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Objective. Monolithic crystal detectors are increasingly being applied in positron emission tomography (PET) devices owing to their excellent depth-of-interaction (DOI) resolution capabilities and high detection efficiency. In this study, we constructed and evaluated a dual-ended readout monolithic crystal detector based on a multiplexing method. Approach. We employed two 12 × 12 silicon photomultiplier (SiPM) arrays for readout, and the signals from the 12 × 12 array were merged into 12 X and 12 Y channels using channel multiplexing. In 2D reconstruction, three methods based on the centre of gravity (COG) were compared, and the concept of thresholds was introduced. Furthermore, a light convolutional neural network (CNN) was employed for testing. To enhance depth localization resolution, we proposed a method by utilizing the mutual information from both ends of the SiPMs. The source width and collimation effect were simulated using GEANT4, and the intrinsic spatial resolution was separated from the measured values. Main results. At an operational voltage of 29 V for the SiPM, an energy resolution of approximately 12.5 % was achieved. By subtracting a 0.8 % threshold from the total energy in every channel, a 2D spatial resolution of approximately 0.90 mm full width at half maximum (FWHM) can be obtained. Furthermore, a higher level of resolution, approximately 0.80 mm FWHM, was achieved using a CNN, with some alleviation of edge effects. With the proposed DOI method, a significant 1.36 mm FWHM average DOI resolution can be achieved. Additionally, it was found that polishing and black coating on the crystal surface yielded smaller edge effects compared to a rough surface with a black coating. Significance. The introduction of a threshold in COG method and a dual-ended readout scheme can lead to excellent spatial resolution for monolithic crystal detectors, which can help to develop PET systems with both high sensitivity and high spatial resolution. [ABSTRACT FROM AUTHOR]

A 50 × 50 × 10 mm3 monolithic gadolinium aluminum gallium garnet (Gd3Al2Ga3O12; GAGG):Ce crystal coupled to a 8 × 8 silicon photomultiplier (SiPM) array was developed; it showed very good system uniformity and a high energy resolution of 7.4% at 662 keV. By using a convolutional neural network-based positioning algorithm and a fan-beam calibration method, the detector achieved a position resolution of ∼1.4 mm and a depth of interaction resolution of ∼2 mm. Based on this high-performance monolithic detector, we developed a coded aperture gamma camera. A 1-mCi Cs-137 source centered at a 2-m distance from the mask could be reconstructed with a signal-to-noise ratio of 6.5 in 1 s. Furthermore, the imaging ability of a low-energy Am-241 source and a low-activity Cs-137 source when the background-to-signal ratio was approximately 1:1 and a double low-activity source (Cs-137 and Na-22) was demonstrated. It is shown that the monolithic-crystal-based coded aperture gamma camera can achieve high performance and has a large potential for further improvement. [ABSTRACT FROM AUTHOR]

The continuous progress made in wearable energy harvesting technology is delivering sophisticated devices with increasing power outputs, which are possible to provide sustainable energy supply for body sensors to achieve energy-autonomous wireless sensing systems. This paper reports the development and characterisation of a wearable energy harvesting powered wireless sensing system with system-level strategies to address the challenges in energy harvesting, power conditioning, wireless sensing and their integration into a system. The system comprises four parts: (1) a magnetically plucked wearable knee-joint energy harvester (Mag-WKEH) to scavenge energy from knee-joint motions during human walking, (2) a power management module (PMM) with a maximum power point tracking (MPPT) function, (3) an energy-aware interface (EAI) for dealing with the mismatch between the energy generated and demanded, and (4) an energy-aware wireless sensor node (WSN) for data sensing and transmitting. Experiments were performed with a human subject wearing the system and walking on a treadmill at different speeds. The experimental results showed that as the walking speed increased from 3 to 7 km/h, the power output of the Mag-WKEH increased from 1.9 ± 0.12 to 4.5 ± 0.35 mW, and the generated power was able to power the WSN to work at duty cycles from 6.6 ± 0.36% to 13 ± 0.5% with an active time of 2.0 ± 0.1s. In each active time, the WSN was able to sample 482 readings with an interval of 10 ms from the sensors and transmit all data to a base station at a distance of 4 m. [ABSTRACT FROM AUTHOR]

A compact, springless, easy-to-process kirigami-inspired TENG (KI-TENG) is developed. The frequency responses of the KI-TENG under the influence of mass, acceleration, and initial distance are investigated in detail to optimize its structural design. Moreover, the TENG coupled with the kirigami structure could collect ultra-wide-band vibration energy and as a sensor measuring acceleration. [Display omitted] • A compact and springless kirigami-inspired TENG (KI-TENG) is developed. • The frequency response characteristics of the KI-TENG are investigated. • The KI-TENG can harvest ultra-wide-band vibration energy from 2 to 49 Hz. • The output of the KI-TENG at different vibration tilt angles is explored. • The KI-TENG can effectively monitor acceleration changes from 1 to 9 m/s2. Triboelectric Nanogenerators (TENGs) based on spring-assisted structures play a central role in scavenging vibrational energy that is widely available in the natural environment. However, they suffer from difficulties in adjusting the stiffness and bonding the springs to the triboelectric layer. Here, a kirigami-inspired TENG (KI-TENG) with a kirigami structure is demonstrated, which can be used as an ultra-wide-band vibrational energy harvester and self-powered acceleration sensor. The triboelectric layer of the KI-TENG can be easily processed into the kirigami structure with one or two-degree-of-freedom by laser cutting technology. The frequency responses of the KI-TENG under the influence of mass, acceleration, and initial distance are investigated in detail to optimize the structural design. With optimized structural parameters, the KI-TENG can not only harvest broadband vibration energy from 2 to 49 Hz in vertical vibration state but also obtain high output performance over a wide frequency range in horizontal vibration state. Moreover, the KI-TENG can be used as a sensor measuring acceleration from 1 to 9 m/s2. This work demonstrates a compact TENG coupled with the kirigami structure for energy harvesting and active sensing, which has great prospects in intelligent plants, artificial intelligence, and the internet age. [ABSTRACT FROM AUTHOR]