Application of a microwave acoustoelectronic sensor on a diamond substrate to determine the properties of solutions of substances

Rapid determination of liquid properties is essential for various fields of human endeavor, such as medicine, pharmacology, and various chemical industries. To this end, we have developed an acoustoelectronic liquid sensor based on a High overtone Bulk Acoustic Resonator using microwave longitudinal bulk acoustic waves. Sensor is designed to measure the acoustic impedance of liquids. The sensor is built on a multilayer piezoelectric structure composed of "Al/Al0.72Sc0.28N/Mo/(100) diamond". To protect the sensitive element from potential chemical damage from the analytes being tested, a metal housing is used, with the thin-film piezoelectric transducer "Al/Al0.72Sc0.28N" located within the housing. The analytes are placed on the opposite free side of the diamond substrate, and the sensor has been tested on aqueous solutions of NaCl, glycerol, and isopropyl alcohol at various concentrations. The samples weighed several milligrams. The relationship between the electrical reflection coefficients of the sensor and the acoustic impedance of liquids and solutions was found to be linear. Thanks to the high chemical tolerance and abrasion resistance of a diamond substrate, this sensor can be reused for studying a wide range of substances, including aggressive liquids, without any loss of performance.