Gerald Ostermayer

Monitoring the tire pressure at cars using passive SAW sensors

In our paper we present the application of surface acoustic wave (SAW) sensors to the continuous monitoring of the tire pressure in road vehicles. With these, the tire pressure can be read out in every phase of driving. We show the implemented prototype setup for measurement of the tire pressure, the applied SAW sensors, improved versions and the interrogation setup. The problems in practical application are discussed. Experimental results measuring the tire pressure during test rides are presented.

Wireless sensing using oscillator circuits locked to remote high-Q SAW resonators

This paper introduces a method of wireless read out of high Q surface acoustic wave (SAW) resonator sensors. The resonator is excited by a short RF pulse and decays after switching off the interrogating signal. In the measurement system, a gated phase locked loop (GPLL) locks to the resonance frequency of the SAW resonator within a few bursts. Then the frequency of the GPLL oscillator is synchronized to the resonance of the sensor and can be measured easily. The concept is intended to yield an alternative to interrogators with expensive signal processing. Considering the inherent limitations, the proposed system presents a low cost solution for temperature, force, torque, etc. measurements. We describe the sensors, the signals, and the implemented system. Results of temperature measurements using quartz resonators are presented, and merits and disadvantages are discussed.

CDMA for wireless SAW sensor applications

A well known spread spectrum technique is used to get the sensor information from an individually addressed SAW sensor. Coded ID tag type and BPSK type SAW sensors are picked out of a number of sensors by correlating the received signal with the known code of a particular sensor. The ID-tag type and BPSK-coded SAW sensors function is observed as a scaling of time and shape respectively. The time scaling factor is equal to the mechanical extension of the substrate of a sensor due to temperature, etc. This scaling factor is evaluated by use of correlative signal processing techniques. The principal concept, mathematical simulations, numerical estimations and finally an overview of the implemented SAW sensor system are shown. Preliminary results for readout of OOK and BPSK coded passive remote SAW sensors using the wavelet transform processed within a SAW convolver are presented.

Spread spectrum techniques for wirelessly interrogable passive SAW sensors

Recently surface acoustic wave (SAW) sensors for temperature, pressure, strain, etc. were investigated and tested. They use the change in SAW time delay due to the quantity to be measured. Increasing interest was initiated by the possibility of wireless readout. It is shown here, that the well known spread spectrum techniques (chirp impulse compression, CDMA, etc.) allows an increase of both, sensitivity and accuracy of measurement and a discrimination of several sensors interrogated. Some applications (temperature measurement with mK resolution, coded sensors) are demonstrated. We show some mathematical simulations and preliminary experimental results.

Correlative signal processing in wireless SAW sensor applications to provide multiple-access capability

We present a new method of evaluating the information of interest in the output response of surface acoustic wave (SAW) sensors. A well-known spread-spectrum technique is used to get the sensor information from an individually addressed SAW sensor. On-off keying-coded SAW sensors are picked out of a number of sensors by correlating the sensor response signal with a replica of the known response signal of a particular sensor. The influence of a measurement quantity (e.g., temperature, pressure, current, voltage,...) on a SAW sensor can be observed as a scaling of time and shape of the sensor response signal. This scaling factor is evaluated by use of correlative signal processing techniques. A main advantage of this method is the capability of multiple access, i.e., to distinguish different sensors in the range of a single interrogation system. Since this technique makes it possible to deal with sensor response signals overlapping in the time domain, sensors can remain short and, therefore, cheap. The principle of operation, limits of the method, and experimental results for temperature measurements are also presented.

Wavelet transform with a SAW convolver for sensor application

To obtain the sensor information from an individually addressed SAW sensor, the use of coded ID-tag type SAW sensors is combined with the tool of wavelet transform, a type of correlative signal processing. The function of SAW sensors (ID-tag type) is observed as a scaling of time and shape respectively. The time scaling factor is equal to the mechanical extension of the substrate of a sensor for temperature, etc. This scaling factor is evaluated by calculating the wavelet transform. The fundamental concept, mathematical simulations, numerical estimations and finally, an overview of the implemented SAW sensor system using the wavelet transform processed within a SAW convolver are shown. Preliminary results are presented.

Multiple access to SAW sensors using matched filter properties

In this paper we present a method of solving the problem of access to more than one passive surface acoustic wave (SAW) sensor in the range of a single interrogation system. The sensor informations of the SAW sensors are evaluated almost simultaneously by use of the correlation property of BPSK-coded sensors. We show the principal concept, mathematical simulations, numerical estimations and finally an overview of the design of such a SAW sensor system.

SAW sensors and correlative signal processing-a method providing multiple access capability

We present a method of solving the problem of access to more than one passive surface acoustic wave (SAW) sensor in the range of a single interrogation system. The sensor information of the SAW sensors are evaluated almost simultaneously by use of the correlation property of binary phase shift keying (BPSK) coded sensors. In general a SAW sensor is affected by a measurement quantity in two ways: a change of the length of the substrate and a change of the propagation velocity of the SAW. Both influences yield a time scaling of the sensors impulse response. If the interrogation signal is exactly the time-inverse of the sensors impulse response the sensor will answer with its autocorrelation function (ACF). By changing the time scaling factor s/sub INT/ of the interrogation signal one gets different correlation functions with of course different peaks. The highest peak will appear if the scaling factors of the sensor impulse response and the interrogation signal are identically. This matching scaling factor s/sub M/ provides a means of evaluating the measurement quantity. All the used sensors have the same code but different time delays. So the received signal is a succession of correlation peaks due to the different sensors. By time windowing one is able to evaluate the information of each sensor almost simultaneously. We show the principal concept, mathematical simulations, numerical estimations and finally a method to improve the system performance.

Evaluation of handover algorithms for packet transmissions in WCDMA

The wideband CDMA (WCDMA) solution for UMTS/IMT-2000 is currently being globally standardized within the 3rd Generation Partnership Project (3GPP). In order to facilitate mobile multimedia communications, WCDMA is being highly optimized for efficient packet transmissions. This paper evaluates macro diversity gains for high bitrate packet transmissions in a WCDMA system. Comparisons are made with hard handover which does not provide macro diversity. Evaluations have been made for both uplink and downlink by means of detailed computer simulations including fast fading and fast power control. The results show that in the downlink, the gain of macro diversity depends on the characteristics of the radio channel. The largest gain is achieved for channels with limited multipath propagation. In the uplink, macro diversity is shown to be essential in order to provide good system capacity.

Comparison of one- and two-dimensional slow fading models in mobile radio system simulations

This paper investigates the behavior of two different slow fading models in cellular mobile radio systems. A one-dimensional and a two-dimensional model are compared with respect to their influence on the results of system level simulations for cellular systems. A disadvantage of most known slow fading models is that they cannot handle the correlation behavior of shadowing in two dimensions. Recently a new model, which provides a two-dimensional correlation property, was proposed by Cai and Giannakis (2003). We show that this model gives different results for system capacity and handover rates than the well known one-dimensional models