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Understanding the complexity of the brain ultimately requires insight into the decoding of local microcircuit functionality by noninvasive approaches. Recently, the new field of Spintronics is attracting a lot of attention with its noninvasive abilities to sense the magnetic field of neurons and to modulate their firing with spintronics devices. The two emerging tools are transcranial magnetic stimulation (TMS) and magnetic encephalography (MEG). The proposed nano-TMS device will use magnetic nanowires—the electromagnetic coils’ nanoscale cousins—to generate focused and programmable magnetic fields. Preliminary theoretical calculations show that proposed devices can provide programmable, focused stimulation for noninvasive neuromodulation of neural microcircuits with unprecedented high spatial and temporal resolutions. The nano-MEG is based on a simple version of the magnetometer capable of imaging the neural connections in the brain. The proposed magnetometer will realize the simple quantum limit (SQL) of the ferromagnetic resonance (FMR) of a “YIG” oscillator and/or spin-torque nano-oscillators (STNO) using a phase-locked loop (PLL) synchronized to a quartz clock. This micro-to-nano-metric technology is comparable with silicon integrated circuits and promises a “laboratory on a chip” approach to MEG that permits millions of detectors to be used. The design is aimed at reducing the massive magnetic screening associated with the usual superconducting quantum interference devices (SQUID) or optically pumped magnetometers (OPM).

U uvodu je utvrđeno da oduvijek vrijeme mjerimo koristeći se periodom nekog stabilnog fizikalnog sistema. U prvom dijelu sadržaja obrađujući temu perioda mehaničkog sata preko osnovnih teorema napetosti, naprezanja i općenito klasične mehanike te rješavajući problem pobuđenog harmonijskog oscilatora s pravokutnim pulsom vidimo kako su realni problemi oblikovali fizikalnu teoriju i koliko su zahtjevni. U drugom djelu sadržaja obrađujući temu perioda pizoelektrika u kvarcnom satu preko osnovnih teorema napetosti, naprezanja i općenito klasične elektrodinamike vidimo kako uspostavljamo analogije s sistemima čija su nam teorijska rješenja već poznata, odnosno proces stvaranja spoznaje inverzan onom u prvom dijelu sadržaja. Zaključak omogućava kritički osvrt studentu na proučeno i sadašnji trenutak., It is established in the introduction that we have always measured time using the period of some stable physical system. In the first part of the content dealing with the topic of the mechanical clock period through basic theorems of tension, stress and classical mechanics in general and solving the problem of excited harmonic oscillator with rectangular pulse we see how real problems have shaped physical theory and how demanding they are. In the second part of the content, dealing with the topic of the period of piezoelectrics in the quartz clock through the basic theorems of voltage, stress and classical electrodynamics in general, we see how to establish analogies with systems whose theoretical solutions are already known. The conclusion allows the student a critical review of what has been studied and the present moment.

Gravity field measurement by free-falling atoms has the potential for very high stabilityover time as the measurement exposes a direct, fundamental relationship between massand acceleration. However, the measurement rate of the current state-of-the-art limitsthe performance at short timescales (greater than 1 Hz). Classical inertial sensors operateat much faster response times and are thus natural companions for free-falling atomsensors. Such a hybrid device would gain the ultra-high stability of the free-falling atomsensor while greatly extending the bandwidth to higher frequency using the classicalsensor. This requires the stable bandwidth of both devices to overlap sufficiently. Wehave developed opto-mechanical inertial sensors (OMIS) with good long term stability forjust this purpose. The sensors are made of highly stable fused silica material, feature amonolithic optical cavity for displacement readout, and utilize a laser diode stabilized toa molecular reference. With no temperature control and only the thermal shieldingprovided by the vacuum chamber, this device is stable down to 0.1 Hz which overlapswith the bandwidth of free-falling atom sensors. The OMIS are self-calibrating byconverting the fundamental resonances of a molecular gas into length using thefree-spectral range of the optical cavity, FSR = c/2nL, and then sampling the OMISmechanical damping rate and resonance frequency using a nearby piezo. Thisacceleration calibration is potentially transferable to a companion free-falling atomsensor. Readout is performed by modulating the cavity length of the OMIS with onecavity mirror being the OMIS itself and the other being a high frequency resonator. Thehigh frequency resonator is driven by a nearby piezo well above the response rate of theOMIS and acts like an ultrastable quartz clock. The resulting highly stable tone isdemodulated by the readout electronics. For the low finesse optical cavity used here, thisyields a displacement resolution of 2x10-13 m/√Hz and a high frequency accelerationresolution of 400 ng /√Hz. At 0.1 Hz the acceleration resolution is 1.5 μg /√Hz limited bythe stability of our vibration isolation stage. The OMIS dimensions are about 30 mm x 30mm x 5 mm and can be fiber coupled to enable co-location with other sensors or asstandalone devices for future gravimetry both on Earth and in space

In early 2017, researchers managed to slip a flexible sliver of polymer next to a pig’s heart. The device—placed between the heart and the fibrous wall that encases it, called the pericardium—squished and expanded with each contraction. It also converted the physical strain of its movement into electrical energy stashed into a capacitor. When hooked up to a commercial pacemaker, the device produced a steady pulse of 130 beats per minute—effectively using the heart’s own mechanical motions to power an implanted pacemaker. Devices such as this one, being tested here on a bovine heart, could harvest the body’s own energy to work like a pacemaker. Image credit: Canan Dagdeviren (Massachusetts Institute of Technology, Cambridge, MA). The study, led by materials scientist Zhong Lin Wang of the Georgia Institute of Technology in Atlanta, demonstrated how self-powered electronics could lead to a new generation of smaller pacemakers and other implanted devices that improve safety and performance, last longer, and obviate the need for invasive battery-replacement surgeries (1). Wang and several other researchers envision a world in which batteries are a thing of the past: deep-brain implants powered by electric impulses, cochlear implants fueled by inner ear vibrations, bone implants that stimulate tissue repair, and shoes and clothes that turn every bodily movement into a source of power. When solid materials, such as some ceramics, crystals, proteins, or bone, are pulled or stretched, charged particles in their crystal structure are dislodged, creating a flow of ions—and thus, an electric current known as piezoelectricity. This ability to convert mechanical energy to electricity has been known for centuries; one of its most famous applications was in developing piezoelectric sonar transducers to detect submarines during World War I. Piezoelectric materials are now widely used in cigarette lighters, quartz watches, and more. But while studying the potential …

Seafloor pressure gauges are used in marine geodesy to detect vertical displacement of the seafloor. Instrumental gauge drift is often larger than the sought after geophysical and oceanographic signals. We performed a 12 month laboratory test on two new methods that aim to reduce pressure gauge drift in Paroscientific Digiquartz and other pressure transducers. In one method, a reference quartz oscillator (RQO) is installed adjacent to but isolated from the Bourdon tube whose stress is measured by a vibrating quartz force transducer. In another method, the pressure gauge is periodically connected to accurately measured atmospheric pressure as a reference to allow drift calculation. We found that the RQO is not a good predictor of gauge drift. However, determining drift by periodic exposure to atmospheric pressure is effective. These drift estimates were compared to estimates determined with an absolute piston gauge calibrator; the average difference between drift rates of the two methods is 0.00 ± 0.05 kPa/year. Finally, we tested the stability of the quartz clocks used in the Paroscientific electronics and found that they are not a significant contributor to drift.

International audience; Wireless Sensors Networks (WSN) are more and more used in structural health monitoringapplications since they represent a less expensive and non-invasive way to monitorinfrastructures. Most of these applications work by merging or comparing data fromseveral sensors located across the structure. These data often comprise measurementsof physicals phenomenons evolving with time, such as acceleration and temperature.To merge or compare time-dependent data from different sensors they need to be synchronizedso all the samples are time-stamped with the same time reference. An initialsynchronization of the sensors is needed because sensors are independent and thereforecan not be all started at the same time. Subsequent re-synchronizations are also neededsince the sensors keep track of time using their imperfect local clock. A quartz clock willdrift in time due to the sensitivity of the quartz oscillator to its environmental conditions ;thus, synchronization accuracy depends on the quality of the oscillator, environmentalconditions, re-synchronization frequency and time reference quality. The required accuracyof the synchronization depends on applications, for instance, one needs millisecondaccuracy to analyze vibration data, microsecond for acoustic data and nanosecond totime-stamp electromagnetic propagation. Sensors can be synchronized by exchangingtiming information as in the RBS [1], TPSN [2] and FTSP [3] protocols or through anexternal timing reference such as the PPS signal transmitted by the GPS as in [4] and [5].While the first option might be less power hungry, our work in this paper focus on thesecond option as it allows for a better synchronization accuracy. This paper presents asmart-sensor able of time-stamping samples as well as measuring its clock offset andfrequency from a noisy PPS signal. We implemented it on an FPGA to get high speedcounters without software overhead.We then used a Kalman filter to track the offset withmore accuracy and to adjust the sample time-stamps of the sensors. This work is aimingat having the highest time accuracy as possible while minimizing its consequence onsensor power-consumption.

There has been an increasing demand for smart devices and smart furniture for home automation, monitoring, and security applications. In this paper, we present a novel method of integrating the function of wireless energy harvesting from ambient RF signals to a conventional quartz clock for home applications. The most attractive feature is that the clock itself is used as the power receiving device, thus no additional antennas are needed. A simple rectifier is designed to directly match with the clock antenna and rectify the power captured by the clock. As a design example, a clock rectenna using the proposed new idea achieves good energy conversion efficiency (up to 65%) over its operating frequency bands at around 1.4-1.5, 1.9-2.1, and 2.4-2.8 GHz, respectively. Moreover, a wireless environmental sensor is integrated with the clock and powered by using the harvested power from the proposed clock rectenna. This novel design greatly expands the functionality of the quartz clock without affecting its size and appearance. We believe that the proposed energy harvesting quartz clock could be adopted for smart home applications. This work was supported in part by the EPSRC, U.K., and in part by the Spanish Ministry of Education, Culture and Sport under a grant for predoctoral contracts for the University Teacher Training (FPU). The work of A. Lopez-Yela was supported by the University Carlos III of Madrid (UC3M) Scholarship for predoctoral students. Publicado

The quartz clock, the first to replace the pendulum as the time standard and later a ubiquitous and highly influential technology, originated in research on means for determining frequency for the needs of telecommunication and the interests of its users. This article shows that a few groups in the US, Britain, Italy and the Netherlands developed technologies that enabled the construction of the new clock in 1927-28. To coordinate complex and large communication networks, the monopolistic American Telephone and Telegraph Company, and national laboratories needed to determine and maintain a common 'standard' frequency measurement unit. Exploiting novel piezoelectric quartz methods and valve electronics techniques, researchers in these organizations constructed a new crystal-based frequency standard. To ensure its accuracy they compared it to an accepted absolute standard - an astronomical clock, constructing thereby the first quartz clock. Other groups, however, had different, though connected, technological aims, which originated from the diverse interests of the industrial, governmental and academic institutes to which they belonged, and for which they needed to measure, control and manipulate with frequencies of electric oscillations. The present article suggests a comparative examination of the research and development paths of these groups on their incentives, the technological and scientific resources they utilized, and the kind of research carried out in the various institutional settings.

In global navigation satellite systems (GNSS) navigation the receiver and satellite clocks play a key role. The receivers are usually equipped with inaccurate quartz clocks, which experiment large drift relative to system time and consequently offset growing very fast; receiver manufactures bound the magnitude of the receiver clock offset to prevent it becomes too large and the actual bounding procedures vary from one manufacturer to another. The most common approach consists of introducing discrete jumps when the offset exceeds a threshold (usually 1 ms). This method is common in low-cost GNSS receivers and influences several applications as differential positioning, cycle-slip detection, precise point positioning technique, absolute positioning with Kalman filter. In this work some techniques to detect and account for millisecond clock jump, suitable for code positioning of a single receiver with Kalman filter, are proposed. Two deterministic algorithms to detect receiver clock jumps are shown: in measurement and parameter domain. The technique in measurement domain uses current pseudorange measurements compared with pseudorange and Doppler measurements at previous epoch; the technique in parameter domain compares current and previous least squares estimations of receiver clock bias, considering the clock drift. Two different approaches are described to account for the clock jumps, once detected, a deterministic one, consisting of fixing the pseudorange discontinuities, and a statistic one, consisting of suitably varying the Kalman filter settings. A static GNSS data set is processed with and without the proposed algorithms to demonstrate their efficiency.

The increased interest of the public in UTC and the leap second demands popular explanations on its background, practice, and future. This paper gives some hints on how to talk about this matter to different audiences and to journalists. It concentrates on the following topics: 1. Background: Explaining the difference between the slow increase of the length of day (LOD) with time on the one hand and the rather large frequency of leap seconds on the other hand 2. Prospects: The future of the time system with and without leap seconds 3. History: The end of the Earth as the most precise clock around 1935

Based on digital speckle temporal sequence correlation and speckle projection, an experimental platform was developed to measure the dynamic 3D shape measurement in this paper. Speckle patterns generated by computer were projected onto the quartz clock surface by a white-light projector, and the deformed speckle patterns were acquired by a camera. Programming was written to implement the algorithm to reconstruct every motion of the running clock's pointers. Beyond that, a simple Newton's cradle was established, and the collision course between three steel balls was reconstructed. These experimental results show that the method can be used for dynamic 3D shape measurement, which has an effect on the reconstruction of objects with characteristics of steep variation, isolation and small details.

Quartz clocks are the most common timekeepers of all. Billions of quartz oscillators are manufactured annually for use inside clocks, watches, mobile phones, computers, radios, and televisions. In this article, Part 2 of a five-part series, I discuss the evolution of quartz clocks, beginning with the discovery of piezoelectricity.

The determination of the astronomical azimuth of a line is not a difficult task for surveyors any more. The aim of this paper is to analyze the theoretical details and errors in order to propose the use of ordinary total stations, for an easy, efficient and accurate determination of the astronomical azimuth of a line by the hour angle method via Polaris sightings. As many modern total stations have a built – in quartz clock they can register automatically the UTC time as well as the angle measurements (horizontal and zenith) of each observation. The total fieldwork time needed is about 10 minutes and the accuracy that may be achieved is about ± 2". This procedure will be proven to be easier than the determination of the geodetic azimuth of the same line. The calculation is independent and the result is free of the errors that the coordinates of a survey mark may contain, because they are not used. However good positional data is required from other sources. Astronomical azimuths are an alternative...

The T2L2 experiment (Time Transfer by Laser Link), on-board Jason-2, with an orbit at 1335 km, since June 2008 allows the clock synchronization between ground clock (generally H-maser) and space clock (quartz Ultra Stable Oscillator (USO) DORIS) with a stability of a few picoseconds over 100 seconds. In common view, when two laser stations see T2L2, the time transfer stability is less than 10 picosecondes over few seconds. In order to perform non-common view time transfer for synchronizing distant ground clocks, it is important to precisely characterize the on-board oscillator at least on 10,000 seconds (maximal flight time between two distant stations). The key is to study the space environment on the Jason-2 orbit, to separate deterministic and stochastic behaviors of the USO (shift and drift). We show that T2L2 is able to provide accurate frequencies, which are deduced from the ground to space time transfer over each laser station (few 10−13). Since 2008, these time transfers helped us to create an on-board frequency data base. The major contributors to these frequency variations on 10,000 seconds are temperature and space radiation especially due to the South Atlantic Anomaly (SAA) (in which Jason-2 pass through). Aging can be considered as a linear drift during 10,000 seconds and the effect of radiation like a very small shift over each SAA overflight. The effect of the temperature is drived by the on-board temperature measurement. A model is realized to represent these effects on USO with a RMS of few 10−13 over 10,000 seconds. Space phenomena are also playing an important role in long term. Actually, if we consider both accumulation dose received by radiation and aging, we can explain 99.9 % of the global frequency variation of the USO since the beginning of the T2L2 mission.

An automatic power-generating system (AGS) which converts kinetic energy into electric energy for quartz watches was tested as a power source for implantable cardiac pacemakers. An automatic power-generating mechanism and a capacitor (0.33 F) were removed from a quartz watch (SEIKO) and encapsulated in a polyvinyl case. Characteristics of the AGS were investigated by acceleration equipment. The capacitor in the AGS was charged to 2.0 V (0.66 J) by placing it on the equipment for about 30 minutes. The equipment has a 2 Hz cycle and generates +/- 1.7 G at the end of each half cycle. The AGS (fully charged to 2.0 V) was used as the power source for a pulse generator circuit built using commercially available CMOS IC. The circuit generated pulses of 0.5 ms width at 1 Hz (60 pulses min-1). The voltage of the AGS was maintained at 1.6 V while it was being charged by the accelerations. The generator supplied pulses of 0.75 V, 1.47 mA through a 510 omega load. With fully charged AGS, the generator was also used to pace a mongrel dog's heart at 140 beats min-1 for 60 minutes. During pacing, the AGS supplied 420 mJ to the circuit and the cardiac muscle. The AGS was placed on the right ventricular wall of the mongrel dog under anaesthesia. Energy of 80 mJ is stored in a capacitor by the heart beating at about 200 beats/min for 30 minutes. Thus the AGS generated 13 microJ per heart beat. This result suggests that the AGS may supply enough energy for use in a cardiac pacemaker.

An up to now unknown high “inner time precision” in isocratic gas chromatography (GC) and high pressure column liquid chromatography (HPLC) has been realized using quartz clock driven A/D converters and special statistically evaluating integration software. This millisecond level inner time precision is detectable by two very linear data correlations: a) the log of adjusted retention times (log(t R′)) versus the molecular weight of separated members of homologues and b) the peak width at half height versus correct k-values of the homologues. The inner time precision at the millisecond level is not lost by slight errors (up to seconds) in the starting times of GC or HPLC determinations. The correlation coefficient of the two linear data correlations allows a thorough analysis of instrument quality. The highly linear correlation of peak width and k in a wide range of mobile phase speeds is in disagreement with theoretical models of chromatography. Especially the rule of variance additivity is not valid in isocratic elution chromatography.

This paper presents the working prototype of a composite clock. This apparatus combines the stability of several references clocks for different duration. A voltage-controlled quartz oscillator is driven by a hydrogen maser clock for mid-term stability and by a cesium atomic clock for long-term stability. The best clock stability at a given averaging time is transfered to the VCO by a special control system using two comands.

A high resolution, digitally tuned quartz oscillator with excellent phase noise and temperature stability has been developed for space applications and is being utilized in the Iridium NEXT constellation, the largest commercial satellite constellation in the world. Significant effort has been expanded to optimize the quartz resonator design, the double oven circuitry and the digital tuning scheme. The oscillator is implemented using readily available space qualified parts.

Electronic systems are systems comprising electronic devices, circuits and components which are designed to accomplish certain complex functions. Examples are cell phones, computers, electronic music systems like MP3 players, anti-lock braking systems (ABS), quartz watches, implantable cardiac pacemakers, and many others. Usually, electronic systems do not contain only electronic components like integrated circuits but also mechanical, optical and other ones providing functionalities far beyond of pure electronic devices. An often used term for such miniaturised systems is micro- or nano-opto-electro-mechanical systems (NOEMS, MOEMS or simply nano- or microsystems). To accomplish the complex functions of such systems packaging has to integrate the function components into a working system, has to maintain these system functions independently of ambient and operating conditions, and has to couple the system to its environment, e.g. the operator or costumer of the system.

Supported by the natural potential difference between anoxic sediment and oxic seawater, benthic microbial fuel cells (BMFCs) promise to be ideal power sources for certain low-power marine sensors and communication devices. In this study a chambered BMFC with a 0.25 m(2) footprint was used to power an acoustic modem interfaced with an oceanographic sensor that measures dissolved oxygen and temperature. The experiment was conducted in Yaquina Bay, Oregon over 50 days. Several improvements were made in the BMFC design and power management system based on lessons learned from earlier prototypes. The energy was harvested by a dynamic gain charge pump circuit that maintains a desired point on the BMFC's power curve and stores the energy in a 200 F supercapacitor. The system also used an ultralow power microcontroller and quartz clock to read the oxygen/temperature sensor hourly, store data with a time stamp, and perform daily polarizations. Data records were transmitted to the surface by the acoustic modem every 1-5 days after receiving an acoustic prompt from a surface hydrophone. After jump-starting energy production with supplemental macroalgae placed in the BMFC's anode chamber, the average power density of the BMFC adjusted to 44 mW/m(2) of seafloor area which is better than past demonstrations at this site. The highest power density was 158 mW/m(2), and the useful energy produced and stored was ≥ 1.7 times the energy required to operate the system.

An essential component of any space vehicle is the onboard master oscillator. The proper operation of the entire payload is dependent on the performance of the master oscillator (or onboard clock). One of the major concerns for quartz clocks in space is the effect of space radiation. Quartz is inherently sensitive to naturally occurring radiation in space. The exact nature of the radiation experienced in space is a function of the orbital dynamics of each particular application, and the impact of that radiation on quartz oscillator performance depends on each particular mission's requirements. Extensive tests on Earth have revealed some very interesting results that can be used to predict performance in space. This has made possible the development of a radiation compensated quartz crystal oscillator, with improved frequency aging performance. The frequency aging rate is extremely important for predicting the expected performance of these oscillators after 10 or 15 years in space. In this paper we will present data on the effects of oscillator aging-rate performance when subject to some commonly encountered space radiation environments.

This chapter contains sections titled: Introduction The Concept of a Slip Aligners for Terminating Digital Links Timing Impairments: Jitter and Wander Impact of Slips Network Performance Objectives for Slip Control Parameters Linked to Clock Behavior Atomic and Quartz Clocks Synchronization Methods Primary Reference Source (PRS) PRS Implementation in Telecommunication Networks Synchronization Equipment at Slave Nodes Specification of Slave Clocks Jitter and Wander Specifications for Digital Networks Wander Model for the Synchronized Network Remarks This chapter contains sections titled: References

Enhancing the positioning precision is the primary pursuit of global positioning system (GPS) users. To achieve this goal, most studies have focused on the relationship between GPS receiver clock errors and GPS positioning precision. This study utilizes undifferentiated phase data to calculate GPS clock errors and to compare with the frequency of cesium clock directly, to verify estimated clock errors by the method used in this paper. The frequency stability calculated from this paper (the indirect method) and measured from the National Standard Time and Frequency Laboratory (NSTFL) of Taiwan (the direct method) match to 1.5 × 10 −12 (the value from this study was smaller than that from NSTFL), suggesting that the proposed technique has reached a certain level of quality. The built-in quartz clocks in the GPS receivers yield relative frequency offsets that are 3‐4 orders higher than those of rubidium clocks. The frequency stability of the quartz clocks is on average two orders worse than that of the rubidium clock. Using the rubidium clock instead of the quartz clock, the horizontal and vertical positioning accuracies were improved by 26‐78% (0.6‐3.6 mm) and 20‐34% (1.3‐3.0 mm), respectively, for a short baseline. These improvements are 7‐25% (0.3‐1.7 mm) and 11% (1.7 mm) for a long baseline. Our experiments show that the frequency stability of the clock, rather than relative frequency offset, is the governing factor of positioning accuracy.

The evolution of various fields of science, technology, trade or legal metrology is intimately connected with the ability to relate measurements with each other that were performed at different places and different instants of time. For this purpose a practical system of units of measurement i.e. the International System of Units (SI) has been established by international cooperation [1]. In this SI, the metre and the second represent the base units of length and time, respectively. From all units these two can be realized with by far the highest accuracy since they are based on frequency measurements and most accurate clocks. In contrast to clocks based on mechanical properties of macroscopic bodies, e.g., pendulum clocks, quartz clocks or pulsars, the frequency reference for a suitable oscillator in atomic clocks is mainly determined by the intrinsic properties of suitable absorbers like atoms, molecules or ions. These atomic properties are determined by fundamental constants resulting from the basic interactions between the elementary constituents of matter. Following the generally accepted idea that the properties of each atomic absorber of a selected species are the same, identical clocks can be set up in any desired number and at any desired place.

Fivefold decrease of RMS jitter of 1 pps pulse from GPS receiver after SA switch-off and relatively short period required to filter it out has enabled the construction of GPS synchronized frequency sources of parameters almost order of magnitude better than with SA. New design challenge has been to achieve 10-11 frequency accuracy over time period of 1000 seconds. Basic block diagram of GPS disciplined frequency source is presented in fig 1. The only non purely digital blocks of the source are quartz oscillator and digital to analog converter D/A and their specs decide about the parameters of the output frequency signal. Design requirements for internal quartz oscillator as well as digital to analog converter based on required minimal frequency control loop time of about 10000 seconds have been derived and presented. To summarize, quartz oscillator has to exhibit aging not worse than 3 • 10-11/24h and temperature coefficient 1•10-12/°C while digital to analog converter has to be an 18-bit device with 1 LSB differential nonlinearity and extremely low temperature coefficient. Alternately as devices with very low temperature drift are very expensive, the converter can take its reference voltage from the oscillator, where the reference source is temperature stabilized. This of course places higher demands on the oscillator voltage reference source.© (2004) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.

Space programs requiring precision time-keeping and stable frequency generation have been fitted with atomic frequency standards and super-stable quartz oscillators. However, the challenge has been to predict the clock performance in space based on tests conducted on Earth. This paper focuses on the actual performance of rubidium atomic frequency standards and quartz oscillators in space, and demonstrates that the performance in space is predictable from modeling and tests carried out on Earth. Actual test data obtained on Earth as well as data from space are presented. Aging performance and the effects of natural radiation are addressed. Data are presented from a space-based rubidium clock, designed and manufactured by Frequency Electronics, Inc., that is achieving fractional-frequency aging rates of 3 /spl times/ 10/sup -14//day and long-term Allan deviation of 1 /spl times/ 10/sup -15//spl radic/t, and similarly, quartz clocks that are realizing aging rates of 1-2 /spl times/ 10/sup -12//day and long-term Allan deviation of 1.6 /spl times/ 10/sup -14//spl radic/t. Furthermore, the paper also addresses performance in the presence of solar flares and other space phenomena.

Low-power timekeeping methods have been developed that provide improved accuracy over the full military temperature range. These methods provide tradeoffs of accuracy vs. power consumption dependent upon the application. The system achieves this performance by using a microcomputer-compensated crystal oscillator (MCXO) to periodically update a low-power oscillator clock system. This technique does not substantially increase the power dissipation because the MCSO is turned on for only a few seconds each time to recalibrate the clock oscillator frequency. Using this technique, a clock oscillator of +or-5*10/sup -6/ over the temperature range can be made to approach the +or-*10/sup -8/ accuracy of the MCXO. >

The behaviour of the steered quartz clock of the ”BlackJack” GPS receiver on-board CHAMP is characterized. The receiver clock estimates from onground orbit determination and clock offsets as reported within the CHAMP navigation solution are presented, compared, and discussed. No long term trend can be detected in the first 20 months of the mission. In the short term the clock estimates oscillate at orbital frequencies and at standard deviations around the μs.

Previous developments on a 2.1MHz quartz have demonstrated that thermal, ageing and shock performances are improved by at least one order of magnitude compared to a 32kHz quartz. The temperature behavior is a flat cubic function, and therefore positive and negative deviations with respect to the reference temperature are compensated. A field test on 20 watch samples containing an oscillator built around this quartz showed that over a 3-year period, the maximum deviation is less than 3 seconds/year. Note that these results are obtained without any temperature compensation scheme. As the power consumption of a 2.1 MHz quartz oscillator (2.3/spl mu/A) is not compatible with the power consumption of standard watch oscillator circuits ( >

An automatic power generating system developed for quartz watches was tested as a power source for implantable cardiac pacemakers. An automatic power generating mechanism and a capacitor (0.33 F) were taken out of a quartz watch and encapsulated in a polyvinyl case (AGS). Characteristics of the AGS were investigated by reciprocating equipment (2 Hz). The capacitor in the AGS was charged to 2.0 V (0.66 J) by placing it on the equipment for about 30 minutes. The AGS. which was charged, to 2.0 V was used as a power source for a pulse generator circuit that was made by the commercially available CMOS IC. The pulse generator supplied pulses of 0.5 msec width through a 510 /spl Omega/ load at 1 Hz (60 bpm). The voltage of the AGS was maintained at 1.6 V while it was being charged by the reciprocations. The pulse generator supplies a pulse of 0.75 V, 1.47 mA through a 510 /spl Omega/ load. The AGS, which was placed on the wall of the right ventricle in a mongrel dog under anesthesia, stored 80 mJ in a capacitor at about 200 bpm during 30 minutes.

A crystal oscillator is described that uses various unusual techniques to achieve double-oven class temperature stability with a single oven. Stability of better than 1 part in 10/sup 11/ over a temperature range of -40/spl deg/ to +85/spl deg/ C has been demonstrated. The use of the single stage oven allows for a form factor with a relatively low height (19 mm. or 3/4 inch) for an oscillator of this performance class. The low profile facilitates card-based designs. In timekeeping applications such as wireless and telecom synchronization, the temperature coefficient of frequency (tempco) is more important than ever. The temperature extremes involved in wireless base stations increase the error due to temperature while the use of GPS timing receivers to discipline quartz oscillators greatly reduces the error due to aging, leaving tempco as the major component. Numerous design innovations are described such as a hermetic oven mass assembly and a non-ovenized digital temperature controller. This controller permits automated optimization of the oven set point and thermal gain. An overview of a novel zero-gradient oven technique used to achieve the double-oven performance is given, with more details in a related paper. Frequency pulling due to the oscillator circuit components is greatly reduced by a novel balanced-bridge controlled oscillator circuit that is described briefly here and in more detail in another related paper.

Publisher Summary This chapter discusses the frequency control devices. Frequency control devices provide the precise time and frequency on which modem electronics depends. A vibrating quartz crystal, i.e., a quartz resonator, is the "heart" of nearly all frequency control devices. Quartz clocks provide accurate time and quartz oscillators are the sources of precise frequency. Time is important not only for the daily schedules of human beings, but also, for example, for determining the sequence of events that take place inside computers, and for time-tagging the information that flows through communication systems. Frequency sources are essential for determining the frequencies of radio and TV transmissions, radar systems, communication and navigation systems, etc. Frequency control technology took a great leap forward in the 1920s when quartz was first utilized to realize crystal resonators for the stabilization of oscillators, thereby launching the field of modem frequency control. With the introduction of quartz control, timekeeping moved from the sun and stars to small, man-made sources that exceeded astronomy-based references in stability.

While the standard quartz watch maybe less expensive, engineers still prefer to use atomic clocks because of the many advantages they offer. A good example is the new atomic clock that operates using a radio signal linked to the atomic standard. Its core is the size of a grain of rice, i.e. chip-scale, because it is made with standard microelectronic manufacturing techniques. The chip-scale clock uses some of the same principles as the standards institute's primary clock, which is about the size of a compact automobile. In both, electromagnetic radiation causes cesium atoms in a vapor, which is enclosed in a cell, to oscillate at a stable frequency. In the primary clock, the radiation is a microwave field, while in the chip-scale clock it is pulses of infrared light from a laser, and everything but the vapor is solid state. The chip-scale clock is a work in progress but researchers have built a physics package, which contains the enclosure for the cesium atoms, the laser, the optics and the photodiodes.

Double ultrasonic beam acousto-optical modulators require high precision driving electric signals for stable control of frequency ratio and phase shift. The high precision digital synthesis method has been developed for the generation of high quality periodic signals. Maximum frequency range of synthesized waveforms is determined by the speed of available random access memory (RAM) and an available D/A converter. A computer-based digital function generator can generate any arbitrary type of signal in the frequency range determined by the speed of RAM and the D/A converter. Frequency stability is determined by the quartz clock of the D/A converter and is in the order of 1/107. Periodic waveforms can be synthesized, stored, and then played continuously by looping through the RAM buffer.© (1992) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.

Celestial and Mechanical Clocks.- Oscillations and Fourier Analysis.- Oscillators.- Quartz Clocks.- The Language of Electrons, Atoms, and Quanta.- Magnetic Resonance.- Corrections to Observed Atomic Resonance.- The Rubidium Clock.- The Classical Cesium Standard.- Atomic and Molecular Oscillators.- The Hydrogen Maser.- The Confinement of Ions.- The NASA Mercury Ion Experiment.- Optical Frequency Oscillators: Lasers.- Laser Cooling of Atoms and Ions.- Application of Lasers to Microwave Standards.- Measurement of Optical Frequency.- Applications: Time-Based Navigation.- Concluding Thoughts.

Cardiac pacemakers and quartz watches both contain CMOS circuits, and it is known that any solid state circuit can be damaged both by radiation and by strong electro-magnetic fields, but are they likely to be affected by diagnostic or therapeutic X-rays? This is a question not infrequently asked by the radiotherapist of the physicist or the patient of the radiographer.

An inexpensive, high capacity counting device has been made for time analysis of light pulses by time-amplitude conversion. In order to allow for particularly long storage times, it has two channels with a capacity of 10 12 pulses. The result is protected from power cuts. The total recording time is measured by a quartz clock.

Quartz resonators have been adapted for communications, but in recent years mostly for wristwatches and clocks, since the quartz-oscillator circuit which incorporates a piezoelectric quartz crystal resonator has a very stable frequency. Thanks to quartz resonators, time accuracy of wristwatches has been improved rapidly. Quartz resonators for wristwatches and clocks amount to over 60% of total quartz resonators manufactured in Japan. This paper touches upon the characteristics, details of technical advancement, the analysis methods, the manufacturing technique and finally the future trend of quartz resonators for wristwatches.

A description is given of a time-to-digital converter with 2 ns time resolution and 130 ns dead time. A 125 MHz quartz clock and a cable interpolator provide the base time. Non-conventional gating circuitry has been implemented to successfully eliminate the 'odd and even' effect.

Suitably cut quartz crystals exhibit a temperature dependent resonance frequency. This can be used for a fully digital temperature measurement system. Various properties of several mass producted sensor quartzes have been measured over the temperature range −25°C to 75°C, including temperature coefficient, non-linearity, reproducibility and influence of lead temperature. A single conventional circuit for analog quartz clocks is used as an oscillator, divider and as a noise-immune two-wire digital transmission system. The supply current is modulated with a factor of > 100 in temperature-dependent time intervals of approximately 1 s. This technique is especially suitable for microprocessors with an internal counter. With single poiny calibration, system accuracies are in the range 10 mK– 100 mK.

The author describes the principles of an approach to video recording that does not use electromechanical components. The basis of the method is that analog modulation, after being converted to digital modulation, is photographically recorded on a film or transparency (square or rectangular), using the principle of matrix scanning. The speed of the scanning is determined by the characteristics of the matrix, type of digital coding, and the length of the recording and is controlled by an electronic clock, such as a quartz clock. The problems raised by this approach are discussed. >

The construction, operation, and testing of the standard are described. The resonance employed is that due to the hyperfine splitting of caesium, having a frequency of approximately 9192 Mc/s. The transitions between the two atomic states F, m f (4,0) and F, m F (3, 0) are detected in an atomic-beam chamber, in which the length of the transition region is 47 cm, giving a width of resonance, at half deflexion, of 350 cycles, and a standard deviation of setting to the peak of the resonance of ± l c/s . It is shown that the geometrical parameters of the beam chamber such as slit widths, alinement of the beam, and shape of the pole-pieces of the deflecting magnets are relatively unimportant, and that other parameters, including the pressure in the beam chamber, the temperature of the oven, from which the caesium atoms are evaporated, and the radio-frequency power exciting the transitions can be varied throughout wide limits without causing changes in resonant frequency exceeding 1 part in 10 10 . A unidirectional magnetic field is applied over the transition region to remove the field-dependent resonant lines of the Zeeman pattern from the central line which depends on the field to only a second-order extent. It has been found that a satisfactory resonance is obtained with a field as low as 0.05 Oe at which the total effect of the field on the frequency is only 1 c/s. The dependence of the frequency on the phase conditions in the two-cavity resonators carrying the exciting field is studied, and it is concluded that the phases can be made sufficiently close to enable the frequency to be defined with a precision of ± 1 part in 10 10 . The resonator is used as a passive instrument to calibrate the quartz clocks, usually at intervals of a few days; and it is estimated that the clocks calibrated in this way provide at all times the atomic unit of frequency and time interval with a standard deviation of ± 2 parts in 10 10 . The quartz clocks are also calibrated in terms of astronomical time and the results are compared for the period from June 1955 to June 1956. For operational purposes the frequency of the resonance was taken as 9 192 631 830 c/s which was the value obtained in terms of the unit of uniform astronomical time made available by the Royal Greenwich Observatory in June 1955. The value is being determined in terms of the second of ephemeris time, which has now been adopted by the International Committee of Weights and Measures as the unit of time, but to obtain the accuracy required the comparison must be extended over a long interval in view of the difficulties associated with the astronomical measurements.

A theoretical analysis is given of the effects of random noise in various types of electronic clocks. Leaving aside the amplitude noise problems, the study concentrates on "linewidth" problems and analyzes the difference between quartz clocks and quantum devices. It covers the following main points: choice of the best scheme for tube clocks; nonlinear theory of thermal noise; non-linear theory of flicker noise; immunity of Robinson's oscillator to flicker noise. The analysis gives some hope that tube quartz clocks may be built with as high a linewidth quality as atomic clocks.

In a conventional β-γ coincidence counting system, the partially correlated β and γ series of pulses with their associated chain dead times, (τ β , τ γ ), gives place to an overlapping process on the coincidence channel, whose transmission factor φ ( A 0 , τ β , τ γ ) becomes poorly defined for the general case. In this context, the “Shared-Dead-Time” (SDT) system has been conceived to impose a total time correlation between both chains blocking intervals by inserting simultaneously a common dead-time from a single paralysis generator which is triggered by the pooled counting pulses. As a result, identical transmission factors are obtained for the three counting channels. The extra cost in counting losses is well compensated by a good definition of dead-time for coincidences whose two first moments of its interval density get known. A novel dead-time circuit using fast linear gates as blocking elements and post-integration into the paralysis loop is introduced as an option for high count rates. The “SAMAR” instrumentation system incorporates a single “live-time” 1 MHz quartz clock and automatisms. The SDT system has been tested by Muller's two-oscillator method, slightly modified. Preliminary results proved the non-extending character of the new dead-time circuit and the qorking ability of the SDT two-branch loop.

A review is given of the present (1959) seismological stations in Sweden, i.e. Uppsala, Kiruna, Skalstugan, and Goteborg, as well as of older stations, which are no longer in operation, i.e. Vassijaure, Abisko, and Lund, including all pertinent information. The disturbing effect of the loose ground at Lund in distinction from the four first-mentioned stations is clearly demonstrated. The very good ground at Uppsala, Kiruna, Skalstugan, and Goteborg, together with the use of modern equipment of high magnification has made these stations, especially Uppsala and Kiruna, very sensitive. This is obvious from the number of recorded earthquakes. The method of time measurements, including direct recording of time signals, is described, and means to reach a high time accuracy are outlined, including the recommendation to use quartz clocks. Long-period (0.5–2 min) disturbances on the long-period Benioff combinations were mainly due to air currents in the seismometer room and were eliminated by providing the seismometers with special covers. The method of ground amplitude determinations is outlined, especially for the Benioff instruments, and typical magnification curves are given. Comparisons of ground amplitudes from simultaneous records of BenioffE, N and WiechertE, N and of BenioffZ′ and GrenetZ′ have been made. The amplitude comparison between Benioff and Wiechert has given a new estimate of the effect of friction (especially of the recording pen against the paper) in the Wiechert apparatus.