Cold-Chain Temperature RFID: The EM4325 Semi-Passive UHF + Temp Sensor (Passive vs BAP vs Active)
A cold chain must "prove the range was held without opening the box." Temperature RFID splits into passive (reads only when interrogated), semi-passive BAP (battery-driven interval monitoring, like the EM4325), and active. This guide covers the three and the EM4325 (UHF Gen2 + temp sensor + SPI), and states honestly: the EM4325 natively does snapshots + interval alarm monitoring; full point-by-point logging needs a companion MCU.
The cold-chain proof problem
The core requirement of a cold chain (pharma, vaccines, blood bags, food) is to "prove, without opening the box, that the goods stayed within the allowed temperature range the whole way." A temperature-logging/sensing RFID tag exists for exactly this: it records temperature in the tag, read out wirelessly by a reader on receipt without unpacking. EM Microelectronic positions the EM4325 precisely for cold-chain monitoring, sensor monitoring, e-seals and supply-chain track-and-trace. But "how completely it can record" depends on which kind of tag it is — and that decides whether you buy the right part.
Passive vs semi-passive (BAP) vs active
Temperature-logging RFID comes in three kinds, differing in "whether there's a battery, and whether it can measure without a reader." Passive: no battery, it can only take one temperature reading at the instant a reader powers it (a snapshot); cheap and maintenance-free, but can't prove every moment in transit. Semi-passive / battery-assisted passive (BAP): a small battery drives only the sensing and monitoring logic (readout still uses RF backscatter; the battery isn't used to transmit), so it can self-monitor at a set interval independently of the reader; long read range, robust comms, moderate cost — the EM4325 is this kind. Active: has its own transmitter and can beacon in real time continuously, longest range but most power-hungry and most expensive. Most cold-chain proof-of-compliance uses BAP.
What the EM4325 is
The EM4325 is a UHF EPC Gen2 tag IC: compliant with EPC Class-1 Gen-2, EPC Class-3 Gen-2, and ISO/IEC 18000-63 (Type C) and 18000-64 (Type D), operating in the UHF band (the EPC Gen2 norm is 860–960MHz); it has an integrated temperature sensor usable in both passive and BAP modes, switching automatically. Temperature range is about −40°C to +60°C, with a selectable accuracy of ±0.5 / ±1 / ±2°C (9-bit; calibrated at +5°C on wafer — for critical applications, re-calibrate in the finished form factor). Memory is a 4kbit EEPROM (EPC/UII plus about 3kbit user memory). It also has a programmable 4-bit port configurable as SPI (as master or slave) — effectively a "UHF RF front-end + temperature sensor" that can pair with a host MCU as an embedded device's Gen2 interface. In BAP mode the chip read sensitivity is −31dBm with an open-field range in excess of 50m (passive-mode range is much shorter).
⚠️ Native = snapshot + interval alarms; full logging needs an MCU
Here is a point that must be stated clearly and is often misunderstood: what does the EM4325 natively record? Passive mode is snapshot only (one reading when interrogated). BAP mode runs the built-in "Monitor Function": it samples at a set interval (16 steps, 5 minutes to 8 hours), checks alarm thresholds for over-temperature, under-temperature, low battery and tamper, and timestamps the alarms with an on-chip real-time clock — note this is "alarm-type self-monitoring + timestamp," NOT a full point-by-point temperature history. If what you need is a complete temperature-curve data logger, EM's own approach is to add an external MCU over SPI (for example EM Micro's own EM6819) to implement the logging. So be precise in copy and planning: EM4325 single-chip = snapshot + interval alarm monitoring; full point-by-point logging = EM4325 + a companion MCU.
How to choose
Only need "scan-and-verify temperature at receiving/dispatch" → passive snapshot suffices (cheapest, no battery, no maintenance), but can't prove every moment in transit. Need "full cold-chain proof / over-temperature alarms" → BAP (like the EM4325): battery-driven interval monitoring + timestamps, long range and robust comms; note the battery is single-use/replaceable, so trade off sampling interval (5 min–8 hr) against battery life. Need "a complete point-by-point temperature curve" → EM4325 + a companion MCU (SPI); don't expect a deep log from the single chip. Need "real-time location / continuous transmission" → only then consider active (most expensive, most power-hungry). On accuracy, choose ±0.5°C for strict ranges like vaccines/blood; general food can relax it to save power. JLink Technology is an authorized EM Microelectronic distributor supplying the EM4325 (semi-passive temperature-sensing UHF) and the low-power MCU EM6819 to pair with it; tell us your temperature range, monitoring interval, read range and whether you need full logging, and we will help with selection and solution planning, and reply with samples, datasheets and pricing.
Products mentioned
EM4325 UHF RFID + Sensor IC (EPC Gen2 / BAP)
The EM4325 is a UHF RFID smart-sensor IC from EM Microelectronics compliant with EPC Class-1 Gen2 and ISO 18000-63, supporting battery-assisted passive (BAP) or fully passive operation, with an on-chip absolute temperature sensor, 4096-bit EEPROM, and a 4-bit GPIO/SPI interface to on-tag devices — for cold-chain temperature logging, sensor tags, and supply-chain telemetry.
EM4425 (em|echo-V) NFC + UHF Dual-Frequency RFID IC
The EM4425 is a single-chip dual-frequency RFID tag IC from EM Microelectronics, integrating both HF (NFC, 13.56MHz) and UHF (RAIN/EPC Gen2v2, 860~960MHz) interfaces, with AES-128 encryption and digital signature support. One chip can be read both by smartphone NFC at close range and by UHF for long-range inventory — ideal for brand authentication and supply-chain traceability.
EM6819 Ultra-Low Power 8-bit MCU
The EM6819 is an ultra-low power 8-bit RISC microcontroller from EM Microelectronics. Built on CMOS process, it operates down to 0.9V and achieves nA-level sleep current. Features integrated LCD driver, timers, ADC, and rich peripherals — ideal for battery-powered consumer electronics and smart card applications.
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