The Radar Imager for Mars Subsurface Experiment instrument has conducted the first rover-mounted ground-penetrating radar survey of the Martian subsurface. A continuous radar image acquired over the Perseverance rover’s initial ~3-kilometer traverse reveals electromagnetic properties and bedrock stratigraphy of the Jezero crater floor to depths of ~15 meters below the surface. The radar image reveals the presence of ubiquitous strongly reflecting layered sequences that dip downward at angles of up to 15 degrees from horizontal in directions normal to the curvilinear boundary of and away from the exposed section of the Séitah formation. The observed slopes, thicknesses, and internal morphology of the inclined stratigraphic sections can be interpreted either as magmatic layering formed in a differentiated igneous body or as sedimentary layering commonly formed in aqueous environments on Earth. The discovery of buried structures on the Jezero crater floor is potentially compatible with a history of igneous activity and a history of multiple aqueous episodes.

This letter presents a 28 GHz 2-dimensional (2-D) multi-beam array antenna fed by a planar 4 × 4 cascaded Butler matrix (CBM). Utilizing the proposed concept of 3—D to planar CBM topology transition, the 4 × 4 U-slot antenna array integrated with planar CBM can be implemented with a multi-layers lamination without additional connectors or routing lines. Due to the simplified topology of the circular sub-BM, whose width is only 0.5 $\lambda_0$ (free space wavelength at 28 GHz), none of the crossovers is needed to assemble the radiation elements at the outputs of the CBM. The dimension of the proposed 2-D beam steering system has been dramatically reduced to $3.3 \ \lambda_0 \times 5.9 \ \lambda_0$ , which is, to best of our knowledge, the smallest in this application area. A prototype has been fabricated and measured. The measured results show a well-controlled input matching in the operation band from 26 GHz to 29 GHz. Besides, 16 spatial orthogonal beams with maximal 15.22 dBi gain at 28 GHz scanning a conical space with the maximal cone angle of 77.4° in the elevation plane and 136.8° in the azimuth plane by feeding at different inputs, which agree well with the simulated results.

Human gait reflects health condition and is widely adopted as a diagnostic basis in clinical practice. This research adopts compact inertial sensor nodes to monitor the function of human lower limbs, which implies the most fundamental locomotion ability. The proposed wearable gait analysis system captures limb motion and reconstructs 3D models with high accuracy. It can output the kinematic parameters of joint flexion and extension, as well as the displacement data of human limbs. The experimental results provide strong support for quick access to accurate human gait data. This paper aims to provide a clue for how to learn more about gait posture and how wearable gait analysis can enhance clinical outcomes. With an ever-expanding gait database, it is possible to help physiotherapists to quickly discover the causes of abnormal gaits, sports injury risks, and chronic pain, and provides guidance for arranging personalized rehabilitation programs for patients. The proposed framework may eventually become a useful tool for continually monitoring spatio-temporal gait parameters and decision-making in an ambulatory environment.

Context.Electric field measurements of the Time Domain Sampler (TDS) receiver, part of the Radio and Plasma Waves (RPW) instrument on board Solar Orbiter, often exhibit very intense broadband wave emissions at frequencies below 20 kHz in the spacecraft frame. During the first year of the mission, the RPW/TDS instrument was operating from the first perihelion in mid-June 2020 and through the first flyby of Venus in late December 2020.Aims.In this paper, we present a year-long study of electrostatic fluctuations observed in the solar wind at an interval of heliocentric distances from 0.5 to 1 AU. The RPW/TDS observations provide a nearly continuous data set for a statistical study of intense waves below the local plasma frequency.Methods.The on-board and continuously collected and processed properties of waveform snapshots allow for the mapping plasma waves at frequencies between 200 Hz and 20 kHz. We used the triggered waveform snapshots and a Doppler-shifted solution of the dispersion relation for wave mode identification in order to carry out a detailed spectral and polarization analysis.Results.Electrostatic ion-acoustic waves are the most common wave emissions observed between the local electron and proton plasma frequency by the TDS receiver during the first year of the mission. The occurrence rate of ion-acoustic waves peaks around perihelion at distances of 0.5 AU and decreases with increasing distances, with only a few waves detected per day at 0.9 AU. Waves are more likely to be observed when the local proton moments and magnetic field are highly variable. A more detailed analysis of more than 10 000 triggered waveform snapshots shows the mean wave frequency at about 3 kHz and wave amplitude about 2.5 mV m⁻¹. The wave amplitude varies asR^−1.38with the heliocentric distance. The relative phase distribution between two components of the E-field projected in theY − ZSpacecraft Reference Frame (SRF) plane shows a mostly linear wave polarization. Electric field fluctuations are closely aligned with the directions of the ambient field lines. Only a small number (3%) of ion-acoustic waves are observed at larger magnetic discontinuities.

The delta deposits in Jezero crater contain sedimentary records of potentially habitable conditions on Mars. NASA’s Perseverance rover is exploring the Jezero western delta with a suite of instruments that include the RIMFAX ground penetrating radar, which provides continuous subsurface images that probe up to 20 meters below the rover. As Perseverance traversed across the contact between the Jezero crater floor and the delta, RIMFAX detected a distinct discontinuity in the subsurface layer structure. Below the contact boundary are older crater floor units exhibiting discontinuous inclined layering. Above the contact boundary are younger basal delta units exhibiting regular horizontal layering. At one location, there is a clear unconformity between the crater floor and delta layers, which implies that the crater floor experienced a period of erosion before the deposition of the overlying delta strata. The regularity and horizontality of the basal delta sediments observed in the radar cross sections indicate that they were deposited in a low-energy lake environment.

This paper presents an ultra-miniaturized implant antenna with a volume of 22.22 mm ³ in the Medical Implant Communication Service (MICS) frequency band 402-405 MHz to be integrated with a leadless cardiac pacemaker. The proposed antenna has a planar spiral geometry with a defective ground plane exhibiting a radiation efficiency of 3.3% in the lossy medium with more than 20 dB of improved forward transmission, while the coupling can be further enhanced by adjusting the thickness of the antenna insulation and the antenna size according to the application area. The implanted antenna demonstrates a measured bandwidth of 28 MHz, covering beyond the MICS band needs. The proposed circuit model of the antenna describes the different behaviors of the implanted antenna over a wide bandwidth. The antenna interaction within human tissues and the improved behavior of the electrically small antenna are explained in terms of radiation resistance, inductance, and capacitance that are obtained from the circuit model. The results are demonstrated using electromagnetic computations and are validated by the measurement using liquid phantom and animal experiments.