MwSensors

Biomedical Applications

The modern industry is interested in new universal adaptable and affordable sensor concepts in a wide range of applications which can be satisfied with microwave sensors. They are very versatile and can perform in different environments ranging from industrial, environmental to even biomedical applications. In many scenarios where dielectric properties of a certain object are of importance, microwave sensors can be employed. Their advantages lie in the facts that they can sense fast, continuous, non-invasively, non-destructive and in a contact-less way. Another reason is that most materials, organic and inorganic, have a specific frequency behavior which can provide information about their structure and function. Microwave sensor arrays are able to extract this information by retrieving these spectral signatures and give a spatial distribution of several materials under test (MUTs) simultaneously.

Fig. 1. Principle of operation for a planar metamaterial sensor. From the reflected and/or transmitted signal the information about the dielectric properties of the MUT and its distribution within the sensor array can be derived through the extraction of a capacitive profile.
Fig. 1. Principle of operation for a planar metamaterial sensor. From the reflected and/or transmitted signal the information about the dielectric properties of the MUT and its distribution within the sensor array can be derived through the extraction of a capacitive profile.

The research of the microwave engineering group in this field is focused on developing planar microwave sensors arrays for analysis and treatment in biomedical applications. All studied sensors have in common that they transduce the dielectric properties of materials under test in their direct vicinity into an electric signal. One of the main novelties of the developed sensor concepts is the array feature which allows making a simultaneous analysis of several materials under test with a single readout signal, or a relative characterization of one material with information about its spatial distribution. Additionally, the use of metamaterial structures as building elements for the development of the sensors gives them high flexibility in terms of geometry and operating frequency, enabling miniaturization and increased sensitivity by enhanced field interaction. The advantage of subwavelength image pixel resolution resulting from the discrete metamaterial unit cells was found as an additional feature.

The thorough examination of the sensor capabilities and proof-of-concept demonstration has been done in a wide range of application scenarios ranging from cytological studies in a microfluidic lab-on-chip environment to cancer detection and treatment in tissues. The purpose of the sensor that analyzes dielectric properties of cells is to monitor several separated cell samples simultaneously for changes in the concentration, the cell’s developing cycle stage or their vitality, for example, to monitor their specific reaction after drug exposure in a semi-automated way.

Fig. 2. Planar metamaterial sensor with integrated microfluidic channels for cytological screening.
Fig. 2. Planar metamaterial sensor with integrated microfluidic channels for cytological screening.
Fig. 3. Bioheat transfer mechanisms in organic tissue. Conduction and forced convection due to blood perfusion are highlighted.
Fig. 3. Bioheat transfer mechanisms in organic tissue. Conduction and forced convection due to blood perfusion are highlighted.

As for the medical environment the developed devices are particularly interesting because they offer the completely new possibility to operate the sensor in a dual mode: First, it is used as sensing device to screen the tissue for abnormalities. Secondly, for the first time, by changing the applied signals the device is used for treatment of cancer tissue by means of thermal ablation therapy. This procedure allows tumorous tissue to be eradicated in a highly focused way. Furthermore, the sensor is able to control the ablated area by operating again in sensing mode after the ablation procedure to ensure proper eradication of the cancer tissue with sufficient margins that will prevent its recurrence.

Fig. 4. Thermal measurements. a) Ablation with second ring pair of the SRR array, b) Ablation with third ring pair of the SRR array, c) Loaded SRR array.
Fig. 4. Thermal measurements. a) Ablation with second ring pair of the SRR array, b) Ablation with third ring pair of the SRR array, c) Loaded SRR array.

Team Biomedical Applications

Name Raum Tel. E-Mail
Carolin Hessinger, geb. Reimann, M.Sc.
S3|06 429-28449
Sönke Schmidt , M.Sc.
S3|06 417-28451

Chipless Wireless Sensors & RFID

Polarization separated sensor readout.
Polarization separated sensor readout.

Passive chipless RFID and wireless sensor tags (i. e. tags without active power supply and without silicon ‘chip’-based information handling) allow for identification and measurement in environments that cannot be accessed by ‘conventional’ approaches, either for technical or economical reasons. The research of the microwave engineering group in this field is focused on novel tag designs and concepts for passive chipless RFID and wireless sensors. The work is thereby strongly influenced by the metamaterial approach. Up to now, there are three main ‘platforms’ on which many wireless sensors and RFID tags have reached prototype status.

Dielectric resonator high temperature sensor demonstration

The ‘delay line’ platform utilizes ‘left-handed’ metamaterial transmission lines to arange a backscatter signal in time-domain that encodes either digital information or analog sensor values. A vital component of this approach is a novel passive and chipless phase modulation scheme that allows for a tremendous increase of the tag's information capacity as well as for the ability of phase-encoding of measured values.

The ‘microresonator’ platform realizes the idea of a miniaturized antenna structure that acts as a backscatter particle, either been used to encode a single information symbol or to represent a measured value. Within this approach, multi-symbol RFID tags have been realized as well as sensors for mechanical parameters like strain and bending.

Working principle of polarization separated sensor readout.
Working principle of polarization separated sensor readout.
Measurement result of 2D displacement sensor (one dimension).
Measurement result of 2D displacement sensor (one dimension).

A different approach that separates interrogation and response signal by means of polarization forms the third platform, called ‘polarization separation’. Different sensors have been realized within this context, e. g. a mechanical 2D displacement sensor.

A special interest is furthermore on temperature sensing by the utilization of temperature-sensitive materials, especially barium-strontium-titanate. Temperature sensors have successfully been realized on the delay line and on the polarization separation platform. Aim of this work is especially the temperature range between 100°C and 1000°C, where conventional wireless temperature sensors are not able to work. Recently, a temperature sensor based on a dielectric resonator approach has been realized that is capable of temperature measurements up to 800°C. The sensor is demonstrated in the short video above.

Team Chipless Wireless Sensors

Name Raum Tel. E-Mail
Alejandro Jiménez Sáez, M. Sc.
S3|06 427-28456

Publications