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A piezoelectric material couples mechanical deformation with electric polarization. In a linear small-signal description, one convention writes $D_i=d_{ijk}{\sigma }_{jk}+{ϵ}_{ij}{E}_j$: applied stress contributes to electric displacement. The converse effect produces strain when an electric field is applied.

A quartz element can generate an electrical signal under mechanical loading, while an applied alternating voltage can drive a mechanical resonance. This reciprocity makes piezoelectric materials useful for sensors, actuators and frequency control. The coefficients depend on direction and crystal symmetry; an isotropic scalar coefficient cannot describe every orientation of a single crystal.

A piezoelectric transducer converts mechanical stress into an electrical signal, or an applied electric field into mechanical deformation, using a piezoelectric material. The two directions enable both acoustic reception and transmission.

An ultrasound element is driven electrically to launch a pulse and then detects returning pressure waves through its generated charge or voltage. Mechanical resonance, electrical loading and acoustic coupling determine its bandwidth and sensitivity. The crystal response is therefore only one part of the complete instrument calibration.

Quartz is a crystalline form of silicon dioxide, $\mathrm{Si}{\mathrm{O}}_2$. Its ordered structure distinguishes it from amorphous silica glass.

It is piezoelectric material: suitable mechanical deformation changes electric polarization. Quartz resonators exploit the reproducible mechanical resonance of a shaped crystal to stabilize an oscillator, linking crystal symmetry with time and frequency measurement.