In this dissertation, applications of thermoacoustic (TA) effect in breast cancer detection and wireless communications are explored. Thermoacoustic imaging (TAI) is a promising candidate for breast cancer detection. TAI creates an image of the internal morphological features of a dielectrically lossy sample by employing generated acoustic waves from absorbed microwave energy in the sample owing to the thermoacoustic effect based on thermoelastic expansion. Malignant tissues, usually embracing higher dielectric loss, absorbing more energy and emanating stronger acoustic waves than the surrounding healthy tissues, may be distinguished in the image. Besides high contrast inherited from microwave imaging and excellent resolution inherited from ultrasound imaging, TAI is also non-ionizing and noninvasive compared with other existing breast cancer imaging modalities. A potential clinically feasible TAI system is more cost-efficient and compact than mammography and especially MRI. Two sets of breast model are investigated by simulations in this work. The first set is made of a slab-shaped breast model. The main purpose of this study is to perform safety evaluation of TAI and calculate the amount of microwave power needed to generate a detectable acoustic pressure. The second set employs four realistic numerical breast phantoms to study the feasibility of applying contrast agents to TAI for breast cancer imaging, which is named as contrast-enhanced TAI (CETAI). The presented results unveil the promising potential of CETAI as a complementary safe, rapid, sensitive, accurate, high-resolution and breast-density-insensitive tomography for 3-D breast cancer detection. Compressive sensing (CS) is applied to significantly reduce the required number of measurements and expedite CETAI applications in breast cancer detection. Results show that the total measurements can be reduced by at least a factor of 13, which is very favorable to potential clinical applications. The second application of TAI explored in this work is wireless communications, which is referred to as thermoacoustic communications (TAC). It is proposed as a potential complementary method to mitigate the challenge in conventional wireless communication from air to water, in which the electromagnetic wave cannot penetrate deep in water. TAC employs a microwave antenna in air to irradiate the water surface with a microwave signal encoded with information to be communicated. Due to the thermoacoustic effect, acoustic waves are subsequently emanated from the water near the surface and propagate in the water with much less attenuation than electromagnetic waves and thus can propagate a longer distance in the water. Finally, an underwater device with an acoustic transducer can detect the generated acoustic signals and the information is acquired by decoding the signals. Its working principle is presented and proof-of-concept experiments are demonstrated. Parametric studies are performed to investigate the dependence of the generated acoustic signals on relevant parameters. Bit rate and link budget of TAC are derived to evaluate the probability of its potential practical applications.