High-Accuracy Ultrasonic Rangefinders via pMUTs Arrays Using Multi-Frequency Continuous Waves

This paper reports a high-accuracy in-air reflective rangefinder via two pieces of 492 kHz 5by5 multipled piezoelectric micromachined ultrasound transducers (pMUTs) array using multi-frequency continuous waves (MFCW). The MFCW-based rangefinder owns high accuracy intrinsically because the distance information is extracted from the phase difference, which can cancel the random noise out in numerous repeating periods. Experiment results show that the 3σ accuracy of the short distance measurement (<100mm) is 0.0711 mm with 0.096 mm/° first-order resolution and 1.934 μm/° second-order resolution, which is 1.8208 mm for long distance measurement (100mm-300mm) with 0.481 mm/° first-order resolution and 1.954 μm/° second-order resolution.

To promote underwater construction, the tools such as underwater robotic manipulator system, underwater vehicles and so on are necessary. Furthermore, these system need an accurate 3D position parameters. If no position information for automatic control system that system is difficult to be operated. Hence, it is important to take position information. Although 3D position camera can offer 3D position parameters, it has still some deviation. In addition, the manipulator system need accurate distance information for fast and accurate operation. Hence, an accurate distance measurement system is necessary for a remotely teleoperated robotic manipulator system for underwater constructions. This paper focus on the distance measurement study to offer a accurate target distance information. The information can combine with 3D position camera to obtain more accurate 3D position parameters to offer a useful position information for underwater constructions, with a remotely teleoperated robotic manipulator system. In this paper, three distance measurement system, includes commercial ultrasonic distance measurement system, fabricated ultrasonic system and a laser distance measurement system is study. The commercial distance measurement system have a distance measurement system rang 8~35 cm, plusmn0.1 cm. However, a short distance measurement is difficult to be measured with the measurement system. On the other side, the fabricated measurement system can measure a short distance. Information from 0~5 cm, accuracy plusmn0.3 cm. The fabricated distance measurement system fabricated with PZT thin film. In this study, a horn is added to improve the accuracy of distance measurement. In addition, the laser distance measurement system, measurement system is used to measure the distance information also in this study. The combination of these distance measurement system to form a multiple range distance measurement can offer a long measurement range for accurate distance measurement underwater. A detailed experiment is to be studied in the future. Furthermore, the distance measurement system has been offered a distance measurement in a remotely teleoperated robotic manipulator system for underwater constructions

The light detection and ranging (LiDAR) system is an emerging photonic technology in various applications such as autonomous vehicles, drones, robots, and high-precision 3D imaging. Since conventional LiDAR has employed mechanical beam-steering, the scanning speed is restricted and more power consumption is required. On the other hand, Silicon optical phased array (Si OPA) is a promising solution that can replace the mechanical scanning LiDAR due to the advantages of electrical scanning, small footprint, and low operating power. In this study, we demonstrated a 10 m distance measurement with Si OPA using the time-of-flight (ToF) method. We developed an optical pulse generator for high distance accuracy measurement utilizing an electrical pulse generator, radio frequency amplifier, diplexer, and distributed feedback laser diode to generate an optical output pulse with a 300 ps pulse width. The Si OPA was fabricated using complementary metal-oxide-semiconductor (CMOS) compatible processes with an 8-inch silicon-on-insulator wafer. Considering Si chip loss and beam-forming efficiency, the erbium-doped fiber amplifier was used at the front end of the input of Si OPA. An avalanche photodiode that has high speed and sensitivity was utilized as a receiver and the converted optical pulse was observed by a real-time oscilloscope. Using this ToF distance measurement platform, we achieved a 10 m distance measurement with a ranging error of 1.2 cm using Si OPA. Si OPA-based distance measurement platform will allow the realization of 3-dimensional image sensing and further improvement will enable high-accuracy long-distance measurement.

Application of neural networks for extraction of distance and reflectance in pulsed laser radar

Hole is the most common symmetrical geometric structure of mechanical parts, and aperture and hole center distance are important measured dimensions in machining. However, existing visual measurement methods often require high equipment installation accuracy and low measurement accuracy. To solve the problem of projection deformation of the measured hole: Firstly, a local coordinate system is created, and the coordinate plane of the coordinate is parallel to the end face of the measured hole. Secondly, a cone is established, the end face of the measured hole is alike to the bottom face of the cone, and the optical center of the camera is the vertex. The space equation of the cone is represented by the coordinates of the center point of the hole. Finally, a cutting plane is established near the imaging plane of the camera, and the intersection line equation between the plane and the cone is obtained, and the diameter of the measured hole and the coordinates of the center of the circle are obtained through the parameters of the intersection line equation. In order to solve the problem of errors in edge points of the hole, geometric constraints based on the center of the circle are used to improve measurement accuracy. This experiment takes the automobile insert mold as the measured part and uses the measurement model of this paper to measure the aperture and hole center distance of the mold. The measurement results show that the measurement accuracy of the aperture is 0.018 mm, the measurement accuracy of the center distance of the hole is 0.05 mm, and the maximum relative error is 2.2%.

The realization of a coherent frequency-modulated continuous-wave LIDAR aimed for the accurate measurement of short distances employing a distributed feedback tunable twin-guide laser diode is demonstrated. Theoretical calculations on the ultimate limits in accuracy of distance measurements as determined by the laser phase noise are carried out. A relative accuracy of 8x 10-5 (8 μm) for a single-shot measurement has been achieved at a distance of 10 cm, which is significantly better than expected from the laser linewidth. The results presented here prove the predictions calculated from theory.

A new phase unwrapping method based on dual-frequency fringe is proposed to improve both high accuracy and large measurement range of three-dimensional shape measurement by synthesizing the projected dual-frequency fringes obtaining higher and lower frequencies. The lower-frequency one is their phase difference, which can help unwrap the wrapped phase of the higher-frequency one from their phase sum. In addition, the relationship between the measuring accuracy and the frequencies of the projected fringes is studied to guide the frequency selection in actual measurement. It is found that the closer the two frequencies are, the higher the measurement accuracy will be. The computer simulation and experiment results show the viability of this method.

Traditional PMUT ultrasonic ranging systems usually possess a large measurement blind area under the integrated transmit–receive mode, dramatically limiting its distance measurement in confined spaces, such as when determining the clearance of large bearing components. Here, a broadband PMUT rangefinder was designed by integrating six types of different cells with adjacent resonant frequencies into an array. Through overlapping and coupling of the bandwidths from the different cells, the proposed PMUTs showed a wide –6 dB fractional bandwidth of 108% in silicon oil. Due to the broadening of bandwidth, the device could obtain the maximum steady state with less excitation (5 cycles versus 14 cycles) and reduce its residual ring-down (ca. 6 μs versus 15 μs) compared with the traditional PMUT array with the same cells, resulting in a small blind area. The pulse–echo ranging experiments demonstrated that the blind area was effectively reduced to 4.4 mm in air or 12.8 mm in silicon oil, and the error was controlled within ±0.3 mm for distance measurements up to 250 mm. In addition, a specific ultrasound signal processing circuit with functions of transmitting, receiving, and processing ultrasonic waves was developed. Combining the processing circuit and PMUT device, the system was applied to determine the axial clearance of the main bearing in a tunneling machine. This work develops broadband PMUTs with a small blind area and high resolution for distance measurement in narrow and confined spaces, opening up a new path for ultrasonic ranging technology.

Most of the traditional distance measurement using electromagnetic waves or electromagnetic pulse time of flight to obtain distance information. It has been widely used in various fields ranging. Accuracy and high resolution can get by the method. Ranging in many occasions does not need high accuracy and resolution. For example, it can reverse radar, blind obstacle avoidance, etc. This paper presents a new distance measuring device that based on infrared light intensity modulation. Moreover the device combine with the fuzzy control theory, so called fuzzy location device based on infrared light intensity modulation. The device includes the infrared modulation transmission unit, collimating unit, infrared receiver unit, background light sensor unit and data processing unit. If alarm distance is n m, data processing unit set infrared light intensity of infrared modulation transmission unit and the light intensity threshold of infrared receiver unit by look-up table with fuzzy control theory. It is according to the current background light intensity. Once the receiving light intensity exceeds the threshold, the system alerts. The paper expounds the working principle, fuzzy control theory on the domain and fuzzy rules domain, the experimental results of the device and analysis in detail. It shows that the device is small, low cost and suitable for a large number of used when it dose not need high accuracy and resolution measurement

This paper presents a dual-frequency piezoelectric micromachined ultrasonic transducer (pMUT) array based on thin ceramic PZT for endoscopic photoacoustic imaging (PAI) applications. With a chip size of 7 × 7 mm2, the pMUT array consists of 256 elements, half of which have a lower resonant frequency of 1.2 MHz and the other half have a higher resonant frequency of 3.4 MHz. Ceramic PZT, with outstanding piezoelectric coefficients, has been successfully thinned down to a thickness of only 4 μ by using wafer bonding and chemical mechanical polishing (CMP) techniques and employed as the piezoelectric layer of the pMUT elements. The diaphragm diameters of the lower-frequency and higher-frequency elements are 220 μm and 120 μm, respectively. The design methodology, multiphysics modeling, fabrication process, and characterization of the pMUTs are presented in detail. The fabricated pMUT array has been fully characterized via electrical, mechanical, and acoustic measurements. The measured maximum responsivities of the lower- and higher- frequency elements reach 110 nm/V and 30 nm/V at their respective resonances. The measured cross-couplings of the lower-frequency elements and higher-frequency elements are about 9% and 5%, respectively. Furthermore, PAI experiments with pencil leads embedded into an agar phantom have been conducted, which clearly shows the advantages of using dual-frequency pMUT arrays to provide comprehensive photoacoustic images with high spatial resolution and large signal-to-noise ratio simultaneously.

Length is one of the fundamental physical quantities and its precise measurement is very important for science and technology. Laser-based distance metrology technique is a powerful tool, which is widely applied in geodetic monitoring, environmental monitoring and precision measurement engineering including in space applications. Since the invention of the optical frequency comb (OFC) at the beginning of this century, it has been used as a versatile tool for many applications, such as frequency metrology, spectroscopy, etc. OFC has played an important role in distance metrology enabling the developed techniques to achieve high accuracy in long distance measurement. In the time domain, OFC is a pulse train, which can measure distance with time of flight method or correlation detection method. In the frequency domain, spectrum of OFC consists of a series of discrete lines with equal frequency difference. Methods of dispersive interferometry, multi-heterodyne interferometry, and multi-wavelength interferometry are the techniques proposed and demonstrated in spectral domain distance metrology. Though distance metrology techniques based on OFC have been developed for tens of years, there are still challenges that need to be overcome. In most applications the measurements are completed in the air, where the results are influenced by refractive index of air. As the OFC is a multi-wavelength laser source, refractive index of air is difficult to determine. The other challenge is complexity and high cost of measurement system. Until now, to my knowledge, there is no commercial rangefinder which is based on OFC. The large size, complex configuration and high price are the bottlenecks restricting OFC’s entrance into industrial applications.

Ultra-wideband (UWB) communication is attracting increased interest for its high-accuracy distance measurements. However, the typical current consumption of tens to hundreds of mA during transmission and reception might make the technology prohibitive to battery-powered devices in the Internet of Things. The IEEE 802.15.4 standard specifies two UWB physical layer interfaces (PHYs), with low- and high-rate pulse repetition (LRP and HRP, respectively). While the LRP PHY allows a more energy-efficient implementation of the UWB transceiver than its HRP counterpart, the question is whether some ranging quality is lost in exchange. We evaluate the trade-off between power and energy consumption, on the one hand, and distance measurement accuracy and precision, on the other hand, using UWB devices developed by Decawave (HRP) and 3db Access (LRP). We find that the distance measurement errors of 3db Access devices have at most 12 cm higher bias and standard deviation in line-of-sight propagation and 2-3 times higher spread in non-line-of-sight scenarios than those of Decawave devices. However, 3db Access chips consume 10 times less power and 125 times less energy per distance measurement than Decawave ones. Since the LRP PHY has an ultra-low energy consumption, it should be preferred over the HRP PHY when energy efficiency is critical, with a small penalty in the ranging performance.

Recently developed methods to measure distances in proteins with high accuracy by "exact" nuclear Overhauser effects (eNOEs) make it possible to determine stereospecific assignments, which are particularly important to fully exploit the accuracy of the eNOE distance measurements. Stereospecific assignments are determined by comparing the eNOE-derived distances to protein structure bundles calculated without stereospecific assignments, or an independently determined crystal structure. The absolute and relative CYANA target function difference upon swapping the stereospecific assignment of a diastereotopic group yields the respective stereospecific assignment. We applied the method to the eNOE data set that has recently been obtained for the third immunoglobulin-binding domain of protein G (GB3). The 884 eNOEs provide relevant data for 47 of the total of 75 diastereotopic groups. Stereospecific assignments could be established for 45 diastereotopic groups (96 %) using the X-ray structure, or for 27 diastereotopic groups (57 %) using structures calculated with the eNOE data set without stereospecific assignments, all of which are in agreement with those determined previously. The latter case is relevant for structure determinations based on eNOEs. The accuracy of the eNOE distance measurements is crucial for making stereospecific assignments because applying the same method to the traditional NOE data set for GB3 with imprecise upper distance bounds yields only 13 correct stereospecific assignments using the X-ray structure or 2 correct stereospecific assignments using NMR structures calculated without stereospecific assignments.

Under the laser tracker measurement of angle subsystem environment,signal acquisition system of laser tracker incremental encoder based on FPGA was designed in this paper. The FPGA in this system was mainly responsible for the encoder signal acquisition, processing, and generating timing signals, data caching mechanism and asynchronous output of the data. This paper detailedly introduced quadrupler frequency, phase discrimination, counting, latches, and UART asynchronous serial port output sub-modules in the process of signal acquisition of FPGA, which was implemented by Verilog HDL language. Online logic analyzer of the Quartus software acquired the value of encoder signal in real time, and the rationality of the design was verified ultimately.

The purpose of this study was to assess the accuracy of distance and volume measurements obtained by three-dimensional ultrasonography. A tissue-mimicking phantom was scanned using a prototype three-dimensional sonographic imaging system to verify distance measurements. Measurements were taken from the reconstructed three-dimensional sonographic data and compared to the real distances. Volume measurements were obtained by scanning 30 balloons of various shapes, sized 23 ml to 2400 ml. Each balloon was scanned twice in two orientations; three different masks were accomplished for each volume. Each volume measurement of 180 three-dimensional sonographic measurements was compared to conventional two-dimensional ultrasonographic volume estimates and to the actual, measured balloon size. Distance measurements had a mean error of 0.02 +/- 3.65% (range, -4.27 to 7.18%). Two-dimensional sonographic volume estimates using traditional scanner based methods had a mean error of 13.7 +/- 10.1%. Three-dimensional sonographic volume measurements had a mean error of 2.2 +/- 2.9% for regular and irregular objects over the entire range of volumes. The masking required 10 to 30 min. The field of view varied from 10 to 24 cm with a mean object depth of 9.8 cm. Three-dimensional ultrasonographic methods can provide accurate volume measurements of regular and irregular objects and offer improved accuracy compared to traditional two-dimensional methods.