effect on the car.

It was at this point in early 2008 that Transense Technologies were invited to propose a KERS F1 torque sensing system comprising hardware, interrogation electronics and application software.

A 2009 spec F1 engine running at up to 18,000 rpm will generate very high centripetal accelerations, acting inwards, on a sensor mounted on the shaft surface – approaching 4000g for the shaft in question. This means that a force equal to 4000 times the weight of the sensor acts outwards trying to tear it away from the shaft.  In addition engine vibrations are intense, circa 100g, while operational temperatures range from 70 to 170°C.

Transense employed their surface acoustic wave (SAW), quartz substrate, dual and triple resonator sensors to opposing sides of the shaft within a hermetically sealed cavity.  A non-contacting radio frequency (RF) rotary coupler provided two way signal connection between sensors and miniaturised interrogation electronics located within the electric motor power electronics and control box.

Software, which analyses the RF signals using a Discrete Fourier Transform (DFT) algorithm to generate independent torque and temperature signals with 3 kHz update rate, together with further code enabling the FIA to check that performance of the KERS torque system stayed within their requirements, was also provided by Transense.

Static torque measuring performance (linearity, repeatability, hysteresis, creep and rotation) was established initially at Transense laboratories near Oxford.  Typically at 120°C, the combined errors were less than 1% of full scale.


A string of 3 F1 KERS shafts being calibrated within an environmental chamber over the full operational range of torque and temperature

Development proceeded in close co-operation with the electronics and engine suppliers to the F1 race team.  Visits from FIA technical representatives were made to understand SAW technology and to ensure that company systems were in place to provide software version control and retrospective traceability.

Dynamic testing, at the engine manufacturer’s facility, were carried out on both electric and engine dynamometers.  The acid test on the actual racecar followed.

Manufacturing and calibration of KERS shafts including bonding of quartz dies, gold wire interconnects, hermetic sealing and calibration to meet the 2009 season’s requirements were completed at Transense.


Clarence Pilgrim carries out gold wire bonding operations on an F1 KERS shaft in the Class 10,000 clean room

In a typical race weekend, F1 cars run 2 practice sessions, 1 – 3 qualifying sessions and the race itself, totalling up to 500 miles.  As the 2009 season closes, Transense have supplied one race team with torque sensing systems throughout, which have enabled it to demonstrate the benefits of kinetic energy recovery and to make some exceptional passing manoeuvres!

Article contributed by Dr. Ray Lohr, October 2009

Technical Publications

Modelling of a wireless SAW system for multiple parameter measurement V. Kalinin
2001 IEEE International Ultrasonics Symposium. Atlanta, October 8-10
Non-contact torque sensors based on SAW resonators J. Beckley, V. Kalinin, M. Lee, K. Volyansky
2002 IEEE International Frequency Control Symposium. New Orleans, May 29-31, pp. 202-213
Low cost thin film based surface acoustic wave vibration sensors for vibrational gyroscope M. D. J. Potter, P. B. Kirby, M.Y. Lim, V. A. Kalinin, A. Lonsdale
2002 IEEE International Frequency Control Symposium. New Orleans, May 29-31, pp. 220-224
Resonant SAW Sensors for Wireless Mechanical Strain and Temperature Measurements V. Kalinin, R. Lohr
2003 CTR Workshop - Piezoelectric Resonators for Sensor Applications, Villach, Austria, Sep 25-26, Session 7
Influence on Non-Uniform Strain on Characteristics of One-Port SAW resonators V. Kalinin, A. Leigh
2003 IEEE Ultrasonic Symposium, Honolulu, Oct 5-8, pp. 1412-1415


In a typical modern vehicle's Engine Control Unit ('ECU'), torque is inferred from in-vehicle sensors measuring air and fuel flow, temperature and ignition timing in conjunction with 'look-up tables' derived from dynamometer tests of sample engines by the vehicle manufacturer. The problems associated with this approach are that, due to manufacturing tolerances, engines are not identical and they change their characteristics over their service life. Accurate real-time torque measurement can improve engine control, resulting in better fuel efficiency and can also provide for smoother ratio changes within automatic transmissions improving NVH (noise, vibration and harshness) and perceived quality. Torque measurement in driveshafts and torque splitters enables better control of actual torque to the individual road wheels for stability and traction control in four wheel drive vehicles. Specific applications of Transense's SAW torque sensors include:

  • Electrical Power Assisted Steering
  • Flexplate: situated between the crankshaft and torque convertor, the flexplate sensor provides direct measurement of engine output torque for engine and transmission control
  • Transmission output shaft: provides real time torque information to optimise the control of automatic transmissions
  • Torque splitter: enables optimised torque distribution between axles in 4WD applications
  • Driveshaft: individual sensors enable torque vectoring for improved stability control during cornering

Contactless Torque Transducer


  • Two SAW resonators on a single quartz die
  • Hermetic package
  • A pair of RF couplers
  • An annular PCB carrying RF ASIC and DSP

Torque sensors - New Generation



  • Enhanced torque sensor die incorporating temperature resonator
  • Improved bonding: die to package; package to structural component

Granted Patents


Ref Title Country Patent/Grant No
T0008 Electrical Signal Coupling Device GB 2350487
US 6,478,584
T0010 Pressure Monitor System EP/GB 1198361
T0012 Remote interrogation of the frequency difference between two SAW devices used for pressure measurement GB 2355801
T0022 Package SAW Device Using Pressure Sensor EP/DE 60136943.2
US 6,865,950
GB 2372328
EP/FR 1325296
T0028 Contactless SAW Torque Sensor with Improved Temperature Stability EP/DE P60204161.9
EP/GB 1438555
CN ZL02820375.5
TW 1251077
US 7,202,589
EP/FR 1438555
T0031 Interrogation Method for Passive Tyre Pressure and Temperature Monitoring System EP/GB 1419476
TW I264384
CN ZL02816494.6
JP 4356089
EP/FR 1419476
US 7,065,459
EP/DE 60203805.7
T0036 Improved Method for Tracking a Resonant Frequency US 7,089,794
JP 4126434
GB 2387724
T0037 Pressure monitor incorporating SAW device EP/FR 1485692
US 7,151,337
TW 1266046
EP/GB 1485692
CN ZL03810957.3
JP 4320593
EP/DE 60312493.3
T0039 Modified Interrogation Method with RF Power Supply GB 2397379
T0040 Valve Antenna US 7,185,535
EP/DE 60330235.1
TW 1287512
EP/FR 1506100
EP/GB 1506100
JP 4721092
T0041 Clip on Torque Sensor GB 2393521
US 7,222,541
T0044 Improvements in the Construction of SAW Sensors GB 2413215
T0049 Interrogation Method for Passive Tyre Pressure and Temperature Monitoring System GB 2411239
T0051 Method and Apparatus for Electronic Storing of Calibration/Identification Data for a Wireless Linear Passive Sensor GB 2411960
T0052 Split-ring coupler incorporating dual resonant sensors US 7,515,021
JP 4366615
GB 2413710
T0053 SAW based tyre pressure sensor valve adaptor EP/GB 1765609
EP/DE P602005011805.5
EP/FR 1765609
US 7,779,681
T0058 Large Diameter RF Rotary Coupler EP/FR 1856761
CN ZL200680007447.5
EP/DE P602006001587.9
EP/GB 1856761
US 7,782,159
T0059 SAW pressure and temperature sensor using part of the substrate as a diaphragm US 7,841,241
CN ZL200680018091.5
TW I411771
GB 2426590
T0060 SAW Torque and Temperature Sensor EP/FR 1882169
EP/GB 1882169
JP 4904549
EP/DE 602006006564.7
CN ZL 200680017446.9
US 7,795,779
T0063 Method for in-system auto zeroing of a torque sensor in an automatic transmission drive train (AUTO ZEROING) US 7,212,935
T0065 Improved method and apparatus for measuring torque and or strain in a powertrain (FLEXPLATE SENSOR) EP/GB 1994386
EP/DE 1994386
US 7,770,471
EP/FR 1994386
JP 5190826
T0066 TPMS Safety Band Sensor Attachment Options (INTELLIBAND SENSOR) GB 2438182
T0068 Post Assembly  Automatic Adjustment of TPMS Sensor Preload (PRELOAD ADJUSTMENT) JP 5029851
EP/DE 2032960
EP/GB 2032960
EP/FR 2032960
CN ZL200780023344.2
US 7,798,006
TW I408062
T0070 Apparatus for and method of attaching a strain sensing element to a substrate (ANNULAR GROOVE) EP/GB 2076746
EP/DE 602007025161.3
US 8,127,629
T0072 SAW Torque & Temperature Sensor with Improved Sensitivity (OPTIMISED AL FILM) GB 2450168
EP/FR 2160580
EP/GB 2160580
EP/DE 6020080458539
JP 5387919
US 8082800
T0074 Transense/SCHOTT Package for a Strain Sensor US 7,886,607
EP/FR 2056085
EP/DE 602008005230.3
T0075 Runflat Band Link & TPMS Sensor (INTELLIBAND LINK SENSOR) GB 2451705
T0077 Stowable Antenna for TPMS  GB 2456387
T0078 Calibration Procedure for Flexplate Torque & Temperature Sensors (1 or 2 POINT CALIBRATION) US 7,844,414
EP/GB 2071291
EP/FR 2071291
EP/DE 2071291
GB 2455596
T0080 Combined High Pressure (300 bar) and Temperature Industrial SAW sensor US 8,141,428
GB 2549516
T0081 Pressure Sensor with Adjustable Preload EP/DE 602009001775.6
EP/GB 2148180
EP/FR 2148180
T0085 Improved Interrogation Method US 8,296,087
GB 2468899
T0088 Tyre Pressure and Tread Depth Probe (OTR) GB 2460115
T0089 Tyre Pressure and Tread Depth Probe (Truck) GB 2406647
T0092 Antenna for coupling ESD sensitive measurement devices located in High Voltage electric fields US 9,419,334
T0093 Quartz Substrate Orientations for Compact Monolithic Differential Temperature Sensor, and Sensors Using Same EP/DE 2781022
EP/FR 2781022
EP/GB 2781022