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The wireless monitoring of key physiological parameters such as heart rate, respiratory rate, temperature, and pressure can aid in preventive healthcare, early diagnosis, and patient-tailored treatment. In wireless implantable sensors, the distance between the sensor and the reader device is prone to be influenced by the operating frequency, as well as by the medium between the sensor and the reader. This manuscript presents an ex vivo investigation of the wireless linkage between an implantable sensor and an external reader for medical applications. The sensor was designed and fabricated using a cost-effective and accessible fabrication process. The sensor is composed of a circular planar inductor (L) and a circular planar capacitor (C) to form an inductor–capacitor (LC) resonance tank circuit. The reader system comprises a readout coil and data acquisition instrumentation. To investigate the effect of biological medium on wireless linkage, the readout distance between the sensor and the readout coil was examined independently for porcine and ovine tissues. In the bench model, to mimic the bio-environment for the investigation, skin, muscle, and fat tissues were used. The relative magnitude of the reflection coefficient (S11) at the readout coil was used as a metric to benchmark wireless linkage. A readable linkage signal was observed on the readout coil when the sensor was held up to 2.5 cm under layers of skin, muscle, and fat tissue. To increase the remote readout distance of the LC sensor, the effect of the repeater coil was also investigated. The experimental results showed that the magnitude of the reflection coefficient signal was increased 3–3.5 times in the presence of the repeater coil, thereby increasing the signal-to-noise ratio of the detected signal. Therefore, the repeater coil between the sensor and the readout coil allows a larger sensing range for a variety of applications in implanted or sealed fields.

Self-powered sensor systems that are able to harvest energy from surrounding vibrations are a promising solution for wearable devices, Internet of Things (IoT) and sensing in challenging industrial environments. An automated, adjustable system for testing piezoelectric energy harvester devices is necessary to ensure that developed solutions provide sufficient energy output, minimal losses and reliability of all components under a range of operating conditions. Herein we propose a novel and unique solution as a standalone software tool developed in Python with optional electronics to achieve automated characterisation of electrical properties of vibration powered energy harvesters. Due to its unique modular construction, the tool can be applied to a variety of experimental conditions, to enhance and facilitate piezoelectric materials characterisation and validate self-powered devices for wide spectrum of industrial applications, including long-term performance and fatigue testing. We demonstrate its performance and capabilities by testing piezoelectric materials and electronic circuits at a range of conditions such as (i) high temperature piezoelectric material characterization, (ii) high temperature rectifying circuit performance, and (iii) room temperature investigation of an energy harvesting device. We release the software and hardware described in this work as an open-source tool freely available to broader audience.

The energy harvesting capability of resonant harvesting structures, such as piezoelectric cantilever beams, can be improved by utilizing coupled oscillations that generate favourable strain mode distributions. In this work, we present the first demonstration of the use of a laminated carbon fibre reinforced polymer to create cantilever beams that undergo coupled bending-twisting oscillations for energy harvesting applications. Piezoelectric layers that operate in bending and shear mode are attached to the bend-twist coupled beam surface at locations of maximum bending and torsional strains in the first mode of vibration to fully exploit the strain distribution along the beam. Modelling of this new bend-twist harvesting system is presented, which compares favourably with experimental results. It is demonstrated that the variety of bend and torsional modes of the harvesters can be utilized to create a harvester that operates over a wider range of frequencies and such multi-modal device architectures provides a unique approach to tune the frequency response of resonant harvesting systems.