New Publications are available for Piezoelectric and ferroelectric devices
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New Publications are available now online for this publication.
Please follow the links to view the publication.An automated performance testing system for piezoelectric micromotors
http://dl-live.theiet.org/content/conferences/10.1049/ic_20060463
The performance of micro-scale piezoelectric motors is characterised primarily in terms of their torque, speed and efficiency. In order to be meaningful these parameters must be measured concurrently and an effective test system is therefore essential for design, development, device optimisation and assessment of reliability. At the micro-scale, conventional methods of testing rotary motors, such as pulley brakes, are not easy to implement due to size constraints and the difficulty in measuring small dynamic forces. An automated method of testing a 5 mm diameter flextensional ultrasonic motor has been created which derives performance measurements from the transient start up and stopping behaviour of the motor using a simple non-contact position encoder. The method gives full performance characteristics in less than a second and it is scaleable for use with other sizes and other types of motor. Furthermore, it provides a generic technique for non-contact measurements of position, angle or velocity that can be rapidly cycled as part of a development programme. The method has shown sufficient sensitivity, using basic components, to measure torque in the range 10-200 μNm and speed in the range from 0 to over 2000 rpm. The torque and speed ranges are only dependant on the sensitivity of encoder instrumentation, inertial load on the motor and data acquisition. This system is believed to be a significant improvement over previously-reported work and the test format has greater applicability for micro-motors that are used for their positioning capabilities.Robust control of microvibrations
http://dl-live.theiet.org/content/conferences/10.1049/ic_19971333
Equipment on-board satellites is often mounted on lightweight panels where microvibrations have to be suppressed to achieve the required level of stability. In the work reported here, attention is restricted to one such mass loaded panel which is an acceptable compromise between problem complexity and the need to gain useful insights as to the benefits (and limitations) of linear active control schemes. The sensors and actuators for the active control scheme to be designed (and eventually implemented) are twin patches of piezoelectric material bonded onto opposite faces of the panel. The use of linear optimal control laws augmented by loop transfer recovery is investigated. (5 pages)Applications of ferroelectrics in uncooled thermal imaging: Part 2
http://dl-live.theiet.org/content/conferences/10.1049/ic_19971052
Summary form only given. This paper will continue the description of the use of ferroelectric detectors in uncooled thermal imaging from Pt. I which concentrated on the present generic range of hybrid detector arrays. The new research centred around an integrated technology for the ferroelectric arrays will be described. In this technology, the ferroelectric detector material is directly deposited onto the silicon readout IC (ROIC) by either sol-gel processing or sputtering. To thermally isolate the elements from the ROIC, the ferroelectric is deposited onto a sacrificial layer and patterned so that, on etching, a thin microbridge of the ferroelectric and its electrodes is constructed standing on two narrow legs above the silicon surface. The technology should lead to full wafer scale production with no ceramic preparation, reticulation or bonding giving substantial cost reductions and improved performance in comparison with the hybrid arrays. Topics being addressed are the ferroelectric films, and the bridge micro-engineering and materials. The present hybrid array programme description will be concluded with a video tape of scenes from the application of the 100×100 array to fire-fighting in the helmet mounted CairnsIRIS system, and of the 256×128 array to night driving in simple trials. (1 page)A system that monitors whether or not tyres on wheeled vehicles are under or over inflated which may be further developed to measure tyre pressures. This system may then in turn be used to detect overloaded axles
http://dl-live.theiet.org/content/conferences/10.1049/ic_19970278
Traffic 2000 Ltd. have become world leaders in piezo electric technology for the traffic industry. We have devised various types of piezoelectric detectors that have led to the design of a tyre monitoring system. We are able to measure speed very accurately indeed in free flowing traffic, axle passage from 0 to 150 mph and width of wheels. We are able to monitor bicycle passage in mixed traffic roads, differentiate between bicycle, motorbikes, cars, and all manner of commercial vehicles. (11 pages)Micro-actuation using thin film piezoelectric elements
http://dl-live.theiet.org/content/conferences/10.1049/ic_19971055
Interest in the use of thin film actuators arose in work on scanning probe microscopes. The cantilever in such instruments, typically 100 μm long, is subject to unwanted vibration from the environment. This building and air borne vibration limits the imaging resolution of the instrument. The conventional approach is to mount the instrument on a massive isolation table. This solution is expensive and prevents the portability of the instrument. As an alternative, active vibration control of the cantilever has been investigated. Piezoelectric and electrostatic actuation have been investigated. (3 pages)Two emission modes from ferroelectric emitters
http://dl-live.theiet.org/content/conferences/10.1049/ic_19970400
In recent years, ferroelectric emitters have received considerable attention. There are a number of applications for these devices including triggering gas switches to illuminating flat screen displays. There is still, however, controversy surrounding the nature of the emission process. One explanation is that the emission is due to the repulsion of surface screening electrons when the polarization is rapidly switched. The other is that the electrons are emitted from a surface plasma initiated at metal-insulator boundaries. Here, the authors report observations which demonstrate clearly for the first time that both types of emission can occur from the same sample and that the charge densities emitted are very similar. (3 pages)Ferroelectrics, microsystems and nanotechnology
http://dl-live.theiet.org/content/conferences/10.1049/ic_19971048
Summary form only given. This talk will review the subject of nanotechnology and explore how new materials can be used to integrate sensing and actuation functions onto semiconductor chips, with the ultimate objective of permitting nanoscale fabrication and information storage. Ferroelectric materials offer a wide range of properties which can be used in such microsystems and nanotechnology, particularly the pyroelectric effect for thermal infrared detection and imaging and the piezoelectric effect for sensors (sound, acceleration, etc.), and for actuators (motors, pumps). The potential for ferroelectric thin and thick films to contribute to these fields will be discussed, and problems reviewed, especially from the aspect of materials and process integration. Specific examples of the factors critical to the growth and behaviour of the materials will be given and novel processing for the fabrication of thin and thick films of ferroelectrics discussed. (1 page)Interface electronics for resistive and piezoelectric polymer gas sensors
http://dl-live.theiet.org/content/conferences/10.1049/ic_19961296
An electronic interface has been designed and built which allows changes in the properties of hybrid conducting polymer sensors to be measured by a host computer. It has analogue circuitry which is used to measure polymer resistance, and digital circuitry which provides a measure of the period of oscillation of piezoelectric element (PZE) with a polymer deposit. Initial tests were made with physically separate sensor types but the design is intended for a hybrid sensor with a single polymer deposit on a PZE. A Field Programmable Gate Array (FPGA) has been configured to act as a period meter, which achieves a resolution of better than 1 part in 2 million. An embedded single-chip microcontroller accepts simple commands from a host computer and coordinates the activity of analogue multiplexers, a precision ADC, and the FPGA to give 1 reading per second from and array of 6 hybrid sensors. Other features have been included which allow for temperature measurement and control, numerical pre-processing as well as programmable gain and offset. The result is a superior instrument which aims to meet the emerging needs of industrial and research applications. (4 pages)Thin film piezoelectric layers for sensing and actuation in microstructures
http://dl-live.theiet.org/content/conferences/10.1049/ic_19961220
Silicon micromachined sensors and actuators that incorporate piezoelectric materials are considered. Widespread application has been restricted by the properties of the materials available. The prospects for micromachined piezoelectric devices have improved since it became possible to deposit PbZr<sub xmlns="http://pub2web.metastore.ingenta.com/ns/">x</sub>Ti<sub xmlns="http://pub2web.metastore.ingenta.com/ns/">1-x</sub>O<sub xmlns="http://pub2web.metastore.ingenta.com/ns/">3</sub> layers over large areas with goad uniformity and reproducibility. Considerable progress has been made in developing process technologies for integrating PbZr<sub xmlns="http://pub2web.metastore.ingenta.com/ns/">x</sub>Ti<sub xmlns="http://pub2web.metastore.ingenta.com/ns/">1-x</sub>O<sub xmlns="http://pub2web.metastore.ingenta.com/ns/">3</sub> thin films layers with surface and bulk micromachined structures. As incorporation of these materials in silicon microstructures becomes established it will be possible to consider the integration of bipolar and CMOS electronics with the sensors and actuators. Material and process integration techniques developed to incorporate thin film PbZr<sub xmlns="http://pub2web.metastore.ingenta.com/ns/">x</sub>Ti<sub xmlns="http://pub2web.metastore.ingenta.com/ns/">1-x</sub>O<sub xmlns="http://pub2web.metastore.ingenta.com/ns/">3</sub> onto bulk micromachined structures are described. The design of a triaxial accelerometer and the processing steps required are outlined. (1 page)Defects in quartz related to interstitial Li and Na ions as revealed by luminescence
http://dl-live.theiet.org/content/conferences/10.1049/cp_19960069
Quartz usually contains Al impurities substituted for Si in the lattice. Monovalent ions, e.g. Li<sup xmlns="http://pub2web.metastore.ingenta.com/ns/">+</sup> and Na<sup xmlns="http://pub2web.metastore.ingenta.com/ns/">+</sup>, provide then the charge compensation at the Al. These monovalent ions (M<sup xmlns="http://pub2web.metastore.ingenta.com/ns/">+</sup>) have been found to affect considerably the thermoluminescence (TL) of quartz, effects involving migration of M<sup xmlns="http://pub2web.metastore.ingenta.com/ns/">+</sup> ions along the c-axis channels in quartz. Thus, the glow curve of Li containing quartz subjected to certain double irradiation procedures involving migration of Li ions away from the Al was shown in the past to exhibit a very strong TL peak near 190K. Radiation induced drift of M<sup xmlns="http://pub2web.metastore.ingenta.com/ns/">+</sup> ions in quartz has also been known to produce acoustic losses and frequency offsets in quartz resonators. The TL peaks related with the migration of the M<sup xmlns="http://pub2web.metastore.ingenta.com/ns/">+</sup> ions give an insight into the radiation induced drift of the interstitials in quartz. It provides thus a good tool for the investigation of the related Q<sup xmlns="http://pub2web.metastore.ingenta.com/ns/">-1</sup> losses and frequency offsets in quartz resonators. The present paper reviews some earlier results on the M<sup xmlns="http://pub2web.metastore.ingenta.com/ns/">+</sup> related defects in quartz and describes results of still unpublished work on the topic.Actuators and their mechanisms in microengineering
http://dl-live.theiet.org/content/conferences/10.1049/ic_19960698
The subject of actuation in microengineering is an expanding area of study. Many aspects need to be considered - the actuation mechanism, how well it scales to the micro level, the materials involved, process compatibility, reliability, and comparison with alternative techniques - are all criteria in reaching a final judgement. There are many different types of actuation mechanisms used in microengineering including: electrostatic, electromagnetic, piezoelectric, magnetostriction, electrostriction, thermal, and shape memory alloy mechanisms. None has dominance over any other, and the choice of mechanism is a balance between many different factors. (3 pages)Characteristics of high frequency fundamental rectangular quartz crystal resonators
http://dl-live.theiet.org/content/conferences/10.1049/cp_19960003
Interest in high frequency fundamental (HFF) quartz crystals is soaring in the fields of telecommunications and instrumentation. High speed communication systems require high frequency references and fundamental mode resonators have preference when either a large pulling range, a large bandwidth or a low spurious level in the spectrum are required. A manufacturing process has been developed which combines photolithographic batch technology and wet chemical local thinning on wafer. Thus, it is possible to produce HFF rectangular AT resonators with inverted mesa structure in large quantities and at reduced labor cost. A crystal was designed at 50 MHz (membrane thickness 33 micrometers) and sufficient quantities are being produced for technological characterisation and assessment. The AT-HFF resonator is very robust due to single ended rigid mounting and encapsulation in a hermetically sealed SMD ceramic package (8×3.6×1.8 mm<sup xmlns="http://pub2web.metastore.ingenta.com/ns/">3</sup>). Electrical, thermal and environmental characteristics of this type of quartz crystal are presented.Contribution of a 3D numerical simulation to the design of micro-machined quartz microstructures
http://dl-live.theiet.org/content/conferences/10.1049/cp_19960076
This paper is an attempt to prove the interest of a 3D simulation for micromachining of quartz. For this purpose new results related to doubly rotated plates are discussed. The 3D simulation based on the tensorial model of dissolution constitutes a convenient computer aided design for masks patterns. However, care must be taken because, for quartz crystal, the major problem remains the accurate adjustment of the dissolution slowness surface.Analysis of medium-term frequency instability of high stability quartz oscillators
http://dl-live.theiet.org/content/conferences/10.1049/cp_19960100
Various types of high stability quartz oscillators have been elaborated and produced on a small scale. Systematic investigations of long-term frequency stability of the oscillators have been carried out. Typical parameters of currently manufactured ITR OCXOs are shown as well as measurement results of short-term frequency stability, for average time from 1 ms to 100 s. According to definitions given in actual standardization documents, long-term instability is the frequency change observed in conditions assuring elimination of other influences on oscillator frequency, especially temperature and supply voltage. During investigations we observed and determined the slow frequency fluctuations of the true long-term characteristics of the measured oscillators. The results of investigation and calculation procedures used for data processing in order to increase the confidence level of frequency/time characteristics determination, are presented.Quartz crystal units with bar piezoelements vibrating in double-shear mode
http://dl-live.theiet.org/content/conferences/10.1049/cp_19960028
Summary form only given. Investigations aimed at improving crystal unit characteristics over the range 400-1000 kHz resulted in designing quartz crystals operating in a double-shear mode. The investigations were realized on the base of quartz crystal bars having a rectangular cross section of close cross sizes, with length being along X-axis. Vibrations of such bars may be approximately interpreted as a superposition of two shears-in thickness and in width of the piezoelements. Crystal units operating in the above mentioned mode have high electrophysical parameters: dynamic resistance 5-100 Ohm, motional inductance 2-20 H, quality factor 10<sup xmlns="http://pub2web.metastore.ingenta.com/ns/">5</sup>-2×10<sup xmlns="http://pub2web.metastore.ingenta.com/ns/">6</sup>, capacitance ratio up to 350, high temperature-frequency stability and low aging. Calculation results showed that quartz crystal units may have high temperature stability by changing the cut angle and dimensions of the piezoelements.High-precision IC quartz oscillator
http://dl-live.theiet.org/content/conferences/10.1049/cp_19960041
Development of satellite communication and navigation, along with adoption of synchronous techniques for data transmitting and processing, promotes an enhanced demand for compact high-stability quartz oscillators of TCXO and VCXO-types. Solving a topical problem-to minimize quartz oscillator dimensions-is presented based on development of a dedicated IC. Considered is an approach to realization of a self-exited oscillator using differential amplifiers and a model of two-terminal networks with a negative impedance. Described are the IC main stages. The reduction of TCVCXO volume down to 15 cm<sup xmlns="http://pub2web.metastore.ingenta.com/ns/">3</sup> is attained at instability for frequency of (3-20) MHz with Allan's variance up to (2-5).10<sup xmlns="http://pub2web.metastore.ingenta.com/ns/">-12</sup>.Frequency jumps on BVA and other precision quartz crystal resonators and burst-noise on overtone mode high-frequency quartz crystal resonators
http://dl-live.theiet.org/content/conferences/10.1049/cp_19960027
Frequency jumps have been observed on BVA and other precision quartz crystal resonators/oscillators during prolonged and continuous operation. To date frequency-jump phenomena have not been well understood as these jumps have been designated as micro-jumps or abrupt frequency jumps irrespective of the nature of the jumps. In this paper, these frequency jumps will be classified into three distinct and separate categories and these are: (i) Intermittent Frequency Jumps, (ii) Discrete Frequency Jumps, and (iii) Abrupt Frequency Jumps. To characterise and distinguish these frequency jumps, apart from continuous and prolonged operation, other resonator/oscillator parameters, such as g-sens, retrace, drive-level-dependence, bandbreaks (i.e., dips), phase-noise etc. have also to be measured. Intermittent and discrete frequency jumps can be correlated to one or more resonator/oscillator parameter. Finally burst-noise observed on overtone-mode high-frequency quartz crystal resonators will be reviewed and explanations will be given to demonstrate why this noise process cannot be correlated to known crystal resonator parameter variations. As in the case of abrupt frequency jump, a new resonator model is required to explain this burst-noise phenomenon.Evaluation of mini-BVA resonators for space applications: tests program and results
http://dl-live.theiet.org/content/conferences/10.1049/cp_19960008
There is a growing need for ultrastable quartz oscillators operating under the special environmental conditions usually required in space program applications. This is the case for radiocommunications, navigation, precise positioning and scientific programs especially in the case of satellite applications. Under those conditions an evaluation program based on general rules ESA/SCC has been launched in 1992 for precise space evaluation of mini-BVA resonators. A special Process Identification Document (PID) has been established which includes fabrication processes and test procedures. 21 resonators have been fabricated according to the proposed PID. Then a test program has been defined and resonators have been space evaluated with interesting results which are discussed. Finally, it appeared that performances goals have been obtained. In conclusion special resonators can be fabricated by LCEP with guaranteed performance.An insitu technique for the resolution of aging contributions between quartz resonators and oscillator circuits
http://dl-live.theiet.org/content/conferences/10.1049/cp_19960101
The in situ technique has been validated with theory and demonstrated by experiment. This powerful technique may now be used to investigate both component and parametric behavior in quartz oscillators. Such issues as drive level dependency and short term frequency “pops” may be better understood through the technique. Aging models, particularly those involved with prediction, will benefit from the separation of crystal resonator from circuitry.SC-cut resonator operating in anharmonic modes with B-mode reduction
http://dl-live.theiet.org/content/conferences/10.1049/cp_19960054
The design of a SC-cut resonator for which the C-mode has a lower resistance than the B-mode (typical ratio 1.5) is presented. This result is obtained by using an antisymmetric anharmonic mode with a particular geometry and connection of the electrodes. Experimental results (motional resistance, thermal behaviour) are given for a third overtone, 10 MHz, resonator.Mechanical characterisation of a polysilicon accelerometer
http://dl-live.theiet.org/content/conferences/10.1049/ic_19961219
This paper describes a measurement system which has been developed to determine, experimentally, the dynamic characteristics of microstructures. These characteristics include dynamic mode shape of free vibration, natural frequencies and modal damping factors. The system is demonstrated by determining the dynamic characteristics of a polysilicon accelerometer designed and produced at DRA Malvern. The accelerometer takes the form of a 2 μm thick polysilicon plate supported at as corners by beam like ligaments. Acceleration causes bending defections of the plate against the elasticity of the ligaments and this is taken as a measure of acceleration. The mechanical design of the sensor was carried using finite element analysis (ANSYS). In the experimental evaluation of the dynamics of the accelerometer the sensor was mounted within a general purpose piezoelectric staging and excited into vibration by applying a swept sine excitation to the piezoelectric. Using a laser vibrometer the notion of an array of selected test points on the accelerometer was measured and point frequency response functions calculated over a frequency range of 0 to 100 kHz. Using this data the dynamic mode shapes, natural frequencies and modal damping factors were calculated and the experimental behaviour of the sensor observed by animating a wire framed drawing of the structure. The mechanical damping of the accelerometer is determined by the behaviour of the squeeze film between the plate and the supporting substrate. (7 pages)Effects of crystal mount resonance, under random vibration, on the close to carrier phase noise
http://dl-live.theiet.org/content/conferences/10.1049/cp_19960042
The phase noise of quartz crystal oscillators under vibration is degraded, mainly due to the acceleration sensitivity of the quartz crystal element. It is shown that if a crystal mount resonance is excited by a random vibration profile then the phase noise close to the carrier, outside the random vibration profile, can be further substantially degraded. A consequence is that the vibration sensitivity would seem to increase rapidly at low vibration frequencies. For example, a crystal oscillator with a resonance at 1950 Hz subjected to a random vibration profile of 0.01 g<sup xmlns="http://pub2web.metastore.ingenta.com/ns/">2</sup>/Hz extending from 100 Hz to 3000 Hz compared with a profile of 100 to 500 Hz, where the resonance is not excited, can have over 40 dB degradation in the phase noise at 20 Hz from the carrier. The resonance level is shown to become non-linear with vibration power, possibly due to the large acceleration amplification of the resonance, 100 to 300 times. The vibration level where the resonance becomes non-linear varies by two orders of magnitude and starts as low as 0.0003 g<sup xmlns="http://pub2web.metastore.ingenta.com/ns/">2</sup>/Hz. This phenomenon is demonstrated for four oscillators and investigated under varying acceleration levels in an attempt to quantify the nonlinear behavior. The nonlinear behaviour of the resonance is believed to produce intermodulation of the mechanical vibration which leads to the degradation of the close to carrier phase noise.A method for quartz oscillator synchronization by GPS signal
http://dl-live.theiet.org/content/conferences/10.1049/cp_19960024
In the paper a GPS controlled frequency reference source has been described. The source combines the advantages of very good short term stability of high quality quartz oscillator with advantages of GPS signal over the long term. Details of the internal workings of the source have been presented. The deviation of the local oscillator from the ideal reference is determined by counting the pulses of the multiplied local oscillator frequency between successive GPS pulses. Special arrangement of counting circuitry eliminates discrete error. The correction voltage at the oscillator's control input consists of two terms. One term is computed from averaging the counted pulses over 1s interval and is thus responsible for minimizing the short term frequency deviation. The other term is computed from the accumulated phase time drift. The control algorithm ensures that the frequency accuracy averaged over one day is significantly better than 10<sup xmlns="http://pub2web.metastore.ingenta.com/ns/">-11</sup> and the peak accumulation of phase time drift does not exceed 200 ns.Active tuning of crystal oscillators
http://dl-live.theiet.org/content/conferences/10.1049/ic_19961249
In this paper four systematic methods are described for the active tuning of crystal oscillators. The four methods are compared with respect to power consumption and maximum attainable carrier-to-noise ratio. It is concluded that the parallel resonance mode has to be preferred for active on-chip crystal tuning. (6 pages)High frequency fundamental mode resonators: equivalent electrical data dependence on electrode properties and blank surface
http://dl-live.theiet.org/content/conferences/10.1049/cp_19960002
High frequency fundamental mode crystals in the frequency range from 40 to 200 MHz show different electrical properties compared to conventional overtone quartz crystals in the same frequency range. They show lower electrical Q-values, different pullabilities and anharmonic modes as result of variations of the blank-electrode thickness ratio. We present the behaviour of anharmonic modes and C<sub xmlns="http://pub2web.metastore.ingenta.com/ns/">0</sub>/C<sub xmlns="http://pub2web.metastore.ingenta.com/ns/">1</sub>-ratios under various conditions using FEM methods, but also compare our results with experimental data of planoparallel crystals and inverted MESA-structured crystals, respectively.Influence of electrode mass-loading on the electrical equivalent circuit of the trapped-energy AT-cut quartz resonators
http://dl-live.theiet.org/content/conferences/10.1049/cp_19960052
The static C<sub xmlns="http://pub2web.metastore.ingenta.com/ns/">0</sub> and motional C<sub xmlns="http://pub2web.metastore.ingenta.com/ns/">n</sub> capacitance of the electrical equivalent circuit of the AT- and BT-cut quartz resonators are computed. Another comparison is done for an infinitely large plane parallel plate, for plane parallel energy trapped resonators, by considering the mass loading of electrodes and for the energy trapped resonator by considering the mass loading of electrodes and the spherically contoured surface of the plate.The measurement of transient electromagnetic torque in high-performance electrical drives
http://dl-live.theiet.org/content/conferences/10.1049/cp_19960917
A method of measuring transient electromagnetic torque for electrical motor drives is described that uses a commercially-available force-measurement platform. The platform contains crystals which develop charges as a result of the piezoelectric effect. The crystals are sensitive to forces in the three orthogonal directions in space. Measurements of the charges produced by these crystals facilitate the transient stator-reaction forces to be measured directly. The motor torque may then be derived by using a simple linear combination of the measured forces. The technique has the advantage that the motor can be used without modification. It has been successfully employed in a comparative study of the transient responses of high performance, vector controlled induction motor drives.Phase noise figures comparison in transistor amplifiers of different types
http://dl-live.theiet.org/content/conferences/10.1049/cp_19960093
Ultrastable quartz oscillators must be specially designed so as to match resonator parameters and electronic circuitry characteristics. Recently we have pointed out that our results have never been really resonator limited (at least for BVA units) and that further improvements would largely depend on progress in amplifiers. In order to improve the output signal stability of ultrastable oscillators it is necessary to reduce oscillating loop phase noise and to minimize phase noise of each stage of output amplifier as well. In this paper, each type of bipolar transistor amplifier configuration is considered: Common Emitter (CE), Common Collector (CC) and Common Base (CB). Power spectral density (PSD) of phase noise is calculated from the partial derivative of transfer function argument versus transistor and components parameters variations. In such a calculation, those variations are assumed to be uncorrelated. After this theoretical calculation, the PSD of each basic configuration (i.e., CE, CC, CB) is analysed. Results are compared and discussed taking into account criteria as stage gains, input or output impedances. Consequences are discussed in terms of amplifier performances and oscillator stabilities.Comparison of passive and active aging of SC-cut and AT-cut crystals
http://dl-live.theiet.org/content/conferences/10.1049/cp_19960009
This paper reports on the results of pre-aging of four different types of OCXO crystal units. It compares the aging behaviour for a passive aging at +80°C over 28 days and 12 days at different drive levels and the active aging in the following 34 days with the crystals continuously operating in oscillators. For the aging rates good correlation was found. One crystal of each group was additionally aged for 240 days. The measured long-term aging results are compared to the aging prediction derived from the first 30 days.Laser ablated ferroelectric and superconducting thin films for microwave applications
http://dl-live.theiet.org/content/conferences/10.1049/ic_19960599
Electrically tunable microwave components incorporating high temperature superconductors offer both controllability and low conductor losses. Potential applications for such technology are, for example, electrically steerable phase-array antennas, and frequency agile filters. Changes in the resonant frequency of a microwave circuit in response to an applied electric field can be achieved by incorporating ferroelectric materials into the resonant structures. Tunability is achieved since the dielectric constant of the ferroelectric layer can be modified by the electric field. Clearly, an understanding of the behaviour of hybrid superconductor-ferroelectric materials at microwave frequencies is essential in order to realise practical applications. In this paper we present data for the response of a coplanar resonator. Layers of strontium titanate (STO) and YBa<sub xmlns="http://pub2web.metastore.ingenta.com/ns/">2</sub>Cu<sub xmlns="http://pub2web.metastore.ingenta.com/ns/">3</sub>0<sub xmlns="http://pub2web.metastore.ingenta.com/ns/">7</sub> (YBCO) are laser ablated onto an MgO substrate and the resonator is photolithographically etched onto the surface of the YBCO. (5 pages)Theoretical and experimental investigations of frequency transient process caused in crystal plates under local heating
http://dl-live.theiet.org/content/conferences/10.1049/cp_19960029
Summary form only given. It is known that nonuniformly heating produces an additional frequency shift in anisotropic crystal plates. This affect is most pronounced when the crystal is spot heated. Temperature gradients appearing along the plate cause mechanical stresses that lead to frequency change. Theoretical investigations of the local heating effect on resonator frequency are carried out. Dependence of frequency control efficiency was investigated in relation to size of heater, number of excited harmonics, cut angle, piezoelement thickness and coefficient of heat exchange with the environment. Using MATLAB and MATCAD software, maps of heat and stress fields were calculated for different heating conditions. The corresponding frequency shift was calculated. This process is essential for many practical applications such as frequency control in low-noise PLL system. It is shown that the form of transient process depends on the ambient temperature and has two time constants. Most of the parameters of local heating controlled oscillator are shown: frequency setting process; control characteristics; phase noise. The obtained theoretical results are close to experimental ones.Relationship between amplitude and resonant frequency in quartz crystal resonators
http://dl-live.theiet.org/content/conferences/10.1049/cp_19960010
In this paper we report results of measurements on the resonant frequency of crystal resonators as a function of drive current (amplitude). Previous studies indicate that the resonant frequency increases as the square of the driving current. If we assume that the limiting factor in the flicker frequency noise of crystal resonators is the noise in the drive current, then the quadratic dependence suggests that crystal resonators should be driven at low current for better frequency stability. Frequency versus amplitude measurements were made on SC-cut, 5th overtone, 100 MHz crystal resonators using a network analyzer. As expected, the measurements show a general quadratic dependence of frequency versus drive current. Nevertheless, some crystals exhibit phase (frequency) jumps at certain drive currents and certain temperatures. Phase modulation (PM) noise measurements were made in test oscillators at several currents to see if there is a correlation between the amplitude-frequency effect and flicker of frequency noise. Our results indicate that the flicker of frequency noise varies with current, but the current at which the flicker of frequency noise is the lowest is not necessarily the lowest current (as the quadratic relation of v<sub xmlns="http://pub2web.metastore.ingenta.com/ns/">0</sub> versus drive current suggests).Composite resonator spectroscopy of quartz ferrobielastic twinning under uniaxial stress
http://dl-live.theiet.org/content/conferences/10.1049/cp_19960070
In the present work, the acoustic waves in X-cut quartz crystals subjected to uniaxial stress were used as a tool for investigation the ferrobielastic twinning phenomenon. The propagation characteristics of media was measured using the previously developed composite resonator spectroscopy. Al-ZnO-Al layers were deposited on one of the X-faces of quartz samples forming composite resonators structures. It was observed that the position of peaks for longitudinal waves increased with the increase of the compressive stress. The ferrobielastic switching was characterized by an abrupt decrease of frequency of peaks. Subsequent increase of pressure resulted in the smaller slope of frequency vs. stress dependence than before twinning. The quantitative and qualitative explanation of the observed data and the evaluation of the sound velocity are given.High performance, crystal oscillators for space applications
http://dl-live.theiet.org/content/conferences/10.1049/cp_19960043
A family of space qualified, high performance, oven compensated, crystal oscillators have been developed employing stress compensated (SC-cut) resonators. The oscillators use rugged oven designs, robust enough to withstand launch vibration while reducing thermal losses to ensure low power operation. Electronic circuits are implemented using thick film hybrid technology, with interconnections via film wire flexible circuits, to achieve minimum size, weight and high reliability. Typical frequency stabilities of ± few pp10<sup xmlns="http://pub2web.metastore.ingenta.com/ns/">8</sup> over -40°C to +75°C, coupled with ageing rates of less than ±1pp10<sup xmlns="http://pub2web.metastore.ingenta.com/ns/">10</sup>/day have been achieved with power consumptions of less than 450 mW. Phase noise at 1 kHz offset is -153 dBc/Hz. Environmental testing includes vibration, thermal vacuum and radiation.Double-mode excitation of quartz crystals without dips of activity on the C and B modes
http://dl-live.theiet.org/content/conferences/10.1049/cp_19960053
Summary form only given. Doubly-rotated cut quartz resonators excited on the main C-mode and the thermosensitive B-mode simultaneously appear to be the most promising way for essential improvement of the basic performance of MCXOs and temperature sensors. This article elucidates the physical origins of the phenomena and searches for an effective method of designing double-mode resonators for improved operation. Careful exploration of the frequency spectrum of the fundamental mode and the 3d overtone SC-cut crystals while ambient temperature changes, allows one to identify spurious mode interactions with the B-mode. Furthermore, the dependence of the interaction intensity on the “energy trapping” in the crystal plate has been revealed and explained. The C-mode activity showed no noticeable fluctuations within the temperature range of -40 to +70 °C, while the B-mode activity deviated within 30 per cent for the fundamental mode and within 10 per cent for the 3d overtone crystals.Influence of loss on the critical frequencies of ceramic resonators
http://dl-live.theiet.org/content/conferences/10.1049/cp_19960030
Piezoresonators are often characterised by equivalent circuits. Loss then usually appears as an ad hoc addition to the circuit. Future stability and manufacturing reproducibility requirements dictate a more detailed understanding of the types of loss mechanisms and their disposition in equivalent networks. The effects of a lossy piezoelectric coupling coefficient, k*, on the complex resonance frequencies of a plate resonator driven in a simple thickness mode are explored.Frequency stability of 1x10<sup xmlns="http://pub2web.metastore.ingenta.com/ns/"> - 13</sup> in a compensated sapphire oscillator operating above 77 K
http://dl-live.theiet.org/content/conferences/10.1049/cp_19960059
We report on tests of a compensated sapphire oscillator (CSO) which shows frequency-stable operation at temperatures above 77 K. The frequency stability for this oscillator shows an apparent flicker floor of 7.5×10<sup xmlns="http://pub2web.metastore.ingenta.com/ns/">-14</sup> for measuring times between 3 and 10 seconds, and stability better than 2×10<sup xmlns="http://pub2web.metastore.ingenta.com/ns/">-13</sup> for all measuring times between 1 and 100 seconds. These values are approximately the same as for the very best available quartz oscillators. Previously, high stability in sapphire oscillators had only been obtained with liquid helium cooling. Recent improvements include a more careful analysis of the AC frequency-lock “Pound” circuitry that now enables the oscillator to reliably attain a stability 6 million times better than its fractional resonator linewidth. Measurements to date have been made with a resonator quality factor Q≈2×10<sup xmlns="http://pub2web.metastore.ingenta.com/ns/">6</sup>. Frequency stability of 2×10<sup xmlns="http://pub2web.metastore.ingenta.com/ns/">-14</sup> is projected for a resonator Q of 10<sup xmlns="http://pub2web.metastore.ingenta.com/ns/">7</sup>, a value about one third of the intrinsic sapphire Q at this temperature.Precision, low power, analogue TCXO using a single integrated circuit
http://dl-live.theiet.org/content/conferences/10.1049/cp_19960102
We have designed a single chip TCXO which is capable of temperature compensation to better than ±0.1 ppm over -50 to +90°C. Off-chip components are limited to a decoupling capacitor, the crystal, and a filter capacitor for low-noise applications.Low dose proton radiation sensitivity of quartz resonators
http://dl-live.theiet.org/content/conferences/10.1049/cp_19960075
The results of the testing of 4 MHz, 10.24 MHz and 10.95 MHz 3rd overtone SC-Cut quartz crystals confirms the earlier work of Norton and Suter on 5th overtone AT-Cut, SC-Cut crystals. The testing showed that low dose rate radiation sensitivity is manufacturing lot dependent. Frequency variations due to low dose rate proton and gamma ray exposures varied between <1×10<sup xmlns="http://pub2web.metastore.ingenta.com/ns/">-11</sup> and 4×10<sup xmlns="http://pub2web.metastore.ingenta.com/ns/">-10</sup> per Rad. The majority of the crystals exhibited radiation sensitivities of 3-5×10<sup xmlns="http://pub2web.metastore.ingenta.com/ns/">-11</sup> per Rad. The hypothesis that a nonlinear relationship exists between low dose rate and high total dose rate was confirmed. Testing indicated that the majority of crystals exhibited a conditioning effect during successive exposures to low dose radiation. The effect on performance of these types of sensitivities is highly system dependent. However, the capability exists to screen low sensitivity resonators for use in applications where this characteristic is important.Specification of long term reliability of frequency control products
http://dl-live.theiet.org/content/conferences/10.1049/cp_19960083
The paper is intended to highlight some technical, commercial and legal issues in the specification of frequency control products, which are of concern to manufacturers. The difficulties inherent in predicting frequency ageing are looked at as are some legal implications.A specific LSIC intended for synthesizer-type DTCXO
http://dl-live.theiet.org/content/conferences/10.1049/cp_19960045
Thermocompensated crystal oscillators are widely used in cases when high frequency stability, low power consumption and short time of coming into readiness are needed. Digital methods of frequency compensation provide the highest frequency stability parameters. Popular as they are digital thermocompensated oscillators have the stability that usually does not surpass ±5×10<sup xmlns="http://pub2web.metastore.ingenta.com/ns/">-7</sup> in a wide temperature interval. Much higher frequency stability can be achieved in a DTCXO of a synthesizer type (DSTCXO). Several tens of microcircuit packages would be needed in order to construct a DSTCXO using discrete components. With the purpose of DSTCXO dimensions minimization a specific LSIC has been developed comprising nearly all oscillator elements. The microcircuit was intended for interaction with frequency sensor of temperature. The resolution of synthesizer is 10 ppb. When a double mode quartz oscillator is used temperature stability comes as high as ±3 ppb.Performance of a cryogenic sapphire dielectric resonator
http://dl-live.theiet.org/content/conferences/10.1049/cp_19960060
In this paper we present details of the design and operation of a cryogenic sapphire dielectric resonator. This includes controlling the resonator's temperature to better than 90 μK and the effect of paramagnetic impurities on the predicted performance. We also discuss room temperature observations on the efficiency of the novel microwave choke arrangement. Finally we present some preliminary stability measurements for our Mark I system.Quartz oscillators: deriving oscillation condition by symbolic calculus
http://dl-live.theiet.org/content/conferences/10.1049/cp_19960092
This paper presents the method used to derive the oscillation condition by using symbolic calculus. The program is based on the full nonlinear Barkhausen criterion method. The behaviour of an oscillator is described by a complex polynomial called the characteristic polynomial. This polynomial enables us to calculate the steady state features of the oscillation as well as the differential equation for transient analysis in the time domain. The literal determination of this characteristic polynomial involves lengthy algebraic calculations and cannot be done by hand as the electronic oscillator circuit involves too many components. We recently developed a formal calculus program allowing to automatically obtain all necessary equations for oscillation analysis. We propose new methods to calculate them in an optimal form.Analysis of microstructures incorporating ferroelectric thin films
http://dl-live.theiet.org/content/conferences/10.1049/ic_19951469
We have been working on sensors that involve the integration of ferroelectric thin films with micromachined structures. Both surface and bulk micromachining techniques are under development for integrated infrared detector arrays and accelerometers, respectively. These devices take advantage of the pyroelectric or piezoelectric properties of the thin films. A sol-gel route has been used to deposit the ferroelectric thin film, enabling direct integration with the micromachined structures. PbZr<sub xmlns="http://pub2web.metastore.ingenta.com/ns/">x</sub>Ti<sub xmlns="http://pub2web.metastore.ingenta.com/ns/">1-x</sub>O<sub xmlns="http://pub2web.metastore.ingenta.com/ns/">3</sub> (PZT) films with compositions of x=0.3 and x=0.5 have been used for the infrared detector arrays and accelerometers respectively. Several different techniques have been used to assess these films including X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM) and Raman spectroscopy. (2 pages)Piezoelectric films in silicon-based microactuation structures
http://dl-live.theiet.org/content/conferences/10.1049/ic_19950568
We have established a process for the deposition of multi-micron piezoelectric films which is compatible with fabrication of micro-mechanical actuator structures, and have fabricated such actuators, and demonstrated their operation. While some of these accomplishments have been reported by other groups, we know of none that have achieved all of them in an integrated fabrication process. However, considerable work is still required to optimise the material performance and fabrication processes, as well as to investigate specific applications. (3 pages)Passivation for three-dimensional actuation microstructures using ECR-CVD
http://dl-live.theiet.org/content/conferences/10.1049/ic_19950574
Xaar actuators have been fabricated using PZT as a substrate with aspect ratios of the order of 6:1. The fabrication of a passivation layer of suitable quality, to ensure adequate device lifetime, requires a significant improvement over standard PECVD depositions of inorganic coatings. In this paper Electron Cyclotron Resonance Chemical Vapour Deposition (ECR-CVD) has been used for the deposition of silicon nitride barrier films on PZT. (3 pages)Colour and greyscale in ferroelectric liquid crystal displays
http://dl-live.theiet.org/content/conferences/10.1049/ic_19950862
As portable equipment becomes more sophisticated it requires advanced electronic displays at least equivalent in image quality to that of CRTs, but with the advantages of low weight, power and volume. The performance of the current generation AMTN LCDs is at least equivalent to typical CRTs, but because of the processing difficulties associated with their manufacture, the production costs are very high, and their availability low. Despite the predicted improvements in yields and availability over the next three years, custom AMTN displays will nevertheless remain prohibitively expensive in low volumes. Moreover, AMTN technology has limitations for meeting future requirements in: a. High absolute resolution (1000 lpi) miniature helmet mounted displays; b. Large area (20" diagonal) wide angle of view, direct view displays. DRA's latest generation of LCDs based on ferroelectric liquid crystal (FLC) technology has demonstrated 1000 lpi resolution in a 6 mm square device. It has also developed drive schemes and materials capable of producing a 1280×1024 display with 4-bit greyscale. (6 pages)High speed piezoelectric actuators in a soft product assembly and manipulation environment
http://dl-live.theiet.org/content/conferences/10.1049/ic_19951050
This paper discusses the need for a high speed handling system for use with soft products. At present the system contends with snack food packets and the placement of these products onto a pre-slit card. The project has a wide scope for high speed components incorporating piezoceramics. Although piezoceramic usage is rapidly becoming more widespread in industry, it has not been incorporated into soft product handling. (3 pages)Piezoelectric motors and their electronic supply
http://dl-live.theiet.org/content/conferences/10.1049/ic_19951053
The piezoelectric motor is a new type of electrical drive utilizing the inverse piezoelectric effect for electromechanical energy conversion. Piezoelectric motors exhibit very high torques at low speed levels. When the electrical power source is switched off, the rotor is clamped due to high frictional forces, making this motor ideal for a variety of positioning tasks (gearless systems). Additional advantages of piezoelectric motors are a very low noise emission and the absence of magnetic interference. (3 pages)Piezomotors using flexure hinged displacement amplifiers
http://dl-live.theiet.org/content/conferences/10.1049/ic_19951055
The design and construction of two different piezomotors developed by the authors is briefly described. Both employ flexure hinged mechanical displacement amplifiers to increase the output movement of stack-type piezoelectric actuators to enable them to be applied to rotation generating mechanisms. The first example is a harmonic piezomotor. The harmonic drive principle enables the production of an externally commutated motor which can be driven as a conventional stepping motor for open-loop applications and which yields a very fine rotational increment. The use of piezoelectric actuators makes the motor power consumption almost zero in holding situations, which gives it an advantage over conventional electromagnetic motors in some applications. The second prototype piezomotor presented is based on a roller clutch mechanism. Using one, or more, piezo-stack actuators and a roller clutch as the rotational motion converter, this motor has a very simple structure and requires only a single phase power input. To achieve effective movement of the motor using commercial tolerance roller clutches, the output movement of the piezo-stacks is again magnified by flexure hinged displacement amplifiers. (5 pages)