An air filtration apparatus comprising: an air filter having an inlet surface and an outlet surface , the air filter configured to filter air flowing therethrough from the inlet surface to the outlet surface ; one or more thermoelectric sensors having an upstream sensing surface and a downstream sensing surface , the upstream sensing surface being positioned adjacent the inlet surface of the air filter , and the downstream sensing surface being positioned adjacent the outlet surface of the air filter , the one or more thermoelectric sensors comprises a first thermoelectric sensor having the upstream sensing surface and a second thermoelectric sensor having the downstream sensing surface ; sensing circuitry connected to the thermoelectric sensors , configured to receive signals from the thermoelectric sensors and process the signals to obtain status information of the air filter ; and a flexible substrate to support the first and second thermoelectric sensors and the sensing circuitry , the flexible substrate including first and second portions connected by an off-center portion , the first and second portions respectively connecting the first and second thermoelectric sensors to the sensing circuitry supported by the off-center portion , the off-center portion is attached to a periphery of the air filter , and the first and second portions are bendable such that the first thermoelectric sensor and the second thermoelectric sensor face with respect to each other, wherein the first thermoelectric sensor and the second thermoelectric sensor are positioned to be offset with respect to the periphery of the air filter such that the second thermoelectric sensor is not blocked by the first thermoelectric sensor . an air filter having an inlet surface and an outlet surface , the air filter configured to filter air flowing therethrough from the inlet surface to the outlet surface ; one or more thermoelectric sensors having an upstream sensing surface and a downstream sensing surface , the upstream sensing surface being positioned adjacent the inlet surface of the air filter , and the downstream sensing surface being positioned adjacent the outlet surface of the air filter , the one or more thermoelectric sensors comprises a first thermoelectric sensor having the upstream sensing surface and a second thermoelectric sensor having the downstream sensing surface ; sensing circuitry connected to the thermoelectric sensors , configured to receive signals from the thermoelectric sensors and process the signals to obtain status information of the air filter ; and a flexible substrate to support the first and second thermoelectric sensors and the sensing circuitry , the flexible substrate including first and second portions connected by an off-center portion , the first and second portions respectively connecting the first and second thermoelectric sensors to the sensing circuitry supported by the off-center portion , the off-center portion is attached to a periphery of the air filter , and the first and second portions are bendable such that the first thermoelectric sensor and the second thermoelectric sensor face with respect to each other, wherein the first thermoelectric sensor and the second thermoelectric sensor are positioned to be offset with respect to the periphery of the air filter such that the second thermoelectric sensor is not blocked by the first thermoelectric sensor . <EOS>