Implementation of On-Off Passive Wireless Surface Acoustic Wave Sensor Using Coding and Switching Techniques DIV

Methods and systems for passive wireless surface acoustic wave devices for orthgonal frequency coded devices to implement ON-OFF sensors reusing orthogonal frequency code and distinguishing between ON and OFF states using additional PN sequence and on/off switches producing multi-level coding as well as external stimuli for switching and identification of a closure system. An embodiment adds a level of diversity by adding a dibit to each surface acoustic wave devices, thus providing four different possible coding states. The PN on-off coding can be with the dibit for coding in a multi-tag system

Implementation of On-Off Passive Wireless Surface Acoustic Wave Sensor Using Coding and Switching Techniques

Methods and systems for passive wireless surface acoustic wave devices for orthgonal frequency coded devices to implement ON-OFF sensors reusing orthogonal frequency code and distinguishing between ON and OFF states using additional PN sequence and on/off switches producing multi-level coding as well as external stimuli for switching and identification of a closure system. An embodiment adds a level of diversity by adding a dibit to each surface acoustic wave devices, thus providing four different possible coding states. The PN on-off coding can be with the dibit for coding in a multi-tag system

Passive Wireless Saw Sensors With New And Novel Reflector Structures Design And Applications

Surface acoustic wave (SAW) devices are a solution for today’s ever growing need for passive wireless sensors. Orthogonal frequency coding (OFC) together with time division multiplexing (TDM) provides a large number of codes and coding algorithms producing devices that have excellent collision properties. Novel SAW noise-like re- flector (NLR) structures with pulse position modulation (PPM) are shown to exhibit good auto- and cross-correlation, and anti-collision properties. Multi-track, multi-transducer approaches yield devices with adjustable input impedances and enhanced collision properties for OFC TDM SAW sensor devices. Each track-transducer is designed for optimum performance for loss, coding, and chip reflectivity. Experimental results and theoretical predictions confirm a constant Q for SAW transducers for a given operational bandwidth, independent of device and transducer embodiment. Results on these new NLR SAW structures and devices along with a new novel 915 MHz transceiver based on a software radio approach was designed, built, and analyzed. Passive wireless SAW temperature sensors were interrogated and demodulated in a spread spectrum correlator system using a new adaptive filter. The first-ever SAW OFC four-sensor operation was demonstrated at a distance of 1 meter and a single sensor was shown to operate up to 3 meters. Comments on future work and directions are also presente

Surface Acoustic Wave (Saw) Delay Lines & Rfid on Silicon/ Aluminium Nitride

Surface Acoustic Wave (SAW) devices exploit the principle of transducing radio frequency waves into mechanical sound waves propagating across surface of piezoelectric material. These mechanical waves are generated, detected, or reflected by set of metal electrodes. Physical phenomena or unique identification code information can be extracted from the measured /reflected waves based on its different properties such as time delay, phase change or frequency change. Radio identification code implementation methods as well as simulation of SAW device are reviewed in this report. Time pulse position coding is chosen because it provides less sensitivity to variations in temperature and SAW wave velocity. In addition, it is straightforward to implement and simplifies the reader design. To successfully implement the device, proper modeling and simulation is carried out to extract device physical and response parameters such as centre frequency, finger pairs’ number, spacing, scattering parameters and frequency response of the system. The equivalent circuit model is used in this study due to faster simulation speed and efficiency. Aluminum nitride (AlN) is chosen as piezoelectric material due to its high SAW velocity speed, higher coupling factor, cheaper fabrication cost and its chemical characteristics close to that of Silicon Non-reactive with normal semiconductor process chemicals and gases. Data processing and analysis is performed on SAW delay lines implemented on Aluminum nitride to extract device characteristics such as surface acoustic wave velocity, coupling coefficient and center resonance frequency

Design, Analysis And Implementation Of Orthogonal Frequency Coding In Saw Devices Used For Spread Spectrum Tags And Sensors

SAW based sensors can offer wireless, passive operation in numerous environments and various device embodiments are employed for retrieval of the sensed data information. Single sensor systems can typically use a single carrier frequency and a simple device embodiment, since tagging is not required. In a multi-sensor environment, it is necessary to both identify the sensor and retrieve the sensed information. This dissertation presents the concept of orthogonal frequency coding (OFC) for applications to SAW sensor technology. OFC offers all advantages inherent to spread spectrum communications including enhanced processing gain and lower interrogation power spectral density (PSD). It is shown that the time ambiguity in the OFC compressed pulse is significantly reduced as compared with a single frequency tag having the same code length and additional coding can be added using a pseudo-noise (PN) sequence. The OFC approach is general and should be applicable to many differing SAW sensors for temperature, pressure, liquid, gases, etc. Device embodiments are shown and a potential transceiver is described. Measured device results are presented and compared with COM model predictions to demonstrate performance. Devices are then used in computer simulations of the proposed transceiver design and the results of an OFC sensor system are discussed

Design And Simulation For Encoded Pn-ofc Saw Sensor Systems

Surface acoustic wave (SAW) sensors provide versatility in that they can offer wireless, passive operation in numerous environments. Various SAW device embodiments may also be employed for retrieval of the sensed data. Single sensor systems typically use a single carrier frequency and a simple device embodiment since tagging is not required. However, it is necessary in a multi-sensor environment to both identify the sensor and retrieve the information. Overlapping sensor data signals in time and frequency present problems when attempting to collect the sensed data at the receiver. This dissertation defines a system simulation environment exclusive to SAW sensors. The major parameters associated with a multi-device system include the transmitter, the channel, and the receiver characteristics. These characteristics are studied for implementation into the simulation environment. A coupling of modes (COM) model for SAW devices is utilized as an accurate software representation of the various SAW devices. Measured device results are presented and compared with COM model predictions to verify performance of devices and system. Several coding techniques to alleviate code collisions and detection errors were investigated and evaluated. These specialized techniques apply the use of time, frequency, and spatial diversity to the devices. Utilizing these multiple-access techniques a multi-device system is realized. An optimal system based on coding technique, frequency of operation, range, and related parameters is presented. Funding for much of this work was provided through STTR contracts from NASA Kennedy Space Center

Surface Acoustic Wave (saw) Cryogenic Liquid And Hydrogen Gas Sensors

This research was born from NASA Kennedy Space Center’s (KSC) need for passive, wireless and individually distinguishable cryogenic liquid and H2 gas sensors in various facilities. The risks of catastrophic accidents, associated with the storage and use of cryogenic fluids may be minimized by constant monitoring. Accidents involving the release of H2 gas or LH2 were responsible for 81% of total accidents in the aerospace industry. These problems may be mitigated by the implementation of a passive (or low-power), wireless, gas detection system, which continuously monitors multiple nodes and reports temperature and H2 gas presence. Passive, wireless, cryogenic liquid level and hydrogen (H2) gas sensors were developed on a platform technology called Orthogonal Frequency Coded (OFC) surface acoustic wave (SAW) radio frequency identification (RFID) tag sensors. The OFC-SAW was shown to be mechanically resistant to failure due to thermal shock from repeated cycles between room to liquid nitrogen temperature. This suggests that these tags are ideal for integration into cryogenic Dewar environments for the purposes of cryogenic liquid level detection. Three OFC-SAW H2 gas sensors were simultaneously wirelessly interrogated while being exposed to various flow rates of H2 gas. Rapid H2 detection was achieved for flow rates as low as 1ccm of a 2% H2, 98% N2 mixture. A novel method and theory to extract the electrical and mechanical properties of a semiconducting and high conductivity thin-film using SAW amplitude and velocity dispersion measurements were also developed. The SAW device was shown to be a useful tool in analysis and characterization of ultrathin and thin films and physical phenomena such as gas adsorption and desorption mechanisms

2012 PWST Workshop Summary

No abstract availabl

Coded acoustic wave sensors and system using time diversity

An apparatus and method for distinguishing between sensors that are to be wirelessly detected is provided. An interrogator device uses different, distinct time delays in the sensing signals when interrogating the sensors. The sensors are provided with different distinct pedestal delays. Sensors that have the same pedestal delay as the delay selected by the interrogator are detected by the interrogator whereas other sensors with different pedestal delays are not sensed. Multiple sensors with a given pedestal delay are provided with different codes so as to be distinguished from one another by the interrogator. The interrogator uses a signal that is transmitted to the sensor and returned by the sensor for combination and integration with the reference signal that has been processed by a function. The sensor may be a surface acoustic wave device having a differential impulse response with a power spectral density consisting of lobes. The power spectral density of the differential response is used to determine the value of the sensed parameter or parameters

Surface Acoustic Wave (Saw) Delay Lines & Rfid on Silicon/ Aluminium Nitride

Surface Acoustic Wave (SAW) devices exploit the principle of transducing radio frequency waves into mechanical sound waves propagating across surface of piezoelectric material. These mechanical waves are generated, detected, or reflected by set of metal electrodes. Physical phenomena or unique identification code information can be extracted from the measured /reflected waves based on its different properties such as time delay, phase change or frequency change. Radio identification code implementation methods as well as simulation of SAW device are reviewed in this report. Time pulse position coding is chosen because it provides less sensitivity to variations in temperature and SAW wave velocity. In addition, it is straightforward to implement and simplifies the reader design. To successfully implement the device, proper modeling and simulation is carried out to extract device physical and response parameters such as centre frequency, finger pairs’ number, spacing, scattering parameters and frequency response of the system. The equivalent circuit model is used in this study due to faster simulation speed and efficiency. Aluminum nitride (AlN) is chosen as piezoelectric material due to its high SAW velocity speed, higher coupling factor, cheaper fabrication cost and its chemical characteristics close to that of Silicon Non-reactive with normal semiconductor process chemicals and gases. Data processing and analysis is performed on SAW delay lines implemented on Aluminum nitride to extract device characteristics such as surface acoustic wave velocity, coupling coefficient and center resonance frequency