Rapid High-Frequency Measurements of Electrical Circuits by Using Frequency Mixer and Pseudo-Random Sequences

Frequency-response measurements at high frequencies have been shown to provide a valuable design tool in various fields of electronics. These measurements are often challenging when using most commercially available measurement tools due to their relatively low maximum sampling frequency and long measurement time. This effectively prevents frequency-response-based low-cost applications where fast and reliable measurements are required. This paper proposes the use of a combined frequency mixer applied with pseudo-random sequences. In this method, the applied pseudo-random excitation is upconverted to high frequencies by the mixer, and once injected into the device being tested, the system response is downconverted to lower frequencies. The method provides a low-cost solution that can be applied for rapid high-frequency measurements by using only modest data-acquisition tools. Experimental results based on a high-frequency resonator are presented and used to demonstrate the effectiveness of the proposed methods

Piezoelectric sensitivity of a layered film of chitosan and cellulose nanocrystals

Free-standing biodegradable films were fabricated by mixing cellulose nanocrystals and nanofibers with a water-based chitosan solution. The piezoelectric sensitivity of the films was measured to find out their suitability in sensing and actuation applications. Also their structure was evaluated with scanning electron microscopy. Our initial results show that a simple solvent casting method can be used to prepare films with varying piezoelectric properties. The composite films of chitosan and cellulose nanocrystals were noticed to have a phase-separated layered structure, resulting in an interesting side-dependent piezoelectric response. Moreover, the sensitivity values of plain chitosan were close to those of a non degradable commercial sensor material polyvinylidene fluoride. The fabrication process has to be studied further to control and optimize the structure and piezoelectric properties of the films.publishedVersionPeer reviewe

Inductively coupled passive resonance sensor for monitoring biodegradable polymers in vitro

Capacitive sensors can be used to monitor changes in materials by monitoring complex permittivity. Inductively coupled passive resonance sensors provide means to make short range wireless permittivity measurements if the sensors are embedded in the tested material. In this study, inductively coupled sensors were embedded in biodegradable polymers, which are important materials in regenerative medicine. However, it is challenging to observe their decay especially in vivo. After preparing the samples by compression moulding, the encapsulated sensors and a reference series were immersed in buffer solution. The signals from the passive resonance sensors were measured for eight weeks. In addition, mechanical and chemical testing was periodically carried out to monitor the state of the reference series. The wirelessly measured signals are compared with water absorption, flexural modulus, glass transition temperature and viscosity.publishedVersionPeer reviewe

Bioresorbable Conductive Wire with Minimal Metal Content

The emergence of transient electronics has created the need for bioresorbable conductive wires for signal and energy transfer. We present a fully bioresorbable wire design where the conductivity is provided by only a few micrometers thick electron-beam evaporated magnesium layer on the surface of a polymer fiber. The structure is electrically insulated with an extrusion coated polymer sheath, which simultaneously serves as a water barrier for the dissolvable magnesium conductor. The resistance of the wires was approximately 1 Ω cm–1 and their functional lifetime in buffer solution was more than 1 week. These properties could be modified by using different conductor materials and film thicknesses. Furthermore, the flexibility of the wires enabled the fabrication of planar radio frequency (RF) coils, which were wirelessly measured. Such coils have the potential to be used as wireless sensors. The wire design provides a basis for bioresorbable wires in applications where only a minimal amount of metal is desired, for example, to avoid toxicity

Distance-Independent Contactless Interrogation of Quartz Resonator Sensor with Printed-on-Crystal Coil

A novel quartz crystal resonator sensor, which embeds a conductive printed planar coil that enables electromagnetic contactless interrogation techniques is presented. An aerosol-jet process is used to precisely and accurately deposit electronic inks onto a 330 µm-thick bare piezoelectric quartz crystal to print the planar coil and the electrodes. The proposed interrogation technique enables distance-independent operation, and is based on the measurement of the reflected impedance of the quartz resonator sensor through the planar primary coil of the coupled inductors. The resonant frequency, measured without contact using the primary coil connected to an impedance analyzer, results 4.790260 MHz. Contactless operation distances up to 12.2 mm have been obtained. The experimental results have a maximum deviation of about 50 Hz, i.e. 10.5 ppm, with respect to reference measurements taken via contact probes