Wireless surface acoustic wave (SAW) sensors have some unique features that make them promising for industrial metrology. Their decisive advantage lies in their purely passive operation and the wireless readout capability allowing the installation also at particularly inaccessible locations. Furthermore, they are small, low-cost and rugged components on highly stable substrate materials and thus particularly suited for harsh environments. Nevertheless, a sensor itself does not carry out any measurement but always requires a suitable excitation and interrogation circuit: a reader. A variety of different architectures have been presented and investigated up to now. This review paper gives a comprehensive survey of the present state of reader architectures such as time domain sampling (TDS), frequency domain sampling (FDS) and hybrid concepts for both SAW resonators and reflective SAW delay line sensors. Furthermore, critical performance parameters such as measurement accuracy, dynamic range, update rate, and hardware costs of the state of the art in science and industry are presented, compared and discussed.

This article utilizes a topology optimization approach to design planar multilayer transitions between substrate integrated waveguides (SIWs) and rectangular waveguides (RWGs). The optimization problem is formulated based on the modal field analyses and Maxwell's equations in the time domain solved by the finite-difference time-domain (FDTD) method. We present a time-domain boundary condition based on the Klein-Gordon equation to split traveling waves at homogeneous waveguide ports. We employ the boundary condition to compute portal quantities and to devise an adjoint-field system that enabled an efficient computation of the objective function gradient. We solve design problems that include more than 105,000 design variables by using less than 400 solutions of Maxwell's equations. Moreover, a new formulation that effectively combats the development of in-band resonances in the design is presented. The transition configuration allows the direct mount of conventional RWG sections on the circuit board and aims to cover the entire K-band. The guiding structure of the optimized transition requires blind vias, which is realized by a simple and cost-efficient technique. In addition, the transition is optimized for three different setups that can be used to provide different field polarizations. The proposed transitions show less than 1-dB insertion loss and around 15-dB return loss over the frequency interval 18-28 GHz. Several prototypes are fabricated with an excellent match between the simulation and measurement results.

Radar sensors have been widely used to estimate speed and displacement of remote targets. A novel market for contactless radar sensing is emerging in the field of automatization and process analysis, where non destructive testing and evaluation methods are desired. Here, modern radar systems offer various advantages over conventional sensors since they enable the contactless, continuous, and cost-efficient measurement of static or dynamic ranges. These can further be used for vibration and vital sign characterization. Advances in microwave technology, an increasing integration density, and the development of novel algorithms keep boosting the performance of the systems. After introducing the most common operation principles, such as unmodulated and frequency-modulated continuous-wave radar, different design aspects and building blocks of cutting-edge systems are explained in detail. In the second part, selected applications are described in detail. These include the sheet thickness monitoring of metallic foils, and the measurement of the ground speed of vehicles with the latest approaches. Exemplary low-power radar systems are presented to show the limits in terms of power consumption while still offering a high measurement precision. In addition, the topics of mechanical vibration sensing and vital sign sensing are addressed by introducing tailored systems.

Joint communication and sensing (JCAS) holds great potential in a variety of applications because it combines radar signaling and data transmission into a single system. This means that both applications share their spectrum or even their waveform within the RF spectrum, a scarce and expensive resource. Meanwhile, research on beyond 5G and 6G is increasing tremendously. The advance of software-defined radio, where the signal processing mainly takes place in software, allows different implementations for communication and sensing [1] . Another reason for the integration of both into one system is the growing sensor density, which entails mutual interference. Furthermore, sharing hardware requires a sustainable and resource-efficient solution in the field of RF engineering.

This paper presents a topology optimization approach to design planar transitions between a microstrip line (MSL) and a rectangular waveguide (RWG) in the K-band. The transition comprises two sub-transitions: one from the MSL to a substrate integrated waveguide (SIW) and the second from the SIW to the RWG. Both are on the same substrate and can be manufactured with a standard printed circuit board process. This leads to a very cost-effective solution compared with other approaches. A WR-42 waveguide can easily be surface mounted to the transitions using a standard flange. The transitions have been fabricated, and their measured performance shows good agreement with the simulations. The MSL-SIW transition has a broadband behavior and the SIW-RWG transition still reaches a relative bandwidth of 10%.

Short-range noncontact microwave radar systems have undergone significant development in recent years [1]. Driven by advances in modern monolithic microwave integrated circuitry, printed circuit board (PCB) technologies, and embedded computing, highly integrated portable radar systems with good motion sensitivity can today be realized at relatively low cost. Radar systems have emerged in a variety of new application fields including industrial sensing [2], [3], human vital-sign detection [4], [5], and structural health monitoring [6].